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Degradability of aluminum in acidic and alkaline solutions

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... An alternative approach is to remove the oxide layer from the Al using acid or base (either, as Al is amphoteric); it is simple and uses low-cost reagents and equipment. Strongly acidic solutions favored to promote the reaction are HCl and H 2 SO 4 [49,50], while NaOH and KOH are suitable strong alkalis that can expedite H 2 generation [30,32,39,40,51]. ...
... In acidic solutions, the anion type plays an essential role in forming active sites on the Al surface by attacking the oxide layer [50]. Anions also split water molecules and further evolve H 2 . ...
... Cl À in solution is less mobile than the other anions, but it migrates more intensively into the oxide layer, while SO 4 2À predominantly adsorbs at the oxide/solution interface [55]. The doubly charged SO 4 2À ions have a stronger adsorptive affinity for the Al surface and any adsorbed water (in contrast to singly charged Cl À ), which hampers metal dissolution, and thus makes hydrogen production by H 2 SO 4 slower than by HCl [50]. In alkaline reactions, the concentration of alkali is a crucial determinant of the chemical reactivity of Al, which is the first step in initiating its reaction with H 2 O [41]. ...
Article
The reaction of Al and H2O is a promising method for the renewable production of H2 (an environmentally friendly fuel whose combustion produces only water), because it does not directly include fossil fuels conversion. This reaction was studied at extreme pH values as low as 1 and as high as 13.5 with HCl, H2SO4, and NaOH, and at low hydrothermal temperatures of 40-100 °C. Factors such as pH, temperature, and solution medium influenced H2 production, which was considerably greater at higher temperatures and more extreme pH (acidic or alkaline). Alkaline conditions consistently favored more rapid H2 production than acidic conditions. Under the most extreme conditions, the activation energy was ∼60 kJ mol⁻¹ for both acidic and alkaline reactions. A model predicting H2 production in acidic reactions was derived from the reaction mechanism and kinetics. The model yielded a good fit to on-site measurements at the Tamagawa and Zao hot springs in northeast Japan. This study would aid the development of industrial H2 production systems using natural acidic hot springs or alkaline industrial wastewater.
... Ground aluminium exhibits low polarisation resistance (R p = 10 kΩ cm 2 ), high current density (i corr = 314 nA/cm 2 ), a negative corrosion potential (E corr ) of −0.73 V and a pitting potential (E pit ) only 10 mV above E corr . A slightly changed corrosion performance was obtained after etching the aluminium only in NaOH solution due to changes in the morphology and composition of the surface hydroxylated film [41]. ...
... First is the etching, i.e., removal of the native oxide layer, which is unstable above pH 8.3 [45]. During etching, the formation of the hydroxylated aluminium Al (OH) 4 − surface takes place (reaction 4) [41,46]. ...
... up to 1 week. These two solutions were chosen because they are commonly used in the laboratory praxis and because, at these conditions, aluminium and aluminium oxide are expected to be less stable [1,41,43]. The WCAs remained higher than 150°even after 1 week of air exposure, suggesting that the modified surface exhibits a prominent lasting quality under these conditions, which is favourable for the potential applications. ...
Article
This study aimed to fabricate a highly hydrophobic aluminium surface in a one-step ultrasound process in a sodium hydroxide solution containing various alkoxysilanes. The latter were based on the trimethoxysilane of various type and length of the introducing group at the silyl bond (SiC): Ra-Si(OMe)3 and Rf-(CH2)2-Si(OMe)3, where Ra and Rf are alkyl and perfluoroalkyl introducing groups, respectively, and OMe is the methoxy group. The effect of methoxy and ethoxy groups at the siloxy bond was additionally investigated for perfluorodecyl silanes. The corrosion performance was studied using potentiodynamic electrochemical techniques. The wettability, morphology, surface topography and surface composition of treated aluminium surfaces were characterised using an optical tensiometer, a scanning electron microscope coupled with an energy dispersive X-ray spectrometry system, a contact profilometer and a Fourier transform infrared spectroscopy system. Micro-/nanostructures formed on the treated aluminium surfaces lead to an increase in the water contact angle from 71° for ground surface, up to 115° for the surface treated with alkyl silanes and up to 155° for that treated with fluoroalkyl silanes with a long chain. The superhydrophobic coatings show corrosion-resistant behaviour in chloride solution, while the durability in slightly acidic/alkaline solutions indicates the excellent water-repellent nature of the coatings, the self-cleaning ability for different types of pollutants and improved anti-icing properties with freezing and melting delay.
... However, the protective efficiency is highly reduced in polluted acidic environments (i.e. acid rain), in marine (the presence of chloride ions) saline acid environments, or in alkaline media, such as cementitious materials and alkaline detergents [2][3][4][5]. Alumina is stable in aqueous solutions in the pH range of 4.0-8.5. The corrosion attack in inorganic acids or bases is usually uniform and regular [1,4]. ...
... Alumina is stable in aqueous solutions in the pH range of 4.0-8.5. The corrosion attack in inorganic acids or bases is usually uniform and regular [1,4]. One of the most aggressive media is sodium hydroxide (NaOH), where aluminate ions − Al(OH) 4 are formed [4]. ...
... The corrosion attack in inorganic acids or bases is usually uniform and regular [1,4]. One of the most aggressive media is sodium hydroxide (NaOH), where aluminate ions − Al(OH) 4 are formed [4]. To improve corrosion resistance of aluminium under such aggressive service conditions, various coating systems have been employed. ...
Article
The aim of this study was to prepare transparent hybrid sol-gel coatings to serve as a barrier for corrosion protection of aluminium. The coatings were synthesised using silicon precursors tetraethyl orthosilicate (TEOS) and organically modified silicon precursor 3-methacryloxypropyltrimethoxysilane (MAPTMS) which were then mixed with different amounts of zirconium(IV) propoxide (ZTP) chelated using methacrylic acid (MAA). The synthesis process was followed using in-situ Fourier transform infrared spectroscopy and liquid-state ¹H, ¹³C and ²⁹Si nuclear magnetic resonance spectroscopy. The coating properties, such as transparency, topography, chemical composition, morphology and wettability were evaluated. Corrosion properties were analysed using electrochemical methods in ∼0.1 N NaCl in a pH range between 3 and 10. The chemical stability was evaluated in strongly alkaline solution. Homogeneous composition of the coatings was achieved through condensation reactions between Si- and Zr-based precursors. Obtained coatings were highly transparent, increased the contact water angle for polar and non-polar liquids compared to bare substrate, and improved the cleaning properties. The electrochemical measurements confirmed remarkable barrier protection in NaCl solutions of various pHs, especially for coatings with high Zr/Si ratios. In harsh media such as 0.1 N NaOH, the coating with low Zr/Si ratio was more stable. The results were interpreted in terms of different degrees of polycondensation of Si species as a function of Zr content in the coating. The importance of chemical speciation of the sol during synthesis were emphasised as this affects the subsequent coating properties.
... This deposition rate is highly influenced by the Al oxidation rate and this oxidation rate is affected by the pH and temperature of the media [18]. It is observed that Al dissolution rate increases in acidic media and lowest in the neutral media [19][20]. The measured pH values of these baths are 1.3, 1.6 and 7.8 for the primary bath (P), P with NaH2PO2 and P with NaBH4 respectively. ...
... This might be a combined outcome of the acidic solution and high deposition temperature (95° C). The Al dissolution rate increases rapidly in high temperatures such as 60 to 80° C [18,20]. Additionally primary bath for deposition consisting of chloride solution and Al dissolves vigorously in high Clconcentration [20]. ...
... The Al dissolution rate increases rapidly in high temperatures such as 60 to 80° C [18,20]. Additionally primary bath for deposition consisting of chloride solution and Al dissolves vigorously in high Clconcentration [20]. ...
Article
Al-induced electroless process is used to fabricate Sn films on the mild steel substrates. The deposition reaction was performed by designing a Fe-Al galvanic couple where the optimum geometric area ratio between Fe-Al was 0.3. Additionally, NaBH4 and NaH2PO2 reducing agents were also added to enrich the deposit morphology and composition. The film surfaces were characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy and x-ray diffraction measurements. The analysis showed dense, uniform tin deposits with the presence of boron and phosphorous. The X-ray diffraction results confirmed the polycrystalline tetragonal structure with mostly (211) texture having an average 18 nm crystallite size. The anti-corrosion performance of these tin films has been studied by immersion in saltwater, open circuit potential measurement test, potentiodynamic polarization test, and electrochemical impedance spectroscopy. The effect of the coating thickness was also considered in anti-corrosion performance. The analysis showed the tin coated steel has commendable corrosion resistant property and the corrosion rate can be decreased up to 16 times with the addition of these coatings irrespective of the film thickness.
... This behavior differs from that of many other minerals that were found to be effectively dissolved under strong acidic conditions. 23,24 The main objective of this study was to investigate Pb dissolution in organic acids. However, it can be of interest to study its behavior in mineral acid such as HNO 3 . ...
... The progress of the reaction in HNO 3 up to total dissolution while pH stabilized aer 30 min was probably due to the effect of nitrates known as strong oxidants. 24,32 In the literature it was reported that in nitric acid H + and NO 3 À played an inverse role leading to a competing process between oxide growth and metal dissolution and that increasing the concentration of HNO 3 helps in developing and sustaining a passive lm on metal surface while in diluted solution nitrate ion played the role of corrosion promoter. 32 Our experiments were carried out under diluted conditions and it seems from the results obtained that the promoting effect of nitrates was more effective than that of ligands. ...
Article
Full-text available
A series of experiments were conducted to examine the effects of three organic acids (propionic, malic and citric acids) on the rate of Pb dissolution in order to evaluate its potential environmental pollution risk. The effects of acid concentration, agitation device, temperature and hydrodynamic conditions were investigated. The results show that propionic acid which contained the lowest number of functional groups had the greatest effect on Pb dissolution. In fact, it dissolved 100% of Pb particles after 35 min at the concentration of 5 mM at 25 °C while 92.1 and 47.6% were dissolved by malic and citric acid, respectively, under the same conditions. It was also found that the effect of the nature of the acid interfered with that of particle size and the hydrodynamic conditions making the system complicated to interpret totally.
... This evolution indicates that the metal surface is covered with a film which could be composed by the corrosion product and/or oxides. The pre-immersion air-formed oxide film (Al2O3) can exist in an acidic solution [14], and its stability depends on the anions' effect, rather than on the solution's pH [37]. It is worthy to note that Pourbaix diagram [38] does not mention the existence of this oxide in the pH range below 4. ...
... It is very difficult to get an aluminum surface free from an oxide film, due to its high reactivity with oxygen [49][50]. Therefore, it is reasonable to admit the formation of an oxide on aluminum and Al-22% Si alloy in the sulfuric acid solution, since it was proven that ions are not very aggressive for aluminum, even if the pH is low [37,43,51]. We can thus assign the capacitive loop to the global oxidation process of the base metal and of the silicon alloy at the metal/oxide/H2SO4 interface. ...
Article
Full-text available
The electrochemical degradability of Al-20% Mg and hypereutectic Al-22% Si industrial alloys was evaluated in an aggressive acidic environment, namely 1 M H2SO4, using potentiodynamic polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) techniques. The microstructure and constituting phases of the surface alloys were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), coupled with Energy Dispersive X-ray Spectroscopy (EDX). It was found that the two alloys' corrosion behavior mainly depends on their crystalline phases. The presence of the active intermetallic ß- Al3Mg2 phase in the Al alloy with high Mg content induced a preferential Mg dissolution, which caused a severe intergranular attack on this alloy by the corrosive solution. Meanwhile, the Al alloy containing high Si content, which presented the eutectic Al-Si phase, showed a uniform and weaker dissolution. It was also observed that a rise in temperature reduced the corrosion performance of the two studied alloys, as these corroded faster than pure aluminum.
... The corrosion is more destructive in acidic medium. Hydrochloric acid medium is used for pickling in chemical and process industries in which aluminium metal matrix composites are applied [7]. ...
... Also, it is clear from the figures that the percentage variation of strengthening leads to the decrease in current density. Thus, the addition of ZrC particles will diminish the corrosion resistance of the composites [5][6][7][8]. ...
Article
Full-text available
This paper aims to investigate the corrosion behavior of zirconium carbide (ZrC) reinforced Al - Si metal matrix composites (MMCs) in a mixture of acidic solution using weight loss method. The composites are prepared by powder metallurgy method. Al-12Si-xZrC composites containing 0, 5, and 10 weight percentage of ZrC particles are compacted in a die set assembly and sintered in an inert gas muffle furnace. The acidic solutions used for corrosion are 1 N HCl, 1 N H2SO4 and 1 N HNO3. The corrosion characteristics of Al-12Si-xZrC composites and the pure Al were experimentally evaluated. The corrosion test was carried out at different weight proportions of the samples in various concentrations of the acid such as 1 N HCl, 1 N H2SO4 and 1 N HNO3 for different exposure time (i.e., 24 h, 72 h, 144 h and 216 h), respectively. The results specified that corrosion rate of composites was lower than that of base metal Al under the corrosive atmosphere, regardless of exposure time and acidic solutions used as corrodents. Al-12Si-xZrC composites become more corrosion resistant as the ZrC content is increased. This is because of the development of stable oxide layer above the specimens. Scanning electron microscopy (SEM) confirms the degree of attack of acidic solution on the surface of the examined material.
... The corrosion is more destructive in acidic medium. Hydrochloric acid medium was used for pickling, chemical and process industries wherein aluminium metal matrix composites are used [7]. ...
... Also, it is clear from the figure that the percentage variation of strengthening lead to the decrease in current density. For evidence, the addition of ZrC particles will diminish the corrosion resistance of the composites [5][6][7][8]. ...
Article
This paper is to investigate the corrosion behavior of Zirconium Carbide (ZrC) reinforced Al-Si metal matrix composites (MMCs) in a mixture of acidic medium using weight loss method. The composites are prepared by powder metallurgy method. Al-12Si-x ZrC composites containing 0, 5, 10 and 15 weight percentage of ZrC particles are compacted in a die set assembly and sintered in an inert gas muffle furnace. The acidic mediums used for corrosion is 1 N HCl, 1 N H2SO4 and 1 N HNO3. The corrosion characteristics of Al-12Si-x ZrC composites and the Al were experimentally evaluated. The corrosion test was carried out at different weight proportions of the samples in various concentrations of the acid such as 1 N HCl, 1 N H2SO4 and 1 N HNO3 for different exposure time (i.e., 24h, 72h, 144h and 216h) respectively. The results specified that corrosion rate of composites was lower than that of base metal Al under the corrosive atmosphere regardless of exposure time and acidic mediums used as corrodent. Al-12Si-x ZrC composites become more corrosion resistant as the ZrC content is increased. This is because of the development of stable oxide layer above the specimens. Scanning Electron Microscopy (SEM) confirms the degree of attack of acidic medium on the surface of the examined material.
... The corrosion is more destructive in acidic medium. Hydrochloric acid medium was used for pickling, chemical and process industries wherein aluminium metal matrix composites are used [7]. ...
... Also, it is clear from the figure that the percentage variation of strengthening lead to the decrease in current density. For evidence, the addition of ZrC particles will diminish the corrosion resistance of the composites [5][6][7][8]. ...
Article
Full-text available
This paper is to investigate the corrosion behavior of Zirconium Carbide (ZrC) reinforced Al-Si metal matrix composites (MMCs) in a mixture of acidic medium using weight loss method. The composites are prepared by powder metallurgy method. Al-12Si-x ZrC composites containing 0, 5, 10 and 15 weight percentage of ZrC particles are compacted in a die set assembly and sintered in an inert gas muffle furnace. The acidic mediums used for corrosion is 1 N HCl, 1 N H2SO4 and 1 N HNO3. The corrosion characteristics of Al-12Si-x ZrC composites and the Al were experimentally evaluated. The corrosion test was carried out at different weight proportions of the samples in various concentrations of the acid such as 1 N HCl, 1 N H2SO4 and 1 N HNO3 for different exposure time (i.e., 24h, 72h, 144h and 216h) respectively. The results specified that corrosion rate of composites was lower than that of base metal Al under the corrosive atmosphere regardless of exposure time and acidic mediums used as corrodent. Al-12Si-x ZrC composites become more corrosion resistant as the ZrC content is increased. This is because of the development of stable oxide layer above the specimens. Scanning Electron Microscopy (SEM) confirms the degree of attack of acidic medium on the surface of the examined material.
... In addition to the electrochemical oxidation, another factor that may have aided in increasing the removal of the pollutants is the dissolution of the cathode, no great differences were observed between the dissolutions with the change of the support electrolyte, however, analyzing the variation of the initial pH, it is It is possible to observe that there are higher acidic pH solutions, followed by the basic pH and the neutral pH, as shown in figure 2. For acidic pH, the dissolution can be explained by the embrittlement of the oxide layer of aluminum under these conditions, once this phenomenon occurs, the aluminum is exposed to the effects of water evolution and corrosion by chemical attack [13] . For the basic pH, the dissolution is justified by the tendency of aluminum to undergo chemical corrosion under conditions of higher pH. ...
... Further removal of TOC with sodium nitrate at acidic pH without the association of the higher mass loss of the cathode under these conditions indicates that, in this case, the removal was not caused by the chemical coagulation from the cathodic dissolution. Nitric acid and nitrate species under acidic conditions are naturally oxidizing organic matter [13] , so the removal of carbon can be justified by the chemical attack of nitrate to the dye molecule during the process, witch occurs simultaneously to the oxidation and coagulation mechanisms studied. In this sense, nitrate is considered a better support electrolyte for promoting greater removal of TOC in comparison to chloride, although chloride results of faster color removal by the generation of oxidant species. ...
Conference Paper
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The association of the electrochemical oxidation (EO) method with electrocoagulation (EC) through the cathodic dissolution phenomenon is able to increase the effluent purification efficiency by using more removal mechanisms. In the present work, the effect of the supporting electrolyte (NaCl, NaNO 3 and Na 2 SO 4) and the initial pH (4, 7 and 10) on the degradation and removal of Red Remanzol RB 133% with platinum anode and aluminum cathode was studied. The color removal results showed that the presence of Cl-contributes significantly in color removal, reaching 100% removal at 5 minutes of experiment. In TOC removal, the presence of nitrate degraded organic species in acidic conditons, obtaining 39.77% of TOC removal. It was also found that the initial pH 4 favors EC by weakening the oxide layer of aluminum and EO by inhibiting reactions of oxygen evolution. The results obtained provided a further knowledge to the parameters that affect the EO/EC process removal efficiency.
... Aluminum leaching is also easily obtained in these conditions, as expected from Fig. 1. Sulphuric, hydrochloric or nitric acid are used (Boukerche et al., 2014), H 2 SO 4 being most commonly applied (Sun et al., 2016). ...
... Similarly aluminum sulphate solutions can be obtained by attack with sulphuric acid (Das et al., 2007;How et al., 2017). A similar reaction can also occur when treating aluminium metal with bases such as soda producing sodium aluminate solution with the evolution of hydrogen (Andersen, 2006;Boukerche et al., 2014). Pretreatment of aluminum by ball milling allows the reaction of aluminum also with tap water (David and Kopac, 2012). ...
Article
The waste materials available as sources of silicon and aluminum for producing porous materials like amorphous silicas, aluminas, amorphous silica-aluminas, and zeolites, to be used as catalyst and adsorbents, are briefly summarized. The procedures for preparing these materials from wastes are also taken into account. The limits of this approach in terms of economy and environmental protection are also briefly considered. It is concluded that mesoporous materials can be prepared from wastes, but care to product quality and to overall process efficiency is needed.
... With progressing exposure of aluminium to an alkaline solution, Al(OH)3 starts to limit the diffusion rate of ions reducing the corrosion rate [4,6,8]. Furthermore, the corrosion rate of aluminium in alkaline solutions is greatly influenced by physico-chemical properties of the environment, such as temperature, pH, conductivity etc. Detailed information on the corrosion mechanism of aluminium and its alloys in alkaline environments can be found in [9][10][11][12][13][14]. ...
Article
Full-text available
The efficiency of AA5754 aluminium alloy corrosion inhibition achieved with maleic, malic, succinic, tartaric, citric, tricarballylic acids and serine in alkaline environment (pH 11) was examined. Selected corrosion inhibitors are characterized by different numbers and distribution of carbonyl and hydroxyl groups within their molecules. We have proposed and verified a novel approach for determining the adsorption isotherms based on the impedance measurements in galvanostatic mode (g-DEIS), allowing to distinguish subtle changes in the adsorption dynamics. It was shown that g-DEIS precisely determines the inhibitor concentration required for the full coverage of aluminium surface with the adsorbed inhibitor monolayer. Our approach was then cross-verified with the ellipsometry, cyclic polarization and classic EIS measurements, while the SEM and XPS analyses served to determine changes in the surface topography and chemistry. We have demonstrated that the investigated compounds significantly decelerate the corrosion rate of AA5754 at low inhibitor concentrations. Inhibition efficiency exceeds 99% at 6.9 mM for tricarballylic, 8.1 mM for citric and 12.0 mM for tartaric acid. The inhibition efficiency was primarily dependent on the high number of carbonyl groups in the molecule, while the inhibition provided by monocarboxylic amino acid (serine) was negligible, reaching 60% at 20 mM. The plotted isotherms fitted the Langmuir adsorption model, with similar values of Gibbs free energy for each studied inhibitor. The adsorption of carboxylic acids onto the surface of aluminium occurred via ligand exchange mechanism. On the basis of electrochemical and XPS studies, we claim that the role played by hydroxyl groups is secondary, while their presence slightly worsens the corrosion resistance of aluminium.
... Generally, the corrosion resistance of the aluminum alloys in many corrosive environments is high because of the formation of a natural thin alumina film on their surface upon exposure to humid air [1]. The natural alumina film can provide excellent resistance against the corrosive species in the pH between 4.0 and 8.5 [2]. However, the protective capacity of the alumina film is failed in acidic and alkaline environments and also in the presence of chloride ions. ...
Article
In this work, MIL-53 (Al) nanoparticles were synthesized and then were characterized by SEM, EDS, FTIR, TGA, and BET techniques. Afterwards, the nanoparticles were incorporated in hybrid (TEOS + GPTMS) sol-gel coating as nano-filler and the obtained nanocomposite was applied on Al 2024 alloy. Micro-sized defects were disappeared from surface of the coating after addition of the nanoparticles. Uniform distribution of the nanoparticles in the matrix of the sol-gel coating was confirmed by TEM. Also, average roughness of the coating was reduced from 76 to 17 nm after addition of the MIL-53 (Al) nanoparticles. Thermal stability of the sol-gel coating was improved by the nanoparticle incorporation. The FTIR method was also successfully used to confirm the chemical interaction between the incorporated nanoparticles and the silica coating. The results of the EIS tests in Harrison's corrosive media indicated that the corrosion resistance of the sol-gel coating was remarkably enhanced after incorporation of the MOF nanoparticles in 1 g L⁻¹ concentration so that the polarization resistance of the nanocomposite coating was about 68 times higher than the neat coating after 24 h immersion. This result was attributed to the chemical interaction between the silica matrix and embedded nanoparticles and so, formation of more compact silica structure.
... However, Al-Zn-Mg alloy dissolves faster in alkaline solution than in acid solution due to ready thinning of the passive film. In alkaline solution, the overall reaction is governed as follows [33]: ...
Article
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Stress corrosion cracking (SCC) susceptibilities of Al-Zn-Mg alloys without and with Scandium addition were evaluated in 3.5% NaCl solution at different pH and different strain rate, using slow strain rate test technique. The results indicate that Sc addition reduces grain size and width of precipitation free zones, and transforms grain boundary precipitates from continuous distribution into interrupted distribution by inhibiting recrystallization. In solution at pH 1, pH 3 and pH 7, Sc addition reduces the degree of localized corrosion of alloy surface and SCC susceptibility of Al-Zn-Mg alloy. However, in solution at pH 10 and pH 12, grain refinement significantly promotes the diffusion of hydrogen atoms into matrix, thus Sc addition increases SCC susceptibility of Al-Zn-Mg alloy. Under different strain rate conditions, Sc addition can all reduce SCC susceptibility of Al-Zn-Mg alloy in solution at pH 1, pH 3 and pH 7, and can all increase SCC susceptibility of Al-Zn-Mg alloy in solution at pH 10 and pH 12. As a result, Sc modified Al-Zn-Mg alloy in practical applications should be avoided in alkaline environments.
... In alkaline solution, the corrosion involves the electrochemical dissolution of Al [53,64], via both anodic and cathodic processes occurring simultaneously on the metal-electrolyte interface [63,65]. To understand the underlying mechanism of the corrosion, it is important to explore which partial anodic and partial cathodic reactions are involved, and which of them prevails in the gross corrosion reaction. ...
Article
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This article reports the influence of the state of artificial ageing on the hardness, tensile properties and corrosion behavior of an Al-Mg-Si alloy. Pitting corrosion in 0.1 M NaOH solution and susceptibility to intergranular corrosion (IGC) have been systematically investigated, covering highly under-aged to highly over-aged states. In alkaline solution, corrosion rate increases with the progress of ageing; while for a given state of ageing, it initially increases with immersion time followed by rapid reduction since corrosion is controlled by the competition of formation and dissolution of Al(OH)3plus Al2O3film as determined by FESEM, EDS, and XRD characterizations. The IGC susceptibility of the selected alloy is found to be governed by the microstructure as determined by the state of ageing since it is controlled by the anodic dissolution of the precipitate free zones while closely neighboured grain boundary precipitates act as cathode. It is identified as slight to moderate pitting in highly under-aged, moderate to heavy pitting in under-aged, pitting with localized ICG in peak-aged, localized to uniform IGC in over-aged, and uniform IGC to etching in highly over-aged state. It is adjudged that apart from the inclusions like AlCrMnFeSi, the changes in the precipitation such as �” (Mg5Si6), �’ (Mg9Si6) and � (Mg2Si) within the grains and at the grain boundaries with progress of artificial ageing play a pivotal role on mechanical properties and corrosion characteristics of the Al-Mg-Si alloy.
... Thus, when NO3and H + are present, a competition between oxide film growth and metal dissolution occurred [22]. This was observed in our previous study [23]. Thus, at 2M NO3it can be supposed that the oxide film growth on zinc surface was more important that at 0.5M NO3 -leading to decrease Zn dissolution. ...
Article
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A series of experiments were conducted to examine the effect of citric acid on the dissolution of zerovalent zinc. The effects of citric acid concentration, the presence of anions and temperature were studied. The results have shown that zinc dissolution registered a maximum of 34% with 0.5M citric acid after 270 min and that the nature of anions present with citric acid affected differently the dissolution rate. In fact, the presence of 2M nitrates with 0.5M citric acid dissolved totally zinc after 30min while 91.85% and 13.15% were dissolved in the presence of 2M chlorides and sulfates respectively after 270min. SEM analyses have shown that the morphology of the corroded surface depended on the composition of the solution. The kinetic study has shown that zinc dissolution was controlled by the chemical reaction in all cases and that the activation energy was 39.3 kJ mol-1.
... In EGR and ACAC systems, the use of aluminium alloys is limited due to corrosion by the exhaust gases, which are acidic in nature and contain water [15,16]. Corrosion occurring on the air side of heat exchanger tubes is a critical issue and is currently the main issue for continued down-gauging and weight reduction [11,17,18]. ...
Article
A combination of glow discharge optical emission spectroscopy sputtering and local electrochemical measurements was used to determine electrochemical changes upon brazing in a multi-layered Aluminium sheet (AA4343/AA3xxx/AA4343) with an additional low-Cu (AA3xxx) interlayer. Ecorr values from potentiodynamic polarization, galvanic corrosion behaviour by ZRA, microstructure and composition by SEM and TEM were investigated and compared to those obtained for sheet without the interlayer. Inward diffusion of Si from clad, and outward diffusion of Cu from core are found to degrade the corrosion properties of conventional sheet, whereas presence of interlayer reduced outward diffusion of Cu and hence improved corrosion protection.
... For this reason, we infiltrated aqueous solutions of 10% and 100% Phosphate-Buffered Saline (PBS) as well as a NaCl solution over the aluminum waveguide surface, using the microfluidic channels. Buffer solutions with pH levels around 7 were used in order to avoid pH changes that may harm the surface of the aluminum transducer [36][37][38], also mimicking the pH of blood (pH= ∼7.4) making the proposed sensor suitable for future biosensing applications. The different sample fluids were delivered to the sensing area of each sensor using a syringe pump (neMESYS 290N) via Polytetrafluoroethylene tubes while software controlled fluidic valves were utilized to easily select which fluid is injected in the sensor. ...
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Optical refractive-index sensors exploiting selective co-integration of plasmonics with silicon photonics has emerged as an attractive technology for biosensing applications that can unleash unprecedented performance breakthroughs that reaps the benefits of both technologies. However, towards this direction, a major challenge remains their integration using exclusively CMOS-compatible materials. In this context, herein, we demonstrate, for the first time to our knowledge, a CMOS-compatible plasmo-photonic Mach-Zehnder-interferometer (MZI) based on aluminum and Si3N4 waveguides, exhibiting record-high bulk sensitivity of 4764 nm/RIU with clear potential to scale up the bulk sensitivity values by properly engineering the design parameters of the MZI. The proposed sensor is composed of Si3N4 waveguides butt-coupled with an aluminum stripe in one branch to realize the sensing transducer. The reference arm is built by Si3N4 waveguides, incorporating a thermo-optic phase shifter followed by an MZI-based variable optical attenuation stage to maximize extinction ratio up to 38 dB, hence optimizing the overall sensing performance. The proposed sensor exhibits the highest bulk sensitivity among all plasmo-photonic counterparts, while complying with CMOS manufacturing standards, enabling volume manufacturing.
... Where i corr and i corr(inh) are the corrosion current density for the aluminum electrode in 4 M NaOH solution with and without additives, respectively. The reaction mechanism of aluminum in alkaline electrolyte has been established, which could be divided into a multistep electrochemical process and a serial of chemical reactions [58,59]: ...
Article
The low anode utilization and large capacity loss of aluminum due to the severe self-corrosion in alkaline electrolyte extremely restrict the practical applications of aluminum-air batteries. The vital challenge lies in the issue to slow down the self-corrosion rate without decreasing the discharge performance of aluminum anode. In this work, the application of zinc sulfate (ZnSO4) and sodium alginate (SA) as electrolyte additives to mitigate the corrosion of aluminum is investigated by hydrogen evolution test as well as the electrochemical measurements. The results show that zinc sulfate decreases the corrosion rate of aluminum mainly by restraining the cathodic reaction and exerts positive effect on the improvement of discharge performance for aluminum-air batteries. The hybrid ZnSO4/SA additive exhibits higher inhibition efficiency for the corrosion of aluminum than single ZnSO4 or SA, the adsorbed SA stabilizes zinc layer and improves the protective performance. Moreover, the cell voltage is prominently elevated while the discharge capacity increases from 162.46 to 267.41 mAh cm⁻² with the dosage of 10 mM ZnSO4 and 1 g/L SA. A possible model is also proposed to elaborate the influence mechanism of the additive on the self-corrosion behavior and discharge performance of aluminum-air batteries.
... The SEM image of corroded sample immersed in pH 1 solution clearly shows pores due to the uniform degradation of alloys. High aggressive attack of chloride ions breaks down of the passive film formed on the surface of the alloys [18]. The weight percentages of elements found by corresponding EDX analysis of the SEM are 42.14% ...
Article
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Corrosion behaviour of hypereutectic Al-19Si automotive alloy in different pH=1, 3, 5, 7, 9, 11, and 13 environments was carried out using conventional gravimetric measurements and was complemented by resistivity, optical micrograph, scanning electron microscopy (SEM) and X-ray analyzer (EDX) investigations. Gravimetric analysis confirmed that the highest corrosion rate is shown at pH 13 followed by pH 1. Minimum corrosion occurs in the pH range of 3.0 to 11 due to establishment of passive layer on the surface. The highest corrosion rate at pH 13 is due to the presence of sodium hydroxide in the solution which dissolves the surface oxide film at a steady rate. At pH 1, it can be attributed that the presence of aggressive chloride ions serves to pick up the damage of the passive films at localized regions. With varying exposure periods by both, the environment complies with the normal corrosion rate profile that is an initial steep rise followed by a nearly constant value of corrosion rate. Resistivity increases in case of pH 1 solution for the higher pit formation and decreases at pH 13 due to formation of thin film. The SEM image of corroded samples immersed in pH 1 solution clearly shows pores on the surface and in pH 13 solution, and the corrosion layer seems more compact and homogenous and not porous.
... Moreover, results suggested a potential use of a natural product, GL, as a sanitizing agent which can be used in place of alkaline detergents, generally responsible for aluminum corrosion [59] and nanoparticle release and accumulation in food, and in turn, in the human body [60]. GL is a natural product rich in flavonoids [48,61], in particular naringin, hesperidin and nobiletin, which already showed strong antibacterial activity against all tested bacteria [62][63][64][65]. ...
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One of the main concerns of food industry is microbial adhesion to food contact surfaces and consequent contamination. We evaluated the potential bacteriostatic/bactericidal efficacy of aluminum surfaces with different large-scale roughness (0.25, 0.5 and 1 m) before and after the surface treatment with a special anodizing based on titanium oxide nanotechnology (DURALTI) and after 3 different sanitizing treatments, e.g., UV, alcohol and a natural product named Gold lotion. Four Gram-negative (Escherichia coli ATCC 25922, Salmonella typhimurium ATCC 1402, Yersinia enterocolitica ATCC 9610 and Pseudomonas aeruginosa ATCC 27588) and four Gram-positive (Staphylococcus aureus ATCC 6538, Enterococcus faecalis ATCC 29212, Bacillus cereus ATCC 14579 and Listeria monocytogenes NCTT 10888) were screened. As far as concerns aluminum surfaces without nanotechnology surface treatment, an overall bacteriostatic effect was observed for all strains with respect to the initial inoculum that was 106 CFU/ml. Conversely, an overall bactericidal effect was observed both for Gram-negative and -positive bacteria on DURALTI-treated aluminum disks regardless of roughness and sanitizing treatment. These results are innovative in terms of the great potential of the antibacterial activity of nanotechnologically-treated food contact surfaces and their combination with some sanitizing agents that might be exploited in food industry.
... That is, oxide-layer corrosion exposes more Al surface and boosts H 2 production. Similar phenomena that emphasize surface defect sites corresponding to dissolution results were discussed [23,38]. ...
Article
Hydrogen is gaining attention as an energy source, but its production through fossil-fuel use is not environmentally friendly. A more sustainable source could be the hydrothermal reaction involving aluminum and water reaction, which owns technical issues on aluminum passivation and material sources for the upscale application. This study analyzes the aluminum-water hydrothermal reaction at laboratory and field scales and includes an environmental assessment of H2 fuel production involving hot-spring water with extremely low pH (~1) and boiling temperature (~373 K). Acidic hot-spring alternates water sources, and its unique feature activates aluminum surface by attacking oxide layer, hence enables H2 generation. Aluminum waste sources include dross and cutting chips, which could replace primary aluminum metal. The highest H2 yield could be obtained of about ~55 mmol H2 gAl⁻¹ for the chip (almost reached theoretical yield) and a smaller amount of ~20 mmol H2 gAl⁻¹ for dross. The environmental assessment comprises carbon dioxide emissions and energy consumption from the overall H2 fuel system resulting in a reduced environmental impact. The proposed hydrogen production method encourages hydrogen energy development from the local scale. In addition, the use of aluminum waste materials is a new and useful waste management strategy than direct disposal, and hot-springs use advances its direct utilization.
... This is probably related to the nature of the anion of each acid. In the literature, there is an increasing interest on the effect of anions on the dissolution of minerals [25]. In fact, it was reported that the aggressivity of chlorides in metal oxides dissolution was due to the formation of chloro-complexes as adsorbed species with high value of adsorption constant that leads to enhance the metal oxide dissolution [21]. ...
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In this study the leaching of NiO from NiO/α-Al2O3 catalyst in acidic (HCl, HNO3 and H2SO4) and ammoniacal ((NH4)2CO3, CH3COONH4) media was investigated. The effects of leachant concentration, liquid/solid ratio, stirring speed and temperature were studied. It was found that 100% of nickel was dissolved after 30min of reaction with HCl at 2M, 80°C and liquid/solid ratio of 50mL/g, while HNO3 and H2SO4 dissolved 77.15% and 46.12% respectively under the same operation conditions. Mixing two strong acids led to a synergetic effect on nickel leaching at the beginning of the reactions followed by a rapid stabilization in dissolution. Ammoniacal leaching was less efficient than acidic one registering 41.43% with ammonium carbonate and 29.16% with ammonium acetate after 180min. However, the addition of chlorides to ammonium carbonate led to totally dissolve NiO.
... Les ions nitrate permettraient de limiter la dissolution de Al (III). [120] L'ion aluminate soluble AlOH4précipiterait d'abord sous forme de Al(OH)3 sur la surface d'aluminium. Dans les solutions à pH 7 ou plus, cependant, la transformation de l'hydroxyde Al(OH)3 en boehmite AlOOH est thermodynamiquement favorisée, en particulier sous un potentiel anodique appliqué. ...
Thesis
L’objectif de cette thèse est de comprendre les processus associés à l’électrodépôt d’uranium pour sélectionner les meilleures conditions et améliorer la qualité des cibles utilisées pour des recherches en physique nucléaire. Les couches minces d’uranium ont été préparées par électroprécipitation dans l’isobutanol, sur un substrat en aluminium. Les électrolyses ont été réalisées avec un montage à deux électrodes en imposant une tension. Une partie a été consacrée à la définition de l’électrolyte, en tenant compte de la viscosité, la densité, la conductivité électrique et des propriétés redox. Le principe de l’électroprécipitation consiste à la production d’ions OH⁻ à la cathode. Ces ions réagissent ensuite avec l’élément à déposer pour former un hydroxyde ou un oxyde hydraté qui précipite à la cathode. L’isobutanol est un solvant visqueux et peu conducteur.Lors de l’électrolyse, les ions OH⁻ se concentrent au voisinage du substrat et forment un « mur basique ». Les résultats montrent qu’il est préférable de rajouter de l’eau en fort excès par rapport à la quantité nécessaire pour atteindre le pH de début de précipitation et pour réagir avec la totalité de l’uranium initialement en solution. Une concentration de 1 mol.L⁻¹ d’eau permet d’obtenir avec de bons rendements des cibles homogènes et peu rugueuses. Pour améliorer la conductivité de la solution, il faut aussi rajouter des ions à une concentration supérieure ou égale à 2×10⁻³ mol.L⁻¹. L’uranium sous forme de sel de nitrate est soluble et totalement dissocié en cation UO₂²₊ à des pH inférieurs à 4 en solution aqueuse. L’acide nitrique a été sélectionné comme additif. Cependant, en présence de HNO₃,l’aluminium est corrodé et sa surface est dégradée. Ceci peut provoquer une mauvaise adhérence du dépôt au substrat.Pour limiter cette corrosion néfaste à la qualité de la cible, il faut limiter la teneur en acide nitrique à des concentrations inférieures à 3×10⁻³ mol.L⁻¹. Des feuilles de Al de différentes épaisseurs ont été caractérisées. Plus la feuille est mince,moins elle est rugueuse. Ceci est intéressant car les cibles pour les mesures en physique doivent être réalisées sur des feuilles les plus minces possibles. Des dépôts d’uranium ont pu être préparés avec des rendements supérieurs à 90%, mais avec des rendements faradiques faibles. La durée d’électrolyse doit être limitée car plus le temps est long, plus le dépôt d’uranium devient rugueux. Les analyses électrochimiques indiquent que la formation des ions OH⁻ est principalement réalisée par réduction de l’eau. Cette réaction s’accompagne de la formation d’hydrogène gazeux qui peut détériorer localement le dépôt. Les résultats ne permettent pas de conclure si les ions nitrate participent aussi à la formation des ions OH⁻ car ils sont 1000 fois moins concentrés que l’eau. Dans ces conditions, on ne peut pas non plus savoir si l’uranium (VI) est réduit pendant l’électrolyse. On observe la formation de deux couches, avec une couche supérieure constituée de plaques très lisses et séparées de fissures plus ou moins larges. Le traitement thermique du dépôt favorise la formation des fissures. Si le substrat est prétraité pour le rendre plus lisse, la couche déposée est plus uniforme, avec une rugosité moindre et une adhérence améliorée. Les analyses chimiques des dépôts suggèrent la formation d’un hydroxyde d’uranium (VI) hydraté et de studtite.
... The coating thickness was measured by cross-section scanning electron microscopy images and varied depending on the substrate (31.1 ± 8.2 nm and 18.7 ± 4.0 nm, for AA1100 and AA2024, respectively) ( Figure S1, supporting file). Those differences in the ZrO 2 coating thicknesses are associated to the presence of thick and stable Al 2 O 3 and Al(OH) 3 passivating layers in AA1100 grade after treatment with alkaline solutions (dissolution of Al(OH) 4 − ) and neutralization [49]. In AA2024 surfaces, the alkaline etching of Al surface prevents such thick structures in a certain way, due to the oxide/hydroxide enrichment with Cu compounds (dealloying process) in presence of basic solutions [50,51]. ...
Article
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In this work, the use of ZrO2 nanocoating in aluminum substrates, generated by controlled electrochemical chronoamperometry in hexafluorozirconic acid solutions (H2ZrF6·5H2O), resulted in a lower porous films than that obtained by chemical conversion coating. After the application of an epoxy coating, long-term cyclic immersion corrosion tests and scratch tests proved the superior protection of the dual system and the coating lifespan, thanks to the enhanced adhesion of ZrO2 intermediate layer and the organic coating. As zirconium-based electrolytes are considered more friendly bath if compared to that of other conversion coating processes, like chromating, phosphating or anodizing processes, the study opens new insights to the protection of structural metals in sectors such as automotive, naval and aerospace industries. The main advantages are the employment of lightweight intermediate pre-treatment (nanoscale), compared to conventional ones (microscale), and reduction of waste slurry (electrolyte bath free of additives).
... These produced compounds acting as filler can occupy the previously corroded positions and contribute to the strong anticorrosion ability of aluminum and aluminum alloys after the air pollutants are oxidized [37]. It was found that Al dissolution was affected by the molecular interaction between anions and aluminum instead of the solution pH [38]. In addition, the SO 2 , NO 2 , and NO gases have a synergistic effect on the corrosion of aluminum and its alloys in the atmosphere [39]. ...
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Aluminum windows are crucial components of building envelopes since they connect the indoor space to the external environment. Various external causes degrade or harm the functioning of aluminum windows. In this regard, inspecting the performance of aluminum windows is a necessary task to keep buildings healthy. This review illustrates the deterioration mechanisms of aluminum windows under various environmental conditions with an intention to provide comprehensive information for developing damage protection and inspection technologies. The illustrations reveal that moisture and chloride ions have the most detrimental effect on deteriorating aluminum windows in the long run, while mechanical loads can damage aluminum windows in a sudden manner. In addition, multiple advanced inspection techniques potential to benefit assessing aluminum window health state are discussed in order to help tackle the efficiency problem of traditional visual inspection. The comparison among those techniques demonstrates that infrared thermography can help acquire a preliminary defect profile of inspected windows, whereas ultrasonic phased arrays technology demonstrates a high level of competency in analyzing comprehensive defect information. This review also discusses the challenges in the scarcity of nanoscale corrosion information for insightful understandings of aluminum window corrosion and reliable window inspection tools for lifespan prediction. In this regard, molecular dynamics simulation and artificial intelligence technology are recommended as promising tools for better revealing the deterioration mechanisms and advancing inspection techniques, respectively, for future directions. It is envisioned that this paper will help upgrade the aluminum window inspection scheme and contribute to driving the construction of intelligent and safe cities.
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This paper presents results of our continuing project on the mechanochemical activation of Al-based composites for hydrogen generation [1,2]. A series of bi- and ternary Al, Sn, and/or In composites were mechanochemically prepared and their reactivities towards neutral pH water at ambient conditions determined. Hydrogen generation was compared to previously reported data from related studies in Refs. [1] and [2]. Scanning electron microscopy (SEM) energy dispersive x-ray spectrometer (EDS) analysis suggests that Sn and In could be distributed relatively homogeneously onto and into Al particles exteriors and interiors, respectively. Such distribution allowed continuous micro-galvanic activity between anodic Al and cathodic Sn and In during hydrolysis reactions. X-ray diffraction indicated that in-situ Sn–In intermetallic phase formation was determined by the Sn:In mol ratio of each composite. The formed Sn–In phases included Sn4In and SnIn3. Some AlSn phases were detected in ternary composites. Reactive composites (>95% yield) exhibited relatively similar reactivities and it was found that composites containing various intermetallic phases had shorter induction periods than composites containing a single intermetallic phase.
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Scanning electron microscopy, potentiodynamic polarization method, and electrochemical impedance spectroscopy were used to study the corrosion behavior of AD31 (AA6063) aluminum alloy in acid (pH 3) 0.05 M NaCl solutions containing 3 mmol dm–3 of NaVO3 inhibitor. It was found that the corrosion of AD31 alloy in acid sodium chloride solutions predominantly occurs locally at aluminum/intermetallic particle phase boundaries and is limited by the electrochemical stage of charge transfer. It was shown that introduction of sodium vanadate can reduce the rate of selective dissolution of magnesium from the alloy and provides a protective effect on the level of 7–10%.
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Hydrogen can be one of the key elements as source of future energy requirement. Water splitting reaction is an important route for generation of hydrogen as maximum fraction of hydrogen constitute in water. The present work describes the experimental investigation for generation of hydrogen through water splitting reaction in flow conditions with the aid of metal aluminum and sodium hydroxide as an activator. The hydrogen generation through water splitting reaction at various concentrations of NaOH, viz. 0.5 N and 1 N and the flow rates ranging from 0.2 to 10 ml/min was studied. The yield of hydrogen generated is reported for each NaOH concentration and flow rate. The yield of hydrogen generated at all the considered concentrations and flow rates was found to be greater than 98 %. The shrinking core model has been modified and developed for predicting the conversion of aluminum in the reaction system as per the prevailing conditions and rate controlling mechanism. The RMSE value of predicted conversion of Al was found to be 0.0351 which signify that the model agrees well with the experimental data.
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The kinetics of the heterogeneous reaction of metal aluminum with water was studied in presence of NaOH as an activator for generating the hydrogen. Aluminum (Al) powder of average size of 100 µm and foil of thickness of 11 µm were utilized to study the effect of the shape of particles of aluminum on hydrogen generation. The hydrogen generation was reported at various concentrations of NaOH, ranging from 0.12 N to 0.67 N. The fractional conversion of Al was found to be 0.66 at 0.12 N and 1.0 at 0.185 N, 0.37 N, 0.54 N, 0.65 N NaOH concentration. The activation energy of the reaction has been determined at the stoichiometric concentration of 0.185 N NaOH at the temperature ranging from 298 to 323 K. An attempt was made to model the reaction using Shrinking Core Model (SCM) for determining the rate controlling mechanism for the heterogeneous reaction. The reaction was observed to follow the first order kinetics and the average value of reaction rate constant using Al power and foil was found to be 27.322 x 10 ⁻⁴ cm/min and 2.125 x 10 ⁻⁴ cm/min respectively.
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The individual and combined effects of Bi and In on the morphology change and reactivity towards hydrogen release of Al during mechanochemical preparation of binary and ternary Al composites were determined. Subsequently, successfully prepared reactive composites were hydrolyzed with neutral pH waters under ambient conditions with the purpose of hydrogen generation. Reactive ternary composites were analyzed by scanning electron microscopy and X-ray diffraction. Results showed that phases found in the AlBiIn composites were Al, BiIn, BiIn3, and Bi3In5. In some cases Bi and In that did not partake in intermetallic BiIn phase formation were also found. The intermetallic phases between Bi and In were identified and characterized. It was concluded that the reactivity of ternary composites towards hydrogen yield were governed by the in situ formed intermetallic phases, and the remaining Bi and In that did not undergo intermetallic phase formation.
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Aluminum sheets-based mirrors are finding applicability in high-temperature solar concentrating technologies because they are cost-effective, lightweight and have high mechanical properties. Nonetheless, the reflectance percentages obtained by electropolishing are not close to the reflectance values of the currently used evaporated films. Therefore, controlling key factors affecting electropolishing processes became essential in order to achieve highly reflective aluminum surfaces. This study investigated the effect of both the electropolishing process and previous heat treatment on the total reflectance of the AA 1100 aluminum alloy. An acid electrolyte and a modified Brytal process were evaluated. Total reflectance was measured by means of UV–Vis spectrophotometry. Reflectance values higher than 80% at 600 nm were achieved for both electrolytes. Optical microscopy and scanning electron microscopy images showed uneven dissolution for the acid electropolished samples causing a reflectance drop in the 200-450 nm region. The influence of heat treatment, previously to electropolishing, was tested at two different temperatures and various holding times. It was found that reflectance increases around 15% for the heat-treated and electropolished samples versus the non-heat-treated ones. A heat treatment at low temperature combined with a short holding time was enough to improve the sample total reflectance.
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The electrochemical behavior of aluminum in tannin from Acacia mearnsii bark was evaluated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in media under three different pH conditions: acid, alkaline, and neutral. A relationship among pH, polymerization grade (PG), zeta potential, surface, and electrochemical properties was observed in the inhibition performance of the tannin. At high pH, the oligomer structure of the tannin was affected, resulting in a low PG (4) and high zeta potential (−75 mV), and consequently, the inhibition efficiency decreased (68%) in comparison with that in acid (99%) and neutral media (96%). The values obtained indicate a physisorption mechanism for the aluminum corrosion inhibition in the studied conditions.
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For decades, zinc- and aluminum-based coatings have been considered the best material choice for steel corrosion protection since they may act as a protective barrier and show sacrificial behavior. These coatings are often prepared by galvanizing methods. However, their application by thermal spraying techniques (wire arc spraying, WAS and flame spraying, FS) has been proved as a cost-effective solution for the preparation of long-term corrosion-resistant coatings. This review selectively collects the most relevant information about the application and performance of these two techniques on Zn and Al coatings for corrosion protection. The report summarizes separately the Zn and Al data from the effect of the spraying parameters on coating properties on the one hand, and the results shown in long-term studies carried out in relevant and real exposure conditions, on the other. Finally, this review includes a description and comparison of the most recent advances found out with the novel and emerging spray technique, cold gas spray, for the deposition of Zn and Al coatings for corrosion protection purposes. Nevertheless, the use of this technique has not reached the stage of wide industrial application yet and therefore its long-term performance is unknown, which suggests that there is still room for further development.
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The hydrolysis of aluminum (Al) is a relatively simple method for on-demand hydrogen generation for niche (low-power, <1 kW) proton exchange membrane fuel cell applications. The hydrolysis of Al in neutral pH water and under standard ambient conditions is prevented by the presence of a thin surficial oxide layer. A promising method to enable Al’s spontaneous hydrolysis is by its mechanochemical activation (ball milling) with certain metals (e.g., Bi, Sn, In, Ga). This overview presents several aspects relating to the changes occurring in Al particles during ball milling, e.g., the structural and morphological behavior of Al during ball milling procedures (with and without the presence of activation metals), and the distribution and homogenization of Al and various activation metals. The formation of galvanic cells between anodic Al and cathodic activation metals (relative to Al) is discussed. A summary of the existing Al composites for on-demand hydrogen generation is presented. The paper concludes with a discussion of activation metal recovery, and the effects thereof on the economic feasibility of Al composites for hydrogen generation.
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Transient electronics represents a class of technology defined by components that physically or chemically disintegrate, dissolve, or otherwise disappear in a controlled manner for application opportunities that lie outside of those that can be addressed with conventional, permanent devices. Materials and system designs that allow for initiation of the transient processes upon well-defined trigger events are of particular interest for uses in areas such as hardware-level data security, unrecoverable proprietary electronics, and certain classes of temporary biomedical implants. Progress relies on the development of advanced materials for this purpose and a detailed understanding of the mechanisms by which they respond to various physicochemical stimuli. This review summarizes a diverse range of materials recently explored in this context, with responsiveness to changes in temperature, exposure to water, illumination with light, and delivery of electrical current. Subsequent sections present demonstrations of these materials as the basis for triggered transient devices with active operation. Strategies that exploit a cascade or a combination of triggering events represent important additional trends in this field of technology, laying the groundwork for a broad range of electronic devices with precisely controlled lifetimes.
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The purpose of this paper is to investigate the microstructural and corrosion behaviors of Al–B4C nanocomposites fabricated by the stir casting technique. Two parameters included the stirring time and temperature have changed in the manufacturing process to affect the characteristics of nanocomposites. Both the optical microscopy (OM) and the field emission scanning electron microscopy (FESEM) were utilized for microstructural evaluations. Moreover, the X-ray diffraction (XRD) and the energy dispersive spectroscopy (EDS) methods were used to identify various phases and to study the elemental analysis of specimens, respectively. In addition, the polarization and electrochemical impedance spectroscopy (EIS) techniques were employed to peruse the corrosion properties of fabricated nanocomposites in various corrosive environments. The FESEM images showed that B4C nanoparticles were distributed uniformly in the aluminum matrix. Polarization test results demonstrated that the corrosion rate of Al–B4C nanocomposites decreased to lower than 99% compared to the aluminum alloy in 0.6 M NaCl solution; however, such a reduction was about 22–42% in 2 M NaOH solution. The EIS test results depicted that the total increase in the charge transfer resistance values for Al–B4C nanocomposites was about 23–59% with respect to the aluminum matrix in 0.1 M HCl solution. Regression analysis results displayed that for acidic solutions (such as HCl and H3BO3) the stirring temperature was more effective than the stirring time to reduce the corrosion rate.
Article
Al and Al2O3 film react with strong acid or alkaline solution, bring the extensive corrosion. To decrease the corrosion, Al is first pretreated with a small amount of HCl, NaOH, NaAlO2 and a mixture of NaAlO2+Al(OH)3 in this work. Al pretreatment allows for the rapid removal of oxide film, shortens the induction time and ensures the initial Al–H2O reaction rate. Typically, immersion of the pretreated Al by a mixture of NaAlO2+Al(OH)3 into water, generates hydrogen rapidly without an induction time, and the average H2 generation rate reaches 5.5 mL min⁻¹. As the Al–H2O reaction proceeds, the potential changes, which is similar to hydrogen evolution of pretreated Al in water. Hydrogen generated rapidly with the consecutive addition of Al, and the initial hydrogen generation rate reaches ~37 mL min⁻¹. Therefore, Al pretreatment by a mixed alkaline solution is an effective method to accelerate hydrogen generation for the first cycle. Rapid and consecutive hydrogen generation by the Al–H2O reaction could provide on-demand and high-purity hydrogen, meet some equipment requirements and promote the competition in renewable-energy sources.
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The corrosion inhibition ability of l‐malic acid (MaA) and l‐aspartate acid (AsA) against corrosion of the AA5052 alloy in 4 M sodium hydroxide–ethylene glycol solution is investigated. The presence of MaA and AsA in corrosion solution shows a remarkable inhibition of hydrogen evolution of the AA5052 alloy. AsA has the better inhibition effect for the self‐corrosion of the AA5052 alloy and its max protection efficiency is 82.1%. This shows that the Mulliken charges of the nitrogen atom of the amine group on the AsA is lower than the Mulliken charge of the oxygen atom of the hydroxyl group on the MaA; the total Mulliken charge of AsA is lower than MaA, and AsA has a higher EHOMO and a lower energy gap, ΔN. The amine group and carboxyl group on the AsA is easier to coordinate with Al3+ ions to form a stable complex. The corrosion inhibition ability of l‐malic acid (MaA) and l‐aspartate acid (AsA) against the corrosion of AA5052 alloy in 4 M sodium hydroxide–ethylene glycol solution is investigated. The presence of MaA and AsA in corrosion solution shows a remarkable inhibition of hydrogen evolution. AsA has a better inhibition effect for the self‐corrosion of AA5052 alloy and its max protection efficiency is 82.1%.
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Hexabromocyclododecane (HBCD) has been listed in Annex A of the Stockholm Convention on Persistent Organic Pollutants (POPs) in 2013, but till now there is a lack of efficient methods for its degradation. In this study, nanoscale zero-valent aluminum (nZVAl), an excellent reductant with a very low redox potential of E0(Al3+/Al0) = -1.662 V and strong electron transfer ability, was used to reductively degrade HBCD. Nearly 100% HBCD was degraded within 8 h reaction at 25 °C in ethanol/water (v/v, 50/50) solution without pH adjustment. And about 67% cyclododecatriene (CDT) was obtained, which is the complete debromination product. What's more, the yield of Br- could achieve nearly 100% after optimizing conditions. The reaction was strongly promoted by increasing the dosages of nZVAl or decreasing the initial concentration of HBCD. The temperature had the most significant influence and the degradation was completed in 40 min with elevating the reaction temperature to 45 °C. The reaction mechanism was further revealed through the characterization of nZVAl particles before and after the reaction by SEM-EDS, TEM, HRTEM, XRD, and XPS. It was found that, after corrosion of the oxide film on the surface of nZVAl, metallic aluminum inside was exposed. The reactive sites were provided and electrons released were transferred from nZVAl to HBCD, causing HBCD degraded to dibromocyclododecadiene (DBCD) and then CDT by reductive debromination. These findings imply that nZVAl can degrade HBCD efficiently with no extra energy input and this offers a new idea for better treatment of HBCD.
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Hydrogen is one of the important non-conventional energy sources because of its high energy content and non-polluting nature of combustions. The water splitting reaction is one of the significant methods for hydrogen generation from non-fossil feeds. In the present paper, the hydrogen generation has been experimentally investigated with water splitting reaction using metal aluminum in presence of potassium hydroxide as an activator under flow conditions. The rate of hydrogen generation was reported in the annular micro- reactor of 1 mm annulus using various flow rates of aqueous 0.5 N KOH ranging from 1 ml/min to 10 ml/min. The complete conversion of aluminum was observed at all the flow rates of aqueous KOH. The hydrogen generation rate was observed to depend on the flow rate of liquid reactant flowing through the reactor. At 1 ml/min of 0.5 N KOH, hydrogen generates at an average rate of 3.36 ml/min which increases to 10.70 ml/min at 10 ml/min of aqueous KOH. The Shrinking Core Model was modified for predicting the controlling mechanism. The rate of hydrogen generation was observed to follow different controlling mechanisms on various time intervals at low flow rates of aqueous KOH. It was observed that chemical reaction controls the overall rate of hydrogen generation at higher flow rates of aqueous KOH.
Article
The present study reports the effect of the addition of room temperature liquid metal gallium on hydrogen generation in water splitting reaction using aluminum. The various proportions of gallium used were 13%, 23%, 33% and 50% weight by weight gallium of the total weight of metals (aluminum and gallium) in the reaction. The hydrogen generation at these additions of gallium was studied at various concentrations of aqueous KOH viz. 1 N, 1.5 N and 2 N and at various reaction temperatures of 50, 60 and 70 °C. The optimum proportion of gallium was found to be 23% at which the hydrogen generation rate was observed thrice than the hydrogen generation rate in absence of gallium. The temperature of the reaction was observed to be dominant over the gallium addition at 60 and 70 °C. The gallium used in the reaction was completely recovered and reused in the reaction.
Article
The study aims to describe the effect of the hot cross-rolling process on the physical and corrosion properties of hot-pressed Al/30 wt%B4C composite. The starting powders were milled by planetary mill machine and then were sintered by a hot pressing machine at 600 °C for one h under 50 MPa pressure in a vacuum. Hot cross-rolling was carried out in 8 and 16 passes after soaking at 773 K (500 °C) for 20 min. Sample characterization takes place through electrochemical corrosion tests, X-ray diffraction, scanning electron microscope and density. The results showed that performing the hot cross-rolling process on the samples leads to an increase in corrosion resistance and density. The 50% hot cross rolled sample had the highest corrosion resistance and density value. The corrosion resistance of the samples was reduced in H3BO3, NaCl and NaOH solutions, respectively. In H3BO3 solution, the continuity of the protective oxide layer is largely preserved, which leads to higher corrosion resistance in this solution than other solutions.
Article
Pyrene-phenylglycinol tangled ratiometric sensor (R)-1 was developed for the detection of Al3+ ion over other metal ions. Ratiometric behaviour of (R)-1 for Al3+ ion explained through monomer emission and excimer quenching leads to avoiding the π-π interactions of bis-pyrene rings. Pull-push to push-pull binding mechanism is successfully explained by DFT and sensing of Al3+-ions demonstrated in living cells. The LOD of (R)-1 for Al3+ downs to nanomolar concentrations which is lower than the allowed concentration of drinking water set by the (World Health Organization) WHO.
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Cassava starch graft copolymer (CSGC) was prepared by grafting acryl amide (AA) onto cassava starch (CS). The inhibition effect of CSGC on the corrosion of aluminium in HNO 3 solution was studied by weight loss, electrochemical techniques, scanning electron microscope (SEM), atomic force microscope (AFM), contact angle images and X-ray photoelectron spectroscopy (XPS). Quantum chemical calculation and molecular dynamic simulation were performed to theoretically investigate the adsorption mechanism. CSGC is an effective novel inhibitor, and shows higher inhibition efficiency than either CS or AA. The adsorption of CSGC on aluminium surface obeys Langmuir isotherm. CSGC is a mixed-type inhibitor, while mainly retards the anodic corrosion. EIS consists of a large capacitive loop at high frequencies followed by a small inductive one at middle frequencies and the second capacitive loop at low frequency values, and the impedance strengthens with the concentration of CSGC. SEM and AFM confirms the corrosion of aluminium surface is prominently retarded after adding CSGC to the media. Contact angle image suggests that the inhibited aluminium surface is of hydrophobic nature. XPS provides the evidence of the adsorptive inhibitor of CSGC on aluminium surface. Quantum chemical calculation and molecular dynamic simulation can be well theoretically elucidate that CSGC shows higher adsorption and inhibition ability than CS.
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Solar cell wafer industry is classified as one of the most complex electronic industries that produces a significant proportion of waste in the form of broken/damaged cells or cells having some defects in their chemical composition that can generally be called Rejected Solar Cell Wafers (RSCWs). Although these wastes contain valuable metals (e.g. Silver (Ag), Aluminum (Al), and Silicon (Si)), unfortunately there is currently no obvious strategy for recovery of these metals and landfilling is considered the primary option for their disposal what can lead to serious soil contamination and human health risks if the waste is not treated properly. This research aims to develop an integrated technology to recover all these metals as high added value nano/micro products with total recovery rate > 98%, thus achieving the sustainability and goals of circular economy. Milling process was used as a pretreatment to break the chemical and mechanical bonds between Ag electrodes, Al electrode, and Si layer of RSCW samples to increase the surface area for reaction. The pretreatment was followed by leaching process using Nitric Acid (HNO3) with concentration > 60% to dissolve Ag and break the chemical bonds between spherical Al microparticles in the Al paste layer. Thus the particles were separated and only a small amount of the Al was dissolved from the surface of the particles since due to the high concentration of HNO3 passivation of Al occurred, forming a thin layer from Aluminum Oxide (Al2O3) that prevented the further dissolution of Al. Under the effect of soundwaves, the separated particles began splitting further and exfoliate into Al nanocrystals. After that, micro-filtration process was used to extract Si microparticles from the leached solution and the extracted particles were purified by etching process using Hydrofluoric acid (HF) to remove Silicon Nitride contamination. Centrifugal process was used to separate Al nanocrystals from the leached solution. Finally, Hydrochloric acid (HCl) was added to the remaining saturated solution to recover AgCl. SEM-EDS, FTIR, ICP, XRD, and TEM were used to analyze and examine the selected wafers and recovered materials. Also, the economic performance, sustainability, and CO2 emissions of the advanced technology were evaluated.
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The in-situ hydrogen generation through water splitting reaction using waste aluminum wires has been studied in presence of room temperature liquid metal gallium and alkaline activator potassium hydroxide. Various proportions of gallium i.e. 50%, 75%, 90% and 95% (weight by weight of the total metal in reaction) were used in order to study the effect of gallium addition on the water splitting reaction. The effect of addition of gallium on the water splitting reaction was also studied and co-related with various concentrations of activator (0.5 N and 1.0 N aqueous KOH) and reaction temperature (50, 60 and 70 °C). The effect of gallium was found to be more prominent at 0.5 N and 50 °C as compare to the 1.0 N and higher temperatures of 50 and 60 °C. The 12 fold increase in hydrogen generation rate was observed for 0.5 N aqueous KOH at 90% gallium addition and 1.0 N aqueous KOH at 75% gallium addition. The added gallium was completely recovered from the reaction. The Shrinking Core Model has been applied to the experimental data for predicting the rate controlling mechanism. The diffusion was predicted as the rate controlling step for maximum cases.
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The corrosion behaviour of Al in 2 M HCl solution in the absence and presence of phenylhydrazine, urea, thiourea, N-allylthiourea, and thiosemicarbazide is investigated using different chemical and electrochemical techniques. The inhibition efficiencies of these compounds increase with increasing their concentration and molecular weights. The inhibitive action of these compounds is discussed in terms of blocking the electrode surface by adsorption of the inhibitor molecules according to Langmuir isotherm. The thermodynamic parameters Kads and ΔGads° are calculated and discussed. The values of ΔGads° reveal strong physisorption of the inhibitors on the metal surface.
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The corrosion behaviour of aluminium in 1.0 mol l–1 solutions of HCl, H2SO4, HNO3 and HClO4 has been investigated in the presence and absence of added Cl– ions. The rate of corrosion of the metal in HCl and in acid solutions containing Cl–, was significantly higher than in the other solutions studied and is attributed to Cl– pitting. The rate of corrosion was found to be zero order overall with an observed rate constant dependence on Cl– of the form (kobs–k0)=kK2[Cl–]2/(K1[O2]+K2[Cl–]) where K1 and K2 are, respectively, the equilibrium constants for O2 and Cl– adsorption on the metal surface. The addition of the sodium salts of N-n-butyl, N-ethyl and N-phenyl dithiocarbamates was found to have an accelerating effect on the corrosion rate, whereas the addition of the quadridentate macrocyclic amine cyclam (1,4,8,11-tetraazacyclotetradecane) and its open-chain analogue DND (3,7-diazanonane-1,9-diazine) was found to offer inhibition characteristics. These latter rates were investigated at 30, 35, 40, 45 and 50 °C in various amine concentrations. A mechanism involving three competitive equilibria, viz. molecular oxygen adsorption, Cl– adsorption and inhibitor adsorption, followed by a rate-determining chloride ion catalysed dissociation step is proposed for the reaction. Finally, the pitting potentials of Al in aggressive acid solutions containing various Cl– concentrations were determined from anodic polarization curves. These data were discussed and correlated to the overall mechanism of pitting corrosion.
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The recycling of waste metallic aluminum with high chemical exergy, which consumes a large quantity of electricity in the refining process, is insufficient. In particular, the so-called dross generated during the remelting process a part of recycling requires expensive treatment, particularly when the metallic concentration is less than 20%, before it can be landfilled. The purpose of this study is to produce hydrogen from waste aluminum sources. such as dross, using an aqueous solution of sodium hydroxide in a beaker and an autoclave. During the study, the effects of temperature of the aqueous solution on the rate of hydrogen generation are to be chiefly examined. The result obtained from an XRD analysis showed that the white product that precipitated during the experiments contained aluminum hydroxide, the rate of hydrogen generation significantly increased with the concentration of sodium hydroxide and temperature of the aqueous solution. and the activation energy was 68.4kJ mol(-1). In the autoclave experiments, hydrogen is released quickly, along with an increase in the inner pressure to a minimum of 1.0 MPa and an increase in the temperature above 473 K. The results suggested a possibility of a new cost effective process of hydrogen production from waste aluminum along with the by prodution of sodium hydroxide. The life cycle assessment (LCA) of the proposed process for producing not only I kg of hydrogen but also 26 kg aluminum hydroxide from waste aluminum was carried out to assess the energy requirement and amount of carbon dioxide emissions. Results suggest that the energy requirement of our process is only 2% and the amount of carbon dioxide emissions is 4%, in comparison to a conventional method.
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A mathematical model for simulating a passive aluminium (Al) surface with a pit in which active electrochemical metal dissolution occurs has been developed. The model includes hydrolysis products of Al and the species obtained as a result of homogeneous reactions between chloride and Al3+ ions and Al hydrolysis products. The model does not assume the equilibrium state in solution: all terms in homogeneous reactions are treated explicitly using kinetic constants taken from the literature. The validity of assuming reaction equilibrium has been addressed. Solution potential values and species concentrations are predicted for different dissolution current densities. The acidity in the pit is explained by the hydrolysis of Al3+; an analytical expression for the pH values at the pit bottom for a given dissolution current density is presented.The model is applied to a real capillary geometry used in electrochemical microcell experiments. It was found that for rcap/rpit
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Various aluminum-smelting by-products from three production sources were received and characterized. The waste materials were tested for compound identification and environmental acceptance. A coarse metallic aluminum recovery test using an Eddy Current separator (ECS) was performed using two different Circuit configurations. White dross performed equally well with either Circuit, while black dross processing shows significant difference on the separation results. It was found that ECS technology was effective for particle sizes down to 6-10 mesh.
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Production of hydrogen using aluminum and aluminum alloys with aqueous alkaline solutions is studied. This process is based on aluminum corrosion, consuming only water and aluminum which are cheaper raw materials than other compounds used for in situ hydrogen generation, such as chemical hydrides. In principle, this method does not consume alkali because the aluminate salts produced in the hydrogen generation undergo a decomposition reaction that regenerates the alkali. As a consequence, this process could be a feasible alternative for hydrogen production to supply fuel cells. Preliminary results showed that an increase of base concentration and working solution temperature produced an increase of hydrogen production rate using pure aluminum. Furthermore, an improvement of hydrogen production rates and yields was observed varying aluminum alloys composition and increasing their reactive surface, with interesting results for Al/Si and Al/Co alloys. The development of this idea could improve yields and reduce costs in power units based on fuel cells which use hydrides as raw material for hydrogen production.
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A series of activated carbons with different degrees of activation were oxidized with H2O2, (NH4)2S2O8 and HNO3 in order to introduce different oxygen surface complexes. Changes in the surface chemistry of the activated carbons after their oxidizing treatments were studied by different techniques including temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FTIR), titrations with HCl and NaOH, measurements of the pH of the point of zero charge and catalytic dehydration of methanol. Results showed that treatment with (NH4)2S2O8 fixed the lowest amount of both total oxygen and surface acid groups. However, this treatment yielded the acid groups with the highest acid strength. This could be because it favors fixation of carboxyl groups close to other groups, such as carbonyl and hydroxyl, which enhances their acidity.
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Das Korrosionsverhalten der handels?blichen A1-Legierungen 1060, 1 100, 3003 und 5052 wird in Abh?ngigkeit von der HNO3-Konzentration und der Temp. untersucht.
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Effects of applied potential and solution temperature Ts on the pitting corrosion of pure aluminium (Al) were investigated in 0.01 M NaCl solutions containing various sulphate (SO42-) ion concentrations using a potentiodynamic polarisation experiment, the potentiostatic current transient technique, ac impedance spectroscopy and atomic force microscopy (AFM). The potentiodynamic polarisation curves showed a rise in the pitting potential Epit values and a simultaneous increase in anodic current density at potentials much higher than the Epit value as the SO42- ion concentration increases. This implies that SO42- ions impede pit initiation at potentials below Epit but enhance pit growth above EPit. This was confirmed from the larger pit growth rate parameter b values of pure Al exposed to SO42- ion-containing chloride solutions during the abrading action than those exposed to SO42- ion-free chloride solution. Furthermore, at Ts=25°C, the charge density Q values for the Al metal dissolution in the presence of SO42- ions were smaller than the value in its absence. By contrast, as validated by the capacitance values and the AFM images of the re-anodized specimens, an enhanced metal dissolution was observed in SO42- ion-containing chloride solutions at Ts=60° and 80°C. From the experimental findings, it is suggested that SO42- ions act as inhibitors of pitting corrosion on pure Al below Epit and at Ts=25°C, whereas they act as promoters at Ts=60° and 80°C. This originates from the accelerated dissolution of the bare metal extensively exposed to the temperature-sensitive Cl- ion attack, which occurs at potentials above Epit.
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Corrosion processes affecting industrially-significant metals in nitric acid solutions and attendant vapors are reviewed. Consideration is given to the various corrosion mechanisms that operate and the major factors that exert an effect on corrosion rates, including welding, cold work, NO. xgases, dissolved species, radiation, solution boiling, heat transfer, and liquor-lines. Corrosion test methods are discussed. .
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The study investigates the influence of nickel and magnesium additions to AA1050 aluminium alloy on the alloy electrochemical behaviour in sodium hydroxide and hydrochloric solutions under conditions relevant to industries that use alkaline etching as a standard surface treatment procedure and to the lithographic and electronic industries where surface convolution is assisted by pitting in hydrochloric acid. Scanning and transmission electron microscopes were used to characterize the intermetallic particles, and scanning Kelvin probe microscopy was utilised in monitoring the surface potential. Nickel is shown to be incorporated into second phase particles, which mostly consisted of Al3Fe and α-(AlFeSi) phases, resulting in enhanced cathodic activity on the aluminium surface. Consequently, the dissolution rates of the superpure aluminium, alloys without nickel addition and alloy with nickel addition are increased respectively in sodium hydroxide, and increased pitting is respectively promoted in hydrochloric acid. In contrast, the addition of magnesium to the alloy had negligible influence on the etching and pitting behaviour.
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Cathodic current—time transients were recorded on high-purity aluminium immersed into a neutral 2 M NaCl solution, when subjected to a potential pulse from a potential around the open-circuit potential, to different negative values. Hydration of the oxide layer occurs at potentials more negative than −1700 mV vs. SCE, whereupon hydrogen is evolved at the metal—hydrated oxide interface. A linear Tafel function is obtained for the maximum current attained in that potential region with a slope of 110 mV dec−1 indicating that the Volmer reaction is the rate-determining step, and the exchange current density for hydrogen evolution at aluminium is estimated at 5 × 10−11 A cm−2. Anodic current responses to the return of the potential to the rest values were also recorded at three different time scales. The presence of some substances, formed at the more negative potentials, other than gaseous hydrogen, was detected and their dependence on potential and cathodic pulse duration is discussed.
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The research of alternative processes to obtain clean fuels has become a main issue because of the concerns related to the current energy system, both from economical and environmental points of view. Hydrogen storage and production methods are being investigated for stationary and portable applications. Up to now, a significant part of H2 production on demand was thought to be fulfilled by using chemical hydrides, but recent studies have proved the limitations of this approach. Conversely, H2 production based in the corrosion of light metals in water solutions is an interesting alternative. Among all of them, Al is probably the most adequate metal for energetic purposes due to its high electron density and oxidation potential. But concerning H2 production from Al corrosion in water, a major issue remains unsolved: metal passivation due to the formation of Al(OH)3 inhibits H2 evolution. In this work we show the last results obtained for the generation of H2 from water using Al powder using diverse alkaline solutions. It is confirmed that corrosion is not affected solely by the solution pH but also by the nature of the ionic species found in the aqueous medium. Moreover, we describe the AlHidrox process, which minimizes Al passivation under mild conditions by the addition of different inorganic salts as corrosion promoters, allowing 100% yields and flow rates up to 2.9 L/min per gram of Al. The feasibility of the process has been regarded in terms of stability (by conducting several successive runs) and self-initiation without an external heating.
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Al-1Cu solid solution and a 2024-T3 (UNS A92024) industrial alloy were tested for localized corrosion resistance in sulfate and chloride solutions, with and without a dilute boric acid (H3BO3)/borate addition (0.01 M H3BO3 adjusted to pH 7). The susceptibility to pitting and crevice corrosion was enhanced by the low concentration of weak acid in the buffer, which prevents alkalization at cathodic sites and the consequent consumption of cathodic current by alkaline dissolution of the adjacent alloy matrix. In the presence of a weak acid, there is more cathodic current available to drive remote pits and crevice corrosion sites. A range of techniques including coupled electrodes and electrochemical noise was used.
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Analysis of results of steady-state potentiostatic measurements on iron in the neutral and nearly neutral borate solutions is complicated by the fact that the metal is in the state of active-passive transition near the free-corrosion potential. This difficulty is overcome using the method of neural network simulation. The study of the behavior of neural-network model shows that chloride and sulfate ions can promote or inhibit iron dissolution depending on their concentration and the pH value of solution. The ambiguous effect of anions is explained by the fact that, when they are adsorbed at the metal, they prevent its cations from passing to the solution, and, entering into the metal-water adsorption complexes, they assist the decomposition of complexes thus promoting the dissolution. Sulfate ions, compared with chloride ions, are, probably more adsorption-active with respect both to iron and to water adsorbed on it.
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The mechanism of corrosion of 99.99% purity aluminum in alkaline solutions was investigated, through detailed examination of open-circuit potential transients. These transients displayed a characteristic time dependence, in which the potential first decreased over a few seconds to a minimum of −1.7 to −1.9V vs. Ag/AgCl, and then slowly increased over a period of hours. The value of the minimum potential of electropolished foils, along with its dependence on pH and aluminate (Al(OH)4-) ion concentration, indicated that it was determined by the Nernst potential for the oxidation of surface aluminum hydride (AlH3). This finding supports the direct role of hydride in the dissolution process. The increase of anodic polarization after the minimum potential occurred in two stages, the first correlated with the buildup of surface hydride, and the second with surface enrichment of Cu and Fe impurities.
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The adsorption of sulphate ions on Zn and Al was studied in 0.5 M NaClO4 supporting electrolyte at various pH values in the range of pH=2–7 by radiotracer techniques. It was found in both cases that the adsorption of sulphate passes over maximum in the pH range studied.The phenomena observed are interpreted by the assumption that the main component of the overall process is anion adsorption on the protonated oxides/hydroxides formed as a result of corrosion. At low pH values the steady state coverage with respect to these products should be very low owing to their dissolution; consequently the extent of anion adsorption induced must also be very low. At higher pH values where no protonation occurs the adsorption of anions decreases significantly.
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Aluminium is highly resistant to most of the acid­ ic and neutral solutions due to the formation ofa protective oxide film on its surface. Aluminium equipments, commonly used in textile industries, frequently come in contact with oxalic acid solu­ tions which are used as a neutralizer during the processing of fibresI•2• Failure of such apparatus due to corrosion in oxalic acid is widely reported in textile and metallurgical industries. Hence, the understanding of corrosion behaviour of alumini­ um alloys in oxalic acid solutions is very much desirable. In the present investigation, an attempt has been made to elucidate the corrosion behaviour of 1060 and 1100 aluminium alloys in different concentrations of oxalic acid, at 25°C.
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The experimental potential-pH diagram of the aluminum water system has been obtained in aluminum salt solutions. A theoretical diagram has been calculated and the comparison between the two has been made. The results may be explained with the assumption of the formation at the surface of the electrode of the two hydride forms AlH//3 and AlH** plus **2.
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A pit model was developed on the assumption that the metal ions hydrolyze inside the pits and that the corrosion products are transported by diffusion. Concentrations of Me**2** plus , Me (OH)** plus , and H** plus ions, as a function of pit depth and current density, for Zn, Fe, Ni, Co, Al, and Cr were calculated. The main reason for passivity breakdown at the initial stages of pit growth, was found to be the localized acidification due to metal ions hydrolysis. Assuming a critical pH value for pit initiation, various experimental facts are explained.
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Atomic emission spectroelectrochemistry (AESEC) was used to monitor the release of Al from 99.99% aluminum (1199 alloy) and Al, Mg, and Cu from 2024 Al alloy in 30g/l NaCl electrolyte as a function of pH. The cathodic dissolution of Al was demonstrated and attributed to an increase in the pH at the interface due to the water reduction reaction. The dissolution of Mg was also observed but was a more complex function of current probably depending on the interfacial pH and the Al dissolution rate. The detachment of copper-rich particles was observed as very rapid spectroscopic emission transients (peak width
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Structure and rate of formation of natural and thermally formed oxide films on Al are discussed. It is shown that these films consist of a layer of barrier-type oxide, the thickness of which is primarily a function of temperature, and a porous layer, the thickness of which is determined by time and natural forces associated with the environment. Effects of temperature and environment on the formation rate and ultimate thickness of these layers are described.
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This paper was presented as a keynote address at a conference on the Control and Exploitation of the Corrosion of Aluminum Alloys held at Cranfield, Bedfordshire, England, on April 5-8, 1983. The review was organized by a consideration of the four steps involved in localized corrosion. Adsorption of the rective anion on the oxide covered aluminum. Chemical reaction of the adsorbed anion with the aluminum ion in the aluminum oxide lattice on the precipitated aluminum hydroxide. Thinning of the oxide film by dissolution. The direct attack of the exposed metal by the anion, perhaps, assisted by an anodic potential. The experimental work reported in the literature is evaluated within this framework.
Article
The critical pitting potential determined potentiostatically of pure is −0.40V (SHE). This value is not greatly sensitive to temperature (0–40°C), to small alloying additions of Mn or Mg, nor to thickness of oxide film produced by anodizing. The value is more active the higher the Cl− concentration, but becomes more noble with additions to of nitrates, chromates, acetates, benzoates, or sulfates. The latter act as pitting inhibitors which are effective in the order as listed. Dissolved Cu++ in trace amounts deposit on the Al surface as Cu which then acts as an efficient cathode, shifting the corrosion potential of aluminum to the critical pitting potential. Trace amounts of Fe+++ and Pd++ act similarly. Anodized surfaces effectively retard penetration of the oxide by Cu ++ thereby delaying onset of pitting, but they are not similarly effective when Al is coupled to Cu. The mechanism of pitting is interpreted in terms of competitive adsorption of Cl− with oxygen for sites on the metal surface. Extraneous anions compete in turn with Cl− ions, making it necessary to shift the potential in the positive direction in order for Cl− to adsorb followed by pit initiation. Similarities in adsorption parameters of various anions other than Cl− on Al and 18‐8 stainless steel are pointed out.
Article
The effect of α,ω‐polymethylenediamines on the corrosion of iron in deaerated was investigated by polarization measurements and colorimetric analysis of solution. The adsorption of these inhibitors at the metal/solution interface was monitored by measurement of the double layer capacitance using the single pulse method. 1,3‐propanediamine was found to be a better inhibitor than ethylenediamine, but no further improvement in per cent inhibition resulted upon increasing the chain length from . Increased inhibitor efficiency for hydrocarbon chains longer than eight carbon atoms was attributed to the concomitant decreased solubility. On a relative solubility basis, the C6‐diamine was more efficient than the C12‐diamine, although both inhibitors produced 90% inhibition at a reduced concentration of 0.1. The double layer capacitance was approximately constant at 21 µF/cm2 for the C2‐ through C8‐diamines, and alternated between 6 and 14 µF/cm2 for the C9‐ through C12‐diamines. The constancy at 21 µF/cm2 suggets that diamines with up to 8 carbon atoms are adsorbed in the same configuration, probably the flat position. The subsequent reduction and alternation in capacitance is believed due to a structuring of the adsorbate similar to that in the bulk where certain physical properties oscillate with carbon number. Colorimetric analysis of solutions with and without additions showed the dissolution rates to be higher than those measured by the polarization technique, possibly due to the “chunk” effect, in which dislodged grains of metal contribute to the total but not faradaic corrosion.
Article
The behaviour of freshly generated surfaces of aluminium in acidic nitrate solution is presented. The surfaces were generated by guillotining in situ, both in open circuit and under galvanostatically applied anodic current density. In the absence of externally applied polarisation, the open-circuit potential shows a logarithmic increase with time of polarisation. The form of the open-circuit potential transient is interpreted as high-field growth kinetics of the passivating oxide film, accompanied by the cathodic reduction of water or of nitrate anions under Tafel’s Law: both reduction reactions are detected in different regimes. The gradient, ∂E/∂ log t, of the open-circuit potential with time, is the Tafel slope of the cathodic reaction. At longer times, the formation of pores in the growing surface oxide is detected as a peak followed by a shallow decay in the potential transient. When the metal is galvanostatically anodically polarised, the potential of the freshly generated metal surface rises more rapidly and rises further, the extent of both depending on the applied current density. At low applied current densities, the oxide forms pores detected as a maximum in the potential, provided the potential remains lower than the pitting potential. At sufficiently high applied current density, the potential rises until the pitting potential is reached. Thence the potential falls a little followed by a constant mean value. The experiments show the pitting potential of aluminium in nitrate solution to be ∼1.6 V(SCE), dependent on the nitrate concentration.
Article
a b s t r a c t An innovative electrochemical approach was developed for reducing or eliminating in situ the oxide bar-rier layer from the pore bottom tips of anodic aluminium oxide films. The procedure was based on includ-ing in the usual anodization process additional steps of re-anodization at constant current density, and whose current density halves from step to step. In this way, we managed to completely remove the oxide barrier layer in samples fabricated by the hard anodization procedure in oxalic acid at 120 V. By gener-ating a suitable disturbance when the system is in steady state, we can modify the relationship between the oxide formation and dissolution rates for the aluminium–alumina-electrolyte system. The resulting structure (porous alumina with open pores) remains on the aluminium substrate after the process has been carried out, so this method could be used to fabricate a transfer mask for developing new devices. This study could provide new bridges towards novel applications of anodic aluminium films in such fields as electronics, magnetics or sensors.
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Effect of Cl− and ions on the corrosion behavior of 20% SiCp reinforced 6061-Al metal matrix composite has been studied using techniques like immersion, potentiostatic polarization, electrochemical impedance spectroscopy and scanning electron microscopy. The present investigation also identifies atomic force microscopy as one of the informative tools to reveal the extent of corrosion with a semi-quantitative approach. The corrosion parameters derived from different techniques revealed that the accelerated corrosion by Cl− is considerably suppressed in presence of in the medium. The ions can afford corrosion resistance to the matrix even in aerated conditions by autocatalytic conversion to nitrite and thereby suppresses the accompanying oxygen reduction reaction.
Article
Electrochemical etching of hard aluminium foil was studied at 100C in NaCl solutions without and with Na2SO4 in concentrations up to 1.0m. Addition of Na2SO4 resulted in an increase in electric capacitance, in refinement of etch configuration and in an increase in tunnel density per unit volume. A decrease in the number of pits from which the tunnels grew also occurred. The capacitance increased with increasing concentration of Na2SO4 up to about 0.351 m, and then decreased. Sulphate ions depressed the formation of pits on the outer oxide-covered surface, but enhanced the growth of the pits and the formation of tunnels from the pits. It is suggested that the retardation of pit nucleation and the acceleration of tunnel growth in the presence of SO 4 2– ions can be explained by a partial replacement of Cl– ions from the oxide and metal surface, respectively. Smaller diameter tunnels may be due to the formation of Al2(SO4)3 which can, in part, replace more aggressive AlCl3, and to an easier formation of a passivating film on the tunnel walls owing to their slower dissolution in the presence of Al2(SO4)3.
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Reaction of aluminum powder and foil with dilute aqueous NaOH solutions was studied. The kinetic characteristics of the process were determined, and its mechanism was discussed.
Article
Effects of applied potential and solution temperatureT s on the pitting corrosion of pure aluminium (Al) were investigated in 0.01 M NaCl solutions containing various sulphate (SO42-) ion concentrations using a potentiodynamic polarisation experiment, the potentiostatic current transient technique, ac impedance spectroscopy and atomic force microscopy (AFM). The potentiodynamic polarisation curves showed a rise in the pitting potentialE pir values and a simultaneous increase in anodic current density at potentials much higher than theE pit value as the SO42~ ion concentration increases. This implies that (SO42-) ions impede pit initiation at potentials belowE pit but enhance pit growth aboveE pit. This was confirmed from the larger pit growth rate parameterb values of pure Al exposed to (SO42-) ion-containing chloride solutions during the abrading action than those exposed to (SO42-) ion-free chloride solution. Furthermore, at 7s=25°C, the charge densityQ values for the Al metal dissolution in the presence of (SO42-) ions were smaller than the value in its absence. By contrast, as validated by the capacitance values and the AFM images of the re-anodized specimens, an enhanced metal dissolution was observed in (SO42-) ion-containing chloride solutions at 7s=60° and 80°C. From the experimental findings, it is suggested that (SO42-) ions act as inhibitors of pitting corrosion on pure Al belowE pit and at 7s=25°C, whereas they act as promoters at 7s=60 ° and 80°C. This originates from the accelerated dissolution of the bare metal extensively exposed to the temperature-sensitive Cl ion attack, which occurs at potentials aboveE pit
Article
Radioactive labeling method, electrochemical techniques and X-ray photoelectron spectroscopy (XPS) were applied to study sulfate and chloride adsorption/incorporation at the passive films on pure aluminum in 0.1 mol dm−3 NaClO4 containing sulfate or chloride ions. We found that the anion adsorption was pH dependent and occurred over a broad electrode potential range. Under open-circuit conditions, the adsorption of sulfate anion is controlled by solution pH, surface charge and the stability of the aluminum-oxide film. The surface concentration of chloride is smaller than that of sulfate and also depends on pH, but slightly. The degree of adsorption irreversibility between the two anions is different, most likely due to a dissimilar extent of the incorporation of sulfate and chloride in the oxide film. We demonstrate that the relative amount of irreversibly bonded sulfate increases with the solution pH and exposure time. Under well-controlled potential conditions, the sulfate coverage increases with the electrode potential until the passive film breakdown occurs. When aluminum undergoes pitting, sulfate removal from the surface is observed. In contrast to sulfate, the surface coverage of chloride increases with anodic polarization even above the pitting potential. The cathodic polarization reduces both the sulfate and chloride coverage due to the high local pH and the destabilization of the passive film.
Article
Corrosion pit initiation in chloride solutions is given by an electrode kinetic model which takes into account adsorption of chloride ions on the oxide surface, penetration of chloride ions through the oxide film, and localized dissolution of aluminum at the metal/oxide interface in consecutive one-electron transfer reactions. A previous model has been extended here to consider that penetration of chloride ions can occur by oxide film dissolution as well as by migration through oxygen vacancies. Pit initiation occurs by chloride-assisted localized dissolution at the oxide/metal interface. The electrode kinetic model leads to a mathematical expression which shows that the critical pitting potential is a linear function of the logarithm of the chloride concentration (at constant pH), in agreement with experiment. The model also predicts that the critical pitting potential is independent of pH (at constant chloride concentration), also in agreement with experiment. Corrosion pit propagation leads to formation of blisters beneath the oxide film due to localized reactions which produce an acidic localized environment. The blisters subsequently rupture due to the formation of hydrogen gas in the occluded corrosion cell. Calculation of the local pH within a blister from the calculated hydrogen pressure within the blister gives pH values in the range 0.85 to 2.3.