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Degradability of aluminum in acidic and alkaline solutions
... Therefore, HCl is chosen as Al2O3 removing agent to maintain the initiate process before Al dissolution phase. According to research of Boukerche, et al. (2014), Al2O3 can be destroyed by immersing into HCl for 4320 minutes and into NaOH for 330 minutes with concentration of 0.5 M [2]. Thus, the presence of chloride ions and H + ions in well-corrosion initiation are not as aggressive as OHions. ...
... Therefore, HCl is chosen as Al2O3 removing agent to maintain the initiate process before Al dissolution phase. According to research of Boukerche, et al. (2014), Al2O3 can be destroyed by immersing into HCl for 4320 minutes and into NaOH for 330 minutes with concentration of 0.5 M [2]. Thus, the presence of chloride ions and H + ions in well-corrosion initiation are not as aggressive as OHions. ...
... Figure 2 shows the total gas volume yielded from each concentration variation Generally, the increasing concentration of NaOH leads to less significant effectivity of HCl pretreatment which HCl variability to volume seems to be more dominant when the concentrations of NaOH are 0.5 M and 1.5 M. This has been stated by [2] that reaction rate of aluminum dissolution is typically fast using OHions, which improve the slope of the kinetics. ...
Utility of aluminum series AA5XXX, 6XXX, and 7XXX emerges. However, scrap waste remains unrecycled and ends up in municipal solid waste landfills. It is known that aluminum related reactions maybe problematic for landfill operations by generating undesired heat, liquid leachate, and gases. Aluminum produces hydrogen as it reacts readily with water at room temperature to form aluminum hydroxide. In most cases, it may not conventionally take place due to the presence of aluminum oxide that naturally coats the materials preventing it from direct contact with water. The layer can be detached using an acidic solution, such as HCl. HCl solution is prepared to remove the Al 2 O 3 protective layer under acidic conditions. NaOH solution is added into the water to promote hydrogen production afterward. Aluminum scrap with a constant mass of 0.5 grams added to 250 ml of NaOH solution in which the concentrations varied by 0.5 M, 1.5 M, and 3 M. As the pretreatment, it was soaked into 1 M, 2 M, and 3 M HCl solutions for 1 minute. The measurement result shows that aluminum treated with 3 M HCl and reacted in 3 M NaOH yielded 532 ml of hydrogen gas. However, hydrogen concentration in total produced gas volume decreases as NaOH and HCl increase. This result is also confirmed using FTIR spectroscopy which shows the reaction with less NaOH concentration yielded more bayerite form.
... 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]. ...
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.
... Insights into how HVAC systems degrade can be gleaned from investigating how the materials they are commonly made of degrade. In a study about how aluminum reacts in acidic and alkaline solutions, it was found that the most common source of degradation was from direct contact with alkaline solutions [16]. It was more difficult to predict the effects in acidic environments, as it depended on other factors such as concentration and temperature. ...
... Another compared HVAC components across 21 locations in the USA using three environmental and four non-environmental factors, wherein a machine learning model suggested temperature, component age and precipitation were the most relevant features to predict HVAC degradation rate [21]. In summary, the literature [12][13][14][15][16][17][18][19][20][21] shows that relative humidity, freeze-thaw cycles, pH, radiation, the presence of water, and temperature could be factors in HVAC infrastructure degradation. ...
Environmental factors degrade civil infrastructure that is critical to humankind’s way of life. Sustainable asset management and capital allocation of infrastructure require an understanding of which factors most impact degradation. Heating, ventilation, and air conditioning (HVAC) system inspection records spanning 14 years from 49 locations across the USA were compiled and associated with the environmental conditions to which they were exposed. Nine environmental features were explored in this study: precipitation, minimum humidity, maximum humidity, minimum temperature, maximum temperature, wind speed, radiation, pH, and freeze–thaw cycles. Installation date, or age, was the lone nonenvironmental feature considered. Decreased precipitation, fewer freeze–thaw cycles and moderate temperatures led to lower degradation rates, while higher humidity led to higher degradation rates across the HVAC sections studied. Random forest models revealed that the most critical environmental features in predicting degradation rate were precipitation and radiation. However, feature importance varied in models that only considered subsets of the data based on either HVAC component type, initial condition of the HVAC section, or degradation rate. The results presented herein provide some insights into HVAC asset management, and the methodology used can be applied to other infrastructure systems.
... Its thickness, composition, and porosity depend on several parameters, such as temperature, surface structure, topography, or other metal impurities present in the structure [22,24]. Such films are stable in a pH range between 4.5 and 8 [25], but in more aggressive acidic [26,27] and alkaline media [27,28], they can be dissolved [27,28]. In addition, pits can be formed in a chloride-containing corrosive environment due to the passive film breakdown [22,29,30]. ...
... Its thickness, composition, and porosity depend on several parameters, such as temperature, surface structure, topography, or other metal impurities present in the structure [22,24]. Such films are stable in a pH range between 4.5 and 8 [25], but in more aggressive acidic [26,27] and alkaline media [27,28], they can be dissolved [27,28]. In addition, pits can be formed in a chloride-containing corrosive environment due to the passive film breakdown [22,29,30]. ...
This study deals with the combination of two corrosion protection strategies for aluminium: barrier protection (provided by a 3.8 μm thick hybrid sol–gel coating) and aluminium pore sealing via the use of a 100 nm thick layer of aluminium oxide. A Si–O–Zr hybrid sol–gel coating (TMZ) was synthesised by combining two separately prepared sols (i) tetraethyl orthosilicate and 3-methacryloxypropyl trimethoxysilane and (ii) zirconium(IV) n-propoxide chelated with methacrylic acid. The synthesis of the Si–O–Zr hybrid sol–gel was evaluated at various stages using real-time infrared spectroscopy. A 100 nm thick Al2O3 film was prepared via thermal atomic layer deposition at 160 °C using trimethyl aluminium and water as precursors. The coating and film properties were assessed via focused ion beam/scanning electron microscopy coupled with energy-dispersive X-ray spectrometry. Sealing with the Al2O3 film did not affect the microstructure and composition of the underlying sol–gel coating. The coating’s corrosion performance in 0.1 M NaCl solution was evaluated using electrochemical impedance spectroscopy. Compared to individual coatings, the multilayer TMZ/Al2O3 coating ensured prolonged (more than three weeks) durable corrosion protection for the aluminium. The impedance magnitude increased by two orders compared to the uncoated substrate (|Z|10 mHz from 16 kΩ cm2 to almost 830 MΩ cm2). Thus, the pore sealing of the sol–gel coating using an ALD alumina film produced a protective multilayer coating system, with |Z|10 mHz remaining above 5 MΩ cm2 after four weeks in NaCl solution.
... Al 2 O 3 could hydrolyze in the solution into Al(OH) 3 , it also could react with H + in a low pH solution (pH < 4). 39,40 Following the immersion test described in the Appendix, partial dissolution of Al 2 O 3 particles was observed, as shown in Figure A1. Additionally, the measurement results indicate a higher pH below that of the Al 2 O 3 particles. ...
... First, the deposits would be reacted with H + in the solution, leading to a reduction in the concentration of H + . 23,40 Second, the deposits may obstruct the transfer of ions in the solution, resulting in the depleted hydrogen ions not being replenished in time. 12,39 Finally, a conjecture suggests that the dissolved carbon dioxide in solution may be more readily adsorbed onto the deposits compared to the carbon steel surface. ...
This study presents the impact of mineral deposits (SiO2, Al2O3, and CaCO3) on the corrosion behavior of X65 pipeline steel in CO2-containing brine solution with low pH. The study investigates the initiation and propagation of under deposit corrosion (UDC) using a wire beam electrode (WBE) partially covered by different mineral deposit layers, in conjunction with electrochemical measurements and surface characterization. The results indicate that the corrosion behavior varies, depending on the characteristics of the deposit. During the test period, the Al2O3-covered steel acted as the main anode with more negative potential, while the bare steel acted as the cathode. The SiO2-covered steel acted as the cathode with more positive potential and a localized FeCO3 layer formed beneath the silica mineral. The CaCO3-covered steel initially acted as an anode with a more negative potential but transformed into the cathode at the end of the test. Additionally, shallow and small pits were observed beneath the deposits with the depth in the sequence Al2O3 > SiO2 > CaCO3.
... Aluminium corrosion causes facility failure [2] which can disrupt supply of goods and services, can even be fatal. Also it is of environmental concern [3] considering that at elevated levels, it causes Alzheimer's disease. The use of organic inhibitors which possess hetero− atoms are environmentally friendly because of their characteristics of strong chemical activity and low toxicity [4], this has necessitated research interests in this area. ...
... FT-IR (UATR-TWO™) ν max/cm − 1 : 2849 and 2914 (CH3 ), 1670, 1591, 1476, 1250, 970 and 846 (Pc ring), 1089 (Ar− O− C). UV-Vis (DMSO) λ max (nm) (log ε): 691 (5.27), 622 (4.61), 367 (4.89), 355(4.82). ...
The adsorption behaviors of 2,9,16,23 tetrakis(4-(tert-butyl)phenoxy)phthalocyanine (1) and gallium (III) 2,9,16,24 tetrakis(4-(tert-butyl)phenoxy)phthalocyanine (2) were studied as corrosion inhibitors at the aluminum−HCl solution interface. In addition to weight loss (gravimetric) and electrochemical methods, the study includes measurements utilizing scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction. The findings of the characterization show that the inhibitor molecules were well adsorbed on the aluminum surface, supporting the gravimetric and electrochemical measurements. At 28°C and the greatest inhibitor concentration (10 μM), the potentiodynamic polarization method gave inhibition efficiency values of 95.2% (1) and 89.1% (2). These compounds showed good corrosion inhibition efficiencies as mixed-type corrosion inhibitors, but they also had a significant anodic character. Theoretical simulations produced conclusions that closely match experimental data.
... It is clear that aluminum's surface was substantially more deteriorated in an alkaline environment (NaOH) as shown in Fig. 9. This is a result of the environment's intense effervescence, which is brought on by the creation of H 2 gas [10]. In general, the turbulence seen in aluminum with NaOH is likely produced by the breakdown of the protective layer [10]. ...
... This is a result of the environment's intense effervescence, which is brought on by the creation of H 2 gas [10]. In general, the turbulence seen in aluminum with NaOH is likely produced by the breakdown of the protective layer [10]. In the most negative potentials, particularly in pure aluminum and the 'PM-0.5' ...
... It is clear that aluminum's surface was substantially more deteriorated in an alkaline environment (NaOH) as shown in Fig. 9. This is a result of the environment's intense effervescence, which is brought on by the creation of H 2 gas [10]. In general, the turbulence seen in aluminum with NaOH is likely produced by the breakdown of the protective layer [10]. ...
... This is a result of the environment's intense effervescence, which is brought on by the creation of H 2 gas [10]. In general, the turbulence seen in aluminum with NaOH is likely produced by the breakdown of the protective layer [10]. In the most negative potentials, particularly in pure aluminum and the 'PM-0.5' ...
The electrochemical behavior of Al–Al9Co2–Al13Co4 aluminum matrix composites for room temperature in (1 M) NaOH environment was studied. In this work, the impact of sintering time (4 h, 8 h, 24 h, 48 h, and 72 h) and cobalt content (0.5, 1, 3, and 5%at) on the corrosion performance of these composites was investigated. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to study electrochemical corrosion. Raman spectroscopy was used to characterize the film surface of the composites; while scanning electron microscope (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) was used to evaluate the microstructure after polarization. Improvements in corrosion resistance were shown by adjusting the heat treatment settings. The Al-5% Co alloy treated after 48 h of sintering showed the greatest resistance. Corrosion and deteriorating were seen to occur preferentially on some phases. The nobility of the intermetallic compounds of the Al-Co binary system in terms of chemical composition and crystal structure is discussed.
... It revealed that F4 is composed of 90.8 wt % silicon (Si), 5.98 wt % aluminium (Al), 1.02 wt % silver (Ag), 0.21 wt % copper (Cu), 0.31 wt % lead (Pb), 0.42 wt % tin (Sn) and traces of other metals such as calcium, zinc and iron ( Figure S1). Considering the sensitivity of battery performance to contaminants, [20] F4 material required further purification to obtain a higher silicon content. In this study, hydrochloric acid (HCl) was selected as the leaching reagent to minimize possible reactions with Si. ...
... Another commonly employed reagent -nitric acid (HNO 3 ) -oxidises Al to Al 2 O 3 and Si to SiO 2 in which the high-purity Si will become less valuable. [20,22] The HCl treatment removes metals through the formation of soluble metal chlorides -aluminium chloride (hydrated AlCl 3 ), silver chloride (AgCl), copper chloride (CuCl 2 ) and tin chloride (SnCl 2 ) etc. This allows purified silicon to be collected through simple filtration followed by thorough rinsing and overnight drying. ...
The massive adoption of renewable energy especially photovoltaic (PVs) panels is expected to create a huge waste stream once they reach end‐of‐life (EoL). Despite having the highest embodied energy, present photovoltaic recycling neglects the high purity silicon found in the PV cell. Herein, a scalable and low energy process is developed to recover pristine silicon from EoL solar panel through a method which avoids energy‐intensive high temperature processes. The extracted silicon was upcycled to form lithium‐ion battery anodes with performances comparable to as‐purchased silicon. The anodes retained 87.5 % capacity after 200 cycles while maintaining high coulombic efficiency (>99 %) at 0.5 A g⁻¹ charging rate. This simple and scalable process to upcycle EoL‐solar panels into high value silicon‐based anodes can narrow the gap towards a net‐zero waste economy.
... This signified high turbulence of the exposed surfaced due to more rigorous gas evolution and resulted in higher degree of pitting formation. As a result of the occurring turbulence, the product layer could not stabilize thereby increasing the weight loss of the alloy in the sample [31]. ...
... A conclusive observation from microscopy reveals that optical microscopy technique only accounts for showing visible intergranular corrosion as a result of low magnification and depth of focus associated with optical microscopes [28,36]. Furthermore, we can conclude here that the degree of pitting and corrosion of sample transcends across grains so many regions of intergranular corrosion are overlapped with aggravated pitting or trans-granular corrosion [11,31,39]. What makes them further indistinguishable is the Fig. 13. ...
In the present study, the corrosion behavior of aluminum Al-7075 tempered (T-6 condition) alloy was evaluated by immersion testing and electrochemical testing in 1.75% and 3.5% NaCl environment at acidic, neutral and basic pH. The data obtained by both immersion tests and electrochemical corrosion tests (potentiodynamic polarization and electrochemical impedance spectroscopy tests) present that the corrosion rate of the alloy specimens is minimum for the pH=7 condition of the solution due to the formation of dense and well adherent thin protective oxide layer. Whereas the solutions with acidic and alkaline pH cause shift in the corrosion behavior of aluminum alloy to more active domains aggravated by the constant flux of acidic and alkaline ions (Cl− and OH−) in the media which anodically dissolve the Al matrix in comparison to precipitated intermetallic phases (cathodic in nature) formed due to T6 treatment. Consequently, the pitting behavior of the alloy, as observed by cyclic polarization tests, shifts to more active regions when pH of the solutions changes from neutral to alkaline environment due to localized dissolution of the matrix in alkaline environment that ingress by diffusion through the pores in the oxide film. Microscopic analysis also strengthens the results obtained by immersion corrosion testing and electrochemical corrosion testing as the study examines the corrosion behavior of this alloy under a systematic evaluation in marine environment.
... 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. ...
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.
... 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. ...
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.
... Moreover, the capability to modify surface chemistry through nanocoating, without altering desired nanotopography, may address challenges associated with the stability of nanoengineered metal oxides like AAO in harsh chemical environments. [36,37] Despite their thermal and mechanical durability, [38] AAO substrates can undergo pitting corrosion and dissolution of the oxide layer when exposed to the reactive anions in chlorine-based solutions, and their nanoporous structure is at risk of disintegration in extreme acidic (pH < 3) or alkaline (pH > 9) cleaning solutions, [39,40] which limits its applicability. Developing a surface nanocoating that enhances the chemical resistance of AAO while preserving its antibiofouling properties is essential for practical applications. ...
Decoupling certain material surface properties can be key to attaining critical property‐activity relationships that underpin their antibiofouling performance. Here, orthogonal nano‐engineering (ONE) is employed to decouple the influences of nanotopography and surface chemistry on surface antibiofouling. Nanotopography and surface chemistry are systematically varied with a two‐step process. Controlled nanotopography is obtained by electrochemical anodization of aluminum, which generated anodic aluminum oxide (AAO) surfaces with cylindrical nanopores (diameters: 15, 25, and 100 nm). To modify surface chemistry while preserving nanotopography, an ultrathin (≈5 nm) yet stable zwitterionic coating of poly(divinylbenzene‐4‐vinylpyridyl sulfobetaine) is deposited on these surfaces using initiated chemical vapor deposition (iCVD). Antibiofouling performance is assessed by quantifying 48‐h biomass formed by gram positive and negative bacteria. The ONE surfaces demonstrated enhanced antibiofouling performance, with small‐pore nanotopography and zwitterionic chemistry each lowered biomass accumulation by tested species, with potential additive effects. The most effective chemistry‐topography combination (ZW‐AAO15) enabled an overall reduction of 91% for Escherichia coli, 76% for Staphylococcus epidermidis, 69% for Listeria monocytogenes, and 67% for Staphylococcus aureus, relative to the uncoated nanosmooth control. Additionally, the composite ZW coating exhibited encouraging anticorrosion properties under both static and turbulent cleaning conditions, vital to antibiofouling applications in healthcare and food industries.
... However, under acidic conditions like 0.5 M HCL, the role of this oxide protective layer is altered, similar to what occurred under the previous alkaline solution. According to the literature, the dissolution of this oxide layer or re-passivation of the metal may occur under acidic environments through the following reactions [38]. ...
... The electrochemical corrosion mechanism of aluminum in dilute HNO 3 solution can be involved as following reactions in anode [98,124]: ...
... However, within pH range of 5 to 8.5, corrosivity has little effect on it. When the pH is beyond such bounds, the rate of corrosion increases significantly (Boukerche et al., 2014). Another example is lead and the pH rises significantly outside the range of 4 -10 (Wasim et al., 2017). ...
The challenge of data availability for accurately assessing a location's level of corrosivity has lingered for so long and as such, researchers are constantly seeking factors with great influence that can assist in describing how corrosive a location will be toward buried oil and gas infrastructure. Alternative measures are required for making rapid and realistic investment decisions because accumulating these factors to make perfect sense is sometimes time-consuming and expensive. Using MATLAB mathematical computational analysis, this study capitalizes on this gap to build a 3D corrosivity signature and model for Delta state in Nigeria to aid in rapid and realistic investment decision-making. The soil pH and resistivity were identified as key variables that determine the extent of corrosion in this investigation. Vertical Electrical Soundings were utilized to collect soil resistivity data, which was then combined with the soil pH to create a 3D corrosivity signature and model with a 98% R-square factor. During the study, potential limitations were found, and recommendations were made.
... 57 As can be seen from eqn (6), severe hydrogen evolution side reactions occur along with the main reaction. According to the research of Boukerche et al., 58 the dissolution of the oxide lm in low-concentration acidic solutions such as HCl is much slower than that in alkaline solutions with the same concentration. Although the oxide layer on the aluminum surface can inhibit hydrogen evolution to a limited extent, the weaker dissolution ability of the acidic electrolytes on the oxide layer leads to a longer activation process of aluminum anodes, which also increases the polarization of the battery. ...
Aluminum-air batteries (AABs) are attracting increased attention for their high energy density, low cost, and excellent security. Nonetheless, the commercialization process is hindered by two major hurdles, i.e., anode polarization...
... The activation energy for etching of (17 ± 4) kJ mol −1 found during this work is in agreement with the activation energy for aluminum dissolution in alkaline conditions observed previously. [52][53][54][55][56] This value has been reported to be between 10.76 and 68.4 kJ mol −1 . The observed activation energy is too low to be associated with typical covalent bond formation or breaking, and too low to be associated with the oxygen lattice diffusion in aluminum oxide. ...
Alkaline etching is a common pretreatment for aluminium surfaces. Etching behaviour was compared between an alloy based on post-consumer scrap (PCS) and several model alloys of rolled AA3005 and extruded AA6060 with systematically varied amounts of Mn, Cu, and Ni. Analysis of concentrations of alloy elements in the etching solution by inductively coupled plasma mass spectrometry (ICP-MS) shows that significant fractions of the investigated elements Cu, Fe, Mg, Mn, Ni, and Zn dissolve. Surface analysis of samples in different stages of the etching process show (i) an increase in oxide layer thickness with etching time, (ii) an enrichment of important alloy elements and impurities (Cr, Cu, Fe, Mg, Mn, Si) near the metal/oxide interface, and (iii) the deposition of Mg, Fe, Si-containing aluminium hydroxide on the surface. A comparison with open circuit potential measurements and time-resolved electrochemical polarisation resistance measurements enables a detailed analysis of the etching mechanism. The aluminium dissolution rate during etching is limited by the transport of species through the oxide precursor layer, making it potential-independent. Differences in etching rates between different alloy classes, evidenced by mass loss measurements, are related to differences in the cathodic or anodic reaction mechanisms (hydrogen evolution or metal dissolution) during etching.
... However, within a roughly pH range of 5 to 8.5, corrosivity has little effect on it. When the pH is beyond such bounds, the rate of corrosion increases signi cantly(Boukerche et al. 2014). Another example is lead and the pH rises signi cantly outside the range of 4-10(Wasim et al. 2017 ...
The challenge of data availability for accurately assessing a location's level of corrosivity has lingered for so long and as such, researchers are constantly seeking factors with great influence that can assist in describing how corrosive a location will be toward buried oil and gas infrastructure. Alternative measures are required for making rapid and realistic investment decisions because accumulating these factors to make perfect sense is sometimes time-consuming and expensive. Using MATLAB mathematical computational analysis, this study capitalizes on this gap to build a 3D corrosivity signature and model for Delta state, Nigeria to aid in rapid and realistic investment decision-making. The soil pH and resistivity were identified as key variables that determine the extent of corrosion in this investigation. Vertical Electrical Soundings were utilized to collect soil resistivity data, which was then combined with the soil pH to create a 3D corrosivity signature and model with a 98% R-square factor. During the study, potential limitations were found, and recommendations were made.
... Despite Al's tremendous advantages relative to other metals, it is not always fully resistant to corrosion. The protective oxide film instantaneously formed on Al only resists corrosion properly in aqueous media with a narrow pH range of 4.0 to 7.5, but dissolves significantly upon exposure to strongly acidic or alkaline electrolytes, leaving the base metal at risk of corrosion [5][6][7]. ...
Novel cyano-benzylidene xanthene derivatives were synthesized using one-pot and condensation reactions. A diprotic Brønsted acid (i.e., oxalic acid) was used as an effective catalyst for the promotion of the synthesis process of the new starting xanthene–aldehyde compound. Different xanthene concentrations (ca. 0.1–2.0 mM) were applied as corrosion inhibitors to control the alkaline uniform corrosion of aluminum. Measurements were conducted in 1.0 M NaOH solution using Tafel extrapolation and linear polarization resistance (LPR) methods. The investigated xanthenes acted as mixed-type inhibitors that primarily affect the anodic process. Their inhibition efficiency values were enhanced with inhibitor concentration, and varied according to their chemical structures. At a concentration of 2.0 mM, the best-performing studied xanthene derivative recorded maximum inhibition efficiency values of 98.9% (calculated via the Tafel extrapolation method) and 98.4% (estimated via the LPR method). Scanning electron microscopy (SEM) was used to examine the morphology of the corroded and inhibited aluminum surfaces, revealing strong inhibitory action of each studied compound. High-resolution X-ray photoelectron spectroscopy (XPS) profiles validated the inhibitor compounds’ adsorption on the Al surface. Density functional theory (DFT) and Monte Carlo simulations were applied to investigate the distinction of the anticorrosive behavior among the studied xanthenes toward the Al (111) surface. The non-planarity of xanthenes and the presence of the nitrile group were the key players in the adsorption process. A match between the experimental and theoretical findings was evidenced.
... Generally, the corrosion resistance of the aluminum alloy in different corrosive environment is high because of the formation of a thin alumina film on their surface when exposed to humid air. The alumina film can provide good resistance against the corrosion species when the pH is between 4.0 and 8.5 [2]. Thus, protective layer of the alumina film is attacked electrochemically in acidic and alkaline environments and also in the presence of chloride ions. ...
The present research explores the synthesis of imidazolium based ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) and its application for the protection of aluminum alloy (AA) in 1 M H2SO4 electrolyte using gravimetric, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), response surface methodology (RSM), density functional theory (DFT) and MD-simulation respectively. The studied (IL) showed appreciable inhibition efficiencies of 84.21 % for gravimetric, 90 % for PDP and 87.10 % for the EIS at 0.80 g/L inhibitor concentration and 313 K, respectively. The results of EIS and PDP reveal the corrosion inhibition process is charge transfer controlled, and the studied IL acts as a mixed type inhibitor. The optimization result via RSM model gave an optimum prediction of 84.21 % at 0.8g/L inhibitor concentration at 313 K. Adsorption of [BMIM][Cl] on the aluminum surface obeyed the Frumkin adsorption isotherm. The scanning electron microscope (SEM) and atomic force microscopy (AFM) revealed the formation of protective film of the inhibitor on the aluminum surface. Theoretical modeling were used to correlate the experimental results. The best fit of the theoretical models were functions of molecular structure and fractions of electron transferred from the inhibitor to the aluminum surface.
... 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]. ...
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.
... 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]. ...
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).
... 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. ...
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.
... 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]. ...
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.
... 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]. ...
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.
... 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]: ...
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.
... 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. ...
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.
The reliable and durable corrosion protection of commercially attractive aluminum alloys like AA2024-T3 is the subject of world-wide intensive scientific research. Thus, the quality of the preliminary treatments and the coating primers is of key importance in this field. In this aspect, Anodic Aluminum Oxides (AAO) and Cerium Conversion Coatings (CeCC) appear to be the most perspective approaches for the formation of coating primers. The present systematic study offers results of a comparative elucidation of the properties of CeCC deposited under different regimes on AAO formed on the AA2024-T3 aircraft alloy. The formation of CeCC was performed either spontaneously, or under different electrochemical regimes. The samples were subjected to analyses that included: (i) preliminary color characterization and contact angle measurements, (ii) surface observations by optical metallographic (OMM) and scanning electron (SEM) microscopy, (iii) element distribution by means of Energy dispersive X-ray (EDX) and X-ray Photoelectron (XPS) spectroscopy and (iv) corrosion tests. The latter were performed by applying Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Scanning (PDS) after 24 h of exposure to a 3.5% NaCl model corrosive medium (MCM). For completeness, the experiments were extended to 672 h of exposure for the samples with superior barrier ability. The analysis of results obtained from the employed analytical techniques has revealed that spontaneous and cathodic depositions at low current densities are suitable for formation of uniform CeCC layers. Conversely, the application of higher current densities and alternating current (AC) or anodic deposition regimes had adverse effects.
Graphical abstract
Though fly ash from the incineration of municipal solid waste (MSW-FA) is considered hazardous waste, its huge and increasing volumes and potential value due to high concentrations of salts and heavy metals such as copper and zinc have attracted commercial interest in mining it for resources. The associated treatments used for extracting these resources may make it economically feasible to extract other constituents from the residuals, adding another potential pathway towards a zero-waste society. This review assesses the feasibility of using zeolites, synthesized from precursors extracted from MSW-FA, as sorbents for the recovery of nutrients (ammonium, nitrate, and phosphate) and heavy metals. It is possible to tailor the properties of the zeolites; however, the large variability in reported adsorption capacities and specificities, as well as the inherent heterogenic nature and variable composition and concentrations of most nutrient- or heavy metal-rich waste streams, make such tailoring challenging. A remaining important issue is the transfer of unwanted micropollutants from the MSW-FA or waste stream to the final products and the loss of surfactants from surfactant-modified zeolites during adsorption and/or desorption of nitrate and/or phosphate. Nonetheless, the recovery process is benefited by high concentrations of the target compounds and low concentrations of competing ions.
Hydrogen (H2) generation via metal hydrolysis is a promising eco-friendly technique that has been widely accepted by the industrial sector. This work mainly focuses on stable H2 production through a simple surface-etching process by hydrofluoric acid (HF) to expel the passive aluminum oxide (Al2O3) layer. The HF-treated aluminum (Al) metal is allowed to react with liquid gallium (Ga) adopting Al–Ga hydrolysis in three different electrolytic solutions of hydrochloric acid (HCl), sodium hydroxide (NaOH), and neutral sodium chloride (NaCl) solutions (named Ga-Al-water reaction). Significantly, the high H2 productivity of 95.9% achieved in 0.4 M NaCl solution at various temperatures (35–65 °C), further maintained the long-term stability of 92.3% for about 25 h at 35 °C. Density functional theory (DFT) calculations confirm the spontaneity of the initial Al oxidation by the Ga liquid metal, leading to spontaneous water-splitting reactions. Furthermore, the Ga catalyst was recovered even after five reusability cycles without productivity decay. This method yields aluminum hydroxide (Al(OH)3) as reaction byproducts which could enable resource circulation in pharmaceutical, textile dyeing, and various chemical industries. This study demonstrates the feasibility of the new Ga-Al-water system with an enhanced Ga–Al contact for large-scale H2 production from seawater and portable fuel cell devices.
The corrosion behavior of 5A06 aluminum alloy in N2O4 was investigated to explore the influence of immersion time. The XPS results confirmed the existence of corrosion products N-H and nitrate after immersion in the N2O4 medium. Surface morphology analysis showed that the pitting mainly initiated around the intermetallic and their vicinity. The reason is the dissolution of the aluminum matrix around the intermetallic AlFeMn and the dealloying of magnesium in Mg2Si. The dissolution of the aluminum matrix near the AlFeMn precipitate and the dissolution of the AlMg precipitate lead to intergranular corrosion. Intergranular corrosion appeared after being immersed for three months and gradually developed into exfoliation corrosion. Eventually, the corrosion mechanism of aluminum alloy in the N2O4 system was discussed.
In this study, the anionic state of Ceftriaxone sodium (Cefx) and Ceftazidime (Cefz) medication corrosion inhibition capabilities for Al in 0.1 M NaOH solution are explored using various electrochemical analyses. Furthermore, the morphological structure and surface chemical composition of the impact of these drugs on the Al substrate in NaOH are investigated. For the prediction and analysis of interactions between molecule structure and inhibition efficiency, quantum chemical calculations (QC), Monte Carlo simulations (MC), and molecular dynamics (MD) simulations (MD) are performed. The electrochemical findings reveal that the inhibitory effectiveness increases with increasing drug concentrations and declines with rising temperature, reaching a maximum value of 78.4% for 300 ppm Cefx while 59.5% for 300 ppm Cefz at 293 K, implying that Cefx outperforms for Cefz. In addition, the studied drugs act as cathodic inhibitors, and their adsorption is spontaneous and mixed type adsorption in its nature that obeys Freundlich isotherm for Cefz while Temkin isotherm is the best-fitted one for Cefx. Surface analysis and wettability measurements imply that Cefx and Cefz shield the Al against corrosion by surface adsorption and generating a protective hydrophobic film. Thermodynamic activation parameters in the absence and presence of 300 ppm of the studied drugs are calculated and discussed. The energies of the border molecular orbitals and computed molecular parameters for the investigated drugs revealed that anionic Cefx is more readily adsorbed on the Al surface than Cefz. This finding is validated further using MC and MD simulations. Overall, the proposed cephalosporin drugs delivered a cost-effective and facile approach for boosting the efficiency of corrosion inhibitors for Al under aggressive conditions.
The metal slabs studied in this work are used to protect the walls of the motorway tunnels and to improve the lighting conditions inside the tunnel. Their installation causes an increase in the cost of the work, consequently, the coatings must be resistant to corrosion and must not require frequent maintenance in order to be functional for long periods. The material chosen to produce these artifacts is aluminum, but despite this metal being generally resistant to chemical attack, the analyzed coating still suffered corrosion. The sampled and analyzed slab was covered with white titanium-based paint on the side facing the street and a transparent protective resin on the side facing the wall. This preliminary study uses a different approach through microanalysis of metal slabs. For this reason, the corroded slab was studied through different analytical techniques (microscope, SEM-EDS, XRF and Raman analyses) in order to identify the causes of corrosion of the metal slab. The observations made it possible to hypothesize a corrosion process divided into different stages.
In this study, the corrosion behavior of high-frequency welded micro-fin tubes was investigated using a bi-layered material of Al–1.1Mn–0.5Cu–0.1Ti core alloy with 10% (∼65 µm) one side cladding of Al–1.2Zn alloy. Open-circuit potential, potentiodynamic anodic polarisation tests, zero resistance ammetry (ZRA) measurements, acidified synthetic seawater testing (SWAAT), and full immersion tests were employed to assess the corrosion behaviour of the material. To link the corrosion with microstructural features, scanning electron microscopy and energy-dispersive X-ray spectroscopy, focused ion beam microscopy, and scanning transmission electron microscopy were used. The results showed that the Al–1.2Zn alloy surface sacrificially dissolves, providing cathodic protection to the nobler underlying core material in acidic and neutral environments. Whereas a catastrophic corrosion on the Al–1.1Mn–0.5Cu–0.1Ti core surface (i.e. the devoid of clad surface area of width 220–350 μm) was seen when coupled with Al–1.2Zn in highly alkaline solutions.
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.
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.
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.
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.
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.
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.
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%.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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. .
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
The electrochemical behaviour of aluminium and Al-silicon alloys in aqueous solutions containing different concentrations of chloride ions was investigated. Electrochemical impedance spectroscopy (EIS) and polarization techniques were used. The electrodes were anodically passivated under galvanostatic control. The effect of formation voltage on the stability of the passive film was studied. The open-circuit impedance measurements have shown that the dissolution of the anodic oxide formed on aluminium or aluminium alloys follows the empirical relation: C−1 is proportional to the oxide film thickness. B represents the rate coefficient of the oxide film dissolution. The results revealed that the presence of chloride ions even in the oxidizing medium (1 M HNO3) delays the passivation of the material. Complex plane analysis of the formed oxide film indicates that the corrosion resistance increases as the concentration of chloride ions increases. For naturally passivated electrodes, the corrosion resistance decreases as the concentration of chloride ions increases. This behaviour was explained by film repair-film removal equilibria.
Suppression of the parasitic corrosion while maintaining the electrochemical activity of the anode metal is one of the serious problems that affects the energy efficiency of aluminum-air batteries. The need to use high-purity aluminum or special aluminum-based alloys results in a significant increase in the cost of the anode, and thus an increase in the total cost of energy generated by the aluminum-air battery, which narrows the range of possible applications for this type of power source. This study considers the process of parasitic corrosion as a method for hydrogen production. Hydrogen produced in an aluminum-air battery by this way may be further employed in a hydrogen-air fuel cell (Hy-air FC) or in a heat engine, or it may be burnt to generate heat. Therefore, anode materials may be provided by commercially pure aluminum, commercially produced aluminum alloys, and secondary aluminum. These materials are much cheaper and more readily available than special anode alloys of aluminum and high-purity aluminum. The aim of present study is to obtain experimental data for comparison of energy and cost parameters of some commercially produced aluminum alloys, of high-purity aluminum, and of a special Al–ln anode alloy in the context of using these materials as anodes for an Al-air battery and for combined production of electrical power and hydrogen.
The inhibitive action of leaf extracts of Sansevieria trifasciata on aluminium corrosion in 2 M HCl and 2 M KOH solutions was studied using the gasometric technique. The results indicate that the extract functioned as a good inhibitor in both environments and inhibition efficiency increased with concentration. Synergistic effects increased the inhibition efficiency in the presence of halide additives. Temperature studies revealed a decrease in efficiency with rise in temperature and corrosion activation energies increased in the presence of the extract. A mechanism of physical adsorption is proposed for the inhibition behaviour. The adsorption characteristics of the inhibitor were approximated by Freundlich isotherm.