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In this study, for the first time, the corrosion mitigation ability of zinc intercalated kaolin (K) as an inorganic and cost-effective nanocontainer was studied. The impact of kaolin modification by zinc ions on the epoxy ester coating corrosion protection ability was surveyed by EIS (Electrochemical impedance spectroscopy) and salt spray tests. XRD (X-Ray diffraction) results showed that feeding the kaolin particles by zinc ions increased the interlayer space of the galleries. The Rct (charge transfer resistance) values obtained from the EIS analysis of the scratched coating were found to be around 9800, 34693, and 52188 Ω cm² for neat, K, and KZn (modified K particles with Zn ions) epoxy coated samples after 6 h from immersion. The physical and thermal-mechanical properties of the epoxy ester composite coating reinforced with. KZn particles were assessed by DMTA and tensile tests. Results proved that the addition of modified kaolin particles had reinforced the mechanical characteristics, including the ultimate strength and Young’s modulus.
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... CPE is an alternative element for the ideal capacitance (C) since the surface of the metal is not homogenous, and it is porous. This element is composed of Y 0 (admittance) and n (exponent) [50][51][52][53][54][55]. ...
... (1)) and Neumann's (Eq. (2)) [32,[50][51][52]63]: ...
Article
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Article
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Chapter
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... Detection of the Zr ions and N atoms in the EDS results is good evidence for the inhibitive film formation within the scratch region. The film formation mechanisms were explained before [110]. ...
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Chapter
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Chapter
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A simple and flexible method has been developed to fabricate reversibly switchable nanocontainers (by layer by layer assembly) using zinc phosphate (ZP) nanoparticles as a core material and subsequent deposition of oppositely charged species of polyelectrolyte (polyaniline and polyacrylic acid) and organic corrosion inhibitor (immidazole). Immidazole was entrapped between polyaniline (PANI) and polyacrylic acid (PAA). The PAA nanovalve can control the access of immidazole molecules to and from the nanocontainers. The average particle size of the synthesized nanocontainer was found to be in the range of 250–500 nm. X-ray diffraction (XRD), particle size analysis (PSA), zeta potential, and fourier transform infrared spectroscopy (FTIR) analysis confirms the successful formation of the layered structure of nanocontainers. UV-vis spectroscopy was used to analyze the release rate of immidazole in media of different pH as a function of time. This core-shell nanostructure can have potential applications in corrosion inhibition paint formulation.
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Nonmetallic (based on polymers or oxides) and metallic protective coatings are used to protect metal products against the harmful action of the corrosion environment. In recent years, self-healing coatings have been the subject of increasing interest. The ability of such coatings to self-repair local damage caused by external factors is a major factor contributing to their attractiveness. Polymer layers, silica-organic layers, conversion layers, metallic layers and ceramic layers, to mention but a few, are used as self-healing coatings. This paper presents the main kinds of self-healing coatings and explains their self-healing mechanisms.
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The present work focuses on the use of layered double hydroxides (LDH) as containers for corrosion inhibitors in an epoxy coating. 2-Benzothiazolylthio-succinic acid (BTSA), used as corrosion inhibitor, was intercalated by co-precipitation in magnesium–aluminum layered double hydroxides. The obtained LDH–BTSA was characterized by infrared spectroscopy, X-ray diffraction and scanning electron microscopy. BTSA release from LDH–BTSA in NaCl solutions was investigated by UV–vis spectroscopy. The inhibitive action of LDH–BTSA on carbon steel corrosion was characterized by electrochemical methods and the protective properties of an epoxy coating containing LDH–BTSA were evaluated by electrochemical impedance spectroscopy. It was shown that the BTSA was intercalated in the layered double hydroxide and its loading was about 33%. The BTSA release was dependent on the NaCl concentration in the electrolyte. The polarization curves obtained on the carbon steel sample showed that the LDH–BTSA is an anodic inhibitor. Its efficiency was about 90% at a concentration of 3 g/l. The impedance results showed that the incorporation of LDH–BTSA (3%) in the epoxy matrix improved the corrosion protection of the carbon steel.
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The aim of this research was to investigate the influence of temperature variation on the formation and protective behavior of calcium carbonate scale deposited on steel electrodes in artificial seawater. Chronoamperometry measurement, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and x-ray diffraction (XRD) were employed for analysis. An increase in temperature from 20 to 50 °C accelerated the oxygen reduction reaction, which increased the nucleation/deposition rate. The chronoamperometry, SEM and XRD results indicated that complete coverage of the electrode surface was achieved at higher temperatures because a denser layer of scale deposits covered the entire surface of the metal and acted as a barrier against the passage of oxygen. The EIS results showed that better corrosion protection was obtained after deposition that included a stepwise decrease in temperature, indicating fewer pathways through the deposited layer onto the electrode surface.
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The secondary metabolites of Solanum trilobatum-L was extracted from its leaves and their components were separated by column chromatography as Fraction-A and Fraction-B. The functional groups of the extracts were identified by FT-IR spectroscopy. The inhibition efficiency of the extract and its fractions were tested for mild steel in 1 M HCl and 3% NaCl by potentiodynamic polarization and electrochemical impedance spectroscopic techniques. Plant extracts act as mixed type inhibitors in all experimental conditions, and Fraction-A has more inhibition efficiency (I.E) than crude extract and Fraction-B. The protective layer of adsorbed extract constituents were confirmed by morphological study. The surface coverage and time constant for adsorption of extract molecules were calculated using Rct and Cdl values.
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Various Standard methods such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization study (PDS) and atomic force microscopy (AFM) have been utilized to study the corrosion characteristics of reinforcing steel in concrete in without and with various concentrations of Ricinus communis (R. communis) in NaCl media in different time intervals. The ability of the plant extract to produce protective layer on steel surface in concrete and mixed mode (anodic as well as cathodic) inhibitive action have been established from the findings of electrochemical measurements (EIS & PDS). Further, the formation of protective layer on the steel surface by plant extract has been supported by surface morphology analysis (AFM). The adsorption of R. communis extract on steel surface followed the Temkin adsorption isotherm. The results of density functional theory (DFT) analysis brought out the active centers of major ingredients responsible for adsorption of molecules present in R. communis over the steel surface that influenced the anti-corrosion potential of plant extract. The increase in compressive strength and splitting tensile strength of concrete has been observed. The inhibitive mechanism of the R. communis extract against reinforcing steel corrosion in concrete in 3.5% NaCl media has also been proposed.
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We reported the preparation of epoxy coatings incorporated with a composite filler of poly(styrenesulfonate)-polyaniline/reduced graphene oxide (PSS-PANI/rGO) and their performance on the mechanical and anticorrosion properties. The rGO platelets were first dispersed in the PSS solution, followed by in situ oxidative polymerization of aniline. The resulting PSS-PANI/rGO composite was then blended with a bisphenol-A type epoxy at different loadings by tri-roller mill, and was subsequently cured with a curing agent. The ultimate tensile strength and tensile toughness of the epoxy composite at a loading of only 0.5 wt% PSS-PANI/rGO were improved by 39% and 127%, respectively, when compared to the respective values of the pristine epoxy. This was ascribed to their strong interfacial bonding upon curing by the reaction between the PANI and epoxy. Furthermore, the potentiodynamic polarization of the carbon steels coated with the epoxy/PSS-PANI/rGO composite revealed that the anticorrosion performance was greatly improved when compared to those with the neat epoxy and epoxy/rGO coatings. The superior anticorrosion effect was attributed to its larger tortuosity of diffusion pathways, improved interfacial strength between the epoxy and filler, and the passivation layer formed by the presence of polyaniline which was confirmed by X-ray photoelectron spectroscopy. The improved anticorrosion and toughness would allow the coatings to withstand externally mechanical impact and prevent corrosion effectively.
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The recent shortage of fossil fuel sources and the growing environmental concerns have considerably affected the necessity to search for alternative energy sources. The tremendous increase in energy demands in the transportation and industrial sectors has strengthened efforts to identify sustainable alternative fuel sources. In this regard, biodiesel can be considered a promising substitute for diesel. However, biodiesel is corrosive when it comes in contact with metals. The present study aims at investigating the sustainability of additive-doped biodiesel upon exposure of copper-based materials. A static immersion test was conducted at room temperature (25 °C–27 °C) for 2160 h. The metals used in the experiment were copper, leaded bronze, and phosphorous bronze. The investigated fuel was 100% palm biodiesel without and with additives (500 ppm), including tert-butylamine, benzotriazole, propyl gallate, pyrogallol, and butylated hydroxytoluene. The corrosion rate of the metals was determined at the end of the experiment via weight loss measurement. The metals were further characterized via scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction analysis. Results showed that the corrosion rate of copper was considerably higher than those of the other metals. X-ray diffraction analysis indicated the presence of copper carbonate and cupric oxide on the copper surface that was exposed to biodiesel. The occurrence of these compounds could be attributed to the high concentrations of carbon dioxide and oxygen in the biodiesel when additive was absent. Gas chromatography–mass spectrometry data showed that the unsaturated molecules in biodiesel could reduce the sustainability of metals upon exposure to biodiesel. However, metal surface degradation was significantly reduced in the presence of additives. In particular, benzotriazole and tert-butylamine considerably improved the sustainability of biodiesel by limiting metal surface degradation.
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Titanium dioxide-decorated graphene oxide nanocomposite (TiO2-GO) was synthesized with the help of 3-aminopropyltriethoxysilane (APS) and characterized by Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results revealed that TiO2 was decorated to GO by chemical bonds. Then TiO2-GO nanocomposite was modified with γ- (2,3-epoxypropoxy) propyltrimethoxysilane (GPTMS) before introducing into epoxy resin to form an epoxy coating (TiO2-GO-f-EP) on AA-2024 aluminum alloy for good anticorrosion properties. The scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, salty spray and UV aging measurements were carried out to confirm that the TiO2-GO-f-EP coating exhibited good anti-corrosion performance. The corrosion current density of TiO2-GO-f-EP coating was nearly two orders of magnitude lower than that of pure epoxy coating and the adhesion loss after UV aging test changed 86%–57%, compared with pure epoxy coating. The superiority of TiO2-GO-f-EP coating is related to the TiO2-GO addition which can enhance anti-UV aging performance of the epoxy coating and the GPTMS modification that may ensure TiO2-GO nanocomposite's good dispersion into epoxy resin and improve the cross-linking density and adhesion strength of the epoxy coating.
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This study reports an eco-friendly water-borne epoxy (EP) with enhanced corrosion protection performance by embedding graphene oxide (GO). For this purpose, the dispersion of the GO in ethanol is improved by modifying the GO nanosheets with hydrophilic dopamine (DA), owing to the π-π interactions between the GO and self-polymerized polydopamine (PDA) as well as the covalent bonding between DA and GO. Results obtained from transmittance electron microscopy (TEM), scanning probe microscopy (SPM) Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, UV–vis absorbance spectroscopy and X-ray photoelectron spectroscopy (XPS) reveal the successful modification of PDA on the surface of GO nanosheets. Besides, the GO/EP and GO-PDA/EP coatings are applied on the steel substrates and their corrosion protection performance is investigated via electrochemical measurements, scanning electron microscopy (SEM) and scanning vibration electrochemical technology (SVET). Results demonstrate that inclusion of well-dispersed GO-PDA nanosheets leads to the remarkable improvement in the corrosion protection performance of water-borne EP coating.
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This work aims at revealing the key factors that limit the cleaner production level of a pickling process. By comparing the difference in their characteristics and the corrosion behaviors in an acidic medium, three kinds of sample, including the matrix steel (AS), the naturally-corroded carbon steel (NR) and the carbon steel treated under high temperature oxidation (OR), after immersed in the experimental solutions with or without hexamethylenetetramine (HA), were characterized with the methods, such as, electrochemical polarization, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results indicated, no matter which kind of rust layers, the adsorption of HA on their surface all accorded with the same adsorption isotherm. Although the rust layers did not change the adsorption pattern of HA directly, but their steric effect would influence the adsorption potential of HA; the forming process of rust layers (under different environmental conditions) heavily influenced their composition, structure, and the interface roughness between the rust layer and the metal matrix, and also influenced the corrosion behavior of samples in an acidic medium, which were the key factors that limited the cleaner production level of a pickling process. These results indicated that an object-oriented pickling strategy should be adopted for a practical pickling process.
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Low-cost, environmentally friendly, cation exchange pigments derived from naturally occurring bentonite clay are shown to significantly enhance resistance to corrosion-driven cathodic delamination in organic coatings adherent to iron surfaces. A scanning Kelvin probe (SKP) is used to study the delamination kinetics of pigmented and unpigmented poly-vinyl-butyral (PVB)-based coatings applied to polished iron substrates. The bentonite clay is used both in its native form and exhaustively exchanged with a range of divalent alkali earth and trivalent rare earth metal cations. For the best performing divalent cation-exchanged pigment, the dependence of coating delamination rate on pigment volume fraction is determined and compared with that of a conventional strontium chromate (SrCrO4) inhibitor. An inhibition mechanism is proposed for the bentonite pigments whereby underfilm cation release and subsequent precipitation of sparingly soluble hydroxides reduces the conductivity of the underfilm electrolyte.
Article
An epoxy organic coating containing zinc aluminum polyphosphate (ZAPP) pigments with and without a hexafluorozirconic acid based conversion coating (ZrCC) pretreatment was applied on carbon mild steel (St 37) in order to investigate the corrosion resistance behavior and adhesion of the coating to substrate. Optimization of pigment volume concentration (PVC) and conversion coating application conditions was carried out and also the interaction of organic and conversion coating was studied using electrochemical impedance spectroscopy (EIS), salt spray and pull-off adhesion tests. Appropriate anti-corrosion properties was gained from organic coating samples with PVC = 30% and conversion coating applied from a solution with pH and acid concentration of 4.5 and 0.01 M, respectively. Results indicated that using conversion coating as a pretreatment before applying organic coating, improves adhesion of the coating to the substrate (by 1–2 MPa) and also provides an effective corrosion protection in long periods of immersion time. The highest corrosion resistance was obtained for pigmented organic coating sample with Zr conversion coating pretreatment after 4 weeks of immersion in NaCl 3.5 wt.%. Field emission scanning electron microscope and energy dispersive X-ray spectroscopy (FE-SEM/EDS) also proved the presence of about 5 wt.% of zirconium at the interface of coating and substrate not only at the onset of immersion but also after 4 weeks of immersion time. Results taken from this research, can clarify the key role of surface modification at interface of coating and substrate in adhesion and also the retention of anti-corrosion properties over the course of time even for an anti-corrosion pigment reinforced organic coating sample.
Article
A protective coating was produced by dispersing mesoporous silica nanocontainers, loaded with sodium molybdate, as corrosion inhibitor, in an epoxy layer. The corrosion properties of the composite coatings were assessed by electrochemical impedance spectroscopy. Results showed remarkable corrosion resistance of epoxy/mesoporous silica loaded with corrosion inhibitor (epoxy/MSInh) and self-healing ability of coating in the chloride medium during eight weeks of immersion. Epoxy/MSInh had the greatest Rct values for all immersion times, which could be attributed to the release of molybdate ion from the nanocontainers as well as barrier resistance of these inorganic mesoporous silica particles. This value at the first day of immersion in the chloride medium was 318.4 kΩ cm2, while it was 71.3 and 23.5 kΩ cm2 for epoxy and epoxy/mesoporous silica (epoxy/MS), respectively. Rct for epoxy, epoxy/MS, and epoxy/MSInh after the last day of immersion (56 day) was determined as 10.1, 15.9, and 24.4 kΩ cm2, respectively. Corrosion inhibitors were released from nanocontainers in response to corrosion damage in the scratched zone. Besides, the analytical investigation showed the oxidation state of Mo was (Mo (VI)), which could be attributed to the formation of Fe2(MoO4)3 or molybdenum oxides.
Article
Experimental cation exchange capacities (CEC) of kaolinites were determined and compared to theoretical calculations of CEC. The comparison reveals that the exchangeable cations occur mostly on the edges and on the basal (OH) surfaces of the mineral. It also shows that permanent negative charge from isomorphous substitution of AP + for Si 4+ is insignificant. The CEC of kaolinite strongly depends on the particle size (both thickness and diameter in the (00l plane) and pH value. Particle size is more important than crystallinity in affecting kaolinite CEC. This study shows that the hydroxyls on the exposed basal surfaces may be ionizable in aqueous solutions. The amount of negative charge on the edges and the exposed basal hydroxyls depends on pH and other ion concentrations. A higher pH value gives rise to more negative charges, which lead to a higher CEC value. This study indicates that charge from broken edges and exposed OH planes rather than charge from A1/Si substitution determines the kaolinite CEC, even at zero point charge. A high CEC in some kaolinites is found to be due to smectite layers on the surface of the kaolinite crystals.
Article
Mesoporous silica nanocontainer powders were applied as corrosion inhibitor hosts and dispersed in the polypyrrole matrix. Then, the release and corrosion resistance of these composite coatings were studied with and without inhibitor in NaCl solution. Results showed that in higher pHs and more aggressive chloride media, the release content of corrosion inhibitor is higher. OCP, ICP, XRD, EIS, and FTIR results showed that the substrates were better protected in the presence of released corrosion inhibitor from mesoporous silica compared to the coatings without inhibitor. Then, the corrosion inhibitor reacted with substrate and made a protective phase during corrosion.
Article
Purpose Kaolin is a soft white mineral which has a large array of uses. It is most commonly referred to as “China clay”. Sources of this mineral can be found all over the world, its uses are multiple and diverse. It is a mineral belonging to the group of alumino‐silicates with the chemical composition Al2Si2O5(OH)4. It is white, soft, plastic clay mainly composed of plate‐like particles. It is a unique industrial mineral, which remains chemically inert over a relatively wide pH range. The purpose of this paper is to study the difference in performances of untreated or natural kaolin, thermally treated kaolin or so‐called “calcined kaolin” and chemically treated kaolin using ammonium molybdate to convert the γ‐Al2O3 naturally found in kaolin to α‐Al2O3 which possesses one of the most known stable crystalline phases (corundum) in alkyd based anticorrosive paint formulations used for protection of steel. Design/methodology/approach The different kaolins were characterized using different analytical and spectro‐photometric techniques. The pigments were characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Evaluation of these pigments using international standard testing methods (ASTM) was estimated. The extender pigments were then incorporated in solvent‐based paint formulations based on medium oil‐modified soya‐bean dehydrated castor oil alkyd resin. The physico‐mechanical properties of dry films and their corrosion properties using accelerated laboratory test in 3.5% NaCl for 28 days were tested. Findings The results of this work revealed that calcined kaolin was better in its performance in protection of steel than kaolin, while chemically treated kaolin varied in its performance according to the concentration of modifier or dopant. Practical implications Kaolin has a large array of uses. These pigments can be applied in other polymer composites, e.g. rubber and plastics as reinforcing agent. Originality/value The untreated and treated kaolins are environmentally friendly pigments which can impart high anticorrosive behaviour to paint films with concomitant cost saving.
Article
A wide variety of inhibitive pigments is now being offered as possible alternatives to chromate and lead compounds for painted metals protection. Unfortunately, the most wide spread of these substitute pigments, zinc phosphate, has, at present, raised some environmental concern because phosphate causes the eutrophication of water courses and zinc itself is toxic. The aim of this research was to study the anticorrosive performance of a mixture consisting of zinc phosphate, modified zeolite and clay (bentonite) in order to diminish phosphate content in paints. The zeolite and the clay were exchanged with La(III) ions, as inorganic green inhibitor. In the first step, the anticorrosion protection by La(III) ions in solution was assessed by electrochemical tests. In the second step, an epoxy-polyamide paint formulated with the pigment mixture applied on galvanized panels was studied by salt spray test and electrochemical noise measurements (ENM). The results showed that it was possible to replace part of the zinc phosphate content in the paint with the exchanged zeolite and the clay.
Article
Nanocomposite coatings which were applied on carbon steel panels based on epoxy cerium nitrate–montmorillonite (MMT) were synthesized and formulated. Nanoparticles were incorporated into epoxy resin by mechanical and sonication processes. The state of dispersion, dissolution, and incorporation were characterized by optical microscopy, sedimentation tests, X-ray diffraction, and transmission electron microscopy. To investigate anticorrosive properties of nanocomposite coatings, electrochemical impedance spectroscopy and salt spray tests were employed. The experimental results showed that epoxy cerium nitrate–MMT nanocomposite coatings were superior to the neat epoxy in corrosion protection effects. In addition, it was observed that the corrosion protection of nanocomposite coatings was improved as the clay loading was increased up to 4–2 wt% cerium nitrate.
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Direct applicaion of a “modified” Scherrer equation, B = Kλ/D cos θ, is made in the determination of the mechanical thickness of thin highly oriented gold films. A relationship between the measured width at half intensity, B, of the observed x-ray diffraction profile, and the linear crystallite dimension, D (in this case the film thickness), is utilized. The constant K was evaluated experimentally to be 0.9118 from a series of gold films under 600 Å in thickness. From a rederivation of the equation, a value of K equal to 0.8859 is adopted for use in this study. The value obtained by Scherrer in the original formulation was 0.9394.Accuracy of this method is dependent on the success in measuring the actual width, at half intensity, of a diffraction peak obtaiend from the gold thin film. Broadening of the observed Au(111) peak profiles, used in the analysis, were found to be appreciable relative to bulk gold sample profiles. An empirical instrumental broadening correction was applied to the data to obtain improved results. Calculated film thicknesses were compared to those obtained by flame atomic absorption analysis and transmission/reflection visible spectroscopy and were found to be in good agreement. Results from a series of gold film thickness determinations is given, and a description of the methodology is provided regarding determinations of metal film thicknesses in the 100–500 Å range.
Article
Strength and toughness are commonly two contradictory properties in polymer materials. For polymer elastomers, the addition of stiff filler frequently results in enhanced stiffness but reduced toughness and ductility. Inspired by biomimetic studies, here we demonstrate a new method that can simultaneously improve strength and toughness while maintaining the good ductility of polyurethane elastomers. This method constructs sacrificial bonds and hidden lengths at the interface of graphene nanosheet/polyurethane (GN/PU) composites by exploiting covalently and non-covalently functionalized GNs (HO-GNs). GNs are prepared by reduction of graphene oxide with hydrazine. The residual functional groups such as hydroxyl and epoxide groups on GNs enable PU oligomer chains to be covalently bonded to GNs by sequentially reacting with diisocyanate and polyethylene glycol oligomer. Non-covalently bonded PU oligomer chains are formed by the π–π interaction between GNs and pyrene derivatives. Both Fourier transform infrared spectra and thermogravimetric results provide direct evidence for the covalent bonding in HO-GNs while fluorescence spectra and decay curves confirm the existence of non-covalent bonding. The resulting HO-GNs exhibit a good dispersion capacity in organic solvents and the PU matrix, improving the load transfer and the particle mobility in GN/PU composites. Upon loading, both rupture of the π–π interaction (sacrificial bonds) and release of the hidden length (dissociation of H-bonds between the PU oligomer and polymer chains) enable the composite to exhibit high toughness and ductility nearly identical to the neat polyurethane (strain at break >900%). This approach is expected to be helpful for developing novel strong, tough and highly ductile polymer elastomers.
Article
In order to obtain homogeneous dispersion and strong filler-matrix interface in epoxy resin, graphene oxide was functionalized via surface modification by hexachlorocyclotriphosphazene and glycidol and then incorporated into epoxy resin to obtain nanocomposites via in situ thermal polymerization. The morphology of nanocomposites was characterized by scanning electron microscopy and transmission electron microscopy, implying good dispersion of graphene nano-sheets. The incorporation of functionalized graphene oxide effectively enhanced various property performances of epoxy nanocomposites. The storage modulus of the epoxy nanocomposites was significantly increased by 113% (2% addition) and the hardness was improved by 38% (4% addition). Electrical conductivity was improved by 6.5 orders of magnitude. Enhanced thermal stability was also achieved. This work demonstrates a cost-effective approach to construct a flexible interphase structure, strong interfacial interaction and good dispersion of functionalized graphene in epoxy nanocomposites through a local epoxy-rich environment around graphene oxide sheets, which reinforces the polymer properties and indicates further application in research and industrial areas.
Article
The exquisite structure of natural materials manifests the importance of particle mobility and load transfer in developing advanced polymer nanocomposites; however, it is difficult to concurrently meet these two mutually exclusive requirements. To address this issue, we demonstrate an approach that constructs a hierarchical, flexible interphase structure in epoxy nanocomposites through a local amine-rich environment around graphene sheets (GNs) and volume exclusion effect of grafting chains. Long-chain aromatic amines, which are chemically similar to the curing agent, are covalently bonded on the surface of GNs by diazonium addition. They play multifold roles in the structure formation of epoxy composites, (1) promoting the exfoliation and molecular level dispersion of GNs in the matrix, (2) serving as a linker between GNs and epoxy networks for improved load transfer, (3) modulating the stoichiometric ratio around GNs to construct a hierarchical structure that can dissipate more strain energy during fracture. With the addition of 0.6 wt% amine-functionalized GNs, the resulting composite exhibits significant mechanical improvements, 93.8 and 91.5% increases in fracture toughness and flexural strength, respectively. This approach affords a novel design strategy for developing high-performance structural composites.
Article
Mg–Al layered double hydroxides, loaded with tungstate anions, were synthesized via the co-precipitation method. The obtained compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), inductively coupled plasma (ICP), and transmission electron microscopy (TEM), respectively. The ICP results demonstrated the partial anion-exchange process, involving the release of tungstate anions from layered double hydroxide by the chloride anions. Polarization measurements showed that the filtrate as electrolyte possessed a low corrosion current density value of 3.042μA/cm2. The electrochemical impedance spectroscopy (EIS) exhibited that the coating could effectively protect the alloy from corrosion. The function of the layered double hydroxide loaded with tungstate doped in organic coating was also discussed.
Article
The concepts of cation and anion exchange capacity, as applied to kaolinite, are critically examined. By attention to experimental detail it was possible to obtain reproducible measurements of ion uptake. Contrary to classical ideas the new data show no evidence for any definite cation exchange capacity. The cation uptake depends upon the cation chosen, the electrolyte concentration and pH, and on whether the experiment is done from aqueous or 95%-ethanol solvent. Apparent “capacities” as high as 25 μequiv/g of kaolinite were obtained with Ca2+ and Cs+ from the nonaqueous solvent and as low as 12 μequiv/g of kaolinite with Li+ from aqueous solutions. The data suggest complex ion exchange reactions on heterogeneous -SiOH and -A1OH sites. They do not support the simple model of isomorphous substitution charge plus basic edge sites so often assumed in the past.
Article
We investigated the effect of silica nanoparticles on the mechanical property and fracture toughness of two epoxy systems cured by Jeffamine D230 (denoted J230) and 4,4′-diaminodiphenyl sulfone (denoted DDS), respectively. Toughening mechanisms were identified by a tailor-loaded compact tension method which quantitatively recorded the deformation of a damage zone in the vicinity of a sub-critically propagated sharp crack tip. 20wt% silica nanoparticles' fraction provided 40% improvement in Young's modulus for both systems; it improved the toughness of J230-cured epoxy from 0.73 to 1.68MPam1/2, and for the other system improved from 0.51 to 0.82MPam1/2. The nanoparticles not only stiffen, strengthen and toughen epoxy, but reduce the effect of flaws on mechanical performance as well. In both systems, nanosilica particle deformation, internal cavitation and interface debonding were not found, different to previous reports. This could be due to the various hardeners used or different identification techniques employed. The toughening mechanisms of the J230-cured nanocomposite were attributed to the formation and development of a thin dilatation zone and nanovoids, both of which were induced, constrained and thwarted by the stress fields of the silica nanoparticles. Regarding 10wt% silica-toughen epoxy cured by J230, a thicker and shorter dilatation zone was found, where neither nanoparticles nor nanovoids were observed. With regard to the DDS-cured system, much less dilatation and voids were found due to the hardener used, leading to moderately improved toughness.
Article
A new thiomorpholine-functionalized nanoporous mesopore Mobil Composition of Matter No. 41 (MCM-41), abbreviated as TMMCM-41, was synthesized and applied as a sensing material in construction of a cadmium carbon paste electrode. The electrode composition of 20.1%wt TMMCM-41, 54.0% graphite powder, 25.9% paraffin oil showed the stable potential response to Cd2+ ions with the Nernstian slope of 28.6 mV decade−1 (±1.8 mV decade−1) over a wide linear concentration range of 10−6 to 10−2 mol L−1 with a detection limit of 6 × 10−7 mol L−1. The electrode has fast response time and long-term stability (more than 4 months). The proposed electrode was used to determine the concentration of cadmium in tap water contaminated by this metal and cadmium electroplating waste water samples.
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Abstract This study fabricates Amine (NH2)-functionalized graphene oxide (GO)/polyimide(PI) composite films with high performance using in-situ polymerization. Linear poly(oxyalkylene)amines with two different molecular weights 400 and 2000 (D400 and D2000) have been grafted onto the GO surfaces, forming two types of NH2-functionalized GO (D400-GO/D2000-GO). NH2-functionalized GO, especially D400-GO, demonstrated better reinforcing efficiency in mechanical and thermal properties. The observed property enhancement are due to large aspect ratio of GO sheets, the uniform dispersion of the GO within the PI matrix, and strong interfacial adhesion due to the chemical bonding between GO and the polymeric matrix. The Young's modulus of the composite films with 0.3 wt% D400-GO loading is 7.4 times greater than that of neat PI, and tensile strength is 240% higher than as of neat PI. Compared to neat PI, 0.3 wt% D400-GO/PI film exhibits approximately 23.96 °C increase in glass transition temperature (Tg). The coefficients of thermal expansion below Tg is significantly decreased from 102.6 μm/°C (neat PI) to 53.81 μm/°C (decreasing 48% ) for the D400-GO/PI composites with low D400-GO content (0.1 wt%).This work not only provides a method to develop the GO-based polyimide composites with superior performances, but also conceptually provides a chance to modulate the interfacial interaction between GO and the polymer through designing the chain length of grafting molecules on NH2-functionalized GO.