Corrosion protection of aluminum 6061 in NaCl solution by silane–zeolite composite coatings

Anticorrosion properties of silane?Czeolite composite coatings applied on aluminum substrates have been investigated. The composite coatings were prepared with different zeolite microparticles concentration (from 500 to 8000?ppm). Physico-chemical tests (Fourier transform infrared spectroscopy, adhesion, scanning electron microscopy, and contact angle measurements) have been carried out to evaluate the homogeneity and structural properties of the coatings. The coatings that resulted were highly hydrophobic for all zeolite contents and showed a relatively good adhesion performance. Corrosion protection performances in 3.5% NaCl solution were evaluated by means of polarization tests, evidencing good barrier characteristics of the composite layer.     

Degradation of metal–polymer composite submitted to uniaxial deformations in 3.5% NaCl solution

This research evaluated the degradation performance of metal–polymer laminates. The material employed was an electrolytic chromium-coated steel (ECCS) sheet, protected by polyethylene teraphthalate (PET). This composite was submitted to uniaxial deformations simulating those occurring in the formation of containers. Later, it was electrochemically tested in 3.5% NaCl?w/v solution and characterised by scanning electron microscope (SEM). Finally, an evaluation of the degradation activity was made to determine the potential performance of the composite in canning applications. The results indicated that the deformation–degradation correlations of the layers depended on the plastic deformation, strain energy, surface quality of the PET polymer free from defects (with respect to a control sample), lack of continuity of the chromium oxide layer at the interface level due to the generation of microcracks, grain deformation in the metallic layers – both of ECCS and chromium layer – due to the generation of Lüder’s bands, loss of adherence detected by electrochemical tests and surface morphological changes of the protective polymer by uniaxial deformations.     

Synthesis mechanism of AlN–SiC solid solution reinforced Al2O3 composite by two-step nitriding of Al–Si3N4–Al2O3 compact at 1500 °C

The in-situ controllable synthesis of AlN–SiC solid solution reinforcement in large-sized Al–Si₃N₄–Al₂O₃ composite refractory by two-steps nitriding sintering was examined. In the first step, a dynamic Al@AlN structure was constructed in the composite by pre-nitriding at 580 °C. During the subsequent sintering process, it cracked above ∼900 °C, and micronized Al cluster (mixture of droplets and vapor) was extracted out gradually. As a result, multiple AlN mesophases were formed through different reaction paths, including i) initial AlN shell formed by solid Al with N₂, ii) reaction of Al cluster with N₂, and iii) reaction of Al cluster with Si₃N₄ from 900 °C to 1500 °C. The Si₃N₄ precursor serves as both a solid nitrogen source and an active Si source, and the controllable reaction between Al and Si₃N₄ leading to uniformly distributed AlN and Si mesophases. AlN–SiC solid solution is significantly formed when liquid Si appears. The shell, granule and whisker SiC–AlN solid solution were observed mainly depending on the dynamic AlN mesophase. The SiC–AlN solid solution reinforced Al₂O₃ materials is a novel promising refractory for large-scale blast furnace lining.     

Corrosion inhibition of carbon steel by N,N′-Dimethylaminoethanol in simulated concrete pore solution contaminated with NaCl

The inhibition behavior of N,N′-Dimethylaminoethanol (DMEA) as an organic corrosion inhibitor for carbon steel in simulated concrete pore solution contaminated with chloride ions encountered in the Mediterranean seawater (0.5 mol L^?1), at different temperatures, was investigated by means of weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results obtained confirm that DMEA is an efficient corrosion inhibitor over the whole range of temperatures studied; it can significantly reduce the corrosion rate of carbon steel. The inhibition efficiency (IE%) increases as the DMEA concentration rises; it reaches its maximum average value of 80% at about 0.125 mol L^?1. The corrosion inhibition of carbon steel by DMEA occurs through chemisorption of inhibitor molecules on the active sites, according to the Langmuir isotherm; this leads to the formation of a passive layer on the metal surface which separates the metal from direct contact with the corrosive medium and hence keeps the interface in a passive state. Furthermore, the activation parameters of corrosion processes were determined and discussed.     

Corrosion behavior of TiN and TiN/Ti composite films on Ti6Al4V alloy in Hank’s solution

Surface films of TiN and TiN/Ti were deposited on Ti6Al4V alloy by arc ion plating (AIP). Open-circuit potential, potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) were employed to investigate the corrosion performance of TiN and TiN/Ti films in Hank’s simulated body fluid at 37 °C and pH 7.4. Scanning electron microscopy (SEM) was used to study the surface morphology of the corroded samples after the potentiodynamic polarization tests. The results show that the TiN and the TiN/Ti films can provide effective protection for the Ti6Al4V substrate in Hank’s fluid, and the TiN/Ti composite film showed a corrosion resistance superior to that of the TiN film. The outer TiN layer of the composite film mainly acted as an efficient barrier to corrosion during short-term experiments. In contrast to the bare Ti6Al4V, no pitting was observed on the surface of the TiN and TiN/Ti films deposited on the bare alloy after potentiodynamic polarization.     

Microstructure and phase transformations in the AlN–Al2O3 pseudo-binary system

The microstructure and phase transformations in the AlN–Al₂O₃ pseudo-binary system of samples having an AlN content in mol% ranging between 44 and about 0 are reported as a function of the thermal treatments. The nature of the phase equilibria, temperature and composition range and coherence degree of the different phases were studied by using various complementary experimental techniques.     

The corrosion resistance of microsilica-containing Al2O3–MgO and Al2O3–spinel castables

Microsilica addition in Al₂O₃–MgO and Al₂O₃–spinel castables helps to improve their flowability and partially accommodate their residual expansion after firing. Nevertheless, there is a lack of conclusive statements in the literature regarding the effects of microsilica on one of the main requisites for steel ladle refractories: corrosion resistance. In the present work, the performance of alumina–magnesia and alumina–spinel with or without microsilica when in contact with a steel ladle slag was evaluated based on three aspects: the material's physical properties, its chemical composition and the microstructural features before the slag attack. According to the attained results, microsilica induced liquid formation and pore growth during sintering, favoring the physical slag infiltration. Moreover, due to this liquid, CA₆ was formed in the matrix, mainly for the Al₂O₃–spinel composition, which also favored the castable dissolution into the molten slag.     

Corrosion and passivation of amorphous and crystalline FeCr alloys in ethanol/water/HCl mixtures

The corrosion and passivation of Type 304 SS and of the amorphous alloys Fe-10Cr-13B-7C and -13P-7B, respectively, have been studied by polarization curves and impedance spectroscopy in deaerated ethanolic/0.5 N HCl solutions with different water contents. For stainless steel and the 13B-7C amorphous alloy, the same passivation mechanism is effective as in aqueous media. The water molecules are directly involved in the formation of the passive film. The alloy with 13% phosphorus appears to show two separate regions of film formation: at low potentials, a thick, porous and less protective film is formed than at more noble potentials. The synergistic interaction of chromium, water and metalloids in film formation may be explained with the concept of charge/size ratio of the different dissolution products.     

Preparation of AlN–Al2O3 composites exhibiting antibacterial and water purification properties

This study aimed to develop new antibacterial and water purification materials without heavy metal contamination. Herein, AlN–Al₂O₃ composites were prepared by changing the content of AlN in raw material. The results showed that AlN, Al₂O₃, aluminum oxynitride, and yttrium aluminum garnet phases were generated by adjusting the AlN: Al₂O₃ ratio. The difference in the ability of AlN and aluminum oxynitride to release substances such as ammonium ions and aluminum hydroxide when reacting with water resulted in remarkably different pH values of the sample immersion solution, which led to an increase in the material antibacterial efficiency with the addition of AlN. Similar results were also obtained with zinc ion absorption. Therefore, AlN–Al₂O₃ composite ceramics can potentially be used as novel antibacterial and water purification materials without heavy metal contamination through the release of ammonium ions for conferring antibacterial effects and of aluminum hydroxide for absorbing heavy metals and suspended impurities.     

Electrical conductivity of spark plasma sintered Al2O3–SiC and Al2O3-carbon nanotube nanocomposites

The electrical conductivity of alumina-silicon carbide (Al₂O₃–SiC) and alumina-multiwalled carbon nanotube (Al₂O₃-MWCNT) nanocomposites prepared by sonication and ball milling and then consolidated by spark plasma sintering (SPS) is reported. The effects of the nanophase (SiC and MWCNTs) and SPS processing temperature on the densification, microstructure, and functional properties were studied. The microstructure of the fabricated nanocomposites was investigated using field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The phase evolution was determined using X-ray diffraction (XRD). The room-temperature direct current (DC) electrical conductivity of the monolithic alumina and nanocomposites was determined using the four-point probe technique. The EDS mapping results showed a homogenous distribution of the nanophases (SiC and MWCNTs) in the corresponding alumina matrix. The room-temperature DC electrical conductivity of monolithic alumina was measured to be 6.78 × 10⁻¹⁰ S/m, while the maximum electrical conductivities of the alumina-10 wt%SiC and alumina-2wt%MWCNT samples were 2.65 × 10⁻⁵ S/m and 101.118 S/m, respectively. The electrical conductivity increased with increasing nanophase concentration and SPS temperature. The mechanism of electrical conduction and the disparity in the electrical performance of the two investigated nanocomposite systems (alumina-SiC and alumina-MWCNT) are clearly described.     

Microstructures and Corrosion Resistance of Al2O3—C Based Refractories to the Melts Containing Titania

The corrosion resisance of the Al2O3-C based refrac-tories in melts containing titania has been studied by quasi-station immersion and rotary immersionThe corrosion rate is decreased with the addition of graphite carbon and ZrO2 in the refractories.The corrosion mehanism of Al2O3-C refractories is the oxidization of graphite carbon by the oxides of the melts and the formation of deteriorate layer,For the Al2O3-C-ZrO2 refractories,the corrosion behavior is due to the interaction between melts and refrac-tories,The new compounds of FeO.SiO2,SiZrO4,Feo.3CaO,2CaO.SiO2 and CaO.SiO2 are formed in the deteriorate layer.     

The Formation of γ—AlON Spinel in the Reaction of Al2O3—AlN—MgO System

The stabilization of γ-aluminium oxyni-tride spinel(γ-AlON) has been investigated by addition of MgO,MgAl2O4,etc.,in reaction process.The results indicated that there are wider solid solution areas near ,Al2O3-rich side in AlN-Al2O3-MgO ternary systems,The content of stabilized AlON phase in samples is related to heating temperatures,additives,etc.The lattice parameters of their AlON phases could be well describedby the equation: a0=0.7900 0.0375[MgO] 0.015[AlN](nm)     

Fabrication and mechanical properties of Al2O3–TiC ceramic composites synergistically reinforced with multi-walled carbon nanotubes and graphene nanoplates

In this study, Al₂O₃–TiC composites synergistically reinforced with multi-walled carbon nanotubes (MWCNTs) and graphene nanoplates (GNPs) were prepared via spark plasma sintering (SPS). The effects of the MWCNT and GNP contents on the phase composition, mechanical properties, fracture mode, and toughening mechanism of the composites were systematically investigated. The experimental results indicated that the composite grains became more refined with the addition of MWCNTs and GNPs. The nanocomposites presented high compactness and excellent mechanical properties. The composite with 0.8 wt% MWCNTs and 0.2 wt% GNPs presented the best properties of all analysed specimens, and its relative density, hardness, and fracture toughness were 97.3%, 18.38 ± 0.6 GPa, and 9.40 ± 1.6 MPa m^1/2, respectively. The crack deflection, bridging, branching, and drawing effects of MWCNTs and GNPs were the main toughening mechanisms of Al₂O₃–TiC composites synergistically reinforced with MWCNTs and GNPs.     

Voltammetry and coulometry with immersed thin layer electrodes—I. Model for effects of solution resistivity in linear sweep voltammetry

A model for the resistance-induced potential distribution at thin layer electrodes during linear sweep voltammetric experiments is considered and results of calculations based on this model are presented. It is shown that cell geometry is an extremely important factor in determining the extent to which linear sweep voltammograms are affected by solution resistivity. Cell geometries providing for a radially uniform current path are superior to those where a parallel current path exists. Other important factors include electrode area and placement of the Luggin capillary.     

Effects of a low amount of C on the phase transformations in the AlN–Al2O3 pseudo-binary system

The effects of a low amount of C on the phase transformations in the AlN–Al₂O₃ pseudo-binary system are reported in samples having an AlN content in mol% ranging between 44 and about 0. Various complementary experimental techniques were used to determine the nature of the phase equilibria. Carbon is embedded in the components of three eutectics as a function of the average chemical composition of the sample in AlN. In two of them, a component belonging to the quaternary system Al–O–N–C and having a wide composition range was found. Its X-ray and neutron diffraction spectra are well refined with a hexagonal crystalline structure.     

Effect of Ultrasound on the Structural and Textural Properties of Al–Fe Pillared Clays in a Concentrated Medium

A modification of bentonite with the Al–Fe mixed system in a concentrated medium was performed, assisting the intercalation with ultrasound. The solid pillaring agent and clay powder were placed in a dialysis membrane in contact with a minimum amount of water, and ultrasound was used to promote species exchange. Al–Fe pillared clays (2, 5 and 10 mol% Fe) were characterized by XRF, CEC, XRD, H₂-TPR and N₂ adsorption at 77 K, revealing changes in the structural and textural properties of the modified clays in the presence of ultrasound during the intercalation. The catalytic properties of pillared clays were evaluated by using the catalytic wet peroxide oxidation of phenol in a diluted aqueous medium, showing an activity comparable to that of a solid modified through the conventional method.     

Synthesis of AlN powder from Al(OH)3 by reduction–nitridation in a mixture of NH3–C3H8 gas

Aluminum nitride (AlN) powders were synthesized by gas-reduction–nitridation of aluminum hydroxide (Al(OH)₃) powders using a mixture of NH₃ and C₃H₈ gases. A high conversion to AlN (over 70% of naitridation ratio) and single-phase AlN were achieved over 1200 °C. The specific surface area of the products decreased with increasing of reaction temperature and soaking time, and products obtained contain much lesser oxygen than those of the previous researches. The reason why such nanosized AlN powders were easily obtained from Al(OH)₃ was considered to be the higher surface areas of transition alumina formed by dehydration of Al(OH)₃ during firing.     

Slag Corrosion Resistace of β－Sialon－Al2O3 Composites－Part I. Thermodynamics and Mechanism

Slag corrosion resistance of β－Sialon and β－Sialon-Al2O3 composites has been studied .The effects of FeO content and temperature on corrosion rate have been investi-gated by mens of dip method(static and self-rotating).The corrosion process and microstructural analysis.It is shown that FeO preferentially attacks β-Sialon in the composite and the protruded corundum grains would gradualy fall off into the slag.     

Influence of layer number and sintering temperature on microstructural,tribological, and corrosion behavior of Al2O3–TiO2 multilayer coatings

The effects of layer number (2, 4, and 6-layer) and sintering temperature (800, 900, 1000, and 1100 °C) on the microstructure, wear, and corrosion properties of Al₂O₃–TiO₂ multilayer coatings deposited on 316L stainless steel plates using the sol-gel dip coating technique were investigated. The wear characteristics were measured through ball-on-disc type dry sliding tests using an Al₂O₃ ball under a 1 N load, whereas the corrosion features were determined by potentiodynamic polarization tests conducted in a 3.5 wt% NaCl solution. Anatase, rutile, α-Al₂O₃, and γ-Al₂O₃ phases were obtained in the hybrid coatings, depending on the sintering temperatures. However, at 1100 °C, the coating did not adhere well to the substrate due to passive oxide film formation on the 316L plate, leading to spalling. Besides, the surface homogeneity deteriorated in the 6-layer coated sample due to higher organic removal and residual stresses. The corrosion rate decreased with the increasing number of layers, but the sensitivity to corrosion varied due to changes in surface properties. The 4-layer coated sample sintered at 1000 °C achieved the highest wear strength (improved by up to 71.1%) and corrosion resistance (increased by up to 90.4%) due to its decreased porosity and homogeneously distributed finer particles.     

Electropolymerization of 2-hydroxybenzothiazole (2-OHBT) in water–methanol media: electrochemical behaviour in NaCl (3%) solution

A new insulating thin polymer (<0.1m) formed by the electropolymerization of 2-OHBT is reported. The anodic oxidation of 2-OHBT on copper, iron and platinum in alcohol and alcohol–water solutions are investigated using cyclic polarization and chronoamperometry. Scanning electronic microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) are performed to confirm the presence of the organic layer. Based on the results obtained, a model for the formation mechanism is proposed. The corrosion behaviour of the coated copper is studied in NaCl (3%) solution by impedance spectrometry and anodic polarization. The results of these experiments show a decrease in the dissolution of copper due to the barrier properties of the organic coating.