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The corrosion protection of Mg–Al alloys by flame thermal spraying of Al/SiC particles (SiCp) composite coatings was evaluated by electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution. The volume fraction of SiCp varied between 5 and 30%. The as-sprayed Al/SiCp composite coatings revealed a high number of microchannels, largely in the vicinity of the SiCp, that facilitated the penetration of the electrolyte and the subsequent galvanic corrosion of the magnesium substrates. The application of a cold-pressing post-treatment reduced the degree of porosity of the coatings and improved the bonding at the coating/substrate and Al/SiC interfaces. This resulted in improved corrosion resistance of the coated specimens. The effectiveness of the coatings slightly decreased with the addition of 5–30 vol.% SiCp compared with the unreinforced thermal spray aluminium coatings. [ABSTRACT FROM AUTHOR]

Abstract: Co3O4 nanoparticles have been obtained by stoichiometric combustion synthesis: in particular 4 nitrates-aspartic routes each with different fuel ratio (ranging 0.5-2.5) have been studied. It has been determined through XRD that the crystalline structure present in all obtained powders was the face-centered cubic corresponding to Co3O4 and it has been evaluated an average crystallite size ranging between 21 and 76nm. As regards to the effect of fuel ratio on physical properties, an increment on the crystallite average size and a drop on the specific surface area with the increase of the fuel ratio has been observed. [Copyright &y& Elsevier]

Abstract: The work addresses the influence of Mn and Mo additions on corrosion resistance of AISI 304 and 316 stainless steels in 30wt.% H2SO4 at 25 and 50°C. Corrosion mechanism was determined by gravimetric tests, DC polarization measurements and electrochemical impedance spectroscopy (EIS). The morphology and nature of the reaction products formed on the material surface were analysed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). Reduction of temperature from 50 to 25°C drastically decreased the corrosion rate of AISI 304 and 316 stainless steels in sulphuric acid solution. Mn additions did not affect significantly the general corrosion resistance due to its low ability to form insoluble compounds in acid medium. Meanwhile, the formation of molybdenum insoluble oxides enhanced the corrosion performance. [Copyright &y& Elsevier]

Abstract: The work addresses the influence of cementation and electrodeposition of copper coatings on the corrosion resistance of AISI 304 stainless steel immersed in 30wt.% H2SO4 at temperatures of 25 and 50°C. Corrosion process was evaluated by gravimetric tests, DC measurements and electrochemical impedance spectroscopy (EIS). The specimen surfaces were analysed by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. The corrosion performance of AISI 304 stainless steel in sulphuric acid solution was greatly improved by copper coatings. The amount of copper deposited by the cementation process was sufficient to protect the stainless steel of corrosion. A greater amount of copper obtained by electrodeposition treatments does not supply further improvement in the corrosion behaviour. The improved corrosion resistance is related to copper dissolution at the initial stages of immersion tests and the presence of Cu2+ in the solution, which makes the medium more oxidizing, increasing the stability of the passive layer. In addition, the presence of copper at the surface reduces the overpotential of cathodic reaction, enabling the transition from an active region to the passive one. [Copyright &y& Elsevier]

Abstract: The influence of Cr concentration on the corrosion resistance of Fe73.5Si13.5B9Nb3Cu1 and Co73.5Si13.5B9Nb3Cu1 metallic glasses was studied by DC electrochemical methods in different concentrations of H2SO4 (1, 3 and 5M) at room temperature. Gravimetric tests were performed to establish the reliability of the data obtained electrochemically. Every test was determined with the same material in different states: amorphous, nanocrystalline and crystalline. In all cases metallic glasses and nanocrystals showed better resistance to corrosion in the tested conditions with increasing chromium concentration. However, in test conditions, the Fe-based materials maintained a high corrosion rate. The corrosion resistance of Co-based materials was slightly greater than that of Fe-based materials. [Copyright &y& Elsevier]

Abstract: The influence of the SiCp proportion and the matrix concentration of four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) modified by lanthanum-based conversion or electrolysis coating was evaluated in neutral salt fog according to ASTM B 117. Lanthanum-based conversion coatings were obtained by immersion in 50°C solution of La(III) salt and lanthanum electrolysis treatments were performed in ethylene glycol mono-butyl ether solution. These treatments preferentially covered cathodic areas such as intermetallic compounds, Si eutectic and SiCp. The kinetic of the corrosion process was studied on the basis of gravimetric tests. Both coating microstructure and nature of corrosion products were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDS) and low angle X-ray diffraction (XRD) before and after accelerated testing to determine the influence of microstructural changes on corrosion behaviour during exposure to the corrosive environment. The corrosion process was more influenced by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement. Both conversion and electrolysis surface treatments improved the behaviour to salt fog corrosion in comparison with original composites without treatment. Additionally, electrolysis provided a higher degree of protection than the conversion treatment because the coating was more extensive. [Copyright &y& Elsevier]

The influence of Cr concentration on the corrosion resistance of Fe73.5Si13.5B9Nb3Cu1 metallic glass in simulated marine atmospheres with chlorides (Cl−) was studied. Cyclic polarisation measurements were carried out to study susceptibility to localised corrosion. All the tests were carried out with the same material in different states: amorphous, nanocrystalline and crystalline. DC current electrochemical techniques were used to analyse the corrosion kinetics. Gravimetric tests were used to establish the reliability of the data obtained electrochemically. The study also focused on the modification of the magnetic properties in the material as a result of exposure to an aggressive medium and Cr addition. [ABSTRACT FROM AUTHOR]