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The effect of concentration and nature of particles (dielectric Al2O3, broadband semiconducive SiC, and conductive Nb2N and Ta2N) on the adhesion of particles to the surface of coatings and the composition of electrochemical composite coatings deposited from Cr(III) sulfate-oxalate solution suspensions of various concentrations is studied. Adding particles of any nature to the solution does not affect the character of the formation of an X-ray amorphous chromium matrix and the content of hydrogen in the coating. The mechanisms of inclusion of Al2O3, SiC, Nb2N + Ta2N particles in chromium layers are different. In the former case (Al2O3 and SiC), the inclusion of particles is determined by kinetic factors (in the absence of current, there is no adhesion of particles), while, in the latter case, the particles demonstrate a strong adhesion in the absence of current. Accordingly, the distribution of SiC and Al2O3 particles depends on the depth by contrast to Nb2N and Ta2N particles, whose concentrations close to the substrate do not noticeably differ from those in the bulk and surface layers of the coating. An increase in the temperature of solution promotes the codeposition of chromium and these particles. [ABSTRACT FROM AUTHOR]

The effect of temperature and solution components of the chemical catalytic reduction on the composition of Ni-W-B alloy coatings is studied. The x-ray photoelectron spectroscopy in combination with the layer-by-layer profile analysis is used to determine the chemical state of elements and the composition of surface and bulk layers of the coatings containing 28 and 1.8 wt % (10 and 12 at. %) tungsten and boron, respectively. The surface of such coatings is shown to contain up to 90 and 80 at. % reduced nickel and boron, respectively. The deposits have amorphous structure. The effect of thermal treatment conditions on the structure and microhardness of the coatings is investigated. The coatings with a tungsten content of 10 at. % are shown to be nonmagnetic. [ABSTRACT FROM AUTHOR]

The hydrogen content in electroplated chromium layers and multilayer nickel–chromium coatings applied by periodic current from sulfate–oxalate baths is discussed. Chromium electroplating at periodic and pulsed currents is found to increase the hydrogen content to 54 cm3 /g as compared with 24 cm3 /g for chromium deposits obtained in a direct-current mode. The hydrogen content in multilayer Ni–Cr coatings is found to be substantially lower. As shown by mass-spectrometric studies, hydrogen preferentially absorbs in chromium layers. The peculiarities of concurrent hydrogen evolution and chromium deposition giving supersaturated solid solutions are discussed. [ABSTRACT FROM AUTHOR]

The effect of temperature and solution components of the chemical catalytic reduction on the composition of Ni-W-B alloy coatings is studied. The x-ray photoelectron spectroscopy in combination with the layer-by-layer profile analysis is used to determine the chemical state of elements and the composition of surface and bulk layers of the coatings containing 28 and 1.8 wt % (10 and 12 at. %) tungsten and boron, respectively. The surface of such coatings is shown to contain up to 90 and 80 at. % reduced nickel and boron, respectively. The deposits have amorphous structure. The effect of thermal treatment conditions on the structure and microhardness of the coatings is investigated. The coatings with a tungsten content of 10 at. % are shown to be nonmagnetic. [ABSTRACT FROM AUTHOR]

The hydrogen content in electroplated chromium layers and multilayer nickel–chromium coatings applied by periodic current from sulfate–oxalate baths is discussed. Chromium electroplating at periodic and pulsed currents is found to increase the hydrogen content to 54 cm3 /g as compared with 24 cm3 /g for chromium deposits obtained in a direct-current mode. The hydrogen content in multilayer Ni–Cr coatings is found to be substantially lower. As shown by mass-spectrometric studies, hydrogen preferentially absorbs in chromium layers. The peculiarities of concurrent hydrogen evolution and chromium deposition giving supersaturated solid solutions are discussed. [ABSTRACT FROM AUTHOR]

The electrochemical and corrosion behavior of chromium electroplates formed in sulfuric acid solutions of Cr(III) in the presence of oxalates was studied by measuring steady-state polarization curves in 0.5 M H2SO4 solution. These electroplates demonstrate no active dissolution region and their open-circuit potentials are located in the passivity region, i.e. shifted substantially in the positive direction as compared with those of metallurgical chromium and electroplates from standard chrome-plating baths. The results of X-ray photoelectron spectroscopy (XPS) studies evidence that the passive metal surface layer several nanometers thick consists of chromium oxides with incorporated carbides formed during electroplating. It is supposed that the peculiarities of the corrosion and electrochemical behavior of the deposits under study can be attributed to the presence in them of chromium carbides, which operate as cathodic agents. At the same time, the formation of these carbide compounds during the cathodic deposition of chromium electroplates from sulfuric acid Cr(III) solutions in the presence of sodium oxalate is a result of electrocatalytic activity of metal chromium. The latter assumption is confirmed by XPS analysis of surface layers formed during the exposure of chromium to sulfuric acid solutions containing organic substances. [Copyright &y& Elsevier]