Preparation and study of Cr2O3 electrocoatings

Graphite support was electrolytically coated with Cr2O3 fi om a 0.1 M aqueous solution of chromium nitrate hydrate with ethanol additives. On substrate material polycrystalline Cr2O3 was formed at current densities from 3 to 35 mA/cm(2) and deposition time of 5 to 30 min. The coating weight increased with current density and deposition time. Microstructural investigation shows that sintering of the Cr2O3 coatings at 1100 degreesC for 1 hour in reducing atmosphere causes the densification of the coating. Structural characterisation of the electrodeposited coatings, by X-ray diffraction method and optical microscopy has been performed. The role of the (OH)(-) groups during electrodeposition process by NMR method was carrying out. Generation of the (OH)(-) groups and their migration in the solution lead to a change of the solution pH, The sintering process in a reducing atmosphere enhanced the densification of the coatings by reducing of the partial pressure as reported elsewhere. The densification process occurs by filling the microcracks between the islands with condensed chromia droplets. The electrodeposition process occurs in three distinct stages. In the first stage, on the cathode the germs of a porous layer appear, then the coating becomes relative homogeneous and, finally, ruggedness appears.