ELECTROCHEMICAL CHROMIUM(II) OXIDE COATINGS ON NONOXIDE CERAMIC SUBSTRATES

SiC and TiB2 were electrochemically coated with Cr2O3 from a 0.1M aqueous solution of chromium nitrate hydrate with ethanol additives. On both substrate materials polycrystalline Cr2O3 was formed at current densities from 5 to 50 mA/cm(2) and deposition durations of 5 to 30 min. The coating weight increased with current density and with deposition time. The as-deposited coatings contained microcracks due to drying shrinkage. Microstructural observations indicate that sintering of the Cr2O3 coatings on TiB2 at 1100 degrees C for 1 h in a reducing atmosphere in a closed graphite crucible causes the densification of the coating via a liquid phase, which forms by oxidation of TiB2. Under similar conditions, the Cr2O3 coatings on SiC may be sintered via an evaporation-condensation mechanism.