ELECTROCHEMICAL CHROMIUM(II) OXIDE COATINGS ON NONOXIDE CERAMIC SUBSTRATES

SiC and TiB2 were electrochemically coated with Cr2O3 from a 0.1M aque ous solution of chromium nitrate hydrate with ethanol additives. On bo th substrate materials polycrystalline Cr2O3 was formed at current den sities 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 sh rinkage. Microstructural observations indicate that sintering of the C r2O3 coatings on TiB2 at 1100 degrees C for 1 h in a reducing atmosphe re in a closed graphite crucible causes the densification of the coati ng via a liquid phase, which forms by oxidation of TiB2. Under similar conditions, the Cr2O3 coatings on SiC may be sintered via an evaporat ion-condensation mechanism.