Preparation and high temperature oxidation of SiC compositionally graded graphite coated with HfO2

SiC compositionally graded (SCG) graphite was coated with sol-gel-derived HfO2 films and oxidized at 1500 degreesC in air. SCGed graphite was produced by reaction of graphite with molten Si at 1450 degreesC for 10 h. The sol-gel HfO2 precursor solution was prepared by dissolving HfCl4 in ethanol and refluxing with diethanol-amine and HNO3 and was coated on SCGed graphite by dipping. The HfO2-coated SCGed graphite was produced by decomposition of the precursor under conditions determined from the results of TG, DTA, and MS analysis. Oxidation of HfO2-coated SCGed graphite was performed at 1500 T in air. revealing a small eight loss (0.6 mg cm(2)) after 15 h. It as found that HfO2-coated SCGed graphite exhibits extremely high oxidation resistance. which may be due to the formation of HfSiO4 acting to heal pores or cracks. (C) 2002 Elsevier Science Ltd. All rights reserved.