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

SiC compositionally graded (SCG) graphite was coated with sol–gel-derived HfO2 films and oxidized at 1500 °C in air. SCGed graphite was produced by reaction of graphite with molten Si at 1450 °C 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 °C in air, revealing a small weight loss (0.6 mg cm−2) after 15 h. It was 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.