A thermoanalytical study on the oxidation of ZrC and HfC powders with formation of carbon

The oxidation of ZrC and HfC powders was thermoanalytically investigated by simultaneous thermogravimetry (TG), differential thermal analysis (DTA) and mass spectrometry (MS) at various oxygen pressures (PO2) between 0.5 and 40 kPa in the temperature range 20–1000 °C. TG results showed that the oxidation of ZrC and HfC begins at a fixed temperature of 380 and 400 °C, respectively, independent of PO2 and the type of sample. The degree of reaction, defined for the complete carbide–oxide transformation, reached a maximum of 103–160%, then gradually returning to 100% at higher temperatures. For the oxidation of ZrC, a sharp exothermic DTA peak appeared at PO2≥10 kPa with the corresponding CO2 evolution but broad DTA and CO2 evolution peaks occurred at PO2≤5 kPa. The oxidation of HfC gave two exothermic DTA peaks at all pressures, the higher temperature peak agreeing with the CO2 evolution. Oxidation exceeding 100%, related with the formation of carbon, is discussed from the results of TG, DTA, MS and X-ray analysis.