Thermodynamic and experimental study of carbon formation on carbides under hydrothermal conditions

Abstract

Thermodynamic analyses for the corrosion of SiC, TiC, TaC, NbC, WC and B₄C in the temperature range 300–1000 °C in high-pressure steam have been conducted using a Gibbs energy minimization computer code. The calculated results are compared to experimental results for corrosion of these carbides in a hydrothermal fluid above the critical point. The formation of carbon has been predicted and observed for all these carbides, except B₄C. Carbon is formed at low H₂O : carbide molar ratios. Lower pressure also promotes carbon formation. For a high H₂O : carbide molar ratio, the carbon will be oxidized to CO and CO₂. The hydrothermal method can be used for producing carbon coatings of nanometre to micrometre thickness on the surface of carbides.