Oxidation of HIPed TiC ceramics in dry O₂, wet O₂, and H₂O atmospheres

Isothermal oxidation of dense TiC ceramics, fabricated by hot-isostatic pressing at 1630°C and 195 MPa, was performed in Ar/O₂ (dry oxidation), Ar/O₂/H₂O (wet oxidation), and Ar/H ₂O (H₂O oxidation) at 900°-1200°C. The weight change measurements of the TiC specimen showed that the dry, wet, and H ₂O oxidation at 850°-1000°C is represented by a one-dimensional parabolic rate equation, while the oxidation in the three atmospheres at 1100°and 1200°C proceeds linearly. Cross-sectional observation showed that the dry oxidation produces a lamellar TiO₂ scale consisting of many thin layers, about 5 μm thick, containing many pores and large cracks, while H₂O-containing oxidation decreases pores in number and diminishes cracks in scales. Gas evolution of CO₂ and H₂ with weight change measurement was simultaneously followed by heating the TiC to 1400°C in the three atmospheres. Cracking in the TiO ₂ scale accompanied CO₂ evolution, and the H ₂O-containing oxidation produced a small amount of H₂. A piece of single crystal TiC was oxidized in ¹⁶O₂/H ₂¹⁸O to reveal the contribution of O from H₂O to the oxidation of TiC by secondary ion mass spectrometry.