Purification of hot-pressed ZrCO into ZrC by a laser treatment

Pellets of zirconium oxycarbide ZrC 0.82 O 0.14 , obtained by hot pressing of zirconia and zirconium carbide, were irradiated by an ytterbium-doped fibre laser in argon atmosphere (incident power density = 24.7 kW cm −2 , beam diameter 0.7 mm). The surface of the samples, heated at 3300 °C and more, i.e. near the melting, released its oxygen, leading to the carbide ZrC 0.75 despite the presence of traces of oxygen in the cell of treatment ( estimated around 1 Pa). A mechanism is proposed for explaining this result, based on the thermodynamical stability of the carbide, higher at these temperature and oxygen pressure than the oxide. Oxygen of the oxycarbide evolved in the form of the gaseous species ZrO, while the grains of the oxycarbide, converted into the carbide, grew from 2 to 20 μm. Similarly, the traces of dioxygen present inside the treatment cell react with the carbide, giving ZrO (gas), and do not form any oxidised solid phase. This opens interesting future prospects in the field of the production of oxygen-free zirconium carbide powders.