Rare earth-doped ZrB2-MoSi2 ceramics: Densification and oxidation behavior

The effect of rare earth oxides (REO), Nd₂O₃ and Eu₂O₃, on the densification and oxidation behavior of pressureless sintered ZrB₂-MoSi₂ ceramic composites was investigated. Addition of REO results in the formation of REO-silicates which are liquid at the sintering temperature and contribute to matter transfer mechanisms. Oxidation studies at 1500 °C for 0.5–4 h evidenced that Eu₂O₃ can improve oxidation resistance in the ZrB₂-MoSi₂ system, especially after prolonged exposition, whilst Nd₂O₃ induces faster degradation of the ceramic. It was found that the Eu dispersed both in silica and in zirconia modifies the rheological properties of the glassy phase thus playing an important role in hindering oxygen inward from the atmosphere to the subsurface, resulting in a noticeable improvement of the oxidation resistance.