Effects of Y₂O₃ addition on the sinterability and microstructure of mullite (part 1) - phase transformation and sinterability -

The effect of addition of Y₂O₃ on the sinterability and microstructure of mullite was studied by differential thermal analysis, X-ray powder diffraction, scanning and transmission electron microscopy, and dilatometry. The mullite powder compacts containing 2-10 wt% Y₂O₃ were sintered at 1500°C in air. The solid state reaction of Y₂O₃ and mullite during the sintering process produced some crystalline phases of yittrium silicates and α-Al₂O₃. The product phases were dependent on the amount of Y₂O₃ addition. The yittrium silicate and Al₂O₃ melted into a liquid phase at higher sintering temperature, which enhanced the sinterability of mullite powders. During the furnace cooling process, the liquid phase crystallized, and different crystalline phases were obtained depending on the amount of Y₂O₃.