Liquid phase sintering of bimodal size distributed alumina powder mixtures

Fine and coarse alumina powder mixtures (non-additive specimen) and those containing the additive formed liquid phase during firing (additive specimen) were compacted and fired at 1400-1600 degrees C. Liquid phase sintering proceeded markedly at 1400-1500 degrees C and additive specimens had much higher relative density than non-additive specimens at 1500 degrees C. As the liquid phase sintering proceeded, the open pore volume decreased abruptly, but the open pore size changed depending on the packing structure. The open pore size decreased in the specimens where the fine particles formed matrix structure, while it increased in the specimens where the coarse particles formed skeletal structure. At 1600 degrees C all additive specimens having different mixing ratios of fine and coarse powders had similar microstructure and the same relative density of 97%. However, spherical large pores were formed and remained in all additive specimens even at 1600 degrees C. The bending strength of those specimens was about 400 MPa.