Effect of B2O3 on the sintering behavior and phase transition of wollastonite ceramics

By adding B2O3 powder into alpha wollastonite ceramics synthesized by solid-state reaction, the sintering temperature of wollastonite ceramics lowered by 300degreesC and temperature that exhibit maximum density decreased by about 400degreesC. In addition, we found that liquid-phase sintering observed in wollastonite-B2O3(WB) ceramics is due to melting of calcium borate which is confirmed by DTA measurement. Phase transition between alpha wollastonite and beta wollastonite is observed in WB ceramics, while no phase transition is observed in alpha wollastonite. In WB ceramics, beta wollatonite started to appear at 900degreesC, and above 950degreesC, phase transition from alpha phase to beta phase took place and only alpha wollastonite remained above 1100degreesC. Especially, the sample sintered at 950degreesC was composed of almost beta wollastonite in the case of W5B. In addition, we observed abnormal grain growth due to liquid phase in the sintered sample.