Effects of Lithium Oxide on Crystallization of Willemite in Ceramic Glazes

Abstract

This research aims to investigate the effect of alumina and silica content on willemite crystallization in Na2O-K2O-Li2O-CaO-(ZnO)-Al2O3-SiO2 glaze system and the effect of Li2O doping into the willemite glaze on the willemite crystallization behavior. The willemite glaze is prepared by mixed the ingredients of glaze that calculated from the phase diagram of the SiO2-ZnO-Al2O3 system, the glazes fired at the different firing temperatures of about 1100-1300°C and the soaking times was about 2, 3, and 4 hours. The results found that the willemite crystal glaze can be provided from the glaze formula G1, G6, G11, G16, and G21 when glazing on the stoneware and porcelain clays with sintering at 1250°C, but when glazing the dolomite clay with only the glaze formula G1, the crystals present at 1200°C. Next, the different soaking times about 2, 3, and 4 hours are studied follow as the crystallization and crystal growth process that carries out following the glazes are fired at 1250°C, downward to 1100°C and soak at 1100°C for stoneware and porcelain clay, and fire at 1200°C and downward to 1000°C for the dolomite clay. Therefore, the effect of the alumina and silica addition in higher quantity has resulted in a decrease of willemite crystallization, because alumina is a refractory raw material that melted at high temperatures and it affects to reduce the flow ability of the glaze during the firing process. Moreover, the doping of Li2O into the willemite glaze is also studied. It found that the 3-5 wt.% Li2O doped is affected by greater flow ability and increasing the amount of crystal more than the basic glaze. It described that the Li2O could be reduced the melting temperature of the glaze, and increased the amount of willemite crystal cause the glaze's strength is increased. It concludes that the Li2O content affects to improve the flow ability with support of the willemite crystallization in the Na2O-K2O-Li2O-CaO-(ZnO)-Al2O3-SiO2 glaze system.