The role of K2O on sintering and crystallization of glass powder compacts in the Li2O–K2O–Al2O3–SiO2 system

The effects of K2O content on sintering and crystallization of glass powder compacts in the Li2O–K2O–Al2O3–SiO2 system were investigated. Glasses featuring SiO2/Li2O molar ratios of 2.69–3.13, far beyond the lithium disilicate (LD-Li2Si2O5) stoichiometry, were produced by conventional melt-quenching technique. The sintering and crystallization behaviour of glass powders was explored using hot stage microscopy (HSM), scanning electron microscopy (SEM), differential thermal (DTA) and X-ray diffraction (XRD) analyses. Increasing K2O content at the expense of SiO2 was shown to lower the temperature of maximum shrinkage, eventually resulting in early densification of the glass-powder compacts. Lithium metasilicate was the main crystalline phase formed upon heat treating the glass powders with higher amounts of K2O. In contrast, lithium disilicate predominantly crystallized from the compositions with lower K2O contents resulting in strong glass–ceramics with high chemical and electrical resistance. The total content of K2O should be kept below 4.63 mol% for obtaining LD-based glass–ceramics.