CONTRIBUTION OF MANGANESE OXIDE TO THE THERMAL-EXPANSION OF SOME SILICATE-GLASSES AND THEIR CRYSTALLINE SOLIDS

The thermal expansion characteristics of some lithium silicate materials containing various MnO/CaO and MnO/MgO ratios together, in some cases, with Al2O3/Li2O replacement have been examined. The coefficients of thermal expansion were determined at different temperatures to detect the local structure changes induced by MnO, and its contribution with CaO and MgO to the thermal expansion of both glass and crystalline solids. The addition of MnO replacing CaO decreases the thermal expansion of the glasses, while MnO/MgO replacement increases this property. A large, abrupt decrease in the expansion coefficient of the glasses was observed following Al2O3/Li2O replacement. On crystallization, the expansivity of the glasses was markedly changed. It was greatly affected by crystallization of various Mn-silicate varieties and/or aluminosilicate solid solutions. Correlation between the expansion data and the contribution of the incorporated cations in the glass structure as well as the crystal phase composition of the crystalline solids are discussed.