CRYSTALLIZATION CHARACTERISTICS OF SOME LITHIA CALCIA MAGNESIA BOROSILICATE GLASSES

The crystallization process of the glasses based on the lithium-borosilicate system containing CaO and/or MgO has been investigated by X-ray diffractometry, DTA and scanning electron microscopy (SEM). Lithium metasilicate was formed as a major phase constituent during the crystallization of the glasses. However, lithium disilicate and alpha-quartz were crystallized as well. On the addition of CaO at the expense of B2O3, calcium silicate (wollastonite) and calcium berate were crystallized together with varieties of lithium berate phases including lithium diborate, lithium tetraborate and lithium pyroborate, which were mostly formed as functions of the CaO/B2O3 and Li2O/B2O3 ratios in the glasses, as well as the heat treatment applied. Pyroxene phase of diopsidic [CaMgSi2O6] type was also formed due to the replacement of CaO and MgO instead of B2O3 and Li2O, respectively. The role played by the glass oxide constituents in determining the crystalliza tion characteristics of the glasses, as well as the conditions at which the crystallized phase assemblages were formed, are discussed.