Devitrification of Glasses in the Akermanite‐Gehlenite System

The devitrification behavior of specimens with compositions 2CaO · (1‐ x )MgO · x Al 2 O 3 · (2‐ x )SiO 2 , 0≤ x ≤1, was studied. The crystallizing phases were identified by X‐ray diffraction, and the transformation temperatures were determined by differential thermal and/or thermodilatometric analysis. The microhomogeneity of the glasses was investigated by electron microscopy and small‐angle X‐ray scattering. Glasses with x ≤0.6 devitrify through an intermediate phase, merwinite. Conclusions are drawn about the mechanism of devitrification, taking into account phase separation and the possible distribution of the different anions in the glasses studied. The activation energy for the first stage of devitrification was calculated on the basis of a Johnson‐Mehl growth‐rate equation for x = 0.4.