The effect of Cr2O3 as a nucleating agent in iron-rich glass-ceramics

In this work, the effect of Cr2O3 as a nucleating agent, in iron rich glasses has been investigated by means of DTA, XRD and density measurements. By Cr2O3 addition, from 0.4 to 1.0 wt%, a lowering of the crystallisation peak temperature resulted in the DTA trace, the maximum effect corresponding to 0.7 wt%. By evaluating the degree of crystallisation of the glass at 0.7 wt% Cr2O3, the highest efficiency in the nucleation process also corresponds. The optimum values for the nucleation and crystallisation time and temperature, determined for 0.7 wt% Cr2O3 addition, have been 70 min at 630 degrees C and 30 min at 800 degrees C. The crystalline phases formed at different thermal treatment temperatures of the parent glass have been investigated by XRD; the spinel is the only phase after the nucleation, pyroxene is the major phase after the crystallisation. The results of this study, have highlighted that a small percentage of Cr2O3 strongly affects the spinel formation thereby reducing the time and temperature of the thermal treatment and enhancing the degree of crystallisation of high iron content glasses. (C) 1999 Elsevier Science Limited. All rights reserved.