Evaluation of the degree of crystallisation in glass-ceramics by density measurements

A theoretical procedure has been developed with the aim of obtaining an accurate and rapid estimation of the degree of crystallisation in jarosite glasses by measuring the densities of the parent glass and, after the thermal treatment, of the glass-ceramic. Compositions were prepared by mixing jarosite waste with granite scraps and glass cullet, yielding three different glass-batchs, melted at 1450 degrees C, quenched and thermal treated to obtain glass-ceramics with different degrees of crystallisation. Density measurements were carried out by means of a helium displacement pycnometer. The results were compared with the degree of crystallisation as evaluated by XRD and showed a good agreement. The method is applicable if the variation of density connected to the phase transformation is sufficiently large. In the formation of pyroxene and magnetite phases, with large density variation compared to the parent glass, it is precise and easily applicable. (C) 1999 Elsevier Science Limited. All rights reserved.