Thermal expansion investigation of iron rich glass-ceramic

A theoretical procedure was developed with the aim of obtaining an estimation of the crystallisation fraction in glass-ceramics by means of thermal expansion measurements. The theoretical model was applied to the crystallisation of an iron rich glass composition yielding magnetite and pyroxene as crystalline phases.The crystallisation mechanism was investigated by means of DTA, XRD, FTIR, TEM; the thermal expansion by Differential Dilatometer. A relationship between the weight fraction of crystal phase and the linear thermal expansion coefficient was obtained. The values of the fraction of crystal phase, evaluated by means of dilatometric measurements, showed a good agreement with the results obtained by means of density variation and XRD analyses.The crystallisation kinetic of the iron rich glass, at 630 and 700 °C, was also investigated by dilatometry and the variation of CTE as a function of the crystallisation time explained in terms of increasing of the apparent viscosity of the residual glass.