X-ray diffraction methods to determine crystallinity and preferred orientation of lithium disilicate in Li-Zn-silicate glass-ceramic fibres

Abstract

Three X-ray diffraction methods for the evaluation of the microstructural features shown by glass-ceramic fibres obtained by various heat treatments have been developed and discussed. Fibres made of a Li-Zn-silicate glass of the following chemical composition were investigated (mol%): SiO2 66.75, Li2O 23.45, ZnO 8.00, K2O 1.00, P2O5 0.80. The first method is devoted to measure the preferred crystal orientation of lithium disilicate crystals which begin to grow starting from 580°C with thec-axis lying preferentially normal to the fibre external surface. This method has employed a four-circle diffractometer by means of which the intensity distribution of the equatorial 002 X-ray reflection could be evaluated. The other two methods regard the crystallinity content determination of lithium disilicate formed at 590°C as well as at 620°C either after a nucleation step at 480°C or at 500°C, or without any nucleation treatment. These two methods, namely the Hermans and Weidinger and the Wakelin, Virgin and Crystal methods, have been transferred for the first time from the organic polymer science to glass-ceramic materials. The results obtained with both methods have been compared together and have been found in good agreement.