BULK AND SURFACE CRYSTALLIZATION OF LEAD TETRAGERMANATE GLASS - A DTASTUDY

The surface and bulk crystallisation of lead tetragermanate glass has been studied by differential thermal analysis. The influence of the sp ecific surface area of the sample and the nucleation heat-treatment on the crystallisation is pointed out. Infrared spectroscopy measurement s suggest that the addition of PbO to germanium oxide leads to a chang e in the coordination number of germanium atoms from 4 to 6. The phase s which crystallise during the DTA runs were identified by X-ray diffr action as hexagonal and monoclinic PbGeO4O9. The activation energy of crystal growth was also evaluated from DTA curves. A value of about 30 0 kJ mol(-1) was calculated from surface and bulk crystallisation.