Crystallization of Calcium Phosphate Glass Having Short Chain Structure

Crystallization characteristics of the glass having the molar ratio, CaO/P2O5=1.22 and/or (CaO+H2O)/P2O5=1.28, of which average chain length (Pn) was estimated to be 7, were studied by means of high temperature microscopy, high temperature X-ray diffraction technique and IR absorption spectroscopy.1. Crystalline phases formed in the glass below ca. 650°C consisted of tromelite and trace of β-calcium metaphosphate.2. Crystal growth rate, G (μ/min), of tromelite in the blown film sample at 680°-740°C was represented by the following equation: logG=25.6-25.0×103/T.3. The overall isothermal crystallization curves of the glass powder in size from 44 to 74μ at 600°-650°C were coincided with the Kolmogorow-Avrami equation, where Avrami exponent (m) had different two values depending on the crystallinity (V), and no induction period for the crystallization was found in all the curves.4. In the range V 0.6, the crystallization was found to contain the thermal nucleation and the three-dimensional growth.5. The activation energy for the growth was approximately in accordance with the energy for the crystallization, the values, 110-130kcal/mole, being comparable with P-O-P bond energy.6. The crystallization of the glass seemed reasonable to be in part accompanied by the polycondensation resulted from evolution of OH-radicals from P-O-P chain ends.