Crystallization of beryllium metaphosphate glass

Crystallization of beryllium metaphosphate glass powders in size from 44 to 74 μm was studied with a high-temperature X-ray diffractometer. 1) Crystalline phase formed in the glass during heating above 6000C is a high-temperature polymorph of beryllium metaphosphate. It transforms into α-Be(PO3)2 reversively. 2) The so-called ''β-Be(PO3)2'' described in ASTM card was never crystallized out of the glass. It is found that the crystal is not a polymorph of beryllium metaphosphate but has a chemical composition of BeO : P2O5 : H2O=1 : 1 : 1. 3) Spherulite formed in the blown film glass shows periodic extinction rings when viewed under a polarization microscope, indicating twisting of the lamellas. 4) From J-M-A plot of the crystallization data, Avrami exponent m=4 is obtained through overall crystallization. This indicates the thermal nucleation and the three dimensional growth. The apparent activation energy for the crystallization is ca. 70 kcal/mol. (auth.)