Effect of Glassy Phase Separation on Nucleation in Fluor-richterite Composition Glass
Studies on Crystallization in Fluor-richterite Composition Glass IV
1970 Volume 78 Issue 904 Pages 411-420
Details
1970 Volume 78 Issue 904 Pages 411-420
Fluor-richterite (Na⋅NaCa⋅Mg5⋅Si8:O22F2) composition glass was subjected to the heat treatments for glassy phase separation, nucleation and crystal growth and the phase separation and the crystallization were studied by the electron microscopy and X-ray powder diffraction method. The effect of glassy phase separation on the nucleation was discussed. The results obtained were as follows:
1) As previously reported by the author, droplets were formed by the glassy phase separation in the sample after heating at the temperature of glassy phase separation treatment in the range from 550 to 650°C. The number and the grain size of the droplets varied with the temperature and the time of heat treatment.
2) Crystallization was observed in the sample after heating at the temperature above 600°C. At lower temperatures in the crystallization temperature range, the crystallization appeared to start from the surface of droplets that had formed before the crystallization. A layer structure crystal such as fluor-mica or fluor-talc crystallized in preference to fluor-richterite.
3) At the temperature of nucleation treatment of 725°C, most of the droplets disappeared rapidly, the layer structure crystal decomposed slowly and the fluor-richterite crystallized.
4) The sample heated at 600°C or 625°C for a long time contained a larger number of droplets and a small amount of crystalline phase and was converted to a translucent glass-ceramics by the heat treatments for nucleation and crystal growth. The translucent glass-ceramics was characterized by the smallest size and the largest number of fluor-richterite microcrystals and a small amount of residual glass.
5) It was considered that the nucleation sites were given on the droplet surfaces by the reaction between the droplet surface having a three-dimensional random network structure and the cation or the silicate anion present in the matrix glass phase and that the number of nucleation sites varied with the temperature and the time of the heat treatment for glassy phase separation. The layer structure crystal and fluor-richterite were nucleated on these sites and fluor-richterite was nucleated on the surface of the layer structure crystal.
