Glasses containing various amounts of aluminum and fluorin were crystallized by the heat treatment. Bending strengths of the crystallized glasses were measured, the crystalline phases were identified by X-ray diffraction method, and the microstructures were examined by electron-microscopy. The relation between the microstructure and the bending strength was studied.
The results obtained are summarized as follows:
1) The crystallized glass having the highest bending strength (42kg/mm2) was obtained from the glass containing limited amounts of aluminum and fluorin under the optimum conditions of heat treatment.
2) The crystalline phases existing in the crystallized glasses were two kinds of fluoramphibole and two kinds of fluor-mica. The chemical composition of crystalline phases changed with that of the glass.
3) The differences of the grain size and the amount of each crystalline phase between the outor surface layer and the inner part of the crystallized glass were observed.
4) The thickness of the outer surface layer was about 150μ and especially the microstructure of the outer surface layer of about 10μ in thickness differed extremely from that of the inner part.
5) It was considered that the microstructure of the outer surface layer influenced dominantly on bending strength of the crystallized glass.