Study of Polycrystalline Material Obtained by Devitrification of Powdered Potassium-Lead Silicate Glass

Abstract

Regarding devitrification of the glass which has chemical composition of K₂O⋅4PbO⋅8SiO₂, effects of particle size and heating processes on properties of resulting polycrystalline material were investigated. Rate of nucleation, rate of nuclei growth, ratio of crystalline phase to vitreous phase and bending strength of products are measured under various conditions of particle size, heating temperature, heating time and other heating treatments.
The results obtained are as follows.
(1) The glass softens in the temperature range of 450°C to 500°C and is devitrificated in the temperature range of 580°C to 780°C.
(2) For nucleation, the temperature of 680°C is the most favorable and smaller particle size of the original glass is the more favorable since the nucleation tends to occur near the surface of the glass.
(3) Rate of crystal growth is relatively large in the temperature range of 660°C to 720°C and attains to the maximum of 60μ/hr at 770°C.
(4) The glass is devitrificated most rapidly and most uniformly under the condition of the particle size under 325 mesh and the heating temperature of 680°C, where the rate of nucleation exceeds the rate of nuclei growth.
(5) Though the glass of this composition belongs to ones hard to be devitrificated, we have been able to obtain a polycrystalline product containing crystalline phase over 95% by heating after moulded for 2 hours at 450°C, at the rate of 0.1°C/min between 450°C and 550°C and 2.5°C/min between 550°C and 680°C and holding for 2 hours at 680°C, which consists of microcrystals of a few micron size and has the bending strength of 1000kg/cm² to 1400kg/cm².