Abstract
Glasses within the ternary system Li2O‐B2O2SiO2 containing less than 25.6% Li2Ocan be broadly classified into three groups according to their behavior during cooling or heating. One group, containing either more than 18% Li2Oor less than 20% SiO2, yields clear glasses during slow or rapid cooling. The second group, containing approximately 5 to 15% Li2O and 26 to 90% SiO2, yields dense white opal glass during slow or rapid cooling. The third group, located at the outer edge of the second group, cools to room temperature as clear glasses but develops opacity when reheated to temperatures between 550° and 8800°C. It has been shown by electron microscopy that the opacity is due to liquid immiscibility, the matrix glass containing well‐formed spheres of the dispersed phase. Some of the clear glasses of both groups have been shown to consist of two immiscible phases. The size of the dispersed units in the spontaneous opal glasses and also the reheat opal glasses can be controlled by the variation of the reheat treatments. The phase separation reported here is beyond the resolution of the petrographic microscope and can be detected only with the high resolution of the electron microscope. Accessory evidence is given to show that the phases are non‐crystalline.
Published Version
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