Crystallization of CaO−Al2O3−SiO2 and CaO−MO−Al2O3−SiO2 (M=Mg, Zn) glasses
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A range of CaO−Al2O3−SiO2 glasses have been prepared by fusion of pure starting materials in platinum crucibles. Compositions containing large amounts on network formers, Al2O3 and SiO2, are difficult to crystallize. If the amount of network former is reduced, glasses will self-nucleate and crystallize more readily, but the products of crystallization tend to react with water. This conflict has been partly resolved by adding MgO and ZnO and tailoring compositions so as to produce a phase, variously designated “Q” or “pleochroite”, ideally Ca20Al32-2vMgvSivO68, withv close to 4. Pleochroite crystallizes with a typically fibrous morphology. Preliminary experiments on fragments and melt-cast glass rods indicate that these compositions can be heat treated without deformation to yield highly crystalline, transparent ceramics.
KeywordsPolymer Crystallization SiO2 Platinum Al2O3
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