Development of Machinable Glass Ceramics Containing Rare Earth Oxides

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Machinable glass Ceramics, which can be cut, ground drilled and milled by equipment used for machining and fast -machining of metals, are being used as heat-resistant materials, electrical insulation, chemically durable materials etc. Usually, machinable glass-ceramics contain mica, which has high cleavability, obtained by precipitating mica in glass, by sintering etc. Unfortunately, this intrinsic property of mica also imparts reduced hardness and elastic modulus compared to ordinary glasses. Rare-metal oxide containing aluminosilicate glass ceramics were found to be good machinability by the authors. It is purposes of the present study to improve the machinabilty of the glass Ceramics of higher hardness and elastic modulus and higher electrical insulation because of nonalkaline composition. Several series of Y203-containing aluminosilicate glasses were prepapared by an ordinary melting method, and their physical properties, such as Vickers hardness, surface roughness and so forth. Crystalization behaviors were at the same time studied for the samples substituted for alakaline earth oxide or kinds of rearth earth oxides in theses glasses. Sol-gel process were adopted to make the machinable glass cermics of these kinds. Crystallized samples were successfullly lathed and their surface roughness was examined. Higher amounts of alkaline earth oxide introduction leads to some correlatation to the surface roughness and harness and/or volume fraction of cryatallization.