Mitsui Mining Co., Ltd.

Akria Mathumoto

Keiichiro Koba

Yoshinori Koyanagi

Katsuya Eguchi

Toshio Hamasaki

Disclosed is a glass-ceramic product having a chemical composition, as expressed in terms of oxides with the exception of F, in the weight range of 35 to 60% SiO.sub.2, 10 to 20% Al.sub.2 O.sub.3, 12 to 25% MgO, 5 to 15% K.sub.2 O and 4 to 15% F, containing no B.sub.2 O.sub.3, and containing 40 to 70% by weight of fluorophlogopite microcrystals. This glass-ceramic product has a flexural strength of not less than 1500 kgf/cm.sup.2, a heat resistance of about 1100.degree. C., excellent dielectric properties and good machinability, and is a material capable of extending the range of use of high performance ceramics. The aforesaid glass-ceramic product can be made by dissolving, in a solvent consisting essentially of a polar solvent, compounds (consisting largely of alkoxide compounds) of the metallic components and a fluorine compound in such proportions as to give a final product having the aforesaid chemical composition, hydrolyzing these compounds, dehydrating and drying the resulting gel, and heat-treating the resulting dry solid.

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Tochigi, Japan

Akria Mathumoto