Sumitomo Metal Industries, Inc.

Yasuki Yoshitomi

Tadahisa Arahori

Shunichi Etoh

Kazumasa Mori

Kuniaki Nakagawa

A high-strength machinable ceramic capable of high-precision fine machining has a coefficient of thermal expansion close to that of silicon and preferably a uniform blackish color which facilitates image processing of machined parts. The ceramic comprises a main constituent and a sintering aid. The main constituent comprises 30&#x2013;59.95 mass % of boron nitride, 40&#x2013;69.95 mass % of zirconia, optionally up to 20 mass % of silicon nitride and 0.05&#x2013;2.5 mass % (calculated as an element) of at least one coloring additive, which is selected from C, Si, elements of Groups IIIA&#x2013;IVB in the fourth period, elements of Groups IVA&#x2013;VB in the fifth period, elements of Groups IVA&#x2013;VIB in the sixth period of the long form periodic table, and compounds of these elements.

Machinable ceramic

A low-thermal-expansion, rigid and wear-resistant ceramic is provided. The low-thermal-expansion ceramic of the invention includes 60 vol % to 99.9 vol % of at least one selected from the group consisting of cordierite, spodumene and eucryptite and 0.1 vol % to 40 vol % of at least one selected from the group consisting of carbides, nitrides, borides and silicides of group IVa elements, group Va elements and group VIa elements, and boron carbide. The ceramic has a porosity of 0.5% or less and a thermal expansion coefficient, at 10&#xb0; C. to 40&#xb0; C., of 1.5&#xd7;10/&#xb0; C. or less.

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Higashiosaka, Japan

Yasuki Yoshitomi