Gte Laboratories Incorporated

Anthony P Moschetti

Helmut Lingertat

J Thomas Smith

Carr L Quackenbush

Vincent W Nehring

A method of preparing fully dense silicon nitride based ceramic articles comprises the steps of blending a metal oxide component and silicon nitride, wherein a portion of the silicon nitride comprises acicular crystals; comminuting the powder mixture to reduce the aspect ratio of the acicular crystals to an average of less than about 3; pressing the comminuted powder to form a compact; and pressureless sintering the compact to a fully dense ceramic body. Powder mixtures and powder compacts for forming fully dense silicon nitride based ceramic bodies are also disclosed.

Silicon nitride based ceramics and method

Sintered silicon nitride-silica-yttria ceramic articles having silica-rich or yttria-rich casing layers are disclosed. The surface layers are formed by sintering pre-compacted bodies in a powder setter bed to produce unitary sintered bodies having surface layers in which the atom ratio of yttrium to silicon has a smooth gradient from the surface of the article to the interior body of the article.

Sintered silicon nitride ceramic articles having surface layers of

Dense, composite, polycrystalline ceramic articles comprising silicon nitride, silicon dioxide, and yttrium oxide and having thin surface layers of controlled composition are formed by sintering pre-pressed compacts embedded in setter bed powder mixtures having compositions of silicon nitride, silicon dioxide, and yttrium oxide which differ from that of the pressed compact. Employing the method of this invention, articles are produced which have surface layers in which the minor phase of the article is enriched with either yttrium or silicon.

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Acton, MA, United States of America

Anthony P Moschetti