Silicon nitride ceramic having devitrified intergranular glass phase and a process for its preparation

摘要

The invention relates to a silicon nitride ceramic having a high strength both at low temperatures and at temperatures above 1000 C., and to a process for its preparation.PPThe silicon nitride ceramic contains, as the primary phase, -silicon nitride and, as a crystalline secondary phase, an yttrium compound which has been caused to crystallize out from the intergranular glass phase by thermal after-treatment. Teh yttrium-containing, crystalline secondary phase has the following d-values in an X-ray diffraction pattern using Cu-K radiation: 4.69 ; 4.05 ; 3.48 ; 3.20 ; 3. 06 ; 2. 81 ; 2.40 ; 2.07 ; 2.03 ; and 1.87 , the most intense diffraction reflection having the d- value 3.06 .+-.0.01 . A residue of amorphous glass phase is present in the ceramic as a further phase between the crystal grains.