Process for the manufacture of shaped articles from reaction-bon

Chemistry of inorganic compounds – Silicon or compound thereof – Binary compound

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264 65, 501 97, C04B 3558, C01B 21063

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active

046876553

ABSTRACT:
The invention is a process for the manufacture of shaped articles of reaction-bonded silicon nitride in which pre-shaped articles of silicon powder are heated in a first stage under a nitrogen gas pressure of at least 6 MPa at a heating rate of not more than 50.degree. C. per hour to a reaction temperature below the melting point of silicon, the article is maintained at the reaction temperature for at least 0.5 hours and subsequently, in a second stage, heating the article at a heating rate of at least 500.degree. C. per hour to a temperature above the melting point of silicon and maintaining the article at that temperature for from 1 to 7 hours. The process can nitridate both pre-shaped articles consisting of silicon powder and, optionally, up to 15% by weight Si.sub.3 N.sub.4 powder and those containing up to 10% by weight of a sintering aid such as Y.sub.2 O.sub.3. In the former case, porous shaped articles having a density of from 87 to 91% TD and, in the latter case, dense shaped articles having a density of more than 98% TD, are obtained. In all cases, in a total nitridation time of less than 15 hours, a conversion of at least 95% of the silicon originally present into silicon nitride is achieved, which, in the finished shaped article, is substantially in the .beta.-modification.

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Kryl, J. A., Chem. Abstracts, 100:179168w.
Fujikawa et al, "Hot Isostatic Pressing: Its Application in High Performance Ceramics", 10-83, Japan.
Moulson, "Reaction-Bonded Silicon Nitride: Its Formation and Properties", 1979, pp. 1017-1051.

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