Process for the manufacture of shaped articles from reaction-bonded silicon nitride by nitridation under elevated nitrogen gas pressure

US4687655A · kind A · utility

Assignee

• Elektroschmelzwerk Kempten GmbH · DE

Inventors

• Klaus Hunold · Kempten, DE
• Alfred Lipp · Bad Wörishofen, DE
• Klaus Reinmuth · Durach, DE
• Peter Arnold · Earby, GB
• Johannes Napholcz · Kempten, DE

Key dates

• Filing date: Apr 11, 1986
• Grant date: Aug 18, 1987
• Expiry date: Apr 11, 2006

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C04B2235/77
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

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 silico…