The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Mar. 27, 1990
Filed:
May. 30, 1989
NGK Spark Plug Co., Ltd., Nagoya, JP;
Abstract
The invention relates to a ceramic heater element consisting of a sintered body of a silicon nitride base ceramic and a resistance heating wire such as a tungsten wire embedded in the ceramic body. The ceramic contains Al.sub.2 O.sub.3 and AlN besides Si.sub.3 N.sub.4 and is produced by using Y.sub.2 O.sub.3 as sintering aid. The ceramic body is improved in strength and also in stability of the ceramic structure at temperatures up to about 1300.degree. C. by rendering the grain boundary phase of the sintered ceramic a crystalline phase comprising either 2Y.sub.2 O.sub.3.Si.sub.2-x Al.sub.x N.sub.2-x O.sub.1-x (0.ltoreq.x<2) or 3Y.sub.2 O.sub.3.5Al.sub.2 O.sub.3. The heater element is produced by preparing a powder mixture in which (Si.sub.3 N.sub.4 +Al.sub.2 O.sub.3 +AlN) amounts to 90-98 wt %, the balance being the sintering aid, with proviso that (Al.sub.2 O.sub.3 +AlN)/Si.sub.3 N.sub.4 is from 0.02 to 0.08 by weight and that (Al.sub.2 O.sub.3 /AlN) is from 0.2 to 2.0 by weight, compacting the powder mixture into a desirably shaped body with insertion of the heating wire and sintering the shaped body preferably by a hot press sintering method. For example, the heater element is used in a glow plug for a diesel engine.