Ngk Spark Plug Company, Limited

Shunkichi Nozaki

Yukihiro Kimura

Masakazu Watanabe

Akiyasu Okuno

Yasuhiko Suzuki

Yasushi Matsuo

Isamu Fukuura

Rokuro Kambe

Kazuho Tatematsu

Norio Kato

Kiminori Horiki

Masakazu Iwai

The invention relates to a ceramic heater for use, e.g., as a glow plug for a diesel engine or as an igniter for an oil or gas burner. The ceramic heater has a nonoxide ceramic body having a heating part and a supporting part and a heating resistor embedded in the heating part of the ceramic body. The material of the heating resistor is W, WC, tungsten alloy or a metal nitride such as TiN or TaN. According to the invention the heating part of the ceramic body is formed of aluminum nitride ceramic, which is high in heat conductivity and resistant to oxidation at high temperatures, at least in a core region in contact with the heating resistor, and the supporting part is formed of silicon nitride ceramic which is low in heat conductivity at least in a surface region. The ceramic body is made by uniting a heating part entirely formed of aluminum nitride ceramic and a supporting part entirely formed of silicon nitride ceramic with interposal of a joint part which is formed of mixed ceramic of aluminum nitride and silicon nitride with a gradient of the proportion of aluminum nitride to silicon nitride, or by thoroughly covering a core formed of aluminum nitride ceramic with silicon nitride ceramic.

Ceramic heater

A ceramic glow plug comprises a ceramic heater formed by embedding a metal wire in a sintered Si.sub.3 N.sub.4 -based ceramic. The ceramic heater is brazed to the inner surface of an axial bore of a metal tube and the metal tube is brazed to the inner surface of an axial bore of a metal holder. The tip of the ceramic heater extends from the metal tube and metal holder and is coated with highly heat and corrosion resistant material to minimize erosion and corrosion due to combustion gases. The coating consists essentially of a thin CVD film of alumina (Al.sub.2 O.sub.3) having a thickness of 2 .mu.m deposited on a precoating AlON layer having a thickness of 0.5 .mu.m formed on the exposed surface of the tip. Alternatively, the protective coating may consist of thin CVD film of silicon carbide (SiC) or silicon nitride (Si.sub.3 N.sub.4) formed directly on the exposed surface of the tip.

Silicon nitride glow plug with alumina corrosion and erosion protective

A ceramic heater comprising a ceramic substrate is described which has formed thereon a layer of a silicide of an element selected from groups IVa, Va and VIa of the periodic table. The heater has stable temperature vs. resistance characteristics, has high mechanical strength and produces the desired temperature in a very short period of time.

A process for producing a silicon carbide heating element is disclosed comprising: adding boron or a boron compound in an amount corresponding to from 0.3 to 3.0% by weight as boron, and carbon or a carbon compound in an amount corresponding to from 0.1 to 6.0% by weight as carbon, to a SiC powder having an average particle size of 1.0.mu. or less; blending and molding the mixture; conducting a primary sintering in vacuum or in an inert atmosphere, except nitrogen; and thereafter conducting a secondary sintering at from 1500.degree. to 2300.degree. C. in a pressurized nitrogen atmosphere to produce a silicon carbide heating element having a density of at least 80% based on the theoretical density and an electrical resistivity of 1.0 .OMEGA.-cm or less.

Process for producing silicon carbide heating elements

Sintered silicon carbide materials are described, which have a metallized surface consisting essentially of a composition comprising 10 to 90% by weight of Si, balance a mixture of at least two components selected from Fe, Ni and Co. A process for producing the silicon carbide sintered materials having the metallized surface is also described.

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Aichi, Japan

Shunkichi Nozaki