Ngk Spark Plug Company, Limited

Hiroki Watanabe

Masaya Ito

Katsura Matsubara

Kouji Funaki

The present invention relates to a ceramic heater which is capable of preventing an electric conduction defect of a heat-generating resistor from being caused by a supplied current, thus being excellent in voltage endurance, and a glow plug containing the ceramic heater. The ceramic heatercontained in the glow plughas an insulative ceramic base materialand the heat-generating resistorembedded in the insulative ceramic base material. The heat-generating resistorhas, as main components, an electrically conductive compound, silicon nitride and a grain boundary amorphous glass phase. The amount of the rare earth element contained in the heat-generating resistor is less than 2% by volume in terms of its oxide and, further, a molar ratio R=(A/A+B) of the mol number A of the amount of the rare earth element in terms of its oxide to a total of the mol number A and a mol number B, which is the amount of excess oxygen in terms of silicon dioxide, is 0.3 or less. By achieving such a constitution, the heat-generating resistor is capable of preventing electric conduction defects and of being excellent in voltage endurance.

Ceramic heater and glow plug having the same

A silicon nitride sintered material containing a silicon nitride component and silicon carbide having an average particle size of 1 &#x3bc;m or less in an amount of at least 1 mass % and less than 4 mass %, based on 100 mass % of the silicon nitride component. The carbide is dispersed in the silicon nitride component, and the silicon nitride sintered material has a thermal expansion coefficient of at least 3.7 ppm/&#xb0; C. between room temperature and 1,000&#xb0; C. The silicon nitride component contains a rare earth element in an amount of 15-25 mass % as reduced to a certain oxide thereof and Cr in an amount of 5-10 mass % as reduced to a certain oxide thereof, and a crystalline phase is present in intergrain regions of the sintered material.

Silicon nitride sintered material and production process thereof

A silicon nitride sintered material containing silicon nitride, a Group 4 through 6 element, a rare earth element, and silicon carbide, characterized in that the amount of the rare earth element as reduced to a certain oxide thereof is 5.7-10.3 mol %; the ratio by mol of subtraction remainder oxygen amount calculated in relation to the oxygen contained in the sintered material, the remainder oxygen amount being expressed in terms of silicon dioxide, to the amount of oxygen contained in the sintered material is at least 0.50 and less than 0.70; a four-component crystalline phase of rare earth element-silicon-oxygen-nitrogen is not present; and the thermal expansion coefficient is at least 3.7 ppm/&deg; C. between room temperature and 1,000&deg; C.

A silicon nitride&mdash;tungsten carbide composite sintered and process for preparing the same which contains silicon nitride and tungsten carbide, and is characterized in that the total in amounts of an entirety of rare earth elements as reduced to certain corresponding oxides thereof, the elements being contained in the sintered material, and excess oxygen as reduced to silicon dioxide is 6-20 mass %; the ratio, on a mol basis, of (the amounts of rare earth elements as reduced to the certain corresponding oxides thereof)/(the amounts of the rare earth elements as reduced to the corresponding oxides thereof&plus;the amount of excess oxygen as reduced to silicon dioxide) is 0.3-0.7; a crystalline phase is present in an intergrain region of the sintered material; and an effective firing temperature range within which a flexural strength of at least 800 MPa is obtained encompasses at least 100 degrees. Also disclosed is a glow plug having a ceramic heater comprising the silicon nitride&mdash;tungsten carbide composite sintered material.

Silicon nitride-tungsten carbide composite sintered material, process for preparing the same and glow plug

A silicon nitride-tungsten carbide composite sintered material which contains silicon nitride and tungsten carbide, and characterized in that in an arbitrary cross-section of the sintered material, the ratio of the area of a tungsten carbide portion to that of the entirety of the cross-section is 20-35%, and a tungsten carbide aggregation portion having a longitudinal length of at least 5 &mgr;m is present in the arbitrary cross-section. The production process includes firing raw material powder containing tungsten carbide powder and two silicon nitride powders having different particle sizes.

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Gifu, Japan

Hiroki Watanabe