Abstract: A ceramic heater including a columnar substrate and a heat generation resistor embedded in the substrate. A taper surface (12) having a contour L1 extending along an imaginary ellipse E is composed of a plurality of successively arranged curved surfaces which decrease in radius of curvature toward the forward end with respect to the direction of an axis P. The taper surface (12) is such that the distance between the end points M1 and M2 of the contour L1 is large in the direction of the axis P, and the angle between the axis P and a tangential line of the contour L1 on the side toward the forward end surface (11) is larger than the angle between the axis P and a tangential line of the contour L1 on the side toward the side circumferential surface (15).

Abstract: A ceramic heater including a columnar substrate and a heat generation resistor embedded in the substrate. A taper surface (12) having a contour L1 extending along an imaginary ellipse E is composed of a plurality of successively arranged curved surfaces which decrease in radius of curvature toward the forward end with respect to the direction of an axis P. The taper surface (12) is such that the distance between the end points M1 and M2 of the contour L1 is large in the direction of the axis P, and the angle between the axis P and a tangential line of the contour L1 on the side toward the forward end surface (11) is larger than the angle between the axis P and a tangential line of the contour L1 on the side toward the side circumferential surface (15).

Abstract: A green ceramic heater including a green heating resistor formed of an electrically conductive ceramic (e.g., silicide or carbide of a metal element such as W, Ta, or Nb) and an insulative ceramic (e.g., silicon nitride) and power supply leads (e.g., made of W), a first end of each power supply lead being connected to a corresponding end of the green heating resistor, the green heating resistor and the power supply leads buried in a green substrate formed of a material (e.g., silicon nitride) is fired, and subsequently, the resultant ceramic heater is heat-treated at 900 to 1,600° C., to thereby enhance flexural strength of the ceramic heater. The heat treatment is preferably carried out prior to forming a glass layer on an outer circumferential surface of the ceramic heater.

Abstract: A ceramic heater includes a silicon nitride ceramic substrate and a heating member embedded in the silicon nitride ceramic substrate. An Al-thickened layer is formed in a surface layer portion of the silicon nitride ceramic substrate. The Al-thickened layer has an Al concentration higher than that of an internal layer portion of the silicon nitride ceramic substrate. The Al-thickened layer assumes such a graded composition structure that the Al concentration increases toward the surface of the silicon nitride ceramic substrate.

Abstract: In the production of a silicon nitride sintered body through a hot press method, a sintering aid protecting agent is added to the raw material. The employable protecting agents are metallic elements such as Ta, W and Mo and compounds of the metallic elements such as nitrides and silicides. Conversion of these elements and compounds to carbides occurs preferentially to reduction of the sintering aid. Thus, it becomes possible to suppress reduction of the sintering aid in a reducing atmosphere formed, for example, of carbon monoxide, which is generated particularly when a graphite pressing die is employed.

Abstract: A green ceramic heater including a green heating resistor formed of an electrically conductive ceramic (e.g., suicide or carbide of a metal element such as W, Ta, or Nb) and an insulative ceramic (e.g., silicon nitride) and power supply leads (e.g., made of W), a first end of each power supply lead being connected to a corresponding end of the green heating resistor, the green heating resistor and the power supply leads buried in a green substrate formed of a material (e.g., silicon nitride) is fired, and subsequently, the resultant ceramic heater is heat-treated at 900 to 1,600° C., to thereby enhance flexural strength of the ceramic heater. The heat treatment is preferably carried out prior to forming a glass layer on an outer circumferential surface of the ceramic heater.

Abstract: The invention comprehends a silicon nitride sintered body having consistent qualities, a process for producing the same, a ceramic heater employing the silicon nitride sintered body as a substrate and a glow plug containing the ceramic heater as a heat source. In the production of a silicon nitride sintered body through a hot press method, a sintering aid protecting agent is added to the raw material. The employable protecting agents are metallic elements such as Ta, W and Mo and compounds of the metallic elements such as nitrides and silicides. Conversion of these elements and compounds to carbides occurs preferentially to reduction of the sintering aid. Thus, it becomes possible to suppress reduction of the sintering aid in a reducing atmosphere formed, for example, of carbon monoxide, which is generated particularly when a graphite pressing die is employed.

Abstract: A ceramic heater extending in an axial direction to have an elongate shape includes (a) a basal body; (b) a lead wire embedded in the basal body; and (c) a heating element embedded in the basal body. This heating element includes (1) a matrix ceramic phase; (2) conductive ceramic particles dispersed in the matrix ceramic phase; (3) a portion in which an end portion of the lead wire is embedded; and (4) a reference zone in terms of concentration of a particular element (e.g., rare-earth element). The heating element may include a condensed zone in terms of concentration of the particular element. The ceramic heater can be free from the condensed zone, or at least its formation is minimized to have a thickness of not greater than 5 &mgr;m. With this, the ceramic heater is improved in bending strength.

Abstract: The invention comprehends a silicon nitride sintered body having consistent qualities, a process for producing the same, a ceramic heater employing the silicon nitride sintered body as a substrate and a glow plug containing the ceramic heater as a heat source. In the production of a silicon nitride sintered body through a hot press method, a sintering aid protecting agent is added to the raw material. The employable protecting agents are metallic elements such as Ta, W and Mo and compounds of the metallic elements such as nitrides and silicides. Conversion of these elements and compounds to carbides occurs preferentially to reduction of the sintering aid. Thus, it becomes possible to suppress reduction of the sintering aid in a reducing atmosphere formed, for example, of carbon monoxide, which is generated particularly when a graphite pressing die is employed.

Abstract: A ceramic heater includes a silicon nitride ceramic substrate and a heating member embedded in the silicon nitride ceramic substrate. An Al-thickened layer is formed in a surface layer portion of the silicon nitride ceramic substrate. The Al-thickened layer has an Al concentration higher than that of an internal layer portion of the silicon nitride ceramic substrate. The Al-thickened layer assumes such a graded composition structure that the Al concentration increases toward the surface of the silicon nitride ceramic substrate.

Abstract: A ceramic heater extending in an axial direction to have an elongate shape includes (a) a basal body; (b) a lead wire embedded in the basal body; and (c) a heating element embedded in the basal body. This heating element includes (1) a matrix ceramic phase; (2) conductive ceramic particles dispersed in the matrix ceramic phase; (3) a portion in which an end portion of the lead wire is embedded; and (4) a reference zone in terms of concentration of a particular element (e.g., rare-earth element). The heating element may include a condensed zone in terms of concentration of the particular element. The ceramic heater can be free from the condensed zone, or at least its formation is minimized to have a thickness of not greater than 5 &mgr;m. With this, the ceramic heater is improved in bending strength.

Abstract: A ceramic heater of required heating properties is made available in that adjusting elements made solid in an electric conductive element are added other than electric conductive elements of an heating resistor in a ceramic heater. Accordingly, resistance temperature coefficient is changed, not largely changing other properties of heating materials.

Abstract: Ceramic raw powder containing conductive ceramic powder is mixed with a prescribed quantity of a molding assistant containing carbon component. This mixture is molded into a prescribed shape of a resistive heating element to thereby produce a heating element mold. A composite mold is prepared by embedding the heating element mold into molds of a ceramic substrate. The composite mold is sintered at a sintering temperature of 1700.degree. C. or higher. During a process of rising temperature to the sintering temperature, the composite mold is kept in an oxygen containing atmosphere having an oxygen partial pressure of 2.times.10.sup.-4 to 1.0 Torr for 7 minutes or longer at a temperature of 1200.degree. C. or higher.