Kabushiki Kaisha Toyota Chuo Kenkyusho

Nippondenso Co., Ltd.

Hideyuki Masaki

Osami Kamigaito

Yasuo Nakamura

Masami Oki

Masatoshi Suzuki

Haruo Doi

Toshio Kandori

A silicon nitride base sintered body having high strength and high density is formed by a normal sintering, namely by sintering without pressure. The sintered body is produced of silicon nitride and the metal oxides yttrium oxide and cerium oxide. A silicon nitride base sintered body having yet a higher strength and higher density can be produced by heating yttrium oxide and cerium oxide together for forming Y.sub.2 O.sub.3.2CeO.sub.2 before sintering.

Method for producing a silicon nitride base sintered body

A silicon nitride based ceramic is formed of silicon nitride and at least two metal oxides of such a type that when the metal oxides are heated separately they form a spinel. Combination of said metal oxides and said silicon nitride as fine powders and sintering same at a specified temperature for a specified period of time results in a silicon nitride based ceramic having improved mechanical and chemical properties.

Sintered silicon nitride base ceramic and said ceramic

Method for producing a sintered silicon nitride base ceramic and said

A resistor built-in spark plug comprising an insulator formed therein with an axially extending bore, a terminal nut fitted in an upper end portion of the bore, a center electrode fitted in a lower end portion of the bore, a resistor arranged in a central portion of the bore, one copper-glass electrode interposed between the resistor and the terminal nut, and another copper-glass electrode interposed between the resistor and the center electrode, such resistor being made by firing (calcining) and solidifying a resistor powder mixture consisting of 30 to 10 volume % of a principal resistor component containing tin oxide, 35 to 85 volume % of insulating ceramic filler powder of a higher electric resistivity than the principal resistor component which is selected from the group consisting of quartz glass, alumina, zircon, zirconia, silica (SiO.sub.2) and .beta.-spodumene, and 35 to 5 volume % of glass powder having a softening temperature in a range between 300.degree. and 600.degree. C. One or both of the two copper-glass electrodes may consist of two electrode layers, one copper-glass layer maintained in contact wth the resistor and having a higher copper content than the other copper-glass electrode layer.

Resistor built-in spark plug

A resistor built-in spark plug comprises an insulator formed with an axially extending inner hole, a stem fitted in the upper part of said hole in said insulator, a center electrode fitted in the lower part of said hole, a resistor disposed in the central part of said hole, and copper-glass electrode layers disposed between said resistor and said stem and between said resistor and said center electrode. Said resistor is made by firing and solidifying powder of resistor mixture consisting of 75 to 38 volume percent of main resistor component containing tin oxide and 25 to 62 volume percent of glass powder with softening temperature of 300.degree. to 600.degree.C. Said copper-glass electrode layers are made by firing and solidifying a mixture of copper powder and glass powder with the softening temperature of above 530.degree.C and more than 30.degree.C higher than the softening point of glass in the resistor portion.

Growing community of inventors

Nagoya, Japan

Hideyuki Masaki