Abstract: Silicon nitride-alumina composite ceramics composed of silicon nitride crystals, .alpha.-alumina crystals and .beta.'-sialon crystals, wherein the silicon nitride crystals and the .beta.'-sialon surrounded the .alpha.-alumina crystals so as to prevent the connection of the .alpha.-alumina crystals. And a method for producing the silicon nitride-alumina composite ceramics which has the steps of preparing a mixture powder composed of 20 to 70 wt % of alumina powder and silicon nitride powder as a remainder, the average particle diameter of the alumina powder being two or more times as large as that of the silicon nitride powder, and firing the mixture powder in an atmosphere of inactive gas.

Abstract: A pressure detector has a cylindrical housing projecting into an atmosphere the pressure of which to be measured, a pressure chamber formed within the housing, to which is the pressure to be measured is introduced, a metallic diaphragm formed on a surface of one portion of a wall defining the pressure chamber, which deforms in accordance with changes in the pressure which is to be measured, and a strain gauge provided in the diaphragm for generating an output signal corresponding to the strain generated due to the deformation of the diaphragm. The strain gauge is composed of a diamond monocrystal plate and a diamond semiconductor film formed on the diamond monocrystal plate. On the diamond monocrystal plate are piled a titanium film, a platinum film, and a gold film, in sequence. The gold film is joined to the diaphragm by brazing.

Abstract: A pressure sensor includes a metal diaphragm provided at the end of a pressure introduction portion, a glass layer bonded to a surface of the metal diaphragm opposite to the pressure introduction side thereof, and a semiconductor chip acting as a semiconductor strain gauge bonded to the surface of the glass layer.

Abstract: A ceramic heater has a heater element made of a mixture including MoSi.sub.2 and Si.sub.3 N.sub.4 powder as a main ingredient and silica (SiO.sub.2) powder as an additive, a heater support member made of an electrically insulating ceramic sintered body for supporting the heater element and an electric current supply means for supplying an electric current to the heater element. The composition of the mixture for the heater element is defined so as to satisfy the following formula: 0.035.ltoreq.B/A<0.35 where A is the amount of Si.sub.3 N.sub.4 expressed by mol percent of the total amount of the main ingredient of MoSi.sub.2 and Si.sub.3 N.sub.4 and B is the amount of SiO.sub.2 expressed by mol percent of the total amount of the main ingredient of MoSi.sub.2 and Si.sub.3 N.sub.4.

Abstract: A sintered ceramic electric heater suitably applicable to a glow plug of a diesel engine has a heater element formed of an electrically conductive sintered ceramic integrally sintered with a support member made of an electrically insulating sintered ceramic material. The heater element is formed as a sintered body of a mixture of MoSi.sub.2 powder having an average diameter not greater than 2 .mu.m and 35 to 75 mol % of Si.sub.3 N.sub.4 powder. The average particle diameter of the Si.sub.3 N.sub.4 powder is at least twice as large as that of the MoSi.sub.2 powder so that electrically interconnecting MoSi.sub.2 particles surround scattered Si.sub.3 N.sub.4 particles whereby the resistance of the heater element becomes equal to that of MoSi.sub.2 and the temperature coefficient of the heater element is increased.

Abstract: A sintered ceramic heater, particularly a heater for a glow plug of a diesel engine, includes a sintered ceramic heater, which generates heat upon receiving an electric current, supported by an electrically insulating sintered ceramic body. The heater element includes a U-shaped cross-section outer portion integrally sintered with and covering a central portion. Each portion is formed of a sintered ceramic body of a mixture of electrically conductive ceramic powder having an average diameter of not more than 2 .mu.m and selected from the group consisting of MoSi.sub.2, WSi.sub.2, TiB.sub.2 and TiC, and 35-75 mol % of electrically insulating ceramic powder, e.g., Si.sub.3 N.sub.4. The central and outer portions have the same composition.

Abstract: A glow plug for an internal combustion engine is disclosed. The glow plug of the present invention comprises a heater support member projecting into a combustion chamber of an internal combustion engine, the heater support member being formed of an electric insulating material; a heater member affixed to the outer surface of the heater support member, the heater member being formed of an electrically conductive, heat- and oxidation-resistant ceramic material; at least three lead wires for power supply embedded in the heater support member, one end of the lead wires being connected each independently to the heater member; and a power switching means interposed between the other ends of those lead wires and a power source for connecting the power source selectively between the lead wires. By the selective connection between the lead wires performed by the power switching means, a plurality of heater elements having different resistance values are formed within the heater member.

Abstract: A ceramic heater comprising a supporting member made of an electrically insulating ceramic and a heater element made of a ceramic having excellent oxidization resistance, thermal shock resistance and high bending strength at a high temperature is disclosed. The heater element is formed by sintering a mixture composed of MoSi.sub.2 and 10 to 70 mol % of Si.sub.3 N.sub.4. By adding 3 to 10 mol % of at least one material selected from the group consisting of Al.sub.2 O.sub.3, a mixture of Al.sub.2 O.sub.3 and MgO and MgAl.sub.2 O.sub.4 to the above mixture, a heater element having a sufficient sintering degree can be obtained even by atmospheric sintering.

Abstract: An engine preheating apparatus in which an actuation circuit for a glow plug mounted in the engine is provided with a starting resistor of barium titanate of which the resistance value abruptly increases at a specific temperature, and a normal-operation resistor connected in parallel to the starting resistor. When the starting resistor is low in temperature and hence has a small resistance value, a large current is supplied to the glow plug, whereas when the starting resistor is high in temperature and therefore has a high resistance, a comparatively small current is supplied to the glow plug through the normal-operation resistor. The starting resistor is comprised of plural resistor elements of barium titanate as a main component and plural electrode plates alternately pressed one on each other. Each of the electrode plates is in pressure contact with each of heat radiators, so that the heat generated by the resistor elements is radiated from the radiators through the electrode plates.