Abstract: A gas sensor comprising a first measuring chamber for introducing a gas to be measured, a second measuring chamber for detection of the gas to be measured, and as pump cells a first pump cell having a pair of pump electrodes, and a second pump cell having a measuring electrode and an auxiliary pump electrode, wherein a porous alumina sintered body having communicating pores of 500-1100 ? in average pore diameter and 6-16% in porosity is formed as an electrode protective layer on the surface of at least the measuring electrode of the second pump cell in such a manner that the alumina sintered body covers the measuring electrode. The gas sensor can be use for long period of time because of the protective layer.

Abstract: An alumina sintered body having communicating pores of 400–1100 ? in average pore diameter and 4–16% in porosity and being obtainable by mixing first alumina particles 1 having a particle diameter of 0.2–0.7 ?m and a sphericity of 0.7–1.0 as an aggregate and second alumina particles having a particle diameter of 0.01–0.1 ?m as a pore forming material to embed a plurality of the second alumina particles 2 in the spaces between the first alumina particles 1, and sintering the mixture at a temperature of 1200–1400° C. The alumina sintered body can be used for a part for various gas permeable industrial materials inclusive of protective film for gas sensors, and the like.

Abstract: A gas sensor comprising a first measuring chamber 11 for introducing a gas to be measured, a second measuring chamber 12 for detection of the gas to be measured, and as pump cells a first pump cell 31 having a pair of pump electrodes 21 and 22, and a second pump cell 32 having a measuring electrode 23 and an auxiliary pump electrode 24, wherein a porous alumina sintered body having communicating pores of 500-1100 ? in average pore diameter and 6-16% in porosity is formed as an electrode protective layer 50 on the surface of the measuring electrode 23 as at least one of a pair of the electrode 23 and 24 of the second pump cell 32 in such a manner that the alumina sintered body covers the measuring electrode 23. The gas sensor can be use for long period of time because of the protective layer.

Abstract: An alumina sintered body having communicating pores of 400-1100 ? in average pore diameter and 4-16% in porosity and being obtainable by mixing first alumina particles 1 having a particle diameter of 0.2-0.7 ?m and a sphericity of 0.7-1.0 as an aggregate and second alumina particles having a particle diameter of 0.01-0.1 ?m as a pore forming material to embed a plurality of the second alumina particles 2 in the spaces between the first alumina particles 1, and sintering the mixture at a temperature of 1200-1400° C. The alumina sintered body can be used for a part for various gas permeable industrial materials inclusive of protective film for gas sensors, and the like.

Abstract: An aluminum nitride sintered body is provided comprising metal elements contained in an amount of not more than 100 ppm for each metal element except for aluminum and assuming black color of a lightness of not more than N 4 according to the definition of JIS Z 8721. The aluminum nitride sintered body has preferably a relative density of at least 99.3% and crystal grains constituting the sintered body have an average particle diameter of at least 0.6 .mu.m but not more than 4.0 .mu.m. A powder of aluminum nitride obtained by reduction nitriding method is sintered at a temperature of at least 1,800.degree. C. under a pressure of at least 120 kg/cm.sup.2. Sintering temperature is preferably not more than 2,000.degree. C. and the sintering is preferably effected for at least 2 hrs but not more than 5 hrs.

Abstract: A ceramic heater includes a substrate made of aluminum nitride, a resistive heating element buried in the substrate and made of a metal having a high melting point, and terminals electrically connected to the resistive heating element and buried in said substrate. The terminals are made of a metal having a high melting point and a coefficient of thermal expansion not smaller than that of the substrate. The metal of the resistive heating element has a coefficient of thermal expansion not smaller than that of the substrate. The coefficient of thermal expansion of each of the terminals and the resistive heating element is in a range from 5.0.times.10.sup.-6 /.degree.C. to 8.3.times.10.sup.-6 /.degree.C.

Abstract: A ceramic heater composed of a ceramic substrate and a resistant heating element embedded within the ceramic substrate along a predetermined planar pattern is obtained by holding a convolution of a spiral-coiled high melting metallic filament in the above predetermined planar pattern and heat-treating the convolution at a temperature not higher than a primary recrystallization commencement temperature of the high melting metal under a non-oxidative atmosphere to provide the resistant heating element, embedding the resulting resistant heating element within a ceramic shaped body, and then, sintering the ceramic shaped body.