Abstract: An La2O3 powder and an SiO2 powder are mixed with each other, and then heated. By heating, a porous material of LaXSi6O1.5X+12 (8?X?10) as a composite oxide is produced. Subsequently, the porous material is pulverized to obtain a powder, and the powder is added to a solvent to prepare a slurry. The slurry is solidified in a magnetic field to prepare a compact. After that, the compact is sintered, and an oxide ion conductor is obtained thereby.

Abstract: An La2O3 powder and an SiO2 powder are mixed with each other, and then heated. By heating, a porous material of LaXSi6O1.5X+12 (8?X?10) as a composite oxide is produced. Subsequently, the porous material is pulverized to obtain a powder, and the powder is added to a solvent to prepare a slurry. The slurry is solidified in a magnetic field to prepare a compact. After that, the compact is sintered, and an oxide ion conductor is obtained thereby.

Abstract: An La2O3 powder and an SiO2 powder are mixed with each other, and then heated. By heating, a porous material of LaXSi6O1.5X+12 (8?X?10) as a composite oxide is produced. Subsequently, the porous material is pulverized to obtain a powder, and the powder is added to a solvent to prepare a slurry. The slurry is solidified in a magnetic field to prepare a compact. After that, the compact is sintered, and an oxide ion conductor is obtained thereby.

Abstract: An La2O3 powder and an SiO2 powder are mixed with each other, and then heated. By heating, a porous material of LaXSi6O1.5X+12 (8≦X≦10) as a composite oxide is produced. Subsequently, the porous material is pulverized to obtain a powder, and the powder is added to a solvent to prepare a slurry. The slurry is solidified in a magnetic field to prepare a compact. After that, the compact is sintered, and an oxide ion conductor is obtained thereby.

Abstract: There is disclosed a silicon nitride sintered body produced by sintering a molded article which comprises a mixture of a silicon nitride powder as the main component and plural kinds of sintering additives, wherein said silicon nitride powder is set to be 0.1 to 1.0 &mgr;m in average grain size, and said plural kinds of sintering additives includes first and second sintering additives, said first sintering additive comprising oxide powders of at least one element of Group 3a element, said second sintering additive comprising oxide powders of at least one element selected from Zr (zirconium), Hf (hafnium), Nb (niobium), Ta (tantalum) and W (tungsten), said first sintering additive having the average grain size set to be 0.1 to 10 times as large as the average grain size of said silicon nitride powder and being incorporated in an amount ranging from 0.

Abstract: A silicon nitride reaction-sintered body having a high mechanical strength without surface working can be produced by (1) forming a silicon powder mixture of at least two types of silicon powders having substantially independent particle size distribution ranges into a green body, the silicon powder mixture having an average particle size ranging from 5 .mu.m to 300 .mu.m; (2) heating the green body in a nitrogen-containing atmosphere for nitrogenation; and (3) sintering the nitrogenated green body at a temperature of 1900.degree. C. or higher.

Abstract: A composite powder having a specific surface area of 7 m.sup.2 /g or more is produced by mixing a silicon powder with a carbonaceous powder and a sintering aid powder, and heat-treating the resultant mixed powder in a nitrogen-containing atmosphere at a temperature of 1,450.degree. C. or lower thereby nitriding and carbonizing silicon in the mixed powder. The temperature elevation speed in the heat treatment for nitriding and carbonizing is less than 2.degree. C./minute at least in a range from a temperature at which the nitriding and carbonizing of silicon starts to take place to a temperature at which the composite powder is kept for nitriding and carbonizing of silicon. The composite sintered body is produced by sintering such a composite powder at a temperature of 1,600.degree. C. to 2,200.degree. C.

Abstract: A composite sintered body of silicon nitride and silicon carbide is manufactured by sintering a composite powder or green body of silicon nitride and silicon carbide in a nitrogen gas atmosphere. The composite powder having a percentage of .alpha.-silicon nitride which is at least 30% based on all silicon nitride is produced by mixing a silicon powder with a carbonaceous powder and a sintering aid powder, and heat-treating the resultant mixed powder in a nitrogen-containing atmosphere at a temperature of 1,450.degree. C. or lower thereby nitriding and carbonizing silicon contained in the mixed powder to produce a composite powder, a temperature elevation speed being less than 2.degree. C./minute. The composite green body having a percentage of .alpha.

Abstract: A silicon nitride reaction-sintered body having a high mechanical strength without surface working can be produced by (1) forming a silicon powder mixture of at least two types of silicon powders having substantially independent particle size distribution ranges into a green body, the silicon powder mixture having an average particle size ranging from 5 .mu.m to 300 .mu.m; (2) heating the green body in a nitrogen-containing atmosphere for nitrogenation; and (3) sintering the nitrogenated green body at a temperature of 1900.degree. C. or higher.

Abstract: A sintered composite body of silicon nitride and silicon carbide is manufactured by mixing a silicon powder with a carbonaceous powder and a sintering additive, producing a mixture, molding the mixture into a molded body, heat-treating the molded body in an atmosphere containing a nitrogen gas for thereby simultaneously nitriding and carbonizing silicon contained in the molded body, and subsequently firing the molded body in a nitrogen gas atmosphere. A composite powder of silicon nitride and silicon carbide which is produced by simultaneously nitriding and carbonizing silicon contained in the molded body has a content of .alpha.-type silicon nitride which is at least 30% of all silicon nitride in the composite powder. To produce such a composite powder, a silicon powder is mixed with a carbonaceous powder and a sintering additive, producing a mixture, and the mixture is heat-treated in an atmosphere containing a nitrogen gas at a temperature of at most 1450.degree. C.

Abstract: In the method of heat-treating a silicon nitride sintered body which was produced from silicon nitride powder and sintering aid powder in order to provide it with an increased crystallinity, the silicon nitride sintered body is heat-treated in a non-oxidizing atmosphere under conditions such that the silicon nitride sintered body is embedded in at least one selected from the group consisting of powders of W, Mo, Ta, Re and carbides thereof.

Abstract: A silicon nitride sintered body having a composition of 1.5-3.0 weight % of Y.sub.2 O.sub.3, 0.1-1.0 weight % of Al.sub.2 O.sub.3 and balance substantially Si.sub.3 N.sub.4, a weight ratio of Y.sub.2 O.sub.3 /Al.sub.2 O.sub.3 being 2.5 or more, which has a density of 3.0 g/cm.sup.3 or more and has a structure in which the minor axes of grains are substantially 6 .mu.m or less. This silicon nitride sintered body is produced by preparing a powder mixture containing Y.sub.2 O.sub.3 powder, Al.sub.2 O.sub.3 powder and silicon nitride powder in the above proportions, the silicon nitride powder having an oxygen content of 1.2 weight % or less, a specific surface area of 9-11 m.sup.2 /g and a metal impurity content of 200 ppm or less; and sintering the powder mixture at a temperature of 1900.degree.-2100.degree. C. and a pressure of 5 kg/cm.sup.2 G or more in a nitrogen atmosphere.