Abstract: A plastic molding composition includes a powder, gelatin, a polar solvent, and an adhesion reducer. The powder contains at least one of a ceramic particle and a metal particle. The adhesion reducer reduces adhesion of the gelatin so that a molded product, which is molded from the composition with a molding die, is removed from the molding die without being broken. The adhesion reducer is a water-soluble or water-dispersible compound. The adhesion reducer has a HLB value, calculated by Griffin's method, ranging from 10 to 20.

Abstract: A plastic molding composition includes a raw powder, gelatin, a polar solvent, and a plasticizer. The raw powder contains at least one of a ceramic particle and a metal particle. The plasticizer reduces the minimum amount of the solvent necessary to give flowability to the composition. The plasticizer is a water-soluble or water-dispersible compound. The plasticizer has a ratio of hydroxyl number to carbon number per molecule in a range from 8% to 100%. The plasticizer is in solid or liquid form. When the plasticizer is in liquid form, the plasticizer has volatility equal to or lower than volatility of water.

Abstract: A plastic molding composition includes a powder, gelatin, a polar solvent, and an adhesion reducer. The powder contains at least one of a ceramic particle and a metal particle. The adhesion reducer reduces adhesion of the gelatin so that a molded product, which is molded from the composition with a molding die, is removed from the molding die without being broken. The adhesion reducer is a water-soluble or water-dispersible compound. The adhesion reducer has a HLB value, calculated by Griffin's method, ranging from 10 to 20.

Abstract: A plastic molding composition includes a raw powder, gelatin, a polar solvent, and a plasticizer. The raw powder contains at least one of a ceramic particle and a metal particle. The plasticizer reduces the minimum amount of the solvent necessary to give flowability to the composition. The plasticizer is a water-soluble or water-dispersible compound. The plasticizer has a ratio of hydroxyl number to carbon number per molecule in a range from 8% to 100%. The plasticizer is in solid or liquid form. When the plasticizer is in liquid form, the plasticizer has volatility equal to or lower than volatility of water.

Abstract: An alumina sintered body comprises alumina crystals as a main phase and a grain boundary phase made up of crystalline Y2Si2O7 and amorphous SiO2 at grain boundaries of the alumina crystals wherein when the alumina sintered body is taken as 100 wt %, the high melting phase is present in the range of from 0.1 wt % to 15 wt %. There is also provided a method for preparing the alumina sintered body, which method comprising a first mixing step P1 of mixing, at least, a yttria powder having an average particle size of 60 to 100 nm and a silica powder having a given average particle size to provide a mixed slurry and a second mixing step of further mixing an alumina powder having an average particle size of 0.5 to 1.0 ?m in the mixed slurry.

Abstract: An alumina sintered body comprises alumina crystals as a main phase and a grain boundary phase made up of crystalline Y2Si2O7 and amorphous SiO2 at grain boundaries of the alumina crystals wherein when the alumina sintered body is taken as 100 wt %, the high melting phase is present in the range of from 0.1 wt % to 15 wt %. There is also provided a method for preparing the alumina sintered body, which method comprising a first mixing step P1 of mixing, at least, a yttria powder having an average particle size of 60 to 100 nm and a silica powder having a given average particle size to provide a mixed slurry and a second mixing step of further mixing an alumina powder having an average particle size of 0.5 to 1.0 ?m in the mixed slurry.

Abstract: An alumina compound sintered compact, having a principal component of alumina, a method of manufacturing the same, and a spark plug employing such an alumina compound sintered compact are disclosed. The alumina compound sintered compact contains alumina, mullite, zircon, zirconia and a specified metal oxide composed of an oxide of at least one element selected from Group III elements excepting Mg, Ca, Sr, Ba and actinoid, wherein the alumina compound sintered compact contains 0.5 to 10 total parts by weight of mullite, zircon and zirconia, 0.5 to 10 parts by weight of the specified metal oxide and a balance of substantially alumina based on 100 parts by weight in total. The spark plug for an internal combustion engine includes a porcelain insulator made of the alumina compound sintered compact.

Abstract: An alumina composite sintered body 1 in which fine particles 2 are dispersed in the crystal grains 4 and/or at the crystal grain boundaries 3 of an alumina sintered body obtained by sintering alumina crystal grains 4; an evaluation method thereof; and a spark plug using the alumina composite sintered body 1. Arbitrary regions in the cross-section of the alumina composite sintered body 1 are taken as analysis surfaces, and when the cross-sectional areas of the fine particles 2 contained in each analysis surface are measured, the ratio of the cross-sectional areas occupying in the area of the analysis surface is from 1 to 20%; when the cross-sectional areas of the fine particles 2 contained in each of analysis surfaces adjacent to each other are measured, and the cross-sectional area is converted into a circle having the same area, the diameter of the circle is from 0.

Abstract: An alumina-based ceramic composition comprising a composite sintered body of alumina as a main component and a composition of at least one element selected from Al, Si, Mg and rare earth elements, wherein an amount of the composition of at least one element selected from Al, Si, Mg and the rare earth elements is not greater than 5 parts by weight on the basis of 100 parts by weight of alumina as the main component, and a spark plug using this alumina-based ceramic composition for an insulator.