A method of forming a ceramic material includes providing a mixture of solid powder, which includes precursors of crystalline aluminum silicate, amorphous fluxing agent, and amorphous modifier. The method also sinters the mixture of solid powder at 1600? C. to 1800? C. to form the ceramic material, which includes 100 parts by weight of the crystalline aluminum silicate having a chemical formula of AlSi.sub.xO.sub.1.5+2x, wherein x is 0.21 to 0.35, 10 to 15 parts by weight of the amorphous fluxing agent, and 5 to 10 parts by weight of the amorphous modifier.

A polycrystalline silicon carbide sintered material includes silicon carbide grains having a median equivalent diameter of between 1 and 10 microns, the material having a total porosity of less than 2% by volume of the material, and a silicon carbide mass content of at least 99%, except for the free carbon, wherein in the material the mass ratio of the content of SiC having a beta-type crystallographic form to the content of SiC having an alpha-type crystallographic form is less than 2.

A part made of composite material includes fiber reinforcement including silicon carbide fibers presenting an oxygen content less than or equal to 1% in atomic percentage; and a matrix present in the pores of the fiber reinforcement and including at least one sintered silicate phase including at least one rare earth silicate, mullite, or a mixture of mullite and of at least one rare earth silicate, the matrix including at least a first phase including mullite and a second phase, different from the first phase, including at least one rare earth silicate.

The present invention provides a gallium nitride sintered body and a gallium nitride molded article which have high density and low oxygen content without using a special apparatus. According to the first embodiment, a gallium nitride sintered body, which is characterized by having density of 2.5 g/cm.sup.3 to less than 5.0 g/cm.sup.3 and an intensity ratio of the gallium oxide peak of the (002) plane to the gallium nitride peak of the (002) plane of less than 3%, which is determined by X-ray diffraction analysis, can be obtained. According to the second embodiment, a metal gallium-impregnated gallium nitride molded article, which is characterized by comprising a gallium nitride phase and a metal gallium phase that exist as separate phases and having a molar ratio, Ga/(Ga+N), of 55% to 80%, can be obtained.

Composite material comprising aluminum nitride (AlN) material, less than 80 weight percent cubic boron nitride (cBN) grains dispersed within the AlN material and less that 5 weight percent sinter promotion material, the composite material including no more than about 1.5 percent porosity.

The present invention provides a gallium nitride sintered body and a gallium nitride molded article which have high density and low oxygen content without using a special apparatus. According to the first embodiment, a gallium nitride sintered body, which is characterized by having density of 2.5 g/cm.sup.3 to less than 5.0 g/cm.sup.3 and an intensity ratio of the gallium oxide peak of the (002) plane to the gallium nitride peak of the (002) plane of less than 3%, which is determined by X-ray diffraction analysis, can be obtained. According to the second embodiment, a metal gallium-impregnated gallium nitride molded article, which is characterized by comprising a gallium nitride phase and a metal gallium phase that exist as separate phases and having a molar ratio, Ga/(Ga+N), of 55% to 80%, can be obtained.

A polycrystalline diamond comprising diamond particles, wherein: the content of the diamond particles is more than 99% by volume based on the total volume of the polycrystalline diamond: the median diameter d50 of the diamond particles is 10 nm or more and 200 nm or less; and the dislocation density of the diamond particles is 0.1?10.sup.15 m.sup.?2 or more and less than 2.0?10.sup.15 m.sup.?2.

A silicide-based composite material is disclosed, comprising a silicide of Mo, B, W, Nb, Ta, Ti, Cr, Co, Y, or a combination thereof, Si3N4, and at least an oxide, as well as and a process for producing the same.

In the present invention, in producing a SiC single crystal in accordance with a solution method, a crucible containing SiC as a main component and having an oxygen content of 100 ppm or less is used as the crucible to be used as a container for a SiC solution. In another embodiment, a sintered body containing SiC as a main component and having an oxygen content of 100 ppm or less is placed in the crucible to be used as a container for a SiC solution. The SiC crucible and SiC sintered body are obtained by molding and baking a SiC raw-material powder having an oxygen content of 2000 ppm or less. SiC, which is the main component of these, serves as a source for Si and C and allows Si and C to elute into the SiC solution by heating.

Embodiments relate to a method for manufacturing a silicon nitride sintered body with high thermal conductivity, which includes the steps of: a) obtaining a slurry by mixing a silicon nitride powder and a non-oxide based sintering aid; b) obtaining a mixed powder by drying the slurry; c) forming a compact by pressurizing the mixed powder; and d) sintering the compact.