Methods for preparing ceramic matrix composites using melt infiltration and chemical vapor infiltration are provided as well as the resulting ceramic matrix composites. The methods and products include the incorporation of sacrificial fibers to provide improved infiltration of the fluid infiltrant. The sacrificial fibers are removed, such as decomposed during pyrolysis, resulting in the formation of regular and elongate channels throughout the ceramic matrix composite. Infiltration of the fluid infiltrant can then take place using the elongate channels resulting in improved density and an improved ceramic matrix composite product.

A shaped composite body of a reaction-bonded, silicon-infiltrated mixed ceramic, the microstructure of which is determined by primary grains of crystalline B.sub.4C grains (1) of mean grain size d50>100 ?m and <500 ?m and a fraction of >10%, by weight, and <50%, by weight, and by primary grains of a finer silicon carbide with d50<70 ?m and a fraction of >10%, by weight, and <50%, by weight, and the primary grains are siliconized (3) bonded by secondarily formed silicon carbide with a fraction of >5%, by weight and <25%, by weight, in a silicon carbide matrix having a free metallic silicon (2) content of >1%, by weight, and <20%, by weight.

A ferrite sintered magnet includes a composition expressed by a formula (1) of Ca.sub.1-w-xLa.sub.wA.sub.xFe.sub.zCo.sub.mO.sub.19. In the formula (1), w, x, z, and m satisfy a formula (2) of 0.30w0.50, a formula (3) of 0.08x0.20, a formula (4) of 8.55z10.00, and a formula (5) of 0.20m0.40. In the formula (1), A is at least one kind of element selected from a group consisting of Sr and Ba. Cr is further contained at 0.058 mass % to 0.132 mass % in terms of Cr.sub.2O.sub.3.

Antiballistic armour plate includes a ceramic body including a hard material, provided, on its inner face, with a back energy-dissipating coating. The ceramic body is monolithic. The constituent material of the ceramic body includes grains of ceramic material having a Vickers hardness that is higher than 15 GPa, and a matrix binding the grains, the matrix including a silicon nitride phase and/or a silicon oxynitride phase, the matrix representing between 5 and 40% by weight of the constituent material of the ceramic body. The maximum equivalent diameter of the grains of ceramic material is smaller than or equal to 800 micrometres. The constituent material of the ceramic body has an open porosity that is higher than 5% and lower than 14%. The metallic silicon content in the material, expressed per mm of thickness of the body, is lower than 0.5% by weight.

A method for forming a ceramic matrix composite article includes laying up a first group of plies; laying up a second group of plies, the first and second groups of plies being adjacent to each other; compacting the first group of plies and the second group of plies in the same processing step; and performing a first infiltration process on the first group of plies. The method also includes performing a second infiltration process on the second group of plies, the first infiltration process being one of a melt infiltration process or a chemical vapor infiltration process, and the second infiltration process being the other of the melt infiltration process or the chemical vapor infiltration process.

A method for manufacturing high-purity aluminum hydroxide and alumina material is disclosed, which includes the steps of: reacting aluminum metal with a mixture of organic base and water to form aluminum hydroxide suspension; removing water by filtration to form aluminum hydroxide slurry, and for manufacturing alumina material, further drying/baking the slurry to form aluminum oxide powders. The method is amenable to mass production of high-purity aluminum hydroxide and aluminum oxide containing total silica and non-aluminum metal impurities less than 0.005% and having a bulk density higher than 3.0 g/cc. In addition, the invention also provides high-purity aluminum hydroxide and aluminum oxide prepared by using the method disclosed and bulk products prepared therefrom.

A polycrystalline sintered ceramic material of very low electrical resistivity includes by mass more than 95% silicon carbide (SiC), less than 1.5% silicon in another form than SiC, less than 2.5% carbon in another form than SiC, less than 1% oxygen (O), less than 0.5% aluminum (Al), less than 0.5% of the elements Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, less than 0.5% alkali elements, less than 0.5% alkaline earth, between 0.1 and 1.5% nitrogen (N), the other elements forming the complement to 100%, wherein the grains of the above material have a median equivalent diameter of between 0.5 and 5 micrometers, the mass ratio of SiC alpha (?)/SiC beta (?) is less than 0.1, and the total porosity represents less than 15% by volume of the material.

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 2.0?10.sup.15 m.sup.?2 or more and 4.0?10.sup.16 m.sup.?2 or less.

A porous ceramic of the present disclosure contains yttrium zirconate and yttrium oxide, and at least one of them is a main component. A member for a semiconductor manufacturing apparatus such as a shower plate, a plug or the like in a semiconductor manufacturing apparatus is made of the above porous ceramic.

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.