Abstract: Al.sub.2 O.sub.3 -Er.sub.2 O.sub.3 ceramic abrasive grains comprising a second phase consisting of aluminum oxides and erbium oxides in the form of reaction products surrounding a first phase and the first phase exclusive of the second phase and substantially consisting of alpha alumina only, the size of the crystal grain consisting of two phases being below 1 micron, which are obtained by a sol-gel process wherein erbium precursor is incorporated before sintering in an amount of 0.05-0.4 wt % in a form of Er.sub.2 O.sub.3, which is suitable for lapping composition, grinding wheel, grinding disc and coated abrasive articles.

Abstract: Method for producing mono-crystalline alumina grains comprising fusing alna materials in the presence of halide to induce oxyhalide phase at grain boundaries, cooling and solidifying fused materials and separating oxyhalide phase by means of inorganic acid or alkali before or after crushing, and said alumina materials are composed of either aluminum oxides alone or aluminum oxides and at least one of the metallic oxides selected from the group consisting of chromium oxide, titanium oxide and vanadium oxide.

Abstract: Alumina-zirconia lapping abrasives containing tetragonal zirconia at a rate of 30% or less and optionally containing at least one oxide selected from the group consisting of yttrium oxide, calcium oxide, magnesium oxide, titanium oxide and other rare earth oxide in the form of solid solution, which are produced by fusing alumina-zirconia abrasive materials, quenching fused materials to obtain an ingot, crushing the ingot and subjecting the crushed ingot to a heat treatment at a higher temperature than the phase transition temperature of zirconia.

Abstract: Sintered aluminous abrasive grains having a density of at least 95% of theoretical density and having an alpha alumina crystal size of smaller than one micron. Which are obtained by drying and crushing a lithium containing alumina dispersion and sintering the crushed objects at 1100.degree.-1500.degree. C., said abrasive grains have the strength and hardness equal to or higher than conventional abrasive grains, superior properties in grinding resistance and wear resistance and superior self-sharpening property in course of grinding.

Abstract: Fused zirconia refractory materials having high-temperature resistance and corrosion resistance which includes 1-14 30 wt % of calcia and 0.05-2 wt % of yttria or rare earth minerals including yttria as a stabilizer of zirconia, which are produced by the process comprising adding and mixing calcia and yttria or rare earth minerals including yttria to zirconia materials as a stabilizer, fusing the mixed materials in an electric arc furnace, cooling slowly the fused materials to obtain an ingot, crushing the ingot to particles and oxidizing and annealing the particles.

Abstract: Molten oxide of grinding material, refractory material, etc., being poured into a circular casting space formed between coaxially arranged inner and outer cylinders and cooled by the water contained in the inner cylinder. Thus, the molten oxide is cooled radially from the center of the inner cylinder and solidified. The outer cylinder includes two segments which separate from each other for facilitating putting the molten oxide into the casting space and taking the resulting solidified product out of the casting space.