Abstract: An yttria-based slurry composition comprising yttria, an aqueous silica binder system or an aqueous ammonium zirconium carbonate binder system and a fluorine compound, which is selected from ammonium fluoride, ammonium hydrogen difluoride, sodium fluoride, potassium fluoride, sodium hydrogen difluoride and/or potassium hydrogen difluoride and a method of stabilizing an yttria-based slurry composition comprising yttria and an aqueous silica binder system or an aqueous ammonium zirconium carbonate binder system which method comprises treating the composition, preferably treating the binder system, with a fluorine compound which is selected as indicated above.

Abstract: An yttria-based slurry composition comprising yttria, an aqueous silica binder system or an aqueous ammonium zirconium carbonate binder system and a fluorine compound, which is selected from ammonium fluoride, ammonium hydrogen difluoride, sodium fluoride, potassium fluoride, sodium hydrogen difluoride and/or potassium hydrogen difluoride and a method of stabilizing an yttria-based slurry composition comprising yttria and an aqueous silica binder system or an aqueous ammonium zirconium carbonate binder system which method comprises treating the composition, preferably treating the binder system, with a fluorine compound which is selected as indicated above.

Abstract: Method for producing a mold for use in casting reactive metals comprising preparing a slurry of a yttria-based refractory composition and a binder, and using said slurry as a mold facecoat by applying said slurry onto a surface of a mold pattern, wherein said yttria-based refractory composition is obtainable by (a) mixing particles of a yttria-based ceramic material and a fluorine containing dopant, and (b) heating the resulting mixture to effect fluorine-doping of said yttria-based ceramic material.

Abstract: Method for producing a mold for use in casting reactive metals comprising preparing a slurry of a yttria-based refractory composition and a binder, and using said slurry as a mold facecoat by applying said slurry onto a surface of a mold pattern, wherein said yttria-based refractory composition is obtainable by (a) mixing particles of a yttria-based ceramic material and a fluorine containing dopant, and (b) heating the resulting mixture to effect fluorine-doping of said yttria-based ceramic material.

Abstract: Method for producing a mold for use in casting reactive metals comprising preparing a slurry of a yttria-based refractory composition and a binder, and using said slurry as a mold facecoat by applying said slurry onto a surface of a mold pattern, wherein said yttria-based refractory composition is obtainable by (a) mixing particles of a yttria-based ceramic material and a fluorine containing dopant, and (b) heating the resulting mixture to effect fluorine-doping of said yttria-based ceramic material.

Abstract: Method for producing a mold for use in casting reactive metals comprising preparing a slurry of a yttria-based refractory composition and a binder, and using said slurry as a mold facecoat by applying said slurry onto a surface of a mold pattern, wherein said yttria-based refractory composition is obtainable by (a) mixing particles of a yttria-based ceramic material and a fluorine containing dopant, and (b) heating the resulting mixture to effect fluorine-doping of said yttria-based ceramic material.

Abstract: The present invention pertains to a process for preparing an abrasive based on corundum with a grain shape factor exceeding 0.6.

Abstract: Abrasive material with particularly high abrasive performance is obtained in that the ceramic material contains an additive of 0.01 to 15 percent by weight, preferably 0.1 to 3 percent by weight of a chromium compound.

Abstract: Ceramic sintered body, in particular abrasive grain, based on .alpha.-Al.sub.2 O.sub.3, said body being arranged in such a manner that improved abrasive results are achieved, said body being bound into a structure by means of a glass-like ceramic binder and showing a drop in hardness from its center to its edge of less than 1800 N/mm.sup.2, preferably less than 1000 N/mm.sup.2, and, in particular, less than 500 N/mm.sup.2.

Abstract: Sintered microcrystalline ceramic material based on .alpha.-Al.sub.2 O.sub.3 with an addition of 0.01 to 2.0 weight percent of a cerium compound, consisting of a microcrystalline matrix and 0.1 to 30 volume percent whisker-like needles, whereby said cerium compound is mainly present in the needles. The whisker-like needles give this material a special tenacity combined with good abrasive results.

Abstract: Sintered microcrystalline ceramic material based on .alpha.-Al.sub.2 O.sub.3 with an addition of 0.01 to 2.0 weight percent of a cerium compound, consisting of a microcrystalline matrix and 0.1 to 30 volume percent whisker-like needles, whereby said cerium compound is mainly present in the needles. The whisker-like needles give this material a special tenacity combined with good abrasive results.

Abstract: A sintered, microcrystalline abrasive material consists of at least 99.5%, by weight, of .alpha.-Al.sub.2 O.sub.3 crystallites having a size of less than 2 .mu. and the material having a density of at least 97% of the theoretical density. This abrasive material has a very high abrasive property and can be used in grinding bands or discs.

Abstract: An abrasive material of great hardness and high tenacity particularly suitable for high-pressure grinding consists essentially of a sintered, microcystalline .alpha.--Al.sub.2 O.sub.3 abrasive material having a purity of least 98.5% and a density of at least 95% of theoretical density, the .alpha.--Al.sub.2 O.sub.3 crystallites of the material being smaller than 4.mu., preferably smaller than 3.mu..