An alumina sintered body including an inner layer in which alumina crystal grains contained have an average aspect ratio of 1.0 to 2.0 and an outer layer which covers at least a part of the inner layer from outside and in which alumina crystal grains contained have an average aspect ratio of more than 2.0, the alumina sintered body being free from silicon except unavoidable impurities.

A porous ceramic particle may have a particle size of at least about 200 microns and not greater than about 4000 microns. The porous ceramic particle may further have a particular cross-section that may include a core region and a layered region overlying the core region. The layered region may include overlapping layered sections surrounding the core region. The core region may include a core region composition and a first layered section may include a first layered section composition. The first layered section composition may be different than the core region composition.

A porous ceramic particle may have a particle size of at least about 200 microns and not greater than about 4000 microns. The porous ceramic particle may further have a particular cross-section that may include a core region and a layered region overlying the core region. The layered region may include overlapping layered sections surrounding the core region. The core region may include a core region composition and a first layered section may include a first layered section composition. The first layered section composition may be different than the core region composition.

A shaped abrasive particle including a body having a first major surface, a second major surface, and a side surface joined to the first major surface and the second major surface, and the body has at least one partial cut extending from the side surface into the interior of the body.

A composition which comprises a soluble or partially soluble phosphate, a refractory material and less than 1% of an oxide or hydroxide of magnesium or calcium. The composition may be mixed with water to form an investment casting slurry into which a wax pattern may be dipped. Slurry coated onto the pattern may be set by applying a stucco composition which comprises an oxide or hydroxide of magnesium or calcium. Coats of set slurry may be built up on the pattern to form an investment casting shell.

Ceramic particles for use in a solar power tower and methods for making and using the ceramic particles are disclosed. The ceramic particle can include a sintered ceramic material formed from a mixture of a raw material and MnO. The sintered ceramic material can include about 0.01 wt % to about 10 wt % MnO, about 0.1 wt % to about 20 wt % Fe.sub.2O.sub.3, and about 0.01 wt % to about 10 wt % Mn.sub.2O.sub.3. The ceramic particle can have a size from about 8 mesh to about 170 mesh.

Various shaped abrasive particles are disclosed. Each shaped abrasive particle includes a body having at least one major surface and a side surface extending from the major surface.

A method of making magnetizable abrasive particles includes: moistening the outer surfaces of ceramic particles with waterglass to provide moistened ceramic particles. Magnetizable particles are contacted with the moistened ceramic particles to provide powder-coated ceramic particles. The powder-coated ceramic particles are heated to at least a temperature sufficient to bond the magnetizable particles of the powder-coated ceramic particles to the respective ceramic particles thereby providing the magnetizable abrasive particles. On a respective basis, each magnetizable abrasive particle comprises a respective ceramic particle having a magnetizable particles bonded thereto.

A method for producing an alumina sintered body, including: a step of applying an alkaline earth metal compound onto a surface of an alumina raw material which is an unsintered alumina compact or an alumina sintered body; and a step of subjecting the alumina raw material to which the alkaline earth metal compound has been applied to heat treatment at a temperature of 1200 C. or more for 5 minutes or more and 300 minutes or less.

An abrasive particle having a body including a first major surface, a second major surface opposite the first major surface, and a side surface extending between the first major surface and the second major surface, such that a majority of the side surface comprises a plurality of microridges.