A new method and apparatus is applied to manufacture boehmite and sol gel abrasive grain with greatly reduced raw material cost. The raw material starts from alumina trihydrate, which is transferred to highly dispersible alumina monohydrate under hydrothermal treatment in an agitated zirconium-steel or titanium-steel cladding plate high pressure reactor. Then the highly dispersed and deionized sol is converted to sintered high-density microcrystalline ceramic abrasive grain by sol-gel process.

The present invention aims to provide a simple and efficient method for manufacturing -alumina particles, main component particles of which each have a crystal face other than the face [001] as a main crystal face and a polyhedral shape other than a hexagonal bipyramidal shape. According to the method for manufacturing -alumina particles of the present invention, when an aluminum compound is calcined in the presence of a specific content of a metal compound, -alumina particles each having a particle diameter of 50 m or less, a degree of crystallization of 90% or more, and a polyhedral shape can be obtained.

An object of the present invention is to provide an inorganic oxide powder suitable for forming an inorganic oxide porous membrane, which is superior in lithium ion conductivity and has insulation performance, on at least one surface of a positive electrode, a negative electrode and a separator which constitute a lithium ion secondary battery. The present invention relates to an inorganic oxide powder for use in forming an inorganic oxide porous membrane having insulation performance on at least one surface of a positive electrode, a negative electrode and a separator which constitute a lithium ion secondary battery, wherein the powder has 1) an oxide purity of 90% by weight or higher; 2) an average particle diameter of 1 m or less; and 3) an average three-dimensional particle unevenness of 3.0 or higher.

A method for synthesizing a sol solution for forming porous alumina films having high heat resistance and high specific surface area and excellent adhesion to various substrate surfaces is provided. The method can include preparing an alkoxysilane and an aluminum solution, precipitating a silicon compound adsorbed on aluminum hydroxide in a solution of the alkoxysilane and the aluminum solution, and washing the precipitate filtered from the mixed solution with water to prepare a precipitate cake. A slurry solution is prepared by adding water to the precipitate cake, a pH adjusting treatment is performed on the slurry solution, and then an autoclave treatment is performed to prepare SiO.sub.2Al.sub.2O.sub.3 containing sol solution. A pH value of the slurry solution is controlled within a specific pH range in which the solution state of the SiO.sub.2Al.sub.2O.sub.3 containing sol solution after the autoclave treatment is a sol state.