A process for producing alumina, the process having a seeding phase and a precipitation phase. During the seeding phase a seed mixture is produced by adding an aluminium salt to an aqueous solution and then adding an alkaline metal aluminate to the mixture while maintaining the seed mixture at generally neutral pH. The precipitation phase produces precipitated alumina by simultaneously adding aluminium salt and alkaline metal aluminate to the seed mixture while maintaining a pH from 6.9 to 7.8. The recovered precipitated alumina has at least one, preferably all the following characteristics: i) a crystallite size of 33-42 Ang.: in the (120) diagonal plane (using XRD).; ii) a crystallite d-spacing (020) of between 6.30-6.59 Ang.; iii) a high porosity with an average pore diameter of 115-166 Ang.; iv) a relatively low bulk density of 250-350 kg/m.sup.3; v) a surface area after calcination for 24 hours at 1100 C. of 60-80 m.sup.2/g; and vi) a pore volume after calcination for one hour at 1000 C. 0.8-1.1 m.sup.3/g.

The invention pertains to methods of producing aluminum trioxide in the form of powders or agglomerations with particles having a porous honeycomb structure, which can be used as catalyst substrates, adsorbents and filters for the chemical, food, and pharmaceutical industry. The method of production of aluminum oxide in the form of powders or agglomerations with particles having a porous honeycomb structure involves the treatment of the aluminum salt with a solution of an alkaline reagent, washing of the sediment and thermal treatment thereof. The technical result of the invention is the production of aluminum oxide in the form of separate particles with given structure and properties, specifically, with particle porosity of 60-80% and a porous structure represented by extensive parallel channels with near hexagonal packing, with dimension of the channels at the diameter of 0.3 to 1.0 micron and length up to 50 microns. For this, the aluminum salt used is crystals of aluminum chloride hexahydrate, which are treated with an excess aqueous solution of ammonia at temperature of 20-80 C. to form boehmite, and the heat treatment is done at 450-650 C. until aluminum oxide is formed.

The invention pertains to methods of producing aluminum trioxide in the form of powders or agglomerations with particles having a porous honeycomb structure, which can be used as catalyst substrates, adsorbents and filters for the chemical, food, and pharmaceutical industry. The method of production of aluminum oxide in the form of powders or agglomerations with particles having a porous honeycomb structure involves the treatment of the aluminum salt with a solution of an alkaline reagent, washing of the sediment and thermal treatment thereof. The technical result of the invention is the production of aluminum oxide in the form of separate particles with given structure and properties, specifically, with particle porosity of 60-80% and a porous structure represented by extensive parallel channels with near hexagonal packing, with dimension of the channels at the diameter of 0.3 to 1.0 micron and length up to 50 microns. For this, the aluminum salt used is crystals of aluminum chloride hexahydrate, which are treated with an excess aqueous solution of ammonia at temperature of 20-80 C. to form boehmite, and the heat treatment is done at 450-650 C. until aluminum oxide is formed.

A side stream subsystem can be used to remove impurity species from the recirculating alkali metal chloride solution in certain electrolysis systems. Silicon and/or aluminum species can be removed via precipitation after introducing an alkali metal hydroxide and magnesium chloride in a side stream line in the subsystem. The invention can allow for a substantial reduction in raw material and capital costs.

A side stream subsystem can be used to remove impurity species from the recirculating alkali metal chloride solution in certain electrolysis systems. Silicon and/or aluminum species can be removed via precipitation after introducing an alkali metal hydroxide and magnesium chloride in a side stream line in the subsystem. The invention can allow for a substantial reduction in raw material and capital costs.

A method of manufacturing high-density beads of high-purity alumina, in which general aluminum hydroxide is dissolved in a sodium hydroxide solution. Insoluble impurities are removed to thus manufacture a pure sodium aluminate solution. High-purity aluminum hydroxide is manufactured. The manufactured high-purity aluminum hydroxide is subjected to a hydrothermal reaction, thus removing both crystal water and sodium. Sulfuric acid and ammonia are not used, raw material powder uncontaminated with impurities is manufactured by performing atomization using pulverizing media, and the powder as a raw material and ultrapure water are used to manufacture seeds. While the atomized powder and the ultrapure water are put onto a rotating plate, steps are performed until a desired size is obtained, thus manufacturing highly densified beads. A sintering process is performed in order to maintain a molding shape and to increase a density, followed by a classification process.

A method of manufacturing high-density beads of high-purity alumina, in which general aluminum hydroxide is dissolved in a sodium hydroxide solution. Insoluble impurities are removed to thus manufacture a pure sodium aluminate solution. High-purity aluminum hydroxide is manufactured. The manufactured high-purity aluminum hydroxide is subjected to a hydrothermal reaction, thus removing both crystal water and sodium. Sulfuric acid and ammonia are not used, raw material powder uncontaminated with impurities is manufactured by performing atomization using pulverizing media, and the powder as a raw material and ultrapure water are used to manufacture seeds. While the atomized powder and the ultrapure water are put onto a rotating plate, steps are performed until a desired size is obtained, thus manufacturing highly densified beads. A sintering process is performed in order to maintain a molding shape and to increase a density, followed by a classification process.

A method of producing a high-purity nano alumina powder, in which general aluminum hydroxide is dissolved in a sodium hydroxide solution to give a sodium aluminate solution, most insoluble impurities other than sodium are removed using a micro filter to give a pure sodium aluminate solution. A seed is added thereto so as to precipitate nano aluminum hydroxide as a nano slurry under optimal precipitation conditions. The nano aluminum hydroxide slurry is filtered, dried, disintegrated, and then calcined at a low temperature of 900 C. or less, thus achieving the mass production of high-purity nano alumina having a particle size of 200 nm or less, whereby high-purity alumina nanoparticles can be produced in an environmentally friendly manner at low cost.

A method of producing a high-purity nano alumina powder, in which general aluminum hydroxide is dissolved in a sodium hydroxide solution to give a sodium aluminate solution, most insoluble impurities other than sodium are removed using a micro filter to give a pure sodium aluminate solution. A seed is added thereto so as to precipitate nano aluminum hydroxide as a nano slurry under optimal precipitation conditions. The nano aluminum hydroxide slurry is filtered, dried, disintegrated, and then calcined at a low temperature of 900 C. or less, thus achieving the mass production of high-purity nano alumina having a particle size of 200 nm or less, whereby high-purity alumina nanoparticles can be produced in an environmentally friendly manner at low cost.

A sintered compact has a first material, a second material, and a third material. The first material is cubic boron nitride. The second material is a compound including zirconium. The third material is an aluminum oxide and the aluminum oxide includes a fine-particle aluminum oxide. The sintered compact has a first region in which not less than 5 volume % and not more than 50 volume % of the fine-particle aluminum oxide is dispersed in the second material. On arbitrary straight lines in the first region, an average value of continuous distances occupied by the fine-particle aluminum oxide is not more than 0.08 m and a standard deviation of the continuous distances occupied by the fine-particle aluminum oxide is not more than 0.1 m.