摘要:
An alumina composition, an alumina molded article, prepared from the alumina composition, an alumina ceramic prepared by sintering the alumina molded article, and a process for producing the ceramic; the alumina composition comprising α-alumina particles having a ratio of the shortest diameter to the longest diameter of from 0.3 to 1; and a size distribution of not more than 5, as expressed in terms of a D₉₀/D₁₀ ratio, wherein D₁₀ and D₉₀ represent a cumulative 10% diameter and a cumulative 90% diameter, respectively, of a cumulative distribution depicted from the small diameter side, or comprising α-alumina particles having a polyhedral shape; a D/H ratio of from 0.5 to 3.0, wherein D represents a maximum particle diameter parallel to a hexagonal lattice plane of a hexagonal close-packed lattice of α-alumina, and H represents a particle diameter perpendicular to the lattice plane; and a size distribution of not more than 5, as expressed in terms of a D₉₀/D₁₀ ratio, wherein D₁₀ and D₉₀ are as defined above.
摘要:
A process for producing α-alumina power constituted by α-alumina single crystal particles comprises calcining at least one of transition alumina and a transition alumina precursor, in a gas atmosphere containing (1) at least 5% of F, Cl, Br and/or I, (2) at least 1% HF, HBr and/or HI, or (3) a component prepared from at least 1%, based on the total gas atmosphere, of F gas, Br gas and/or I gas, and at least 0.1% of steam. The percentages are by volume and based on the total gas atmosphere. The α-alumina single crystal particles have high purity, homogeneity, a narrow primary particle size distribution and an octahedral or higher polyhedral shape. The powder can be obtained from alumina raw materials of a variety of different kinds in an industrially advantageous manner, and is suitable as a raw material for abrasives, sintered products, plasma spraying materials, fillers, single crystals, supports for catalysts, fluorescent substances, encapsulants, ceramic filters and spacers for liquid cells.
摘要:
A complex metal oxide powder composed of fine particles, each in an approximately spherical shape, is provided by a method for producing a complex metal oxide powder, which method comprises heating at least two kinds of metal salts, or a complex metal salt comprising at least two kinds of metals, to a temperature at which transition to a complex metal oxide occurs, and calcining the metal salts or the complex metal salt in an atmosphere containing a halogenated hydrogen gas.
摘要:
A translucent alumina sintered body wherein the total content of an alkali metal element and an alkaline earth metal element is 50 ppm or less, and the linear transmittance of a light having a wavelength of 600 nm is 40% or more at a thickness of the sintered body of 0.85 mm.
摘要:
A process for producing α-alumina powder comprises calcining transition alumina and/or a transition alumina precursor which transforms to transition alumina on heating, in a gas atmosphere containing (1) a hydrogen halide, (2) a component prepared from a halogen and steam or (3) a halogen, and in the presence of seed crystals and/or a shape-controlling agent. The product α-alumina powder comprises particles of a substantially octahedral or eicosa-hedral shape, a pre-determined structure, and a narrow primary particle size distribution; the powder is particularly useful as a raw material for preparing abrasives, fillers, sinters or spacers.