A high-purity microparticle alumina powder which has excellent slurry properties and sintering properties, excellent fluidity and formability, and excellent dielectric properties in the high-frequency region. In this high-purity microparticle alumina powder, the 50% particle diameter (D.sub.50) in the volume particle size distribution and the BET specific surface area (S.sub.BET) satisfy the relations represented by the formula D.sub.500.20 m and the formula D.sub.50S.sub.BET2.010.sup.6 m.sup.3/g, and the content of sodium (Na), silicon (Si), iron (Fe) and calcium (Ca) is each less than or equal to 10 ppm.

A high-purity microparticle alumina powder which has excellent slurry properties and sintering properties, excellent fluidity and formability, and excellent dielectric properties in the high-frequency region. In this high-purity microparticle alumina powder, the 50% particle diameter (D.sub.50) in the volume particle size distribution and the BET specific surface area (S.sub.BET) satisfy the relations represented by the formula D.sub.500.20 m and the formula D.sub.50S.sub.BET2.010.sup.6 m.sup.3/g, and the content of sodium (Na), silicon (Si), iron (Fe) and calcium (Ca) is each less than or equal to 10 ppm.

A method comprising contacting high-purity acid, high-purity aluminum, and high-purity water to form a first solution in a heated non-contaminating vessel, wherein the aluminum is employed in at least a stoichiometric amount relative to the acid, heating the first solution in a non-contaminating container, to provide a mother liquor and solid aluminum salts, separating the solid aluminum salts from the mother liquor, heating the solid aluminum salts in a non-contaminating crucible, to provide alpha aluminum oxide, and, optionally, washing the alpha aluminum oxide with high-purity water after some or all of the heating of the solid aluminum salts to provide the alpha aluminum oxide.

A system, process and related sintered article are provided. The process includes supporting a piece of inorganic material with a pressurized gas and sintering the piece of inorganic material while supported by the pressurized gas by heating the piece of inorganic material to a temperature at or above a sintering temperature of the inorganic material such that the inorganic material is at least partially sintered forming the sintered article. The inorganic material is not in contact with a solid support during sintering. The sintered article, such as a ceramic article, is thin, has high surface quality, and/or has large surface areas.

A plate-like alumina powder production method of the present invention comprises placing a transition alumina and a fluoride in a container such that the transition alumina and the fluoride do not come into contact with each other and then performing heat treatment to obtain a plate-like -alumina powder. The transition alumina is preferably at least one selected from the group consisting of gibbsite, boehmite, and -alumina. It is preferable that the amount of the fluoride used is set such that the percentage ration of F in the fluoride to the transition alumina is 0.017% by mass or more. The container preferably has a volume such that a value obtained by dividing the mass of F in the fluoride by the volume of the container is 6.510.sup.5 g/cm.sup.3 or more. The heat treatment is preferably performed at the temperature of 750 to 1,650 C.

An alumina sintered body according to the present invention has a degree of c-plane orientation of 90% or more as determined by Lotgering's method from an X-ray diffraction profile obtained by irradiating a plate surface with X-rays in a range of 2=20 to 70. The alumina sintered body has no pores when a cross-sectional surface formed in a direction perpendicular to the plate surface is polished using an Ar.sup.+ ion beam and a mask and is examined under a scanning electron microscope at a magnification of 5,000 times. The alumina sintered body has a total mass fraction of impurity elements other than Mg and C of 100 ppm or less. This alumina sintered body has a high degree of orientation, high density, and high purity and thus has a higher optical translucency than those known in the art.

96 parts by mass of a -alumina powder, 4 parts by mass of a an AlF.sub.3 powder, and 0.17 parts by mass of an -alumina powder as a seed crystal were mixed by a pot mill. The purities of each raw material were evaluated, and it was found that the mass ratio of each impurity element other than Al, O, F, H, C, and S was 10 ppm or less. In a high-purity alumina-made sagger having a purity of 99.9 percent by mass, 300 g of the obtained mixed powder was received, and after a high-purity alumina-made lid having a purity of 99.9 percent by mass was placed on the sagger, a heat treatment was perforated at 900 C. for 3 hours in an electric furnace in an air flow atmosphere, so that an alumina powder was obtained. The value of AlF.sub.3 mass/container volume was 0.016 g/cm.sup.3.

Mesoporous and macroporous hydroconversion catalyst: a predominantly calcined alumina oxide matrix; a hydrogenating-dehydrogenating active phase with at least one VIB metal, optionally at least one VIII metal, optionally phosphorus,
said active phase being at least partly co-mixed in said predominantly calcined alumina oxide matrix.

Preparation process for a residue hydroconversion/hydrotreating catalyst by co-mixing of the active phase with a particular alumina.

Use of the catalyst in hydrotreating processes, in particular hydrotreating of heavy feedstocks.

The invention concerns a process for the preparation of an amorphous mesoporous and macroporous alumina, comprising at least one step for dissolving an acidic precursor of aluminium, a step for adjusting the pH by adding at least one basic precursor to the suspension obtained in step a), a step for co-precipitation of the suspension obtained at the end of step b) by adding at least one basic precursor and at least one acidic precursor to the suspension, a filtration step, a drying step, a shaping step and a heat treatment step.

The invention also concerns an amorphous mesoporous and macroporous alumina with a bimodal pore structure having: a specific surface area S.sub.BET of more than 100 m.sup.2/g; a median mesopore diameter, by volume determined by mercury intrusion porosimetry, of 18 nm or more; a median macropore diameter, by volume determined by mercury intrusion porosimetry, in the range 100 to 1200 nm, limits included; a mesopore volume, as measured by mercury intrusion porosimetry, of 0.7 mL/g or more; and a total pore volume, as measured by mercury porosimetry, of 0.8 mL/g or more.

This application discloses methods and processes for preparation of high purity aluminum hydroxide and high purity aluminum oxide. The method of preparing high purity aluminum hydroxide involves reacting aluminum with water in the presence of one or more catalysts and one or more complexing agents that can react with non-aluminum metal impurities to form soluble complexes for effective removal through rinsing.