Boehmite produced by a seeded hydyothermal process and ceramic bodies produced therefrom
AssigneeNorton Company
InventorRalph Bauer
Life of this patent
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Abstract
Microcrystalline boehmite suitable for conversion to anhydrous alumina products is produced by hydrothermal treatment of precursor alumina raw material at controlled pH and in the presence of microcrystalline boehmite seed material. Reaction mix may include submicron seed material for seedling for later conversion of the microcrystalline boehmite to alpha alumina. Removal of metal cations by ion exchange is employed when high purity product is required. Other materials may be added to reaction mix. Production of alumina products, catalysts, and ceramic bodies is disclosed.
Claims27
A method of making a microcrystalline boehmite product comprising heating under autogenous pressure a boehmite alumina precursor in an aqueous medium having a pH selected from a value of 5 or less and 8 or higher and in the presence of boehmite seed particles finer than 0.02 microns, said seed particles being present in an amount greater than 7.5% by weight of the precursor alumina, calculated as Al.sub.2 O.sub.3, said heating being carried out above 130.degree. C. for a time sufficient to substantially convert said precursor to microcrystalline boehmite.
A method of producing alpha alumina bodies comprising the steps of:
- reacting hydrated alumina boehmite precursor in an autoclave in the presence of acidified water, boehmite seed material having a crystal size less than 0.02 microns, and submicron seed material of a type and in an amount effective to promote the formation of alpha alumina upon firing, while maintaining the temperature and pressure at conditions under which boehmite is a stable phase for a time sufficient to convert the major portion of said precursor to microcrystalline boehmite;
- firing said microcrystalline boehmite at temperatures sufficient to convert said boehmite to alpha alumina.
The method of producing gamma alumina bodies comprising the steps of:
- reacting a hydrated alumina boehmite precursor in an autoclave in the presence of acidified water and boehmite seed material having a crystal size less than 0.02 microns while maintaining the temperature and pressure at conditions under which boehmite is a stable phase for a time sufficient to convert the major portion of said precursor to microcrystalline boehmite,
- firing said microcrystalline boehmite for a time and at a temperature effective to convert said boehmite to gamma alumina.
A method of producing microcrystalline boehmite comprising reacting in an autoclave a hydrated alumina boehmite precursor in the presence of water and boehmite seed material having a crystal size less than 0.02 microns, the temperature, pressure, and pH being maintained at conditions under which boehmite is a stable phase for a time sufficient to convert the major portion of said precursor to microcrystalline boehmite.
A method of producing high purity microcrystalline boehmite comprising the steps of
- (1) providing an aqueous medium containing an aluminum oxide precursor of boehmite and at least 5% by weight, based on alumina precursor solids calculated as trihydrate, of boehmite seed material having a particle size finer than 0.02 microns,
- (2) heating in an autoclave said medium under at least autogenous pressure to convert said precursor to boehmite, and
- (3) removing metal cations from said aqueous medium by contact of said medium with an ion exchange medium.
Dependencies are inferred from the claim text.