Abrasive material and method
AssigneeNorton Company
InventorsThomas E. Cottringer, Ronald H. van de Merwe, Ralph Bauer, Walter A. Yarbrough
Life of this patent
Estimating the term…
Abstract
The hardness and microstructure of aluminous abrasives produced from alumina gels are enhanced by introduction of seed material as by wet vibratory milling of the material with alumina media, or by the direct addition of very fine alpha alumina particles in the amount of 1% or less.
Claims41
An alumina gel containing dispersed alpha alumina seed particles in an amount and size such that drying said gel and firing it at a selected temperature between 1200.degree. and 1500.degree. and for a selected time of 15 minutes or less which are sufficient to convert the alumina of the gel to alpha alumina having a hardness of at least 16 GPa, will transform said alumina to alpha alumina having a crystal size less than about 1 micron.
A method of making polycrystalline ceramic bodies containing alpha alumina, comprising the steps of:
- providing a gelled dispersion of sub-micron hydrated alumina particles, said dispersion including an effective amount of sub-micron alpha alumina seed particles for facilitating the conversion of said hydrated alumina to alpha alumina upon sintering;
- drying said gelled dispersion;
- and
- firing the dried gel to a temperature of between 1090.degree. C. and 1500.degree. C. for a time sufficient to convert said hydrated alumina particles to a strong body having a matrix of alpha alumina crystals said matrix having a density of at least 90% of theoretical.
A method of making polycrystalline ceramic bodies containing alpha alumina having an alpha alumina particle size of about 0.4 micron or below, comprising the steps of:
- providing a gelled dispersion of sub-micron hydrated alumina particles, said dispersion including an effective amount of sub-micron alpha alumina seed particles for facilitating the conversion of said hydrated alumina to alpha alumina upon sintering;
- drying said gelled dispersion;
- and
- firing the dried gel to a temperature between 1090.degree. C. and 1500.degree. C. for a time selected to convert said dried gel to a ceramic body, the major portion of which is made up of alpha alumina crystals of about 0.4 micron or below in size.
A method of making ceramic bodies containing alpha alumina, comprising the steps of:
- drying a gelled dispersion of sub-micron hydrated alumina particles, said dispersion including dispersed alpha alumina seed particles in an amount and size such that firing said dispersion at a selected temperature between 1200.degree. and 1500.degree. C. and for a selected time of 15 minutes or less sufficient to convert the hydrated alumina particles to alpha alumina having a hardness of at least 16 GPa, will transform said particles to alpha alumina having a crystal size no larger than 0.4 microns, and
- firing the dried gel to a temperature below 1500.degree. C. for a time sufficient to convert said hydrated alumina particles to alpha alumina, said bodies having a density of at least 90% of theoretical.
A polycrystalline ceramic body consisting essentially of alpha alumina crystals or a mixture of alpha alumina crystals and spinel crystals, at least 20% of said body, when examined with a scanning electron microscope at a magnification of 5000 times, appearing as generally equiaxed crystals having a size of about 0.4 microns or less, and any portion of said alpha alumina crystals that are individually larger than one micron consisting essentially of lath shaped crystals, said body having a hardness of at least 16 GPa and including at least 87% alumina by weight including that contained in any spinel.
A polycrystalline ceramic body having a hardness of at least 16 GPa, including at least 87 weight per cent stoichiometric equivalent of alumina, and consisting essentially of alpha alumina crystals or of a mixture of alpha alumina crystals and crystals of an alumina containing spinel, characterized in that when examined with a scanning electron microscope at a magnification of 5000 times, at least a substantial portion of said body appears as generally equiaxed crystals with a size of not more than about 0.4 microns and in that any portion of said alpha alumina crystals that are individually larger than about 1 micron consists essentially of lath shaped crystals.
A polycrystalline ceramic body consisting essentially of:
- (a) a matrix consisting essentially of alpha alumina crystals or a mixture of alumina spinel crystals and at least 30% by weight alpha alumina crystals, said crystals having a size of about 0.4 microns or less, said crystals being by weight predominantly alumina, and
- (b) ceramic particles dispersed throughout said matrix.
A polycrystalline ceramic body consisting essentially of alpha alumina crystals having a size no greater than about 0.4 microns and a hardness of at least 16 GPa, said body being substantially free from crystalline cells.
A method of making a polycrystalline ceramic body comprising:
- (a) providing a hydrated alumina sol including dispersed submicron alpha alumina particles formed by milling a water containing fluid phase with milling media that contain alpha alumina;
- (b) gelling and drying said hydrated alumina sol;
- and
- (c) firing said dried gel to convert at least part of the alumina in said dried gel to alpha alumina.
In the sol-gel process for forming alumina-based ceramic abrasive grain, the process comprising:
- a. preparing a dispersion of alpha alumina monohydrate particles;
- b. gelling the dispersion;
- c. drying the gel dispersion to form a solid;
- d. calcining the solid;
- and
- e. sintering the calcined solid, the improvement comprising providing in said solid submicron sized alpha alumina particles or equivalent nucleation centers as seed material for facilitating the conversion of at least a portion said alpha alumina monohydrate particles to polycrystalline alpha alumina.
Alumina-based sol-gel ceramic wherein the alumina present as such therein consists essentially of submicron sized alpha alumina crystals, said body having a density of at least 95% of theoretical.
A sol-gel ceramic body comprising polycrystalline alpha alumina, the alumina present as such in said body consisting essentially of submicron alpha alumina crystals, said body having a hardness of at least 18 GPa.
A process for forming analumina-based ceramic, comprising:
- (a) preparing a gelled dispersion of hydrated alumina particles;
- (b) drying the gelled dispersion to form a solid;
- (c) calcining and firing the solid;
- and
- (d) providing in said solid submicron sized alpha alumina particles or equivalent nucleation centers as seed material for facilitating the transformation of at least a portion of such hydrated alumina particles to polycrystalline alpha alumina.
A ceramic body comprising a seeded sol-gel polycrystalline alpha alumina matrix having abrasive particles dispersed therein.
Dependencies are inferred from the claim text.