Microcrystalline abrasive material and method of manufacture

Claim 1

A method of manufacturing a sintered, microcrystalline α-Al 2 O 3 abrasive material having a purity of at least 98.5% and a density of at least 95% of theoretical density, the α-Al 2 O 3 crystallites of the material being smaller than 4μ, which comprises the steps of (a) preparing a mixture of finely milled, calcined alumina and 1 to 60%, by weight, of a highly dispersable α-aluminum oxide monohydrate, (b) reacting said mixture with water and an acid, (c) homogenizing the reacted mixture until a formable mass has been obtained, (d) forming the mass into shaped bodies, and (e) sintering the shaped bodies for 5 minutes to 2 hours at a temperature between 1300° C. and 1700° C.

Claim 2

A method of manufacturing a sintered, microcrystalline α-Al 2 O 3 abrasive material having a purity of at least 98.5% and a density of at least 95% of theoretical density, the α-Al 2 O 3 crystallites of the material being smaller than 4μ, which comprises the steps of (a) preparing a mixture of finely milled, calcined alumina and 1 to 60%, by weight, of a highly dispersable α-aluminum oxide monohydrate, (b) reacting said mixture with water and an acid, (c) homogenizing the reacted mixture until a formable mass has been obtained, (d) forming the mass into shaped bodies, and (e) sintering the shaped bodies for 5 minutes to 2 hours at a temperature between 1300° C. and 1700° C.

Claim 15

A method of manufacturing a sintered, microcrystalline α-Al 2 O 3 abrasive material having a purity of least 98.5% and a density of at least 95% of theoretical density, the α-Al 2 O 3 crystallites of the material being smaller than 4μ, which comprises the steps of (a) suspending a mixture of finely milled, calcined alumina and 1 to 60%, by weight, of a highly dispersable α-aluminum oxide monohydrate in water. (b) adding an acid to the suspension until the same has a pH-value between 2 and 3. (c) milling the acidified suspension until the grain size is less than 2 μm. (d) removing sufficient water from the milled suspension to obtain a formable mass, (d) forming the mass into shaped bodies, and (e) sintering the shaped bodies for 5 minutes to 2 hours at a temperature between 1300° C. and 1700° C.

Claim 16

A method of manufacturing a sintered, microcrystalline α-Al 2 O 3 abrasive material having a purity of least 98.5% and a density of at least 95% of theoretical density, the α-Al 2 O 3 crystallites of the material being smaller than 4μ, which comprises the steps of (a) suspending a mixture of finely milled, calcined alumina and 1 to 60%, by weight, of a highly dispersable α-aluminum oxide monohydrate in water. (b) adding an acid to the suspension until the same has a pH-value between 2 and 3. (c) milling the acidified suspension until the grain size is less than 2 μm. (d) removing sufficient water from the milled suspension to obtain a formable mass, (d) forming the mass into shaped bodies, and (e) sintering the shaped bodies for 5 minutes to 2 hours at a temperature between 1300° C. and 1700° C.

Claim 18

A method of manufacturing a sintered, microcrystalline α-Al 2 O 3 abrasive material having a purity of at least 98.5% and a density of at least 95% of theoretical density, the α-Al 2 O 3 crystallites of the material being smaller than 4μ, which comprises the steps of (a) suspending calcined alumina in water, (b) milling the calcined alumina until the grain size is less than 2μ. (c) adding an amount of highly dispersable α- aluminum oxide monohydrate sufficient to produce a mixture of the calcined alumina and the α-aluminum oxide monohydrate wherein the monohydrate constitutes between 1 and 60%, by weight, (d) adding an acid to the mixture until the same has a pH-value between 2 and 3, (e) milling the acidified mixture for no more than three hours, (f) removing sufficient liquid from the milled mixture to obtain a formable mass, (d) forming the mass into shaped bodies, and (e) sintering for 5 minutes to 2 hours at a temperature between 1300° C. and 1700° C.

Claim 19

A method of manufacturing a sintered, microcrystalline α-Al 2 O 3 abrasive material having a purity of at least 98.5% and a density of at least 95% of theoretical density, the α-Al 2 O 3 crystallites of the material being smaller than 4μ, which comprises the steps of (a) suspending calcined alumina in water, (b) milling the calcined alumina until the grain size is less than 2μ. (c) adding an amount of highly dispersable α- aluminum oxide monohydrate sufficient to produce a mixture of the calcined alumina and the α-aluminum oxide monohydrate wherein the monohydrate constitutes between 1 and 60%, by weight, (d) adding an acid to the mixture until the same has a pH-value between 2 and 3, (e) milling the acidified mixture for no more than three hours, (f) removing sufficient liquid from the milled mixture to obtain a formable mass, (d) forming the mass into shaped bodies, and (e) sintering for 5 minutes to 2 hours at a temperature between 1300° C. and 1700° C.