Process for producing sintered .alpha.-Al.sub.2 O.sub.3 bodies and their use
AssigneeH.C. Starck GmbH
InventorsPaul Moltgen, Pirmin Wilhelm, Josef Schmoll
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Abstract
Microcrystalline bodies based on .alpha.-Al.sub.2 O.sub.3 are made by drying sub-micron powders, press compacting and shock sintering at an intermediate sinter temperature range of 1,300.degree. to 1,550.degree. C., i.e. bringing the compact up to such range in under 60 seconds, preferably under 10.
Claims22
A process for producing sintered, microcrystalline bodies based on .alpha.-Al.sub.2 O.sub.3, characterized in that the following steps are performed:
- (a) deagglomerating or comminuting an .alpha.-Al.sub.2 O.sub.3 powder having an average particle size equal to or less than 3 .mu.m as the starting material and adding liquid to form a slip, with said powders comprising the solids content of the slip, with the powders having a particle size under 1 .mu.m,
- (b) drying the slip to a residual moisture content of equal to or less than 6% by weight to leave a dried powder,
- (c) press-compacting the dried powder to form a green body having a density equal to or greater than 60% of the theoretical density, and
- (d) then subjecting the green body to shock sintering at temperatures in the range from 1,300.degree. to 1,550.degree. C., the green body being brought to the sintering temperature from a low temperature of essentially no grain growth to said sinter temperature range in a time equal to or less than 60 seconds, then soaking at such range for under an hour and cooling.
A process for producing sintered abrasive grain and cutting tool materials made .alpha.-Al.sub.2 O.sub.3 material with a sintering temperature intermediate the low sintering temperatures of sol-gel derived crystallites and conventional melt-derived or reduction derived crystallites comprising the steps of
- (a) producing a dispersion in liquid of .alpha.-Al.sub.2 O.sub.3 powders or a precursor thereof of average particle size of the powders 90% of under one micron,
- (b) drying to a residual moisture equal to or less than six percent by weight,
- (c) compacting the powder to 60% or higher of theoretical density
- (d) raising the temperature of the compact from under 500.degree. C. to the range of 1,300.degree. to 1,550.degree. C. in under 60 seconds and then
- (e) soaking at temperature within said range for under one hour and then cooling,
- the process conditions being controlled to achieve a Vickers hardness (HV 0.2) of at least 16 GPa and average primary crystallite size of under 1 .mu.m in the material.
Dependencies are inferred from the claim text.