Aluminum nitride sintered body and production thereof

A process for producing an aluminum nitride sintered body having a thermal conductivity of at least 100 W/mK and a relative density of at least 95%, comprising mixing a minor amount of a sintering additive selected from compounds of Group IIa, IIIa, and IIIb metals of the periodic table with an aluminum nitride starting powder prepared by direct nitriding of metallic aluminum and having a purity of at least 99%, an oxygen content of lower than 1.8% by weight and an Si content of not greater than 0.2% by weight to form a powder mixture, shaping the powder mixture, and baking the shaped mixture at a temperature in the range of 1500.degree.-2100.degree. C. in a non-oxidizing atmosphere for a time sufficient to sinter the mixture.

A method of making an aluminum nitride-based green sheet having improved green strength, which comprises mixing an aluminum nitride starting powder derived by direct nitriding of metallic aluminum and having a purity of at least 99%, an oxygen content of lower than 1.8% by weight and an Si content of not greater than 0.7% by weight with a sintering additive selected from compounds of Group IIa, IIIa, and IIIb metals of the periodic table, an organic polymeric binder, and optionally a plasticizer in an organic solvent to form a slurry, and shaping the slurry into a sheet followed by drying of the sheet, wherein the aluminum nitride starting powder has a particle size distribution in which from 22% to 45% by volume of the powder is made up of particles having a diameter equal to or larger than 3 .mu.m and from 55% to 78% by volume of the powder is made up of particles having a diameter smaller than 3 .mu.m.

An aluminum nitride sintered body produced by baking an aluminum nitride starting powder having an average particle size of not more than 5 .mu.m with a sintering additive selected from compounds of Group IIa, IIIa, and IIIb metals of the periodic table, said aluminum nitride starting powder being derived by direct nitriding of metallic aluminum and having an oxygen content of not greater than 1.8% by weight and an Si content of not greater than 0.2% by weight.

An aluminum nitride sintered body produced by baking an aluminum nitride starting power having an average particle size within a range of 1 to 3 .mu.m with a sintering additive selected from compounds of Group IIa, IIIa, and IIIb metals of the periodic table, said aluminum nitride starting powder being derived by direct nitriding of metallic aluminum and having an oxygen content of not greater than 1.8% by weight and an Si content of not greater than 0.2% by weight.