Process for the production of sintered aluminum nitrides

Claim 1

A process for producing sintered aluminum nitride bodies, comprising: (a) mixing an aluminum nitride powder with a sintering aid, the powder having a surface area of at least 2.5 m 2 /g, comprising at least 95% by weight aluminum nitride, and incorporating impurities in no more than the following amounts: (i) a bound oxygen content of no more than 3% by weight; (ii) metal or metal compounds in an amount of no more than 0.6% by weight, calculated as the metals, and including iron or iron compounds in an amount of no more than 0.1% by weight, calculated as iron, and/or other metals in an amount of no more than 0.1% by weight per individual metal, calculated as the metal; and (iii) silicon or carbon or compounds thereof in an amount of no more than 0.5% by weight, calculated as carbon or silicon; (b) compacting the mixture to form an aluminum nitride body; and (c) subjecting the body to the following sintering cycle: (i) increasing the temperature from room temperature to the sintering temperature at a rate of no more than 250° C. per hour; (ii) introducing an inert gas containing from 1 to 4% by volume hydrogen until the temperature reaches 1200° C.; (iii) continuing to introduce solely an inert gas as the temperature is further increased to the sintering temperature; (iv) sintering the body at a sintering temperature between 1600° and 1900° C.; and (v) cooling the sintered body at a rate of not more than 300° C. per hour.