Abstract: A process for producing an aluminum nitride ceramic body having a composition defined and encompassed by polygon A4F5F6F4 but excluding line F6F4 of FIG. 4, a porosity of less than about 10% by volume, and a thermal conductivity greater than 0.90 W/cm.K at 25.degree. C. which comprises forming a mixture comprised of aluminum nitride powder containing oxygen, yttrium oxide, and free carbon, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges from point F5 up to point F4 of FIG. 4, said compact having an equivalent % composition of Y, Al, O and N outside the composition defined and encompassed by polygon A4F5F6F4 of FIG.

Abstract: A process for producing an aluminum nitride ceramic body having a composition defined and encompassed by polygon ABCFGH of FIG. 2, a porosity of less than about 10% by volume, and a thermal conductivity greater than 0.70 W/cm.K at 25.degree. C. which comprises forming a mixture comprised of aluminum nitride powder containing oxygen, gadolinium oxide, and free carbon, shaping said mixture into a compact, said mixture and compact having a composition wherein the equivalent % of gadolinium and aluminum ranges from point A to point F of FIG. 2, said mixture and said compact having an equivalent % composition of Gd, Al, O and N outside the composition defined and encompassed by polygon ABCFGH of FIG. 2, heating said compact to a temperature at which its pores remain open reacting said free carbon with oxygen contained in said aluminum nitride producing a deoxidized compact, said deoxidized compact having a composition wherein the equivalent % of Al, Gd, O and N is defined and encompassed by polygon ABCFGH of FIG.

Abstract: A process for producing an aluminum nitride ceramic body having a composition defined and encompassed by polygon ABCDEFGH excluding line DE of FIG. 2, a porosity of less than about 10% by volume, and a thermal conductivity greater than 0.70 W/cm.multidot.K at 25.degree. C. which comprises forming a mixture comprised of aluminum nitride powder containing oxygen, an Ln oxide selected from the group consisting essentially of erbium oxide, holmium oxide, a mixture and solid solution thereof, and free carbon, shaping said mixture into a compact, said mixture and compact having a composition wherein the equivalent % of Ln and aluminum ranges from point A up to point E of FIG. 2, said mixture and said compact having an equivalent % composition of Ln, Al, O and N outside the composition defined and encompassed by polygon ABCDEFGH of FIG.

Abstract: A process for producing an aluminum nitride ceramic body having a composition defined and encompassed by polygon P1JFA4 but not including lines JF and A4F of FIG. 4, a porosity of less than about 10% by volume, and a thermal conductivity greater than 1.00 W/cm.multidot.K at 25.degree. C. which comprises forming a mixture comprised of aluminum nitride powder containing oxygen, yttrium oxide, and free carbon, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges between points J and A4 of FIG. 4, said compact having an equivalent % composition of Y, Al, O and N outside the composition defined and encompassed by polgon P1JFA4 of FIG.

Abstract: A process for producing an aluminum nitride ceramic body having a composition defined and encompassed by polygon P1N1KJ but not including lines KJ and P1J of FIG. 4, and a thermal conductivity greater than 1.00 W/cm.multidot.K at 25.degree. C. which comprises forming a mixture comprised of aluminum nitride powder containing oxygen, yttrium oxide, and free carbon, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges between points K and P1 of FIG. 4, said compact having an equivalent % composition of Y, Al, O and N outside the composition defined and encompassed by polygon P1N1KJ of FIG.

Abstract: A process for producing an aluminum nitride ceramic body having a composition defined and encompassed by polygon LT1DM but not including lines LM and DM of FIG. 4, a porosity of less than about 10% by volume, and a thermal conductivity higher than 1.00 W/cm.multidot.K at 25.degree. C. which comprises forming a mixture comprised of aluminum nitride powder containing oxygen, yttrium oxide, and free carbon, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of Yttrium and aluminum ranges from point T1 up to point M of FIG. 4, said compact having an equivalent % composition of Y, Al, O and N outside the composition defined and encompassed by polygon LT1DM of FIG.

Abstract: A process for producing an aluminum nitride ceramic body having a composition defined and encompassed by polygon JKLM but not including line MJ of FIG. 4 and a thermal conductivity greater than 1.00 W/cm.multidot.K at 25.degree. C., preferably greater than 1.42 W/cm.multidot.K at 25.degree. C., which comprises forming a mixture comprised of aluminum nitride powder containing oxygen, yttrium oxide, and free carbon, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges from point L to less than joint J of FIG. 4, said compact having an equivalent % composition of Y, Al, O and N outside the composition defined and encompassed by polygon JKLM of FIG.

Abstract: A process for producing an aluminum nitride ceramic body having a composition defined and encompassed by polygon FJDSR but not including line RF of FIG. 4, a porosity of less than about 10% by volume, and a thermal conductivity greater than 1.00 W/cm.multidot.K at 25.degree. C. which comprises forming a mixture comprised of aluminum nitride powder containing oxygen, yttrium oxide, and free carbon, shaping said mixture into a compact, said mixture and said compact having a composition wherein the equivalent % of yttrium and aluminum ranges from point D up to point F of FIG. 4, said compact having an equivalent % composition of Y, Al, O and N outside the composition defined and encompassed by polygon FJDSR and FIG.

Abstract: A process for producing a polycrystalline aluminum nitride ceramic body having a composition defined and encompassed by line ABCDEFA but not including lines CD and EF of FIG. 1, a porosity of less than about 10% by volume of said body and a thermal conductivity greater than 1.0 W/cm.multidot.K at 22.degree. C. which comprises forming a mixture comprised of aluminum nitride powder and an yttrium additive selected from the group consisting of yttrium, yttrium hydride, yttrium nitride and mixtures thereof, said aluminum nitride and yttrium additive having a predetermined oxygen content, said mixture having a composition wherein the equivalent % of yttrium, aluminum, nitrogen and oxygen is defined and encompassed by line ABCDEFA but not including lines CD and EF in FIG. 1, shaping said mixture into a compact and sintering said compact at a temperature ranging from about 1850.degree. C. to about 2170.degree. C.

Abstract: The process comprises forming a mixture comprised of aluminum nitride powder and free carbon wherein the aluminum nitride has a predetermined oxygen content higher than about 0.8% by weight and wherein the amount of free carbon reacts with such oxygen content to produce a deoxidized powder or compact having an oxygen content ranging from greater than about 0.35% by weight to about 1.1% by weight and which is at least 20% by weight lower than the predetermined oxygen content, heating the mixture or a compact thereof to react the carbon and oxygen producing the deoxidized aluminum nitride, and sintering a compact of the deoxidized aluminum nitride producing a ceramic body having a density greater than 85% of theoretical and a thermal conductivity greater than 0.5 W/cm.multidot.K. at 22.degree. C.

Abstract: The process comprises forming a mixture comprised of aluminum nitride powder and free carbon wherein the aluminum nitride has a predetermined oxygen content higher than about 0.8% by weight and wherein the amount of free carbon reacts with such oxygen content to produce a deoxidized powder or compact having an oxygen content ranging from greater than about 0.35% by weight to about 1.1% by weight and which is at least 20% by weight lower than the predetermined oxygen content, heating the mixture or a compact thereof to react the carbon and oxygen producing the deoxidized aluminum nitride, and sintering a compact of the deoxidized aluminum nitride producing a ceramic body having a density greater than 85% of theoretical and a thermal conductivity greater than 0.5 W/cm.K at 22.degree. C.

Abstract: Low voltage varistors having one or more recesses or dimples which reduces the thickness of the varistor in the recessed areas are provided by an improved process which comprises fitting a pressing surface on a die punch with a resilient material, preferably an abhesive material such as polydimethylsiloxane, having one or more nipples whereby during pressing of a metal oxide varistor powder contained in the die cavity the nipple imparts a depression thereby reducing the thickness of the varistor body in said depression. In addition, the resilient material aids in the distribution of the powder during pressing and with the preferred abhesive material aids also in the release of the pressed body from the die.