Doped silicon nitride article

Claim 2

A process for making a densified silicon nitride article comprising: Step 1--dispersing silicon nitride particles in a dispersion reagent to form a silicon nitride slurry; Step 2--adding a solution of sintering additives to said silicon nitride slurry to form a homogeneous slurry having a pH less than 7; Step 3--drying the product from step 2 to form a dried powder having an essentially uniform coating of said sintering additives on said silicon nitride particles; Step 4--converting said sintering additives of the product from step 3 to their corresponding oxides; Step 5--forming a silicon nitride article from the product of step 4; and Step 6--pressureless sintering the product from step 5 at a temperature less than 1700° C. to form a densified silicon nitride article having a density greater than 98 percent of theoretical density.

Claim 3

A process in accordance with claim 1 wherein said dispersion agent comprises a solution having a high dielectric constant.

Claim 4

A process in accordance with claim 1 wherein said dispersing comprises wet-ball milling.

Claim 5

A process in accordance with claim 1 wherein said forming comprises pressing at 20,000 to 50,000 psig.

Claim 6

A process for making a densified silicton nitride article comprising Step 1--dispersing silicon nitride particles in a dispersion reagent to form a silicon nitride slurry; Step 2--adding a solution of sintering additives to said silicon nitride slurry to form a homogeneous slurry having a pH less than 7; Step 3--drying the product from step 2 to form a dried powder having an essentially uniform coating of said sintering additives on said silicon nitride particles; Step 4--Converting said sintering additives of the product from step 3 to their corresponding oxides; Step 5--forming a silicon nitride articles from the product of step 4; and Step 6--pressureless sintering the product from Step 5 at a temperature equal to or less than 1735° C. in nitrogen to form a densified silicon nitride article having a density greater than 99 percent of theoetical density.

Claim 7

A process for making a densified silicton nitride article comprising Step 1--dispersing silicon nitride particles in a dispersion reagent to form a silicon nitride slurry; Step 2--adding a solution of sintering additives to said silicon nitride slurry to form a homogeneous slurry having a pH less than 7; Step 3--drying the product from step 2 to form a dried powder having an essentially uniform coating of said sintering additives on said silicon nitride particles; Step 4--Converting said sintering additives of the product from step 3 to their corresponding oxides; Step 5--forming a silicon nitride articles from the product of step 4; and Step 6--pressureless sintering the product from Step 5 at a temperature equal to or less than 1735° C. in nitrogen to form a densified silicon nitride article having a density greater than 99 percent of theoetical density.

Claim 8

A process in accordance with claim 1 wherein said sintering additives are selected from the group consisting of soluble salts of yttrium, aluminum, magnesium, lanthanum, cerium, hafnium, zirconium, rare earths, and combinations thereof.

Claim 9

A process in accordance with claim 6 wherein said soluble salts comprise nitrates.

Claim 10

A process in accordance with claim 1 wherein said forming comprises isostatic pressing.

Claim 11

A process in accordance with claim 1 wherein said forming comprises slip casting.

Claim 12

A process in accordance with claim 5 wherein said temperature comprises a temperature equal to or less than 1860° C.

Claim 13

A process in accordance with claim 1 wherein said dispersion agent comprises a one normal ammonium hydroxide solution containing ammonium citrate and ammonium acetate.