Process for sintering silicon nitride compacts

Claim 2

A process for increasing the density of a reaction bonded silicon nitride article, which comprises the step of sintering the reaction bonded silicon nitride article of a density of at least 2.2 g/cm 3 in an atmosphere consisting essentially of nitrogen at substantially atmospheric pressure at a temperature of 1600° to 2000° C., while the article is embedded in a protective powder comprising silicon nitride, boron nitride, or a mixture of silicon nitride and boron nitride, and one or more sintering additives for silicon nitride, said sintering additives being present in the protective powder in an amount of from 3 to 20% by weight, wherein said sintering additives are selected from the group consisting of MgO, Y 2 O 3 , Mg 3 N 2 , CeO 2 and mixtures thereof with Fe.

Claim 3

The process of claim 1, wherein the reaction bonded silicon nitride article to be sintered also comprises one or more sintering additives uniformly dispersed therein in an amount not exceeding 20% by weight, said reaction bonded silicon nitride article to be sintered being formed by forming silicon powder into a compact containing said sintering additives and then nitriding the same to yield said reaction bonded silicon nitride article.

Claim 4

The process of claim 1, wherein the protective powder comprises MgO.

Claim 5

The process of claim 1, wherein the protective powder comprises from 5 to 15% by weight of sintering additives.

Claim 6

The process of claim 1, wherein said compact contains from 1 to 12% by weight of sintering additives.

Claim 7

The process of claim 5, wherein the compact contains MgO and Y 2 O 3 sintering additives.

Claim 8

The process of claim 1, wherein the sintering is carried out at temperature from 1600° to 1900° C.

Claim 9

The process of claim 1, wherein the protective powder is degassed before the sintering treatment.

Claim 10

The process of claim 2, wherein said silicon powder has a density of at least 1.3 g/cm 3 .

Claim 11

The process of claim 2, wherein said silicon powder compact is nitrided at 1350° to 1450° C.

Claim 12

The process of claim 10, wherein said nitriding of said silicon powder compact increases the density thereof without substantial dimensional change, thereby providing said reaction bonded silicon nitride compact of a density of at least 2.2 g/cm 3 .

Claim 13

The process of claim 11, wherein the final density of the sintered silicon nitride article is close to the theoretical density of 3.18 g/cm 3 .

Claim 14

The process of claim 12, wherein said silicon powder has a particle size of from 0.1 to 44μ.

Claim 15

The process of claim 13, wherein said reaction bonded silicon nitride article has a density on the order of 1.5-2.6 g/cm 3 .

Claim 16

The process of claim 1, wherein said protective powder consists essentially of said silicon nitride, boron nitride, or a mixture of silicon nitride and boron nitride, and said one or more sintering additives.

Claim 17

The process for increasing the density of a reaction bonded silicon nitride article, which comprises the step of sintering the reaction bonded silicon nitride article of a density of at least 2.2 g/cm 3 in an atmosphere consisting essentially of nitrogen at substantially atmospheric pressure at a temperature of 1600° to 2000° C., while the compact is embedded in a protective powder consisting silicon nitride, boron nitride or a mixture of silicon nitride and boron nitride, and one or more sintering additives for silicon nitride, said sintering additives being present in the protective powder in an amount of from 3 to 20% by weight, wherein said reaction bonded silicon nitride compact to be sintered also comprises one or more sintering additives selected from the group consisting of MgO, Y 2 O 3 , Mg 3 N 2 , CeO 2 and mixtures thereof with Fe uniformly dispersed therein in an amount not exceeding 20% by weight, said reaction bonded silicon nitride compact to be sintered being formed by forming a silicon powder into a compact containing said sintering aids and then nitriding the same to yield said reaction bonded silicon nitride article.

Claim 18

The process for increasing the density of a reaction bonded silicon nitride article, which comprises the step of sintering the reaction bonded silicon nitride article of a density of at least 2.2 g/cm 3 in an atmosphere consisting essentially of nitrogen at substantially atmospheric pressure at a temperature of 1600° to 2000° C., while the compact is embedded in a protective powder consisting silicon nitride, boron nitride or a mixture of silicon nitride and boron nitride, and one or more sintering additives for silicon nitride, said sintering additives being present in the protective powder in an amount of from 3 to 20% by weight, wherein said reaction bonded silicon nitride compact to be sintered also comprises one or more sintering additives selected from the group consisting of MgO, Y 2 O 3 , Mg 3 N 2 , CeO 2 and mixtures thereof with Fe uniformly dispersed therein in an amount not exceeding 20% by weight, said reaction bonded silicon nitride compact to be sintered being formed by forming a silicon powder into a compact containing said sintering aids and then nitriding the same to yield said reaction bonded silicon nitride article.

Claim 19

The process of claim 1, wherein the reaction bonded silicon nitride article product is structurally and chemically homogeneous.

Claim 20

The process of claim 1, wherein the article is embedded in the protective powder by the steps which consist of placing the article on a layer of the protective powder and then embedding the article in the protective powder.

Claim 21

The process of claim 1, wherein the protective powder consists of silicon nitride and the one or more sintering additives.

Claim 22

The process of claim 1, wherein the protective powder consists of boron nitride and one or more sintering additives.

Claim 23

The process of claim 1, wherein the protective powder consists of silicon nitride, boron nitride and the one or more sintering additives.

Claim 24

A process for increasing the density of a reaction bonded silicon nitride article which comprises the steps of: forming silicon powder into a compact and nitriding the same to yield the reaction bonded silicon nitride article; sintering the reaction bonded silicon nitride article of a density of at least 2.2 g/cm 3 in an atmosphere consisting essentially of nitrogen at substantially atmospheric pressure at a temperature of 1600° to 2000° C., while the article is embedded in a protective powder comprising silicon nitride, boron nitride, or a mixture of silicon nitride and boron nitride, and one or more sintering additives for silicon nitride, said sintering additives being present in the protective powder in an amount of from 3 to 20% by weight, wherein said sintering additives are selected from the group consisting of MgO, Y 2 O 3 , Mg 3 N 2 , CeO 2 and mixtures thereof with Fe.

Claim 25

A process for increasing the density of a reaction bonded silicon nitride article which comprises the steps of: forming silicon powder into a compact and nitriding the same to yield the reaction bonded silicon nitride article; sintering the reaction bonded silicon nitride article of a density of at least 2.2 g/cm 3 in an atmosphere consisting essentially of nitrogen at substantially atmospheric pressure at a temperature of 1600° to 2000° C., while the article is embedded in a protective powder comprising silicon nitride, boron nitride, or a mixture of silicon nitride and boron nitride, and one or more sintering additives for silicon nitride, said sintering additives being present in the protective powder in an amount of from 3 to 20% by weight, wherein said sintering additives are selected from the group consisting of MgO, Y 2 O 3 , Mg 3 N 2 , CeO 2 and mixtures thereof with Fe.

Claim 26

The process of claim 16, wherein the reaction bonded silicon nitride article product is structurally and chemically homogeneous.

Claim 27

The process of claim 16, wherein the article is embedded in the protective powder by the steps which consist of placing the article on a layer of the protective powder and then embedding the article in the protective powder.

Claim 28

The process of claim 16, wherein the protective powder consists of silicon nitride and the one or more sintering additives.

Claim 29

The process of claim 16, wherein the protective powder consists of boron nitride and the one or more sintering additives.

Claim 30

The process of claim 16, wherein the protective powder consists of silicon nitride, boron nitride and the one or more sintering additives.

Claim 31

The process of claim 22, wherein the reaction bonded silicon nitride article product is structurally and chemically homogeneous.

Claim 32

The process of claim 22, wherein the article is embedded in the protective powder by the steps which consist of placing the article on a layer of the protective powder and then embedding the article in the protective powder.

Claim 33

The process of claim 22, wherein the protective powder consists of silicon nitride and the one or more sintering additives.

Claim 34

The process of claim 22, wherein the protective powder consists of boron nitride and the one or more sintering additives.

Claim 35

The process of claim 22, wherein the protective powder consists of silicon nitirde, boron nitride and the one or more sintering additives.