PROCESS FOR PRODUCING SINTERED SILICON CARBIDE BODIES

Abstract

A process for preparing a sintered silicon carbide body including sintering a sample including silicon carbide particles to form a shaped sintered silicon carbide body, the particles containing a silicon carbide core and a surface layer containing carbon and oxygen, the sample having at least 90 weight % being C or Si and having a carbon to silicon molar ratio molC/molSi higher than 1 and a carbon in excess to oxygen molar ratio Cex/molO which is higher than 0.5 and lower than 5.3.

Claims

1. A process for preparing a sintered silicon carbide body comprising a step of: Sintering a sample comprising silicon carbide particles to form a shaped sintered silicon carbide body, said particles containing a silicon carbide core and a surface layer containing carbon and oxygen, said sample having at least 90 weight % being C or Si and having a carbon to silicon molar ratio molC/molSi higher than 1 and a carbon in excess to oxygen molar ratio Cex/molO which is higher than 0.5 and lower than 5.3.

2. The process according to claim 1, wherein no additive is mixed with said sample comprising silicon carbide particles to form a shaped sintered silicon carbide body.

3. The process according to claim 1, wherein said sample comprising silicon carbide has: a carbon to silicon molar ratio which is higher than 1.01 and/or lower than 1.5; and a carbon in excess to oxygen molar ratio C.sub.ex/molO which is higher than 0.5 and/or lower than or equal to 5.

4. The process according to claim 1, wherein the carbon excess of the sample comprising silicon carbide particles is obtained during particle synthesis process.

5. The process according to claim 1, wherein said silicon carbide particles are silicon carbide nanoparticles.

6. The process according to claim 1, wherein said silicon carbide nanoparticles have a particle diameter from 10 to 1000 nm.

7. The process according to claim 1, wherein said silicon carbide nanoparticles are nanowires having a diameter from 10 to 200 of nm and a length from 100 to 1000 nm.

8. The process according to claim 1, wherein said particles comprising silicon and carbon are amorphous and/or beta and/or alpha phase silicon carbide nanoparticles, in particular beta phase silicon carbide nanoparticles.

9. The process according to claim 8, wherein said silicon carbide nanoparticles are produced by laser pyrolysis, wherein the carbon to silicon molar ratio higher than 1 is obtained during laser pyrolysis.

10. The process according to claim 1, wherein the sintering is proceeded with particles comprising silicon and carbon: at a temperature higher to 2100° C. and/or lower to 2400° C.; and at a pressure higher to 60 MPa and/or lower to 80 MPa, to obtain a sintered silicon carbide body.

11. The process according to claim 1, wherein the step of sintering is Spark Plasma Sintering.

12. The process according to claim 1, comprising: (a). filling a mold with the sample comprising silicon carbide particles to form a shaped body, said particles containing a silicon carbide core and a surface layer containing carbon and oxygen, said sample having at least 90 weight % being C or Si and having a carbon to silicon molar ratio molC/molSi higher than 1 and a carbon in excess to oxygen molar ratio Cex/molO which is higher than 0.5 and lower than 5.3 and (b). sintering the mold filled with said sample to obtain the shaped sintered silicon carbide body.

13. The process according to claim 12, wherein said process does not comprise a pre-compaction step of the sample before step (a).

14. A sintered silicon carbide body produced by a process according to claim 1.

15. The sintered silicon carbide body according to claim 14, wherein the relative density of said sintered body is at least 98%.

Description

EXAMPLE 1 OF INVENTION

[0125] Silicon carbide powders used in this example are high-purity n-type, beta-silicon carbide (SiC) nanopowders obtained by a laser pyrolysis process with an average particle diameter of 35 nm and one peak in the particle size distribution. The weight fraction of carbon and silicon in said samples of silicon carbide powders is 98.8 weight %. The oxygen mass concentration of said sample is 1.2 weight %. The SiC nanopowders have a molar carbon to silicon ratio (molC/molSi) of 1.03, meaning a carbon in excess content of 3 molar %, and a molar carbon in excess to oxygen ratio (C.sub.ex/molO) of 1.0. The SiC nanopowders were placed into a graphite mold jacketed with a flexible graphite foil (Papyex® type for example) with a cylindrical shape and a diameter of 20 mm.

[0126] The filled graphite mold is placed in a Spark Plasma Sintering (SPS) machine. SiC nanopowders are flash sintered at a pressure of 65 MPa under vacuum at a temperature of 2200° C. for 20 min. Density of the sintered part is measured with the Archimedes method. Result showed that the sintered silicon carbide obtained above has a relative density of 98.1%.

[0127] When the sintered product obtained in this Example is compared with the sintered product obtained in Comparative Example 1, the use of silicon carbide nanopowders with an excess of carbon and a carbon in excess to oxygen ratio of 1.0 allows to obtain a denser product by using a lower sintering pressure along with a lower sintering temperature.

EXAMPLE 2 OF INVENTION

[0128] The experiment was conducted in the same manner as in Example 1, except that the silicon carbide nanopowders have a molar carbon to silicon ratio (molC/molSi) of 1.04, meaning a carbon in excess content of 4 molar %, and a molar carbon in excess to oxygen ratio (C.sub.ex/molO) of 2.5. The weight fraction of carbon and silicon in said samples of silicon carbide powders is 99.34 weight %.

[0129] The oxygen mass concentration of said sample is 0.66 weight %.

[0130] The obtained sintered product had a relative density of 99.3%, which is a denser product compared to the product of Comparative Example 1.

COMPARATIVE EXAMPLE 2

[0131] This comparative example was carried out to evaluate the impact of molar carbon in excess to oxygen ratio (C.sub.ex/molO) to the density of sintered silicon carbide.

[0132] The experiment was conducted in the same manner as in Example 1 of invention, except that the silicon carbide nanopowders have a molar carbon to silicon ratio (molC/molSi) of 1.05, meaning a carbon in excess content of 6 molar %, and a molar carbon in excess to oxygen ratio (C.sub.ex/molO) of 5.3. The weight fraction of carbon and silicon in said samples of silicon carbide powders is 99.5 weight %. The oxygen mass concentration of said sample is 0.35 weight %.

[0133] The obtained sintered product had a relative density lower than 97%.

[0134] This result suggests that the use of silicon carbide nanopowders with an excess of carbon and a carbon in excess to oxygen ratio higher than 5.3 would not be benefit for improving sintered silicon carbide density.