Low CTE highly isotropic graphite
View Patent ↗A process for producing a graphite article having a CTE of less than about 2.0 ppm/° C. over the temperature range of from 30° C. to 100° C. and an isotropy ratio of less than about 1.5 also advantageously having a thermal shock resistance parameter of greater than about 150×10 3 W/m in both the with-grain and against-grain directions, and the graphite so produced.
1. A method of producing low CTE highly isotropic graphite, comprising:
a. mixing raw powdered needle coke and a catalytic doping agent with binder pitch to form a doped coke mixture;
b. milling the doped coke mixture to create a molding powder;
c. isostatically molding the molding powder into a desired shape to form a green article;
d. graphitizing the processed carbonaceous article to obtain a graphite article having a coefficient of thermal expansion in each direction of no greater than about 2.0 ppm/° C. over the temperature range of from 30° C. to 100° C. and an isotropy ratio of less than about 1.5.
2. The method of claim 1 wherein step d) further comprises baking the green article at a temperature of from about 700° C. to about 1100° C. prior to graphitization to create a baked carbonaceous article.
3. The method of claim 1 wherein the needle coke is petroleum coke.
4. The method of claim 1 wherein the powdered needle coke has a particle size such that 95% is passing about 75 microns.
5. The method of claim 4 wherein about 95% of the powered needle coke is passing about 44 microns.
6. The method of claim 1 wherein the doping agent comprises boron.
7. The method of claim 6 wherein the doping agent comprises boron carbide.
8. The method of claim 6 wherein the doping agent is present in the doped coke mixture at a level of at least about 0.5%.
9. The method of claim 8 wherein the doing agent is present in the doped coke mixture at a level of no greater than about 10%.
10. The method of claim 6 wherein about 95% of the molding powder of step b) passes through a mesh opening of approximately 150 microns.
11. The method of 1 which further comprises purifying the graphite article to provide a graphite article having a boron equivalence of less than about 5.0 parts per million.
12. A graphite article produced in accordance with the method of claim 1 .
13. A graphite article produced in accordance with the method of claim 6 .
14. A synthetic graphite article comprising graphite having a CTE in each direction of no greater than about 2.0 ppm/° C. over the temperature range of from 30° C. to 100° C. and an isotropy ratio of less than about 1.5.
15. The article of claim 14 wherein the CTE in each direction is no greater than about 1.0 ppm/° C. over the temperature range of from 30° C. to 100° C.
16. The article of claim 14 wherein the isotropy ratio is less than about 1.25.
17. The article of claim 16 wherein the isotropy ratio is less than about 1.10.
18. The article of claim 14 wherein the thermal shock resistance parameter is greater than about 150×10 3 W/m in both the with-grain and against-grain directions.
19. The article of claim 18 wherein the thermal shock resistance parameter is greater than about 200×10 3 W/m in both the with-grain and against-grain directions.
20. A synthetic graphite article comprising graphite having an isotropy ratio of less than about 1.5 and a thermal conductivity of at least about 130 W/m-K.
21. The article of claim 20 wherein the isotropy ratio is less than about 1.25.
22. The article of claim 21 wherein the isotropy ratio is less than about 1.10.
23. The article of claim 20 having a CTE in each direction of no greater than about 2.0 ppm/° C. over the temperature range of from 30° C. to 100° C.
24. The article of claim 20 wherein the thermal shock resistance parameter is greater than about 150×10 3 W/m in both the with-grain and against-grain directions.
25. The article of claim 24 wherein the thermal shock resistance is greater than about 200×10 3 W/m in both the with-grain and against-grain directions.