Carbon foam abrasives
The incorporation or blending of from about 1 to about 10% by volume of a “carbide precursor” powder, preferably on the order of <100 microns in size, with a coal particulate starting material and the subsequent production of carbon foam in accordance with the method described herein, results in a carbon foam that exhibits significantly enhanced abrasive characteristics typical of those required in the polishing of, for example glass, in the manufacture of cathode ray tubes.
1. A method of forming an abrasive carbon foam, comprising:
comminuting coal to form a particulate coal;
blending said particulate coal with from about 1 to about 10% by volume of a carbide precursor to form a reactive blend, wherein the carbide precursor is selected from the group consisting of tungsten, silicon and titanium;
heating said reactive blend in a mold under a non-oxidizing atmosphere to a first temperature ranging from about 300° C. to about 600° C., wherein the first heating step includes controlling the pressure ranging from about 50 psi to about 500 psi and soaking at this temperature for a period ranging from about 10 minutes to about 12 hours to form a green foam blend;
carbonizing said green foam blend to form a carbonized foam by heating to a second temperature ranging from about 600° C. to about 1600° C. in an inert atmosphere and holding at said second temperature for a period ranging from about 1 to about 3 hours to form a carbonized foam; and
graphitizing said carbonized foam by heating said carbonized foam to a third temperature ranging from about 1700° C. to about 3000° C. in an inert atmosphere and holding at said third temperature for a period of greater than about one hour to form said abrasive carbon foam.
2. The method of forming an abrasive carbon foam of claim 1 , wherein said coal particulate is a high volatile bituminous coal containing a volatile matter ranging from about 35% to about 45% by weight.
3. The method of forming an abrasive carbon foam of claim 2 , wherein said high volatile bituminous coal exhibits an expansion of at least about 20% as determined by Arnu dilatation.
4. The method of forming an abrasive carbon foam of claim 3 , wherein said high volatile bituminous coal exhibits an expansion of at least about 100% as determined by Arnu dilatation.
5. The method of forming an abrasive carbon foam of claim 2 , wherein said high volatile bituminous coal comprises:
from about 50 to about 60% by weight of fixed carbon; and
less than about 30% by weight inert maceral material;
wherein the high volatile bituminous coal exhibits a vitrinite reflectance in the range from about 0.80 to about 0.95 as determined by ASTM D2798.
6. An abrasive carbon foam, comprising:
a semi-crystalline porous coal-based structure having a density ranging from about 0.2 to about 0.5 g/cm 3 , wherein the density is varied by an introduction of an inert non-oxidizing gas into a reaction vessel; and
wherein the semi-crystalline porous coal-based structure includes a metallic carbide for improving abrasive character of the abrasive carbon foam wherein the carbide precursor is elected from the group consisting of tungsten, silicon and titanium.
7. The abrasive carbon foam of claim 6 , wherein the abrasive carbon foam has a density ranging from about 0.3 to about 0.4 g/cm 3 .
8. A method for producing an abrasive carbon foams, comprising:
comminuting coal to form a particulate coal;
blending said particulate coal with from about 1 to about 10% by volume of a carbide precursor to form a reactive blend for improving abrasive properties of the abrasive carbon foam wherein the carbide precursor is selected from the group consisting of tungsten, silicon and titanium; and
heating said reactive blend in a mold under a non-oxidizing atmosphere to a first temperature ranging from about 300° C. to about 600° C., wherein the pressure is controlled to a range from about 50 psi to about 500 psi; and
soaking at this temperature for a period ranging from about 10 minutes to about 12 hours to form an abrasive carbon foam.
9. The method for producing an abrasive carbon foam of claim 8 , further comprising:
carbonizing said abrasive carbon foam by heating to a second temperature ranging from about 600° C. to about 1600° C. in an inert atmosphere and holding at said second temperature for a period ranging from about 1 to about 3 hours; and
graphitizing said carbonized foam by heating said abrasive carbon foam to a third temperature ranging from about 1700° C. to about 3000° C. in an inert atmosphere and holding at said third temperature for a period of less than about one hour to form;
wherein said carbide precursor comprises a member selected from the group consisting of materials capable of reacting with carbon to form carbides under carbon calcining and graphitizing conditions.
10. The method of forming an abrasive carbon foam of claim 8 , wherein the abrasive carbon foam has a density ranging from about 0.2 g/cm 3 to about 0.5 g/cm 3 .
11. The method for producing an abrasive carbon foam of claim 9 , wherein said carbide precursor is a powder having particle sizes below about 100 microns.
12. The method for producing an abrasive carbon foam of claim 8 , wherein said particulate coal exhibits a free swell index ranging from about 3.5 to about 5.0.
13. The method of forming an abrasive carbon foam of claim 8 , wherein the abrasive carbon foam has a density ranging from about 0.3 g/cm 3 to about 0.4 g/cm 3 .
14. The method of forming an abrasive carbon foam of claim 1 , wherein said particulate coal exhibits a free swell index ranging from about 3.5 to about 5.0.
15. The method of forming an abrasive carbon foam of claim 1 , wherein said carbide precursor comprises a member selected from the group consisting of materials capable of reacting with carbon to form carbides under carbon calcining and graphitizing conditions.
16. The method of forming an abrasive carbon foam of claim 13 , wherein said particulate coal exhibits a free swell index ranging from about 3.75 to about 4.5.
17. The method of forming an abrasive carbon foam of claim 1 , wherein said carbide precursor is powder having particle sizes below about 100 microns.
18. The method of forming an abrasive carbon foam of claim 1 , wherein the abrasive carbon foam has a semi-crystalline, largely isotropic, porous coal-based structure having a density ranging from about 0.2 to about 0.5 g/cm 3 .
19. The method of forming an abrasive carbon foam of claim 18 , wherein the density ranges from about 0.3 to about 0.4 g/cm 3 .
20. The abrasive carbon foam of claim 6 , wherein the abrasive carbon foam has pore sizes of below about 300 μm.
21. The method of forming an abrasive carbon foam of claim 2 , wherein said high volatile bituminous coal has a Gieseler initial softening temperature above about 380° C.
22. The method of forming an abrasive carbon foam of claim 21 , wherein said high volatile bituminous coal has a Gieseler initial softening temperature ranging from about 380° C. to about 400° C.
23. The method of forming abrasive carbon foam of claim 2 , wherein said high volatile bituminous coal has a plastic range of at least about 50° C.
24. The method of forming an abrasive carbon foam of claim 2 , wherein said high volatile bituminous coal has a plastic range ranging from about 75° C. to about 100° C.
25. The method of forming an abrasive carbon foam of claim 2 , wherein said high volatile bituminous coal has a maximum fluidity of at least several hundred ddpm as determined by ASTM D2639.
26. The method of forming an abrasive carbon foam of claim 25 , wherein said high volatile bituminous coal has a maximum fluidity of more than 2000 ddpm as determined by ASTM D2639.