Process for expanding pyrolytic graphite

Claim 2

A PROCESS FOR EXPANDING PYROLYTIC GRAPHITE WHICH COMPRISES PLACING SAID PYROLYTIC GRAPHITE IN A CHAMBER HAVING DIMENSIONS IN WHICH MOVEMENT IN THE DIRECTION PARALLEL TO THE DEPOSITION SURFACE (THE A-B DIRECTION) IS CONSTRAINED BY THE CHAMBER SIDE WALLS, BUT WHICH ALLOWS MOVEMENT ONLY IN THE DIRECTION NORMAL TO THE DEPOSITION SURFACE (THE C-DIRECTION), TREATING SAID PYROLYTIC GRAPHITE WITH AN INTERCALATING AGENT TO CAUSE SAID PYROLYTIC GRAPHITE TO EXPAND IN THE DIRECTION NORMAL TO THE DEPOSITION SURFACE (THE C-DIRECTION) WHILE CONSTRAINING MOVEMENT IN THE DIRECTION PARALLEL TO THE DEPOSITION SURFACE (THA A-B DIRECTION) BY THE SIDE WALLS OF SAID CHAMBER AND CONTINUING SAID TREATMENT FOR A PERIOD OF ABOUT 1 TO ABOUT 120 MINUTES SUFFICIENT TO SUBSTANTIALLY COMPLETELY DELAMINATE SAID EXPANDED PYROLYTIC GRAPHITE, AND HEATING FROM ABOUT 300* TO ABOUT 700*C, SAID DELAMINATED EXPANDED PYROLYTIC GRAPHITE WHILE PERMITTING MOVEMENT IN THE DIRECTION NORMAL TO THE DEPOSITION SURFACE AND CONSTRAINING MOVEMENT OF SAID DELAMINATED PYROLYTIC GRAPHITE IN THE DIRECTION PARALLEL TO THE DEPOSITION SURFACE BY THE SIDE WALLS OF SAID CHAMBERM TO CAUSE SAID DELAMINATED EXPANDED PYROLYTIC GRAPHITE TO EXPAND FURTHER IN THE DIRECTION NORMAL TO THE DEPOSITION SURFACE.

Claim 3

A process as defined in claim 1, wherein said intercalating agent is a metal hsalide selected from the group consisting of metal chlorides, iodides and bromides.

Claim 4

A process as defined in claim 1, wherein said intercalating agent is an acid selected from the group consisting of sulfuric acid and phosphoric acid, or an oxidizing agent selected from the group consisting of nitric acid, chromic acid and perchloric acid, permanganates, and dichromates.

Claim 5

A process as defined in claim 1, wherein said intercalating agent is a mixture of sulfuric acid and an oxidizing agent selected from the group consisting of nitric acid, chromic acid, perchloric acid, potassium chlorate, potassium dichromate, and mixtures thereof, forming graphitE bisulfate.

Claim 6

A process as defined in claim 4, wherein said oxidizing agent is nitric acid.

Claim 7

A process as defined in claim 5, employing as intercalating agent a mixture having a ratio of about 3 parts sulfuric acid to about 1 part nitric acid, by volume, diluted with water to form an aqueous solution containing a ratio of about 100 parts of such mixed acids to about 0.5 to about 50 parts of water, by volume, at a temperature ranging from about ambient to about 125*C.

Claim 8

A process as defined in claim 5, said heating being carried out at a temperature ranging from about 400*C to about 600*C for a period ranging from about 10 to about 30 minutes.

Claim 9

A process as defined in claim 5, employing annealed pyrolytic graphite, said heating being carried out at a temperature of about 500*C, and expanding the pyrolytic graphite from in excess of 1 to about 10 times the original dimension in the c-direction.

Claim 10

A process for expanding pyrolytic graphite, which comprises placing said pyrolytic graphite in a chamber having dimensions in which movement in the direction parallel to the deposition surface (the a-b direction) is constrained by the chamber side walls, but which allows movement only in the direction normal to the deposition surface (the c-direction), treating the pyrolytic graphite with a mixture of sulfuric and nitric acids to form graphite bisulfate and to cause the pyrolytic graphite to expand only in the c-direction in said chamber, while constraining movement in the a-b direction by the side walls of said chamber, and continuing said acid treatment for a period of about 10 to about 60 minutes sufficient to substantially completely delaminate the expanded pyrolytic graphite and form a lamellar compound of pyrolytic graphite, graphite bisulfate, draining excess sulfuric acid-nitric acid solution from said chamber, heating the delaminated lamellar pyrolytic graphite at about 500*C to cause said delaminated pyrolytic graphite to expand further only in the c-direction to a predetermined extent while constraining movement in the a-b direction by the side walls of said chamber, thereby bonding the carbonaceous planes of the expanded pyrolytic graphite and forming an integral uniformly expanded pyrolytic graphite, the resulting expanded pyrolytic graphite being expanded from about 1 to about 10 times its dimension in the c-direction.

Claim 11

A process for expanding pyrolytic graphite, which comprises placing said pyrolytic graphite in a chamber having dimensions in which movement in the direction parallel to the deposition surface (the a-b direction) is constrained by the chamber side walls, but which allows movement only in the direction normal to the deposition surface (the c-direction), treating the pyrolytic graphite with a mixture of sulfuric and nitric acids to form graphite bisulfate and to cause the pyrolytic graphite to expand only in the c-direction in said chamber, while constraining movement in the a-b direction by the side walls of said chamber, and continuing said acid treatment for a period of about 10 to about 60 minutes sufficient to substantially completely delaminate the expanded pyrolytic graphite and form a lamellar compound of pyrolytic graphite, graphite bisulfate, draining excess sulfuric acid-nitric acid solution from said chamber, heating the delaminated lamellar pyrolytic graphite at about 500*C to cause said delaminated pyrolytic graphite to expand further only in the c-direction to a predetermined extent while constraining movement in the a-b direction by the side walls of said chamber, thereby bonding the carbonaceous planes of the expanded pyrolytic graphite and forming an integral uniformly expanded pyrolytic graphite, the resulting expanded pyrolytic graphite being expanded from about 1 to about 10 times its dimension in the c-direction.

Claim 12

A process as defined in claim 9, employing annealed pyrolytic graphite, and wherein said mixture of nitric acid and sulfuric acid comprises a ratio of about 3 parts sulfuric acid and about 1 part nitric acid, by volume, diluted with water to form an aqueous solution containing a ratio of about 100 parts of such mixed acids to about 1 to about 20 parts of water, by volume, said treatment with said aqueous acid solution being carried out at a temperature ranging from ambient to about 125*C, for a period ranging from about 15 to about 30 minutes, said graphite bisulfate formation being accompanied by expansion of the expanded pyrolytic graphite from 2 to 3 times its original dimension in the c-direction, said heating at about 500*C being carried out for about 10 to about 30 minutes, and providing uniformly expanded pyrolytic graphite expanded from about 1 to about 5 times its original dimension in the c-direction.