Manufacture of high density, high strength isotropic graphite

The method of producing a homogeneous, isotropic, graphite article having a density of at least about 2 g/cc, a compressive strength of at least about 20,000 psi, a flexural strength of at least about 8,000 psi, and an isotropic ratio of about 1.05 or less, by the steps comprising

• (a) reducing, to 100 mm mercury or less, the pressure on a homogeneous, isotropic graphite substrate having
• (1) a density of about 1.6 to about 1.95 g/cc;
• (2) an isotropic ratio of about 1.05 or less;
• (3) at least about 15 percent total porosity;
• (4) at least about 50 percent of said total porosity being open porosity contained in interconnected pores open to the surface of said substrate and having an average pore size of about 5 microns or less and a narrow pore size distribution in which at least 90 percent of said open porosity is contained in pores having diameters of less than about 20 microns;
• (b) covering said substrate while under said reduced pressure with a fluid, carbonizable impregnant selected from (1) phenolic and furfural alcohol resins, and (2) petroleum and coal tar pitches having melting points of about 200.degree. C. or less, carbon/hydrogen atom ratios of at least about 1.6, carbon residue values of at least about 60 percent, and less than about 20 weight percent benzene insolubles, at a temperature of at least about 20.degree. C. above the melting point of said impregnant;
• (c) impregnating said substrate and carbonizing said impregnant within said substrate by (1) pressurizing said substrate, while covered with said impregnant, up to a pressure of at least about 10,000 psi and less than about 30,000 psi, (2) heating said substrate up to a temperature of at least about 600.degree. C. correlated with said pressure to maintain the combination of said impregnant and substrate at a pressure of at least about 10,000 psi and less than about 30,000 psi and a temperature of at least about 600.degree. C. for a period of time sufficient to impregnate at least about 80% of said open porosity with said impregnant and carbonize said impregnant within said open porosity;
• and
• (d) graphitizing the resulting carbonized, impregnated substrate by heating it to a temperature of at least about 2400.degree. C., said impregnating, carbonizing and graphitizing steps being conducted at pressures below about 30,000 psi and under pressures correlated with temperatures so that at temperatures above 1800.degree. C. said graphite substrate is not exposed to any substantial pressure capable of increasing said isotropic ratio.