Silicon carbide coated graphite members and process for producing the same

Claim 1

IN THE PROCESS OF APPLYING A SILICON CARBIDE COATING TO A GRAPHITE MEMBER TO PRODUCE A COMPOSITE STRUCTURE, THE STEPS COMPRISING: A. HEAT TREATING AT A TEMPERATURE OF FROM ABOUT 1700*C TO 2400*C AN ISOTROPIC GRAPHITE BODY COMPRISING FINE GRAINED ISOTROPIC GRAPHITE OF A DENSITY OF AT LEAST 1.75 GM/CC AND HAVING A COEFFICIENT OF THERMAL EXPANSION OF ABOUT 7.5 TO 8.3 INCH PER INCH PER DEGREE CENTIGRADE X 10-6, THE GRAPHITE GRAINS BEING OF A MAXIMUM PARTICLE SIZE OF LESS THAN 0.001 INCH, AND CHARACTERIZED BY A RELATIVELY UNIFORM DISTRIBUTION OF MANY INTERCONNECTED FINE PORES OF AN AVERAGE DIAMETER OF ABOUT 5 MICRONS AND LESS, THE PORES EXTENDING TO THE SURFACE OF THE BODY, THE HEAT TREATING BEING APPLIED FOR AT LEAST AN HOUR IN A HALOGEN ATMOSPHERE, THE HALOGEN COMPRISING AT LEAST ONE OF THE GROUP CONSISTING OF CHLORINE AND FLUORINE, THE HEAT-TREATMENT PURIFYING THE BODY TO REDUCE THE ASH IMPURITIES TO A RANGE OF THE ORDER OF 2 TO 10 PPM, B. MACHINING THE HEAT TREATED ISOTROPIC GRAPHITE BODY TO A MEMBER OF PREDETERMINED SHAPE AND SURFACE CONDITION, C. ULTRASONICALLY CLEANING THE MACHINED BODY IN A LIQUID CLEANING THE FLUID TO REMOVE LOOSE SURFACE PARTICLES, D. DEPOSITING SILICON BY A GAS PHASE REACTION ON THE SURFACES OF THE CLEANED ISOTROPIC GRAPHITE MEMBER WHILE AT A TEMPERATURE OF AT LEAST 1000*C BUT BELOW THE MELTING POINT OF SILICON, TO PROVIDE AN INFILTRATABLE LAYER OF SILICON ON THE SURFACES, E. HEATING THE SILICON COATED ISOTROPIC GRAPHITE MEMBER TO A TEMPERATURE AND FOR A PERIOD OF TIME TO CUASE THE SILICON TO MELT AND PENETRATE THE PORES AND CREVICES OF THE GRAPHITE MEMBER AND TO REACT COMPLETELY IN SITU WITH THE GRAPHITE TO FORM A LAYER OF SILICON CARBIDE TO A DEPTH OF AT LEAST ABOUT 5 MILS, AND F. DEPOSITING THEREOVER BY A GAS PHASE REACTION A SEALING LAYER OF SILICON CARBIDE ON THE GRAPHITE MEMBER.