| 摘要 |
1,221,852. Pyrolytic graphite coated carbon articles. GENERAL ELECTRIC CO. 8 April, 1968 [18 April, 1967], No. 16846/68. Heading C1A. [Also in Division H5] A composite graphite body has a smooth surface layer of pyrolytic graphite, the layer extending into the pores of the body to mechanically interlock the surface layer with the particles in the body. The body is coated by heating to 1100‹ C. to 1600‹ C. for 14 to 20 hours in an induction furnace, in a stream of gas such as methane or methane and hydrogen. For this stage of the coating the gas pressure is 0À5 to 1À2 mm. Hg, but for the second stage the pressure is raisedto 0À8 to 2À5 Hg and the temperature raised to between 1600‹ C. and 2100‹ C. These latter conditions are maintained for 6 to 10 hours, after which the furnace is allowed to cool to room temperature for about 12 hours, the pressure being slowly raised to atmospheric pressure. Objects prepared in this way have a coating thickness of 1 to 15 mils, while the depth of penetration of pyrolytic carbon in the pores is 1 to 10 times the thickness of the surface layer. The density of these objects is 1.7 to 1À9. |
