GB1206118A - Improvements in deposition of pyrolytic graphite - Google Patents

Abstract

1,206,118. Moulding tubes. GENERAL ELECTRIC CO. 18 Aug., 1967 [3 Oct., 1966], No. 38101/67. Heading B5A. [Also in Divisions C1, C7 and F2] An article, e.g. a tube of anisotropic pyrolytic material is made by depositing material on to a shaped surface which provides a fault extending through the deposit, a cylindrical portion on one side of the fault, and a portion having a surface of double curvature on the other side of the fault. The portions on either side of the fault are under sufficiently different stress from each other to enable cleavage at the fault upon cracking. The deposition of pyrolytic graphite is particularly described, but metals, e.g. Hf, Mo, Nb, Si, Ta, W, Ti, Zr, and their nitrides, silicides, carbides and borides can also be deposited. Graphite can be deposited from methane/hydrogen by induction heating at 1200-2500‹ C., metals from halogenated derivatives, and nitrides or carbides from said derivatives plus ammonia or carbonaceous gas. As shown in Fig. 3, deposition takes place upon the inside of a tubular mandrel 30 of frangible electrographite, provided at each end with shoulder 36 and portion 38, which are assembled by means of flanges 32, 34. Portions 30, 38 are of simple curvature and shoulder 36 is of double curvature. The deposit contains faults 54, 56, 58, 60 and is stressed in tension on shoulder 36 and in compression on mandrel 30 and portion 38, so that a cleavage takes place at the fault lines, whereby the desired tubular deposit on mandrel 30 is separated from the impure end portion 38. The flanges may extend at 30-150 degrees from the mandrel surface, and flange 34 may be omitted. As shown in Fig. 4, tubular deposits 68 and 70 are separated by a deposit which is under tension, on shoulder 62 of double curvature; cleavage takes place at faults 72, 74.