GB787076A - Improvements in or relating to gas plating - Google Patents

Abstract

787,076. Coating with metals. COMMONWEALTH ENGINEERING CO. OF OHIO. Oct. 20, 1954, No. 30148/54. Class 82(2) An object is coated with metal by heating a thermally decomposable metal-bearing compound to a temperature sufficient to produce vapours of the compound but insufficient to cause its decomposition, separately heating a carrier gas to a temperature above that required to vaporize the compound but below the decomposition temperature of the compound, flowing the heated carrier gas into contact with the heated compound to produce a mixture thereof, and heating the mixture to a temperature below the decomposition temperature of the compound immediately prior to introducing the mixture into a coating zone which contains the object at a temperature high enough to cause decomposition of the metal-bearing compound. Compounds which may be employed are molybdenum carbonyl, tungsten carbonyl, cobalt carbonyl, nickel carbonyl, iron pentacarbonyl, antimony hydride, tin hydride, chromyl chloride, copper nitroxyl and cobalt nitroxyl carbonyl. The carrier gas may be carbon dioxide, nitrogen, helium or argon. As shown in Fig. 1, carbon dioxide from a source 10 is passed into a carburettor 4 containing chromium carbonyl maintained at a constant temperature by a thermostatically controlled oil bath 2, the carbon dioxide being preheated to the same temperature by circulation through the coil 7. The carbon dioxide charged with chromium carbonyl vapour passes through heating jacket 11 and thence into heated chamber 24 the interior of which is thus coated with chromium. In two modifications (i) the carburetter 4 is not enclosed by the coil 7 but is separated from it by a short length of connecting pipe which is also immersed in the oil (Fig; 3, not shown), and (ii) the gas mixture emanat-i ing from heating jacket 11 is passed; through a second coil maintained in a con- stant temperature oil bath, the gas mixture issuing from this coil passing through a second heating jacket before entering the < coating chamber (Fig. 4, not shown). Methods of packing the carburettor are described in which (a) layers of chromium - carbonyl are supported on metal screens which may be separated by layers of glass wool (Figs. 2 and 6, not shown), and (b) glass beads are interspersed with fragments of chromium carbonyl - (Fig. 5, not shown). When the metal-bearing compound is liquid, a carburettor is employed having perforated horizontal screens spaced along its vertical axis.