GB551220A - Improvements in or relating to the thermal deposition of metals in a vacuum - Google Patents

Abstract

551,220. Coating with metals. ALEXANDER. P. Sept. 16, 1941, No. 11864. [Class 82 (ii)] In a process for depositing on a support a bright film of a metal of high vaporization point or magnesium by thermal evaporation in a vacuum, a mixture of platinum or palladium and a small percentage of the coating metal is maintained continuously in the liquid form, and the support is exposed to the vapour from the mixture, the coating metal being fed into the mixture at a rate equal to the average rate of evaporation so as to maintain the percentage of the coating metal in the mixture approximately constant. A wire 6 of the coating metal is fed at an adjustable rate from a spool 7 into a bath 3 of platinum or palladium contained in a refractory vessel 4 on brackets 10 in a vacuum chamber 1 in which the support 2, e.g. of glass or paper, is mounted. A screen 8 shields the wire 6 near the bath 3. The vessel 4 is supported by lugs 9, Fig. 2, in the brackets 10 and is heated by a zig-zag coil 11 of refractory metal, such as tungsten, embedded in refractory material 12. In a modification, the cross section of the bath at the ends is larger than that at the centre and metal electrodes dip into the bath at the ends, for passage of a heating current through the bath, the metal at the ends remaining solid but becoming liquid in the narrow centre part. In a modification, pellets or powder of the coating metal from a hopper are taken by a toothed wheel from the bottom of a hopper and dropped thus at the desired feed rate through a screen into the bath. The coating metal may be one of the following :- gold, nickel, cobalt, iron, copper, aluminium, chromium and silver.