GB634187A - Improvements relating to the coating of metal filaments with electron-emissive materials - Google Patents

Abstract

634,187. Electrophoretic treatment of wire. SYLVANIA ELECTRIC PRODUCTS, Inc. Feb. 14, 1947, No. 4346. Convention date, April 28, 1943. [Class 41] A method of coating metal filaments with electron-emissive materials comprises feeding a filament through a bath consisting of a suspension of the emissive material in a non- aqueous vehicle containing a nitrocotton binder and a conditioner such as triethylene glycol, isopropenol or other hydroxylic organic compound which is capable of lowering the interfacial tension between the suspended solid phase and the liquid phase, and simultaneously maintaining, between the filament and an electrode in the bath, a difference of potential sufficient to cause deposition of a coating by electrophoresis. In the arrangement shown, metal wire 1 is passed over a metal pulley 2 into a glass vessel 3 containing a suspension of finely-divided alkaline earth metal carbonates in an amyl acetate, diethyl carbonate nitrocotton mixture 4. The wire is guided past an arc-shaped cathode 6, through a heater 8 and over, but not touching, a power-driven wheel 10 which dips into a container 11 and conveys nitrocotton lacquer 12 on to the wire. The coated wire is passed through a drier 15 and wound on a spool 17. To increase the coherence of the coating a muffle furnace may be placed between the heater 8 and a pulley 9. The alkaline earth with metal carbonate before use is baked for at least two hours at a temperature of 300‹ to 350 C. to remove moisture and occluded volatile substances. In preparing the suspension, the carbonates, amyl acetate, a solution of nitrocotton in amyl acetate, and the conditioner may be milled in a ball mill and afterwards diluted with further liquor.