GB587039A - Improvements in and relating to the electrophoretic coating of metal articles - Google Patents

Abstract

587,039. Coating by electrophoresis. STANDARD TELEPHONES & CABLES, Ltd. July 21, 1944, No. 14022. Convention date, July 23, 1943. [Class 41] A cathode or heater element for a thermionic valve is coated with aluminium oxide or silicon dioxide or a mixture of these oxides or barium carbonate, strontium carbonate or a mixture of these carbonates by electrophoretic deposition from a suspension of the coating materials in an organic liquid, preferably acetone or methanol, containing a dispersive agent consisting of tannic acid or a mixture of an alkylamine with nitrocellulose, the mixture in the latter case containing not less than 5 per cent. of either constituent. The weight of the coating material in the dispersion may be 3-20 per cent. and that of the dispersive agent 0.3-10 per cent. of the weight of organic liquid. The article is connected as anode. Examples of suitable proportions are (i) aluminium oxide 10 gms., silicon dioxide 0.3 gms., nitrocellulose 0.7 gms., triethanolamine 1.0 gms., acetone 100 mls.; a voltage of 100-300 is employed for a period 10-30 seconds; (ii) aluminium oxide 10 gms., silicon dioxide 0.3 gms., tannic acid 0.3 gms., acetone 100 mls.; a voltage of 22-50 is employed for a period 10-30 seconds and the article is removed while still connected and is then shaken; (iii) double carbonate of barium and strontium 20 gms. nitrocellulose 0.5 gms., triethanolamine 0.8 gms., acetone 100 mls. The suspension is preferably stirred. Deposition may be effected in two or more stages the deposit being fritted after one or more stages by ignition in wet hydrogen at about 1600‹C. Where the alkylaminenitrocellulose mixture is employed as dispensing agent, one of the intermediate fritting stages may be preceded or replaced by heating in air at low temperature to remove carbonaceous residues in the deposit.