GB258219A - Improvements in and relating to process of electro-plating with chromium - Google Patents

Abstract

258,219. Chromium Products Corporation, (Assignees of Hosdowich, J. M.). Sept. 10, 1925, [Convention date]. Chromium. depositing. - The throwing power " of a chromium plating bath containing chromic acid and chromium hydroxide, added as such or in the form of chromium chromate. is improved by the addition of a small proportion of a soluble salt of a. metal below chromium in the electrochemical series; the additional metal is not deposited. A suitable electrolyte is prepared by dissolving 325 gms. of chromic acid in water, heating to boiling and stirring into the hot solution 12 gms. of commercial chromium hydroxide, after solution of which 6 gms. of commercial hydrated ferrous sulphate is added. The solution is then diluted to 1 litre. The cell is preferably fitted with a coil for heating or cooling. The temperature is maintained between 35‹ and 45‹ C. The voltage is from 2.5 to 5 and the current density 0.05 to 0.2 amps. per sq. cm. The bath is regenerated from time to time by addition of chromic acid. No loss of iron occurs except by mechanical wastage. 6 gms. of nickel sulphate may be used instead of ferrous sulphate. Sulphates or chlorides of cadmium, tin, lead, antimony, bismuth, copper and mercury may alternatively be used; the amount may vary from less than 1 up to 30 gms. per litre. The concentration of chromium hydroxide in the bath should be more than sufficient to neutralize anv free acid present other than chromic acid, and the concentration of chromic acid should be at least twice that of the chromium hydroxide and the additional salt. Insoluble anodes of lead or lead oxide or soluble anodes of chromium or its alloys or mechanical mixtures with other metals may be employed.