Electrodeposition of black chromium from self regulating electrolytes

A strong need islelt by a practical plater for a black chrome bath which can be operated around the ambient temperature (30°C) and at normally employed current densities and preferably not associated with any necessity of controlling the catalyst concentration. In the work now reported, experiments were carried out on the solubility of calcium fluoride gt 30°C in chromic acid solutions with a concentration range of .200- 425 g 1 I. Barium hydroxide was introduced in adequate quantities to desulphate chromic acid and also to counteract any drag-in of sulphate. Hullcell experiments were carried out at 23" and 31°C in order to assess approximately the cunent density range over which black chromium deposition was possible. This was followed by experiments in plating to study the effects of different parameters like chromic acid concentration, current density. temperature and duration of deposition on the nature of finish and deposition