On this graph semi dashed line A circumscribes the bright plate area for solution containing 250 g/l CrCO3, and the dashes line B circumscribes a bright plate area for a solution containing about 400 g/l. The complete bright plating area circumscribe by the line X is typical of the behavior of most chromium plating baths. Thus to produce bright deposits from a solution containing 250 g/l chromium acid and 2.5 g/l sulfate at a temperature of 40o, cathode current density between 3.1 and 15.5 A/dm2 may be used at 45oC current density may be 50% higher.
If more rapid plating is desired and sufficient power is available, the temperature is often increased to about 55oC and the current density to about 31 A/dm2. These conditions, when used with the 250 g/l solution for building up a heavy plate for industrial purposes, result in a plating speed of almost 25 µm of chromium per hour. Higher plating speeds can be obtained at higher current densities, but the deposits are apt to be bubbly,” “pebbly,” or nodular.
Chromium Plating at higher temperatures and current densities has been proposed by numerous workers. This idea has been applied successfully to the plating of small articles, but the power required for plating larger objects may be prohibitive or unavailable.
