CHROMIUM ELECTROPLATING

Investigations were made of the fundamentals of Cr deposition from the standpoint of thermodynamic analysis and reaction-rate theory. Equations based on reaction-rate theory provided a more complete analysis of the plating mechanism. An application of reaction-rate theory is discussed which yields an equation relating current density through the cell to voltage drop - across the cathode layer. For Cr plating cells containing H2CrO4, only one of the possible mechanisms of reduction produced a plate. Sulfate ion produced a favorable effect by hindering the liberation of H. Lower-valence Cr ions had no effect on plating reaction and could be plated out in the presence of higher-valence Cr ions. An inclined cathode cell may possibly be adapted for rapid evaluation of I-V curve data. Cr plates with small amounts of Fe as high as 10 seemed to improve plate quality, but did not eliminate the cracking tendency. Cracking in plates may possibly be eliminated by use of addition agents of H2CrO4 and by alloying or other means.