Electrodeposition of chromium coatings from sulfate–carbamide electrolytes based on Cr(III) compounds

We propose an electrolyte based on chromium sulfate (1 mole/liter Cr(III)) and containing both formic acid and carbamide (urea). This electrolyte enables one to get Cr coatings with a thickness of several micrometers. It is shown that the current yield and deposition rate increase as the current density and pH value increase and temperature decreases. We select the optimal conditions of electrolysis under which bright high-quality chromium deposits are obtained. In this case, the deposition rate of the metal varies from 0.5 to 1.5 μm/min. It is shown that the optimal concentration of both formic acid and carbamide is equal to 0.5 mole/liter. The necessity of using certain surface-active substances to prevent the formation of pitting on the surface of the deposit is demonstrated. Moreover, it is discovered that the microhardness of Cr deposits attains its highest values (950–980kg/mm2) for currents with densities of 30–35 A⋅dm−2 and decreases as the pH value and temperature increase. Electrolysis is realized by using titanium–manganese-dioxide anodes and, hence, it is not necessary to separate the cathodic and anodic spaces.