Anodic Deposition of Sulfur in the Oxide Coating of Aluminum at Low Temperature.

Abnormal deposition of sulfur in anodizing aluminum in H//2SO//4-EG-H//2O solutions (where Eg is ethylene glycol) at low temperature (to minus 30 C) is explained by the reducing effect of univalent Al** plus ions in solution at the anode. The deposit is crystalline orthorhombic sulfur and sometimes S**2** minus . The sulfur evaporates on heating to 440 C. The amount of sulfur in the anodized coating depends on bath temperature, current density, the water content of the electrolyte, and the concentration of H//2SO//4. The maximum is 1. 5%.