OXIDATION STATE OF ANODIC TANTALUM OXIDE AFTER HEAT-TREATMENT .1. GALVANOSTATIC METHOD AS APPLIED AFTER HEATING IN VACUUM

During heat-treatment of anodic Ta//2O//5 in vacuum (10**-**5 Torr) at temperatures in the range from 200 degree to 700 degree C oxygen exchange between the anodic oxide, the Ta substrate, and the atmosphere was observed. Galvanostatic reanodization experiments resulted in potential-time (charge) curves which could be used to determine the oxidation state of heat-treated TaO//n as a function of the distance from the electrolyte/oxide interface into the oxide. Profiles of the oxidation state across the oxide were measured for tantalum oxide anodized in 0. 1M H//3PO//4 and 0. 1M H//2SO//4 after heat-treatment at 10**-**5 Torr and 500 degree C. Of several experimental variables, the time of heat-treatment and the oxide thickness were chosen to illustrate the method of determining oxidation state profiles for the case of heat-treatment in vacuum. In all cases treated in this paper the reduction was carried out to the extent that the oxide as a whole exhibited high electronic conductivity.