Abstract
Oxide film growth and formation on In were investigated in 0.01 M Na2B4O7 solutions under natural corrosion conditions by a potentiometric technique. The addition of NaClO4 to the 0.01 M Na2B4O7 solution reduces the rate of oxide film growth. The steady-state potential, Est, was found to depend on the added amount of ClO4- ions and shifts to a more active direction, following the equation, E-st = alpha - beta log CNaClO4. The rate of oxide film formation was found to follow a direct logarithmic relation. The appearance of two segments on E-log t plots confirms the formation of inner and outer oxide layers on the indium surface. The increase in the solution temperature reduces the rate of oxide film repair and shifts Est to more negative values. The rate of oxide film repair is lowered by increasing the added amount of NaClO4. Some micrographs investigated under SEM indicated the absence of any signs of corrosion indication in the free Na2B4O7 solution with the presence of some scratches in the case of ClO4- anions. The activation energies of the oxide film growth were computed in 0.01 M Na2B4O7 solution in the absence and presence of NaClO4 and were found to vary between 7.45 and 28.89 KJ/mol which is less than 40 KJ/mol that confirms that the rate of oxide film formation is controlled by a diffusion process.