Investigation of Effect of ClO4- Ions on the Growth of Indium Oxide Films on In Electrode in Dilute Na2B4O7 Solution by Potentiometric Technique

Abstract

Oxide film growth and formation on In were investigated in 0.01 M Na 2 B 4 O 7 solutions under natural corrosion conditions by a potentiometric technique. The addition of NaClO 4 to the 0.01 M Na 2 B 4 O 7 solution reduces the rate of oxide film growth. The steady-state potential, E st , was found to depend on the added amount of ClO 4 - ions and shifts to a more active direction, following the equation, E st = α - β log C NaClO4 . 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 E st to more negative values. The rate of oxide film repair is lowered by increasing the added amount of NaClO 4 . Some micrographs investigated under SEM indicated the absence of any signs of corrosion indication in the free Na 2 B 4 O 7 solution with the presence of some scratches in the case of ClO 4 - anions. The activation energies of the oxide film growth were computed in 0.01 M Na 2 B 4 O 7 solution in the absence and presence of NaClO 4 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.