THE SELF-REGULATING NATURE OF IN ON THE POTENTIAL OF AL IN 3.5-PERCENT NACL SOLUTION

The role of indium on the corrosion potential of high purity Al (99.99 9%) and commercial purity Al (99.33%)has been investigated, employing potential vs time, polarization and wavelength dispersive X-ray analys is (WDX) techniques. Indium has been found to shift the corrosion pote ntial of Al towards either anodic or cathodic direction depending on t he purity of Al providing an optimum value for cathodic protection of steel. WDX analysis shows that in Al containing Fe, indium reduces the cathodic activity of phases such as Al3Fe. In high purity Al, the dep osited indium provides additional cathodic sites. These processes are responsible for lowering E-corr of commercial purity Al on the one han d and increasing E-corr of high purity Al on the other hand through si mply alloying aluminum of various purity with indium. (C) 1997 Publish ed by Elsevier Science Ltd.