Anodic behaviour of aluminium and its alloys in alkaline media in the presence of inhibitive and complexing substances

Abstract

In order to find out the suitability of four different grades of aluminium, namely 2S, 3S, 57S, and unalloyed aluminium for use as a galvanic anode in 1M-sodium hydroxide solution containing calcium oxide and sodium citrate, the potential-time variation, the anodic polarisation, the anode efficiency and corrosion/behaviour of these grades have been investigated. It has been found that all the above mentioned grades of aluminium behave in a similar manner, and self-corrosion can be reduced by more than 75% by the joint addition of calcium oxide and sodium citrate. However, on the basis of anode efficiency in inhibited 1M-sodium hydroxide solution, 28 grade and unalloyed aluminium seem to be the materials of choice since maximum efficienciesof 93–94% can be obtained by the use of appropriate current densities. Even in these cases, high anode efficienciesof the order of 80–94% are attained only at current densities of 9–12 mA/cm² but the results are less encouraging at lower current densities, and at 3 mA/cm² the anode efficiencieswere between 20% and 40% for alloyed and unalloyed aluminium.