Abstract
The time-dependence of the aluminium-mild steel couple polarity has been investigated in a range of waters and at several temperatures. In waters containing less than 100 ppm of chloride aluminium was generallycathodic to mild steel but above 0·25% chloride it was generally anodic. For intermediate concentrations two polarity reversals were observed over a period offive days: thefirst was related to passivefilmformation or repair and the second to its breakdown. When the temperature was raised polarity reversals occurred in solutions of low chloride content, the minimum temperature for reversal in 100ppm chloride being 40°. Polarisation and electrode potential measurements showed that anodised and sealed aluminium provided strong resistance to the effects of chloride ions there by making such aluminium unreliable for sacrificial cathodic protection of steel.
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