SODIUM CHROMATE AS INHIBITOR FOR AL AND ITS ALLOYS AT pH=11

Corrosion inhibition of Al, Al-Cu, Al-Mg and Al-Zn in 0.001 M NaOH solution at pH=11 has been investigated at four temperatures including 298, 303, 308 and 313 K, with sodium chromate as inhibitor at three concentrations of 5×10-3, 1×10-2 and 5×10-2 M. The results of protection efficiencies indicate that sodium chromate is a good inhibitor for Al and its alloys. Sodium chromate behaved as mixed-type inhibitor, because it shifted corrosion potentials to noble or to active direction. The presence of chromate in corrosive medium led to an increase in Tafel slopes. Activation energies were varied due to the variation in cathodic and anodic sites on metal surfaces.