Colloids as corrosion inhibitors for aluminium‐copper alloy in sodium hydroxide

The inhibition of corrosion of B26S aluminium by various colloidal substances in aqueous sodium hydroxide has been studied. The extent of corrosion decreased with increase in the concentration of the inhibition. At an inhibition concentration of 0.5% and above. The efficiency of the colloids in decimolar sodium hydroxide increased in the order: gelatin < dextrin < glue < agar agar < acacia < tragacanth (86%). The efficiency decreased with increase in the concentration of alkali, the P.I. at an inhibitor concentration of 1.5% in 1M sodium hydroxide being, glue (23%), gelatin (39%), dextrin (47%), agar agar (64%), acacia (71%) and tragacanth (86%). The inhibition appears to be due to the absorption of the inhibitor on the aluminium surface. An increase in temperature also decreased the extent of inhibition. The aver‐age energy of activation for corrosion of B26S aluminium in 0.1M sodium hydroxide appeared to be 12.5 KCal, the value in the presence of the inhibitor being somewhat higher.