Efficiency of alkylamines and alkylammoniumions in retarding the dissolution of Al

Abstract

The dissolution of Al in HCI and NaOH solutions of varying concentrations has beenstudied by the thermometric method, and the dependence of the rise in temperature (Δ T) and the reaction number (R.N.) on solution concentration has been established. The results indicate that metal dissolution in each medium follows a different mechanism. The effect of concentration of a number of alkylamines on the dissolution of Al in 3N HCI and in 2N NaOH has been examined; these additives have been shown to cause a lowering of R.N. The alkylamines are more strongly adsorbed than the alkylammonium ions, and interfere with the anodic reaction. The curves relating the percentage decrease in R.N. to the logarithm of inhibitor concentration are invariably sigmoid in shape, and the inflexions on the curves depend on both the medium and amine used. Inhibition increases with the chain length and number of the alkyl groups of the amine. Retardation of dissolution is due to blocking of the surface by the additive. A relation has been established between the cross-sectional areas of the amine molecules and the concentration necessary to cut down dissolution to the same extent.