Studies on the Kinetics of Aluminium Metal Dissolution in Aggressive Acid Media Containing Inorganic Anions

Abstract

The kinetics of chloride ion pitting and inorganic anions inhibition of aluminium metal corrosion in 1.0M solutions of perchloric acid were studied at 30"C in the ranges 0 ~ Cl-~ 0.8 mol L-1; 0 ~ NO-; ~ 0.18 mol L-1 and'O ~ ST ~ 1,0 mol L-1, where ST represents the sum of sol-and HSO~ species all at an ionic strength I = 2.0. NaC104-The reactions were found to be governed by multistep equilibria in which Cl-, NO ~. HSO;, soland dissolved oxygen 02 (g) compete for the metal surface. The rate of coltosion was found to be zero-order overall with an observed rate constant dependence on CI-of the form: kK K [Cl-f (k-k) = 2 3 obs 0 K [0 ]+K [Cl-]+K K [Cl-f 1 2 2 2 3 where Kl is the equilibria constant for °2(g) adsorption and K2 & K3 are successive adsorption constants for Cl-ions. The addition of nitrate or sulfate ions resulted in the inhibition of aluminium corrosion. The results are discussed in tern\s of multistep competitive equilibria in which the nitrate or the sulfur containing species (SO~-, HS04) screen the metal surface from chloride attack. In all cases a mechanism involving three competitive equilibria viz. molecular oxygen adsorption, Cl-adsorption and inhibitor adsorption followed by a rate determining dissolution step is proposed for the reactions.

Electrochemical Corrosion Behavior of Aluminum in Perchloric Acid

“…Pickling inhibitors, in spite of leaving the corrosion potential virtually unaffected, cause a significant decrease in the corrosion rate [6]. A large number of investigations have been reported on adsorption of anions on aluminum corrosion and their inhibition or stimulation effects on aggressive acid media [7][8][9][10][11][12][13]. Recent study has been concerned with the effects of various inorganic additives, such as nitrate, nitrite, thiocyanate and chromate on the corrosion of aluminum in 1 M HClO 4 at 40˚C [14].…”