The Mechanism and Efficiency of Organic Inhibitors during Pickling of Iron

Experimental proof is submitted to show that the electrochemical or overvoltage theory heretofore advanced to account for the action of inhibitors in pickling solutions does not hold. Results indicate that, due to adsorption, a film is formed over both the metallic iron areas and the oxidized or scaled areas. However, the practical success in the use of inhibitors is due to the greater adsorption of inhibitor at the metallic areas as against that at the oxidized or scaled areas. Accordingly, since the time of diffusion of the acid ions through the inhibitor film will be the longer the greater the thickness of the film, the oxidized or scaled areas will be more readily attacked by the acid than the metallic areas.