Electrochemical evaluation of the effect of binder additives on iron corrosion Available to Purchase

Recent research efforts have emphasized the archivability of metal particle media which utilizes ‘‘passivated’’ iron particles as the magnetic material. Two fundamental processes limit the archival lifetime of such media (1) corrosion of metal particles, and (2) degradation of polymer binder. This paper addresses the first process by quantifying the effect of pH and various binder additives (lubricant, dispersant, polymer degradation products, etc.) on the corrosion of pure iron in aqueous 0.05 M K₂SO₄. This study is unique in its use of electrochemical techniques to adequately quantify the corrosion process. Both ac [electrochemical impedance spectroscopy, (EIS)] and dc polarization techniques have been used. Experimental data showed that the addition of stearic acid (a lubricant) and lecithin (a dispersant) resulted in a decrease in the corrosion rate of iron in K₂SO₄. Five different carboxylic acids of various chain lengths were investigated since such compounds can be viewed as simple models for binder additives, or as polymer degradation products. Except for stearic acid, all of the carboxylic acids significantly accelerated iron dissolution at the corrosion potential. The corrosion rate increased as chain length or pH decreased and as acid concentration increased. The charge involved in passive film formation increased as the solution becomes more acidic, indicating that the passive film was less stable or more difficult to form. In the passive region the corrosion rate was lower than that of the base electrolyte for high concentrations of carboxylic acids.