ELECTROCHEMICAL EVALUATION OF THE EFFECT OF BINDER ADDITIVES ON IRON CORROSION

Recent research efforts have emphasized the archivability of metal par ticle media which utilizes ''passivated'' iron particles as the magnet ic material. Two fundamental processes limit the archival lifetime of such media (1) corrosion of metal particles, and (2) degradation of po lymer binder. This paper addresses the first process by quantifying th e effect of pH and various binder additives (lubricant, dispersant, po lymer degradation products, etc.) on the corrosion of pure iron in aqu eous 0.05 M K2SO4. This study is unique in its use of electrochemical techniques to adequately quantify the corrosion process. Both ac [elec trochemical impedance spectroscopy, (EIS)] and dc polarization techniq ues have been used. Experimental data showed that the addition of stea ric acid (a lubricant) and lecithin (a dispersant) resulted in a decre ase 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 deg radation products. Except for stearic acid, all of the carboxylic acid s significantly accelerated iron dissolution at the corrosion potentia l. The corrosion rate increased as chain length or pH decreased and as acid concentration increased. The charge involved in passive film for mation increased as the solution becomes more acidic, indicating that the passive film was less stable or more difficult to form. In the pas sive region the corrosion rate was lower than that of the base electro lyte for high concentrations of carboxylic acids.