Abstract
The cathodic behavior of tin, indium, and tin-indium alloys in 0.5-M solutions of oxalic, malic, and citric acids has been investigated using potentiodynamic techniques at temperature range of 30-60 A degrees C. The results showed that the corrosion rate (I (corr)) is higher at lower indium percent (0.5% In) and starts to decrease gradually as increase of the In percent up to 5% In (although it is still higher than that of pure tin and lower than that of indium at 5% In) in all examined acids. The positive shift in corrosion potential with simultaneous increase in corrosion rate can be explained on the basis of the depolarizing action of beta-InSn4 phase compared with pure tin. The negative shift in the corrosion potential with much higher corrosion rate in case of alloys IV and V (10% and 20% In, respectively) can be ascribed to the formation of gamma-In3Sn phase which leads to the increase in the anodic to cathodic area ratio. The corrosion of the two investigated metals and their alloys is affected by the formation of soluble complex species with organic acid anions. The aggressiveness of the studied metals and their alloys decreases in the following order of the organic acids employed oxalic > malic > citric acid. The observed activation energy values support that the tested electrodes exhibit higher corrosion rates in oxalic acid solution than the corresponding values in the other investigated acids. X-ray diffraction and scanning electron microscopy photographs elucidated the types of phases formed in the prepared alloys. The presence of a definite amount of indium in tin alloy improves the hardness.