Abstract
The rate of uniform corrosion, the likelihood of pitting and crevice corrosion for aluminum, Al, in white wine were investigated in this paper. In commercial wines, the K2S2O5 is commonly added to induce free-SO2 which reduces the dissolved oxygen and acts as a fungicide in the wine. The spontaneous electrode potential of Al, ESP, in a deaerated wine containing less than 1ppm of free-SO2, at 25°C was measured to be about -600mV vs. SCE. Since the K2S2O5 is an oxidizing agent for the Al, the ESP was ennobled with the addition of K2S2O5 reaching -520mV with a concentration of 1000ppm K2S2O5. The uniform corrosion rate was measured to be 13μm/y at 25°C and this rate was found to depend on the temperature with an activation energy of 42kJ/mol. However, this rate was found to have no dependency on the electrode potential within the ESP range. The critical pitting potential, VC, PIT, measured in the wine containing 25ppm of Cl- was -370mV which was more noble than the ESP, and the pitting corrosion can not occur. The repassivation potential for the growing crevice corrosion, ER, CREV, was measured to be -530mV. It was also found that this potential does not depend on either the temperature or the concentration of K2S2O5. It was observed that the ESP became more noble than the ER, CREV with the addition of 800ppm K2S2O5 at 25°C. At a lower temperature, however, the ESP became more noble than the ER, CREV when a lesser amount of K2S2O5 were added. An effective method to decrease the rate of uniform corrosion is to reduce the holding temperature; however, to effectively prevent the crevice corrosion at these lower temperatures, the K2S2O5 concentration must be kept below 100ppm.
