ROCKWELL INTERNATIONAL THOUSAND OAKS CALIF SCIENCE CENTER
Electrochemical studies of atmospheric corrosion phenomena have been performed over a 42 months period. The kinetics of corrosion reactions occurring under thin electrolyte layers 100-1000 microns have been studied for steel, zinc, Cu and Al by recording potentiodynamic polarization curves using a modified atmospheric corrosion monitor ACM. Normal Tafel behavior was observed, the limiting current for oxygen reduction increased linearly with inverse film thickness. Similar experiments in which corrosion kinetics were determined from polarization resistance measurements using the CORFIT computer program showed that with decreasing film thickness the corrosion reaction becomes charge transfer controlled. Laboratory and outdoor exposure tests have shown that corrosion rates increase drastically when the electrolyte layers become very thin during the drying out process at RH 100. This phenomenon has been studied in detail by evaluating the effects of corrosion product chemistry, RH and SO2. A comparison of corrosion rates obtained under identical conditions in weight loss and electrochemical experiments has been carried out for steel and zinc ad a function of RH and electrolyte concentration. The ACMs have been used extensively to monitor atmospheric corrosion behavior in outdoor exposure. In the final phase of this project surface analyses have been carried out for 4130 steel and zinc which had been corroding under thin electrolyte layers.