Interaction of Iodine with Preoxidized Stainless Steel

The kinetics of the reaction of molecular iodine with preoxidized Type 304 stainless steel was studied by mass spectrometric and gravimetric techniques. The temperature range was 438 to 803 K, and the iodine partial pressures in the 1-atm total pressure water vapor-hydrogen gas ranged from 1.33 to 133 Pa. Examination of the reacted surface by electronic spectroscopies showed localized attack in the form of highly fractured crystalline deposits that contained significant iodine concentrations. The mass spectrometric results revealed no HI in the gas despite favorable thermodynamics for formation of this species. The gravimetric results showed an initial rapid increase in weight followed by a slow, long-term weight change that did not appear to approach saturation. The saturation iodine concentration on the surface due to the initial deposition process was greatest at 573 K. The kinetics of the initial uptake was analyzed by a first-order kinetics model. The characteristic times of attainment of saturation were on the order of 1 h and showed a very small activation energy.