Corrosion of stainless steel by gaseous I2

The adsorption and desorption of gaseous iodine on stainless steel was studied at low temperature under atmospheric conditions. Sorption kinetics were studied by measuring the 131I tracer activity on a stainless steel coupon during loading and purging. Scanning electron microscopy (SEM) photographs and energy dispersive X-ray (EDX) analyses were also obtained at various stages of loading and purging. The iodine uptake and corrosion on stainless steel surface was extensive at room temperature, particularly in air. The adsorbed iodine desorbed only during purging with air and not with N2. This desorption behaviour and the extensive iodine-catalysed corrosion in air are explained by the reaction of oxygen with FeI2 to form iron oxyiodide (FelxOy) solids, and by significant volume changes associated with the formation of Fel2 and Felx0y. These volume changes continuously generate cracks and grain boundaries through which I2 can diffuse to react with Fe. (author)