PNNL

Abstract

In this study, five different metal coupons were evaluated for gaseous iodine [I2(g)] adsorption including two stainless steels (i.e., SS304 and SS316), two Inconel® alloys (i.e., 625 and 718) and pure Ni (i.e., Ni-200) within a dynamic flow-through system where temperature, iodine concentration, flow rate, atmosphere, and relative humidity were controlled. Humidity was shown to be critical to iodine adsorption on SS304 and SS316 and Ni-200 at ambient temperatures. The results presented herein suggest that a moisture mediated reaction is occurring. However, higher humidity levels decrease the adsorption, suggesting an ideal range of humidity for highest corrosion. A comparison of the five metal substrates showed the highest I2(g) adsorption in the following descending order Ni-200 > SS304 > SS316 >718>625.The 625 and 718 Inconel alloys were fairly inert to iodine adsorption under the conditions tested. Characterization by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction of the Ni-200 coupon indicates that NiI2 is formed and flakes off the surface as a black powder. The SS304 and SS316 coupons showed evidence of extensive reactions with I2(g) and formed a much more deliquescent corrosion product, which reacted with air when removed from the flow-through system for weighing on the analytical balance. These findings assist in predicting iodine adsorption behavior on a variety of metal surfaces under various conditions.