Mass transfer kinetics in lithium-stainless steel systems

Austenitic stainless steels have been studied using lithium thermal-convection loops that allow periodic specimen examination without significantly disrupting the lithium flow. Weight change measurements were made as a function of exposure time to characterize the reaction kinetics of both the dissolution and deposition processes. A power curve law was found to accurately describe the weight loss and gain behavior over the entire exposure interval whereas both power curve and straight line fits adequately reflected the weight changes as a function of time at longer exposures. However, weight changes ultimately approached a steady state, in which the dissolution and deposition rates are constant (that is, the weight changes were linearly proportional to exposure time). An Arrhenius analysis of the dissolution rates from a loop experiment in which the maximum loop temperature was varied while the ..delta..T remained fixed yielded an apparent activation energy consistent with a phase boundary reaction as the rate determining step. Determination of steady-state deposition rates for the long-term loop experiments showed that the maximum rate of weight gain was generally not at the minimum temperature specimen position.