COMPUTERIZED SIMULATION OF SILVER AGGREGATION AND CORROSION IN POLYMERIC MEMBRANES

The dynamics of silver aggregation induced by pulse radiolysis in a microheterogenous system have been simulated so as to describe more quantitatively the various processes here involved which have been described in the preceding paper. The ion-exchange membrane is modeled as a network of hydrophilic cavities linked by narrow channels. Adjustment of calculated and experimental values in single or repetitive pulse regimes yields an overall aggregation rate constant k'agg = 5 x 10(4 +/- 1) L.mol-1.s-1. The aggregation process is mostly controlled by the diffusion through the channels (i.e., k'diff congruent-to k'agg), the diffusion being itself restricted to aggregates of nuclearity n less-than-or-equal-to 5 +/- 1 atoms per aggregate. As a matter of fact, both values should depend on the swelling factor. The values given above concern the case where this factor has the lowest value (see Table I of ref 1). During the coalescence, the smallest aggregates undergo a slow corrosion by surrounding H3O+, provided their nuclearity n is less-than-or-equal-to 8 +/- 2 atoms per aggregate. The lower the end-of-pulse stock of silver atoms, the greater the phenomenon. The rate constant of the corrosion of a small silver aggregate is found to be not diffusion-controlled and is equal to k'corr = (5 +/- 3) x 10(-1) L.mol-1.s-1 up to n = 8 +/- 2. No corrosion is observed any longer beyond that value.