A CREVICE-FREE ELECTRODE ASSEMBLY FOR THE DETERMINATION OF REPRODUCIBLE BREAKDOWN POTENTIALS FOR STAINLESS-STEELS IN HALIDE ENVIRONMENTS

In the present study, a 316 wire loop electrode system has been shown to give good reproducible results in a variety of halide environments. An unusual feature of these results is the fact that under all experi mental conditions studied, the Br- ion is found to be considerably (ap prox. 200 mV) more aggressive than the Cl- ion in terms of oxide stabi lity. This trend is also maintained with steels 302 and 304L. The pres ence of SO(4)2- ions in the halide electrolyte does not alter this ord er, nor does chemical pre-treatment in acid solutions prior to pitting potential determinations. Pitting potentials measured for the 316 wir e loop samples are considerably more noble than those measured for sam ples of 316 cut from bar or sheet material. It is tentatively suggeste d that this order of oxide stability may be due to the superior abilit y of Cl- to adsorb at flaws in the developing oxide film, the wire loo p samples containing fewer such flaws.