INVESTIGATION OF THIOSULFATE ADSORPTION ON 316-STAINLESS-STEEL IN NEUTRAL SOLUTIONS BY RADIOACTIVE LABELING, ELECTROCHEMISTRY, AND AUGER-ELECTRON SPECTROSCOPY

We report on thiosulfate adsorption on a 316 stainless steel electrode in neutral solutions by radiochemical, electrochemical, and Auger ele ctron spectroscopy (AES) measurements. In contrast to previous work on thin metal films or metal electrodeposits to model real-life metal (a lloy) samples, our radiochemical approach permits coverage measurement s of labeled adsorbates on smooth solid electrodes of convenient size and thickness. A dedicated electrode preparation yields a reproducible surface for fast and reversible thiosulfate adsorption from a perchlo rate solution. However, on the same time scale, reversible adsorption is impeded in sulfate media. Further, no thiosulfate adsorption occurs in berate buffer solution, and complex thiosulfate adsorption behavio r predominates in solutions containing varying amounts of chloride ani ons, initially increasing with bulk chloride concentration, maximal at 10(-4) to 10(-5)M Cl-, and decreasing at higher chloride concentratio n. We conclude that small amounts of surface chloride assist the thios ulfate adsorption, but increasing surface Cl- coverage becomes competi tive to that of thiosulfate. The chloride adsorption enhancing mechani sm probably results from a destabilization of the locally ordered thio sulfate surface structure. Radiochemistry and AES show that long expos ure to thiosulfate solutions results in permanent thiosulfate immobili zation on the stainless steel surface.