Effects of corrosion and recovery processes on chloride-ion-selective electrode surfaces

Abstract

X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), ion scattering spectroscopy (ISS) and secondary-ion-mass spectrometry (SIMS) have been used to examine the composition of the visible corrosion layer formed on a chloride-ion-selective electrode (ISE) during exposure to a simulant solution containing dissolved Halon fire suppression by-products such as HBr. ISS depth profiling indicates that the Cl− is replaced by Br− forming a corrosion layer about 75 Å thick. Surface recovery of the ISE by aqueous hydrochloric acid etching has also been studied as a function of acid concentration and etchant contact time. Based on XPS data, the optimum etching parameters have been found to be 0.5 mol L−1 aqueous HCl and a contact time of 290 s. XPS, AES, ISS, and SIMS data indicate that the HCl etch removes most of the Br− in the near-surface region, thus providing an in situ means of regenerating chloride-ion-selective electrodes.