Potentiometric chlorine gas sensor using BaCl2-KCl solid electrolyte: The influences of barium oxide contamination

The effects of BaO contamination on the behaviour of a Cl-2 gas sensor using a 0.97BaCl(2)-0.03KCl solid electrolyte have been investigated. The addition of BaO to the electrolyte is found to produce unfavourable effects on both the measuring and reference electrodes through a side reaction such as BaO + Cl-2 --> BaCl2 + (1/2)O-2. The presence of BaO in the vicinity of the measuring electrode results in decreases in the e.m.f. and rate of response, especially when the Cl-2 gas concentration is lowered to a few tens of ppm. Its presence near to the reference electrode, on the other hand, results in the upward deviation of the e.m.f. over the entire range of Cl-2 concentration. The probe prepared in vacuo, free of such BaO contamination, gives e.m.f. values in good agreement with the theoretical ones for Cl-2 gas concentrations between 10 and 1000 ppm, In contrast, the probe prepared in air shows a slower response as well as a more extensive deviation from theory in the low Cl-2 concentration range, suggesting that the electrolyte near the measuring electrode is contaminated with BaO.