An investigation of the attack of platinum and tungsten by Iodine

Abstract

The reactions which are most likely to prove fruitful in elucidating the mechanism of heterogeneous gas reactions are those involving gases having a simple molecular structure, and an investigation was therefore begun by studying the attack of platinum by oxygen at low pressures, as reported in a previous communication. These investigations have now been extended to the reactions of platinum and tungsten with iodine vapour at low pressures. A marked difference in the behaviour of the two metals was to be anticipated from several considerations, firstly, tungsten is much more readily attacked by oxygen than is platinum, and secondly, the effect of iodine on the thermionic emission is different for the two metals. Kalandyk observed that the emission from platinum was greatly enhanced by iodine vapour, whereas Langmuir found that iodine had no influence on the emission from tungsten. The difference in the case of oxidation was accounted for in terms of the large difference in the work functions of the two metals. The thermionic data show that the adsorption of iodine on platinum is stronger than on tungsten, and this can also be ascribed to the difference in the work functions.