Chemisorption of Electronegative Gases on Refractory Metals

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Abstract
This experiment is a study of some aspects of the chemisorption of diatomic gases on metal surfaces for temperatures of 1800°—2200°K and pressures of 4.0–6.0×10−6 torr. The systems studied were chlorine and carbon on tungsten where the carbon was present as a contaminant, and chlorine and hydrogen chloride on hafnium. We observed the flux of atomic negative ions formed from the dissociated gases on the surfaces as functions of temperature concurrently with the thermionic electron flux from the same surfaces. From these data we calculated work functions and sticking probabilities, using the Saha—Langmuir equation. For tungsten, we find that the sticking probability of chlorine was about 4×10−3 and tended to decrease with increase in temperature. The increment in work function was about the order of the experimental uncertainty, 0.50 eV. For hafnium the sticking probability was about 1×10−2 for both chlorine and hydrogen chloride and tended to increase with temperature, especially in the presence of oxygen at a partial pressure of 5×10−6 torr. This temperature dependence we have interpreted as an indication of a contaminated surface. The work function was not noticeably changed by chlorine or hydrogen chloride. Introduction of oxygen into the system caused the work function to increase noticeably.