Interaction of Hydrogen with Tungsten
Measurements were made, under ultra-high vacuum conditions, of the rates and isotherms for the adsorption of hydrogen on tangsten, the rate of desorption of hydrogen from tungsten, and the rate of formation of atomic hydrogen by an incandescent tungsten filament. When hydrogen chemisorbs on tungsten at 77 deg , the sticking probability is 0.1 and two distinct states of binding, alpha and beta , naay be isolated at adsorption pressures as low as 2.5 x 10/sup -9/ mm. Analysis of desorption kinetics of the most tightly bound state, beta , revealed that hydrogen chemisorbs as atoms since evaporation is second order in adsorbed hydrogen. For n/sub beta / < 30 x 10/sup 12/ molecules/cm/sup 2/, v/sub M/ = (5 x 10/sup -3/)n/sup -2/ exp(- 31,000/RT) molecules/cm/sup 2/-sec. At higher coverages, a decrease in heat of desorption was observed, which is due to surface heterogeneity. At equilibrium, the a1aouri adsorbed in the beta state obeyed a Ternkin isotherm between 273 and 373 deg K; evaporation of hydrogen in the beta state occurred down to temperatares as low as 77 deg K. Isosteric heats agreed with heats derived from desorption measurements. The alpha state, populated before the beta state is saturated at 77 deg K, was found proportional to hydrogen pressure and probably consists of molecular hydrogen on top of the primary atomically chemisorbed layer. The rate of evaperation of atomic hydrogen when the filament temperature was raised above 1100 deg K was v/sub A/ = (2.2 x 10/sup 13/)n exp(-- 67,000/ RT) molecules/cm/sup 2/-sec. For pressures below 10/ sup -7/ mm and filament temperatures above 1475 deg K, the fraction of molecules striking the filament surface that is dissociated was constant and at least 0.05. Values of surface coverage and the rate of formation of atomic hydrogen as a function of filament temperature and hydrogen pressure were derived from experimental data.
- Research Organization:
- General Electric Research Lab., Schenectady, N.Y.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-14-012558
- OSTI ID:
- 4175891
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 3 Vol. 32; ISSN JCPSA6; ISSN 0021-9606
- Publisher:
- American Institute of Physics (AIP)
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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