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On the mechanism of H atom production in hot filament activated and gas mixtures
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Image of FIG. 1.
FIG. 1.

Plots showing the variation of with in vacuum (◇) and flows of He (◻) and (○) both maintained at . The inset shows the vacuum data (◇) recast in the form of Stefan–Boltzmann plot [Eq. (1)], demonstrating the expected dependence of .

Image of FIG. 2.
FIG. 2.

Plots showing the dependence of required to maintain a Re HF at (◻) and 2440 K (☆) and 2670 K (○) in . The solid curves are fits to the data in terms of Eq. (2) with values for , , and shown in the inset.

Image of FIG. 3.
FIG. 3.

dependence of required to maintain a Re HF in at (◻), 2440 K (☆), and 2670 K (○).

Image of FIG. 4.
FIG. 4.

dependence of required to maintain a Ta HF in at (◇), 2070 K (△), 2270 K (◻), 2440 K (☆), and 2670 K (○).

Image of FIG. 5.
FIG. 5.

dependence of required to maintain a Re HF in at (◻), 2440 K (☆), and 2670 K (○).

Image of FIG. 6.
FIG. 6.

(a) Plot showing dependence of the relative H atom density [H] measured at from a Ta HF in (◻) and 20 Torr (○), . (b) Van’t Hoff-like plot demonstrating the linear relationship between ln[H] and for the data shown in (a).

Image of FIG. 7.
FIG. 7.

Plot illustrating the variation of [H] with at from a Ta HF with . The trend lines are superposed simply to guide the eye. was adjusted to maintain values of 2270 K (◻) and 2440 K (☆).

Image of FIG. 8.
FIG. 8.

Cycles illustrating the effects of interrupting and reinstating a flow of in a total flow and on the properties and performance of a carburized Ta HF: (a) Variation of with maintained at 75 W (◻), (b) variation of required to maintain (○), and (c) variation in [H], measured by REMPI at , as a result of the changes shown in (b). The superimposed time bars indicate the presence (gray) or absence (white) of the 1% component to the total gas flow.

Image of FIG. 9.
FIG. 9.

Schematic energy profile for dissociative chemisorption of on a metal filament surface and for subsequent H atom desorption steps.

Image of FIG. 10.
FIG. 10.

Plot illustrating the dependences of the catalytic H atom production rate , the free site fraction , and the reaction rates (, 6, −5, −6) predicted by the gas-surface reaction mechanism rate coefficients listed in Table I for a bare Ta HF at .

Image of FIG. 11.
FIG. 11.

Plot illustrating the calculated dependences of the H atom concentrations (in ) and mole fractions at the surface and at from the surface of a bare Ta filament at .

Image of FIG. 12.
FIG. 12.

Van’t-Hoff-like plot showing the dependences predicted by the combined experimental-analytical approach [Eqs. (7), (8), (13), and (15)–(17)] for the H atom concentrations (in ) at the surface and at from the surface, the catalytic dissociation rate (in ), and the density of free surface sites (in ).


Generic image for table
Table I.

An optimized set of rate coefficients for the gas-surface reaction mechanism based on Eqs. (5) and (6) and a bare Ta HF.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: On the mechanism of H atom production in hot filament activated H2 and CH4/H2 gas mixtures