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" Molecular properties controlling the adsorption of gases on solid surfaces "
M. B. Elmoselhi
C. A. Ward
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Latin Dissertation
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| Language of Document
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English
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| Record Number
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1112519
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TLpq303756752
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| Main Entry
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C. A. Ward
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M. B. Elmoselhi
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| Title & Author
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Molecular properties controlling the adsorption of gases on solid surfaces\ M. B. ElmoselhiC. A. Ward
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| College
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University of Toronto (Canada)
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| Date
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1988
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| student score
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1988
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| Degree
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Ph.D.
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| Page No
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1
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| Abstract
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A new quantum-statistical formulation for adsorbed molecules or atoms is presented. It allows one to derive the expressions for the thermodynamic properties, such as chemical potential, entropy and internal energy, in terms of molecular parameters. Thermodynamic relations are used to associate these parameters in a way which provides explicit expressions for the key adsorption quantities such as equilibrium isotherms and heats of adsorption. Moreover, the Statistical Rate Theory (27), with the derived expressions for chemical potentials, is used to analyze the kinetics of the adsorption process in terms of molecular parameters. This approach has been used to examine molecular adsorption of carbon monoxide on well defined crystal planes of Ni(1,1,1) and Ni(1,0,0), and polycrystalline surfaces that are known to be a mixture of both planes. The results have shown consistency in describing the measured equilibrium isotherms. The predicted dependency of the heat of adsorption on coverage is in good agreement with the calorimetric measurements. Moreover, a new type of energy level diagram has been obtained. The diagram indicates, quantitatively, the minimum energy levels for an atom or a molecule when transferred from the gas phase to the adsorbed phase on different planes of the solid crystal. The kinetics of the adsorption-desorption process are fully described in terms of equilibrium properties. The approach has been used to examine the dissociative adsorption of hydrogen on the same crystalline planes of nickel. It provides a new method to identify the rate limiting step in the sequence of processes leading to atomic adsorption. Adsorption isotherms for carbon monoxide and for hydrogen adsorbing on a deposited pure thin film of nickel were measured at 273K. The resultant molecular and atomic properties of the systems CO and H2 on each of Ni(1,1,1) and Ni(1,0,0) were used then to analyze the measured isotherms. The analysis predicted heats of adsorption that are in good agreement with calorimetric measurements for both systems. It also provided an estimate for the surface roughness factor (that is, the ratio between the actual microscopic surface area and the geometric area) of 1.17 0.1 for the polycrystalline surface.
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Applied sciences
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Mechanical engineering
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