Robert A. Pierotti

Significant Structure Theory of Physical Adsorption

The significant structure theory of liquids has been modified to describe the physical adsorption of gases on homogeneous solids. Equations have been derived for the isotherm, the isosteric heat, and the critical properties. Good agreement with experiment is obtained for the systems Ar and Kr on graphite. The lack of mathematical rigor in the foundations of the significant structure theory is compensated for to a certain extent by its good results and its arithmetical and conceptual simplicity. Its departure from a rigorous foundation, however, makes it difficult to make improvements or to understand anomalies.The third‐order dispersion energy correction for molecules adsorbed on a solid as derived by Sinanoglu and Pitzer was used to determine the two‐dimensional lattice energy and the success of the present theory in predicting the heats of adsorption and the critical temperature is a measure of the validity of their work.

The adsorption of benzene on homogeneous substrates

Abstract Adsorption isotherms for benzene adsorbed on P33 (2700°) and on hexagonal boron nitride are reported at five temperatures in the range 0°C. to 50°C. The data span the submonolayer and multilayer regions. Isosteric heats of adsorption and equilibrium heats and entropies of adsorption are presented as a function of surface coverage. An estimate of the heat capacity change on adsorption is given. The data are discussed in relationship to previously reported data. The variation of the lateral interactions with respect to the adsorption potential is discussed.

Rare gas–graphite interaction potentials

The interaction of neon, argon, krypton, and xenon with the graphitized carbon black P33 (2700) is examined using the virial coefficient treatment of physical adsorption. Adsorption isotherm data in the low coverage, Henry’s law region are used to carry out this analysis. A modified Buckingham potential is selected to model the gas–solid interaction potential. A best fitting technique is used to make an unambiguous selection of the interaction potential parameters. A cubic power law decay is found to be the proper choice for the attractive portion of the potential, while the appropriate screening parameters for the exponential, repulsive portion of the potential are determined to be 0.0181, 0.0196, 0.0198, and 0.0215 (nm) for Ne, Ar, Kr, and Xe, respectively. The adatom–adsorbent internuclear separations are 0.307, 0.333, 0.336, and 0.366 (nm) and the gas–solid interaction energies are 384, 1113, 1467, and 1928 (°K) for Ne, Ar, Kr, and Xe, respectively. A surface area of 10.8±0.3 m2g−1 is obtained for the...

Physical adsorption of argon on boron nitride. A two‐surface analysis of high‐temperature adsorption data

A study has been made of the low‐coverage physical adsorption of argon on hexagonal boron nitride using a precision volumetric apparatus. Isotherms are reported at six temperatures in the range 198–273°K at surface coverages of less than about 3% of the BET monolayer volume. Electron micrographs indicate that two crystalline surfaces are exposed, corresponding to the basal plane and crystal edges. The isotherm data exhibit characteristics of adsorption on a slightly heterogeneous surface and are best‐fitted to an adsorption model in which a two‐energy surface is assumed. Adsorption is assumed to obey Henrys law on one surface and a submonolayer model isotherm on the other. Various models are used and compared and the data analyzed to yield values for the gas‐solid interaction energy and surface area for the two surfaces. Estimates are also given for the interaction energy of neon, krypton, and xenon with boron nitride. Comparisons are made between theoretical and experimental values for the interaction e...

High-temperature physical adsorption of argon, krypton, and xenon on hexagonal boron nitride

Abstract The interaction of argon, krypton, and xenon with hexagonal boron nitride was examined utilizing a two-surface gas—solid virial analysis. A precision volumetric apparatus was used to obtain 10 adsorption isotherms in the temperature range 273–368°K. The low coverage, Henrys law isotherm data were used to obtain values for the second gas—solid virial coefficients for ArBN, KrBN, and XeBN. The boron nitride adsorbent consists of higher energy edge sites and basal plane sites. A two-surface virial coefficient treatment was coupled with a graphical fitting technique to separate the effects of the two surface sites. Values of the inert gas-edge and inert gas-basal plane interaction energy are reported for each of the three adsorbates. Also, the surface area for the two surfaces and fraction of edge sites are reported. The results are compared with previous studies for these systems.

The adsorption of krypton on the (1,1,1) face of copper single crystals

Abstract Single crystals of copper were grown which displayed predominantly the (1, 1, 1) plane. The crystals were electropolished and characterized by acid etch patterns, X-ray back reflection orientation and topology techniques and by Auger electron spectroscopy. The crystals having a geometric surface area of 78 cm2 were specially mounted in a bakeable ultrahigh vacuum volumetric adsorption apparatus. Krypton adsorption isotherms were determined on these copper crystals at 78.9°, 91.2°, 98.6°, and 108.0°K. Pressures were measured using an MKS all-welded bakeable capacitance manometer. The isotherm data encompassed the very low coverage region, the monolayer region and for the two lower temperature isotherms a portion of the multilayer region. The low coverage isotherm data were analyzed in terms of the virial approach to physical adsorption. The gas-solid interaction parameter, ϵ 1s ∗ /k , was found to be 1678°K. The virial approach was found to yield reasonably good values of the surface area of the crystals. This is the first application of the virial approach to very small surface area samples. The intermediate coverage region was analyzed in terms of the significant structure theory of adsorption. The analysis yields a value of ϵ 1s ∗ /k of 1654 ± 50°K and a value for the lateral interaction parameter ϵ 1s ∗ /k of 48 ± 7°K. The high value of ϵ 12 ∗ /k and the unusually low value of ϵ 1s ∗ /k are in accord with quantum mechanical theories of many-body interactions involving metal substrates and with the results of the virial analysis of the low coverage data. Isosteric heats of adsorption were determined as a function of coverage. The zero coverage heat, qs10/R, was found to be 1770°K and the slope of the heat versus coverage curve in the monolayer region is about 270°K which is in agreement with the small value of ϵ 12 ∗ /k reported above.

Statistical thermodynamics of aerosols and the gas–solid Joule–Thomson effect

Due to the adsorption of a gas by a solid, it is expected that an aerosol created by dispersing a fine powder in a gas would have unique thermodynamic properties not found in pure or mixed gases. The virial equation of state associated with an aerosol dusty gas is obtained from statistical thermodynamic considerations. In the theoretical model presented here, the aerosol is considered to be a two component fluid made up of solid particles and gas molecules. The aerosol virial equation of state is used to derive an expression for the Joule–Thomson effect associated with a gas–solid dispersion. The magnitude of the gas–solid Joule–Thomson effect is expressed in terms of gas and gas–solid virial coefficients. Previous adsorption data for an argon–porous carbon system is used to obtain gas–solid virial coefficients and to predict the magnitude of the gas–solid Joule–Thomson effect. A significant enhancement of the Joule–Thomson effect is predicted for gas–solid systems which display a strong interaction. For ...

The gas-solid Joule-Thomson Effect

The magnitude of interaction of a gas with a solid is expected to cause an aerosol created by dispersing a fine powder in a gas to have unique thermodynamic properties not found in pure or mixed gases. The virial equation of state associated with a gas-solid aerosol or dusty gas is obtained from statistical thermodynamic considerations. The theoretical model of the aerosol is that of a two component fluid made up of solid particles and gas molecules. The aerosol virial equation of state is used to derive an expression for the Joule-Thomson effect associated with a gas-solid dispersion. The magnitude of the gas-solid Joule-Thomson effect is expressed in terms of gas-gas and gas-solid virial coefficients. Previous adsorption data for an argon-porous carbon system is used to obtain gas-solid virial coefficients and to predict the significant enhancement of the Joule-Thomson effect is predicted for gas-solid systems which display strong interactions. An apparatus was constructed to disperse a fine powder in a flowing gas and measure the thermal changes associated with a pressure drop across a glass orifice. The gas-solid Joule-Thomson effect was examined for 12 different gas-solid systems at a temperature of 302 K. Measurements for a series of aerosols composed of four different carbon adsorbents with argon, nitrogen and carbon dioxide confirm the effect and pose new questions. magnitude of the gas-solid Joule-Thomson effect. A

Solute-Solute Interactions in Dilute Solutions of Gases in Liquids

Equations are developed to extract in-solution solute-solute virial coefficients from gas-liquid phase equilibrium data. Experimental data for the solubility of helium, neon and hydrogen in liquid argon are analyzed and second virial coefficients for these solutes, B 2 * , in liquid argon are determined over the entire liquid range of argon from 84° to 148°K. The values of B 2 * are negative at the lowest temperature and approach zero or positive values as the critical temperature of argon is approached. The magnitude and temperature dependence of the virial coefficients are considered in terms of the reversible work of cavity formation and an effective local density.