Sam S.‐S. Huang

Electron mobilities in gaseous, critical, and liquid xenon: Density, electric field, and temperature effects: Quasilocalization

The mobility μ of electrons in xenon varies with the density n : μαnx. For thermal electrons in the gas, x=−1.0 when n<4×1020 molecule/cm3, independent of temperature. This corresponds to pressures ≲20 atm at 300 K and is characteristic of simple scattering by a polarization field. At higher gas densities x becomes more negative, then passes through a minimum, and μ has a positive temperature coefficient at constant n. At these densities thermal electrons form quasilocalized states in, or suffer enhanced scattering by, microscopic regions of relatively high density. The localization effect maximizes in the critical fluid, at n=5×1021 molecule/cm3 and T=290 K, and appears to be negligible again at n?6.8×1021. In the liquid phase x?+9 up to n=1.2×1022 molecule/cm3, then changes to x?−8 at higher densities. The positive value of x is due to the formation of a conduction band, and the negative value to scattering by the repulsive cores of the closely spaced atoms. In the gas and the low density liquid (n<1.2×...

The phase behavior of two mixtures of methane, carbon dioxide, hydrogen sulfide, and water

Abstract The behavior of two mixtures of CH 4 , CO 2 , H 2 S and H 2 O was studied over a temperature range from ≈37.8° to 204°C at pressures in the 0.4–18.5 MPa range. The work was carried out to determine the composition of the equilibrium phases over a range of experimental conditions within the two- or three-phase envelope for each mixture, and to determine the two- and three-phase boundaries for each mixture within the temperature and pressure range of the study. A variable volume equilibrium cell consisting of a transparent sapphire cylinder was used for the experimental measurements and observations.

Ion and electron mobilities in cryogenic liquids: Argon, nitrogen, methane, and ethane

Ion mobilities at low fields have been measured over the entire liquid range in argon, nitrogen, and methane. Gas‐phase values for argon and nitrogen are also given. Comparison of the ratio of electron to ion mobilities confirmed that the electron remains nearly free in argon and methane liquids but is an anion in liquid nitrogen. At T≲116 K, the product of viscosity and either cation or anion mobility is constant in liquid nitrogen under its vapor pressure. At T>118 K, an abrupt destabilization of the anion in the low density liquid occurs; the breakdown strength of nitrogen should sharply decrease. The utility of breakdown studies in liquid ethane and propane in bridging studies of cryogenic inorganic liquids to studies of normal liquid hydrocarbons is discussed.

Electron transport in gaseous, critical, and liquid benzene and toluene

Electron mobilities μ in the low density gases are independent of electric field strength up to ≳4 Td in benzene and ≳5 Td in toluene. The ratio of the threshold drift velocity (for electron heating) to the speed of low frequency sound in the gas, vd (threshold)/co, is ≳40 in benzene and ≳50 in toluene. The ratios are ≳3 fold higher than those in the saturated cyclic hydrocarbons cyclopentane and cyclohexane. The aromatic molecules have larger inelastic scattering cross sections than do the cycloalkanes for thermal energy electrons. The total scattering cross sections of benzene and toluene each have a minimum for electrons of ∼0.3 eV energy. The value of the total cross section averaged over a Maxwellian energy distribution at 300 K is 82 A2 for benzene and 87 A2 for toluene. A plot of μn against density n for the coexistent vapor and liquid is horizontal at n<1×1020 molecule/cm3 in each vapor, slopes negatively to a minimum at n?1−2×1021, increases to a maximum at n?3×1021 (n/nc=1.5), then plunges as th...

Comparison of transition from low to high density transport behavior for ions and neutral molecules in simple fluids

For cation mobility μ in several simple fluids, the transition from normal gas to liquid type behavior occurs in the density region 0.5≲n/nc≲1.9, which corresponds to the viscosity region 0.6≲η/ηc≲2.5. The subscript c refers to the critical fluids and the other fluids are the coexistence vapor and liquid. The fluids range from monatomic to polyatomic molecules: Ar, Xe, N2, CH4. The semihydrodynamic equation provides a reasonable interpretation of the variation of ημ, or the equivalent ηDe/kT for neutral molecules, with η only in the normal gas regime, where n/nc<0.4 and η/ηc<0.5. Under these circumstances, nμ or nDe/kT is nearly constant. In calculating the polarization interaction contribution to the ion scattering cross section, the largest axis of polarizability of the molecule should be used. As n (or η) increases in the region 0.6<n/nc<1.6 (or 0.7<η/ηc<1.9) the value of nμ (or ημ) increases by ∼60%, whereas nDe/kT (or ηDe/kT) for neutral molecules decreases by ∼20%. The ratio (De/kTμ)n has values 5–6...

The gravity effect and the mobility of electrons in critical neopentane

The rapid change of density with temperature, the high compressibility of the vapor and liquid near the critical region, and the force of gravity make it difficult to avoid a density gradient in the ’’critical fluid’’. Electron mobilities were measured simultaneously in the juxtaposed vapor and liquid so that density changes could be monitored. The mobility in neopentane at the critical density and ∼0.1 K above Tc is 45 cm2/V s; the estimated mobility in the critical fluid is 42 cm2/V s. The effect of electric field strength on the mobility changes sign at the reduced density and temperature n/nc=1.2 and T/Tc=0.995. The reversal is attributed to the Ramsauer–Townsend scattering minimum occurring at an energy slightly above thermal at this density.

Positive ion mobilities in gaseous, critical, and liquid hydrocarbons: Density and temperature effects

Cation mobilities μ+ in liquid hydrocarbons do not obey Walden’s rule (μ+∝η−1.0). Their relationship with the solvent viscosity η is μ+∝η−1.2±0.1, as found earlier for ions in ethers. Ion migration in liquids made up of nonspherelike molecules is more closely linked to solvent molecular rotation than to shear viscosity. Dipole (permanent or induced) rotation is required during ionic displacement to minimize changes in polarization energy. Diffusion coefficients D of ions in liquid n‐hexane are twofold lower than the self‐diffusion coefficient of the hexane molecules over most of the liquid range. There is a cusp in the ratio D (molecule)/D (ion) at the critical point. The lower diffusion coefficient of the ion is attributed to its probable dimeric size and to electrostrictive drag. Mobilities in the critical fluids are 4.3, 5.0, and 5.6 (10−3 cm2/Vs) in cyclopentane, cyclohexane, and n‐hexane, respectively. In the gas phase along the gas–liquid coexistence curve, the density normalized mobilities μ+n are ...

Vapor-liquid equilibrium in selected aromatic binary systems: m-xylene-hydrogen sulfide and mesitylene-hydrogen sulfide

Abstract Huang, S.S.-S. and Robinson, D.B., 1984. Vapor—liquid equilibrium in selected aromatic binary systems: m-xylene—hydrogen sulfide and mesitylene—hydrogen sulfide. Fluid Phase Equilibria, 17: 373–382. Vapor and liquid equilibrium phase compositions have been determined for the m-xylene-hydrogen sulfide and mesitylene—hydrogen sulfide binary systems at temperatures of 310.9, 352.6, 394.3 and 477.6 K and at several pressures from the vapor pressure of the less volatile component to the vapor pressure of hydrogen sulfide or to the critical pressure for the system, whichever was higher. The data have been used to calculate equilibrium ratios for each of the components in the binary systems. The results of Eakin and DeVaney (1974) for the mesitylene—hydrogen sulfide system at 310.9 and 477.6 K are also included for comparison. The data presented are useful in evaluating the properties of condensate reservoir fluids containing hydrogen sulfide and aromatic compounds.

Ionization of liquid argon by x-rays: Effect of density on electron thermalization and free ion yields

Free ion yields were measured in liquid argon as a function of electric field strength at densities 736–1343 kg/m3 (temperatures 149–195 K). The field dependence of the yields was parametrized using the extended Onsager and box models. Over the present density range the total ion yield was constant within 1% and was taken as 4.4, the average of earlier values at 87–91 K. The absence of internal vibrational modes in argon makes its electron thermalizing ability smaller than that of methane. The electron thermalization distance bGP in liquid argon is 3–5 times longer than that in liquid methane at a given ddc(dc = critical fluid density).