Diffusion-controlled adsorption processes

Numerical solutions of differential equations for diffusion-controlled adsorption processes in spherical particles are presented for slow diffusion of gaseous molecules followed by rapid adsorption according to the Langmuir isotherm. As the parameter in the denominator of the Langmuir equation is increased the rate increases and the generalized rate curves shift progressively from that for the linear isotherm, the Langmuir parameter = 0, to the curve of the parabolic law. Adsorption and desorption cycles are considered and parameters are provided for relating any of these processes to the generalized curves. A simple linear equation was shown to approximate the rate curves with moderate accuracy.     

Activated extraction of coal using a hydrogen-donor solvent

The kinetics of the extraction of a high-volatile bituminous coal with 1,2,3,4-tetrahydronaphthalene (tetralin) under the influence of ultrasonic energy has been studied at five temperatures: from 47 to 87°C. The effects of intensity of ultrasonic energy, particle size, and hydrogen content of the coal were also recorded. Analysis of the results showed that a second-order reaction followed by a first-order reaction best describes the kinetics of the extraction process. The enthalpies of the second-order and first-order regions were respectively 8.7 and 2.5 kcal/mol, suggesting essentially physical control. The entropies were respectively ?44 and ?70 e.u. Auxiliary experiments and the kinetic data obtained suggest a model for the extraction process. The mechanism of the overall reaction is undoubtedly complex, but the data indicate that van der Waals and hydrogen-bonding forces are most affected by the ultrasonic energy, although stronger bonding is also affected giving much higher yields than would be expected. From the yields obtained in this study it is concluded that ultrasonic energy acts by rupturing bonds that are not affected by the solvent alone; the bonds affected are either strong hydrogen bonds or aliphatic covalent bonds, but not aromatic bonds.     

Decomposition of sec-butyl acetate on charcoal

The decomposition of sec-butyl acetate on de-ashed 20-to 30-mesh coconut-shell charcoal (1500 m²/g) was studied in a fixed bed reactor in the temperature range 300–375°C, and at partial pressures of 1 atm. and 0.29 atm. The ester decomposed principally to n-butene and acetic acid, and only small amounts of other products were found. The ratio of 1-butene to 2-butene was about 1:1, very close to that observed for thermal decomposition of the ester but far removed from the equilibrium butene ratio. The butene selectivity was independent of conversion. The rate of reaction followed the rate equation r = kA P_E/1 + AP_E This expression corresponds to surface reaction on one site being rate controlling. The activation energy of rate constant k was 32.7 kcal/mole, compared to 46.6 kcal/mole for the gas-phase reaction. The temperature dependence of adsorption constant A showed a heat adsorption of 12 kcal/mole. Gas chromatographic measurements confirmed this value and also showed that ester is the principal adsor-bate on the charcoal.     

Influence of molecular weight and molecular weight distribution on the tensile properties of amorphous polymers

Tensile property data for polystyrene samples of varying polydispersity are correlated with various parametric measures of molecular weight. Traditional measures of molecular weight, such as M?_n, M?_w, and M?_z, are shown to be unable to account for the variation of tensile properties with molecular weight. However, a new molecular weight parameter, termed the failure property parameter, is able to provide a single relationship between tensile strength and the parameter for both the broad and narrow distribution polymers. The form of this parameter is consistent with its having origins in the view that it is the entanglement network in an amorphous polymer that provides the observed strength properties. Specifically for polystyrene, the failure property parameter results indicate that material below 60,000 molecular weight does not contribute to polymer strength. Although the results of this investigation are specifically for polystyrene, the arguments used to develop the failure property parameter are not dependent on polymer chemical structure. Consequently, we believe that both the concepts and definition of this new parameter are applicable to all amorphous polymers.     

Raman Spectroscopy of Nanocrystalline Ceria and Zirconia Thin Films

The results of Raman-scattering studies of nanocrystalline CeO₂ and ZrO₂:16% Y (YSZ) thin films are presented. The relationship between the lattice disorder and the form of the Raman spectra is discussed and correlated with the microstructure. It is shown that the Raman line shape results from phonon confinement and spatial correlation effects and yields information about the material nonstoichiometry level.     

Undercooling,Freezing Point Depression,and Ice Nucleation of Soil Water

Certain aspects of the phenomena of undercooling and ice nucleation in soils are discussed with respect to recently established properties of phase boundary water in soils. Nucleation temperature as a function of water content is given for representative clays. In view of the fact that silicate surfaces seem always to be separated from ice by an interfacial layer of unfrozen, liquid like water a new concept of heterogeneous nucleation is outlined. It is proposed that ice nucleation occurs in the undercooled interfacial water layer at some distance removed from the particle surfaces. This concept, in effect, suggests that heterogeneous nucleation (nucleation of ice due to the influence of a substrate) in all its essential aspects may be only a special case of homogeneous nucleation (no substrate present) of water.     

Oxidation and reforming reactions of CH4 on a stepped Pt(5 5 7) single crystal

The oxidation and reforming kinetics of methane by O₂, CO₂ and H₂O were studied on a stepped Pt(5 5 7) single crystal from 623 to 1050 K under methane rich conditions. The rate of carbon deposition was followed by ex-situ Auger electron spectroscopy under non-oxidative conditions. The apparent activation energy for methane decomposition was significantly lower than the apparent barriers measured for both total oxidation, CO₂ and H₂O reforming. Total oxidation of methane to CO₂ and H₂O followed by combined dry and steam reforming (combined combustion-reforming) led to CO production rates which were higher than direct CO₂ or H₂O reforming rates. The enhanced rates are most likely due to the ability of adsorbed oxygen to prevent carbon nucleation and/or scavenge carbon enabling the reforming reaction to turnover on a larger fraction of sites. Comparable amounts of carbon were found by Auger electron spectroscopy measurements after both direct dry or steam reforming, while combined oxidation-reforming had considerable less carbon. During direct dry or steam reforming, CO₂ and H₂O serve only to scavenge adsorbed atomic carbon, while in the presence of oxygen, carbon is removed by both combustion and reforming routes.     

Creep and Stress Rupture Behavior of an Advanced Silicon Nitride: Part I, Experimental Observations

Cylindrical buttuohead specimens of an advanced silicon nitride were tested in uniaxial tension at temperatures between 1422 and 1673 K. In the range 1477 to 1673 K, creep deformation was reliably measured using high-temperature contact probe extensometry. Extensive scanning and transmission electron microscopy has revealed the formation of lenticular cavities at two-grain junctions at all temperatures (1422–1673 K) and extensive triple-junction cavitation occurring at the higher temperatures (1644–1673 K). Cavitation is believed to be part of the net creep process. The stress rupture data show stratification of the Monkman–Grant lines with respect to temperature. Failure strain increased with increase in rupture time or temperature, or decrease in stress. Fractography showed that final failure occurred by subcritical crack growth in all specimens.     

Removal of fatty soil from glass by surfactants and surfactant-builder compositions

Previous papers have reported radiotagged fatty soil removal from glass either by solvents or by aqueous solutions of sodium tripolyphosphate and other builders. This paper provies soil-removal data for aqueous systems of both pure and built surfactant compositions of the nonionic and alkylbenzene sulfonate types. In general, nonionics are the most effective detergents for the system fatty soil/glass; the 10-mole ethylene oxide adduct products show peak soil-removal. Nonionic surfactants appear most effective for soil removal when used in baths closely approaching their cloud-points. Though modification of hydrophobe by EO addition can affect cloud point, peak soil-removal effectiveness seems to be controlled by hydrophobe selection. Highest soil removal for the alkylbenzene series occurred with the longer alkyl chain (pentadecyl). Admixture of surfactant and sodium tripolyphosphate provided synergistic compositions with certain 10-EO surfactants. Building of anionics markedly improved soil removal over the pure material but seldom exceeded the removal by STP alone. Presented at 34th fall meeting, American Oil Chemists' Society, New York, October 17–19, 1960.     

Influence of a high‐head dam as a dispersal barrier to fish community structure of the Upper Mississippi River

In river systems, high‐head dams may increase the distance‐decay of fish community similarity by creating nearly impermeable dispersal barriers to certain species from upstream reaches. Substantial evidence suggests that migratory species are impacted by dams, and most previous studies in stream/river networks have focused on small streams and headwaters. Here, we assess whether a high‐head dam (Lock and Dam 19; LD 19) on a large river, the Upper Mississippi River (UMR), substantially alters fish community structure relative to variability expected to occur independent of the dam's effect as a fish dispersal barrier. Using fish catch per unit effort data, we modelled the distance‐decay function for the UMR fish community and then estimated the similarity that would be expected to occur across LD19 and compared it with measured similarity. Measured similarity in the fish community above and below LD19 was close to the expected value based on the distance‐decay function, suggesting LD19 does not create an abrupt transition in the fish community. Although some migratory fish species no longer occur above LD19 (e.g., skipjack herring, Alosa chrysochloris), these species do not occur in high abundance below the dam and so do not drive variation in fish community structure. Instead, much of the variation in species structure is driven by the loss/gain of species across the latitudinal gradient. Lock and Dam 19 does not appear to be a clear transition point in the river's fish community, although it may function as a meaningful barrier for particular species (e.g., invasive species) and warrant future attention from a management perspective.