Krypton Adsorption Research Articles

A kinetic and surface study of the thermal decomposition of cellulose powder in inert and oxidizing atmospheres

AbstractThe thermal decomposition of fibrous cellulose powder from 275° to 340°C has been studied by thermogravimetry, scanning electron microscopy, krypton adsorption, and gas‐chromatographic analysis of the gaseous products arising from pyrolysis in various oxidizing and inert atmospheres. The reaction kinetics fit a phase boundary model where the rate is controlled by the movement of an interface through a cylindrical particle and the principal kinetic parameters fit a compensation curve described previously for the decomposition of wood products. An explanation of the physical mechanism of pyrolysis is proposed which is consistent with the observed rate data and the structural changes observed by scanning electron microscopy.

Adsorption of krypton and xenon on zeolite NaX

1. The adsorption of krypton on zeolite NaX was measured in the pressure range from ∿0.1 Pa to ∿14 MPa and the temperature range from 120 to 600°K. The adsorption isosteres are linear in the entire range of studied temperatures and pressures. 2. The adsorption of xenon on the same zeolite was measured in the pressure range from 0.1 to 6 MPa and the temperature range from 370 to 600°K.

Physical adsorption of gases on graphitized carbon black

The Percus-Yevick equation of state is applied to a two-dimensional adsorbed fluid. Calculation of the adsorption isotherm is divided into two parts: the Henry's constant for gas-solid interactions, and the configurational contribution of the two-dimensional film. The theory is compared with experimental data for adsorption of argon and krypton on graphitized carbon black and agreement is excellent. This is the first successful calculation of adsorption isotherms over a wide range of temperature and surface density for which no adjustable parameters are used for the two-dimensional equation of state.

Krypton adsorbed on the graphite basal plane

A grand canonical Monte Carlo simulation of the submonolayer adsorption of krypton onto the basal plane of graphite has been executed. An adsorbed layer in registry with the substrate could not be maintained during any simulation run but some correlation between the adsorbate and adsorbent structure was observed.

Thermodynamic ratios in adsorption system: Krypton-zeolite NaX

1. The initial heat of krypton adsorption on zeolite NaX is 15.3 kJ/mole. 2. The partial molar enthalpy of the adsorbate under isosteric conditions increases with increase in the temperature. 3. The partial molar isosteric heat capacity of the adsorbate is independent of the temperature at small adsorption values, and increases with temperature at high adsorption values.

Alteration of zeolite granule dimensions under krypton adsorption

Dilatometer and adsorption measurements have established that there is a direct proportionality between the change in free energy of the vacancy solution and the relative alteration of the dimensions of the X type calcium and lanthanum ion exchange zeolite under krypton adsorption. Adsorption increases the value of the isotropic coefficient of compression of each of these zeolites by one order of magnitude.

Physical adsorption on patchwise heterogeneous surfaces. 2. Virial coefficient theory analysis of krypton adsorption on graphitized carbon black

Physical adsorption on patchwise heterogeneous surfaces. 2. Virial coefficient theory analysis of krypton adsorption on graphitized carbon black

Alteration of the linear dimensions of NaX zeolite granules under krypton adsorption

1. Study has been made of the isotherms for krypton adsorption on type X zeolites at −50, −93, and −120°C and the accompanying changes in the dimensions of the zeolite granule resulting from this adsorption. 2. For the adsorption of krypton on zeolite NaX at −93°C, the alteration of the zeolite granule dimensions and the differential heat of adsorption are similarly affected by changes in the degree of filling. 3. At low degree of filling, the contraction of NaX zeolites increases with rising temperature.

Adsorption of inert gases on NaCl: I. Adsorptive energy distributions obtained by a new numerical method

High specific surface area samples of sodium chloride are prepared by the electrostatic precipitation and filtration of an aerosol. The krypton and argon adsorption isotherms are measured at liquid nitrogen temperatures and analyzed by using a new numerical algorithm, HILDA. This uses an iterative procedure to determine the “patchwise” adsorptive energy distribution. Adsorption on unisorptic “patches” may be described by the Hill-de Boer, the Fowler-Guggenheim, or the Langmuir equation. The differences between the sodium chloride samples and the effects of annealing upon the surfaces are assessed using HILDA. The analysis also enables the monolayer capacity and hence specific surface area of a sample to be determined.

ChemInform Abstract: INVESTIGATION ON THE SURFACE STRUCTURE OF PRECIPITATED SILVER IODIDE SAMPLES BY KRYPTON ADSORPTION

Detailed experimental isotherms are presented for the adsorption of krypton on precipitated silver iodide samples at temperatures between 77.5 and 79.1 K. Analyses of the variation in surface heterogeneity between samples are presented using a new algorithm, HILDA. The results indicate that despite the presence of a number of homotattic areas attributable to different crystal faces, much of the surface represents a wide distribution of adsorption potentials, and hence heterogeneity.The results of isosteric heat determinations on one sample suggest that the Vm values derived from the HILDA analysis are too large, and that despite its theoretical limitations the B.E.T. method yields values of Vm that are more nearly in agreement with isosteric heat curve predictions.

The surface composition and energetics of type a graphite fibers

The surfaces of Hercules Type A PAN-based graphite fibers both treated (AS) and untreated (AU) were investigated using thermal desorption, krypton adsorption thermodynamics and ISS + SIMS techniques. Surface treatment enhanced the surface energetics of these fibers on 30% of the surface over the untreated fiber. In addition, the surface treatment increases the affinity of the fiber surface for adsorbed material by a factor of 8 over the untreated fiber surface. Surface spectroscopy has shown that one surface constituent is sodium which is present in very large concentration on these fibers.

The adsorption of krypton and xenon at low partial pressures on industrial samples of activated carbon

The adsorption of krypton and xenon at low partial pressures on industrial samples of activated carbon

Adsorption of krypton on the basal plane of graphite: LEED and Auger measurements

The adsorption of krypton on (0001) graphite has been studied by LEED and Auger. Stepwise isotherms are observed and thermodynamic quantities such as the latent heat of two dimensional adsorption and the binding energy of a krypton atom are determined. The mean free path of electrons in krypton is measured. The LEED pattern of the krypton layer shows a √3 × √3 superstructure. Some vibrational properties are examined by LEED and possible implications of the experimental findings are discussed. The potentials and limitations of the techniques used in the present work are critically examined with respect to other techniques.

Investigation on the surface structure of precipitated silver iodide samples by krypton adsorption

Detailed experimental isotherms are presented for the adsorption of krypton on precipitated silver iodide samples at temperatures between 77.5 and 79.1 K. Analyses of the variation in surface heterogeneity between samples are presented using a new algorithm, HILDA. The results indicate that despite the presence of a number of homotattic areas attributable to different crystal faces, much of the surface represents a wide distribution of adsorption potentials, and hence heterogeneity.The results of isosteric heat determinations on one sample suggest that the Vm values derived from the HILDA analysis are too large, and that despite its theoretical limitations the B.E.T. method yields values of Vm that are more nearly in agreement with isosteric heat curve predictions.

The adsorption of water vapour by lithium fluoride, sodium fluoride and sodium chloride

Water vapour adsorption isotherms have been determined volumetrically on samples of LiF, NaF and NaCl at 278.15, 288.15 and 298.15 K. The surface areas of the samples were determined by krypton adsorption at 77.5 K. Infrared measurements showed the presence of occluded solvents and complete removal of these species was effected under vacuum at the following temperatures; LiF, 823 K; NaF, 723 K; NaCl, 623 K. Except in the case of NaF, for which a BET Type II isotherm was obtained, the krypton isotherms exhibited single sharp steps at the following values of P P 0 ; LiF, 0.57; NaCl, 0.15. Similarly with water adsorption, the NaF and NaCl isotherms exhibited a single sharp step at the P P 0 values of 0.30 for NaF and 0.35 for NaCl. The isotherm for LiF outgassed at room temperature was of Type II, whilst for LiF outgassed at 673 K it was of Type III. Throughout the water runs no irreversible uptake was observed. The sharp steps in the krypton and water isotherms were attributed to phase transformations in the monolayer. Isosteric heats of adsorption for water vapour were generally invariant with coverage and close to the enthalpy of liquefaction of water. Theoretical adsorption potential energy calculations were carried out for adsorption of a water molecule above four sites on the (100) planes of the three adsorbents. The total adsorption potential was obtained as a sum of the dispersion, electrostatic, induction and repulsion interactions, and for each solid the most favourable adsorption site was above the cation. For adsorption directly above ions, the greatest contribution to the attractive potential was furnished by the electrostatic interaction. Except for the cation values of LiF and NaCl, the theoretical isosteric heats calculated from the potential curves were significantly lower than the experimental isosteric heats. All the samples possessed active sites depending on the adsorbate and outgassing temperature as follows; LiF (Kr, 298 K) 36%, LiF (Kr, 673 K) 15%, NaF (H 2O, 298 K) 18%, NaCl (Kr, 623 K) 20%, NaCl (H 2O, 623 K) 25%.

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

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 cm 2 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, q s1 0/ 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.

A study of the surface heterogeneity of an anatase sample

Krypton adsorption data for an anatase sample has been obtained at 77.5°K. Comparison has been made between the methods of Ross and Olivier and that of Adamson et al., of interpreting this data in terms of the concept of surface heterogeneity. Using the Hill-de Boer isotherm model in both cases results in comparable distributions, but not exact agreement. If, however, the Adamson method is used with the Langmuir isotherm model, a completely different distribution results, predicting higher adsorption energies. The distribution function obtained is therfore clearly dependent on the model isotherm equation adopted, and the introduction of terms into the mobile film model to account for translational energy barriers could alter the site energy distribution considerably.

Physical adsorption of nitric oxide on low and high energy surfaces

Stepwise isotherms for adsorption of krypton and nitrogen on barium fluoride at 77.5 K indicate a homogeneous surface. In contrast, isotherms for nitric oxide adsorbed on BaF 2 at 77.5 and 90.2 K are of BDDT Type I shape, with no indication of stepwise character. These results are discussed in terms of possible dimerization and adsorbate mobility, and are compared with adsorption on a “low energy” surface, i.e., polyvinylidene chloride (PVDC). Nitric oxide on PVDC at 77.5 and 90.2 K gives shallow Type II isotherms, with corresponding values of the isosteric heat of adsorption close to the value of the enthalpy of sublimation of NO. The initial heats of adsorption for NO on PVDC are consistent with dimerization of the adsorbate. The effective molecular cross-sectional areas of NO, found from comparison with nitrogen BET monolâyer amounts, were 0.10 nm 2 on BaF 2 and 0.125 nm 2 on PVDC. Semiempirical calculations of isosteric heats of adsorption are discussed.

The effect of exchanged cations and heat treatment on the adsorption of carbon monoxide, nitrogen, argon, and krypton on amorphous silica-alumina cracking catalysts

Adsorption isotherms for CO, N 2, Ar, and Kr were measured over the temperature range −50–250 °C over a pressure range of 2–350 Torr on exchanged and unexchanged silica-alumina cracking catalysts that had been evacuated at 250, 450, and 800 °C, respectively. Isosteric heats of adsorption were calculated at surface coverages ranging from 0.1 to 1%. When the samples were evacuated at 250 °C, the adsorption of CO was increased by a factor of about 3.5 when the exchanged cations were Ca and Ba and about 50% for K cations and also for ions of La and Mg. The influence of cations became even greater when the samples were evacuated at 450 °C, the adsorption for the samples exchanged with cations being three times as great on specimens evacuated at 450 °C as for samples evacuated at 250 °C. Evacuation of samples at 800 °C caused the adsorption of CO on the H form of the sample to be substantially the same as for the ones exchanged with calcium ions. The isotherm for the Ca exchanged specimen was substantially the same as for the sample evacuated at 450 °C. Isosteric heats of adsorption in general were highest for La and Ca exchanged samples, somewhat lower for those exchanged with K and least for those containing protons on the exchange sites. However the heats of adsorption on samples evacuated at 800 °C approached 15 kcal/mole of CO both for samples exchanged with Ca ions and for the protonic samples. Corresponding heats of adsorption of nitrogen were in the range of 7–9 kcal/mole of N 2. Heats of adsorption of argon and krypton remained down in the range of 2.5–3.5 kcal/mole for all samples, and were not much influenced by the temperature of evacuation or the exchange of ions on the catalyst surface. The molecules for which the big changes in adsorption with temperature of evacuation and ion exchange of samples were noted were carbon monoxide and nitrogen, both of which have rather high quadrupole moments.

The interaction of krypton and an exfoliated graphite at 77.4 K

An exfoliated graphite sample was prepared having a significant increase in basal plane area over the original highly ordered pyrolytic graphite crystal. The boundary planes of the expanded sample appeared intact and were highly reflective. The krypton adsorption at 77.4 K was at first linear with P P o , then reached a plateau over the range from 0.45 to 0.65, and then increased uniformly to P P o of 0.99, where p is pressure and p 0 is the sublimation vapor pressure of solid krypton. Each desorption branch initiated from several levels of adsorption decreased only slightly to the lowest pressures measured ( P P o ∼ 0.01 ). A model is proposed in which the adsorption process is concomitant with a contraction between adjoining graphite lamellae.