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Average Radius (average + radius)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Perovskite oxide absorbents for oxygen separation

AICHE JOURNAL, Issue 12 2009
Yufeng He
Abstract The fixed-bed oxygen absorption processes of the series of Ba1,xSrxCo0.8Fe0.2O3,, oxides were studied by oxygen partial pressure swing absorption in the temperature range of 300,850°C. The results show that SrCo0.8Fe0.2O3,,, with the smallest A-site ion radius, has the largest oxygen absorption capacity (0.402 mmol/g) at 500°C. The oxygen absorption and desorption kinetics fit well with the pseudo-second-order kinetics model. Comparing the modeling absorption rate coefficient k2 with the desorption rate coefficient k2,, all the oxides studied had higher oxygen absorption rates than oxygen desorption ones. In addition, the combined results of X-ray diffraction analysis, O2 -TPD, room temperature iodometric titration, and thermogravimetric analysis explained the relationship between the oxygen absorption capacities and the average radii of the A-site ions for this series of Ba1,xSrxCo0.8Fe0.2O3,, in the temperature range of 300,600°C. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

X-ray computed tomography of peat soils: measuring gas content and peat structure

HYDROLOGICAL PROCESSES, Issue 25 2008
Nicholas Kettridge
Abstract The potential of using X-ray computed tomography (CT) to (i) analyse individual biogenic gas bubbles entrapped within peats and (ii) produce reliable descriptors of peat structure is examined. Existing approaches used to study biogenic gas bubbles measure the gas content of volumes of peat many orders of magnitude larger than most bubbles, and are, therefore, of little use in helping to understand bubble dynamics. In many peatland studies, the description of peat structures is derived from only a few relatively basic metrics; principally the porosity, the bulk density, and the von Post humification scale. CT is applied to identify and quantitatively analyse the size, location and shape of individual gas bubbles entrapped during the saturation of a 200 cm3 sample of S. fuscum. 3421 gas bubbles were identified, ranging in size from 0·1 mm3 to 99·9 mm3. These gas bubbles were non-randomly distributed, clustered predominantly in the vertical plane. When analysing the peat structure, Sphagnum peat and water are shown to be indistinguishable within CT scans. Peat samples were therefore prepared prior to scanning by flushing the peat with lead (II) nitrate solution to increase the linear attenuation of the Sphagnum. Sphagnum stems and branches were analysed, producing metrics of the peat structure; including stem and branch lengths, radii and orientation. In a 100 cm3 sample of S. magellanicum, the length of all Sphagnum stems totalled 1·82 m, with an average radius of 0·65 mm. The Sphagnum stems and branches were both preferentially orientated in the horizontal direction. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Structure of PbTe(SiO2)/SiO2 multilayers deposited on Si(111)

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2010
Guinther Kellermann
The structure of thin films composed of a multilayer of PbTe nanocrystals embedded in SiO2, named as PbTe(SiO2), between homogeneous layers of amorphous SiO2 deposited on a single-crystal Si(111) substrate was studied by grazing-incidence small-angle X-ray scattering (GISAXS) as a function of PbTe content. PbTe(SiO2)/SiO2 multilayers were produced by alternately applying plasma-enhanced chemical vapour deposition and pulsed laser deposition techniques. From the analysis of the experimental GISAXS patterns, the average radius and radius dispersion of PbTe nanocrystals were determined. With increasing deposition dose the size of the PbTe nanocrystals progressively increases while their number density decreases. Analysis of the GISAXS intensity profiles along the normal to the sample surface allowed the determination of the period parameter of the layers and a structure parameter that characterizes the disorder in the distances between PbTe layers. [source]

Determination of molar mass and solution properties of cationic hydroxyethyl cellulose derivatives by multi-angle laser light scattering with simultaneous refractive index detection

POLYMER INTERNATIONAL, Issue 10 2009
Wei Gao
Abstract BACKGROUND: A complete understanding of the molar mass and solution properties of raw materials in bio/pharmaceutical products under bio-application and natural conditions ensures process control, product performance and quality. Biopolymers including polymeric cationic hydroxyethyl cellulose derivatives (e.g. Polyquaterium-10 or Polymer JR) have long been used in health care formulations including shampoos, lotions, eye drops and contact lens multi-purpose solutions. Previously reported molar masses and conformation of Polymer JR were based on size exclusion chromatography-related techniques, which required highly concentrated buffered salt solutions and organic solvent modifiers to prevent undesirable interactions, and did not represent the isotonic conditions in products and applications. RESULTS: This paper describes the characterization of Polymer JR in saline using a new approach that combines micro-batch mode multi-angle laser light scattering with simultaneous refractive index measurements (MB-MALLS-RI). Mass-average molar mass, z -average radius of gyration and second virial coefficient values in phosphate buffer saline (PBS) were obtained and are discussed in detail. CONCLUSION: The molar mass and solution properties of Polymer JR in PBS, with the same pH and ionic strength as most health care solution products, can be characterized using the MB-MALLS-RI technique. The approach is practical and can be widely used for the analysis of other cationic biopolymers. Copyright © 2009 Society of Chemical Industry [source]

Chain stiffness of heteropolysaccharide from Aeromonas gum in dilute solution by dynamic light scattering

BIOPOLYMERS, Issue 6 2002
Xiaojuan Xu
Abstract Dynamic light scattering measurements have been made on 15 fractions of aeromonas (A) gum, an extracellular heteropolysaccharide produced by the strain Aeromonas nichidenii, with dimethylsulfoxide containing 0.2M lithium chloride as the solvent at 25°C. Data for the translational diffusion coefficient D covering a molecular weight range from 4.5 × 105 to 2.1 × 106 and ratios of the z -average radius of gyration ,s2,z1/2 to the hydrodynamic radius RH (calculated with previous ,s2,z data) suggest that the polymer behaves like a semiflexible chain in this solvent similar to the stiffness of cellulose derivatives. Thus the D data are analyzed on the basis of the Yamakawa,Fujii theory for the translational friction coefficient of a wormlike cylinder by coarse-graining the heteropolysaccharide molecule. Excluded-volume effects are taken into account in the quasi-two-parameter scheme, as was done previously for ,s2,z and [,] (the intrinsic viscosity) of A gum in the same solvent. The molecular weight dependence of RH is found to be explained by the perturbed wormlike chain with a persistence length of 10 nm, a linear mass density of 1350 nm,1, an excluded-volume strength parameter of 1.3 nm, and a chain diameter of 2.8 nm. These parameters are in substantial agreement with those estimated previously from ,s2,z and [,] data, demonstrating that the solution properties (D, ,s2,z, and [,]) of the heteropolysaccharide are almost quantitatively described by the current theories for wormlike chains in the molecular weight range studied. © 2002 Wiley Periodicals, Inc. Biopolymers 65: 387,394, 2002 [source]