Surface Layer Of Particles Research Articles

Characteristics of nanopowders produced by electrical explosion of tin-lead alloy conductors in air

The article discusses the investigations into the phase and chemical composition of nanopowders produced upon electrical explosion of conductors made of tin-lead alloy (POS-61) in air. It is demonstrated that, in the course of electrical explosion and subsequent cooling of the dispersion products, there occurs a slight enrichment (by 3–6 at %) of the surface and subsurface layers of the powder particles with lead in comparison with its content in the initial alloy.

Polymeric three-layered particles for the delivery of prednisolone to the lower gastrointestinal tract in rats

Background: The aim of this study is to investigate the feasibility of three-layered particles as a drug delivery system to the lower part of small intestine. Methods: The particle surface and basement layers were made of enteric polymer, Eudragit® S100, and water-insoluble polymer, ethylcellulose. Prednisolone (PSL), as a model drug, was sealed with the surface and basement layers. After the administration of the test preparations to the duodenum of rats, blood samples were collected and plasma PSL levels were measured by high-performance liquid chromatography. The retention and transit characteristics of the three-layered particles in rat small intestine were studied by direct observation after abdominal incision up to 8 hours. Results: Three-layered PSL particles showed Cmax of 0.32 ± 0.07 μg/mL and Tmax at 6 hours, whereas the mean Cmax and Tmax of PSL powder, as a reference preparation, were 0.42 ± 0.03 μg/mL and 1 hour, respectively. With the direct observations, after administration of particles, about 77.5% of them were detected in duodenum at 1 hour, 45% in distal jejunum at 3 hours, and 50% in proximal ileum at 4 hours. Then, they were gradually transferred to the lower part of the small intestine at 5–8 hours time intervals. In comparison with PSL powder, three-layered particles delayed the intestinal transit and released PSL during their passage through the small intestine. Conclusion: These results suggested that three-layered particles adhered to the gastrointestinal mucosa and sustained the release of drug, resulting in drug delivery to the lower part of gastrointestinal tract.

An analytical solution to calculate bulk mole fractions for any number of components in aerosol droplets after considering partitioning to a surface layer

Abstract. Calculating the equilibrium composition of atmospheric aerosol particles, using all variations of Köhler theory, has largely assumed that the total solute concentrations define both the water activity and surface tension. Recently however, bulk to surface phase partitioning has been postulated as a process which significantly alters the predicted point of activation. In this paper, an analytical solution to calculate the removal of material from a bulk to a surface layer in aerosol particles has been derived using a well established and validated surface tension framework. The applicability to an unlimited number of components is possible via reliance on data from each binary system. Whilst assumptions regarding behaviour at the surface layer have been made to facilitate derivation, it is proposed that the framework presented can capture the overall impact of bulk-surface partitioning. Demonstrations of the equations for two and five component mixtures are given while comparisons are made with more detailed frameworks capable at modelling ternary systems at higher levels of complexity. Predictions made by the model across a range of surface active properties should be tested against measurements. Indeed, reccomendations are given for experimental validation and to assess sensitivities to accuracy and required level of complexity within large scale frameworks. Importantly, the computational efficiency of using the solution presented in this paper is roughly a factor of 20 less than a similar iterative approach, a comparison with highly coupled approaches not available beyond a 3 component system.

IR spectroscopic study of surface properties of amorphous water ice

The state of the surface of amorphous ice with a specific surface area of about 160 m2/g obtained by the condensation of water vapor at 77 K is studied by IR spectroscopy. As the temperature increases to 130–160 K, absorption bands of surface hydroxyl groups vanish, whereas changes in bands characteristic of hydroxyl groups in the bulk of ice are indicative of a phase transition of ice from amorphous to the polycrystalline structure. The surface sites of amorphous ice are characterized with low-temperature adsorption of carbon monoxide. It is shown that there are two types of CO adsorption sites, free hydroxyl groups and oxygen atoms of surface coordinately unsaturated water molecules. Upon adsorption of nitrogen, methane, and carbon monoxide, in addition to the perturbation of surface OH groups, reversible changes in the spectrum are observed in the region of vibrations of bulk hydroxyls, which indicate that the strength of hydrogen bonds between water molecules in the surface layer of icy particles increases approaching the strength of these bonds in the crystal and that the ice surface becomes less amorphous. These results indicate that the properties of the ice surface layer substantially depend on the presence of adsorbed molecules.

Comparative study of the structure of products of plasma modification of globular and fibrillar proteins

The molecular-mass distribution and amino acid composition of globular (albumin, lysozyme) and fibrillar (collagen) proteins subjected to treatment in electron-beam plasmas of various gases were experimentally studied. The samples were treated in the forms of powders and freeze-dried thin films. The electron-beam plasma treatment of powdered collagen resulted in the formation of low-molecular-mass compounds only. The modification of albumin and lysozyme was accompanied by polymerization of the proteins against the background of insignificant degradation. The plasma-stimulated processes occurred in the surface layer of powder particles, whereas the bulk of the sample remained intact. The degradation and polymerization processes in thin films of globular proteins occurred throughout the entire volume of the sample.

Effect of different modification agents on hydrogen-generation by the reaction of Al with water

Three different modification agents, γ-Al 2O 3, α-Al 2O 3, and TiO 2 were used to modify Al particle surfaces. The effect of different modification agents on hydrogen-generation by the reaction of modified Al powder with water was investigated. It was found that different modification agents have different effect on the reaction dynamics of Al with water. The complete hydrogen-generation time of γ-Al 2O 3 modified Al powder is obviously shorter than that of α-Al 2O 3 and TiO 2 modified Al powders, because of their different induction time for the beginning of the reaction. Possible mechanism analyses indicated that the phase transformation and resultant weakening of Al particle surface layer during processing strongly depends on the nucleation energy barrier on modification oxide grains. As γ-Al 2O 3 has a low nucleation energy barrier, the phase transformation of Al particle surface layer is relatively complete so that γ-Al 2O 3 modified Al powder has a short induction and complete reaction time with water. This implies that the Al surface modification probably originates from the phase change of its surface layer.

Diffusion of gaseous products through a particle surface layer in a fluidized bed reactor

This paper examines a solid conversion process during hydrolysis and decomposition of cupric chloride in a thermochemical copper–chlorine (Cu–Cl) cycle of hydrogen production. Reaction rate constants and the time required for complete solid conversion are determined by a shrinking-core model. Diffusion of gaseous reactant occurs through a film surrounding the particle, after which the reactant penetrates and diffuses through a layer of ash to the surface of the unreacted core. The shrinking-core model for spherical particles predicts the reaction of gaseous reactant with solid at the particle surface, and diffusion of gaseous products through the ash, back to the exterior surface of the solid. The hydrolysis reaction is also analyzed with respect to chemical equilibrium conversion and required heat input. Effects of varying operating parameters are examined, including the temperature, pressure, excess steam, inert gas and hydrogen chloride (HCl) in the steam. At a temperature of 375 °C, complete conversion of CuCl 2 can be achieved by controlling the excess steam, operating pressure and inert gas supply. Addition of HCl in the steam supply increases the excess steam requirement for conversion of cupric chloride solid, and the upper limit for HCl concentration increases with temperature and inert gas composition. The addition of inert gas may also reduce the excess steam requirement, thereby reducing the heat requirement. These new results have valuable utility for equipment scale-up in the thermochemical Cu–Cl cycle of hydrogen production.

XAFS Investigation of the Interactions of UVI with Secondary Mineralization Products from the Bioreduction of FeIII Oxides

Biogenic Fe(II) phases (magnetite, green rust, siderite, vivianite, etc.) provide a reservoir of reducing capacity in many subsurface environments that may contribute to the reduction of contaminants such as U(VI). We have examined the uptake and reduction of U(VI) in the presence of biogenic green rust (BioGR), magnetite (BioMAG), and siderite (BioSID) formed during the reduction of Fe(III) oxides by Shewanella putrefaciens CN32. Within 48 h, total solution-phase U(VI) concentrations decreased from 500 microM to 1.5 microM, 392 microM, and 472 microM in the U-BioGR, U-BioMAG, and U-BioSID systems, respectively. Analysis of the samples by U L(III) extended X-ray absorption fine structure spectroscopy (EXAFS) indicated that despite a stoichiometric excess of Fe(II), no more than 6% of U(VI) was reduced to U(IV) in the U-BioSID system, and no more than 22% of U(VI) was reduced in the U-BioMAG system. For comparison, in the U-BioGR system, >99% of U(VI) was reduced to U(IV). Uptake of U(VI) by BioGR and BioMAG was accompanied by formation of nanoparticulate uraninite. The U EXAFS data for the U-BioSID system were consistent with partial U(VI)/U(IV) substitution for Fe(II) in the surface layer of siderite particles and adsorption of U(IV).

Catalytic Activity of Oxidation-Reduction Pre-Treated Ni<sub>3</sub>Al for Methane Steam Reforming

The catalytic activity of oxidation-reduction pre-treated Ni3Al powder for methane steam reforming was examined. The oxidation-reduction pre-treatment consisted of two steps: oxidation in air at various temperatures from 973 to 1373 K, and then followed by reduction in H2 at 873 K. It was found that the oxidation-reduction treatments significantly reduced the onset temperature of activity, i.e., improved the activity of Ni3Al powder at low temperatures. The characterization of Ni3Al surface showed that an outer surface layer of fine NiO particles were formed on the surface of Ni3Al after oxidation. These NiO particles were reduced to metallic Ni by the subsequent reduction treatment, resulting in the high activity for methane steam reforming. These results indicate that the Ni3Al can form highly active surface structure with oxidation-reduction treatment, having excellent heat resistance.

Effects of SiO2 formed on SiC filler particulates on the thermal and mechanical properties of a SiC/Si-C-N composite

SiO2 surface layer of SiC filler particles decreased thermal stability and creep resistance of particulate-reinforced Si–C–N-based ceramic composites made by precursor-impregnation and pyrolysis (PIP) method due to the decomposition of SiO2 at and above 1350°C. The oxide layer could be removed by a pre-treatment of SiC particle compact at 1750°C in Ar before precursor impregnation. The composites fabricated with pre-treated SiC compact show clear improvements in thermal stability and creep resistance.

Decomposition Characteristics of Ethane Hydrate and Propane Hydrate by Microwave Heating

The decomposition of type I ethane hydrate and type II propane hydrate stimulated by 2.45 GHz microwave (MW) were experimentally investigated. The decomposition characteristics of the hydrates under MW heating were analyzed based on the two. step dissociation mechanism accompanied by heat and mass transfer at the crystal surface. Results show that the decomposition behavior of the gas hydrate during MW heating is coupled with the real. time electromagnetic field. Volumetric heating enhances the heat and mass transfer process at the surface layer of the hydrate particles. The time. accumulated thermal effect of MWheating promotes the destruction of the clathrate host lattice. The average decomposition rates of ethane hydrate and propane hydrate obtained in this work range from 0.109 to 0.400 mol . min(-1) . L-1 and from 0.090 to 0.222 mol . min(-1) . L-1, respectively, under incident MW power that ranges from 120 to 540 W. We conclude that the average decomposition rates of ethane hydrate and propane hydrate are faster as the MW power increases within a certain range. The decomposition rates of ethane hydrate are mainly controlled by the MW power. In contrast, the decomposition rates of propane hydrate are controlled by both the MW power and the kinetic mechanismunder relatively higher power.

10.1007/s11455-008-3002-6

We have studied the action of nanosecond-pulsed high-power KrF excimer laser radiation on the composite layer of a soda-lime-silicate glass containing ion-synthesized silver nanoparticles, with the purpose of modifying the material properties by changing the size of metal particles. It is established that, as the number of laser pulses increases, the treatment leads to a decrease in the average size of silver nanoparticles in the ionimplanted layer. However, after the almost complete disintegration of silver particles, a further increase in the number of pulses leads to new growth and a coarsening of the metal particles. The observed phenomena are interpreted in terms of heating of the surface layer of glass and silver particles by nanosecond laser pulses and the related increase in the diffusion mobility of silver atoms in the glass matrix.

Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2-SURF): Degradation of polycyclic aromatic hydrocarbons exposed to O<sub>3</sub>, NO<sub>2</sub>, H<sub>2</sub>O, OH and NO<sub>3</sub>

Abstract. We present a kinetic double-layer surface model (K2-SURF) that describes the degradation of polycyclic aromatic hydrocarbons (PAHs) on aerosol particles exposed to ozone, nitrogen dioxide, water vapor, hydroxyl and nitrate radicals. The model is based on multiple experimental studies of PAH degradation and on the PRA framework (Pöschl-Rudich-Ammann, 2007) for aerosol and cloud surface chemistry and gas-particle interactions. For a wide range of substrates, including solid and liquid organic and inorganic substances (soot, silica, sodium chloride, octanol/decanol, organic acids, etc.), the concentration- and time-dependence of the heterogeneous reaction between PAHs and O3 can be efficiently described with a Langmuir-Hinshelwood-type mechanism. Depending on the substrate material, the Langmuir adsorption constants for O3 vary over three orders of magnitude (Kads,O3 ≈ 10−15–10−13 cm3), and the second-order rate coefficients for the surface layer reaction of O3 with different PAH vary over two orders of magnitude (kSLR,PAH,O3 ≈ 10−18–10−17 cm2 s−1). The available data indicate that the Langmuir adsorption constants for NO2 are similar to those of O3, while those of H2O are several orders of magnitude smaller (Kads,H2O ≈ 10−18–10−17 cm3). The desorption lifetimes and adsorption enthalpies inferred from the Langmuir adsorption constants suggest chemisorption of NO2 and O3 and physisorption of H2O. Note, however, that the exact reaction mechanisms, rate limiting steps and possible intermediates still remain to be resolved (e.g., surface diffusion and formation of O atoms or O3− ions at the surface). The K2-SURF model enables the calculation of ozone uptake coefficients, γO3, and of PAH concentrations in the quasi-static particle surface layer. Competitive adsorption and chemical transformation of the surface (aging) lead to a strong non-linear dependence of γO3 on time and gas phase composition, with different characteristics under dilute atmospheric and concentrated laboratory conditions. Under typical ambient conditions, γO3 of PAH-coated aerosol particles are expected to be in the range of 10−6–10−5. At ambient temperatures, NO2 alone does not efficiently degrade PAHs, but it was found to accelerate the degradation of PAHs exposed to O3. The accelerating effect can be attributed to highly reactive NO3 radicals formed in the gas phase or on the surface. Estimated second-order rate coefficients for O3-NO2 and PAH-NO3 surface layer reactions are in the range of 10−17–10−16 cm2 s−1 and 10−15–10−12 cm2 s−1, respectively. The chemical half-life of PAHs is expected to range from a few minutes on the surface of soot to multiple hours on organic and inorganic solid particles and days on liquid particles. On soot, the degradation of particle-bound PAHs in the atmosphere appears to be dominated by a surface layer reaction with adsorbed ozone. On other substrates, it is likely dominated by gas-surface reactions with OH or NO3 radicals (Eley-Rideal-type mechanism). To our knowledge, K2-SURF is the first atmospheric process model describing multiple types of parallel and sequential surface reactions between multiple gaseous and particle-bound chemical species. It illustrates how the general equations of the PRA framework can be simplified and adapted for specific reaction systems, and we suggest that it may serve as a basis for the development of a general master mechanism of aerosol and cloud surface chemistry.

A Comparison of Catalytic Properties of Cs x H3−x PW12O40 Salts of Various Cesium Contents in Gas Phase and Liquid Phase Reactions

The cesium salts Cs x H3−x PW12O40 of Cs content x = 2 up to x = 3 were tested as the catalysts in the gas and liquid phase reactions. Dehydration of ethanol and transesterification of triglycerides with methanol were selected as the catalytic reactions. Apart from the standard preparation, the catalysts were prepared by two-stage procedure with methanol or water as a solvent. The Cs-salts were characterized by FT-IR, XRD, scanning electron microscopy and energy dispersive X-ray techniques. In turn, the influence of Cs-salts composition on the pH and conductivity of their aqueous colloidal solutions was investigated. The results obtained by the latter techniques were also characteristic for acidity of surface layer of colloidal particles because of surface layer-solution equilibrium. It has been shown that the secondary structure of acidic cesium salts existing in crystalline samples (solid solution of H3PW12O40 in Cs3PW12O40) changes after contacting with polar medium to the system consisting most probably of Cs3PW12O40 core with epitaxial layer of heteropolyacid. This is result of the protons migration from bulk to surface layer of primary particles enhanced by polar medium. It strongly influences the surface acidity of primary particles as well as the activity of Cs-salts in transesterification of triglycerides with methanol. In such polar medium, Cs2HPW12O40 salt becomes the most active catalyst, more active than Cs2.5H0.5PW12O40. An accumulation of partial glycerides and in particular glycerol on the surface of primary particles of Cs-salts resulted in relatively low maximum conversion of triglycerides, most probably due to partial blockage of the catalytic centers. This effect and the almost constant activity of Cs-salts under recycling use in the transesterification experiments are considered to be experimental evidences that methanolysis over Cs-salts was accomplished with the participation of surface protons.

Characterisation of mechanochemically synthesised alane (AlH 3) nanoparticles

A mechanochemical synthesis process has been used to synthesise alane (AlH 3) nanoparticles. The alane is synthesised via a chemical reaction between lithium alanate (LiAlH 4) and aluminium chloride (AlCl 3) at room temperature within a ball mill and at 77 K within a cryogenic mill. The reaction product formed consists of alane nanoparticles embedded within a lithium chloride (LiCl) by-product phase. The LiCl is washed with a solvent resulting in alane nanoparticles which are separated from the by-product phase but are kinetically stabilised by an amorphous particle surface layer. The synthesis of a particular alane structural phase is largely dependent on the milling conditions and two major phases (α, α′) as well as two minor phases (β, γ) have been identified. Ball milling at room temperature can also provide enough energy to allow alane to release hydrogen gas and form aluminium metal nanoparticles. A comparison between XRD and hydrogen desorption results suggest a non-crystalline AlH 3 phase is present in the synthesised samples.

Properties of iron-based soft magnetic composite with iron phosphate–silane insulation coating

This paper investigates the magnetic and structural properties of iron phosphate-aminosilane soft magnetic composites. FTIR spectra, EDX analysis and distribution maps show that the particle surface layer contains a thin layer of iron-phosphate with high coverage of powder surface. The phosphate layer decreases the loss factor and the imaginary part of permeability, as well as increasing the electrical resistivity and the operating frequencies. This layer, which lowers the electrical resistivity and the loss factor, is decomposed by the annealing treatment. The double-layer insulator increases the electrical resistivity and the operating frequency. The siloxane with high thermal stability does not decompose during the annealing treatment. This type of siloxane increases saturation magnetization, electrical resistivity and permeability but decreases microstrain and coercivity.

ECAP vs. direct extrusion—Techniques for consolidation of ultra-fine Al particles

In this study equal channel angular pressing (ECAP) with accommodated backpressure was used as a technique for consolidation of fine atomized monocrystalline ( d 50 = 1.3 μm) Al 99.7% powder. The effect of ECAP on consolidation behavior of powder, microstructure and mechanical properties of subsequent compacts in comparison to conventional direct extrusion (DE) is presented. Consolidation was realized via simple processing route, where complicated step of gastight encapsulating of vacuumed powder was avoided. Both ECAPed and extruded compacts featured sound ultra-fine grained (UFG) microstructures, consisting of elongated grains of intensively sheared powder particles. Grain boundaries of compacts were stabilized with homogenously redistributed nano-scale particles of torn oxide surface layers of initial Al powder particles. UFG character of ECAPed and extruded compacts resulted in their relatively high strengths at room temperature (up to R m = 316 MPa) and especially at elevated temperatures (up to R m = 188 MPa at 300 °C). Inferior ductility of ECAPed compacts ( A ∼2%) compared to extrudants ( A ∼10%) was due to their disadvantageous microstructure texture reflecting deformation along ECAP shearing plane. Owing to grain pinning effect of broken oxide particles, compacts exhibited excellent structural stability with no major microstructural changes and deterioration of mechanical properties determined after 350 °C/20 h annealing. The trade-off between simple processing route and effect of residual porosity on high temperature mechanical properties is discussed.

Effects of fluorine doping on the electrochemical properties of LiV 3O 8 cathode material

A series of fluorine-doped lithium trivanadates LiV 3O 8− y F z ( z = 0, 0.03, 0.05, 0.1, 0.15, 0.2 and 0.5) were synthesized by the solid-state reaction. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscope (SEM) tests show that a proper amount of fluorine substituting for oxygen in LiV 3O 8 can modify its structure and surface morphology. Charge–discharge tests show that the doped samples with a proper amount of fluorine display good cycling stability, high coulombic efficiency and good rate capability, compared with undoped sample. The cyclic voltammetry (CV), area-specific impedance (ASI) and electrochemical impedance spectroscopy (EIS) tests indicate that the doped samples with a low fluorine content can stabilize the interface between the surface layer of the active particles and the electrolyte after cycling, while a high fluorine content form an unstable interface. The fluorine substitution is a convenient and effective method for improving the electrochemical performances of LiV 3O 8.

Nondestructive Spectrometric Study on a Radioactive Particle Embedded in a Marine Sediment

A radioactive particle embedded in a sediment collected from the Irish Sea was examined with spectrometric methods to understand the potential bioavailability of its constituents. Images of the particle surface were acquired in the backscattering mode by scanning electron microscopy. The elemental composition of the particle surface layer was measured using energy dispersive (SEM-EDX) and wavelength dispersive (SEM-WDX) X-ray spectrometers. The investigation showed that the sample consists of a calcite matrix in which uranium is present in the form of separate inclusions. The diameter of U inclusions was less than 10 μm. Synchrotron radiation based X-ray fluorescence in confocal geometry (confocal μ-XRF) was used to determine the spatial distribution of elements in the particle. Three-dimensional reconstructions of the Ca, Cr, Mn, Fe, Zn, Sr, Ba, Pb, and U distributions were performed. The oxidation state of uranium in the different inclusions was determined by synchrotron radiation based X-ray absorption in confocal geometry (confocal μ-XANES). The isotopic composition of uranium was measured by secondary ion mass spectrometry. The results revealed that uranium was depleted in 235U. Pu and other actinides were not detected.

Electrorheological property of M-doped (M=Na, Zr) nano-sized TiO 2 particle materials, influence of surface composition and microstructure

Nano-sized TiO 2 particle materials doped with Na 2O or ZrO 2 have been synthesized. Their composition (including the composition in the surface layer of particles), microstructure and dielectric property have been studied by XRD, BET, XPS, TEM and dielectric analysis. The electrorheological (ER) properties of the materials have shown that both Na-doping and Zr-doping can effectively enhance the ER performance of TiO 2 materials with suitable degree of doping. Especially, the composition in the surface layer of particles plays a dominant role in influencing the ER performance of the particle materials.