Surface activity of foam fractions of a calcium lignosulphonate

Successive foam fractionation has been used to divide a processed calcium lignosulphonate into tractions differing appreciably in surface activity. Static surface tension has been measured by the de Nouy tensiometer and surface tension aging by the sessile bubble (photographic) method. The effect of concentration on surface tension has been determined. The effect of pH at 1% concentration on dynamic surface tension has been determined on freshly prepared solutions.     

Greffage de molécules à la surface du silicium par voie électrochimique

The hydrogentated surface of silicon exhibits remarkable properties, but poor resistance to oxidation. To improve its stability, surface hydrogen has been replaced by several organic groups. Such grafting can be carried out chemically by a multi-step reaction scheme. However, an electrochemical approach allows direct reaction with the hydrogenated surface. The porous-silicon surface has been partially methoxylated by a controlled anodic dissolution. If has also been methylated using a non-destructive anodic process, with a yield of 80%, limited only by steric hindrance. The methylated surface of porous silicon exhibits a stability against oxidation increased by an order of magnitude.     

Analysis and evaluation of permeability techniques for characterizing fine particles Part II. Measurement of specific surface area

The performance of both steady-state and transient permeameters has been evaluated. A number of standard powders was chosen and their surface areas determined by gas adsorption techniques for comparison with surface areas obtained using permeameters. The powders were chosen to cover a wide range o density (0.92 – 18.7 g/cm³) and surface area (0.06 – 350 m²/g).The effect of particle shape, i.e. needles, spherical particles, flakes and irregularly shaped particles on surface area determined by permeametry has also been studied. A linear relationship between BET surface area and that obtained by using a simple U-tube transient flow permeameter has been obtained over a wide range of particle size and macroporosity.The Fisher Subsieve Sizer was chosen as a typical example of a steady-state permeameter, and a number of shortcomings in this instrument have been found. A simple steady-state permeameter was constructed to evaluate the theoretical model as developed in Part I for atmospheric pressure permeametry, and the model has been found to give good values of external surface areas for powders having an average particle size greater than 2 μm. The effect of slip flow for particles less than 1 μm in diameter has been established for atmospheric pressure permeametry.This paper also presents measurements of specific surface area determined by using a more recent permeameter, namely the Permaran. This instrument performed within a reproducibility of ±7% and produced data in agreement with that taken on similar devices and also with the theoretical analysis presented in Part I.The performance of a Knudsen-flow permeameter has been evaluated, and the instrument has been found to give accurate values of external surface area of fine as well as coarse powders.     

Enhancement of CO hydrogenation activity on incompletely reduced nickel wire

Enhanced activity of Ni wire in CO hydrogenation has been observed when the metal surface is incompletely reduced. The catalytic behavior has been studied in a flow reactor for different H₂/CO ratios, and the carbon species accumulated on the metal surface during reaction have been analyzed by Tempera-ture-Progranimed-Surface-Reaction(TPSR). It has been concluded that the surface or sub-surface oxygen remaining on the catalyst due to incomplete reduction plays an important role m determining the metal catalyst behavior. The extent of metal reduction in addition to the metal surface area has to be considered in estimation of the intrinsic activity of Ni catalysts.     

Surface Properties of Ceramic Laminates Fabricated by Die Pressing

The simple die-pressing technique has been used to fabricate thick-layer zirconia/alumina ceramic laminates in the forms of film/substrate and multilayer systems. A "vibration sieve" method is used to achieve uniform layer thickness. In order to suppress surface crack initiation and propagation, the laminates are designed to retain residual compressive stresses in the surface layers. As a result, the surface fracture/fatigue resistance has been significantly improved, and the microhardness of the surface layer has also been increased to a certain degree.     

Influence of interfacial resistance on kinetics of sorption

A model for sorption influenced by rate of transfer to the surface layer of polymeric sheets has been examined. The rate of uptake into the surface layer has been taken to be proportional to the degree of unsaturation of the surface layer. The predicted sorption behaviour has been compared with experimentally observed data which shows a reasonable agreement. A method for calculating diffusion coefficients has been demonstrated. It has been shown that sorption rates could be affected by factors like pressure of the penetrant in the vapour phase and the structure of the surface vis-á-vis that of the bulk. Extension of the model qualitatively, to systems with diffusion coefficients strongly dependent on concentration, indicates the possibility of larger uptake of the penetrant in thinner sheets in an initial time interval. This supports some experimental observations reported earlier. The model supports the experimental work of Long and Richman who observed the time dependence of surface concentrations during sorption.     

The electropolymerisation of acrylamide on carbon fibres

Polyacrylamide has been synthesised at the surface of carbon fibre by the technique of electropolymerisation. Some details of the polymerisation have been presented and a preliminary proposal made for the mechanism responsible. The characterisations of carbon fibre and its surface have always presented a problem; in this work torsional braid analysis has been used to study the polymer present on the surface of the fibre.     

Microporous structures and absorption properties of carbonaceous adsorbents

Two new independent methods for determining the surface area of micropore walls (the geometrical surface of micropores) of carbonaceous adsorbents have been proposed. Their satisfactory agreement has been substantiated experimentally. A comparative analysis of adsorption isotherms of benzene at 293 K on model carbonaceous micro- and supermicroporous adsorbents and of isotherms on mesoporous carbonaceous adsorbents with equal geometrical surface areas has been carried out. A quantitative estimate, under comparable conditions, of the increase in adsorption values in micro- and supermicropores as compared with nonporous or mesoporous adsorbents has been given for the first time.The formal applicability of the BET equation to adsorption isotherms of nitrogen at 77 K and benzene at 293 K on model carbonaceous microporous adsorbents, whose micropore geometrical surface area changed almost four-fold, has been shown. The determined monolayer capacities were close to the preassigned constant limiting adsorption values for the filled micropores. As a result the specific surface areas according to BET for the adsorbents under consideration were nearly equal.     

Size-dependent catalytic and melting properties of platinum-palladium nanoparticles

While nanocatalysis is a very active field, there have been very few studies in the size/shape-dependent catalytic properties of transition metals from a thermodynamical approach. Transition metal nanoparticles are very attractive due their high surface to volume ratio and their high surface energy. In particular, in this paper we focus on the Pt-Pd catalyst which is an important system in catalysis. The melting temperature, melting enthalpy, and catalytic activation energy were found to decrease with size. The face centered cubic crystal structure of platinum and palladium has been considered in the model. The shape stability has been discussed. The phase diagram of different polyhedral shapes has been plotted and the surface segregation has been considered. The model predicts a nanoparticle core rich in Pt surrounded by a layer enriched in Pd. The Pd segregation at the surface strongly modifies the catalytic activation energy compared to the non-segregated nanoparticle. The predictions were compared with the available experimental data in the literature. PACS: 65.80-g; 82.60.Qr; 64.75.Jk.     

煤的表面处理及润湿性研究

煤炭是一种具有大分子网状结构的有机岩石,表面润湿性是其工业应用的重要物性参数。通过原煤及分别经过偶联剂和烷基化处理的煤样表面润湿性的定,对煤表面润湿性进行了初步研究,结果表明,分别经过偶联剂处理和烷基化处理的煤样,其润湿性有一定程度的改善,使煤样表面发生了改性,烷基化反应后煤样的红外测试结果也证明了这一点。     

Measurement of the Metal Surface Acidity/Electronegativity of Pt(110)

In previous work, it has been found that a hydrogen-covered Pt(110) surface is acidic, but quantification of the acidity has not yet been done. In this paper a spectroscopic method is developed to measure the acidity of a metal surface for the first time. The technique involves measuring the intensity of the N–H stretch from the C₅H₄XNH⁺ that forms when hydrogen coadsorbs with pyridine, 2-fluoropyridine and 3-fluoropyridine. The Bethe approximation is then used to estimate the metal surface acidity/electronegativity (MSAEL). The proton affinity/MSAEL of Pt(110) has been determined to be 907 ± 4 kJ/mol at high coverage. This is the first time the MSAEL has been measured on a metal surface. Implications for fuel cell catalysis are discussed.     

Studies of optical haze and surface morphology of blown polyethylene films using atomic force microscopy

Atomic force microscopy (AFM) has been used to examine the inner and outer surfaces of commercial blown polyethylene films. When this technique has been used, direct-space images of surface lamellae have been obtained, and the surface roughness determined. The haziness of the films has been measured, both in the as-produced state and when coated with suitable oil. Thus, both surface and bulk contributions to the apparent turbidity have been estimated. The aim of this study has been to correlate in turn the haziness, roughness, and surface morphology. Results obtained showed that the haze is related primarily to the surface roughness and can be reduced by lowering the frost line. AFM images unveiled lamellar features that were oriented predominantly in the transverse direction. The observed wide-angle X-ray diffraction (WAXD) intensities were consistent with an a-axis type of orientation.     

Potential distribution in a corroding pit

The occurrence of hemispherical corroding pits in metal surfaces has been known for many years, and qualitative explanations have been given to explain the phenomenon in terms of passivation at the uncorroded flat surface. However, the quantitative solution of potential distribution in such a system, which would be necessary for a test of experimental data, has not been made. The problem is complicated by the discontinuity in surface flux at the edge of the pit. The flux normal to the surface inside the pit can be assumed constant over the whole surface since the pit remains hemispherical during corrosion. However, at the pit edge the normal flux is abruptly reduced to zero, and the planar surface acts essentially as an insulator.     

Synthesis, characterization, and properties of a novel acrylic terpolymer with pendant perfluoropolyether segments

A novel acrylic terpolymer with pendant perfluoropolyether (PFPE) segments has been synthesized and fully characterized. By hexamethylene diisocyanate functional groups PFPE monofunctional macromonomers have been grafted on a poly(butyl methacrylate-co-hydroxyethyl acrylate-co-ethyl acrylate) random terpolymer. Such grafted copolymer behaves like an interface-active material, since the perfluoropolyether segments in solvent cast films rearrange themselves at the air-polymer interface by surface segregation. In addition, blends of the above graft copolymer with acrylic base polymers (either the terpolymer itself or a commercial copolymer) have been examined in terms of surface segregation and fluorine enrichment of the external layers.The critical surface tension, γ_c, of solid films made of the neat graft copolymer as well as of the polymer blend has been evaluated by contact angle measurements and Zisman plots. Even a small addition (5 wt%) of the fluorinated copolymer to the acrylic component has been found very effective in lowering the surface tension. The outermost surface composition has been investigated by XPS technique, confirming the strong fluorine enrichment. Furthermore, SEM and EDX analyses have been performed on cross-sectioned films, showing that in the above polymer blends macrophase surface segregation has originated a thick layer made of fluorinated copolymer close to the air-polymer interface.     

Influence of textural properties of activated carbons on Pd/carbon catalysts synthesis for cinnamaldehyde hydrogenation

A set of microporous carbons have been used to prepare Pd/carbon catalysts. The properties of the raw materials have been determined in terms of texture and surface chemistry. A deposition precipitation method has been employed to prepare the final catalysts, leading to well-dispersed palladium particles. The influence of the textural properties as well as the surface chemistry properties has been studied and a correlation was found between the surface in the pores of the support and the Pd dispersion. The chemistry surface properties of the Pd/carbon catalysts were found similar, despite differences in the case of the starting raw materials. The hydrogenation of cinnamaldehyde has been studied and the results obtained favourably compare with those already published. Turnover frequencies were similar whatever the catalyst. High selectivities close to 90% in hydrocinnamaldehyde were obtained at 90% conversion.     

Photochemical degradation of poly(ethylene terephthalate). IV. Surface changes

The chemical, physical, and mechanical changes in the surface properties of poly-(ethylene terephthalate) film produced by ultraviolet light have been examined. Attenuated total reflection infrared spectroscopy has indicated that numerous chemical scission reactions occur in the front surface layer facing the source of irradiation, resulting in the formation of carboxylic acid endgroups. This preferential surface phtodegradation has been confirmed by examining the cross section of irradiated film by electron beam-induced luminescence. Conventional electron microscopy revealed little changes in the surface appearance of irradiated film. However, indirect techniques were devised which indicated that changes do occur in the physical properties of the surface. These observed changes are believed to be responsible for the decrease in film tensile strength, which has been shown to be a surface phenomenon and not a bulk property.     

Fillers for lower density sealants

The effect of surface activation of glass and phenolic microspheres with various gas discharges on the mechanical behavior of formulations based on a dimethylmethylphenylpolysiloxane elastomer has been studied. It has been demonstrated that mechanisms controlling the effect of gas discharge on the surface of fillers of various chemical natures are identical. An increase in the surface energy of the fillers leads to strengthening of interaction between the polymer base and the filler surface and to improvement of mechanical properties.     

Preparation of a high hydrophobic aluminium surface by double zincating process

In this present study, an efficient method has been proposed to develop a high hydrophobic zincated coating on the eva-core aluminium (Al) alloy surface. The double zincating method (Z2) was utilized to develop the required roughness on the Al surface. To control the surface energy, lauric acid (LA) was coated on the surface using the liquid self-assembled monolayers (L-SAMs) method. Surface morphology, the chemical composition of the treated and untreated Al alloy has been studied using scanning electron microscopy (SEM), atomic force microscopy (AFM), optical microscopy and X-ray diffraction (XRD), respectively. The hydrophobicity of the substrates has also been analysed using a contact angle measurement (CA). AFM micrographs show the surface roughness of the Al alloy has been drastically increased with chemical treatments from 0.071 to 0.32 μm. XRD shows the percentage crystallinity of the Al alloy is decreased with double zincating and LA coating from 56.8 to 22.7%. As a result, a high hydrophobicity of Al alloy was induced with a contact angle of 150° upon the double zincating method and L-SAMs coating.     

Structure and composition of the surface layer in polymers modified by elemental fluorine

A model is proposed for the layered structure of a polymer surface modified by elemental fluorine mixed with helium. The composition of the modified surface layer has been determined, and the thermodynamic compatibility of the surface layer, transition layer, and unmodified bulk of the polymer has been studied. The thickness of the modified layers has been calculated as a function of the fluorination conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 897–902, 2005