Properties Of Selective Surfaces Research Articles

Catalytic performance for propane selective oxidation and surface properties of 12-molybdophosphoric acid treated with pyridine

When molybdophosphoric acid, H 3PMo 12O 40, was treated with pyridine and heated in N 2 flow at 420°C as an optimized temperature, a black solid catalyst was formed with a structure of orthorhombic phase and in a reduced state. This reduced H 3PMo 12O 40(Py) catalyst showed a high potentiality in the propane and isobutane oxidation with molecular oxygen to acrylic acid and methacrylic acid above 300°C. It was proved that the higher the reduction degree of the catalyst is, the higher the oxidation activity and selectivity to partial oxidation products are. The FT-IR study revealed that, in the lattice of the heat-treated H 3PMo 12O 40(Py) catalyst, pyridinium ion remained to assume the highly resistant orthorhombic secondary structure against reoxidation, and on the surface, Lewis acid sites were generated with the formation of the primary oxygen-deficient Keggin structure. A possible reaction mechanism was proposed for alkane oxidation, where protons and electrons in the reduced H 3PMo 12O 40(Py) catalyst cooperate to activate molecular oxygen.

Influence of sol-gel SiO2/TiO2 protective coatings on the optical and thermal properties of nickel-phosphorus selective surfaces

A sol-gel coating was applied to an electroless acid-etched Ni-P spectrally selective surface in order to investigate its influence on the optical and thermal properties of the selective surface. The sol-gel process is a low-temperature preparation of glasses, which is of interest considering the lack of resistance of selective surfaces at the high temperatures generally needed to prepare glasses by the melting technique. The application of a glass coating on the Ni-P layer increases its oxidation resistance at high temperatures and improves the optical and thermal properties of this selective surface for heat treatments in air, up to 400 °C.

Influence of supporting dielectric layers on the transmission properties of frequency selective surfaces

Single layer arrays of linear dipole slots and patches symmetrically embedded in a dielectric layer or bonded to its surface illustrate dielectric tuning effects in this mainly computer aided but partly experimental study. After its initial rapid decline as the layer thickness increases, the resonant frequency of the slots varies cyclically about the limiting value for the patches. Contours of transmission level on a frequency/thickness plot illustrate this frequency pulling effect and lead to a discussion of passband shaping and the sensitivity to angle of incidence. Equivalent circuit concepts account for the observed bandwidth and resonant frequency variations. The performance of two experimental surfaces is described, including the influence of trapped waves in the dielectric.

Optical properties of black nickel selective surface by conversion coating process

Optical properties of nickel black selective surfaces, prepared by a conversion coating process, on zincated aluminium alloy surfaces are studied in relation to the processing parameters. It is possible to obtain nickel black surfaces with solar absorptances ranging from 0.95 to 0.97 and thermal emittances ranging from 0.2 to 0.4. The coatings are stable up to 200°C but show degradation under humid conditions. Surface studies indicate that the optical properties may be explicable by the structure of these nickel films.

The total anodization of copper films on platinum: Use as selective surface absorbers at high temperature

A thin film of metallic copper deposited on an inert metallic conductor was totally anodized in a NaOH solution. The resulting anodic copper oxide film is shown to have excellent selective surface properties for use as a solar absorber at high temperatures.

Selective surfaces of anodic copper oxide for solar collectors

The hemispherical spectral reflectance and the hemispherical total emittance were measured for copper oxide films produced by anodic oxidation. The anodic copper oxide films are shown to have desirable selective surface properties for use as solar absorbers.

Composition, optical properties and degradation modes of Cu/(graded metal-carbon) solar selective surfaces

A detailed study is reported of the composition and properties of a production Cu/(graded stainless steel-carbon) selective surface which is incorporated in all-glass evacuated solar thermal collectors. The Auger depth profile, reflectance for wavelengths in the range 0.35–2.5 μm and temperature-dependent emittance for the range 100–300°C were determined for the selective surface before and after heat treatment of the collector at 500°C. The composition, carbon atom bonding states, electrical resistivity, refractive indices (wavelengths, 0.35–2.5 μm), IR transmittance (wavelengths, 2.5–16 μm) and emittance (100–300°C) for a set of homogeneous stainless steel-carbon component layers of the graded layer profile were also determined before and after heat treatment. In addition, a multilayer stack computer model based on the composition profile of the production selective surface and the comprehensive refractive index data for the set of homogeneous component layers was developed. Correlation of the experimental data for the set of homogeneous layers with alterations in reflectance for the multilayer stack resulting from the substitution or removal of component layers in the stack allowed a detailed evaluation of the factors determining production selective surface properties before and after heat treatment. A theoretical study of alternative grading profiles with a view to optimizing the solar selective properties of the surface is also discussed.

Photothermal conversion with cermet films: Implications of the bounds on the effective dielectric function

We investigate the relation between microstructure and spectral properties of cermet selective surfaces by starting from the mathematical bounds on the average dielectric permeability for an isotropic Co-Al 2O 3 model system. We show that for this system the predictions from several effective medium theories all lie inside these bounds. However, qualitatively very different optical properties pertain to different theoretically allowed microgeometries. We stress the importance of assessing the pertinent microstructure before any specific effective medium formulation is attempted for the optical properties.

Surface properties of bacillus Calmette-Guérin-activated mouse macrophages. Reduced expression of mannose-specific endocytosis, Fc receptors, and antigen F4/80 accompanies induction of Ia.

Infection of the mouse peritoneal cavity by bacillus Calmette-Guérin (BCG) markedly alters the surface properties of the macrophages induced, compared with cells obtained from uninfected control animals or after injection of thioglycollate broth. Quantitative binding assays with radiolabeled ligands or antibodies showed that BCG-activated peritoneal macrophages (BCG-PM) expressed one-fourth or less receptor activity for mannose-terminal glycoconjugates as well as reduced levels of Fc receptors and of antigen F4/80 compared with nonactivated macrophages. Endocytosis mediated by mannose-specific receptors was reduced in parallel. In contrast, surface Ia antigen was increased threefold in the same adherent cell population. Radioautographic analysis confirmed that greater than 80% of adherent cells still expressed low levels of the macrophage-specific mannosyl receptor and antigen F4/80, and that I antigens had been induced on 64% of macrophages rather than on other cells. Control experiments established that only the BCG-PM macrophages released H2O2 after stimulation with phorbol myristate acetate, whereas both BCG-PM and thioglycollate-induced macrophages produced superoxide anion and plasminogen activator. The BCG-PM were viable, secreted normal levels of lysozyme, and displayed a stable phenotype after cultivation for 60 h. Inhibitors of oxygen products, prostaglandins, and proteases did not alter reduced endocytosis by BCG-PM. These studies indicated that expression of macrophage surface markers is reversed by BCG-activation, and that their known enhanced ability to lyse target cells extracellularly is associated with decreased endocytosis via specific receptors. Whether these changes are a result of an altered cell population or of modulation of selective surface properties is not known.

The measurement of optical properties of selective surfaces using a solar calorimeter

An instrument has been constructed to measure the solar absorptivity and IR emissivity of surfaces using calorimetric methods to determine their selectivity and hence their possible use in solar energy devices. Absorptivity and total hemispherical emissivity can be calculated as a function of temperature by measuring respectively, the rate at which a thermally isolated sample in an evacuated chamber increases in temperature when exposed to real or simulated sunlight, and the rate at which it cools when shaded. These parameters can be used to compare the relative efficiencies of different surfaces at various operating temperatures.