Influence of moisture content of wood on sound velocity and dynamic MOE of natural frequency- and ultrasonic runtime measurement

This study comprises the analysis of the influence of the moisture content of wood on the dynamic properties—sound velocity and dynamic MOE (considering the density)—of green and dry sawn timber. The main objective was to find applicable functions or factors for the adjustment of the determined properties on the reference condition (moisture content u=12%) for the moisture content range below and above fiber saturation. Therefore, two dynamic measurement methods—measurement of the natural frequency and ultrasonic runtime—were considered. Possible differences in the results, pros and cons of both methods should be identified on the one hand. On the other hand, the applicability of already published moisture adjustments to the given data of both methods should be proved.     

Dry Sliding Behavior of Sub-Micrometer-Sized Suspension Plasma Sprayed Ceramic Oxide Coatings

Almost half of the energy produced by an automotive engine is dissipated by friction in the cylinders, the clutch, etc. In the context of reduction of the emissions of greenhouse gases (GHGs) to mitigate climate global warming (CGW), reduction of energy losses due to friction is a critical issue. Surface treatments appear in such a context, as never than before, to be able to provide pertinent solutions to improve sliding behavior of mechanical parts. Numerous studies have clearly shown that decreasing the scale of coating structure below the micrometer scale was leading to an improvement of its tribological behavior in terms of friction coefficient and wear rate thanks to improved mechanical properties, the toughness in particular. Suspension Plasma Spraying (SPS) appears as a thermal spray process to be able to manufacture thick (i.e., a few tens of micrometers) coatings exhibiting a sub-micrometer-sized or even a nanometer-sized architecture, while keeping the versatility and flexibility of the thermal spray routes: i.e., the ability to process a wide range of material natures onto a wide range of substrate materials of various geometries. This article aims at studying the tribological behavior of several ceramic oxide composite coatings under dry conditions. The structural scale and the effect of composition are considered in particular.     

Untersuchungen von Wiener Lebensmitteln

Ohne Zusammenfassung     

Co–Ni Catalysts Derived from Hydrotalcite-Like Materials for Hydrogen Production by Ethanol Steam Reforming

A series of Co–Ni catalysts, prepared from hydrotalcite (HT)-like materials by co-precipitation, has been studied for the hydrogen production by ethanol steam reforming. The total metal loading was fixed at 40% and the Co–Ni composition was varied (40–0, 30–10, 20–20, 10–30 and 0–40). The catalysts were characterized using X-ray diffraction, N₂ physisorption, H₂ chemisorption, temperature-programmed reduction, scanning transmission electron microscope and energy dispersive spectroscopy. The results demonstrated that the particle size and reducibility of the Co–Ni catalysts are influenced by the degree of formation of a HT-like structure, increasing with Co content. All the catalysts were active and stable at 575 °C during the course of ethanol steam reforming with a molar ratio of H₂O:ethanol = 3:1. The activity decreased in the order 30Co–10Ni > 40Co ~ 20Ni–20Co ~ 10Co–30Ni > 40Ni. The 40Ni catalyst displayed the strongest resistance to deactivation, while all the Co-containing catalysts exhibited much higher activity than the 40Ni catalyst. The hydrogen selectivities were high and similar among the catalysts, the highest yield of hydrogen was found over the 30Co–10Ni catalyst. In general, the best catalytic performance is obtained with the 30Co–10Ni catalyst, in which Co and Ni are intimately mixed and dispersed in the HT-derived support, as indicated by the STEM micrograph and complementary mapping of Co, Ni, Al, Mg and O.     

Time and cost effective methods for testing chemical resistance of aluminium metallic pigmented powder coatings

Polyester based powder coatings containing different types of aluminium metallic flake pigments have been investigated with respect to their chemical stability in acid environments. The metallic flakes are made chemically stable by covering them in silica. The degree of silica coverage and the silica morphology are far more important for the chemical stability of the pigments than the silica thickness. The acid resistance of the final powder coating is found to depend on the pigment embedment depth, on the chemical composition and morphology of the powder coating, and on the silica coating of the pigment. The latter being the single most important factor in our study.     

Impactor Apparatus for the Study of Particle Rebound: Relative Humidity and Capillary Forces

The effect of relative humidity (RH) on the adhesion of particles colliding with a hard surface was studied for submicron particles of liquid oleic acid, solid ammonium sulfate, and solid polystyrene latex (PSL). For this purpose, a three-arm impactor was designed and constructed. The three arms consisted of one impactor having an uncoated impaction plate (i.e., a rebound arm), one impactor having a viscous-liquid-coated impaction plate (i.e., a capture arm), and one impactor having no impaction plate (i.e., a null arm). The particle number concentrations downstream of each arm were measured by condensation particle counters (CPCs). Data were analyzed to obtain the particle rebound fraction. Use of ambient upstage pressure allowed measurements from 5 to 95% RH at the impaction plate. Particle rebound depended strongly on RH, even for non-hygroscopic PSL particles. The rebound fraction for PSL particles dropped monotonically from nearly unity at 50% RH to 0.4 at 95% RH. For ammonium sulfate, the rebound fraction dropped from nearly unity at 25% RH to 0.5 at 70% RH. The decreased rebound at higher RH was explained by the formation of a water meniscus. The resulting capillary forces inhibited particle detachment. A model, taking into account the impact kinetic energy compared to the contact adhesion energy arising from van der Waals and capillary forces, captured the observations well. The reduced rebound arising from increased adhesion at high RH, independent of particle water content, potentially confounds a recent assumption that non-rebounding atmospheric particles are liquid.

Copyright 2014 American Association for Aerosol Research     

Low-temperature photoluminescence study of exciton recombination in bulk GaAsBi

The exciton recombination processes in a series of elastically strained GaAsBi epilayers are investigated by means of time-integrated and time-resolved photoluminescence at T = 10 K. The bismuth content in the samples was adjusted from 1.16% to 3.83%, as confirmed by high-resolution X-ray diffraction (HR-XRD). The results are well interpreted by carrier trapping and recombination mechanisms involving the Bi-related localized levels. Clear distinction between the localized and delocalized regime was observed in the spectral and temporal photoluminescence emission.