Effect Of Structural Degradation Research Articles

Advanced high-iron coal fly ash zeolites for low-carbon emission catalytic combustion of VOCs

Coal fly ash zeolites (CFAZs) with increased iron oxide content were prepared by double-stage alkaline conversion of high-iron lignite coal ash. Catalysts were modified by applying radiofrequency plasma treatment with trifluoromethane (RF CHF3) to increase their surface activity. Textural, compositional, and structural characterization of the parent and plasma-modified zeolites were performed by N2-physisorption, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FT-IR) spectroscopy. Oxidation state and coordination of iron species were studied by Mössbauer spectroscopy, UV-Vis spectroscopy and temperature-programmed reduction method (TPR). Acidic properties were investigated by FT-IR spectroscopy of adsorbed pyridine. The initial and plasma-modified samples were studied under toluene oxidation, where toluene was used as a model VOC. The plasma-modified iron-enriched zeolite was found to exhibit high catalytic activity for VOC oxidation, reaching a 98% toluene conversion rate at 500 °C. Despite some structural degradation effects, the plasma-treated catalysts outperformed the untreated ones in catalytic activity. Furthermore, CO2 adsorption capacity of the plasma-modified zeolite was investigated under dynamic conditions. Although plasma-treated iron-enriched zeolite showed relatively low specific surface area (194 m2/g), high dynamic carbon capture capacity of 3.8 mmol/g was measured. It significantly exceeded the capacity of CFAZs with higher specific surface area, not to mention the pure zeolite phase.

A bounding surface plasticity model for unsaturated structured soils

A bounding surface plasticity model based on the effective stress concept is presented to describe the behaviour of unsaturated structured soils subjected to hydro-mechanical loadings. The structural degradation effects on the compressive and tensile strength are considered through controlling the size of the bounding surface, allowing for a smooth transition of the response from structured to unstructured states. The structural degradation is modelled using a work hardening approach, considering both the effects of stress magnitude and accumulated plastic strain on the degradation process. A void ratio-dependent water retention model is adopted, taking the effect of hydraulic hysteresis into account. Attention is also given to the stiffening effect of a decrease in the degree of saturation on the mechanical response of unsaturated structured soils and the wetting-induced collapse. A radial mapping rule with a mobile centre of homology is adopted to capture the response of the soil under unloading–reloading conditions. The predictive capability of the model is demonstrated through the comparison of the model simulations with experimental data for different conventional laboratory tests including constant-suction oedometer and triaxial shearing and wetting tests.

Growth of short-period InAs∕GaSb superlattices

The purpose of this work is to explore materials for midinfrared detectors that can operate at room temperature. Shorter-period InAs∕GaSb superlattices (SLs) have larger intervalance band separations, which are beneficial for reducing Auger recombination and tunneling current, thus making room temperature operation possible. To test these possibilities, several short-period SLs ranging from 50to11Å were grown and their morphological properties were carefully monitored by transmission electron microscopy. The effect of structural degradation caused by the period reduction on the optical properties was studied using low-temperature photoluminescence (PL). The samples with larger periods (50–32Å) showed excellent structural qualities and produced narrow full width at half maximum (FWHM) of the PL peak (5meV). As the period approached 24Å, slight layer thickness undulations within the SLs were observed and these undulations intensified as the period further reduced to 17Å. These structural degradations strongly influence optical properties causing significant broadening in the FWHM and higher residual carrier concentration in the shorter-period SLs. With slower growth rates, samples with periods as thin as 19Å were grown without significant layer undulations.

Hydrological and environmental impact of earthworm depletion by the New Zealand flatworm ( Artioposthia triangulata)

The predation of earthworms by the New Zealand flatworm is an environmental threat that may have consequences beyond the scope of merely reducing earthworm populations in the UK. The role of earthworms in developing soil structure is substantial and the effect of structural degradation on hydrological processes, following earthworm eradication, may therefore be major, with a resulting increase in flood risk from river systems and decrease in agricultural productivity of economic concern.