In-situ X-ray absorption study of evolution of oxidation states and structure of cobalt in Co and CoPt bimetallic nanoparticles (4 nm) under reducing (H2) and oxidizing (O2) environments

In-situ near edge X-ray absorption fine structure spectroscopy was performed to monitor the oxidation states of Co and CoPt nanoparticles (NPs) of 4 nm size in the presence of H(2) and O(2) in the pressure range of 1 bar and 36 Torr respectively. Platinum helps the rapid reduction of cobalt oxides in hydrogen at a rather low temperature (38 °C). In addition, reversible changes of the oxidation states of cobalt in the Co and CoPt NPs as a function of cycling oxygen pressure (in the range of millitorr to 36 Torr) are quantified and compared. The role of Pt in the process of Co reducing and oxidizing was explored. Our findings permit the prediction of the cobalt oxidation states as the reaction conditions are altered. The experimental results also suggest the presence of tetrahedral structure of Cobalt oxide that differs from the Co(3)O(4) spinel structure.     

Occurrence and environmental behavior of the bactericide triclosan and its methyl derivative in surface waters and in wastewater

The bactericide triclosan and methyl triclosan, an environmental transformation product thereof, were detected in lakes and in a river in Switzerland at concentrations of up to 74 and 2 ng L(-1), respectively. Both compounds were emitted via wastewater treatment plants (WWTPs), with methyl triclosan probably being formed by biological methylation. A regional mass balance for a lake (Greifensee) indicated significant removal of triclosan by processes other than flushing. Laboratory experiments showed that triclosan in the dissociated form was rapidly decomposed in lake water when exposed to sunlight (half-life less than 1 h in August at 47 degrees latitude). Methyl triclosan and nondissociated triclosan, however, were relatively stable toward photodegradation. Modeling these experimental data for the situation of lake Greifensee indicated that photodegradation can account for the elimination of triclosan from the lake and suggested a seasonal dependence of the concentrations (lower in summer, higher in winter), consistent with observed concentrations. Although emissions of methyl triclosan from WWTPs were only approximately 2% relative to those of triclosan, its predicted concentration relative to triclosan in the epilimnion of the lake increases to 30% in summer. Passive sampling with semipermeable membrane devices (SPMDs) indicated the presence of methyl triclosan in lakes with inputs from anthropogenic sources but not in a remote mountain lake. Surprisingly, no parent triclosan was observed in the SPMDs from these lakes. Methyl triclosan appears to be preferentially accumulated in SPMDs under the conditions in these lakes, leading to concentrations comparable to those of persistent chlorinated organic pollutants.     

Mass Transfer Of Contaminants In Rotary Enthalpy Exchangers

The present work is a study of reentrainment of a tracer gas formaldehyde via six rotary air-to-air heat exchangers (all enthalpy exchangers) in the northern part of Sweden. Five exchangers installed in office buildings and one in a day-care centre were included in the study. Formaldehyde in indoor was used as a monitor pollutant and was determined in air samples collected in the ducts at four positions around the rotor of the exchanger, in the supply-air duct and in the exhaust-air duct. Air sampling of homogeneous duct air was performed simultaneously at the four positions using 2, 4-dinitrophenylhydrazine-impregnated glass fibre filters. The sample analysis of formaldehyde was made by high-performance liquid chromatography. The reentrainment of formaldehyde was calculated and found to be 1-9%. These results show that a rotary heat exchanger can be used in buildings where activities produce low levels of air pollutants, provided that the exchanger is properly installed and maintained.     

On constitutive modeling for springback analysis

The springback phenomenon that occurs in thin metal sheets after forming is mainly a stress driven problem, and the magnitude is roughly proportional to the ratio between residual stresses and Young's modulus. An accurate prediction of residual stresses puts, in turn, high demands on the material modeling during the forming simulation.A phenomenological plasticity model is made up of several ingredients, such as a yield condition, a plastic hardening curve, a hardening law, and a model for the degradation of elastic stiffness due to plastic straining.The authors of this paper have recently, [1], showed the importance of a correct modeling of a cyclic stress-strain behavior via a phenomenological hardening law, in order to obtain an accurate stress prediction. The main purposes of the present study are to study the influence of two other constitutive ingredients: the yield criterion and the material behavior during unloading. Three different yield criteria of different complexity are evaluated in the present investigation: the Hill’48 criterion, the Barlat-Lian Yld89 criterion, and the 8-parameter criterion by Banabic/Aretz/Barlat.The material behavior during unloading is evaluated by loading/unloading tension tests, where the material is unloaded/reloaded at specified plastic strain levels. The slope of the unloading curve is measured and a relation between the “unloading modulus” and the plastic stain is established.In the current study, results for four different materials are accounted for. The springback of a simple U-bend is calculated for all the materials in the rolling-, transverse- and diagonal directions. From the results of these simulations, some conclusions regarding constitutive modeling for springback simulations are drawn.     

An excavation method for large vertical cylindrical caverns

Construction of underground storage chambers in rock has traditionally adopted a construction-oriented approach; the cavern design and the method of excavation have been governed by the capabilities of the equipment available. One example is oil storage in unlined horizontal caverns. Today, however, equipment is no longer a limiting factor. The time has come to integrate the construction and operational aspects in the design process. This paper presents a construction concept developed for large vertical rock caverns with a circular or elliptical horizontal cross-section. The method of excavation, called PBM (Pillar Blasting Method), is condensed into a few main operations which are geometrically separated but overlapping in time. PBM is characterized by two main working sites per cavern, and by long-hole bench-drilling, massive blasting rounds, continuous loading and easy ventilation. Recent developments in drilling and blasting techniques are incorporated, such as the water-driven in-the-hole hammer and the electronic ignition system. PBM enables a high rate of excavation and provides a satisfactory working environment with respect to labour safety and human health (a limited exposure to large openings, no exposure to oil mist and to combustion and explosive fumes, etc). Considerable construction cost savings and time savings may thus be achieved compared to conventional methods of excavation for vertical and horizontal caverns of equal storage volume. A preliminary PCT patent (application No PCT/SE95/00324) has been granted. Examples of applications are fresh-water reservoirs, natural gas reservoirs, subsurface hydroelectric pump power plants, and similar objects which require a large underground storage space in preferably unlined rock caverns.     

An efficient inverse approach for material hardening parameter identification from a three-point bending test

The cyclic three-point bending test has been frequently used for the determination of material hardening parameters. The advantage of this test is that it is simple to perform, and standard test equipment can be used. The disadvantage is that the material parameter identification requires some kind of inverse approach. The current authors have previously, successfully been utilizing a method, in which computed force–displacement relations have been fitted to corresponding experimental results. The test has been simulated by means of the Finite Element code LS-DYNA, and the material parameters have been determined by finding a best fit to the experimental results by means of the optimization tool LS-OPT, based on a response surface methodology. A problem is, however, that such simulations can be quite time consuming, since the Finite Element model has to be analyzed numerous times. In the current paper, an alternative numerical methodology will be described, in which instead calculated moment–curvature relations are fitted to experimental ones. This optimization procedure does not involve any solution of the FE problem. The Finite Element problem needs only to be solved a limited number of times in an outer iteration loop. This fact results in a considerable reduced computational cost. It is also demonstrated that the parameters determined by this new method correspond excellently to the ones determined by the conventional method.     

Effect of Preparation Procedure on the Catalytic Properties of Fe-ZSM-5 as SCR Catalyst

Fe-ZSM-5 catalysts, prepared by different methods, have been characterized by BET, ICP-AES, XRD, XPS, NH₃-TPD and NO-TPD and evaluated for NO_x reduction according to standard NH₃-SCR, NH₃ oxidation and NO oxidation, in absence and presence of water. The presence of water has a significant influence on both the SCR and oxidation reactions. The most active catalyst for NH₃-SCR is prepared by ion exchange using FeCl₂ as iron precursor. The XPS results indicate that Fe²⁺ ions are the main active sites for the SCR reactions, while Fe³⁺ ions are the primarily active sites for oxidation of ammonia.     

Methane Oxidation Over Pd Supported on Ceria–Alumina Under Rich/Lean Cycling Conditions

Catalysts with highly dispersed palladium on alumina, alumina doped with 20 wt% ceria and ceria have been prepared, characterized and examined for net-lean methane oxidation. In particular, the activity and selectivity were investigated during rich/lean cycling of the feed. The ceria content is found to influence both the general and the instantaneous activity responses. The results indicate that the active phase of palladium changes between reduced and oxidised Pd during the rich/lean cycling, and that the process is influenced by the presence of ceria.