Analysis of the Influence of Element’s Entropy on the Bulk Metallic Glass (BMG) Entropy,Complexity, and Strength

Metallurgical and Materials Transactions A - Bulk metallic glasses (BMGs) are disordered compounds without a long-range crystalline order. In this paper, we study the effect of an element’s...     

Visible‐light response photocatalytic water splitting over CdS/TiO2 and CdS–TiO2/metalosilicate composites

In this work, we have synthesized two different phases of CdS nanoparticles, CdS/TiO₂ composites and their supported form on ZSM‐5 type metalosilicates (ferrisilicate and aluminosilicate) as CdS–TiO₂/metalosilicate composites. The photocatalytic performance of these samples was evaluated by monitoring the amount of hydrogen evolved from water under visible‐light irradiation. The supported composites of TiO₂–CdS/metalosilicate exhibited a higher photocatalytic activity in the photocatalytic water splitting than that of CdS/TiO₂ composites under visible‐light irradiation, suggesting an important role of support. Metalosilicate as a support, which can offer a very high surface area, provides effective and homogenous dispersion of the CdS/TiO₂ composite on the external surface or within the pores of metalosilicate and inhibits agglomeration of the formed composite. We observed that using the solvothermal method for the synthesis of CdS and the hydrothermal method for the synthesis of CdS/TiO₂ or CdS–TiO₂/metalosilicate results in the enhancement of the photocatalytic activity of these composite compared with other procedures, which has been reported previously. We have realized that the support of the CdS/TiO₂ composite on ferrisilicate enhances the photocatalytic activity; however, using aluminosilicate as a support results in the abatement of the photocatalytic activity in comparison with the unsupported composite. This can be attributed to the presence of partially occupied ‘d’ orbitals in the electronic configuration of Fe³⁺ in the structure of ferrisilicate which can interact with TiO₂ molecular orbitals. This interaction leads to the effective distribution of the composite on the support and the decreasing crystallite size of the composite and then enhancement of the photocatalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and properties of polyurethane networks derived from new soybean oil‐based polyol and a bulky blocked polyisocyanate

BACKGROUND: Developing vegetable oil‐based polyols for polyurethane manufacturing is becoming highly desirable for both economic and environmental reasons. Most vegetable oils do not bear hydroxyls naturally. The objective of this work was to prepare a new soybean oil‐based polyol with high functionality of hydroxyl groups and built‐in (preformed) urethane bonds. RESULTS: A facile and improved method was developed for the transformation of epoxidized soybean oil into carbonated soybean oil under ambient pressure of CO₂ gas, with tetrabutylammonium bromide/calcium chloride as catalyst/co‐catalyst couple. Ring‐opening reaction of the carbonated oil with ethanolamine led to the desired polyol. A one‐pack polyurethane system was prepared via combination of the polyol and a blocked polyisocyanate. The polyol and final polyurethanes were fully characterized, and their physical, mechanical, viscoelastic and electrical insulating properties were studied. CONCLUSION: The application of this newly developed soybean oil‐based polyol for preparation of electroinsulating casting polyurethanes was examined. The prepared soy‐based polyurethanes offered excellent thermal and electrical insulating properties. Also, tunable physical and chemical properties for the final polyurethanes were achieved by replacing part of the soybean oil‐based polyol with poly(propylene glycol) (M_n = 1000 g mol^?1). Copyright © 2008 Society of Chemical Industry     

A New Method for Determination of the Adsorption Isotherm of SDS on Polystyrene Latex Particles Using Conductometric Titrations

Monodisperse polystyrene (PS) latex particles were prepared through a conventional batch emulsion polymerization procedure. After cleaning, the latex was subjected to a surfactant titration by sodium dodecyl sulfate (SDS) and the conductivity was monitored. Using the break point in the conductivity‐concentration curve, the adsorption area of the surfactant molecules at saturation, A_s, was determined as 46 Ų per SDS molecule. In order to determine the contribution of the different ionic species to the conductivity, a simple model based on experimental conductivity measurements was developed. The degrees of counterion binding to the micelles and to the surfactant anions adsorbed onto polymer particles were calculated as 0.770 and 0.849, respectively. The Langmuir adsorption isotherm was determined for the adsorption of SDS onto PS latex particles with Γ_∞ = 7.257 · 10^–10 mol/cm² and K = 1.208 · 10⁵ cm³/mol.     

Investigation of photo-electrochemical response of iron oxide/mixed-phase titanium oxide heterojunction toward possible solar energy conversion

Photocatalysts are part of key strategies to enable green fuel. Photocatalysis and water splitting could be a promising solution to challenges associated with the intermittent nature of sunlight as a huge energy source on Earth. In this study, photo-electrochemical performance and behavior of mixed-phase titanium oxide and iron oxide heterojunction (Ti-TiO_x (High-voltage)-FeO_x electrode) are compared to the photo-electrochemical performance and behavior of titanium oxide nanotubes with the rutile phase and iron oxide heterojunction (TiO_x-nanotubes (H₂SO₄/KF)-FeO_x electrode). The results of photo-electrochemical experiments show that the application of stabilization potential and the presence/absence of dissolved oxygen could not be considered as significant factors affecting the photo-electrochemical properties of the Ti-TiO_x (High-voltage)-FeO_x and TiO_x-nanotubes (H₂SO₄/KF)-FeO_x electrodes. The Ti-TiO_x (High-voltage)-FeO_x electrode shows an anodic photo-electrochemical response in wavelengths shorter than 530 nm and cathodic photo-electrochemical response in wavelengths longer than 530 nm. However, the Ti-nanotubes (H₂SO₄/KF)-FeO_x electrode consistently exhibits the anodic photo-electrochemical response. Both of the prepared heterojunctions are further characterized through Scanning Electron Microscopy, Energy-dispersive X-ray Spectroscopy, Diffuse Reflectance UV–Vis Spectroscopy, X-ray Diffraction, and Attenuated Total Reflectance Spectroscopy methods. These experiments show that despite different morphologies observed in SEM imaging data, the deposited iron oxide layers on both mixed-phase titanium oxide and titanium oxide nanotubes share the same hematite phase structure. However, only iron oxide electro-deposited on the surface of the mixed-phase titanium oxide, which contains both anatase and rutile phases, with vacant sites of oxygen, exhibits un-expected anodic and cathodic photo-electrochemical responses. Furthermore, according to the results of the characterization and photo-electrochemical investigations, the different chemical environment of mixed-phase titanium oxide, and the possible formation of different types of heterojunction structures in mixed-phase titanium oxide and iron oxide, in contrast to the titanium oxide nanotubes and iron oxide, might be considered the possible discernible reasons for the observed different photo-electrochemical responses. This paper sheds new light on photo-electrochemistry of iron oxide/mixed-phase titanium oxide heterojunction for possible solar energy conversion.     

Optimal directionality compensation in processes with input saturation non-linearities

A notion of process directionality in input-constrained processes is defined, and the class of processes that do not exhibit the process directionality is characterized. An optimal directionality compensator for non-linear processes with actuator saturation non-linearities is presented. Given an unconstrained controller output and the characteristic (decoupling) matrix of the process under consideration, the compensator calculates an optimal constrained (feasible) process input that results in a process response as 'close' as possible to the response of the same process to the unconstrained controller output. The compensator can be used for both linear and non-linear processes, irrespective of the type of controller being used. For processes whose non-singular characteristic matrix can be made diagonal by row or column rearrangements, the optimal directionality compensator is identical to a series of limiters (clippers); this class of processes does not exhibit the process directionality over a short time horizon. The performance of the optimal directionality compensator is shown and compared with those of clipping and direction preservation, by numerical simulation of a linear example under decentralized proportional-integral control, a linear example under model-based control, and a non-linear bioreactor under input-output linearizing control.     

The Effects of Production Rate and Initial Pressure Difference (pi – pdew ) in Well Test Analysis of Gas Condensate Reservoirs

Abstract

The theoretical basis for the analysis of well test data presented in this study is the use of a pseudopressure function to linearize the flow of gas condensate in porous media. In this article different techniques to analyze gas condensate well tests using single-phase pseudopressure and two-phase pseudopressure are considered. The main objective of this work was to examine the available methods for well test analysis of gas condensate reservoirs and investigate the effect of production rate and initial pressure difference (p_i – p_dew ) on these methods. Sensitivities of the two-phase pseudopressure methods and single-phase method are presented.

However, at higher endpoint relative permeability, a lower prediction from single-phase pseudopressure analysis is obtained. A lower difference between p_i and p_dew causes larger condensate bank size and larger Region 2 and therefore better prediction of Raghavan's approach.     

ERROR ESTIMATION AND ADAPTIVITY IN FINITE ELEMENT ANALYSIS OF CONVECTIVE HEAT TRANSFER PROBLEMS,PART I: THEORETICAL CONSIDERATIONS

Abstract

This is the first of two articles concerning error estimation and adaptive refinement techniques applied to convective heat transfer problems. This study presents the detailed development of the proposed error estimator. The error estimator takes into account the coupling effects of the dependent variables ( e.g.. velocity and temperature) on the discretization error and, consequently, on the adaptive meshes. An averaging procedure is also proposed as a substitute for the smoothing /recovery procedure used to evaluate the gradients. The implementation of the averaging technique is simple and cost effective. Numerical experiments demonstrate that the proposed methodology results in a dramatic reduction in computational costs.     

Optimization of Pump Scheduling Program in Water Supply Systems Using a Self-Adaptive NSGA-II; a Review of Theory to Real Application

The operation of pumps imposes significant costs on a water distribution system for energy supply and pumps maintenance. To derive an optimum pumps scheduling program, this study presents a multiobjective optimization problem with the objective functions of 1- energy cost and 2- the number of pump switches. The optimization of both objective functions together leads to a multiobjective constrained optimization problem. To solve the problem, the Non-Dominated Sorting Genetic Algorithm, version II, (NSGA-II) is coupled to the EPANET hydraulic simulation model. For constraint handling, some modifications are introduced to the standard NSGA-II to make it self-adaptive through which all constraints of the problem are automatically satisfied. Application of the model to a test example and a real pipe network verifies that the proposed scheme is computationally efficient and reliable. Also, optimization of the real pipe network reveals that by a careful pump scheduling program the total number of pump switches even in optimum operations could be decreased by 69% while the energy cost increases at most by 10%.     

A Comparison Between ECAP and Conventional Extrusion for Consolidation of Aluminum Metal Matrix Composite

In this study, two powder consolidation techniques, equal channel angular pressing (ECAP) and extrusion, were utilized to consolidate attritioned aluminum powder and Al-5?vol.% nano-Al₂O₃ composite powder. The effect of ECAP and extrusion on consolidation behavior of composite powder and mechanical properties of subsequent compacts are presented. It is found that three passes of ECAP in tube at 200?°C is capable of consolidating the composite to 99.29% of its theoretical density whereas after hot extrusion of the composite the density reached to 98.5% of its theoretical density. Moreover, extrusion needs higher temperature and pressing load in comparison to the ECAP method. Hardness measurements show 1.7 and 1.2 times higher microhardness for the consolidated composite and pure aluminum after ECAP comparing with the extruded ones, respectively. Microstructural investigations and compression tests demonstrate stronger bonds between the particles after three passes of ECAP than the extrusion. Furthermore, the samples after three passes of ECAP show better wear resistance than the extruded ones.