Exchange-correlation errors at harmonic and anharmonic orders: the case of bulk Cu

As an aid towards improving the treatment of exchange and correlation effects in electronic structure calculations, it is desirable to have a clear picture of the errors introduced by currently popular approximate exchange-correlation functionals. We have performed ab initio density functional theory and density functional perturbation theory calculations to investigate the thermal properties of bulk Cu, using both the local density approximation (LDA) and the generalized gradient approximation (GGA). Thermal effects are treated within the quasiharmonic approximation. We find that the LDA and GGA errors for anharmonic quantities are an order of magnitude smaller than for harmonic quantities; we argue that this might be a general feature. We also obtain much closer agreement with experiment than earlier, more approximate calculations.     

Split and collectorless flotation to medium coking coal fines for multi-product zero waste concept

The medium coking coal fines of − 0.5 mm from Jharia coal field were taken for this investigation. The release analysis of the composite coal reveals that yield is very low at 10.0% ash, about 25% at 14% ash and 50% at 17% ash level. The low yield is caused by the presence of high ash finer fraction. The size-wise ash analysis of − 0.5 mm coal indicated that − 0.5 + 0.15 mm fraction contains less ash than − 0.15 mm fraction. Thus, the composite feed was split into − 0.5 + 0.15 mm and − 0.15 mm fractions and subjected to flotation separately. The low ash bearing fraction (− 0.5 + 0.15 mm) was subjected to two stages collectorless flotation to achieve the concentrate with 10% ash. The cleaner concentrate (18.9%) with 10% ash was recovered which has an application in metallurgical industries. The concentrate of 30.2% yield with 12.5% ash could be achieved in one stage collectorless flotation which is suitable for use in coke making as sweetener. As the − 0.15 mm fraction contains relatively high ash, collector aided flotation using sodium silicate was performed to get a concentrate of 23.6% yield with about 17% ash. The blending of this product with cleaner tail obtained from − 0.5 + 0.15 mm produces about 35.0% yield with 17% ash and that can be utilized for coke making. The reject from the two fractions can be used for conventional thermal power plant or cement industries using a 23.5% ash after one stage collector aided flotation and the final tailings produced content ash of 61.6% can be used for fluidization combustion bed (FBC). This eventually leads to complete utilization of coal.     

Corrosion of 2205 duplex stainless steel in chloride medium containing sulfate-reducing bacteria

Sulfate-reducing bacteria (SRB) play significant role in the corrosion of stainless steels exposed to marine and soil environment. Sulfate reduction by bacterial species results in the production of H₂S, which can significantly influence the anodic and cathodic processes and ultimately enhances the corrosion of materials. In the present study, 2205 type duplex stainless steel (DSS) coupons in solution-annealed condition were exposed to chloride medium containing SRB species, Desulfovibrio desulfuricans, for 40 days and examined by microscopy. Etching of the duplex structure, pitting as well as crevice attack were noticed. Similar results were obtained by microscopic studies with coupons exposed for 14 days in medium containing SRB followed by anodic polarization. SEM studies, of crevices observed after anodic polarization, indicated that the attack was initiated at the grain boundaries and slowly encroached into austenite grains. The initiation of attack was also evident from AFM studies of coupon exposed under freely corroding conditions for 7 days. ESCA studies reveal that under anaerobic conditions of SRB growth sulfidation of passive film occurs. The modified passive film found to depolarize the cathodic reactions. The nature and mechanism of SRB attack on DSS and possibility of detection at early stages were discussed.     

Selective solid-phase extraction of rare earth elements by the chemically modified Amberlite XAD-4 resin with azacrown ether

A selective solid-phase extraction procedure using chemically modified Amberlite XAD-4 with monoaza dibenzo 18-crown-6 ether was investigated for the preconcentration and separation of La(III), Nd(III) and Sm(III) in synthetic solution. Before loading samples on synthesized adsorbent adjust pH 4.5 by suitable buffer solution. The adsorbed rare earth elements were eluted by 2 M hydrochloric acid. Various parameters like preconcentration, breakthrough capacity, flow rate were investigated. The limits of detection (n = 5) and limits of quantification (n = 5) for La(III), Nd(III) and Sm(III) were founded 3.9, 4.2 and 7.4 μg L^?1 and 13, 15 and 26 μg L^?1, respectively. The eluted metal ions were determined by ICP-AES.     

Double stripe reconstruction of the Pt(111) surface

We have studied the reconstruction of the Pt(111) surface theoretically, using a 2D generalization of the Frenkel-Kontorova model. The parameters in the model are obtained by performingab initio density functional theory calculations. The Pt(111) surface does not reconstruct under normal conditions but experiments have shown that there are two ways to induce the reconstruction: by increasing the temperature, or by depositing adatoms on the surface. The basic motif of this reconstruction is a ‘double stripers with an increased surface density and alternatinghcp andfcc domains, arranged to form a honeycomb pattern with a very large repeat distance of 100–300 Å. In this paper, we have studied the ‘double stripe’ reconstruction of the Pt(111) surface. In agreement with experiment, we find that it is favourable for the surface to reconstruct in the presence of adatoms, but not otherwise.     

Linear Combination of Atomic Orbitals Approximation in Nanocrystalline Yittria-Stabilized Zirconia Synthesized by Citrate–Nitrate Gel Combustion Process

Nanocrystalline yittria-stabilized zirconia (YSZ) compounds with yittria concentration varying between 8 and 12 mol% have been synthesized by gel combustion method followed by heat treatment at 550°C. The YSZs are found to posses stable face centered cubic structure at room temperature by X-ray diffractometry. The lattice parameter ' a ' showed an increasing trend with increasing concentration of yittria. The crystallite size estimated by Scherrer method was in the range of 7–10 nm. Band gap studies showed an increasing trend with increasing yittria concentration and are found to be consistent with respective lattice parameters following the tight binding approximation or linear combination of atomic orbitals approximation.     

Nanocrystalline yttria stabilized zirconia by metal–PVA complexation

Nanocrystalline 8 mol% yttria stabilized zirconia (YSZ) powder was synthesized using polyvinyl alcohol (PVA) as organic precursor and acidic solutions of yttrium oxynitrite and zirconium nitrate. Complex formation was established using Fourier transform infrared (FTIR) spectroscopy and solid state ¹³C nuclear magnetic resonance (NMR) spectroscopy. Thermal stability of the complex was investigated by thermogravimetric analysis (TGA). X-ray diffractometry (XRD) revealed formation of cubic phase YSZ at a temperature as low as 600 °C. The lattice parameter and average crystallite size were calculated from the XRD data. Particle size of the YSZ powder was investigated through transmission electron microscopy (TEM). The band gap of the sintered YSZ pellet was measured by UV–Vis-diffused reflectance spectroscopy (DRS). AC electrical conductivity was measured in air at 1 kHz frequency using a programmable RCL meter. The activation energy was calculated from the conductivity data at different temperatures using the standard Arrhenius equation.     

Mechanical characterization of new glass fiber reinforced epoxy composites

Glass fiber reinforced plastic (GFRP) composites were made using CTPEGA [carboxyl terminated poly(ethylene glycol) adipate] modified epoxy as a matrix and characterized for their flexural properties, impact strength and interlaminar shear stress (ILSS). The volume fraction of glass was about 0.45 for all the composites. The concentration of CTPEGA in the matrix was varied gradually from 0 to 40 phr (parts per hundred parts of resin), to investigate the effect of CTPEGA concentration on the mechanical properties of the composites. It was found that the flexural strength and ILSS gradually decreases with increase in CTPEGA concentration. However, the impact strength of the composites increases up to 20 phr of CTPEGA concentration and decreases thereafter. Scanning electron microscope (SEM) analysis of the fracture surface indicates massive plastic deformation in modified epoxy based composites. Polym. Compos. 25:165–171, 2004. © 2004 Society of Plastics Engineers.     

Enhancement in hydrophobicity of low rank coal by surfactants — A critical overview

The flotation of fine (− 0.5 mm) low rank or oxidized coal is difficult to achieve with the common coal flotation collectors like kerosene, fuel oil or diesel oil (oily collector). The presence of small amounts of oxygen is enough to cause oxidation. The oxidation of coals starts with the physical adsorption of oxygen on the surface to form an oxycomplex followed by chemical adsorption of oxygen to form polar phenolic-OH, carbonyls, phenols and peroxide type oxygenated moieties by the rupture of cyclic rings. The addition of promoter, surfactant or oxygenated functional groups to the collector molecule markedly enhances the flotation of lower rank and oxidized coals due to the hydrogen bonding with the polar part of the coal surface and the reagent. The performance of these reagents is compared with that of oily collectors, namely kerosene, dodecane, nonylbenzene and polar part of the surfactant having an oxygen atom. The mode of addition of non-ionic surfactant with oily collector also has a major role in the flotation response. The addition of non-ionic surfactant after the oily collector has shown a positive effect on yield and grade.     

EVALUATION OF FROTHER PERFORMANCE IN COAL FLOTATION: A CRITICAL REVIEW OF EXISTING METHODOLOGIES

Separation efficiency in flotation depends, to a considerable extent, on the efficiency of the frother used. A successful frother must achieve a delicate balance between froth stability and non-persistency. Ideally, the frother is not supposed to influence the state of the surface of the coal and minerals. In practice, however, interaction does occur between the frother, other reagents, and solid surfaces. Various commercially available frothers can differ slightly or significantly in their influence on the flotation results. Therefore, a plant operator is in a dilemma when it comes to selecting a frother to be used in his plant. This article attempts to critically review the different methodologies, which are available to compare the performance of two or more frothers in order to decide which would best serve the purpose of the plant operator.