Statistical Optimization of Iron Electrodes for Alkaline Storage Batteries

A pressed-plate Fe electrode for alkalines storage batteries, designed using a statistical method (fractional factorial technique), is described. Parameters such as the configuration of the base grid, electrode compaction temperature and pressure, binder composition, mixing time, etc. have been optimised using this method. The optimised electrodes have a capacity of 300 plus /minus 5 mA h/g of active material (mixture of Fe and magnetite) at 7 h rate to a cut-off voltage of 8.86V vs. Hg/HgO, OH exp 17 ref.

Influence of ethanol/water mixture on the undrained shear strength of pure clays

The mechanical properties of clays are highly dependent not only on the stress/strain ratio to which the material is subjected but also on the chemistry of the pore fluids which in turn affects the intergranular or the effective stresses. Atterberg limits and vane shear tests were performed with different pore fluids in order to observe how the fine-grained material mechanically responded. The diffuse double layer theory has been used to interpret the data of vane shear tests in order to explain the variation of geotechnical responses with the different clays. Van der Waals forces and double layer forces were obtained and capillary forces calculated. The results show that while for kaolinite and illite the chemistry of the pore fluids has no influence on the water content and hence on the mechanical behaviour of the material, Na-smectite shows a strong correlation between the dielectric constant of the pore fluids and an increase in undrained shear strength. The data obtained extends an understanding of the influence of the dielectric constant (epsilon) of the pore fluids on the geotechnical properties of fine-grained materials.

Hydrothermal synthesis of a monoclinic VO2 nanotube-graphene hybrid for use as cathode material in lithium ion batteries

The hydrothermal reaction of a mixture of a colloidal dispersion of graphite oxide and ammonium vanadate yielded a hybrid made of graphene and a nanotubular metastable monoclinic polymorph of VO2, known as VO2(B). The formation of VO2(B) nanotubes is accompanied by the reduction of graphite oxide. Initially the partially scrolled graphite oxide layers act as templates for the crystallization of VO2(B) in the tubular morphology. This is followed by the reduction of graphite oxide to graphene resulting in a hybrid in which VO2(B) nanotubes are dispersed in graphene. Electron microscopic studies of the hybrid reveal that the VO2(B) nanotubes are wrapped by and trapped between graphene sheets. The hybrid shows potential to be a high capacity cathode material for lithium ion batteries. It exhibits a high capacity (similar to 450 mAh/g) and cycling stability. The high capacity of the hybrid is attributed to the interaction between the graphene sheets and the VO2(B) tubes which improves the charge-transfer. The graphene matrix prevents the aggregation of the VO2(B) nanotubes leading to high cycling stability. (C) 2012 Elsevier Ltd. All rights reserved.

Synthesis of nanoparticles of the giant dielectric material, CaCu3Ti4O12 from a precursor route

A complex oxalate precursor, CaCu3(TiO)(4)(C2O4)(8)center dot 9H(2)O, (CCT-OX), was synthesized and the precipitate that obtained was confirmed to be monophasic by the wet chemical analyses, X-ray diffraction, FTIR absorption and TG/DTA analyses. The thermal decomposition of this oxalate precursor led to the formation of phase-pure calcium copper titanate, CaCu3Ti4O12, (CCTO) at a parts per thousand yen680A degrees C. The bright-field TEM micrographs revealed that the size of the as synthesized crystallites to be in the 30-80 nm range. The powders so obtained had excellent sinterability resulting in high density ceramics which exhibited giant dielectric constants upto 40000 (1 kHz) at 25A degrees C, accompanied by low dielectric losses.

Remarkable Capacity Retention of Nanostructured Manganese Oxide upon Cycling as an Electrode Material for Supercapacitor

Electrochemical capacity retention of nearly X-ray amorphous nanostructured manganese oxide (nanoMnO2) synthesized by mixing directly KMnO4 with ethylene glycol under ambient conditions for supercapacitor studies is enhanced significantly. Although X-ray diffraction (XRD) pattern of nanoMnO2 shows poor crystallinity, it is found that by Mn K-edge X-ray absorption near edge structure (XANES) measurement that the nanoMnO2 obtained is locally arranged in a δ-MnO2-type layered structure composed of edge-shared network of MnO6 octahedra. Field emission scanning electron microscopy and XANES measurements show that nanoMnO2 contains nearly spherical shaped morphology with δ-MnO2 structure, and 1D nanorods of α-MnO2 type structure (powder XRD) in the annealed (600 °C) sample. Volumetric nitrogen adsorption−desorption isotherms, inductively coupled plasma analysis, and thermal analysis are carried out to obtain physicochemical properties such as surface area (230 m2 g−1), porosity of nanoMnO2 (secondary mesopores of diameter 14.5 nm), water content, composition, etc., which lead to the promising electrochemical properties as an electrode for supercapacitor. The nanoMnO2 shows a very high stability even after 1200 cycles with capacity retention of about 250 F g−1.

Role of Melt Convection on the Thermal Performance of Heat Sinks with Phase Change Material

The role of melt convection oil the performance of beat sinks with Phase Change Material (PCM) is presented in this paper. The beat sink consists of aluminum plate fins embedded in PCM and heat flux is supplied from the bottom. The design of such a heat sink requires optimization with respect to its geometrical parameters. The objective of the optimization is to maximize the heat sink operation time for the prescribed heat flux and the critical chip temperature. The parameters considered for optimization are fin number and fill thickness. The height and base plate thickness of heat sink are kept constant in the present analysis. An enthalpy based CFD model is developed, which is capable Of Simulating phase change and associated melt convection. The CFD model is Coupled with Genetic Algorithm (GA) for carrying out the optimization. Two cases are considered, one without melt convection (conduction regime) and the other with convection. It is found that the geometrical optimizations of heat sinks are different for the two cases, indicating the importance of inch convection in the design of heat sinks with PCMs.

Modeling of dynamic material behavior in hot deformation: Forging of Ti-6242

A new method of modeling material behavior which accounts for the dynamic metallurgical processes occurring during hot deformation is presented. The approach in this method is to consider the workpiece as a dissipator of power in the total processing system and to evaluate the dissipated power co-contentJ = ∫o σ ε ⋅dσ from the constitutive equation relating the strain rate (ε) to the flow stress (σ). The optimum processing conditions of temperature and strain rate are those corresponding to the maximum or peak inJ. It is shown thatJ is related to the strain-rate sensitivity (m) of the material and reaches a maximum value(J max) whenm = 1. The efficiency of the power dissipation(J/J max) through metallurgical processes is shown to be an index of the dynamic behavior of the material and is useful in obtaining a unique combination of temperature and strain rate for processing and also in delineating the regions of internal fracture. In this method of modeling, noa priori knowledge or evaluation of the atomistic mechanisms is required, and the method is effective even when more than one dissipation process occurs, which is particularly advantageous in the hot processing of commercial alloys having complex microstructures. This method has been applied to modeling of the behavior of Ti-6242 during hot forging. The behavior of α+ β andβ preform microstructures has been exam-ined, and the results show that the optimum condition for hot forging of these preforms is obtained at 927 °C (1200 K) and a strain rate of 1CT•3 s•1. Variations in the efficiency of dissipation with temperature and strain rate are correlated with the dynamic microstructural changes occurring in the material.

Thermoanalysis of ammonium perchlorate and sodium nitrate mixture

A binary mixture of ammonium perchlorate-sodium nitrate in molar proportion undergoes partial fusion at 223°C and the transformation of the mixture to sodium perchlorate-ammonium nitrate occurs in the broad endothermic region. The mixture was heated and quenched at various temperatures in a differential thermal analysis assembly. Thermogravimetric analysis, X-ray diffraction, and infrared spectroscopic techniques were used to determine the composition of the quenched sample in order to explain the overall thermal phenomenon. Visual observations of the morphological changes that occur during the course of heating were made using a hot-stage microscope, 30–350°C.

NOx Reduction and Desorption Studies Under Electric Discharge Plasma Using a Simulated Gas Mixture: A Case Study on the Effect of Corona Electrodes

In this study, reduction and desorption of oxides of nitrogen (NOx) were conducted using an electrical discharge plasma technique. The study was carried out using a simulated gas mixture to explore the possibility of re-generation of used adsorbents by a nonthermal plasma desorption technique. Three different types of corona electrodes, namely, pipe, helical wire, and straight wire, were used for analyzing their effectiveness in NOx reduction/desorption. The pipe-type corona electrode exhibited a nitric oxide (NO) conversion of 50%, which is 1.5 times that of the straight-wire-type electrode at an energy density of 175J/L. The helical-wire-type corona electrode exhibited a NOx desorption efficiency almost 4 times that of the pipe-type electrode,indicating the possibility that corona-generated species play a crucial role in desorption.

Estimation of Cavitation Erosion with Incubation Periods and Material Properties

A detailed study of the normalized correlations between the incubation period tc and the properties of various materials tested in a rotating disk device indicates that, at very high intensities, the strength properties influence the duration of tc. The analysis of extensive data from other laboratories for cavitation and liquid impingement erosion also indicates that, while both energy and strength properties influence the duration of tc, the latter ones predominate for a majority of cases. A fatigue-type failure occurs during tc. For estimating the time required to pierce a metallic specimen in a rotating device a relationship tp = 160 tc0.44 is proposed. A detailed study of normalized correlations between erosion resistance (inverse of erosion rate) and tc values of different materials tested in the rotating disk shows that correlations are good. Analysis of data from eight other investigators clearly points out the validity and the usefulness of this type of prediction.

Thermoanalysis of ammonium perchlorate and sodium nitrate mixture

A binary mixture of ammonium perchlorate-sodium nitrate in molar proportion undergoes partial fusion at 223°C and the transformation of the mixture to sodium perchlorate-ammonium nitrate occurs in the broad endothermic region. The mixture was heated and quenched at various temperatures in a differential thermal analysis assembly. Thermogravimetric analysis, X-ray diffraction, and infrared spectroscopic techniques were used to determine the composition of the quenched sample in order to explain the overall thermal phenomenon. Visual observations of the morphological changes that occur during the course of heating were made using a hot-stage microscope, 30–350°C.

Ce1-xRuxO2-delta (x=0.05, 0.10): A New High Oxygen Storage Material and Pt, Pd-Free Three-Way Catalyst

Nanocrystalline Ce1-xRuxO2-delta (x = 0.05 and 0.10) of 8-10 nm sizes have been synthesized by hydrothermal method using melamine as complexing agent. Compounds have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray analysis (EDX) and their structures have been refined by the Rietveld method.The compounds crystallize in fluorite structure and the composition is Ce1-xRuxO2-x/2 where Ru is in +4 state and Ce is in mixed-valence (+3, +4) state. Substitution of Ru4+ ion in CeO2 activated the lattice oxygen. Ce1-xRuxO2-x/2 reversibly releases 0.22[O] and 0.42[O] for x = 0.05 and 0.10, respectively, which is higher than the maximumpossible OSC of 0.22 [O] observed for Ce0.50Zr0.50O2. Utilization of Higher OSC of Ce1-xRuxO2-delta (x = 0.05 and 0.10) is also reflected in terms of low-temperature CO oxidation with these catalysts, both in the presence and absence of feed oxygen. The Ru4+ ion acts as an active center for reducing molecules (CO, hydrocarbon ``HC'') and oxide ion vacancy acts as an active center for O-2 and NO, leading to low-temperature NO conversion to N-2. Thus due to Ru4+ ion, Ce1-xRuxO2-delta is not just a high oxygen storage material but also shows high activity toward CO, hydrocarbon ``HC'' oxidation, and NO reduction by CO at low temperature with high N-2 selectivity for three-way catalysis.

Wear characteristics and bearing performance of aluminium-mica particulate composite material

Some tribological properties of a mica-dispersed Al-4%Cu-1.5%Mg alloy cast by a conventional foundry technique are reported. The effect of mica dispersion on the wear rate and journal bearing performance of the matrix alloy was studied under different pressures and under different interface friction conditions. The dispersion of mica was found (a) to increase the wear rate of the base alloy, (b) to decrease the temperature rise during wear and (c) to improve the ability of the alloy to resist seizure.

A Method for Isolation of Protoplasts from Dermatophytes

A method has been developed to isolate protoplasts from dermatophytes using Novozym 234. A simple technique of flotation in MgSO, has been adapted to separate protoplasts from incubation mixture. Electron microscopic studies confirmed the absence of cell wall material on these protoplasts. The recovery of DNA from protoplasts was higher than from mycelia.

Analysis-By-Synthesis Based Switched Transform Domain Split Vq Using Gaussian Mixture Model

Using analysis-by-synthesis (AbS) approach, we develop a soft decision based switched vector quantization (VQ) method for high quality and low complexity coding of wideband speech line spectral frequency (LSF) parameters. For each switching region, a low complexity transform domain split VQ (TrSVQ) is designed. The overall rate-distortion (R/D) performance optimality of new switched quantizer is addressed in the Gaussian mixture model (GMM) based parametric framework. In the AbS approach, the reduction of quantization complexity is achieved through the use of nearest neighbor (NN) TrSVQs and splitting the transform domain vector into higher number of subvectors. Compared to the current LSF quantization methods, the new method is shown to provide competitive or better trade-off between R/D performance and complexity.