Dielectric properties of Poly(vinylidene fluoride)/CaCu3Ti4O12 composites

The possibility of obtaining relatively high dielectric constant polymer-ceramic composite by incorporating the giant dielectric constant material, CaCu3Ti4O12 (CCTO) in a Poly(vinylidene fluoride) (PVDF) polymer matrix by melt mixing and hot pressing process was demonstrated. The structure, morphology and dielectric properties of the composites were characterized using X-ray diffraction, Thermal analysis. scanning electron microscope, and impedance analyzer. The effective dielectric constant a(epsilon(eff)) of the composite increased with increase in the volume fraction of CCTO at all the frequencies(100 Hz-1 MHz) under study. The dielectric loss did not show any variation up to 40% loading of CCTO, but showed an increasing trend beyond 40%. The room temperature dielectric constant as high as 95 at 100 Hz has been realized for the composite with 55 vol.% of CCTO, which has increased to about 190 at 150 degrees C. Theoretical models like Maxwell's, Clausius-Mossotti, Effective medium theory, logarithmic law and Yamada were employed to rationalize the dielectric behaviour of the composite and discussed. (C) 2010 Published by Elsevier Ltd.

Synthesis and characterization of nano-MnO2 for electrochemical supercapacitor studies

Nanostructured MnO2 was synthesized at ambient condition by reduction of potassium permanganate with aniline. Powder X-ray diffraction, thermal analysis (thermogravimetric and differential thermal analysis), Brunauer-Emmett-Teller surface area, and infrared spectroscopy studies were carried out for physical and chemical characterization. The as-prepared MnO2 was amorphous and contained particles of 5-10 nm diameter. Upon annealing at temperatures >400°C, the amorphous MnO2 attained crystalline α-phase with a concomitant change in morphology. A gradual conversion of nanoparticles to nanorods is evident from scanning electron microscopy and transmission electron microscopy (TEM) studies. High-resolution TEM images suggested that nanoparticles and nanorods grow in different crystallographic planes. Capacitance behavior was studied by cyclic voltammetry and galvanostatic charge-discharge cycling in a potential range from -0.2 to 1.0 V vs SCE in 0.1 M sodium sulfate solution. Specific capacitance of about 250 F g-1 was obtained at a current density of 0.5 mA cm-2(0.8 A g-1).

Studies on the ignition behaviour of boron powder

The ignition behaviour of boron powder, prepared through electrowinning process, was studied by using thermogravimetry coupled with simultaneous differential thermal analysis (TG-SDTA). The dependence of the inception of the ignition reaction on the partial pressure of oxygen, particle size of the boron powder and heating rate was investigated. It was observed that all these factors affect the ignition temperature. Boron powder with a mean particle size of about 10 mu m was found to be susceptible to ignition in oxygen even at 783K. In general, the susceptibility to ignition was found to vary inversely with the degree of crystallinity. Presence of carbon was found to retard the oxidation of boron and raise the ignition temperature. These results are useful in safe handling and storage of finely divided boron powder and in the subsequent production of boron carbide from it. (C) 2009 Elsevier B.V. All rights reserved.

Mineralogical changes and geotechnical properties of an expansive soil interacted with caustic solution

The type and amount of clay mineral plays an important role in the behaviour of fine-grained soils. Clay minerals are the primary source and moisture is often the external agent of swelling in soils. Also soils may exhibit increased/reduced swelling due to interaction with chemicals. Alkalis used in industrial operations are one such example. Concentrations of alkali and mineral type are the key factors in such interactions. The present paper reports the changes in the properties of an expansive Black Cotton soil containing a mixed layer mineral, rectorite upon interaction with high concentration caustic solutions. X-ray diffraction studies have shown that the rectorite present in the soil undergoes changes with increase in the concentration of alkali. Saponite gets transformed to nantronite. Small amount of kaolinitic mineral present in the soil also reacts with alkali producing some changes in its mineralogy. Many hydroxides are produced. Differential thermal analysis studies have been supportive of these changes. Consequent of these changes, the soil-specific surface increases, changes its Atterberg limits and free swell volume increases. The results have been supported by the characteristics and behaviour of samples contaminated in the field with alkali from an alumina extraction plant.

Formation and crystallization of hydrogen-induced amorphous SmFe2H3.6 alloy

On hydrogenation of the Laves phase SmFe2, an amorphous SmFe2H3.6 (a-SmFe2H3.6) alloy was formed between 400 K and 500 K. The amorphous nature of the alloy was confirmed by X-ray diffraction, transmission electron microscopy and thermal analysis. However, SmFe2 absorbed hydrogen in the crystal state below 350 K and decomposed into SmH2 and α-Fe above 550 K. The crystallization behaviour of a-SmFe2H3.6 was investigated by differential scanning calorimetry in combination with electron microscopy. Even after considerable hydrogen desorption (Image ) by an endothermic reaction on heating, the amorphous state was retained. Crystallization of a-SmFe2H3.6 took place in two stages. The first stage involved the precipitation of α-Fe in the amorphous matrix. The second stage involved the decomposition of the remaining amorphous phase into the equilibrium phases SmH2 and SmFe2.

Low-temperature polymer precursor-based synthesis of nanocrystalline particles of lanthanum calcium manganese oxide (La0.67Ca0.33MnO3) with enhanced ferromagnetic transition temperature

We report a simple modified polymeric precursor route for the synthesis of highly crystalline and homogenous nanoparticles of lanthanum calcium manganese oxide (LCMO). The LCMO phase formation was studied by thermal analysis, x-ray powder diffraction, and infrared spectroscopy at different stages of heating. These nanocrystallites (average particle size of 30 nm) possess ferromagnetic-paramagnetic transition temperature (T-c) of 300 K, nearly 50 K higher than that of a single crystal. The Rietveld analysis of the powder x-ray diffraction data of the nanopowders reveals significant lattice contraction and reduction in unit cell anisotropy-these structural changes are correlated to the enhancement in T-c.

Comparison of heat transfer correlations for cryogenic engine thrustchamber design

A comparative study of the correlations available in the literature is made to arrive at an appropriate pair for estimating the coolant-side and hot-gas-side heat transfer coefficients in the thrust chamber of a cryogenic engine. Based on this, the thermal analysis of a supercritical liquid hydrogen cooled engine is carried out. Results are presented for axial variation of heat transfer coefficients and temperature distributions for coolant and exposed wall. Tubular as well as milled channel configurations are considered for coolant flow.

Thermoanalytical studies of hydrazidocarbonic acid derivatives

Preparation, thermal analysis and IR spectra of a number of transition metal hydrazidocarbonates have been described. Metal hydrazido carbonates decompose exothermically through oxalate and carbonate intermediates to the respective metal oxides. Reaction of ammonium carbonate with hydrazine hydrate yields hydrazinium derivative of hydrazidocarbonic acid; N2H3COON2H5

Studies in biogas technology. Part IV. A novel biogas plant incorporating a solar water-heater and solar still

A reduction in the heat losses from the top of the gas holder of a biogas plant has been achieved by the simple device of a transparent cover. The heat losses thus prevented have been deployed to heat a water pond formed on the roof of the gas holder. This solar-heated water is mixed with the organic input for ‘ hot-charging ’ of the biogas plant. A thermal analysis of such a solar water-heater ‘ piggy-backing ’ on the gas holder of a biogas plant has been carried out.To test whether the advantages indicated by the thermal analysis can be realised in practice, a biogas plant of the ASTRA design was modified to incorporate a roof-top solar water-heater. The operation of such a modified plant, even under ‘ worst case ’ onditions, shows a significant improvement in the gas yield compared to the unmodified plant. Hence, the innovation reported here may lead to drastic reductions in the sizes and therefore costs of biogas plants. By making the transparent cover assume a tent-shape, the roof-top solar heater can serve the additional function of a solar still to yield distilled water. The biogas plant-cum-solar water-heater-cum-solar still described here is an example of a spatially integrated hybrid device which is extremely cost-effective.

Structure and explosive sensitivity relation in ring-substituted arylammonium perchlorates

The thermal and explosive characteristics of ring-substituted arylammonium perchlorates have been studied by differential thermal analysis, explosion delay, and impact-sensitivity measurements. The decomposition and dissociation temperatures, as well as activiation energy for explosion, increase with increasing basicity of the corresponding arylamine. These parameters, when plotted against σ, the Hammett substituent constant, show a linear relationship in the case of meta- and para-substituted derivatives. The results indicate that a proton transfer from arylammonium ion to perchlorate ion is involved in the decompostion and also in the explosion process of these arylammonium perchlorates.

Microstructural changes induced by ternary additions in a hypo-eutectic titanium-silicon alloy

Hypo-eutectic Ti-6.5 wt % Si alloy modified by separate additions of misch metal and low surface tension elements (Na, Sr, Se and Bi) has been examined by microscopic study and thermal analysis. Addition of third element led to modification of microstructure with apparently no significant enhancement of tensile ductility, with the exception of bismuth. Bismuth enhanced the ductility of the alloy by a factor of two and elastic-plastic fracture toughness to 9 MPa m–1/2 from a value of almost zero. The improved ductility of bismuth modified alloy is attributed to the reduced interconnectivity of the eutectic suicide, absence of significant suicide precipitation in the eutectic region and increase in the volume fraction of uniformly distributed dendrites. These changes are accompanied by a decrease in the temperature of eutectic solidification.

Perturbation of critical solution temperatures by impurity doping

An expression is developed for the variation of the critical solution temperature of a binary liquid system when a third component (dopant) is added, using an extension of the regular solution theory. The model can be used for UCST, LCST and for closed loop systems and has the correct features in the limiting cases.

Phase relations in the system BiO1.5–SrO–CuO at 1123 K

Phase relations in the system Bi-Sr-Cu-O at 1123 K have been investigated using optical microscopy, electron-probe microanalysis (EPMA) and powder X-ray diffraction (XRD) of equilibrated samples. Differential thermal analysis (DTA) was used to confirm liquid formation for compositions rich in BiO1.5. Compositions along the three pseudo-binary sections and inside the pseudo-ternary triangle have been examined. The attainment of equilibrium was facilitated by the use of freshly prepared SrO as the starting material. The loss of Bi2O3 from the sample was minimized by double encapsulation. A complete phase diagram at 1123 K is presented. It differs significantly from versions of the phase diagram published recently.

Reactivity with hydrogen of pure iron oxide and of iron oxides doped with oxides of Mn, Co, Ni and Cu

Using dynamic TG in H2, X-ray powder diffraction and Mössbauer Spectroscopy the reactivities fot hydrogen reduction of Fe2O3 prepared at different temperatures, Fe2O3 doped with oxides of Mn, Co, Ni and Cu prepared at 300DaggerC from nitrate precursors and intermediate spinels derived from above samples during reduction have been explored. The reactivity is higher for finely divided Fe2O3 prepared at 250DaggerC. The reduction is retarded by Mn, marginally affected by Co and accelerated by Ni and Cu, especially at higher (5 at.%) dopant concentration. These reactivities confirmed also by isothermal experiments, are ascribed to the nature of disorder in the metastable intermediate spinels and to hydrogen rsquospill overrsquo effects.

Precursor Dependent Microstructure Evolution and Nonstoichiometry in Nanostructured Cerium Oxide Coatings Using the Solution Precursor Plasma Spray Technique

A solution precursor plasma spray (SPPS) technique has been used for direct deposition of cerium oxide nanoparticles (CNPs) from various cerium salt solutions as precursors. Solution precursors were injected into the hot zone of a plasma plume to deposit CNP coatings. A numerical study of the droplet injection model has been employed for microstructure development during SPPS. The decomposition of each precursor to cerium oxide was analyzed by thermogravimetric-differential thermal analysis and validated by thermodynamic calculations. The presence of the cerium oxide phase in the coatings was confirmed by X-ray diffraction studies. Transmission electron microscopy studies confirmed nanocrystalline (grain size <14 nm) characteristic of the coatings. X-ray photoelectron spectroscopy studies indicated the presence of a high concentration of Ce3+ (up to 0.32) in the coating prepared by SPPS. The processing and microstructure evolution of cerium oxide coatings with high nonstoichiometry are reported.