Thermal properties of 3BaO–3TiO2–B2O3 glasses

Transparent glasses in the system 3BaO–3TiO2–B2O3 (BTBO) were fabricated via the conventional melt-quenching technique. The as-quenched samples were confirmed to be non-crystalline by differential thermal analysis (DTA). Thermal parameters were evaluated using non-isothermal DTA experiments. The Kauzmann temperature was found to be 759 K based on heating-rate-dependent glass transition and crystallization temperatures. A theoretical relation for the temperature-dependent viscosity is proposed for these glasses and glass-ceramics.

Finding India’s place in the Sun –Prospects for harnessing solar thermal energy

In this article, we describe our ongoing efforts in addressing the environment and energy challenges facing the world today. Tapping solar thermal energy seems to be the right choice for a country like India. We look at three solar-thermal technologies in the laboratory — water purification/distillation, Stirling engine, and air-conditioning/refrigeration.

Synthesis, Thermal stability and Mechanical Behavior of Nano-Nickel

Nanocrystalline materials exhibit very high strengths compared to conventional materials, but their thermal stability may be poor. Electrodeposition is one of the promising methods for obtaining dense nanomaterials. It is shown that use of two different baths and appropriate conditions enables the production of nano-Ni with properties similar to commercially available materials. Microindentation experiments revealed a four fold increase in hardness value for nano-Ni compared to conventional coarse grained Ni. An improved thermal stability of nano-Ni was observed on co-deposition of nano-Al2O3particles.

The electrical switching and thermal behavior of bulk Ge(15)Te(85-x)Sn(x) and Ge(17)Te(83-x)Sn(x) glasses

Bulk Ge(15)Te(85 - x)Sn(x) and Ge(17)Te(83 - x)Sn(x) glasses, are found to exhibit memory type electrical switching. The switching voltages (V(t)) and thermal stability of Ge(15)Te(85 - x)Sn(x) and Ge(17)Te(83 - x)Sn(x) glasses are found to decrease with Sn content. The composition dependence of v, has been understood on the basis of the decrease in the OFF state resistance and thermal stability of these glasses with tin addition. X-ray diffraction studies reveal that no elemental Sn or Sn compounds with Te or Ge are present in thermally crystallized Ge-Te-Sn samples. This indicates that Sn atoms do not interact with the host matrix and form a phase separated network of its own, which remains in the parent glass matrix as an inclusion. Consequently, there is no enhancement of network connectivity and rigidity. The thickness dependence of switching voltages of Ge(15)Te(85 - x)Sn(x) and Ge(17)Te(83 - x)Sn(x) glasses is found to be linear, in agreement with the memory switching behavior shown by these glasses. (C) 2011 Elsevier B.V. All rights reserved.

Synthesis and nonlinear optical properties of Lead Telluride nanorods

Lead Telluride (PbTe) nanorods have been uniformly grown on silicon substrates, using the thermal evaporation technique under high vacuum conditions. The structural and morphological studies are done using X-ray diffraction and scanning electron microscopy. Optical nonlinearity studies using the open aperture z-scan employing 5 ns and 100 fs laser pulses reveal a three-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (gamma) are in the order of 10(-22) m(3) W-2 and for femtosecond excitation it is in the order of 10(-29) m(3) W-2. The role of free carriers and excitons in causing the nonlinearity in both excitation time domains is discussed. Results indicate that PbTe nanorods are good optical limiters with potential device applications. (C) 2011 Elsevier B.V. All rights reserved.

Thermoelectric properties of indium filled and germanium doped Co4Sb12 skutterudites

In-filled and Ge-doped Co4Sb12 skutterudites materials were synthesized by an induction melting process which was followed by annealing at 650 degrees C for 7 days. A structural, compositional, and morphological study was carried out by X-ray diffraction (XRD), electron probe micro analysis (EPMA), and scanning electron microscopy (SEM). The formation of a single skutterudite phase (delta-CoSb3) was confirmed by XRD and the composition of all the samples was verified by EPMA. The homogeneity and morphology of the samples was observed by potential Seebeck microprobe (PSM) and SEM, respectively. The PSM result confirmed the inhomogeneity of the samples. The temperature dependence of the Seebeck coefficient, electrical conductivity, and thermal conductivity were measured in the temperature range of 300-650 K. The samples of In0.16Co4Sb12-xGex (x = 0.05, 0.1, and 0.2) show a negative Seebeck coefficient confirming an n-type conductivity and the In0.16Co4Sb11.7Ge0.3 sample shows a positive Seebeck coefficient confirming a p-type conductivity. There was a change in the Seebeck coefficient from an n-type to a p-type at the doping concentration of x = 0.3 due to the excess Ge which increases in hole carrier concentration. Electrical conductivity decreases with an increase in Ge doping concentrations and with increases in temperature due to the bipolar effect. Thermal conductivity increases with an increase in carrier concentration and decreases when the temperature is increased. The highest ZT = 0.58 was achieved by In0.16Co4 Sb11.95Ge0.05 at 673K and In-filled and Ge-doped Co4Sb12 was not effective in improving the figure of merit. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3677982]

Thermal decomposition of haloethanols: single pulse shock tube and ab initio studies

This paper reports single pulse shock tube and ab initio studies on thermal decomposition of 2-fluoro and 2-chloroethanol at T=1000–1200 K. Both molecules have HX (X = F/Cl) and H2O molecular elimination channels. The CH3CHO formed by HX elimination is chemically active and undergoes secondary decomposition resulting in the formation of CH4, C2H6, and C2H4. A detailed kinetic simulation indicates that the formation of C2H4 could not be quantitatively explained as arising exclusively from secondary CH3CHO decomposition. Contributions from primary radical processes need to be considered to explain C2H4 quantitatively. Ab initio calculations on HX and H2O elimination reactions from the haloethanols at HF, MP2, and DFT levels with various basis sets up to 6/311++G**are reported. It is pointed out that due to strong correlations between A and Eα, comparison of these two parameters between experimental and theoretical results could be misleading.

Structural and dielectric characteristics of Bi2O3-TiO2-SrB4O7 glasses

Glasses of the composition 0.20 Bi2O3 - 0.30 TiO2 - 0.50 SrB4O7 and 0.30 Bi2O3 - 0.45 TiO2 - 0.25 SrB4O7 have been fabricated by conventional glass processing technique. These glasses have been characterized using X-ray powder diffraction (XRD), differential thermal analysis (DTA) and high resolution transmission electron microscopy (HRTEM). The frequency response of the dielectric constant and the loss tangent of these glasses has been studied. The formation of the crystalline bismuth titanate, Bi4Ti3O12 (BiT) phase in the heat treated samples has been confirmed by XRD and HRTEM studies. The measured ET Of the glass-ceramics are found to be in good agreement with those predicted by the logarithmic mixture rule. Optical second harmonic generation (SHG) at 1064 nm has been observed in the heat treated samples and is attributed to the formation of crystalline Bi4Ti3O12 (BiT) phase in the SrB4O7 (SBO) matrix.

Down-to-earth temperatures: The mechanics of the thermal environment

This lecture describes some recent attempts at unravelling the mechanics of the temperature distribution near ground, especially during calm, clear nights. In particular, a resolution is offered of the so-called Ramdas paradox, connected with observations of a temperature minimum some decimetres above bare soil on calm clear nights, in apparent defiance of the Rayleigh criterion for instability due to thermal convection. The dynamics of the associated temperature distribution is governed by radiative and convective transport and by thermal conduction, and is characterised by two time constants, involving respectively quick radiative adjustments and slow diffusive relaxation. The theory underlying the work described here suggests that surface parameters like ground emissivity and soil thermal conductivity can exert appreciable influence on the development of nocturnal inversions.

Structural, thermal and electrical characterization of NdLiMo2O8 electroceramics, using impedance spectroscopy

We report electrical property of a polycrystalline NdLiMo2O8 ceramics using complex impedance analysis. The material shows temperature dependent electrical relaxation phenomena. The d.c. conductivity shows typical Arrhenius behavior, when observed as a function of temperature. The a.c. conductivity is found to obey Jonscher's universal power law. The material was prepared in powder form by a standard solid-state reaction technique. Material formation and crystallinity have been confirmed by X-ray diffraction studies. Impedance measurements have been performed over a range of temperatures and frequencies. The results have been analyzed in the complex plane formalism and suitable equivalent circuits have been proposed in different regions. The role of bulk and grain boundary effect in the overall electrical conduction process is discussed with proper justification. (C) 2011 Elsevier Ltd. All rights reserved.

Simultaneous multilayer scanning and detection for multiphoton fluorescence microscopy

Fast three-dimensional (3D) imaging requires parallel optical slicing of a specimen with an efficient detection scheme. The generation of multiple localized dot-like excitation structures solves the problem of simultaneous slicing multiple specimen layers, but an efficient detection scheme is necessary. Confocal theta detection (detection at 90 degrees to the optical axis) provides a suitable detection platform that is capable of cross-talk-free fluorescence detection from each nanodot (axial dimension approximate to 150 nm). Additionally, this technique has the unique feature of imaging a specimen at a large working distance with super-resolution capabilities. Polarization studies show distinct field structures for fixed and fluid samples, indicating a non-negligible field-dipole interaction. The realization of the proposed imaging technique will advance and diversify multiphoton fluorescence microscopy for numerous applications in nanobioimaging and optical engineering.

Non-Thermal Plasma Applications at Very Low Temperature

Application of non-thermal plasma for gas cleaning is gaining prominence in the recent years. Normally, the gas treatment was carried out at or above room temperature, by the dry type plasma reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the flue gas mixture. We propose the non-thermal plasma process at very low temperature, and report here some interesting results of treatment of NO or N2O with pulsed plasma below — 100°C ambient temperature. Direct methanol synthesis from CH4 and CO2 at very low temperature is also reported. A comparative analysis of the various tests are presented together with a note on the energy consideration