• Volume 28, Issue 7

December 2005,   pages  643-750

• Effect of temperature and 𝛼-irradiation on gas permeability for polymeric membrane

In the present study the polyethersulphone (PES) membranes of thickness (35 ± 2) 𝜇m were prepared by solution cast method. The permeability of these membranes was calculated by varying the temperature and by irradiation of 𝛼 ions. For the variation of temperature, the gas permeation cell was dipped in a constant temperature water bath in the temperature range from 303–373 K, which is well below the glass transition temperature (498 K). The permeability of H2 and CO2 increased with increasing temperature. The PES membrane was exposed by 𝛼-source (${}_{95}$Am$^{241}$) of strength (1 𝜇 Ci) in vacuum of the order of 10-6 torr, with fluence 2.7 × 107 ions/cm2. The permeability of H2 and CO2 has been observed for irradiated membrane with increasing etching time. The permeability increases with increasing etching time for both gases. There was a sudden change in permeability for both the gases when observed at 18 min etching. At this stage the tracks are visible with optical instrument, which confirms that the pores are generated. Most of pores seen in the micrograph are circular cross-section ones.

• High resistivity In-doped ZnTe: electrical and optical properties

Semi-insulating &lt; 111 &gt; ZnTe prepared by In doping during Bridgman growth was found to have a resistivity of 5.74 × 107 ohm-cm, the highest reported so far in ZnTe, with hole concentration of 2.4 × 109/cm3 and hole mobility of 46 cm2/V.s at 300 K. The optical band gap was 2.06 eV at 293 K compared with 2.26 eV for undoped semiconducting ZnTe. Thermally stimulated current (TSC) studies revealed 2 trap levels at depths of 202–222 meV and 412–419 meV, respectively. Photoluminescence (PL) studies at 10 K showed strong peaks at 1.37 eV and 1.03 eV with a weak shoulder at 1.43 eV. Short anneal for 3 min at 250°C led to conversion to a 𝑝-type material with resistivity, 14.5 ohm-cm, indicating metastable behaviour. Raman studies carried out on undoped and In-doped samples showed small but significant differences. Possible models for semi-insulating behaviour and meta-stability are proposed.

• Pressure dependence of elastic properties of ZnX (X = Se, S and Te): Role of charge transfer

An effective interaction potential (EIOP) is developed to invoke the pressure induced phase transition from zinc blende (𝐵3) to rocksalt (𝐵1) structure and anharmonic properties in ZnX (X = Se, S, Te) semiconductors. The effective interaction potential incorporates the long range Coulomb interaction, van der Waals interaction and short-range repulsive interaction up to second neighbour ions within the Hafemeister and Flygare approach as well as the charge transfer effects caused by the electron-shell deformation of the overlapping ions. The van der Waals coefficients are computed by the Slater Kirkwood variation method as a first step. Later on, we evaluate volume collapse, second order and third order elastic constants with pressure pointing to the systematic trends in all compounds of zinc blende structure and their thermal properties such as force constant, Gruneisen parameter, compressibility, Debye temperature etc. The vast volume discontinuity in pressure–volume (PV) phase diagram identifies the structural phase transition from zinc blende (𝐵3) to rock salt (𝐵1) structure and is consistent with those revealed from earlier reports.

• Synthesis and characterization of LiMgyMn2–yO4 cathode materials by a modified Pechini process for lithium batteries

Cubic spinels of composition, LiMgyMn2–yO4, with 𝑦 = 0.0, 0.05, 0.1, 0.15 and 0.2, were synthesized by a modified Pechini process using polyethylene glycol and citric acid. The phase formation and/or crystallization of the precursors were studied by thermal analysis. Products were characterized by X-ray diffraction and SEM analysis. Coin cells were fabricated with lithium as the anode and LiMgyMn2–yO4 as the cathode in an electrolyte of 1 M LiPF6 in a 1 : 1 (v/v) mixture of EC and DEC. The charge–discharge studies were performed and the results were compared with materials prepared by a solid state thermal method.

• Debye temperatures of uranium chalcogenides from their lattice dynamics

Phonon dispersion relations in uranium chalcogenides have been investigated using a modified three-body force shell model. From the phonon frequencies, their Debye temperatures are evaluated. Further, on the basis of the spin fluctuation in the heavy fermion uranium compounds, UPt3 and UBe13, the possible superconducting transition temperatures of chalcogenides are theoretically predicted. The 𝑇c values are in the same range as of those in UPt3 and UBe13.

• Optical, thermal and phase transition studies in Sn1–𝑥Ge𝑥Te

The optical and thermal properties of the mixed semiconducting alloy, Sn1–𝑥Ge𝑥Te, is studied by photo acoustics, for various Ge concentrations and phase transition for a particular concentration is also studied by the same method. The results are compared with the available literature values and discussed.

• Significance of structure–property relationship in alumina based porcelain insulators to achieve quality

The catastrophic failures of porcelain insulators in power lines can be minimized by understanding the structure–property relationship that governs the performance. A study addressing the materials aspects has been conducted on alumina based porcelain insulators used in 25 kV railway traction lines. This article asserts the controls exercised by chemical composition, crystalline structural phases and microstructure on the functional reliability and durability of the insulators. Influences of the total alumina, 𝛼-Al2O3 (corundum) and 𝛼-quartz contents, microstructural features including morphologies of mullite needles, quartz and corundum grains in the alumino silicate glassy matrix, large inhomogeneities in matrix constituents and composition have been highlighted.

• A new high temperature resistant glass–ceramic coating for gas turbine engine components

A new high temperature and abrasion resistant glass–ceramic coating system (based on MgO–Al2O3–TiO2 and ZnO–Al2O3–SiO2 based glass systems) for gas turbine engine components has been developed. Thermal shock resistance, adherence at 90°-bend test and static oxidation resistance at the required working temperature (1000°C) for continuous service and abrasion resistance are evaluated using suitable standard methods. The coating materials and the resultant coatings are characterized using differential thermal analysis, differential thermogravimetric analysis, X-ray diffraction analysis, optical microscopy and scanning electron microscopy. The properties evaluated clearly showed the suitability of these coatings for protection of different hot zone components in different types of engines. XRD analysis of the coating materials and the resultant coatings showed presence of a number of microcrystalline phases. SEM micrographs indicate strong chemical bonding at the metal–ceramic interface. Optical micrographs showed smooth glossy impervious defect free surface finish.

• Effect of heat treatment on properties of steam cured fly ash–lime compacts

Four different varieties of class F fly ashes, collected from different sources from the state of West Bengal (India) were mixed with lime in 9 : 1 wt ratio, followed by compaction of the mixes. The compacts were subjected to steam curing to develop an optimum strength by the reaction between fly ash and lime. The steam cured compacts were heated at different elevated temperatures and free lime content, compressive strength, bulk density and water absorption tendency of these compacts were measured and FTIR spectral changes were studied as a function of the heating temperatures. Kinetics of thermal dehydration of the compacts was also studied from thermogravimetric measurements under non-isothermal condition to ascertain the order of dehydration process and the associated activation energy.

• Polyvinyl alcohol–cellulose composite: a taste sensing material

There are reports of fabrication of taste sensor by adsorbing lipids into Millipore filter paper. With this lipid based sensor, it has been found that the taste sensing efficiency of membrane can be remarkably improved. We have made an attempt to prepare taste sensor material by using functionalized polymer without any lipid. PVA–cellulose composite has been modified to use as the sensor material. The research work covers polymer membrane preparation, morphology study and structural characterization of the membrane and study of the taste sensing characteristics of this membrane for five different taste substances. PVA–cellulose composite membrane was modified by phosphorylation with POCl3. FTIR spectroscopic analysis, XRD analysis and SEM were done to get an idea about the structure and morphology of the prepared phosphorylated PVA–cellulose composite membrane. The sensor characteristics like temporal stability, response stability, response to different taste substances, and reproducibility of sensing performance were studied using phosphorylated PVA–cellulose composite membrane. Sensor device prepared with this membrane has shown distinct response patterns for different taste substances in terms of membrane potential. Threshold concentrations of phosphorylated PVA–cellulose composite membrane for HCl, NaCl, Q-HCl, sucrose and MSG are 0.001 mM, 0.001 mM, 0.001 mM, 0.001 mM and 0.009 mM, respectively. The threshold concentrations are below human threshold concentrations. Membranes also showed characteristic response patterns for organic acids like acetic acid, citric acid, formic acid etc, mineral acids like HCl, H2SO4 and HNO3 salts, bitter substances, sweet substances and umami substances. Sensor device prepared with this membrane has excellent shelf life.

• Uses of 𝛼-Fe2O3 and fly ash as solid adsorbents

Solid adsorbents have shown great promise for control of particulate and non-particulate matter and as gas sensing devices in recent times. In the present study, adsorption of environmental toxic pollutant such as lead ions on solid adsorbents viz. 𝛼-Fe2O3 and fly ash, are reported. Considerable adsorption was observed on fly ash when compared to 𝛼-Fe2O3 surface. These studies are characterized by employing solid state and solution studies.

• Evaluation of gamma and neutron irradiation effects on the properties of mica film capacitors

We present an investigation of gamma and neutron radiation effects on mica film capacitors from an electrical point of view. We have studied quantitatively the effects of gamma and neutron irradiation on mica film capacitors of thickness, 20 and 40 𝜇m (0.7874 and 1.5748 mil) with two different areas, 01 and 04 cm2. The capacitance has been measured at room temperature in the frequency range 100 Hz–10 MHz. Negligible change in the capacitance due to high gamma dose of 60Co, 15 kGy at dose rate 0.25 kGy/h, has been observed. However, appreciable change in the capacitance has been observed due to low doses of fast neutrons (cumulative dose, 115 cGy) with flux ∼ 9.925 × 107 neutrons/cm2 h from 252Cf neutron source of fluence, 2.5 × 107 neutrons/s. We have also observed that the impact of gamma and neutron irradiation is more at frequencies higher than 10 kHz. These results show that the mica capacitors do not show any radiation response below 10 kHz.

The study shows the radiation response of mica film capacitors to gamma and fast neutron radiations. Mica capacitors show low gamma radiation response in comparison to fast neutron radiation, because a total dose of kGy order has been given by gamma source and only few cGy dose has been given by fast neutron source.

• Supramolecular structure of S-(+)-marmesin-a linear dihydrofuranocoumarin

The title compound, C14H14O4, a linear dihydrofuranocoumarin, was isolated from the bark of Aegle marmelos, a plant widely used in Ayurvedic system of medicine for the treatment of various ailments. The crystal structure was determined from X-ray diffraction data using direct methods. The compound crystallizes into monoclinic space group 𝑃21 with unit cell parameters: 𝑎 = 5.721(1) Å, 𝑏 = 13.810(1) Å, 𝑐 = 7.864(2) Å, 𝛽 = 100.39(1)°, 𝑍 = 2. The structure was refined by full-matrix least-squares to a final 𝑅 value of 0.0523 for 1184 observed reflections. The benzopyran moiety is perfectly planar. The dihedral angle between the pyrone and benzene rings is 0.3(1)°. The furan ring has a 2𝛼-envelope conformation. The molecules are linked by O–H…O hydrogen bonds into chains and these chains are linked into sheets by C–H…O hydrogen bonds. Further, the 𝜋−𝜋 stacking and C–H$\ldots\pi$(arene) interactions link all of the sheets into a supramolecular structure.

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