• Volume 28, Issue 3

June 2005,   pages  187-301

• Weak C–H…O hydrogen bonds in alkaloids: An overview

An overview of general classification scheme, medicinal importance and crystal structure analysis with emphasis on the role of hydrogen bonding in some alkaloids is presented in this paper. The article is based on a general kind of survey while crystallographic analysis and role of hydrogen bonding are limited to only those alkaloids whose three-dimensional structure has been reported by us. The C–H…O hydrogen bonding in the solid state in alkaloids has been found to be predominant and this observation makes the role of hydrogen bonding in organic molecular assemblies very important.

• Synthesis and structural characterization of some Pb(B$^{'}_{1/3}$Nb2/3)O3 type materials by two-stage solid-state route

Two-stage columbite solid state reaction route has been used for the preparation of Pb (B$^{'}_{1/3}$Nb2/3)O3 materials (B′ = Mg, Ni and Cd). The columbite precursor phase was structurally characterized using diffraction data. MgNb2O6, NiNb2O6 and CdNb2O6 show orthorhombic structures i.e. pure columbite phase. Final phase materials get stabilized in mixed phase. The diffraction pattern shows that it is a mixture of cubic pyrochlore and perovskite phase. Percentage of perovskite phase was calculated using the band intensities of (110) perovskite and (222) pyrochlore peaks. The calculated percentages show the dominant perovskite phase. Possible reasons for mixed phase are discussed.

• A coprecipitation technique to prepare ZnNb2O6 powders

A simple coprecipitation technique was successfully applied for the preparation of pure ultrafine single phase, ZnNb2O6 (ZN). Ammonium hydroxide was used to precipitate Zn2+ and Nb5+ cations as hydroxides simultaneously. This precursor on heating at 750°, produced ZN powders. For comparison, ZN powders were also prepared by the traditional solid state method. The phase contents and lattice parameters were studied by the powder X-ray diffraction (XRD). Particle size and morphology were studied by transmission electron spectroscopy (TEM).

• Zone refining of cadmium and related characterization

We present the zone refining results of cadmium using horizontal resistive zone refiner under constant flow of moisture free hydrogen gas. The boron impurity in cadmium can be avoided using quartz (GE 214 grade) boat in lieu of high pure graphite boat. The analytical results using inductively coupled plasma optical emission spectrometry (ICPOES) show that majority of the impurities are less than the detection limits. Comparatively, zinc is the most difficult impurity element to remove in cadmium matrix by zone refining.

• Preparation of silver powder through glycerol process

High purity fine silver powder with uniform particle morphology was prepared through glycerol process. The process involves reduction of silver nitrate by glycerol under atmospheric conditions at a temperature below 175°C. Glycerol, in this process, acts as a solvent as well as a reducing agent. The powders prepared through this process were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical analysis. The powders were well crystalline and contained oxygen, carbon and hydrogen as impurities. Overall purity was better than 99.9%. The yield of silver powder was better than 99%.

• Optical and microstructural investigations of porous silicon

Raman scattering and photoluminescence (PL) measurements on (100) oriented 𝑛-type crystalline silicon (𝑐-Si) and porous silicon (PS) samples were carried out. PS samples were prepared by anodic etching of 𝑐-Si under the illumination of light for different etching times of 30, 60 and 90 min. Raman scattering from the optical phonon in PS showed the redshift of the phonon frequency, broadening and increased asymmetry of the Raman mode on increasing the etching time. Using the phonon confinement model, the average diameter of Si nanocrystallites has been estimated as 2.9, 2.6 and 2.3 nm for 30, 60 and 90 min samples, respectively. Similar size of Si crystallites has been confirmed from the high resolution transmission electron microscopy (HRTEM). Using 2TO phonon mode intensity, we conjectured that the disordered Si region around the pores present in 30 min PS dissolved on etching for 90 min. The photoluminescence (PL) from PS increased in intensity and blue shifted with etching time from 2.1–2.3 eV. Blue shifting of PL is consistent with quantum confinement of electron in Si nanocrystallites and their sizes are estimated as 2.4, 2.3 and 2.1 nm for 30, 60 and 90 min PS, respectively which are smaller than the Raman estimated sizes due to temperature effect. Unambiguous dominance of quantum confinement effect is reported in these PS samples.

• DC resistivity of alumina and zirconia sintered with TiC

Pure alumina and zirconia powders were sintered separately with increasing amount of TiC up to ∼ 65 vol.%, as a conducting second phase with an aim to prepare conducting structural ceramics which can be precisely machined by EDM technique. TiC did not help in sintering the parent phase but it decreased the d.c. resistivity of the composite to 1 ohm.cm at ∼ 30 vol.% loading. The conductivity is explained by the effective media and percolation theories.

• Thermal and structural properties of spray pyrolysed CdS thin film

Using photo acoustic technique, the thermal properties of CdS thin films grown by spray pyrolysis are measured. Thermal diffusivity and conductivity in these films decrease at least two orders compared with bulk. These results are compared with our study on nano CdS and the other available literature. The comparison is good. The dependence of thermal diffusivity on the thickness of the layer or the size of the particles on the glass substrate are analysed from the present measurement and discussed. The dependence of thermal diffusivity on the thickness of the layer on the glass substrate is discussed.

• Screen printed nanosized ZnO thick film

Nanosized ZnO was prepared by polyol synthesis. Fluorescence spectrum of the ZnO colloid at varying pump intensities was studied. The powder was extracted and characterized by XRD and BET. The extracted powder was screen printed on glass substrates using ethyl cellulose as binder and turpinol as solvent. Coherent back scattering studies were performed on the screen printed sample which showed evidence of weak localization. The screen printed pattern showed strong UV emission.

• Dip-coated hydrotungstite thin films as humidity sensors

Thin films of a hydrated phase of tungsten oxide, viz. hydrotungstite, have been prepared on glass substrates by dip-coating method using ammonium tungstate precursor solution. X-ray diffraction shows the films to have a strong 𝑏-axis orientation. The resistance of the films is observed to be sensitive to the humidity content of the ambient, indicating possible applications of these films for humidity sensing. A homemade apparatus designed to measure the d.c. electrical resistance in response to exposure to controlled pulses of a sensing gas has been employed to evaluate the sensitivity of the hydrotungstite films towards humidity.

• Superconductivity in dense Mg1–𝑥M𝑥B2 (M = Zr, Nb, Mo;𝑥 = 0.05) materials sintered under pressure

Dense compacts of superconducting MgB2 material have been produced by sintering under 3 GPa pressure and 900°C using a cubic anvil apparatus. The starting material was produced by the powder in tube (PIT) method at low pressure and in argon atmosphere. The effect of substitution of Mg sites with nonmagnetic 4𝑑-transition metals (Zr, Nb, Mo) on the superconducting transition temperature (𝑇c) has been studied by resistivity and susceptibility measurements. The results indicate that there is a small gradual reduction in the transition temperature as we move from Zr to Mo.

• Influence of Cl, Br, NO$^{−}_{3}$ and SO$^{2−}_{4}$ ions on the corrosion behaviour of 6061 Al alloy

The effects of anions like Cl, Br, NO$^{–}_{3}$ and SO$^{2-}_{4}$ on the anodic dissolution of the monolithic Al 6061 alloy have been investigated at neutral pH through immersion testing and electrochemical techniques like potentiodynamic polarization and a.c. impedance spectroscopy. Scanning electron microscopy was employed to characterize the corroded surface and to observe the extent of pitting in different media. From the evaluated corrosion parameters it was found that the dissolution of the matrix was extensively reduced in presence of aqueous solutions containing Br, NO$^{–}_{3}$ and SO$^{2-}_{4}$ ions while Cl ions aggravated corrosion by penetrating into the barrier oxide film on the surface of the material. Pronounced effect of pitting was observed in presence of Cl and the level of pitting in NO$^{–}_{3}$ and Br were mild. In presence of SO$^{2-}_{4}$ ions passivity was extended over a wide potential range and breakdown of passivity occurs when the material was polarized beyond pitting potential. The departure of capacitive behaviour towards resistive behaviour was clearly observed through impedance measurements when investigations were conducted in Cl media and in presence of the other electrolytes. Corrosion rates were, however, controlled during prolonged exposure in the electrolytic media, specially in case of chloride media, due to the predominance of film repair kinetics.

• Effect of cold work and aging on mechanical properties of a copper bearing HSLA-100 steel

Influence of cold working and aging on the mechanical properties of a Cu-bearing HSLA-100 steel has been studied. The steel was given solution treatment at 1000°C, followed by cold rolling to 25, 50 and 80 pct deformations and aging at 600°C for various durations. Substantial improvement in hardness and UTS was observed in the peak aged condition of various treatments, but at the expense of ductility and impactenergy. Extensive scanning electron microscopic studies carried out on impact and tensile fracture surfaces suggest that poor impact energy and low ductility in peak aged condition could be associated with inhomogeneous deformation caused by the existence of coherent precipitates. Other parameters adversely affecting toughness and ductility in various stages of cold work and aging may include high stress concentration at high density dislocation network and dislocation–precipitate interface. Overaging in various treatments resulted in higher impact energy and ductility, presumably due to existence of incoherent precipitates and reduction in stress concentration at dislocation cell boundaries. It is observed that a good combination of high hardness and UTS with high impact energy and ductility could be obtained by a treatment suitable to cause coexistence of coherent and incoherent precipitates.

• Diffusion processes in 𝛽-Zr(Al) phase: a thermodynamic approach

The diffusion behaviour in the 𝛽-Zr(Al) solid solution phase was investigated in the temperature range 1203–1323 K using a thermodynamic approach. The Boltzmann–Matano relation used for determining interdiffusion coefficients and the Darken’s equations used for evaluating the intrinsic diffusion coefficients from velocity of movement of markers in diffusion couples were modified suitably. The composition dependent thermodynamic interdiffusion coefficients were evaluated using chemical potential gradient. Composition and temperature dependence of the thermodynamic interdiffusion coefficients were also established. The thermodynamic intrinsic diffusion coefficients of Al and Zr and their temperature dependence were determined using the modified Darken’s equations.

• Study on electrical properties of Ni-doped SrTiO3 ceramics using impedance spectroscopy

The ceramics, SrTiO3 (ST) and 0.4, 0.8 atom% Ni doped SrTiO3, were prepared by solid state reaction route. The average grain size of undoped and doped samples was measured and found to be 1.2, 1.9 and 3.7 𝜇m, respectively. The impedance measurements were conducted at 400–600°C to separate grain and grain boundary contributions. The grain and grain boundaries relaxation frequencies were shifted to higher frequency with temperature. Bulk resistance of doped and undoped ST ceramics was more or less the same. Single grain boundary resistance of doped sample was higher than that of undoped one, indicating that GB resistance increases with acceptor doping. Activation energies were calculated to confirm the same.

• Role of small amount of MgO and ZrO2 on creep behaviour of high purity Al2O3

Small levels of various dopants have a significant effect on creep in polycrystalline alumina. While most previous studies have examined the effect of ionic size, the influence of valency of dopants on creep has not yet been completely characterized. The present detailed experimental study, utilizing magnesia and zirconia with a similar ionic size, demonstrates that the ionic valency of dopants also plays a crucial role in creep since magnesia does not significantly alter creep whereas zirconia retards creep substantially. Magnesia doped alumina deforms by Coble diffusion creep whereas zirconia doped alumina deforms by an interface controlled diffusion creep process.

• Effects of polyethyleneimine adsorption on rheology of bentonite suspensions

The influence of the cationic polymer, polyethyleneimine polymer (PEI) on the flow behaviour of bentonite suspensions (2%, w/w), was studied. XRD, zeta potential and adsorption studies were done together with rheological measurements. The addition of PEI at concentration ranges of 10-5–4.5 g/l and their rheological properties and stability of bentonite suspensions were studied. The adsorption rates for the bentonite suspensions are very fast. The XRD results showed that the PEG molecules did not intercalate into the layers of the clay.

• Transformations among CE–CVM model parameters for multicomponent systems

In the development of thermodynamic databases for multicomponent systems using the cluster expansion–cluster variation methods, we need to have a consistent procedure for expressing the model parameters (CECs) of a higher order system in terms of those of the lower order subsystems and to an independent set of parameters which exclusively represent interactions of the higher order systems. Such a procedure is presented in detail in this communication. Furthermore, the details of transformations required to express the model parameters in one basis from those defined in another basis for the same system are also presented.

• Environmentally benign novel green pigments: Pr1–𝑥Ca𝑥PO4 (𝑥 = 0–0.4)

Rare earth based materials have recently attracted considerable attention as potential eco-friendly colourants for low temperature as well as high temperature applications. In the present study, we have synthesized a series of Ca-doped PrPO4 compounds with the general formula, Pr1–𝑥Ca𝑥PO4 (𝑥 = 0–0.4 in steps of 0.1) and characterized the compounds by powder X-ray diffraction. All the compositions show a monoclinic monazite structure. The optical properties of the brilliantly coloured pigments [𝐿 (brightness), $a^{\ast}$ (+ red - green), $b^{\ast}$ (+ yellow - blue)] have been examined. These materials can find application as potential green colourants.

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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019