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      Volume 27, Issue 2

      April 2004,   pages  85-216

    • Deposition of metal chalcogenide thin films by successive ionic layer adsorption and reaction (SILAR) method

      H M Pathan C D Lokhande

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      During last three decades, successive ionic layer adsorption and reaction (SILAR) method, has emerged as one of the solution methods to deposit a variety of compound materials in thin film form. The SILAR method is inexpensive, simple and convenient for large area deposition. A variety of substrates such as insulators, semiconductors, metals and temperature sensitive substrates (like polyester) can be used since the deposition is carried out at or near to room temperature. As a low temperature process, it also avoids oxidation and corrosion of the substrate. The prime requisite for obtaining good quality thin film is the optimization of preparative provisos viz. concentration of the precursors, nature of complexing agent, pH of the precursor solutions and adsorption, reaction and rinsing time durations etc.

      In the present review article, we have described in detail, successive ionic layer adsorption and reaction (SILAR) method of metal chalcogenide thin films. An extensive survey of thin film materials prepared during past years is made to demonstrate the versatility of SILAR method. Their preparative parameters and structural, optical, electrical properties etc are described. Theoretical background necessary for the SILAR method is also discussed.

    • Formation and characterization of Y:247 film through spray pyrolysis technique

      Suman Anand O N Srivastava

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      The synthesis of high temperature superconducting films of Y:247 (𝑇c ∼ K) have been successfully achieved. The difficulty in synthesis owing to narrow range of stability of Y:247 has been taken care of through several quenching modes, e.g. quenching of the films synthesized at ∼ 850°C, in air or in liquid nitrogen. The energy dispersive analysis of X-rays (EDAX) and transmission electron microscopy (TEM) studies of the as processed film, Y2Ba4Cu7O14+𝑥, exhibit nearly correct cationic stoichiometry of 2 : 4 : 7; also narrow regions (< 50 Å) of minority Y:124 phase and stacking faults capable of working as flux pinning sites have been invariably found to be present. In addition to Y:247, Ag admixed films have also been investigated. The 𝑇c here is ∼ 70–75 K which is similar to that of the film without silver. Representative estimates of transport critical current density (𝐽c) for Y:247 films is ∼ 103 A/cm2, and with silver corresponding to Y2Ba4Cu7O14+𝑥 (Ag0.1) is found to be ∼ 104 A/cm2.

    • Solid state synthesis and structural refinement of polycrystalline La𝑥Ca1-𝑥TiO3 ceramic powder

      O P Shrivastava Narendra Kumar I B Sharma

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      Perovskite structure based ceramic precursors have a characteristic property of substitution in the ``A" site of the ABO3 structure. This makes them a potential material for nuclear waste management in synthetic rock (SYNROC) technology. In order to simulate the mechanism of rare earth fixation in perovskite, La𝑥 Ca1-𝑥TiO3 (where 𝑥 = 0.05) has been synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and La as starting materials. Solid state synthesis has been carried out by repeated pelletizing and sintering the finely powdered oxide mixture in a muffle furnace at 1050°C. The ceramic phase has been characterized by its powder diffraction pattern. Step analysis data has been used to determine the structure of solid solution of lanthanum substituted calcium titanate. The SEM and EDAX analyses also confirm that the CaTiO3 can act as a host for lanthanum. X-ray data has been interpreted using CRYSFIRE and POWDERCELL softwares. The ℎ, 𝑘, 𝑙 values for different lattice planes have been generated from the experimental data. The lanthanum substituted perovskite crystallizes in orthorhombic symmetry with space group 𝑃 𝑛 𝑚 𝑎 (#62). Following unit cell parameters have been calculated: 𝑎 = 5.410, 𝑏 = 7.631, 𝑐 = 5.382. The calculated and observed values of corresponding intensities, 2𝜃, and density show good agreement. GSAS based calculation for bond distances Ti–O, Ca–O, La–O and bond angles Ti–O–Ca, Ca–O–Ca, La–O–Ti have been reported.

    • Finite element analysis of residual stress in the welded zone of a high strength steel

      Li Yajiang Wang Juan Chen Maoai Shen Xiaoqin

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      The distribution of the residual stress in the weld joint of HQ130 grade high strength steel was investigated by means of finite element method (FEM) using ANSYS software. Welding was carried out using gas shielded arc welding with a heat input of 16 kJ/cm. The FEM analysis on the weld joint reveals that there is a stress gradient around the fusion zone of weld joint. The instantaneous residual stress on the weld surface goes up to 800 ∼ 1000 MPa and it is 500 ∼ 600 MPa, below the weld. The stress gradient near the fusion zone is higher than any other location in the surrounding area. This is attributed as one of the significant reasons for the development of cold cracks at the fusion zone in the high strength steel. In order to avoid such welding cracks, the thermal stress in the weld joint has to be minimized by controlling the weld heat input.

    • Fabrication and characterization of porous hydroxyapatite ocular implant followed by an in vivo study in dogs

      B Kundu M K Sinha M K Mitra D Basu

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      Porous hydroxyapatite ocular implant was fabricated by a novel and simple method using hydroxyapatite powder synthesized in the laboratory. The porosity and pore size of the implant were controlled to make it light in weight as well as suitable for rapid vascularization after implantation. The implant was characterized by X-ray diffraction studies, infrared spectra and chemical analysis for phase purity and chemical composition. The pore morphology and pore size distribution of the samples were investigated by scanning electron microscope (SEM). Thereafter, efficacy of the implant was examined by in vivo study in dogs. Clinical, haematological and radiological studies indicated the suitability of the implant for replacement of the lost eye of human patients.

    • Dielectric behaviour of strontium tartrate single crystals

      S K Arora Vipul Patel Brijesh Amin Anjana Kothari

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      Strontium tartrate trihydrate (STT) crystals have been grown in silica hydrogel. Various polarization mechanisms such as atomic polarization of lattice, orientational polarization of dipoles and space charge polarization in the grown crystals have been understood using results of the measurements of dielectric constant (𝜀') and dielectric loss (tan 𝛿) as functions of frequency and temperature. Ion core type polarization is seen in the temperature range 75–180°C, and above 180°C, there is interfacial polarization for relatively lower frequency range. One observes dielectric dispersion at lower frequency presumably due to domain wall relaxation.

    • Synthesis and dielectric properties of MXTi7O16 (M = Ba and Sr;X = Mg and Zn) hollandite ceramics

      V M Manisha K P Murali S N Potty V Priyadarsini R Ratheesh

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      MXTi7O16 (M = Ba and Sr; X = Mg and Zn) ceramics have been synthesized by the conventional solid state ceramic route. The dielectric properties such as dielectric constant (𝜀r), loss tangent (tan 𝛿) and temperature variation of dielectric constant ($\tau_{\varepsilon r}$) of the sintered ceramic compacts are studied using an impedance analyser up to 13 MHz region. The strontium compounds have relatively high dielectric constant and low loss tangent compared to the barium analogue. The phase purity of these materials has been examined using X-ray diffraction studies and microstructure using SEM method.

    • Magnetic field induced assembling of nanoparticles in ferrofluidic liquid thin films based on Ni𝑥Fe1-𝑥Fe2O4

      V S Abraham S Swapna Nair S Rajesh U S Sajeev M R Anantharaman

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      Ultra fine precursors for ferrofluid synthesis, belonging to the series, Ni𝑥Fe1-𝑥Fe2O4 (where `𝑥’ varies from `0’ to `0.6’ in steps of 0.1), were synthesized. Ferrofluids based on these fine particles were prepared with oleic acid as surfactant and kerosene as carrier. Ferrofluidic thin films were made on glass substrates and magnetic field induced laser transmission was studied. The pattern exhibited by the films under the influence of a magnetic field was observed with the help of a CCD camera. The analysis of results confirms the chain formation of particles in the presence of an applied magnetic field and their saturation at higher applied fields.

    • Magnetically textured ferrofluid in a non-magnetic matrix: Magnetic properties

      Mrudul Gadhvi R V Upadhyay Kinnari Parekh R V Mehta

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      Texturing of two different magnetic fluids were carried out in paraffin wax under the influence of an external magnetic field. The textured samples were characterized using magnetization measurement and a.c. susceptibility techniques. The results are discussed in the light of ratio of anisotropic energy to magnetic and thermal energies.

    • Magnetic properties of ball-milled TbFe2 and TbFe2B

      J Arout Chelvane S Kasiviswanathan M V Rao G Markandeyulu

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      The magnetic properties of ball-milled TbFe2 and TbFe2B were studied by magnetization measurements. X-ray diffraction studies on TbFe2B showed that boron occupied interstitial position in the crystal structure, just as hydrogen did. The value of the saturation magnetization of TbFe2B was found to be smaller than that of TbFe2. This is explained on the basis of a charge transfer between the boron atoms and the 3d band of Fe. The anisotropy of TbFe2B was found to be large compared to that of TbFe2. X-ray diffractograms for the ball milled samples showed that after 80 h of milling, a predominantly amorphous phase was obtained. TbFe2B was found to undergo easy amorphization compared to TbFe2. Magnetization of TbFe2 was found to decrease rapidly with initial milling hours and was found to be constant with further hours of milling. TbFe2B exhibited an anomalous behaviour with an increase in moment with milling hours and this may be due to the segregation of 𝛼-Fe.

    • Immobilization of industrial waste in cement–bentonite clay matrix

      I B Plecas S Dimovic

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      Results of a series of experimental tests performed to determine the influence of matrix characteristics on the leaching mechanism of copper aluminum oxychloride immobilized into cement matrices are presented. The objective of this work was to investigate the leaching mechanism of copper as a constituent of copper aluminum oxychloride (`CAOX’). Transport phenomena involved in the leaching of a waste material from a composite matrix into surrounding water were investigated using three methods based on theoretical equations:

      1. diffusion equation derived for a plane source model,

      2. rate equation for diffusion coupled with a first-order reaction and

      3. the leaching data were also analysed by an empirical method employing a polynomial equation.

      These three methods are compared with respect to their applicability to the leaching data.

    • High effective silica fume alkali activator

      Vladimír Živica

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      Growing demands on the engineering properties of cement based materials and the urgency to decrease unsuitable ecologic impact of Portland cement manufacturing represent significant motivation for the development of new cement corresponding to these aspects. One category represents prospective alkali activated cements. A significant factor influencing their properties is alkali activator used. In this paper we present a new high effective alkali activator prepared from silica fume and its effectiveness. According to the results obtained this activator seems to be more effective than currently used activators like natrium hydroxide, natrium carbonate, and water glass.

    • Evolution of microstructure in flyash-containing porcelain body on heating at different temperatures

      Kausik Dana Swapan Kumar Das

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      15 wt% flyash (a calcined byproduct of thermal power plant) was incorporated in a normal triaxial kaolin–quartz–feldspar system by replacing equivalent amount of quartz. The differences in microstructural evolution on heating the compact mass of both normal and flyash-containing porcelain at different temperatures (1150–1300°C) were examined using scanning electron microscopy (SEM) operating in secondary electron image (SEI) mode. Microstructure of normal porcelain did not show the presence of mullite and quartz grains at 1200°C and the viscosity of silica-rich glass restricted the growth of mullite crystals at 1250°C. Flyash porcelain, on the other hand, shows the presence of primary mullite aggregates in the clay relict and a significant growth of mullite crystals in a low viscosity glassy matrix at 1200°C itself. At 1300°C, both the bodies show a larger region of more elongated (> 1 𝜇m) secondary mullite along with clusters of smaller sized primary mullite (< 1 𝜇m). Small primary mullite crystals in the clay relict can be distinguished from elongated secondary mullite crystals in the feldspar relict in their size. Primary mullite aggregates remain stable also at higher temperatures. XRD studies were carried out for quantitative estimation of quartz, mullite and glass, which supported the SEM observations. An attempt was also made to correlate their mechanical strength with the constituent phases.

    • Li+ ion conductivities in boro-tellurite glasses

      M Harish Bhat M Kandavel Munia Ganguli K J Rao

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      Lithium ion conductivity has been investigated in a boro-tellurite glass system, LiCl.LiBO$_{2}\cdot$TeO2.In the absence of LiCl, the conductivity increases with increasing non-bridging oxygen (NBO) concentration. LiCl addition has little influence on total conductivity although the observed barriers are low. Formation of LiCl clusters appears evident. In the a.c. conductivity and dielectric studies, it is observed that the conductivity mechanism remains the same in all compositions and at all temperatures. A suggestion is made that Li+ ion transport may be driven by bridging oxygen $\leftrightarrow$ non-bridging oxygen (BO $\leftrightarrow$ NBO) switching, which is why the two different types of Li+ ions in the clusters and in the neighbourhood of NBOs, do not manifest in the conductivity studies.

    • Elastic properties and spectroscopic studies of Na2O–ZnO–B2O3 glass system

      V C Veeranna Gowda R V Anavekar

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      Elastic properties, 11B MAS–NMR and IR spectroscopic studies have been employed to study the structure of Na2O–ZnO–B2O3 glasses. Sound velocities and elastic moduli such as longitudinal, Young’s, bulk and shear modulus have been measured at a frequency of 10 MHz as a function of ZnO concentration. Both sound velocities and elastic moduli increase with increasing ZnO concentration. Poisson’s ratio and Debye temperature were also found to increase with ZnO concentration. 11B MAS–NMR and IR spectra show characteristic features of borate network and compositional dependence trends as a function of Na2O/ZnO concentration. The results are discussed in view of borate network and dual structural role of Zn2+ ion into the network. The results indicate that the Zn2+ ions are likely to occupy network forming positions in this glass system.

    • Optical properties of 60B2O3–(40–𝑥)PbO–𝑥MCl2 and 50B2O3–(50–𝑥) PbO–𝑥MCl2 (M = Pb, Cd) glasses

      Shajo Sebastian M Abdul Khadar

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      Optical absorption and transmittance spectra of 60B2O3–(40–𝑥)PbO–𝑥MCl2 and 50B2O3–(50–𝑥) PbO–𝑥MCl2 (M = Pb, Cd) (10 ≤ 𝑥 ≤ 20) glasses of varying composition were recorded in the UV-visible region. Various optical parameters such as optical energy gap (𝐸opt), Urbach energy (𝐸e), refractive index (𝑛0), optical dielectric constant (𝜀), and ratio of carrier concentration to the effective mass (𝑁/𝑚*) were determined. The variation of optical energy gap with increase in the concentration of PbCl2 or CdCl2 is discussed.

    • High pressure effect on MoS2 and MoSe2 single crystals grown by CVT method

      Madhavi Dave Rajiv Vaidya S G Patel A R Jani

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      Single crystals of MoS2 and MoSe2 were grown by chemical vapour transport method using iodine as a transporting agent and characterized by optical microscopy, energy dispersive analysis (EDAX), X-ray powder diffraction (XRD) and Hall mobility at room temperature. The variation of electrical resistance under pressure was monitored in a Bridgman anvil set-up up to 6.5 GPa to identify occurrence of any structural transition. MoS2 and MoSe2 do not undergo any structural transitions under pressure.

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