• Volume 22, Issue 4

      June 1999,   pages  741-826

    • System Cu-Rh-O: Phase diagram and thermodynamic properties of ternary oxides CuRhO2 and CuRh2O4

      K T Jacob T H Okabe T Uda Y Waseda

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      An isothermal section of the phase diagram for the system Cu-Rh-O at 1273 K has been established by equilibration of samples representing eighteen different compositions, and phase identification after quenching by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive analysis of X-rays (EDX). In addition to the binary oxides Cu2O, CuO, and Rh2O3, two ternary oxides CuRhO2 and CuRh2O4 were identified. Both the ternary oxides were in equilibrium with metallic Rh. There was no evidence of the oxide Cu2Rh2O5 reported in the literature. Solid alloys were found to be in equilibrium with Cu2O. Based on the phase relations, two solid-state cells were designed to measure the Gibbs energies of formation of the two ternary oxides. Yttria-stabilized zirconia was used as the solid electrolyte, and an equimolar mixture of Rh+Rh2O3 as the reference electrode. The reference electrode was selected to generate a small electromotive force (emf), and thus minimize polarization of the three-phase electrode. When the driving force for oxygen transport through the solid electrolyte is small, electrochemical flux of oxygen from the high oxygen potential electrode to the low potential electrode is negligible. The measurements were conducted in the temperature range from 900 to 1300 K. The thermodynamic data can be represented by the following equations: {fx741-1} where Δf(ox)Go is the standard Gibbs energy of formation of the interoxide compounds from their component binary oxides. Based on the thermodynamic information, chemical potential diagrams for the system Cu-Rh-O were developed.

    • Mössbauer and XRD studies on the effect of doping iron in KCaY(PO4)2

      T N Sairam G V Narasimha Rao B Viswanathan

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      The effect of doping iron at the yttrium site in hexagonal KCaY(PO4)2 is studied for various concentrations ofx (0≤x≤1), of iron using Mössbauer and X-ray diffraction methods. For low iron concentrations, very little changes in structure are seen but atx≈0·1, onset of new peaks in the XRD pattern is observed. The Mössbauer study of the doped samples reveals that iron has a solubility of up to 2·5% in the parent phase with any excess iron precipitating out to form a new and unknown phase. From a detailed analysis of the X-ray diffraction pattern (corresponding tox=1) of the latter phase, it is found that this phase is rhombohedral with the possible space groupR3.

    • Studies of structural and dielectric properties of Ba5BiTi3Nb7O30 ceramics

      H Sharma Kiran Kumari S N Giri

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      The polycrystalline samples of Ba5BiTi3Nb7O30 (hereafter BBTN) belonging to ferroelectric oxide family of tungsten bronze structure were prepared by high temperature solid-state reaction method. Preliminary X-ray analysis of the samples provided the lattice parametersa=11·9331 Å,b=14·9684 Å, andc=7·0193 Å, and also formation of a single-phase orthorhombic structure at room temperature (303 K). Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (500 Hz to 10 KHz) at room temperature and also as a function of temperature (liquid nitrogen to 160°C) show the dielectric anomaly and structural phase transition at 16·8°C.

    • GMR in Ni/Cu multilayers: an electronic structure study

      S K Ghosh H G Salunke G P Das A K Grover M K Totlani

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      Ab initio self-consistent semi-relativistic spin-polarized TB-LMTO energy band calculations have been carried out on Ni/Cu(100) multilayers, to study the in-plane as well as perpendicular to plane giant magnetoresistance (GMR) effects. The magnetic interaction energies, evaluated as a function of layer thickness, indicate that the antiferromagnetic ordering is a possible ground state for manifestation of GMR. Using the density of states at Fermi level and the Fermi velocity, GMR has been estimated as a function of the Cu spacer thickness.

    • Microstructure and magnetic properties of zinc ferrite thin films produced by pulsed laser deposition

      D Ravinder

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      Zinc ferrite thin films were deposited from a target of zinc ferrite onto a MgO substrate using XeCl excimer laser operating at 308 nm and frequency of 30 Hz. The crystallographic characterizations of the films were performed using X-ray diffraction (XRD). Microstructure, surface morphology, chemical composition and grain size, as well as surface roughness were obtained from scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). The magnetic properties of the thin films were studied in the temperature range 5–300 K and in fields of up to 5 T using SQUID magnetometry. Data on temperature and field dependence of magnetization provide a strong evidence for superparamagnetism.

    • Oxidation of MoSi2 and MoSi2-based materials

      Sheela K Ramasesha K Shobu

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      Oxidation experiments, at 500°C, of MoSi2 and MoSi2-based compounds such as Mo(Al,Si)2 and MoSi2+1 wt% C compacts have been carried out. These compacts were prepared byin situ synthesis and a compaction method, starting from the elemental powders. For comparison, commercial MoSi2 and Mo(Al,Si)2 infiltrated into SiC preform were also studied under similar conditions. It was found that the synthesized high density MoSi2 and Mo(Al,Si)2 infiltrated into SiC preform did not show any oxidation even after 100 h of heating in air. The colour of the polished surfaces of commercial MoSi2, Mo(Al,Si)2 and MoSi2+1 wt% C had changed. The SEM of Mo(Al,Si)2 showed open blisters with rods of MoO3 in them whereas MoSi2+1 wt% C surface had MoO3 rods but no blisters and the oxidation was superficial with no penetration into the compact. It is suggested that in compounds, the presence of small amounts of impurities is not as detrimental to pesting as presence of defects like open pores or cracks. Hence, high density of the compact is essential for the prevention of complete disintegration of the compact.

    • Electrochemical synthesis of Tl-based highTc single-phase superconductor thin films

      L A Ekal N V Desai S H Pawar

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      Co-deposition of the Tl-based superconductors using electrodeposition technique was successfully carried out. Different processing parameters such as deposition potential, current density, deposition period etc were studied. The Tl-based alloyed thin films were deposited at a constant potential of −1·25V with respect to SCE electrode onto silver substrates and oxidized at 850°C in oxygen atmosphere. The samples thus prepared showed superconducting behaviour below 122·5 K and the critical current density was 1·5×103A/cm2. Electrochemical synthesis of Tl-based highTc single-phase superconductor thin films is also reported.

    • Electrical properties of SiO2-doped sodium metavanadate sintered discs

      B V Bahuguna Saradhi G Prasad G S Kumar T Bhimasankaram

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      Impedance of sintered discs of 0·1, 0·25, 0·4 mol% of sodium metavanadate was measured in the frequency range 10 kHz-1 MHz and in the temperature region from room temperature (=30°C) to 450°C. AC conductivity was calculated from the data. DC conductivity was measured in the temperature range 150–450°C. Debye type of relaxation effects were observed in the dielectric loss. The activation energy of the dipoles involved in relaxation was estimated. The activation energy for AC conduction in the temperature above 380°C was calculated. These values are larger than the activation energy of pure sodium metavanadate sample. The relaxation phenomenon observed is explained.

    • A matrix isolation FTIR investigation of laser-ablated uranium oxide in argon and nitrogen matrices

      K Sankaran K Sundararajan K S Viswanathan

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      Uranium oxide was laser-ablated using the second harmonic of a Nd : YAG laser, and the products studied after trapping them in Ar and N2 matrices. The species obtained in the Ar matrix were UO, UO2 and UO3, which represent the primary products of laser ablation. Charge transfer complexes, (UO2+) (O2) and (UO22+)(O22−) were also observed. In the N2 matrix, in addition to the primary ablation products, reaction products with nitrogen were also observed; the prominent among them being UN2 and NUO, together with their complexes with N2. Charge transfer complexes were also seen in these experiments. Features due to NO, N3 and N3 were identified, which clearly point to the role of nitrogen in these reactions.

    • 12C5+ radiation effects in SR-86 track recording polymer

      H S Virk G S Randhawa R Thangaraj D K Avasthi K Asokan

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      The samples of SR-86 polymer were irradiated with12C5+ ions of energy 5·0 MeV/u using fluences of 1011−1014 ions/cm2 at NSC Pelletron in a high vacuum scattering chamber. The optical studies show an increase in absorption of UV or IR in the shorter wavelength region (250–500 nm). The study also reveals that the increase in radiation dose extends the optical absorption region to longer wavelengths. It is observed that the bulk etch rate of this polymer is enhanced after heavy ion irradiation.

    • Studies on the ion-beam modifications in ethylene diamine sulphate

      E Venkateshwar Rao M Ramakrishna Murthy

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      The growth features, defect sub-structure and the influence of ion implantation on the (001) and (100) surfaces of ethylene diamine sulphate (EDS) single crystals have been studied. The surface micromorphology and defect substructure measurements of surface electrical conductivity and microhardness in both as-grown and He+ ion-implanted surfaces of EDS have also been studied. Optical and scanning electron microscopic investigations on the (001) surface of EDS revealed octogonal mother-liquor inclusions and spiral and hopper growth features. Chemical etching of the (100) surface revealed an increase in dislocation density on ion implantation, the etch pit morphology remaining the same. Studies on planar plastic anisotropy in both (001) and (100) surfaces indicated the crystallographic nature of the single crystal. Enhancement of surface electrical conductivity on ion implantation has been attributed to the formation, migration and increase in SO4 ion concentration relative to the as-grown EDS surfaces.

    • Effect of addition of polycarbonate on sheared flow of red mud-filled isotactic polypropylene

      Navin Chand S A R Hashmi

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      Different volume fractions of polycarbonate (PC) were incorporated to improve thermal stability of red mud (RM) filled polypropylene (PP). Effects of PC addition in RM filled PP on shear stress, melt viscosity, and melt elasticity have been determined under different shear rates by using a capillary rheometer. With the increase in shear rate, addition of PC in RM-filled PP reduced its shear stress and melt viscosity. However, recoverable shear strain increased with PC content in the blend.

    • Microcrystalline parameters in native and acid-modified starches

      H Somashekarappa R Somashekar Vasudeva Singh S Z Ali

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      Crystallite size and lattice distortion parameters of starches from cereals, millet, pulse, root and tuber before and after acid modification were determined by wide angle X-ray scattering (WAXS) studies. The (hkl) planes and cell parameters were obtained using a minimization program. Acid modification results in minor changes ind-spacing but there is considerable change in microcrystalline parameters, which has been reported here. Using these data, we have also estimated the changes in the mean shape of the coherent domains in terms of the shape ellipsoid in these starches for various types of acids treatment.

    • Characterization of reinforced syntactic foams using ultrasonic imaging technique

      C S Karthikeyan C R L Murthy S Sankaran Kishore

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      Non-destructive evaluation of defects like voids in syntactic foam reinforced with epoxy compatible chopped strand glass fibres, employing ultrasonic C-scan immersion through transmission method, was under-taken. The results showed that in four of the five similarly processed foam samples, the voids were uniformly spread while in the fifth, which was processed by a different route, a large spread of low dense area was noticed emphasizing the influence that processing technique has on the amount of voids present in the composites.

    • Nucleation studies in supersaturated aqueous solutions of KH2PO4 doped with KBr and K2Cr2O7

      C Mahadevan G Janiland Angel V Anton Sophana V Umayorubhagan

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      Induction periods were measured for various supersaturated aqueous solutions of potassium dihydrogen orthophosphate doped separately with potassium bromide and potassium dichromate by the direct vision method. Various critical nucleation parameters were calculated based on the classical theory for homogeneous crystal nucleation and the results are reported and discussed. The critical nucleation parameters increased with increase in doping concentration for both the dopants considered.

    • Nucleation studies in supersaturated aqueous solutions of urea and thiourea doped with inorganic dopants

      J M Kavitha K Seethalakshmi C Mahadevan Y Premila Rachelin

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      Induction periods were measured for various supersaturated aqueous solutions of urea doped separately with NH4NO3 and NaNO3 and thiourea doped separately with NaCl and KCI by the direct vision method. Based on classical theory for homogeneous crystal nucleation various critical nucleation parameters were calculated and the results are reported and discussed. In all the cases, the critical nucleation parameters increased with increase in doping concentration.

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