• Issue front cover thumbnail

      Volume 31, Issue 6

      November 2008,   pages  825-918

    • Preparation of PbSe nanoparticles by electron beam irradiation method

      Zhen Li Chao Wu Yanyan Liu Tiebing Liu Zheng Jiao Minghong Wu

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      A novel method has been developed by electron beam irradiation to prepare PbSe nanoparticles. 2 MeV 10mA GJ-2-II electronic accelerator was used as radiation source. Nanocrystalline PbSe was prepared rapidly at room temperature under atmospheric pressure without any kind of toxic reagents. The structure and morphology of prepared PbSe nanoparticles were analysed by X-ray diffraction, transmission electron microscope and atomic force microscope. The results indicated that the obtained materials were cubic nanocrystalline PbSe with an average grain size of 30 nm. The optical properties of prepared PbSe nanocrystalline were characterized by using photoluminescence spectroscopy. The possible mechanism of the PbSe grain growth by electron beam irradiation method is proposed.

    • Controlling of morphology of Ni/Al-LDHs using microemulsionmediated hydrothermal synthesis

      Yun Zhao Fenfei Xiao Qingze Jiao

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      A quaternary microemulsion, cetyltrimethylammonium bromide (CTAB)/water/𝑛-hexane/𝑛-hexanol, was selected for the synthesis of Ni/Al-layered double hydroxides (LDHs). Ni/Al-LDHs with nanowire-, spherical-, rod- and tube-like morphologies were prepared via the microemulsion-mediated hydrothermal synthesis. The CTAB concentration played an important role in determining the morphology of Ni/Al-LDHs. The structure, composition and morphology of the obtained Ni/Al-LDH nanostructures were investigated by X-ray diffraction, inductively coupled plasma emission spectroscopy, infrared spectrometer and transmission electron microscopy. A possible formation mechanism of Ni/Al-LDH nanostructures is proposed.

    • Humidity sensing characteristics of hydrotungstite thin films

      G V Kunte S A Shivashankar A M Umarji

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      Thin films of the hydrated phase of tungsten oxide, hydrotungstite (H2WO4.H2O), have been grown on glass substrates using a dip-coating technique. The 𝑏-axis oriented films have been characterized by X-ray diffraction and scanning electron microscopy. The electrical conductivity of the films is observed to vary with humidity and selectively show high sensitivity to moisture at room temperature. In order to understand the mechanism of sensing, the films were examined by X-ray diffraction at elevated temperatures and in controlled atmospheres. Based on these observations and on conductivity measurements, a novel sensing mechanism based on protonic conduction within the surface layers adsorbed onto the hydrotungstite film is proposed.

    • Effect of gamma radiation on optical and electrical properties of tellurium dioxide thin films

      T K Maity S L Sharma

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      Gamma radiation induced changes in the optical and electrical properties of tellurium dioxide (TeO2) thin films, prepared by thermal evaporation, have been studied in detail. The optical characterization of the as-deposited thin films and that of the thin films exposed to various levels of gamma radiation dose clearly show that the optical bandgap decreases with increase in the gamma radiation dose up to a certain dose. At gamma radiation doses above this value, however, the optical bandgap has been found to increase. On the other hand, the current vs voltage plots for the as-deposited thin films and those for the thin films exposed to various levels of gamma radiation dose show that the current increases with the gamma radiation dose up to a certain dose and that the value of this particular dose depends upon the thickness of the film. The current has, however, been found to decrease with further increase in gamma radiation dose. The observed changes in both the optical and electrical properties indicate that TeO2 thin films can be used as the real time gamma radiation dosimeter up to a certain dose, a quantity that depends upon the thickness of the film.

    • Microwave dielectric properties of nanostructured nickel ferrite

      John Jacob M Abdul Khadar Anil Lonappan K T Mathew

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      Nickel ferrite is one of the important ferrites used in microwave devices. In the present work, we have synthesized nanoparticles of nickel ferrite using chemical precipitation technique. The crystal structure and grain size of the particles are studied using XRD. The microwave dielectric properties of nanostructured nickel ferrite samples of three different average grain sizes and those of two sintered samples were studied. The parameters like dielectric constant, dielectric loss and heating coefficient of the nanoparticles samples are studied in the frequency range from 2.4 to 4 GHz. The values of these parameters are compared with those of sintered pellets of the same samples. All these parameters show size dependent variations.

    • Mechanical properties of polyethersulfone modified epoxy/3,3′-bis (maleimidophenyl)phenylphosphine oxide (BMI) intercrosslinked matrices

      R Rajasekaran M Alagar

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      Novel intercrosslinked networks of polyethersulfone modified epoxy-3,3′-bis(maleimidophenyl) phenylphosphine oxide matrix systems are developed. The polyethersulfone modification of epoxy resin is carried out by using tetramethyl ammonium hydroxide (TMAH) as a catalyst. The polyethersulfone modified epoxy systems are further modified with 4–12% 3,3′-bis(maleimidophenyl) phenylphosphine oxide and cured by using diaminodiphenylmethane. Tensile, flexural, impact properties and dynamic mechanical analysis (DMA) are carried out to assess the mechanical behaviour of the prepared neat resin castings. Mechanical studies indicate that the introduction of polyethersulfone into these epoxy resins improves the toughness without any reduction in the stress–strain values. But, the incorporation of bismaleimide (BMI) into the epoxy resin improves the stress–strain properties with a lowering of the toughness. The introduction of both polyethersulfone and bismaleimide into the epoxy resin influences the mechanical properties according to their content percentages.

    • A novel method to control oxygen stoichiometry and thermoelectric properties in (RE)BaCo2O5+𝛿

      T Dasgupta S Sumithra A M Umarji

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      Rare earth cobaltites of the type (RE)BaCo2O5+𝛿 (RE = Y, Gd, Eu and Nd) were synthesized by solid state technique. A novel, fast quenching technique was used to tune the oxygen content in these compounds. Room temperature Seebeck and electrical resistivity measurements were used to infer the oxygen content. A maximum in the 𝑆 and ρ was observed for all the compositions when 𝛿 value was close to 0.5.

    • Thermal diffusion in nanostructured porous InP

      R Srinivasan K Ramachandran

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      Nanostructured porous InP samples were prepared by electrochemical anodic dissolution of InP for various current densities and etching periods. The samples were characterized by SEM and photoluminescence (PL) where a blue shift was observed in PL. Thermal properties studied by photoacoustic (PA) spectroscopy revealed one order decrease in thermal conductivity of porous InP compared to the bulk. Further it is shown that the thermal conductivity of porous InP decreases with decrease in size of the particles.

    • Study of effect of composition, irradiation and quenching on ionic conductivity in (PEG)𝑥 : NH4NO3 solid polymer electrolyte

      R Damle P N Kulkarni S V Bhat

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      We have prepared, characterized and investigated a new PEG-2000 based solid polymer electrolyte (PEG)𝑥: NH4NO3. Ionic conductivity measurements have been made as a function of salt concentration as well as temperature in the range 265–330 K. Selected compositions of the electrolyte are exposed to a beam of 8 MeV electrons and 60Co 𝛾-rays to an accumulated dose of 10 kGy to study the effect on ionic conductivity. The electrolyte samples are also quenched at liquid nitrogen temperature and conductivity measurements are carried out. The ionic conductivity at room temperature exhibits a characteristic peak for the composition, 𝑥 = 46. Electron beam irradiation results in an increase in conductivity for all compositions by a factor of 2–3. Exposure to 𝛾-rays enhances the conductivity by one order of magnitude. Quenching at low temperature has resulted in an increase in conductivity by 1–2 orders of magnitude. The enhancement of conductivity upon irradiation and quenching is interpreted as due to an increase in amorphous region and decrease in crystallinity of the electrolyte. DSC and NMR measurements also support this conclusion.

    • Application of magnetron sputtering for producing bioactive ceramic coatings on implant materials

      J Z Shi C Z Chen H J Yu S J Zhang

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      Radio frequency (RF) magnetron sputtering is a versatile deposition technique that can produce thin, uniform, dense calcium phosphate coatings. In this paper, principle and character of magnetron sputtering is introduced, and development of the hydroxyapatite and its composite coatings application is reviewed. In addition, influence of heat treatment on magnetron sputtered coatings is discussed. The heat treated coatings have been shown to exhibit bioactive behaviour both in vivo and in vitro. At last, the future application of the bioactive ceramic coating deposited by magnetron sputtering is mentioned.

    • Synthesis and characterization of M3V2O8 (M = Ca, Sr and Ba) by a solid-state metathesis approach

      Purnendu Parhi V Manivannan Sandeep Kohli Patrick Mccurdy

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      A solid-state metathesis approach initiated by microwave energy has been successfully applied for the synthesis of orthovanadates, M3V2O8 (M = Ca, Sr, and Ba). The structural, vibrational, thermal, optical and chemical properties of synthesized powders are determined by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, magnetic property measurements and diffused reflectance spectra in the UV–VIS range. The direct bandgap of the synthesized materials was found to be 3.55 ± 0.2 eV, 3.75 ± 0.2 eV and 3.57 ± 0.2 eV for Ca3V2O8, Sr3V2O8 and Ba3V2O8, respectively.

    • Study of aluminium oxide from high-alumina refractory ceramics by thermoluminescence

      V Correcher J Garcia-Guinea R Gonzalez-Martin E Crespo-Feo D Jimenez-Cordero

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      This work is focused on the study of the thermally stimulated blue emission of aluminium oxide (Al2O3) that has been removed from twenty different high alumina-rich refractory bricks. The glow curve sensitivity of several alumina grains are defined by

      1. a maximum centred at about 165°C that can be deconvoluted into two first order kinetic peaks at 157 and 177°C and

      2. a broad structure over 200–220°C that suggests a continuous trap distribution system.

      The isolated grains, analysed by means of X-ray diffraction, are composed of 43% of alumina (Al2O3), 22% of mullite [72% of Al2O3 and 28% of SiO2], 12% of leucite (KAlSi2O6) and 23% of sillimanite [Al2O3.SiO2]. The sample characterization has been performed using X-ray fluorescence and scanning electron microscopy.

    • Relaxor behaviour of (Ba0.5Sr0.5)(Ti0.6Zr0.4)O3 ceramics

      T Badapanda S K Rout S Panigrahi T P Sinha

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      Ba0.5Sr0.5Ti0.6Zr0.4O3 ceramic has been prepared through solid state reaction route. X-ray diffraction shows that the sample has cubic perovskite structure with space group 𝑃𝑚–3𝑚 at room temperature. Temperature dependent dielectric study of the ceramic has been investigated in the frequency range 50 Hz–1 MHz. The density of the sample is determined using Archimedes’ principle and is found to be ∼99% of X-ray density. The dielectric study revealed diffuse phase transition of second order. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates the relaxor-type behaviour in the ceramics. The index of relaxation (𝛾) and the broadening parameter (𝛥) were estimated from a linear fit of the modified Curie–Weiss law. The value of 𝛾 ∼ 1.72 indicates the strong relaxor nature of the ceramic. A remarkably good fit to the Vogel–Fulcher relation further supports such a relaxor nature.

    • Apparent activation energy for densification of 𝛼-Al2O3 powder at constant heating-rate sintering

      W Q Shao S O Chen D Li H S Cao Y C Zhang S S Zhang

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      The apparent activation energy for densification is a characteristic quantity that elucidates the fundamental diffusion mechanisms during the sintering process. Based on the Arrhenius theory, the activation energy for densification of 𝛼-Al2O3 at constant heating-rates sintering has been estimated. Sintering of 𝛼-Al2O3 powder has been executed by the way of a push rod type dilatometer. It is shown that the apparent activation energy does not have a single value but depends directly on the relative density. The apparent activation energy corresponding to lower relative density was higher than that corresponding to higher relative density. In addition, the value of the evaluated activation energy is different at the same density level when the Arrhenius plot involves different heating rates.

    • Synthesis and characterization of monoclinic rare earth titanates, RE2Ti2O7 (RE = La, Pr, Nd), by a modified SHS method using inorganic activator

      K Krishnankutty K R Dayas

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      The nano particles of phase pure rare earth titanates, synthesized by the SHS technique, get well sintered at lower temperatures compared to the compounds formed by the solid-state method. These dielectrics are highly stable and can be used in the microwave frequency range. We report here a modified SHS method to synthesize phase pure monoclinic RE2Ti2O7 at 350°C through the oxide/nitrate precursors using an inorganic compound, ammonium acetate, in place of the general type of organic activators such as urea, alanine etc. The nanopowders of La2Ti2O7, Pr2Ti2O7 and Nd2Ti2O7 on heating exhibit an exothermic behaviour with a broad maxima in the range 267–284°C and become endothermic with maxima in the range 1043–1220°C; interestingly, the phase pure crystalline material is formed at the temperature of exothermic maxima, as confirmed by XRD.

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