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      Volume 35, Issue 6

      November 2012,   pages  919-1038

    • Magneto-dielectric effect in Pb(Zr0.52Ti0.48)O3 filled nanoporous Ni0.5Zn0.5Fe2O4 composite

      Shilpi Banerjee Anindya Datta Asim Bhaumik Dipankar Chakravorty

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      Nanoporous Ni0.5Zn0.5Fe2O4 particles of diameter, ∼ 9.5 nm, were synthesized by citric acid assisted thermal decomposition in an autoclave. The BET surface area measured was 80 m2 g-1 and the average pore diameter was 2.5 nm. By soaking the particles in a suitable precursor solution and then subjecting them to a heat treatment at 923 K for 3 h, Pb(Zr0.52Ti0.48)O3 was grown within the nanopores. X-ray and electron diffraction studies confirmed the presence of both these phases. The nanocomposites showed ferromagnetic behaviour over the temperature range 2–300 K. No ferroelectric hysteresis loop could be found which was consistent with the earlier theoretical prediction of loss of ferroelectricity below a critical thickness of 2.4 nm. Good magneto-dielectric response of the order of 7% at a magnetic field of 9 kOe was recorded for the present system. This is believed to arise due to a negative magnetostriction coefficient of Ni0.5Zn0.5Fe2O4 which exerted a compressive strain on Pb(Zr0.52Ti0.48)O3 thereby lowering the tetragonality in its crystal structure.

    • Surface modified Al2O3 in fluorinated polyimide/Al2O3 nanocomposites: Synthesis and characterization

      Zivar Ghezelbash Davoud Ashouri Saman Mousavian Amir Hossein Ghandi Yaghoub Rahnama

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      Organic–inorganic hybrid materials consisting of inorganic materials and organic polymers are a new class of materials, which have received much attention in recent years. In the present investigation, at first, the surface of nano-alumina (Al2O3) was treated with a silane coupling agent of 𝛾-aminopropyltriethoxysilane (KH550), which introduces organic functional groups on the surface of Al2O3 nanoparticles. Then fluorinated polyimide (PI) was synthesized from 4,4'-(hexafluoroisopropylidene) diphthalic anhydride and 4,4'-diaminodiphenylsulfone. Finally, PI/modified Al2O3 nanocomposite films having 3, 5, 7 and 10% of Al2O3 were successfully prepared by an in situ polymerization reaction through thermal imidization. The obtained nanocomposites were characterized by fourier transform infrared spectroscopy, thermogravimetry analysis, X-ray powder diffraction, UV-Vis spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The results show that the Al2O3 nanoparticles were dispersed homogeneously in PI matrix. According to thermogravimetry analysis results, the addition of these nanoparticles improved thermal stability of the obtained hybrid materials.

    • Nanostructured coatings for super hydrophobic textiles

      M Joshi A Bhattacharyya N Agarwal S Parmar

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      The promising aspects of nanocomposite coatings to mimic the nano roughened self cleaning surface of lotus leaf is explored in this paper. A detailed study on nanosilica and clay based nanocomposite coatings using dip coating and layer by layer self assembly (L–b–L) is being described where lotus leaf effect has been mimicked on the cotton fabric surface using these particles as they develop nanosized surface roughness which helps to produce a super-hydrophobic surface. Nanosilica performs better in creating nano roughness on cotton fabric wherein the contact angle is >150°. The water contact angle of 2 wt% fluoro emulsion (Nuva HPU) treated cotton fabric increases from 115° to 155° when the fabric is pretreated with 0.5 wt% nanosilica emulsion. The water repellency rating of fabric treated with 0.16 wt% nanosilica along with 2 wt% Nuva HPU is comparable to that of 4 wt% Nuva HPU treated cotton fabric. On the other hand, 40 bilayers of nanosilica need to be applied on cotton fabric surface through L–b–L technique to create uniform nano roughening and gives a water repellency rating of 4. The air permeability of L–b–L nanocoated cotton fabric is not adversely affected by the super-hydrophobic nanostructured coating.

    • Comparison of galvanic displacement and electroless methods for deposition of gold nanoparticles on synthetic calcite

      Chamarthi K Srikanth P Jeevanandam

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      Gold nanoparticles have been deposited on synthetic calcite substrate by galvanic displacement reaction and electroless deposition methods. A comparative study has shown that electroless deposition is superior compared to galvanic displacement reaction for uniform deposition of gold nanoparticles on calcite. Characterization of the samples, prepared by two different deposition methods, was carried out by X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy (FE–SEM) and diffuse reflectance spectroscopy (DRS) measurements. FE–SEM studies prove that smaller nanoparticles of gold are deposited uniformly on calcite if electroless deposition method was employed and DRS measurements show the characteristic surface plasmon resonance of gold nanoparticles.

    • Structural and optical properties of Zn doped CuInS2 thin films

      Mahdi H Suhail

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      Copper indium sulphide (CIS) films were deposited by spray pyrolysis onto glass substrates from aqueous solutions of copper (II) sulphate, indium chloride and thiourea using compressed air as the carrier gas. The copper/indium molar ratio (Cu/In) in the solution 1(1:1) and the sulphur/copper ratio (S/Cu) was fixed at 4. Structural properties of these films were characterized. The effects of Zn (0–5%)molecular weight compared with CuInS2 Source and different substrate temperatures on films properties were investigated using X-ray diffraction (XRD) and optical transmission spectra. Optical characteristics of the CuInS2 films have been analysed using spectrophotometer in the wavelength range 300–1100 nm. The absorption spectra of the films showed that this compound is a direct bandgap material and gap values varied between 1.55 and 1.57 eV, depending on the substrate temperatures. Zn-doped samples have a bandgap energy of 1.55–1.95 eV. It was observed that there is an increase in optical bandgap with increasing Zn % molecular weight. The optical constants of the deposited films were obtained from the analysis of the experimentally recorded transmission and absorption spectral data. The refractive index, n and dielectric constants, 𝜀1 and 𝜀2, were also discussed and calculated as a function of investigated wavelength range and found it dependent on Zn incorporation. We found that the Zn-doped CuInS2 thin films exhibit P-type conductivity and we predict that Zn species can be considered as suitable candidates for use as doped acceptors to fabricate CuInS2-based solar cells. The paper presents a study concerning the influence of deposition parameters (temperature of the substrate and concentration of Zn (1–5)% from 0.16 M ZnCl2) on the quality of CuInS2 thin films achieved by spray pyrolysis on glass substrate from solutions containing 0.02 M CuCl2.2H2O, 0.16 M thiourea and 0.08 M In2Cl3.5H2O.

    • Preparation and electrochemical properties of SrCe0.4Zr0.4Yb0.2O2.9 electrolyte

      Juan Li Ruisong Guo Hong Jiang

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      The perovskite Yb-doped strontium cerate–zirconate material, SrCe0.4Zr0.4Yb0.2O2.9, was prepared by solid-state reaction and the structure was characterized by X-ray diffraction. The calcination process of the powder was investigated by thermogravimetric/differential thermal analysis (TG–DTA). The high temperature conductivities were measured by d.c. four-probe technique in the temperature range from 500 to 950°C in wet hydrogen and effect of temperature on conductivity was investigated. The conductivity increased with the elevation of temperature from 500 to 950°C. The highest conductivity of 4.4 × 10-2 S.cm-1 was observed for SrCe0.4Zr0.4Yb0.2O2.9 at 950°C. The current–voltage (𝐼–𝑉) and current–power (𝐼–𝑃) characteristics of the single cell (H2, Pt/SrCe0.4Zr0.4Yb0.2O2.9/Pt, O2) at temperature range from 600 to 850°C were tested. With the temperature increasing from 600 to 850°C, the open circuit voltage (OCV) decreased from 1.164 to 1.073 V and the ionic transfer number decreased from 0.996 to 0.946. At 850°C, the maximum power density of 25.2 mW.cm-2 was observed.

    • Optical and thermal characteristics of glasses based on TeO2

      El Sayed Yousef A E Al-Salami Mario Hotzel

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      Glass samples have been synthesized in quaternary system based on TeO2–oxide within composition, 85TeO2–5Nb2O5–5ZnO–5Ag2O, 68TeO2–5Nb2O5–20ZnO–7Na2O and [(75−𝑥)TeO2–5Nb2O5–20ZnO–𝑥PbO, 𝑥 = 7, 18 mol%]. Structural characterization of the glasses was studied with respect to their thermal stability, refractive indices, third order nonlinear optical susceptibility, IR spectra and Vickers hardness. For four different prepared glasses, density in the range from 5.3744 to 6.0731 g.cm-1, the glass transition temperature (𝑇g) in the range from 326 to 350 °C and refractive indices, 𝑛, in the range from 2.1273 to 2.2123 at 435 nm and Vickers hardness, 𝐻v, in the range from 2.91 to 3.44 GPa were determined. The value of third order nonlinear optical susceptibilities |𝜒(3)| ≈ 17.9 .10-13 esu of glass within composition, 68TeO2–5Nb2O5–20ZnO–7PbO, was measured by using degenerate four-wave mixing (DFWM).

    • Studies on electrical conductivity and dielectric behaviour of PVdF–HFP–PMMA–NaI polymer blend electrolyte

      S K Tripathi Ashish Gupta Manju Kumari

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      Polymer blend electrolytes composed of poly(vinylidene fluoride-co-hexafluoro-propylene), poly(methyl methacrylate) and 1.0 M NaI as salt have been synthesized using solution caste technique by varying the PVdF(HFP)–PMMA blend concentration ratio systematically. A.c. impedance studies were performed to evaluate the ionic conductivity of the polymer electrolyte films. The highest ionic conductivity at room temperature for [PVdF(HFP)–PMMA(4:1)](20 wt%) – [NaI(1.0M)](80 wt%) system is found to be 1.67 × 10-2 S cm-1. XRD studies reveal complete complexation of the salt in the polymeric blend systems. The temperature dependence conductivity has been performed in the range of 303–373 K and it is observed that it obeys the Arrhenius behaviour. It has been observed that the dielectric constant, 𝜀r and dielectric loss, 𝜀i, increases with temperature in the lower frequency region and is almost negligible in the higher frequency region. This behaviour can be explained on the basis of electrode polarization effects. Plot of real part, 𝑀r and imaginary part, 𝑀i vs frequency indicates that the systems are predominantly ionic conductors. The phenomenon suggests a plurality of relaxation mechanism.

    • Synthesis and characterization of nickel/barium hexa-aluminate composite coatings

      Dinesh Kumar Sampada Gurav Vikram Jayaram Sanjay Kumar Biswas

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      Electrodeposition of nickel/barium hexa-aluminate (Ni/BHA) composite coatings has been carried out from a Watt’s bath on mild steel substrate. BHA powders with plate habit were synthesized by solution combustion synthesis followed by heat treatment to ensure complete conversion to the hexa-aluminate phase. Heat treated material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with X-ray analysis. The dispersion behaviour and stability of BHA suspensions with cationic and anionic surfactants at room temperature were studied by dynamic light scattering under different pH. The influence of BHA concentration in the electrolytic bath, deposition temperature, pH, current density and duty cycle on particle incorporation in the coatings were studied and conditions for maximum particle incorporation were established. Coatings with a roughness of about 0.4 𝜇m were produced by using this technique. Effect of BHA content on microhardness was also investigated. A reasonably good thickness of the coatings was achieved in a given set of conditions.

    • Effect of T6 heat treatment on damping characteristics of Al/RHA composites

      D Siva Prasad A Rama Krishna

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      In the present work, effect of T6 heat treatment on the damping behaviour of aluminum/rice husk ash (RHA) composites fabricated by vortex method was studied using dynamic mechanical analyser (DMA) at frequencies ranging from 1 Hz to 25 Hz at room temperature under three-point bending test mode. The matrix material for the present work was A356.2 and reinforced with different weight % of 4, 6 and 8 rice husk ash particles. It was observed that composite exhibits high damping capacities than unreinforced alloy and increases with increase in weight % and the storage modulus increases with the addition of RHA particles but decreases with the increase in weight %. The heat treated composites exhibit higher damping capacity than the composites without heat treatment and increases with the increase in weight % of the reinforcement and loss in the storage modulus was observed and further decreases with the increase in the weight %of reinforcement. The related mechanisms were also discussed.

    • Influence of solvents on properties of solar selective coatings obtained by spray pyrolysis

      Mihaela Dudita Luminita Isac Anca Duta

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      Solar selective coatings for solar thermal flat-plate collectors consisting of crystalline copper oxides and amorphous nickel oxide composites were obtained by robotic spray pyrolyzed deposition. The parameters were optimized for increased spectral selectivity (𝑆): high solar absorptance and low thermal emittance. The coatings were deposited using nickel and copper acetate, dissolved in mixed solvents with various water: ethanol ratios. The coatings’ properties were characterized in terms of crystalline composition (XRD), surface morphology (AFM, contact angle) and optical properties (solar absorptance, thermal emittance and spectral selectivity). Considering the precursor solutions composition (solvent, wetting behaviour), the growth processes were modelled for two different systems: predominant hydrophilic and predominant hydrophobic. The high selectivity values (𝑆 > 30) of the optimized composite coatings were explained based on two parallel mechanisms: intrinsic absorption and multiple reflections generated when absorbers with controlled roughness are deposited.

    • Efficiency enhancement of dye-sensitized solar cells with addition of additives (single/binary) to ionic liquid electrolyte

      H-S Lee S-H Bae C-H Han S S Sekhon

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      The effect of addition of single and binary additives on the performance of dye-sensitized TiO2 solar cells based on electrolytes containing an ionic liquid (IL), 1,2-dimethyl-3-propylimidazolium iodide (DMPII) has been studied. Among the seven additives used, the addition of 2-(dimethylamino)-pyridine (DMAP) to IL resulted in best cell efficiency, which showed further enhancement with the addition of 5-chloro-1-ethyl-2-methylimidazole (CEMI) as second additive. The efficiency of the dye-sensitized solar cell (DSC) based on an electrolyte containing binary additives (DMAP and CEMI in equal molar ratios) has been found to increase by 62.5% from 4.35 to 7.07%. The dependence of different photovoltaic performance parameters (𝑉\oc, 𝐽sc, 𝑓𝑓 , 𝜂) of DSC upon temperature has been studied over a 30–120°C range and only a small decrease in conversion efficiency has been observed. The electrolyte containing binary additives (DMAP and CEMI) shows best cell performance up to 120°C.

    • Synthesis and luminescence properties of BaTiO3:RE (RE = Gd3+, Dy3+, Tb3+, Lu3+) phosphors

      Esra Korkmaz Nilgun Ozpozan Kalaycioglu

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      Gd3+, Dy3+, Tb3+ and Lu3+ doped BaTiO3-based phosphors were synthesized with modified solidstate technique at 1000 °C. The optimization of reaction conditions were carried out by thermogravimetry and differential thermal analysis methods (DTA/TG). The reaction products obtained in an air atmosphere were characterized by X-ray powder diffraction (XRD). Surface and elemental analyses were performed by using an SEM instrument. The excitation and emission spectra were recorded by photoluminescence spectrophotometer (PL). The thermoluminescence (TL) properties of BaTiO3 samples doped with Gd3+, Dy3+, Tb3+ and Lu3+ were investigated.

    • Artificial neural networks for prediction of percentage of water absorption of geopolymers produced by waste ashes

      Ali Nazari

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      In the present work, percentage of water absorption of geopolymers made from seeded fly ash and rice husk bark ash has been predicted by artificial neural networks. Different specimens, made from a mixture of fly ash and rice husk bark ash in fine and coarse form together with alkali activatormade of water glass and NaOH solution, were subjected to permeability tests at 7 and 28 days of curing. The curing regime was different: one set cured at room temperature until reaching to 7 and 28 days and the other sets were oven cured for 36 h at a range of 40–90 °C and then cured at room temperature for 7 and 28 days. To build the model, training and testing using experimental results from 120 specimens were conducted. According to these input parameters, in the neural networks model, the percentage of water absorption of each specimen was predicted. The training and testing results in the neural networks model have shown a strong potential for predicting the percentage of water absorption of the geopolymer specimens.

    • Hydroxyapatite, a biomaterial: Its chemical synthesis, characterization and study of biocompatibility prepared from shell of garden snail, Helix aspersa

      Anjuvan Singh

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      The shell of garden snail (Helix aspersa) is basically made of calcium carbonate. An attempt is made to convert calcium carbonate of garden snail shell to hydroxyapatite. The snail shell was found to decompose within 850°C to all the carbonate phases. The calcined snail shells were then treated with acids followed by different chemicals in ammoniacal media maintaining proper stoichiometry to produce fine hydroxyapatite (HAP) as filter cake with a Ca/P molar ratio of 1.67. The dried HAP powder was extremely pure with a specific surface area of 15 m2/g. The different characterization techniques were adopted both for calcined snail shell and HAP synthesized by X-ray diffraction (XRD), thermal analysis (DTA/TGA), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The surface area and particle size of HAP powder prepared by chemical precipitation route, were also determined by BET and Malvern particle size analyser, respectively. The synthesized powder was soaked in stimulated body fluid (SBF) medium for various periods of time in order to evaluate its bioactivity. The changes of pH of SBF medium were measured. High bioactivity of prepared HAP powder due to the formation of apatite on its surface was observed.

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