• Issue front cover thumbnail

      Volume 35, Issue 4

      August 2012,   pages  489-706

    • Effect of TiO2 nanotube length and lateral tubular spacing on photovoltaic properties of back illuminated dye sensitized solar cell

      Shantikumar V Nair A Balakrishnan K R V Subramanian A M Anu A M Asha B Deepika

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      The main objective of this study is to show the effect of TiO2 nanotube length, diameter and intertubular lateral spacings on the performance of back illuminated dye sensitized solar cells (DSSCs). The present study shows that processing short TiO2 nanotubes with good lateral spacings could significantly improve the performance of back illuminated DSSCs. Vertically aligned, uniform sized diameter TiO2 nanotube arrays of different tube lengths have been fabricated on Ti plates by a controlled anodization technique at different times of 24, 36, 48 and 72 h using ethylene glycol and ammonium fluoride as an electrolyte medium. Scanning electron microscopy (SEM) showed formation of nanotube arrays spread uniformly over a large area. X-ray diffraction (XRD) of TiO2 nanotube layer revealed the presence of crystalline anatase phases. By employing the TiO2 nanotube array anodized at 24 h showing a diameter ∼80 nm and length ∼1.5 𝜇m as the photo-anode for back illuminated DSSCs, a full-sun conversion efficiency (𝜂) of 3.5%was achieved, the highest value reported for this length of nanotubes.

    • CuO/TiO2 nanocrystals grown on graphene as visible-light responsive photocatalytic hybrid materials

      Yuan Fang Rijing Wang Guohua Jiang He Jin Yin Wang Xinke Sun Sheng Wang Tao Wang

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      CuO/TiO2 nanocrystals grown on graphene (CuO/TiO2–GR) were prepared by a simple hydrothermal method using Cu(CH3COO)2.H2O and (NH4)2TiF6 as precursors and graphene oxide (GO) as templates. The asprepared composites were characterizated by TEM, XRD, FT–IR to determine composition and phase purity. The photocatalytic activity of the samples was evaluated by photo-degradation of methylene blue (MB) aqueous solution under UV and visible light illumination. This work may provide new insights into preparing other inorganic graphene-based composites.

    • Effect of annealing time on structural and magnetic properties of laser ablated oriented Fe3O4 thin films deposited on Si(100)

      Shahid M Ramay Saadat A Siddiqi M Sabieh Anwar C Y Park S-C Shin

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      We have fabricated ∼143nm Fe3O4 thin films on Si(100) substrates at 450°C and then annealed them at the same temperature for 30, 60 and 90 min under a vacuum of 10-6 torr with pulsed laser deposition. We studied the effects on the structural and magnetic properties of Fe3O4 thin films. The films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). XRD studies showed pure single phase spinel cubic structure of Fe3O4 with a preferential [111] orientation, independent of substrate orientation at 90 min annealing. Higher magnetization was obtained up to 60 min annealing due to Fe phase but at 90 min, we obtained reduced magnetization of 335 emu/cc. This is attributed to the formation of antiphase boundaries between substrate and film.

    • Influence of nitrogen flow rates on materials properties of CrN𝑥 films grown by reactive magnetron sputtering

      B Subramanian K Prabakaran M Jayachandran

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      Chromium nitride (CrN) hard thin films were deposited on different substrates by reactive direct current (d.c.) magnetron sputtering with different nitrogen flow rates. The X-ray diffraction patterns showed mixed Cr2N and CrN phases. The variations in structural parameters are discussed. The grain size increased with increasing nitrogen flow rates. Scanning electron microscopy image showed columnar and dense microstructure with varying nitrogen flow rates. An elemental analysis of the samples was realized by means of energy dispersive spectroscopy. The electrical studies indicated the semiconducting behaviour of the films at the nitrogen flow rate of 15 sccm.

    • Morphological and compositional engineering of Ni/carbon nanotube composite film via a novel cyclic voltammetric route

      Yu Jun Yang

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      Ni/multi-walled carbon nanotubes (MWCNTs) composite films were deposited on the glassy carbon electrode (GCE) by a Ni plating bath containing homogeneously dispersed MWCNTs using polyvinylpyrrolidone (PVP) as dispersion additive. Incorporation of MWCNTs into Ni matrix was greatly enhanced by the application of cyclic voltammetric (CV) deposition technique. The structure and nature of the Ni/MWCNT were characterized by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). The results show that the content of MWCNT and the morphology of the deposited Ni/MWCNT composite film can be controlled by selecting the appropriate electroplating conditions. Further study indicates that the obtained Ni/MWCNT showed excellent electro-catalytic activity for the oxidation of ethanol in alkaline solution.

    • Spherical and rod-like Gd2O3:Eu3+ nanophosphors—Structural and luminescent properties

      N Dhananjaya H Nagabhushana B M Nagabhushana B Rudraswamy C Shivakumara R P S Chakradhar

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      A comparative study of spherical and rod-like nanocrystalline Gd2O3:Eu3+ (Gd1.92Eu0.08O3) red phosphors prepared by solution combustion and hydrothermal methods have been reported. Powder X-ray diffraction (PXRD) results confirm the as-formed product in combustion method showing mixed phase of monoclinic and cubic of Gd2O3:Eu3+. Upon calcinations at 800°C for 3 h, dominant cubic phase was achieved. The as-formed precursor hydrothermal product shows hexagonal Gd(OH)3:Eu3+ phase and it converts to pure cubic phase of Gd2O3:Eu3+ on calcination at 600°C for 3 h. TEM micrographs of hydrothermally prepared cubic Gd2O3:Eu3+ phase shows nanorods with a diameter of 15 nm and length varying from 50 to 150 nm, whereas combustion product shows the particles to be of irregular shape, with different sizes in the range 50–250 nm. Dominant red emission (612 nm) was observed in cubic Gd2O3:Eu3+ which has been assigned to ${}^{5}D_{0} \rightarrow {}^{7}F_{2}$ transition. However, in hexagonal Gd(OH)3:Eu3+, emission peaks at 614 and 621 nm were observed. The strong red emission of cubic Gd2O3:Eu3+ nanophosphors by hydrothermal method are promising for high performance display materials. The variation in optical energy bandgap (𝐸g) was noticed in as-formed and heat treated systems in both the techniques. This is due to more ordered structure in heat treated samples and reduction in structural defects.

    • An optical tweezer-based study of antimicrobial activity of silver nanoparticles

      Yogesha Sarbari Bhattacharya M K Rabinal Sharath Ananthamurthy

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      Understanding and characterizing microbial activity reduction in the presence of antimicrobial agents can help in the design and manufacture of antimicrobial drugs. We demonstrate the use of an optical tweezer setup in recording the changes in bacterial activity with time, induced by the presence of foreign bodies in a bacterial suspension. This is achieved by monitoring the fluctuations of an optically trapped polystyrene bead immersed in it. Examining the changes in the fluctuation pattern of the bead with time provides an accurate characterization of the reduction in the microbial activity. Here, we report on the effect of addition of silver nanoparticles on bacterial cultures of Pseudomonas aeroginosa, Escherichia coli and Bacillus subtilis. We observe a decrease in the bacterial activity with time for the investigated bacterial samples. This method in our opinion, enables one to track changes in bacterial activity levels as a function of time of contact with the antibacterial agent with greater efficacy than traditional cell counting methods.

    • Effect of starting composition on formation of MoSi2–SiC nanocomposite powder via ball milling

      M Zakeri M Ahmadi

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      MoSi2–SiC nanocomposite powders were successfully synthesized by ball milling Mo, Si and graphite elemental powders. Effects of milling time and annealing temperature were also investigated. The composite formation and phase transformation were monitored by X-ray diffraction. The microstructure of milled powders was studied by SEM, TEM and XRD peak profile analysis. Formation of this composite was completed after 10 and 20 h of milling for 25%SiC and 50%SiC, respectively. High temperature polymorph (HTP) of MoSi2 was obtained at the end of milling (20 h). On the other hand, annealing led to transformation of HTP to low temperature polymorph (LTP) of MoSi2. Mo5Si3 was formed during annealing as a product of a reaction between MoSi2 and excess graphite. Mean grain size <50 nm was obtained for 20 h milled sample on the basis of peak profile analysis and TEM images.

    • Improvement in tensile properties of PVC–montmorillonite nanocomposites through controlled uniaxial stretching

      Adnan Sarfraz Muhammad Farooq Warsi Muhammad Ilyas Sarwar Muhammad Ishaq

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      In this paper we present the results exhibiting an improvement in the tensile properties of polyvinyl chloride (PVC)–montmorillonite nanocomposites through uniaxial stretching. The clay was dispersed in PVC matrix with the help of dodecylamine. PVC–montmorillonite nanocomposites films containing varying amounts of clay (0–5%) were produced through solution elution technique. The films were stretched uniaxially at a constant temperature of 80 °C in three different steps using controlled loads. X-ray diffraction and stress–strain curves were obtained for both unstretched and stretched films in order to determine the improvement in various properties. The controlled uniaxial stretching of films close to the softening temperature of PVC has resulted in enhancement in the degree of crystallinity in the nanocomposites. This improvement in the structural order has also imparted increase in tensile strength and Young’s modulus of the nanocomposite films.

    • Electrochemical oxidation of some basic alcohols on multiwalled carbon nanotube–platinum composites

      Minsoo Koo Jong-Seong Bae Hyun-Chul Kim Dae-Geun Nam Chang Hyun Ko Jeong Hyun Yeum Weontae Oh

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      Some composites of multiwalled carbon nanotubes, which were chemically treated in acidic and/or hydrogen peroxide solution, and platinum nanoparticles were prepared by the simple reduction in glycerol solution. Carboxylated and/or hydroxyl MWNTs were structurally analysed using X-ray photoelectron spectroscopy. In addition, the MWNT–Pt composites were characterized by XRD and TEM in detail. The electrochemical oxidation of some basic alcohols, which was catalyzed by the MWNT–Pt composites, was analysed by cyclic voltammetry. Their catalytic activities were studied with cyclic voltammograms of alcohols.

    • Interface controlled growth of nanostructures in discontinuous Ag and Au thin films fabricated by ion beam sputter deposition for plasmonic applications

      R Brahma M Ghanashyam Krishna

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      The growth of discontinuous thin films of Ag and Au by low energy ion beam sputter deposition is reported. The study focuses on the role of the film–substrate in determining the shape and size of nanostructures achieved in such films. Ag films were deposited using Ar ion energy of 150 eV while the Au films were deposited with Ar ion energies of 250–450 eV. Three types of interfaces were investigated in this study. The first set of film–substrate interfaces consisted of Ag and Au films grown on borosilicate glass and carbon coated Cu grids used as substrates. The second set of films was metallic bilayers in which one of the metals (Ag or Au) was grown on a continuous film of the other metal (Au or Ag). The third set of interfaces comprised of discontinuous Ag and Au films deposited on different dielectrics such as SiO2, TiO2 and ZrO2. In each case, a rich variety of nanostructures including self organized arrays of nanoparticles, nanoclusters and nanoneedles have been achieved. The role of the film–substrate interface is discussed within the framework of existing theories of thin film nucleation and growth. Interfacial nanostructuring of thin films is demonstrated to be a viable technique to realize a variety of nanostructures. The use of interfacial nanostructuring for plasmonic applications is demonstrated. It is shown that the surface Plasmon resonance of the metal nanostructures can be tuned over a wide range of wavelengths from 400 to 700 nm by controlling the film–substrate interface.

    • Effect of lactic acid on nucleation morphology and surface roughness of electroless Ni–P deposition in nanoscale

      A Babanejhad M Hashemi Y Rahmatallahpur Sh A Nozad

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      The present work aims to study effect of lactic acid concentration as complexing agent on surface roughness and nucleation morphology of electroless N–P deposition. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used to study nucleation morphology and surface roughness of deposition. Deposition process started at some initial priority growing centres independently distributed on the substrate. We found that the morphology and surface roughness of deposition strongly depends on the complexing agent concentration. Morphology of initial deposited centres with no concentration of lactic acid was in coniform structure. By increasing the complexing agent concentration, the structure of initial growing centres changed from coniform to nodular shape and the surface roughness of depositions decreased.

    • Effect of soaking time and concentration of NaOH solution on mechanical properties of coir–polyester composites

      S Jayabal S Sathiyamurthy K T Loganathan S Kalyanasundaram

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      The green husk coir fibres were treated with different levels of soaking time and concentration of alkali solution. As a result of alkali treatment, the surface modifications were done on the fibre surface and were studied using scanning electron micrographs. The coir–polyester composites were fabricated using hand lay up process and the mechanical properties (tensile, flexural and impact strength) were evaluated as per ASTM standards. The effect of soaking time and concentration of NaOH solution were studied based on evaluated values of mechanical properties to find out optimum fibre treatment parameters.

    • Degradation and miscibility of poly(DL-lactic acid)/poly(glycolic acid) composite films: Effect of poly(DL-lactic-co-glycolic acid)

      Zhigang Ma Na Zhao Chengdong Xiong

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      The in vitro degradation behaviour of poly(glycolic acid) (PGA) and its composite films containing poly(DL-lactic acid) (PDLLA) and poly(DL-lactic-co-glycolic acid) (PDLGA) were investigated via mass loss, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). All the films were prepared by solution casting, using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as the solvent. Since the degradation rate of PDLLA is lower than that of PGA, those of the PDLLA/PGA composite films decreased. As a compatibilizer, PDLGA improved the compatibility and hydrolytic stability of PDLLA/PGA composite films. Changes in the composite films indicate that this kind of PGA-based composite biomaterial may be applicable to device design for clinical application in the future.

    • Characterization of piezoelectric polymer composites for MEMS devices

      C V Madhusudhana Rao G Prasad

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      Composite piezoelectric ceramics are important materials for transducer applications in medical diagnostic devices and MEMS devices. In micrometer scale the material properties of piezopolymers or piezoceramics do not coincide with that of bulk materials. The present work is aimed at simulating the material properties of piezoceramics and piezo-polymer composite thin films in the micrometer scale and then to determine the piezo-composite material properties. Piezoceramics have very high electromechanical coupling coefficient (𝑘). But they have very high acoustic impedance and they are very brittle especially when thin films are fabricated. Piezopolymer like PVDF has low acoustic impedance and can be fabricated into thin films but it has very low 𝑘 value and high dielectric losses. The combination of piezoceramics and piezopolymers form the piezocomposites, which have suitable material properties for transducer applications. The composites can have different connectivities. For 2–2 composite, we can select two layers or a stack of PZT and PVDF layers. It is intended to determine the material properties both analytically and by simulation using computer simulation ANSYS software which implements finite element method (FEM). Although the simulation process presents approximate results, it can be verified from the large available experimental data from the literature with the simulated data.

    • Application of polyaniline/manganese dioxide composites for degradation of acid blue 25 by hydrogen peroxide in aqueous media

      Ali H Gemeay Rehab G El-Sharkawy Ikhlas A Mansour Ahmed B Zaki

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      The kinetics of catalytic degradation of acid blue 25 dye (AB-25) by hydrogen peroxide using polyaniline/manganese dioxide (PANI/MnO2) composites was investigated. To optimize the degradation kinetics of the dye, several parameters have been varied:

      1. parameters varied during the preparation of PANI/MnO2 composites include: aniline concentration, acid concentration, acid type, amount of 𝛽-MnO2, stirring time and polymerization temperature and

      2. kinetic variables include: [H2O2], dye concentration, amount of composite, pH, addition of salt, and UV-light irradiation.

      The catalytic activity of the composite is obtained when it has

      1. high % PANI content,

      2. high degree of crystallinity, and

      3. high doping ratio. The reaction obeyed second-order kinetics with respect to [H2O2], attains a maximum, and decreases thereafter.

      The degradation decreased when the dye concentration increased. Additionally, the effect of salts on the degradation rate was also studied. The rate of reaction decreases with increasing pH of the medium due to

      1. the conversion of ES form of PANI into EB form and

      2. protonated form of the dye is more facial to be oxidized than the deprotonated form.

      Degradation rate was increased in the presence of UV/H2O2 compared to H2O2 alone. Mechanism was proposed for the catalytic degradation reaction which is in agreement with the experimental data.

    • Mechanical and electrical performance of Roystonea regia/glass fibre reinforced epoxy hybrid composites

      Govardhan Goud R N Rao

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      The present paper investigates mechanical and electrical properties of Roystonea regia/glass fibre reinforced epoxy hybrid composites. Five varieties of hybrid composites have been prepared by varying the glass fibre loading. Roystonea regia (royal palm), a natural fibre was collected from the foliage of locally available royal palm tree through the process of water retting and mechanical extraction. Roystonea regia, 𝐸-glass short fibres were used together as reinforcement in epoxy matrix to form hybrid composites. It has been observed that tensile, flexural, impact and hardness properties of hybrid composites considerably increased with increase in glass fibre loading. But electrical conductivity and dielectric constant values decreased with increase in glass fibre content in the hybrid composites at all frequencies. Scanning electron microscopy of fractured hybrid composites has been carried out to study the fibre matrix adhesion.

    • Percolation based enhancement in effective thermal conductivity of HDPE/LBSMO composites

      Madhusree Kole D Tripathi T K Dey

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      Thermal conductivity of composites with electrically conducting La0.7Ba0.15Sr0.15MnO3 (LBSMO) filler of nanometric grain size in HDPE matrix is investigated. Volume fraction of LBSMO fillers was varied between 0 and 0.30. SEM photographs of the composites show the presence of clusters and percolative paths, particularly for composites prepared with higher filler volume fractions. The effective thermal conductivity of the composites displays significant enhancement with increasing filler content in HDPE. A maximum enhancement of ∼65% compared to that for pure HDPE has been observed for composite with 0.30 volume fraction of LBSMO filler. Most of the models those are generally used to predict the properties of two phase mixtures, has been found either to under/overestimate the measured effective thermal conductivity of the composites. We confirm that the observed rapid increase in the effective thermal conductivity of HDPE/LBSMO composite over the studied range of filler volume fraction (viz. 0–0.30), is predicted very well, considering the effect of percolation as proposed by Zhang et al (2009).

    • Optical, electrochemical and morphological investigations of poly (3,4-propylenedioxythiophene)–sultone (PProDOT–S) thin films

      S Sindhu C R Siju S K Sharma K N Rao E S R Gopal

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      In this paper, we have carried out thin film characterization of poly(3,4-propylenedioxythiophene)–sultone (PProDOT–S), a derivative of electrochromic poly(3,4-propylenedioxythiophene) (PProDOT). PProDOT–S was deposited onto transparent conducting oxide coated glass substrates by solution casting method. Single wavelength spectrophotometry is used to monitor the switching speed and contrast ratio at maximum wavelength (𝜆max). The percentage transmittance at the 𝜆max of the neutral polymer is monitored as a function of time when the polymer film is repeatedly switched. This experiment gives a quantitative measure of the speed with which a film is able to switch between the two states i.e. the coloured and the bleached states. PProDOT–S films were switched at a voltage of 1.9 V with a switching speed of 2 s at 𝜆max of 565 nm and showed a contrast of ∼37%. Cyclic voltammetry performed at different scan rates have shown the characteristic anodic and cathodic peaks. The structural investigations of PProDOT–S films by IR spectra were in good agreement with previously reported results. Raman spectra of PProDOT–S showed a strong Raman peak at 1509 cm-1 and a weak peak at 1410 cm-1 due to the C = C asymmetric and symmetric stretching vibrations of thiophene rings. The morphological investigations carried out by using scanning electron microscope (SEM) of polymer films have shown that these polymers are found to be arranged in dense packed clusters with non-uniform distribution having an average width and length of 95 nm and 160 nm, respectively.

    • Solid state synthesis and photoluminescence of Sr3Y(P𝑥V1−𝑥O4)3: Eu3+ submicrocrystalline rod

      Xiuzhen Xiao Bing Yan

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      Using rare earth coordination polymers with ortho-hydroxylbenzoic acids as rare earth species and composing with organic polymers as the hybrid precursors, Sr3Y(P𝑥V1−𝑥O4)3: Eu3+ (𝑥 = 0.1, 0.3, 0.5, 0.7, 0.9) phosphors has been synthesized. These phosphors present the column-like particles with a width of 250 nm and a length of 1 𝜇m. The value of red emission to orange emission for Eu3+ varies with the V content, indicating that the RO (red/orange) value increases with the increase of V content due to the lower electronegativity of V. Sr3Y(P0.3V0.7O4)3 has been shown to be the best composition among different compositions. Furthermore, the concentration quenching of Eu3+ in Sr3Y(P0.3V0.7O4)3 took place and the optimum concentration of Eu3+ is 5 mol % in the range of 1–9 mol %.

    • Growth, characterization and transport properties of Pb𝑥Zn1−𝑥S mixed crystals

      M Nagabhushana E Nagabushan D Jaya Prakash B Rajam K Yadaiah

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      The polycrystalline Pb𝑥Zn1−𝑥S semiconductor powder with (0 ≤ 𝑥 ≤ 0.5) has been prepared by controlled co-precipitation method from an alkaline medium using thiourea as a sulphide ion source. Pellets are made with these powders applying 10 ton/sq cm pressure and sintered at 800 °C for 2 h in nitrogen atmosphere. X-ray studies of these samples have indicated that the compounds are polycrystalline in nature with mixed hexagonal and cubic structure of ZnS and cubic structure of PbS. Lattice parameters (𝑎 and 𝑐) of all the compounds are determined from the X-ray data and are found to decrease non-linearly with increase in Pb concentration (𝑥). It is also observed that the grain size of the crystallites increases in samples with 𝑥 = 0–0.5. Scanning electron micrographs have shown that both cubic and hexagonal crystallites are present in the mixed crystals. The electrical conductivity in Pb𝑥Zn1−𝑥S is found to decrease with increase in composition (𝑥 = 0–0.5), whereas it increases at all temperatures in all samples. Mobility of charge carrier concentration is found to increase with increasing temperature. The increase in carrier mobility in Pb𝑥Zn1−𝑥S samples may be due to reduced grain boundary potential. In Pb𝑥Zn1−𝑥S samples with 𝑥 = 0–0.3, sum of the activation energy due to charge carriers and grain boundary potential is equal to the activation energy due to conductivity.

    • Analysis of volume expansion data for periclase, lime, corundum and spinel at high temperatures

      B P Singh H Chandra R Shyam A Singh

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      We have presented an analysis of the volume expansion data for periclase (MgO), lime (CaO), corundum (Al2O3) and spinel (MgAl2O4) determined experimentally by Fiquet et al (1999) from 300K up to 3000K. The thermal equation of state due to Suzuki et al (1979) and Shanker et al (1997) are used to study the relationships between thermal pressure and volume expansion for the entire range of temperatures starting from room temperature up to the melting temperatures of the solids under study. Comparison of the results obtained in the present study with the corresponding experimental data reveal that the thermal pressure changes with temperature almost linearly up to quite high temperatures. At extremely high temperatures close to the melting temperatures thermal pressure deviates significantly from linearity. This prediction is consistent with other recent investigations. A quantitative analysis based on the theory of anharmonic effects has been presented to account for the nonlinear variation of the thermal pressure at high temperatures.

    • Microstructure and properties of sintered mullite developed from Indian bauxite

      H S Tripathi A Ghosh M K Halder B Mukherjee H S Maiti

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      Dense mullite aggregates with 72% Al2O3 have been synthesized by reaction sintering of two varieties of Indian bauxite and silica sol. The bauxites used are of inferior grade with different levels of accessory impurities such as Fe2O3, TiO2, CaO. The phase and microstructure development of sintered samples were investigated by XRD and SEM. It was found that morphology of the sintered grain is very much dependent on the impurity level. Mullite formed from bauxite-1 with low impurity is mostly equiaxed, whereas mullite developed from bauxite 2 with higher impurity particularly CaO is needle shaped. Presence of CaO in bauxite was found to be more detrimental than TiO2 and Fe2O3.

    • Effect of substrate type, dopant and thermal treatment on physicochemical properties of TiO2–SnO2 sol–gel films

      I Stambolova V Blaskov S Vassilev M Shipochka A Loukanov

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      Thin nanocrystalline TiO2–SnO2 films (0–50 mol% SnO2) were prepared on quartz and stainless steel substrates by sol–gel coating method. The obtained films were investigated by XRD, Raman spectroscopy and XPS. The size of the nanocrystallites was determined by XRD–LB measurements. We ascertained that the increase of treatment temperature and concentration of SnO2 in the films favour the crystallization of rutile phase. The substrate type influences more substantially the phase composition of the TiO2–SnO2 films. It was established that a penetration of elements took place fromthe substrate into the films. TiO2 films deposited on quartz substrate include a Si which stabilizes anatase phase up to 600 °C. The films which are deposited on stainless steel substrate and treated at 700 °C show the presence of significant quantity of rutile phase. This phenomenon could be explained by the combined effect of Sn dopant as well as Fe and Cr, which also are penetrated in the films from the steel substrate. The titania films doped up to 10 mol% SnO2 on stainless steel possess only 12–17 nm anatase crystallites, whereas the TiO2–(10–50 mol%) SnO2 films contain very fine grain rutile phase (4 nm).

    • Grain refinement of AZ31 magnesium alloy by electromagnetic stirring under effect of grain-refiner

      S Y Gao Q C Le Z Q Zhang J Z Cui

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      The effects of electromagnetic stirring and Al4C3 grain refiner on the grain refinement of semicontinuously cast AZ31 magnesium alloy were discussed in this investigation. The results indicate that electromagnetic stirring has an effective refining effect on the grain size of AZ31 magnesium alloy under the effect of Al4C3 grain refiner. Electromagnetic stirring can `activate’ the Al4C3 particles, resulting in more heterogeneous nucleation sites for the primary 𝛼-Mg grains. But, longer holding time can `deactivate’ the Al4C3 particles and poison the grain refining effect.

    • Application of Kissinger analysis to glass transition and study of thermal degradation kinetics of phenolic–acrylic IPNs

      S Goswami K Kiran

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      Degradation kinetics of sequential IPNs, based on novolac resin and poly (2-ethyl hexyl acrylate), are studied at linear heating rates of 2°C/min, 5°C/min, 10°C/min and 20°C/min by thermogravimetric analyser (TGA). Activation energy (𝐸a) and order (𝑛) of thermal decomposition reaction for IPNs and pure phenolic resin are evaluated from TGA curves using differential method of Freeman and Carroll. Decrease in Tg with an increase of acrylate content in IPNs are seen. Lower activation energy (𝐸a'), as calculated by applying Kissinger equation, for the concerned transition of IPNs, compared to that of pure phenolic resin is quite evident from DSC study.

    • High-pressure physical properties of magnesium silicate post-perovskite from ab initio calculations

      Zi-Jiang Liu Xiao-Wei Sun Cai-Rong Zhang Jian-Bu Hu Ling-Cang Cai Qi-Feng Chen

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      The structure, thermodynamic and elastic properties of magnesium silicate (MgSiO3) post-perovskite at high pressure are investigated with quasi-harmonic Debye model and ab initio method based on the density functional theory (DFT). The calculated structural parameters of MgSiO3 post-perovskite are consistent with the available experimental results and the recent theoretical results. The Debye temperature, heat capacity and thermal expansion coefficient at high pressures and temperatures are predicted using the quasi-harmonic Debye model. The elastic constants are calculated using stress–strain relations. A complete elastic tensor of MgSiO3 post-perovskite is determined in the wide pressure range. The calculated elastic anisotropic factors and directional bulk modulus show that MgSiO3 post-perovskite possesses high elastic anisotropy.

    • RuO2 supported on V2O5–Al2O3 material as heterogeneous catalyst for cyclohexane oxidation reaction

      Yasmina Nesrine Tchenar Abderrahim Choukchou-Braham Redouane Bachir

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      RuO2 supported on V2O5–Al2O3 mixed oxide material was prepared by impregnation method and characterized by XRD, nitrogen adsorption–desorption, SEM, UV-visible and FT–IR spectroscopic techniques. The catalytic activity of the prepared catalyst was evaluated for the liquid-phase oxidation of cyclohexane under mild conditions. In this reaction, conversion of cyclohexane to cyclohexanol and cyclohexanone and the selectivity ratio of cyclohexanol to cyclohexanone were greatly affected by the solvent and the oxidant agent used. The results show that the catalyst exhibit good conversion in polar solvents. The use of acetic acid gives more than 26% conversion in presence of TBHP as oxidant and an ∼40% conversion with hydrogen peroxide as oxidant in presence of an initiator, with 92% selectivity for cyclohexanol product.

    • Synthesis, characterization and in vitro cytotoxicity assessment of hydroxyapatite from different bioresources for tissue engineering application

      Sudip Mondal Rajashree Bardhan Biswanath Mondal Apurba Dey Sudit S Mukhopadhyay Syamal Roy Rajan Guha Koushik Roy

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      In the present study, hydroxyapatite (HAp) is synthesized from different biosources like eggshell, fish scale and bovine bone in a cost effective and ecofriendly way. HAp materials were synthesized from eggshell by wet precipitation method whereas thermal decomposition method was applied in case of fish scale and bovine bone. The phase purity and crystallinity of different calcined HAp powder were determined by XRD and FTIR analyses. The thermogravimetric analysis was carried out to show thermal stability of HAp powder. Average grain sizes of sintered samples were in submicron range. The morphology of the powders were observed under scanning electron microscopy (SEM). The dried powders were wet ball milled for several hours and surfactants like Triton-X small fillers (2 / 4 mm long rod-shaped) were made for in vitro testing. In order to verify the biocompatibility of HAp powders, cytotoxicity evaluation was carried out in RAW macrophage like cell line media for an incubation period of 72 h. The cell attachment studies on HAp compacts show an excellent affinity between cells and compact surface. These results proved high biocompatibility of HAp powders obtained fromdifferent biosources for tissue engineering applications.

    • Incorporation of fluorophosphate into zinc–aluminium–nitrate layered double hydroxide by ion exchange

      El Hassan Elkhattabi Mohamed Badreddine Moha Berraho Ahmed Legrouri

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      The intercalation of fluorophosphate (PO3F2-, FP) in the [Zn–Al] layered double hydroxides (LDHs) was investigated. A nitrate precursor was prepared by coprecipitaion at pH 9. An attempt to intercalate FP by direct coprecipitation reaction led to a poorly crystalline LDH phase. The effects of pH, aging time and anion concentration were studied and allowed to confirm that the best crystalline material, with high exchange extent, was obtained by carrying out the exchange at 25 °C in 0.1 M FP solution at pH 9 with at least 20 h of aging time.

    • Growth, spectral, structural and mechanical properties of struvite crystal grown in presence of sodium fluoride

      K Suguna M Thenmozhi C Sekar

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      Struvite or magnesium ammonium phosphate hexahydrate (MAP) is one of the components of urinary stone. Struvite stones are commonly found in women. It forms in human beings as a result of urinary tract infection with urea splitting organisms. These stones can grow rapidly forming “staghorn-calculi”, which is a painful urological disorder. Therefore, it is of prime importance to study the growth and inhibition of struvite crystals. The growth inhibition effect of struvite crystals in sodium metasilicate (SMS) gel in the presence of sodium fluoride has been carried out. Crystals obtained have been analysed by powder and single crystal XRD, SEM–EDX, FTIR and TG–DTA. The results show that the presence of fluoride significantly affects struvite crystal growth and the characteristics of the crystallites produced. The mechanical property of the grown crystals has been investigated by Vickers microhardness testing. Work hardening coefficient was found to be >1.6 for both pure and doped samples which suggests that the crystal belongs to the family of soft material. Presence of sodium fluoride further softened the crystal.

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