• Issue front cover thumbnail

      Volume 35, Issue 5

      October 2012,   pages  707-918

    • Enhanced thermal conductivity of nano-SiC dispersed water based nanofluid

      O Manna S K Singh G Paul

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      Silicon carbide (SiC) nanoparticle dispersed water based nanofluids were prepared using up to 0.1 vol% of nanoparticles. Use of suitable stirring routine ensured uniformity and stability of dispersion. Thermal conductivity ratio of nanofluid measured using transient hot wire device shows a significant increase of up to 12% with only 0.1 vol% nanoparticles and inverse dependence of conductivity on particle size. Use of ceramic nanoparticles appears more appropriate to ensure stability of dispersion in nanofluid in closed loop single-phase heat transfer applications.

    • Theoretical study on effect of radial and axial deformation on electron transport properties in a semiconducting Si–C nanotube

      Sudhanshu Choudhary S Qureshi

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      We investigate electron transport properties in a deformed (8, 0) silicon carbide nanotube by applying self consistent non-equilibrium Green’s function formalism in combination with the density-functional theory to a two-probe molecular junction constructed from deformed nanotube. The results suggest significant reduction in threshold voltage in the case of both radially compressed and axially elongated (8, 0) SiCNTs, a large difference in current–voltage characteristics was observed. Analysis of frontier molecular orbitals (FMO) and transmission spectrum show bandgap reduction in deformed nanotubes. Deformation introduces electronic states near the Fermi level, enhancing the conduction properties of (8, 0) SiCNT. The FMOs and the orbitals corresponding to peaks in 𝑇(𝐸) around Fermi level obviously has some major contributions from the deformed site. However, localization of the electronic state near the Fermi level is weak in (8, 0) SiCNT, possibly because of its large bandgap.

    • Photoluminescence quenching of semiconducting polymer nanoparticles in presence of Au nanoparticles

      Santanu Bhattacharyya Amitava Patra

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      In this report, we have demonstrated the photoluminescence quenching and energy transfer properties of semiconducting polymer nanoparticles, poly (N-vinylcarbazole) (PVK) in presence of different sized Au nanoparticles by steady state and time-resolved spectroscopy. We have described the quenching phenomena by sphere of action static quenching mechanism and both dynamic and static quenching processes are found in these systems. PL quenching values are 24.22% and 57.3% for 14 nm and 18 nm Au nanoparticles, respectively. It is found that the radiative and nonradiative decay have been modified with the size of Au nanoparticles. PL quenching and shortening of decay time regarding polymer nanoparticles in presence of Au nanoparticles suggest the nonradiative energy transfer process. The values of energy transfer are 6.7%, 49.5% and 53.38% from PVK polymer nanoparticles to 3 nm, 14 nm and 18 nm Au nanoparticles, respectively. Using FRET and SET equations we have calculated the average distance of donor PVK polymer nanoparticles and acceptor Au nanoparticles.

    • Preparation and characterization of silver nanoparticles in natural polymers using laser ablation

      Reza Zamiri B Z Azmi Hossein Abbastabar Ahangar Golnoosh Zamiri M Shahril Husin Z A Wahab

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      In this paper we have done a comparative study on efficiency of natural polymers for stabilizing silver nanoparticles (Ag-NPs) prepared by laser ablation technique. The selected polymers are starch (St), gelatin (Gt) and chitosan (Ct). The fabrication process was carried out through ablation of a pure Ag plate by nanosecond Q-switched Nd–Yg pulsed laser (𝜆 = 532 nm, 360 mJ/pulse). The stability of the samples was studied by measuring UV-visible absorption spectra of the samples one month after preparation. The result showed that the formation efficiency of NPs in St were highest and also the prepared NPs in St solution were more stable than other polymers during one month storage.

    • Analysis of hardness of nanocrystalline coatings of aluminum-rich Ti1−𝑥Al𝑥N

      J Hernández-Torres L García-González L Zamora-Peredo T Hernández-Quiroz A Sauceda-Carvajal P J García-Ramírez N Flores-Ramírez

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      Titanium aluminum nitride coatings were fabricated by a d.c.magnetron sputtering system from a Ti–Al (60/40wt%) target. Coatings were deposited on steel substrates, at a substrate temperature of 250 °C and a bias voltage of –80 V. The nitrogen flow was varied from 1.5–6 sccm and the Ar flow was kept constant at 20 sccm. The morphology and microstructure of the coatings were analysed by X-ray diffraction and scanning electron microscopy. The results of X-ray diffraction showed the presence of two cubic crystalline phases, TiN and AlN, which were confirmed by X-ray photoelectron spectroscopy. The Vicker hardness was obtained by the effective model of indentation. It was observed that the hardness of the coatings decreases from 22.8–9.5 GPa with an increased nitrogen content from 1.5–4.5 sccm. Subsequently, the hardness increased to 22.1 GPa by increasing nitrogen to 6 sccm. The behavior of hardness with grain size variation is consistent with the Hall-Peth relationship. The high value in the hardness of the coatings is mainly attributed to small grain sizes and the compressive stress present.

    • Comparative studies of spray pyrolysis deposited copper sulfide nanostructural thin films on glass and FTO coated glass

      Mehdi Adelifard Hosein Eshghi Mohamad Mehdi Bagheri Mohagheghi

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      Cu𝑥S thin films with different Cu to S molar ratios (0.33 and 0.43) have been deposited by spray pyrolysis method on glass and FTO coated glass substrates using an aqueous solution of copper (II) acetate and thiourea at a substrate temperature of 285°C. The structural, surface morphological, optical and electrical characterizations of the samples were carried out using XRD, FESEM, UV-Vis and PL spectrophotometer and four-probe apparatus, respectively. X-ray diffraction analysis showed that while the layer/glass sample has an individual CuS (covellite) crystalline phase, the layer/FTO sample includes two additional phases of Cu2S (chalcocite) and Cu1.8S (digenite) as well. Optical measurements showed that all these materials have a relatively high absorption coefficient (∼5 × 104–2.3 × 105 cm-1) in the visible region and direct bandgap of the layers was confirmed with the corresponding room temperature PL spectra. With the resistivity measurements at room and higher temperatures (up to 100°C) confirm that all samples are degenerate in nature with high electrical conductivities of ∼103 (𝛺.cm)-1.

    • Influence of different heat treatment programs on properties of sol–gel synthesized (Na0.5K0.5)NbO3 (KNN) thin films

      S Wiegand S Flege O Baake W Ensinger

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      Thin films of (Na0.5K0.5)NbO3 (KNN) were synthesized on Pt/Ti/SiO2/Si substrates with repeated spin-coating after fabrication of the precursor solution by a sol–gel process. The KNN precursor solution was prepared from K- and Na-acetate, Nb-pentaethoxide and 1,3-propanediol. Based on three characteristic temperatures derived from thermal analysis (TG–DTA) experiments, five heat treatment programs were developed. All programs lead to single phase perovskite KNN films with random crystal orientation, but only the programs that included a treatment after each single spin-coating step provided pore free surfaces with grains of about 100 nm size. The lowest leakage current at 150 kV cm-1 was obtained for the temperature program that included pyrolysis and calcination steps after each deposited layer.

    • Preparation of cadmium-doped ZnO thin films by SILAR and their characterization

      S Mondal P Mitra

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      Cadmium-doped zinc oxide (Cd : ZnO) thin films were deposited from sodium zincate bath following a chemical dipping technique called successive ion layer adsorption and reaction (SILAR). Structural characterization by X-ray diffraction reveals that polycrystalline nature of the films increases with increasing cadmium incorporation. Particle size evaluated using X-ray line broadening analysis shows decreasing trend with increasing cadmium impurification. The average particle size for pure ZnO is 36.73nm and it reduces to 29.9 nm for 10% Cd:ZnO, neglecting strain broadening. The strong preferred c-axis orientation is lost due to cadmium doping and degree of polycrystallinity of the films also increases with increasing Cd incorporation. Incorporation of cadmium was confirmed from elemental analysis using EDX. The optical bandgap of the films decreases with increasing Cd dopant. The value of fundamental absorption edge is 3.18 eV for pure ZnO and it decreases to 3.11 eV for 10% Cd:ZnO.

    • Synthesis and characterization of NiPcTSTNa(L) thin films

      M E Sánchez-Vergara V García-Montalvo J Santoyo-Salazar R J Fragoso-Soriano O Jiménez-Sandoval

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      NiPcTSTNa(L) [L=ethylenediamine (EDA); 1,4-diaminobutane (BDA); and 2,6-diamineanthraquinone (AqDA)] thin films were deposited by thermal evaporation. Their surface morphology was studied by AFM and SEM, and their chemical composition determined by EDS. Optical absorption studies of NiPcTSTNa(L) films were performed in the 200–1150 nm wavelength range. The optical bandgap of thin films was determined from the (𝛼 ℎ 𝜈)1/2 vs ℎ 𝜈 plots for indirect allowed transitions. The temperature dependence of electrical conductivity shows a semiconducting behaviour. The amorphous semiconductor films show thermal activation energies of electrical conduction between 3.3 and 3.7 eV.

    • Anti-tumor activity of self-charged (Eu,Ca):WO3 and Eu:CaWO4 nanoparticles

      Cao Lin Cao Jiexin Wang Cong Che Ping Pan De’an Alex A Volinsky

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      Non-stoichiometric (Eu,Ca):WO3 and Eu:CaWO4 nanoparticles with anti-tumor activity are synthesized in a sol–gel method by adding excessive Eu3+ and Ca2+ ions to tungsten oxide crystal structure. Colorimetric assay shows that 10 nm (Eu,Ca):WO3 and Eu:CaWO4 nanoparticles can effectively inhibit growth of mammary cancer cells without any harm to normal cells. Nanoparticles are characterized by X-ray diffraction, high resolution transmission electron microscopy and fluorescence optical spectrometry. Nanomaterials, insoluble in synthesized water, have complicated self-charging surfaces that trap mammary cancer cells. Surface self-charging effect is suggested as the inhibition mechanism.

    • Pd grating obtained by direct micromolding for use in high resolution optical diffraction based sensing

      Ritu Gupta Giridhar U Kulkarni

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      Pd grating patterns have been fabricated using the process of micromolding in capillary employing a Pd alkanethiolate precursor, which could be converted to metal in situ by thermolysis. Thus generated Pd grating were uniform in width (∼950 nm) and spacing (∼450 nm) over millimeter square areas on glass substrates. Importantly, the pattern when used as an optical grating produced a diffraction pattern with a high resolution (> 2000); the intensities of widely separated (diffraction angle, ∼26.8°) diffracted spots could be measured using a simple photodiode. By varying the concentration of Pd precursor (2mMto 25 mM), thickness of the resulting gratings could be adjusted in the range of ∼15–115 nm. By adjusting the grating parameters optimally, a maximum diffraction efficiency of 36% has been achieved. Thus fabricated Pd grating was used as seed catalyst to deposit Cu by electroless plating. The Cu deposition process has also been monitored by employing AFM, SEM and EDS analysis. The diffraction efficiency values corroborate well with the changes in the grating thickness due to Cu deposition. The grating structures presented can be reproducibly fabricated for rapidly emerging optical diffraction based sensing applications. This has been demonstrated in the case of aqueous Cu2+ by depositing the latter electrolessly on Pd.

    • Behaviour of LaAlO3+LnTiTaO6 (Ln= Ce, Pr or Nd) dielectric ceramic mixtures

      Sam Solomon

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      The 0.1LaAlO3+0.9LnTiTaO6 (Ln= Ce, Pr or Nd) ceramics are prepared through solid state ceramic route. The structure of the materials is studied using X-ray diffraction analysis. The microstructure is analysed using scanning electron microscopy. The dielectric properties in the radio as well as in the microwave frequencies are measured and discussed. The photoluminescence of a representative sample is also analysed. The dielectric constant (𝜀r) and temperature coefficient of resonant frequency (𝜏f) are tailored without appreciable change in the quality factor. The measured values of 𝜀r and 𝜏f are compared with the corresponding predicted values. These mixtures can be made useful in optical and microwave communication.

    • Electrical transport and EPR investigations: A comparative study for d.c. conduction mechanism in monovalent and multivalent ions doped polyaniline

      Suresh Kumar Gupta Vandna Luthra Ramadhar Singh

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      A detailed comparative study of electron paramagnetic resonance (EPR) in conjunction with d.c. electrical conductivity has been undertaken to know about the charge transport mechanism in polyaniline (PANI) doped with monovalent and multivalent protonic acids. This work is in continuation of our previous work for further understanding the conduction mechanism in conducting polymers. The results reveal that the polarons and bipolarons are the main charge carriers formed during doping process and these cause increase in electrical conductivity not only by increase in their concentration but also because of their enhanced mobility due to increased inter-chain transport in polyaniline at high doping levels. EPR line asymmetry having Dysonian line shape for highly doped samples shows a marked deviation of amplitudes 𝐴/𝐵 ratio from values close to one to much high values as usually observed in metals, thereby support the idea of high conductivity at higher doping levels. The nature of dopant ions and their doping levels control the charge carriers concentration as well as electrical conductivity of polyaniline. The electrical conductivity has also been studied as a function of temperature to know the thermally assisted transport process of these charge carriers at different doping levels which has been found to follow the Mott’s variable range hopping (VRH) conduction model for all the three dopants used. The charge carriers show a change over from 3D VRH to quasi 1D VRH hopping process for multivalent ions at higher doping levels whereas 1D VRH has been followed by monovalent ion for full doping range. These studies collectively give evidence of inter-chain percolation at higher doping levels causing increase in effective mobility of the charge carriers which mainly seems to govern the electrical conduction behaviour in this system.

    • Straightforward synthesis of hyperbranched polymer/graphene nanocomposites from graphite oxide via in situ grafting from approach

      Qiuhong Xu Yiwen Gong Yuan Fang Guohua Jiang Yin Wang Xinke Sun Rijing Wang

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      The grafting of graphite oxide (GO) with cyclic ether monomers, directly affords grafting with hyperbranched polymers. The resulting nanocomposites show good solubility in the solvents of polymers, exfoliation of graphene in the polymer matrix and excellent mechanical properties and robustness under bending.

    • Preparation, characterization and photocatalytic activity of TiO2/polyaniline core-shell nanocomposite

      Ali Olad Sepideh Behboudi Ali Akbar Entezami

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      Polyaniline (PANI) as a promising conducting polymer has been used to prepare polyaniline/TiO2 (PANI/TiO2) nanocomposite with core-shell structure as photocatalyst. Titanium dioxide (TiO2) nanoparticles with an average crystal size of 21 nm were encapsulated by PANI via the in situ polymerization of aniline on the surface of TiO2 nanoparticles. FT–IR, UV-Vis-NIR, XRD, SEM and TEM techniques were used to characterize the PANI/TiO2 core-shell nanocomposite. Photocatalytic activity of PANI/TiO2 nanocomposite was investigated under both UV and visible light irradiations and compared with unmodified TiO2 nanoparticles. Results indicated deposition of PANI on the surface of TiO2 nanoparticles which improved the photocatalytic activity of pristine TiO2 nanoparticles.

    • Preparation and electrochemical application of a new biosensor based on plant tissue/polypyrrole for determination of acetaminophen

      Gholamhossein Rounaghi Roya Mohammadzadeh Kakhki

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      Banana tissue containing polyphenol oxidase was incorporated into polypyrrole matrix to make a biosensor for the analysis of acetaminophen (ACT). The electrocatalytic behaviour of oxidized acetaminophen was studied at the surface of the biosensor, using various electrochemical methods. The advantages of this biosensor for the determination of acetaminophen are excellent catalytic activity, good detection limit and high exchange current density. The electrochemical and structural properties of the electrode were assessed using cyclic voltammetry, differential voltammetry, chronoamperometric techniques. The analytical properties (sensitivity, 𝐼p) of this biosensor increased with plant tissue loading. Also this new biosensor was successfully applied for determination of acetaminophen in biologic samples.

    • Structure-performance-fouling studies of polysulfone microfiltration hollow fibre membranes

      P S Singh K Parashuram S Maurya P Ray A V R Reddy

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      Hollow fibre microfiltration membranes were prepared by solution spinning process using polymer dope containing different amounts of polysulfone (PS), polyvinylpyrollidone (PVP) and 𝑁,𝑁-dimethylformamide (DMF). Spinning dope having PS: PVP: DMF (w/w) of 15: 5: 80, 15: 7: 78 and 17: 8: 75 were used for spinning to obtain hollow fibres having different dimensions (outer and inner diameters) and pore characteristics. Relatively high water permeability was observed for hollow fibre membrane spun from 15 wt. % solution than 17 wt. % PS solution having the same PVP/PS ratio of 0.47. Decrease of the PVP/PS ratio to 0.33 in the dope solution of 15 wt.%PS solution produced hollow fibre membrane with lower flux. By changing the spinning parameters, fibre with different dimensions were obtained without a significant change in microstructural morphology. The flux decline due to fouling for the permeation of PEO/BSA solution was maximum for the hollow fibre membrane obtained from 15 wt. % PS solution while a steady flux with slight fouling was observed for the hollow fibre membrane obtained from 17 wt. %PS solution, when the PVP/PS ratio was 0.47.

    • Effect of sintering temperature and heating mode on consolidation of Al–7Zn–2.5Mg–1Cu aluminum alloy

      C Padmavathi A Upadhyaya D Agrawal

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      Densification behaviour, phase transformation, microstructural evolution and hardness values of microwave sintered Al–7Zn–2.5Mg–1Cu (7775) aluminum alloy were investigated and compared with conventionally sintered samples. Microwave sintering was performed in 2.45 GHz multimode microwave furnace at temperatures ranging from 570–630 °C. Microwave sintering at a heating rate of as high as 22°C/min resulted in ∼55% reduction of processing time as compared to conventional sintering. A lower sintered density observed in the case of microwave processed samples was attributed to the inhomogeneity in microstructure and phase distribution. The X-ray diffraction results of conventionally sintered samples showed the presence of MgZn2, Mg2Zn11 and CuMgAl2, while only MgZn2 and CuMgAl2 phases were found in the case of microwave sintered samples and in lesser amount. Higher hardness and high standard deviation values were noticed for microwave sintered samples as compared to conventional counterparts.

    • Activation energy for mullitization of gel fibres obtained from aluminum isopropoxide

      Hongbin Tan Yaping Ding Haihong Zhang Jianfeng Yang Guanjun Qiao

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      Gel fibres of mullite precursor were prepared from an aqueous solution of aluminum nitrate (AN), aluminum isopropoxide (AIP) and tetraethylorthosilicate (TEOS). A 4:1 molar ratio of aluminum isopropoxide and aluminum nitrate was optimized to obtain spinnable precursor sol for synthesis of fibres. Thermogravimetry–differential scanning calorimetry (TG–DSC), Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) analyses were used to characterize properties of the gel and ceramic fibres. The precursor gel completely transformed to mullite at 1200 °C. The activation energy of mullite crystallization was 993.5 kJ/mol by the Kissinger equation.

    • Effect of rolling deformation and solution treatment on microstructure and mechanical properties of a cast duplex stainless steel

      S K Ghosh D Mahata R Roychaudhuri R Mondal

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      The present study deals with the effect of rolling deformation and solution treatment on the microstructure and mechanical properties of a cast duplex stainless steel. Cast steel reveals acicular/Widmanstätten morphology as well as island of austenite within the 𝛿-ferrite matrix. Hot rolled samples exhibit the presence of lower volume percent of elongated band of 𝛿-ferrite (∼40%) and austenite phase which convert into finer and fragmented microstructural constituents after 30% cold deformation. By the solution treatment, the elongated and broken crystalline grains recrystallize which leads to the formation of finer grains (<10 𝜇m) of austenite. X-ray diffraction analysis has corroborated well with the above-mentioned microstructural investigation. Enhancement in hardness, yield strength and tensile strength values as well as drop in percent elongation with cold deformation increases its suitability for use in thinner sections. 30% cold rolled and solution treated sample reveals attractive combination of strength and ductility (25.22 GPa%). The examination of fracture surface also substantiates the tensile results. The sub-surface micrographs provide the potential sites for initiation of microvoids.

    • Density variation and piezoelectric properties of Ba(Ti1−𝑥Sn𝑥)O3 ceramics prepared from nanocrystalline powders

      A K Nath Nirmali Medhi

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      Nanocrystalline powders of tin-doped barium titanate with different concentrations of tin have been synthesized by a combination of solid state reaction and high-energy ball milling. The average particle size of the milled powders as determined from TEM analysis was about 5.96 nm. Analysis of all the milled powders using X-ray diffraction method showed single phase perovskite structure. The density variation of the ceramics with sintering temperature has been studied by sintering the samples at different temperatures. Density variation results show that 1350°C is the optimum sintering temperature for tin-doped barium titanate ceramics. SEM micrographs show high density and increasing trend of grain size with increasing content of Sn. The ferroelectricity decreases with increasing concentration of Sn. The electromechanical coupling coefficient also decreases with increasing Sn content corroborating decreasing trend of ferroelectricity. The bipolar strain curves show piezoelectric properties of the prepared ceramics.

    • Role of MgF2 on properties of glass–ceramics

      M Ghasemzadeh A Nemati

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      Formation of machinable glass–ceramic in the system MgO–SiO2–Al2O3–K2O–B2O3–F with and without addition of MgF2 has been investigated. Crystallization of glass sample was done by controlled thermal heat treatment at nucleation and crystallization temperatures. The results showed that MgF2 in high concentration had a synergistic effect and enhanced the formation of interlockedmica crystals. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses were changed in the range of 235–405 kJ/mol, while the crystallization activation energies of samples with addition of MgF2 were changed in the range of 548–752 kJ/mol.

    • Hybrid orientation technology and strain engineering for ultra-high speed MOSFETs

      T K Maiti C K Maiti

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      We report here RF MOSFET performance in sub-45-nm hybrid orientation CMOS technology. Based on the combination of hybrid orientation technology (HOT) and process-induced local strain engineering,MOSFET RF performance is investigated using CAD (TCAD) technology. Transistor optimization on (100) substrate via silicon nitride (Si3N4) cap layer thickness for 𝑛-MOSFETs, Ge mole fraction optimization for 𝑝-MOSFETs on (110) substrates and channel length scaling have resulted in record RF performance, viz. the cut-off frequency, 𝑓T.

    • Controlled radical polymerization of vinyl acetate in presence of mesoporous silica supported TiCl4 heterogeneous catalyst

      M A Semsarzadeh S Amiri M Azadeh

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      The heterogeneous TiCl4 catalysts supported on mesoporous mobile composition of matter (MCM-41) and mesoporous silicone particles synthesized from block copolymer of PPG–PEG–PPG (SPB) complexed with dimethyl formamide (DMF) ligand were used in a controlled free radical reaction with benzoyl peroxide (BPO) initiator in bulk polymerization of vinyl acetate (VAc). In this polymerization process, mesoporous particle of SPB increased the reactivity of TiCl4 catalyst with DMF ligand. The active site formed on the surface and the pores of the catalyst produced specific sequences of VAc on the chain with different thermal and microstructural properties and crystallinity.

    • Bromine pretreated chitosan for adsorption of lead (II) from water

      Rajendra Dongre Minakshi Thakur Dinesh Ghugal Jostna Meshram

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      Pollution by heavy metals like lead (II) is responsible for health hazards and environmental degradation. Adsorption is a prevalent method applied for removal of heavy metal pollutants from water. This study explored adsorption performances of 30% bromine pretreated chitosan for lead (II) abatement from water. Bromine pretreatment alters porosity and specific surface area of chitosan by means of physicochemical interaction with cationic sites of chitosan skeleton, besides imparting anionic alteration at amino linkages of chitosan, to remove lead (II) by chemical interactions on superfluous active sites as characterized by FTIR, SEM, DTA and elemental analysis. Lead adsorptions were studied in batch mode by varying parameters viz. pH, bromine loading, sorbent dosage, initial lead concentration, contact time and temperature. The adsorption equilibrium data was well fitted to Freundlich isotherm and maximum sorption capacity of 30% bromine pretreated chitosan sorbent was 1.755 g/kg with 85–90% lead removal efficiency. Though cost and applicability of sorbent is unproven, yet contrast to raw chitosan derivatives, activated carbons and some resins, 30% bromine pretreated chitosan endow benign and efficient lead abatement technique.

    • Effect of nitrogen flow ratio on structure and properties of zirconium nitride films on Si(100) prepared by ion beam sputtering

      Shahab Norouzian Majid Mojtahedzadeh Larijani Reza Afzalzadeh

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      In this study, zirconium nitride thin films were deposited on Si substrates by ion beam sputtering (IBS). Influence of N2/(N2+Ar) on the structural and physical properties of the films has been investigated with respect to the atomic ratio between nitrogen and zirconium. It was found that the thickness of layers decreased by increasing the F(N2). Moreover, crystalline plane peaks such as (111), (200) and (220) with (111) preferred orientation were observed due to strain energy which associate with (111) orientation in ZrN. Also, the fluctuation in nitrogen flow ratio results in colour and electrical resistivity of films.

    • Synthesis, characterization and photocatalytic reactions of phosphated mesoporous titania

      Pallabi Goswami Jatindra Nath Ganguli

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      Mesoporous titania nanoparticles with a well-definedmesostructure was prepared by hydrothermal process, using nonionic triblock copolymer P123 as surfactant template, modified with phosphoric acid and followed by calcination at 600°C. The sol–gel titania was modified by in situ phosphorylation using phosphoric acid and thereby incorporating phosphorous directly into the framework of TiO2. The resulting materials were characterized by XRD, SEM, TEM, nitrogen adsorption, TGA and DRS. It was found that the structural and optical properties of titania samples are strongly influenced by their phosphate modification. In case of calcined samples a positive effect on the specific surface area for the in situ phosphated sample was found. Mesoporous structure of phosphated titania did not collapse even after calcination at 600°C. The enhanced photocatalytic activity of the synthesized phosphate nanomaterials were evaluated through a study of the decomposition of fluorescein under UV light excitation and compared with undoped titania nanomaterial as well as with commercial titania.

    • Effect of substitution of sand stone dust for quartz and clay in triaxial porcelain composition

      M K Haldar S K Das

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      Quartz and kaolin were partially substituted by sand stone dust (a siliceous byproduct of Indian stone cutting and polishing industries) in a traditional triaxial porcelain composition consisting of kaolin, quartz and feldsper. The effect of substitution upon heating at different temperatures (1050–1150°C) were studied by measuring the linear shrinkage, bulk density, porosity and flexural strength. Qualititative phase and microstructural analysis on selected samples were carried out using XRD and SEM/EDX technique. The results show that the samples of all the batches achieved higher density (2.50 g/cc) and almost full vitrification (<0.1% apparent porosity) at around 1115°C compared to around 1300°C for traditional triaxial porcelain composition. As high as 70 MPa flexural strength was obtained in most of the vitrified samples. No significant variation in physico-mechanical properties was observed in between the composition. XRD studies on selected samples show presence of mainly quartz phase both at low and high temperatures. SEM photomicrographs of the 1115°C heated specimen show presence of quartz grain and glassy matrix. Few quartz grains (20–40𝜇m) are associated with circumferential cracks around them.

    • Phase transitions in coated nickel titanium arch wires: A differential scanning calorimetric and X-ray diffraction analysis

      Manu Krishnan S Seema K Sukumaran Vasant Pawar

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      Shape memory and super-elastic properties of orthodontic nickel titanium wires, which are crucial for its clinical performance are dependent on the austenitic–martensitic phase transitions in its metallic microstructure that happen as a result of temperature or stress. The objective of this study was to compare the austenitic–martensitic phase transitions in new, black oxide coated nickel titanium (0.016 inch, Black Diamond, NiTi) arch wires in the `as-received’ form, from the manufacturer and `retrieved form’ after two months of intraoral use. This was done to analyse whether the new oxide coated nickel titanium wires suffered any significant loss in shape memory and super elasticity properties at the end of two months of intra oral use, findings of which could give valuable inferences prior to its widespread application in clinical practice.

      Five arch wire samples in both groups were investigated for their austenitic–martensitic phase transitions in an in vitro set up, using differential scanning calorimetry (DSC), (−90° to 100°C at a rate of 10°C/min) and X-ray diffraction (XRD) analysis (10° to 90°), as a function of temperature. Martensitic–austenitic thermograms showed an intermediate rhombohedral phase in the heating cycle of both groups, but cooling cycles showed direct reversal from austenitic to martensitic phase. Lower austenitic start (𝐴s = 10.78 ± 0.46° C) and finish (𝐴f = 22.26 ± 0.24° C) temperatures of coated wires compared to the conventional wires showed

      1. ability of the wire to remain in austenitic phase below oral temperature, that permits it to take up greater force during activation,
      2. increased springiness and
      3. consistent force delivery for an extended period of time.

      Statistical analysis with paired Student’s `𝑡’ test did not show any significant difference in mean values of transition temperatures and enthalpies between the two groups which proved similar shape memory and super-elastic properties at the end of intra oral use. Black oxide coating of NiTi wires may, therefore, be effective in diversified oral conditions and may find acceptable for re-use after sterilization. Low enthalpy values (0.92–3.59 j/g) compared to conventional ones, implied complete phase transition at the atomic level that can improve performance of the material in activation and deactivation cycles of NiTi wires. X-ray diffraction analysis of the two groups demonstrated predominance of austenitic phases (A, 110, 220 and 211) with complete reversibility at the atomic level. Discrete crystallographic structure and absence of multiple phases showed complete martensitic–austenitic transition, which authenticated the differential scanning calorimetric findings. This can earn acceptance for the new product in contemporary orthodontic practice with adequate scope for indigenization.

    • Enhanced physicochemical properties of collagen by using EDC/NHS-crosslinking

      Chunrong Yang

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      Collagen-based scaffolds are appealing products for the repair of cartilage defects using tissue engineering strategies. The present study investigated the collagen scaffolds with and without 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/𝑁-hydroxysuccinimide (NHS)-crosslinking. Crosslinking density, matrix morphology, swelling ratio shrinkage temperature and resistance against collagenase digestion were determined to evaluate the physicochemical properties of the collagen matrices with and without crosslinking. The results conformed that the porous structure of collagen was largely preserved and adjusted by crosslinking treatment. Furthermore, crosslinked collagen samples showed significantly reduced swelling ratio and increased resistance against thermal treatment and enzymatic degradation compared to non-crosslinked samples. An in vitro evaluation of MC3T3-E1 cells seeded onto the crosslinked and non-crosslinked collagen matrix indicated that crosslinked collagen was nontoxic and improved cell proliferation. Through this work, it was shown that an osteoconductive collagen matrix with optimized properties used as bioactive and bioresorbable scaffolds in bone tissue engineering could be fabricated through the EDC/NHS-crosslinking method.

© 2017 Indian Academy of Sciences, Bengaluru.