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      Volume 40, Issue 3

      June 2017,   pages  427-614

    • Electrochemical impedance studies of capacity fading of electrodeposited ZnO conversion anodes in Li-ion battery

      G K KIRAN TIRUPATHI RAO PENKI N MUNICHANDRAIAH P VISHNU KAMATH

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      Electrodeposited ZnO coatings suffer severe capacity fading when used as conversion anodes in sealed Li cells. Capacity fading is attributed to (i) the large charge transfer resistance, $R_{\rm ct}$ (300–700 $\Omega$) and (ii) the low Li$^+$ ion diffusion coefficient, D$^+_{\rm Li}$ (10$^{−15}$ to 10$^{−13}$ cm$^2$ s$^{−1}$). The measured value of R$_{\rm ct}$ is nearly 10 times higher and D$^+_{\rm Li}$ 10–100 times lower than the corresponding values for Cu$_2$O, which delivers a stable reversible capacity.

    • SU-8 photoresist-derived electrospun carbon nanofibres as high-capacity anode material for lithium ion battery

      M KAKUNURI S KAUSHIK A SAINI C S SHARMA

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      A binder-free carbon nanofibres web over stainless-steel wafer current collector was fabricated by controlled pyrolysis of electrospun SU-8 photoresist nanofibres. Electrochemical performance of the as-prepared carbon nanofibresweb was investigated by performing charge–discharge experiments at different current densities. At low current density (37.2 mA g$^{−1}, 0.1$C$), SU-8-derived carbon nanofabric showed a large initial discharge capacity (1417 mAh g$^{−1}$) with sufficiently higher initial coulombic efficiency ($\sim$55%). More importantly, this carbon nanofibres web also exhibited excellent rate performance with considerably higher specific capacities at higher current densities (358 mAh g$^{−1}$ at 1C). This superior electrochemical performance, in particular at high current rates, can be attributed to small lithium ion diffusion length andresilience in entangled carbon nanofibres to accommodate volume changes during charging and discharging.

    • Effect of composition on the polarization and ohmic resistances of LSM/YSZ composite cathodes in solid oxide fuel cell

      B SHRI PRAKASH S SENTHIL KUMAR S T ARUNA

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      La0.8Sr0.2MnO$_3$−$\delta$ (LSM)/8 mol% yttria-stabilized ZrO$_2$ (YSZ) (LSM/YSZ) composite cathodes with varying composition are studied for both polarization and ohmic resistance by electrochemical impedance spectroscopy. It was found that total resistance and polarization resistance are lowest for the composite with 60 wt% of LSM (LSM60/YSZ40). However, the ohmic resistance was highest for the same composition and amounted to 60% of the total resistance value. Compositional dependence of resistances has been explained based on the variations of the triple phase boundaries and width of the O$_2$−ion migration path with the composition of the electrode. Based on the observed area specific ohmic resistance values for the composite cathodes, it is proposed to verify the advantages of LSM/YSZ over LSM cathode in anode-supported solidoxide fuel cell with thin electrolyte.

    • Properties of biocomposites based on titanium scaffolds with a different porosity

      A P RUBSHTEIN E B MAKAROVA D G BLIZNETS A B VLADIMIROV

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      Open-porous titanium scaffolds have been widely investigated for orthopaedic and dental applications because of their ability to form composites via bone in growth into pores and promote implant fixation with mother bone. In this work, porous titanium scaffolds coated with a diamond-like carbon were produced, and their ability to form biocomposites was evaluated through in vivo experiments. Three types of the open-porous scaffolds made of spongy titanium granules (porosity 0.3, 0.4 and 0.5, Young’s modulus 4.4, 3.5 and 0.6 GPa) were implanted into a bone defect of sheep. Time dependences ofthe Young’s modulus of titanium scaffold–bone tissue biocomposites were determined through the measurement of Young’s modulus of the extracted scaffolds after 4, 8, 24 and 52 weeks of surgery. The Young’s modulus of biocomposite is dependent not only on the time of composite formation but also on the porosity of scaffold.

    • Synthesis and characterization of ZnO nanostructures with varying morphology

      KHALIDA AKHTAR NAILA ZUBAIR SAIRA IKRAM ZIA ULLAH KHAN HINA KHALID

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      Uniform fine particles of zinc oxide were prepared in three different morphologies and sizes by the controlled precipitation process from aqueous solutions of zinc nitrate in the presence of ethylene glycol. Ammonium hydroxidesolution was used as the precipitant. Composition of the reactant solution, pH and temperature significantly affected the particle uniformity with respect to shape and size. Uniformity in the particles morphological feature was achieved under a narrow set of experimental conditions. pH of the reactant solutions and isoelectric point of zinc oxide were considered the master variables, controlling the particle size. One of the batch of the as-prepared zinc oxide particles was calcined at 750$^{\circ}$C, which increased its crystallinity, changed its various lattice parameters, Zn–O bond length and preferred orientationof the crystal $hkl$ planes. Calcination had little effect on the original morphology of the zinc oxide particles.

    • Structural and optical properties of ZnO thin films prepared by laser ablation using target of ZnO powder mixture with glue

      E A MARTÍN-TOVAR R CASTRO-RODRÍGUEZ L G DAZA J MÉNDEZ-GAMBOA R MEDINA-ESQUIVEL I PEREZ-QUINTANA A IRIBARREN

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      ZnO thin films were deposited on ITO/glass substrates by pulsed laser deposition (PLD) using two different kinds of targets. One of the targets was made of pure ZnO powder and the other one consisted of a mixture of ZnO powder with cyanoacrylate glue. The structural and morphological properties of the films obtained using both targets were compared, in order to determine which one produces samples with properties more suitable for their use as buffer and antireflective layer in CdTe-based solar cells, also different heterostructures were deposited to study the optical properties of the obtained thin films and their utility in the applications mentioned before. The films deposited with the mixture powder target were polycrystalline with preferential orientations in the planes (100) and (101) with a high transmittance in the range of 70–90% in the 540–850 nm wavelength region and showed a high resistivity of $\sim$1.30$\times$102 $\Omega$ cm$^{−1}$, such properties are considered to be appropriate for thin films that are wanted to be used as a buffer and antireflective layer in CdTe solar cells.

    • SiO$_2$/TiO$_2$ multi-layered thin films with self-cleaning and enhanced optical properties

      CIPRIAN MIHOREANU ALEXANDRU ENESCA ANCA DUTA

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      Self-cleaning, high transmittance glazing was obtained by cold spray deposition for glazings. The thin films contain TiO$_2$, SiO$_2$ and Au nanoparticles in different structures which allow for tailoring the optical, hydrophilic and photocatalytic properties. The crystallinity, morphology and surface energy were correlated with the optical transmittanceand reflectance; the transmittance increased from 89.45 (for the glass substrate) to 91.76% when Au nanoparticles were used in the tandem layered structures. The samples containing alternating multi-layered SiO$_2$ and TiO$_2$ thin films without gold nanoparticles show hydrophilic surface; for these layers, the photocatalytic efficiency reaches 40% under simulated solar radiation. A conditioning effect based on adsorption was observed to increase the photocatalytic efficiency. These highly transparent coatings are well suited for glazings and fenestration, showing the self-cleaning effect based on combinedsuperhydrophilicity and photocatalysis.

    • Dependence of the textural properties and surface species of ZnO photocatalytic materials on the type of precipitating agent used in the hydrothermal synthesis

      I STAMBOLOVA V BLASKOV D STOYANOVA I AVRAMOVA L DIMITROV K MILENOVA K BALASHEV S SIMEONOVA A TZONEV L ALEKSANDROV A ELIYAS

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      Three different precipitating agents (NaOH, NH$_4$(H)CO$_3$ and CO(NH$_2$)$_2$) have been applied for the hydrothermalsynthesis of ZnO powder materials, aiming at obtaining various types of porosity and surface species on ZnO. The synthesis procedures were carried out in the presence and in the absence of tri-block copolymer Pluronic (P123,EO20PO70EO20). These materials were characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM)–energy-dispersive X-ray spectroscopy (EDX), BET method and TG–differential thermal analysis (DTA) method, and their photocatalytic activities were tested in the removal azo dye Reactive Black 5 (RB5). The urea precipitant yields spongy-like surface forms and the greatest share of mesopores. It has the highest specific surface area, highest degree of crystallinity of wurtzite ZnO phase and largest content of surface OHgroups in comparison with the other two precipitants. The zinc hydroxycarbonate intermediate phase is missing in the case of NaOH as precipitating agent; therefore, it manifests poorer textural characteristics. The morphology of P123-modified sample is different and consists of needle-shaped particles. The urea-precipitated samples display superior performance inthe photocatalytic oxidation reaction, compared with the other precipitated samples. The other two precipitating agents are inferior in regard to their photocatalytic activity due to greater share of micropores (not well-illuminated inner surface) and different surface morphologies.

    • A study on structural stability of bismuth titanate with lanthanum doping for improved ferroelectric properties

      UMAR AL-AMANI AZLAN AHMAD FAUZI MOHD NOOR

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      Bismuth titanate (Bi$_4$Ti$_3$O$_{12}$) with different lanthanum (La) concentrations (0.25, 0.50, 0.75 and 1.0 mol%) was successfully prepared via soft combustion route. It was found that the change of diffraction peaks shown by X-ray diffraction is attributed to the doping effect in Bi$_4$Ti$_3$O$_{12}$. This was also supported by the presence of additional peak that correspondsto La in the range of 800–860 eV, proved by X-ray photoelectron spectroscopy. In addition, the enlarged region of Bi 4f, Bi 4d, Ti 2p, La 3d and O 1s of doping sample was clearly seen after deconvolution. Based on binding energy position, it can be unambiguously stated that the Ti ions in the tetravalent state are surrounded by the perovskite layer of Bi$_4$Ti$_3$O$_{12}$, whichmay also imply the formation of oxygen vacancies in the vicinity of the Bi$_2$O$_2$ layer. In comparison with Bi$_4$Ti$_3$O$_{12}$, thegreen emission intensity was abruptly decreased with La doping. This indicates that La doping suppresses the formation of oxygen vacancies by stabilizing the adjacent oxide ions. Thus, the improved polarization shown by ferroelectric hysteresis loop is associated with the reduction in oxygen and bismuth vacancies due to La doping.

    • Flexible composite via rapid titania coating by microwave-assisted hydrothermal synthesis

      RICARDO MARQUES E SILVA ANDERSON THESING VINICIUS GONÇALVES DEON ALICE GONÇALVES OSÓRIO BRUNO DA SILVEIRA NOREMBERG NATÁLIA HADLER MARINS MARCELO ORNAGHI ORLANDI FABIANA VILLELA DA MOTTA RUBENS MARIBONDO DO NASCIMENTO NEFTALI LENIN VILLARREAL CARREÑO

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      The aim of this work was to prepare a flexible nanocomposite from ultra-fine titanium oxide (TiO$_2$) growth on carbon fibre via microwave-assisted hydrothermal synthesis (MHS) and to evaluate its photocatalytic properties. The TiO$_2$ nanoparticles were directly grown on the carbon fibre (CF). Thus, a study comparing the conventional titania coating vs. the MHS were performed. The significant layer interaction as a function of the coating method on the visible and dark dye photodegradation performance was observed. Techniques such as X-ray diffraction, electron microscopy (field-emission scanning electron microscope (FESEM)), Raman spectroscopy, among others were used aiming to characterize the different route samples. This study reports a reproducible and single method to manufacture of nanocomposites through the growth ofTiO$_2$ nanoparticle on CF by MHS that allow controlling the thickness layer. Similar procedure of synthesized nanocomposite could be applied in different chemical compositions to advanced applications, based on the electrochemical nanostructure.

    • Ultrasonic-assisted fabrication of superhydrophobic ZnO nanowall films

      S SUTHA R T RAJENDRA KUMAR BALDEV RAJ K R RAVI

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      Zinc oxide-based superhydrophobic surfaces were fabricated on aluminium oxide-seeded glass substrates via sonochemical approach by varying the parameter, the sonication time duration. The fabricated structures have nanowall-like morphology with an average long axis length and thickness of $\sim$300 and $\sim$40 nm, respectively. The surface roughness createdby surface-modified ZnO nanowalls and the air pockets trapped within the dense nanowalls, transformed the hydrophobic glass substrates into superhydrophobic surfaces with water contact angle of 156$^{\circ}$ during 20 min of sonication. An independent analysis was carried out to study the growth of ZnO nanowalls over glass substrates in the absence of the aluminium oxide seed layer and sonication process. The results suggested that the synergistic effect of the aluminium oxide seed layer and sonochemical process can enable the formation of ZnO nanowall structures favourable for superhydrophobic property. A possible growth mechanism of ZnO nanowalls formation during sonication process has been discussed in detail.

    • Partially decomposed PVP as a surface modification of ZnO, CdO, ZnS and CdS nanostructures for enhanced stability and catalytic activity towards sulphamethoxazole degradation

      MAHER DARWISH ALI MOHAMMADI NAVID ASSI

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      In order to prepare stable and efficient photocatalysts, a microwave-furnace-assisted method using ethylene glycol (EG) as a solvent has been employed to obtain metal oxides and metal sulphides nanocatalysts with partial decompositionof the polyvinylpyrrolidone (PVP) cap (P-ZnO, P-CdO, P-ZnS and P-CdS); this associates the protective functionality of PVP with enhanced catalytic activity due to effective carriers transfer. The as-produced catalysts characterization revealed an extended growth of metal oxides compared with metal sulphides, which is attributed to the competition of EG as the source of oxygen with PVP to capsulate metal oxides during the synthesis. Infrared spectra confirmed the PVP–metal complexation and partial decomposition of the polymer. Metal sulphides exhibited a better catalytic activity compared with metal oxides for sulphamethoxazole degradation in UVC light owing to their size and morphology impact; further, P-CdS induced 71% antibiotic degradation after 10 h of illumination with visible light compared with only 48% for P-ZnS, 29% for P-ZdO and 20% for P-CdO due to improved light absorption. Interestingly, around 86% degradation was induced by mixing P-CdS with P-ZnS in 80:20% ratio, indicating an enhanced visible light activity due to improved electron–hole pair separation and high redox potential of P-ZnS.

    • Characterization and optical properties of Pr$_2$O$_3$-doped molybdenum lead-borate glasses

      SANGEETA B KOLAVEKAR N H AYACHIT R V ANAVEKAR

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      Pr$^{3+}$ doped molybdenum lead-borate glasses with the chemical composition 75PbO−[25–($x+y$)B$_2$O$_3$]–$y$MoO$_3$–$x$Pr$_2$O$_3$ (where $x = 0.5$ and 1.0 mol% and y = 0 and 5 mol%) were prepared by conventional melt-quenching technique. Thermal, optical and structural analyses are carried out using DSC, UV and FTIR spectra. The physical parameters,like glass transition ($T_g$), stability factor ($\Delta T$), optical energy band gap ($E_{gopt}$), of these glasses have been determined as a function of dopant concentration. The $T_g$ and optical energy gaps of these glasses were found to be in the range of 290–350$^{\circ}$C and 2.45–2.7 eV, respectively. Stability of the glass doped with Pr$^{3+}$ is found to be moderate ($\sim$40). The results are discussed using the structural model of Mo–lead-borate glass

    • Polymer-assisted co-precipitation route for the synthesis of Al$_2$O$_3$–13% TiO$_2$ nanocomposite

      NEERA SINGH RANABRATA MAZUMDER PALLAV GUPTA DEVENDRA KUMAR

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      The present investigation reveals the effect of processing parameters on the properties of alumina–titania (Al$_2$O$_3$–TiO$_2$) nanocomposites. A polymer-assisted (Pluronic P123 triblock co-polymer) co-precipitation route has been employed to synthesize Al$_2$O$_3$–TiO$_2$ nanoparticles. As a surfactant, pluronic P123 polymer exhibits hydrophobic as well as the hydrophilic nature simultaneously which detains the agglomeration and hence the nano size particle have been obtained. Effect of surfactant concentration on morphology and particle size of product has also been investigated. Thermal behaviour of the prepared powder samples have been studied using differential scanning calorimeter/thermal gravimetric analysis and dilatometer. Formation of aluminium-titanate (Al$_2$TiO$_5$) phase has been confirmed using X-ray diffraction analysis. It has been observed by field emission scanning electron microscopy analysis that the particle size reduced effectively (below 100 nm) when polymer-assisted co-precipitation route is used instead of the simple co-precipitation technique. A highly dense microstructure of sintered samples has been obtained, driven by reduced particle size.

    • Temperature-dependent gas transport and its correlation with kinetic diameter in polymer nanocomposite membrane

      N K ACHARYA

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      Activation energies for permeation of polymer nanocomposite membrane have not been reported so far. A tradeoff relation between permeability and selectivity shows that as permeability increases, the selectivity decreases. Attempts have been made to see this trade-off relation at relatively higher temperature. It is found that selectivity decreases drasticallywith increasing temperature.Apolymer–matrix compositewas prepared by adding silica nanoparticles using casting method. Pure gas permeability was measured using a constant volume–variable pressure method at different temperature ranges from 35 to 70$^{\circ}$C. The Van’t Hoff relation was used to estimate the activation energy for permeation. It is found to decrease as compared with virgin polycarbonate and it increases with kinetic diameter. For the first time, the permeability and selectivity for nanocomposite membrane are reported as a function of temperature. Activation energies for different gases have beencalculated for nanocomposite membrane and comparedwith that of virgin polymer membrane. Decrease in activation energies for permeation ($E_p$) with increasing kinetic diameter has been observed for both the membranes. Selectivity reduces with temperature for both the membranes.Mechanical and thermal properties of nanocomposite membrane have been investigatedusing a dynamic mechanical analyser and differential scanning calorimetry, respectively. Scanning electron microscopy has been used to study surface morphology. The results show modification in physical properties due to incorporation of silica nanoparticles.

    • Ultrasonic and structural features of some borosilicate glasses modified with heavy metals

      YASSER B SADDEEK

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      A quaternary glass system Na$_{1.4}$B$_{2.8}$Si$_x$Pb$_{0.3−x}$O$_{5.2+x}$, with $0 \lt x \lt 0.3$, was prepared and studied by Fourier transform infrared spectroscopy, density and ultrasonic techniques to debate the issue of the role of SiO2 in the structureof lead alkali borate glasses. The results indicate that SiO2 generates an abundance of bridging oxygen atoms, [BO$_4$] and [SiO$_4$] structural units and changes the bonds B–O–B and Pb–O–B to Si–O–Si and B–O–Si. The latter bonds have higher bond strength and higher average force constant than the former bonds. Therefore, the glass structure becomes contractedand compacted, which decreases its molar volume and increases its rigidity. This concept was asserted from the increase in the ultrasonic velocity, Debye temperature and elastic moduli with the increase of SiO2 content. The present compositional dependence of the elastic moduli was interpreted in terms of the electron–phonon anharmonic interactions and the polarizationof Si$^{4+}$ cation. A good correlation was observed between the experimentally determined elastic moduli and those computed according to the Makishima–Mackenzie model.

    • Evaluation of the elastic properties of monovalent oxides using TeO$_2$-based glasses

      A M EMARA S F MANSOUR M Y HASSAAN El SAYED YOUSEF

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      Quaternary tellurite glasses with composition 75TeO$_2$–5WO$_3$–15Nb$_2$O$_5$–5M$_x$O$_y$ in mol%, where M$_x$O$_y$ =(Na$_2$O, Ag$_2$O, ZnO, MgO, CuO, NiO, TiO$_2$, MnO$_2$), were prepared by the normal melt-quenching method. The ultrasonic velocities (longitudinal and shear) were measured in these glasses using the pulse-echo technique at room temperature. Their elastic moduli, microhardness and Debye temperature were calculated and discussed in terms of the modifier’s ionicity and quantitatively in terms of number of bonds per unit volume and the cross-link density. In this study, the values of ultrasonic velocities, elastic moduli, Debye temperature and microhardness were found to be strongly dependent on three factors, namely: (i) modifier’s ionicity; (ii) trigonal pyramid (TeO$_3$)/trigonal bipyramid (TeO$_4$) ratio; and (iii) glass transition temperature $T_g$. We used the Makishima and Mackenzie’s model to calculate the theoretical elastic moduli and to indicatethat the experimental values were in good agreement with the theoretical values.

    • Cation substitution induced blue-shift of optical band gap in nanocrystalline Zn$_{(1−x)}$Ca$_x$O thin films deposited by sol–gel dip coating technique

      NRIPASREE NARAYANAN N K DEEPAK

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      Transparent nanocrystalline Zn${(1−x)}$Ca$_{x}O ($0 ≤ x ≤ 0.20$) thin films were deposited on glass substrates by sol–gel dip coating method. The X-ray diffraction (XRD) pattern revealed the polycrystalline nature of the films withhexagonal wurtzite structure and confirmed the non-existence of the secondary phase corresponding to CaO indicating the monophasic nature of the deposited films. The crystallinity of the films deteriorated with higher dopant concentration due to the segregation or separation of dopant ions in grain boundaries. The lattice parameters and the unit cell volume increased to a higher Ca-dopant concentration. This was due to the successful incorporation of Ca2+ ions with larger ionic radius inthe host zinc oxide (ZnO) lattice. The optical transmittance spectra of the samples showed transmittances above 60% in thevisible spectral range and the absorption edge in the near ultra-violet region got blue-shifted with cation substitution. Theestimated optical energy gaps confirmed the band gap widening with increase in Ca-dopant concentration. The calculatedvalues increased from 3.30 eV for undoped ZnO to 3.73 eV for Zn0.8Ca0.2O thin films giving 13.03% enhancement in theenergy gap value due to the electronic perturbation caused by cation substitution as well as deterioration in crystallinity.

    • Study of $\beta$-phase development in spin-coated PVDF thick films

      BHOOPESH MAHALE DHANANJAY BODAS S A GANGAL

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      A study was conducted to ascertain the effect of variation in spin speed and baking temperature on $\beta$-phase content in the spin-coated poly(vinylidene fluoride) (PVDF) thick films ($\sim$4−25 $\mu$m). Development of $\beta$-phase is dependent on film stretching and crystallization temperature. Therefore, to study the development of $\beta$-phase in films, stretching is achieved by spinning and crystallization temperature is adjusted by means of baking. PVDF films are characterized using Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and scanning electronmicroscopy. It is observed that crystallization temperature lower than 60$^{\circ}$C and increase in spin speed increases the $\beta$-phasecontent in PVDF films. Crystallization temperature above 60$^{\circ}$C reduces $\beta$-phase content and increases α-phase content. It was also observed that viscosity of the PVDF solution affects the β-phase development in films at a particular spin speed.

    • Effects of electrolyte concentration and current density on the properties of electro-deposited NiFeW alloy coatings

      J K YU H SUN L L ZHAO Y H WANG M Q YU H L LUO Z F XU KAZUHIRO MATSUGI

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      NiWP alloy coatings were prepared by electrodeposition, and the effects of ferrous chloride (FeCl$_2$), sodium tungstate (Na$_2$WO$_4$) and current density ($D_K$) on the properties of the coatings were studied. The results show that upon increasing the concentration of FeCl$_2$, initially the Fe content of the coating increased and then tended to be stable; the deposition rate and microhardness of coating decreased when the cathodic current efficiency ($\eta$) initially increased and then decreased; and for a FeCl$_2$ concentration of 3.6 gl$^{−1}, the cathodic current efficiency reached its maximum of 74.23%. Upon increasing the concentration of Na$_2$WO$_4$, the W content and microhardness of the coatings increased; the deposition rate andthe cathode current efficiency initially increased and then decreased. The cathodic current efficiency reached the maximum value of 70.33% with a Na$_2$WO$_4$ concentration of 50 gl$^{−1}$, whereas the deposition rate is maximum at 8.67 $\mu$mh$^{−1}$ with a Na$_2$WO$_4$ concentration of 40 gl$^{−1}$. Upon increasing the $D_K$, the deposition rate, microhardness, Fe and W content of the coatings increased, the cathodic current efficiency increases first increased and then decreased. When $D_K$ was 4 A dm$^{−2}$,the current efficiency reached the maximum of 73.64%.

    • Dependency of annealing behaviour on grain size in Al–TiC composite produced by accumulative roll bonding

      HAMID REZA JAFARIAN JAFAR HABIBI-LIVAR

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      This work investigates the effect of grain size on annealing behaviour in both coarse-grained and ultrafinegrained Al–TiC composite processed by accumulative roll bonding (ARB). Microstructural analysis indicates that annealingbehaviour of the specimens are essentially determined by the level of strain accumulation or number of ARB cycles, i.e., recrystallization phenomenon are accelerated by increasing the level of strain accumulation or number of ARB cycles. Microstructure analysis illustrates that annealing treatment at 200 or 250$^{\circ}$C for the 1-cycle ARB-processed Al–TiC compositehaving coarse grains does not lead to the recrystallization phenomenon, indicating that only recovery appears. In contrast, partial recrystallization occurred after annealing at 250$^{\circ}$C in the 7-cycle ARB-processed Al–TiC composite having ultrafine grains. Furthermore, annealing treatment significantly enhanced elongation for both ultrafine as well as coarse-grained Al–TiC composites in spite of the fact that yield and ultimate strength decreased during annealing treatment. The results proved that yield strength and tensile strengths for both 1-cycle and 7-cycle ARB-processed Al–TiC composites gradually decreased by annealing treatments between 200 and 300$^{\circ}$C. In contrast, ultimate elongation drastically improved by about 100% after annealing at the aforementioned conditions.

    • Synthesis of fluorescent diblock copolymer nanoparticle supported catalyst for the reduction of Cr(VI), p-nitrophenol and rhodamine 6G dye: a comparative study

      P ABINAYASRI M NAGESWARI B MEENARATHI R ANBARASAN

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      A fluorescent diblock copolymer nanocomposite (DBCNC) was synthesized by ring opening polymerization (ROP) method using rhodamine 6G (R6G) dye as an initiator through bulk polymerization technique. ROP of caprolactonewas carried out at 160$^{\circ}$C for 2 h under nitrogen atmosphere in the presence of stannous octoate (Sn(Oct)$_2$) as a catalyst followed by the ROP of tetrahydrofuran in the presence of phthalicanhydride as a co-monomer. Thus, synthesized fluorescent DBCNC was characterized by various analytical tools such as FTIR spectroscopy, UV–visible spectroscopy fluorescenceemission spectroscopy, DSC, TGA and FESEM. The catalytic reduction of p-nitrophenol (NiP), Cr(VI) and R6G was carried out in the presence of DBCNC as a catalyst with the help of UV–visible spectrophotometer. The apparent rate constant ($k_{app}$) and induction time ($T_i$) were determined from the UV–visible spectral data. The nanosized V$_2$O$_5$ was prepared by a simplechemical reduction of bulk-sized V$_2$O$_5$ by using sodium borohydride (NaBH$_4$) as a reducing agent. During the DBC formation, 0.01 g of nanosized V$_2$O$_5$ was added. This type of polymer supports the catalyst which is very much useful in the catalysis industry because of its easy separation and recyclable property.

    • Carrier concentration effect and other structure-related parameters on lattice thermal conductivity of Si nanowires

      IBRAHIM N QADER M S OMAR

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      Lattice thermal conductivity (LTC) of Si bulk and nanowires (NWs) with diameter 22, 37, 50, 56, 98 and 115 nm was investigated in the temperature range 3–300 K using a modified Callaway model that contains both longitudinal and transverse modes. Using proper equations, mean bond length, lattice parameter, unit cell volume, mass density, melting temperature, longitudinal and transverse Debye temperature and group velocity for all transverse and longitudinal modes were calculated for each NW diameter mentioned. Surface roughness, Gruneisen parameter and impurity were used as adjustable parameters to fit theoretical results with experimental curves. In addition, values of electron concentration and dislocation density were determined. There are some phonon scattering mechanisms assumed, which are Umklapp and normal processes, imperfections, phonon confinement, NW boundaries, electrons scattering and dislocation. Dislocationdensity less than 10$^{14}$ m$^{−2}$ for NWs and 10$^{12}$ m$^{−2}$ for bulk has no effect on LTC. Also, electron concentration less than 10$^{22}$ m$^{−3}$ for NWs and 10$^{16}$ m$^{−3}$ for the bulk has no effect. On increasing dislocation density and electron concentration, LTC comparably decreases.

    • Preparation, characterization and mechanical properties of k-Carrageenan/SiO$_2$ nanocomposite films for antimicrobial food packaging

      R VENKATESAN N RAJESWARI T THENDRAL THIYAGU

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      Kappa-Carrageenan (KCG) films have been formulated as a packaging material. This study has been conducted to investigate the effect of incorporating SiO$_2$ nanoparticles inside the KCG matrix, with the aim of enhancing the mechanical and antimicrobial properties of KCG for reinforcement purposes. Films were prepared by solution casting technique with 1.0, 3.0 and 5.0 wt% of SiO$_2$ nano-filler content taking neat KCG as the reference for the study. Structural characterizations of the prepared nanocomposite films were carried out by Fourier transform infrared, scanning electron microscope (SEM) andtransmission electron microscope (TEM) techniques. SEM and TEM showed homogeneous dispersion of SiO$_2$ nanoparticles in the KCG matrix. The tensile strength increased significantly by introducing the SiO$_2$ nanoparticles into the KCG matrix, in which KCG/SiO$_2$ films have greater tensile strength (53.9 MPa) when compared to the KCG polymer (46.8 MPa). The moisture uptake (MU) of nanocomposites decreased when SiO2 was introduced into the polymer matrix. The barrier property of the prepared KCG-based nanocomposite films decreased oxygen transmission rate with loading of different wt%of SiO$_2$. SiO$_2$ nanoparticle-loaded films produced higher zones of inhibition against Staphylococcus aureus and Escherichia coli strains compared to polymer film. This study was intended to find the applications for KCG films containing SiO$_2$ nanoparticles to enhance the shelf-life of foods in the form of biodegradable wrapper.

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