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      Volume 34, Issue 2

      April 2011,   pages  183-416

    • Study of structural transformations and phases formation upon calcination of Zn–Ni–Al hydrotalcite nanosheets

      Zhanshuang Li Yanchao Song Jun Wang Qi Liu Piaoping Yang Milin Zhang

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      In this paper, we describe a general process for the synthesis of highly crystalline Zn–Ni–Al hydrotalcitelike materials. The structure and thermal decomposition of the prepared samples are studied by XRD, FT–IR, TG–DSC, SEM, TEM and N2 adsorption/desorption. The morphology of large-sized, porous and hexagonal platelike Zn–Ni–Al hydrotalcite is affected by calcination temperature. BET specific surface area and pore volume are observed to increase with increase of the calcination temperature up to 700°C followed by a further decrease with increasing temperature.

    • Microbial synthesis of iron-based nanomaterials—A review

      Abhilash K Revati B D Pandey

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      Nanoparticles are the materials having dimensions of the order of 100 nm or less. They exhibit a high surface/volume ratio leading to different properties far different from those of the bulk materials. The development of uniform nanoparticles has been intensively pursued because of their technological and fundamental scientific importance. A number of chemical methods are available and are extensively used, but these are often energy intensive and employ toxic chemicals. An alternative approach for the synthesis of uniform nanoparticles is the biological route that occurs at ambient temperature, pressure and at neutral pH. The main aim of this review is to enlist and compare various methods of synthesis of iron-based nanoparticles with emphasis on the biological method. Biologically induced and controlled mineralization mechanisms are the two modes through which the micro-organisms synthesize iron oxide nanoparticles. In biologically induced mineralization (BIM) mode, the environmental factors like pH, pO2, pCO2, redox potential, temperature etc govern the synthesis of iron oxide nanoparticles. In contrast, biologically controlled mineralization (BCM) process initiates the micro-organism itself to control the synthesis. BIM can be observed in the Fe(III) reducing bacterial species of Shewanella, Geobacter, Thermoanaerobacter, and sulphate reducing bacterial species of Archaeoglobus fulgidus, Desulfuromonas acetoxidans, whereas BCM mode can be observed in the magnetotactic bacteria (MTB) like Magnetospirillum magnetotacticum, M. gryphiswaldense and sulphate-reducing magnetic bacteria (Desulfovibrio magneticus). Magnetite crystals formed by Fe(III)-reducing bacteria are epicellular, poorly crystalline, irregular in shapes, having a size range of 10–50 nm super-paramagnetic particles, with a saturation magnetization value ranging from 75–77 emu/g and are not aligned in chains. Magnetite crystals produced by MTB have uniform species-specific morphologies and sizes, which are mostly unknown from inorganic systems. The unusual characteristics of magnetosome particles have attracted a great interdisciplinary interest and inspired numerous ideas for their biotechnological applications. The nanoparticles synthesized through biological method are uniform with size ranging from 5 to 100 nm, which can potentially be used for various applications.

    • Rayleigh like scattering from silica–titania core-shell particles and their application in protection against harmful ultraviolet rays

      Sudipta G Dastidar P Bharath Arindam Roy

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      In this article we report experimental and theoretical results of angle-dependent laser light scattering of nano titanium dioxide nucleated on silica particles. It was observed that the experimental scattering profile from nano-titania coated silica (TCS) particle resembles that of a Rayleigh scattering. It can be inferred from the light scattering profile that nucleating fine particles onto a surface of a bigger particle (core), the resulting scattering profile is dominated by the smaller particles. Thin film transmittance measurement of TCS particles also supports this claim. The theoretical scattering predictions do not match with the experimental findings and the reasons for the discrepancies are addressed. This Rayleigh-like scattering property of TCS particles can be used in cosmetic formulations as a replacement for nanoparticles to provide protection from harmful ultraviolet rays. This study helps to provide insights into these systems for their potential usage in cosmetics.

    • Metal-coated magnetic nanoparticles for surface enhanced Raman scattering studies

      G V Pavan Kumar N Rangarajan B Sonia P Deepika Nashiour Rohman Chandrabhas Narayana

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      We report the optimization and usage of surfactantless, water dispersible Ag and Au-coated 𝛾 –Fe2O3 nanoparticles for applications in surface-enhanced Raman scattering (SERS). These nanoparticles, with plasmonic as well as super paramagnetic properties exhibit Raman enhancement factors of the order of 106 (105) for Ag (Au) coating, which are on par with the conventional Ag and Au nanoparticles. Raman markers like 2-naphthalenethiol, rhodamine-B and rhodamine-6G have been adsorbed to these nanoparticles and tested for nonresonant SERS at low concentrations. Further, to confirm the robustness of Ag-coated nanoparticles, we have performed temperaturedependent SERS in the temperature range of 77–473 K. The adsorbed molecules exhibit stable SERS spectra except at temperatures >323 K, where the thermal desorption of test molecule (naphthalenethiol) were evident. The magnetic properties of these nanoparticles combined with SERS provide a wide range of applications.

    • Multiple strengthening mechanisms in nanoparticle-reinforced copper matrix composites

      D Bozic J Stasic B Dimcic M Vilotijevic V Rajkovic

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      The multiple hardening mechanisms of a copper matrix have been presented and discussed. The prealloyed ball milled Cu–3 wt.%Al and the atomized Cu–0.6 wt.%Ti–2.5 wt.%TiB2 powders have been used as starting materials. Dispersoid particles Al2O3 and TiB2 were formed in situ. The powders have been hot consolidated. Optical microscopy, SEM, TEM, and X-ray diffraction analysis were performed for microstructural characterization. Increase in microhardness of Cu–3 wt.%Al compacts is a consequence of the crystallite size refinement and the presence of Al2O3 particles. High hardening of Cu–0.6 wt.%Ti–2.5 wt.%TiB2 is a consequence of the presence of modular structure, Cu4Ti$_{(m)}$, and TiB2 particles.

    • Effect of CdS nanoparticles on photoluminescence spectra of Tb3+ in sol–gel-derived silica glasses

      S Rai L Bokatial

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      CdS nanoparticles doped with Tb3+ were synthesized by sol–gel technique. The influence of CdS on the Tb3+ glass was studied by UV-Visible and luminescence spectroscopy. The luminescence intensity of the glasses increased significantly in the presence of CdS nanoparticles. Terbium ions excited into the ${}^{5}D_{3}$ level have a rich emission spectrum in the 400–700 nm range decaying to different ${}^{7}F_{J}$ levels. The intensity of violet and blue luminescence from ${}^{5}D_{3}$ level is highly dependent on Tb3+ concentration, on presence of CdS co-dopant and annealing conditions.

    • Shape control synthesis of low-dimensional calcium sulfate

      Li-Xia Yang Yan-Feng Meng Ping Yin Ying-Xia Yang Ying-Ying Tang Lai-Fen Qin

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      Calcium sulfate nanorods, nanowires, nanobelts and sheets had been synthesized via a facile solution reaction of CaCl2 and H2SO4 in mixed solvents of ethanol/𝑁, 𝑁-dimethylformamide and deionized water at 35°C. The results indicated that well-crystallized CaSO4 nanomaterials with different morphology were obtained by adjusting the volume ratio of ethanol/𝑁, 𝑁-dimethylformamide to deionized water and the reaction time. Samples prepared at 35°C in mixed solvents of 50 mL ethanol and 30 mL water for 1 min and 2 h showed nanowire and sheet morphology, respectively. While increasing the volume ratio of ethanol to deionized water to 78/2, only nanorods were obtained. When 𝑁, 𝑁-dimethylformamide was employed to substitute ethanol, the sample heating at 35°C for 2 h was composed of nanowires in 50 mL 𝑁, 𝑁-dimethylformamide and 30 mL water. Higher volume ratio of 𝑁, 𝑁-dimethylformamide to deionized water caused the formation of nanorods.

    • Synthesis of 𝛾-Al2O3 nanowires through a boehmite precursor route

      Qi Yang

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      Crystalline 𝛾-Al2O3 nanowires with diameter, 20–40 nm, length above 600 nm and aspect ratio above 30 have been successfully synthesized by thermal decomposition of boehmite (𝛾-AlOOH) precursors obtained via hydrothermal route by using AlCl3, NaOH and NH3 as starting materials. Thermogravimetric analysis (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscope (TEM), selected area electron diffraction (SAED) and high resolution transmission electron microscope (HRTEM) were used to characterize the features of the as-made 𝛾-Al2O3 nanowires and their 𝛾-AlOOH precursors. The pH value of the solution and the mixed precipitant play important roles in the formation of 𝛾-AlOOH nanowires. After calcination at 500°C for 2 h, the orthorhombic 𝛾-AlOOH transforms to cubic 𝛾-Al2O3 and retains nanowire morphology.

    • Ferrofluid thin films as optical gaussmeters proposed for field and magnetic moment sensing

      Swapna S Nair S Rajesh V S Abraham M R Anantharaman

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      Ferrofluids belonging to the series, Ni𝑥Fe1−𝑥Fe2O4 and Zn𝑥Fe1−𝑥Fe2O4, were synthesized using cold co-precipitation. Liquid films of these ferrofluids were prepared by encapsulating the ferrofluids in between two optically smooth and ultrasonically cleaned glass plates. Magnetic field induced laser transmission through these ferrofluid films has been investigated. Magnetic field values can be calibrated in terms of output laser power in the low field region in which the variation is linear. This set up can be used as a cheap optical gaussmeter in the low field regime. Using the same set-up, the saturation magnetization of the sample used can also be calculated with a sample that is pre-characterized. Hence both magnetization of the sample, as well as applied magnetic field can be sensed and calculated with a precalibrated sample.

    • On structural, optical and dielectric properties of zinc aluminate nanoparticles

      E Muhammad Abdul Jamal D Sakthi Kumar M R Anantharaman

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      Zinc aluminate nanoparticles with average particle size of 40 nm were synthesized using a sol–gel combustion method. X-ray diffractometry result was analysed by Rietveld refinement method to establish the phase purity of the material. Different stages of phase formation of the material during the synthesis were investigated using differential scanning calorimetry and differential thermogravimetric analysis. Particle size was determined with transmission electron microscopy and the optical bandgap of the nanoparticles was determined by absorption spectroscopy in the ultraviolet-visible range. Dielectric permittivity and a.c. conductivity of the material were measured for frequencies from 100 kHz to 8 MHz in the temperature range of 30–120°C. The presence of Maxwell–Wagner type interfacial polarization was found to exist in the material and hopping of electron by means of quantum mechanical tunneling is attributed as the reason for the observed a.c. conductivity.

    • Influence of dielectric constant of polymerization medium on processability and ammonia gas sensing properties of polyaniline

      Partha Pratim Sengupta Pradip Kar Basudam Adhikari

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      Polyaniline (PANI) was synthesized by the oxidation of aniline hydrochloride in the presence of ammonium persulphate and hydrochloric acid. The polymerization reaction was carried out in several batches in different solvent media by changing the volume ratio of 𝑁,𝑁-dimethyl formamide (DMF) and water as binary solvent mixture. The dielectric constant of the polymerizationmedium for each batch reaction was determined by measuring the capacitance with change in frequency. The UV spectra of the synthesized polyaniline solutions helped us to optimize the ratio of the binary solvent to get sufficient polymer growth and processability. Thin film of processable polyaniline was then deposited on glass slides coated with polyvinyl alcohol (PVA) crosslinked with maleic anhydride (MA). FTIR and XRD studies of the coated film were also done. AFM studies further helped in the morphological study of the film deposited. Finally, conductivity and ammonia gas-sensing property of the polyaniline film were also studied.

    • Synthesis of new (Bi, La)3MSb2O11 phases (M = Cr, Mn, Fe) with KSbO3-type structure and their magnetic and photocatalytic properties

      K Ramesha A S Prakash M Sathiya Giridhar Madras A K Shukla

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      Synthesis and structure of new (Bi, La)3MSb2O11 phases (M = Cr, Mn, Fe) are reported in conjunction with their magnetic and photocatalytic properties. XRD refinements reflect that Bi3CrSb2O11, Bi2LaCrSb2O11, Bi2LaMnSb2O11 and Bi2LaFeSb2O11 adopt KSbO3-type structure (space group, 𝑃𝑛$\bar{3}$). The structure can be described through three interpenetrating networks where the first is the (M/Sb)O6 octahedral network and other two are the identical networks having Bi6O4 composition. The magnetic measurements on Bi2LaCrSb2O11 and Bi2LaMnSb2O11 show paramagnetic behaviour with magnetic moments close to the expected spin only magnetic moments of Cr+3 and Mn+3. The UV-Visible diffuse reflectance spectra are broad and indicate that these materials possess a bandgap of ∼ 2 eV. The photocatalytic activity of these materials has been investigated by degrading Malachite Green (MG) under exposure to UV light.

    • Effect of cobalt substitution on magnetic and transport properties of Nd0.5Sr0.5Mn1−𝑥Co𝑥O3 (𝑥 = 0.1, 0.3 and 0.5)

      Saket Asthana

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      The magnetic and transport properties of the compounds Nd0.5Sr0.5Mn1−𝑥Co𝑥O3 (𝑥 = 0.1, 0.3 and 0.5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn3+–O2−–Mn4+ as compared to Co3+–O2-–Co4+ pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile 𝑒g electrons).

    • Colossal magnetodielectric effect caused by magnetoelectric effect under low magnetic field

      Qian Liu Xiao-Bing Bian Jian-Ping Zhou Peng Liu

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      The colossal magnetodielectric effect is reported in Pb(Zr,Ti)O3/Terfenol-D laminate composite under low magnetic field. When the composite is placed in an external a.c. magnetic field, magnetoelectric effect is produced, as a result, the dielectric properties of the Pb(Zr,Ti)O3 is changed, i.e. magnetodielectric effect. Both the amplitude and resonance frequency change with the external magnetic field. The colossal magnetodielectric coefficient of 5 × 104%at low magnetic field of 20 Oe is achieved near the electromechanical resonance frequency.

    • Synthesis and investigation of optical properties of ZnS nanostructures

      Neslihan Üzar M Çetin Arikan

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      Structural characterizations of wurtzite zinc sulfide (ZnS) nanostructures synthesized by vapour–liquid–solid technique (VLS) were carried out by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses. Spectral dependence of photoluminescence (PL) was also carried out for optical characterization. PL results indicate that the bandgap energy of bulk ZnS which is 3.68 eV at room temperature changes from 3.7 eV to 3.72 eV depending on the size of the structures. We also supported these results by calculating the bandgap energies theoretically with using the infinite potential well approximation for 1D structures.

    • Effect of glass hybridization and staking sequence on mechanical behaviour of interply coir–glass hybrid laminate

      S Jayabal U Natarajan S Sathiyamurthy

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      The interest in fibre-reinforced polymer composites is growing rapidly due to its high performance in terms of mechanical properties, significant processing advantages, excellent chemical resistance, low cost, and low density. The development of composite materials based on the reinforcement of two or more fibre types in a matrix leads to the production of hybrid composites. In the present work, woven coir–glass hybrid polyester composites were developed and their mechanical properties were evaluated for different stacking sequences. Scanning electron micrographs of fractured surfaces were used for a qualitative evaluation of interfacial properties of woven coir–glass hybrid polyester composites. These results indicated that coir–glass hybrid composites offered the merits of both natural and synthetic fibres.

    • IR and Raman spectroscopic studies of sol–gel derived alkaline-earth silicate glasses

      Angelos G Kalampounias

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      IR and Raman spectroscopies have been utilized to study the structure and vibrational modes of sol–gel-derived binary silicate glasses. The present study is motivated by the immense geological significance and focuses on the MO–SiO2 (M = Ca, Mg) binary systems in an effort to unveil the role of the CaO and MgO modifiers when incorporated to the 3D silica structure. Glasses in the composition range 𝑥 = 0, 0.1, 0.2, 0.3 and 0.4 prepared by the sol–gel method were compared with the corresponding glasses formed by appropriate mixing of SiO2 and MO powders through melting and fast cooling. The vibrational spectra of the sol–gel-derived glasses have revealed considerable changes in relative intensities as a function of the MO mole fraction. These changes signify structural modifications on the silica network. The population of the 𝑄3 species was found to increase for both modified silicate systems. The rate of increase is more pronounced in the CaO–SiO2 glasses. The extent of network depolymerization in the porous glass is higher at the same content of alkaline earth oxide compared to the bulk glass. The results are indicative of a more `defective’ nature of the sol–gel glasses compared to the corresponding melt-quenched ones.

    • Life prediction of Ni-base superalloy

      M Aghaie-Khafri M Noori

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      Rene 80 samples were creep–rupture tested in air between 1144 and 1255 K at various stress levels. The mean stress exponent, 𝑛, and the mean activation energy for creep were calculated from the experimental results. The accelerated creep life of the alloy was evaluated by using iso-stress parametric equations and Monkman–Grant method.

    • Precipitation hardening and hydrogen embrittlement of aluminum alloy AA7020

      Santosh Kumar T K G Namboodhiri

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      AA7020 Al–Mg–Zn, a medium strength aluminium alloy, is used in welded structures in military and aerospace applications. As it may be subjected to extremes of environmental exposures, including high pressure liquid hydrogen, it could suffer hydrogen embrittlement. Hydrogen susceptibility of alloy AA7020 was evaluated by slow strain-rate tensile testing, and delayed failure testing of hydrogen-charged specimens of air-cooled, duplexaged, and water-quenched duplex agedmaterials. The resistance to hydrogen embrittlement of the alloy was found to be in the order of air-cooled duplex aged alloy > as-received (T6 condition) > water quenched duplex aged material.

    • Determination of elastic modulus in nickel alloy from ultrasonic measurements

      Nikhat Parveen G V S Murthy

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      Elastic constants relate technological, structural and safety aspects to various materials phenomena and to their fundamental interatomic forces. Hence, they are of fundamental importance in almost all engineering applications. Thus its determination is of utmost importance. The aim of the present investigation is to study the behaviour of elastic constants and the variation on heat treatment in a nickel base super alloy Nimonic 263 by ultrasonic velocity measurements. From the present study it is evident that the elastic moduli of the material are very sensitive to any minor compositional changes, resulting due to the formation of intermetallic phases on heat treatment and can be effectively monitored by ultrasonic.

    • Aqueous slip casting of MgAl2O4 spinel powder

      Ibram Ganesh

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      A stoichiometric MgAl2O4 spinel (MAS) powder was synthesized by calcining a compacted mixture of 𝛼-Al2O3 and calcined caustic MgO at 1400°C for 1 h and was surface treated against hydrolysis using an ethanol solution of H3PO4 and Al(H2PO4)3 after fine grinding. Aqueous suspensions with 41–45 vol.% treated powder were prepared using tetra methyl ammonium hydroxide (TMAH) and an ammonium salt of polyacrylic acid (Duramax D-3005) as dispersing agents. These stable suspensions were consolidated in plaster moulds by slip casting (SC) route for the first time. For comparison purposes, the treated powder was also compacted by die-pressing technique after converting into freeze-dried granules and sintered along with slip cast samples at 1550–1650°C for 1–2 h. The MAS ceramics fabricated by slip casting and die-pressing exhibited comparable properties.

    • Pt–Au/C cathode with enhanced oxygen-reduction activity in PEFCs

      G Selvarani S Vinod Selvaganesh P Sridhar S Pitchumani A K Shukla

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      Carbon-supported Pt–Au (Pt–Au/C) catalyst is prepared separately by impregnation, colloidal and micro-emulsion methods, and characterized by physical and electrochemical methods. Highest catalytic activity towards oxygen-reduction reaction (ORR) is exhibited by Pt–Au/C catalyst prepared by colloidal method. The optimum atomic ratio of Pt to Au in Pt–Au/C catalyst prepared by colloidal method is determined using linear-sweep and cyclic voltammetry in conjunction with cell-polarization studies. Among 3:1, 2:1 and 1:1 Pt–Au/C catalysts, (3:1) Pt–Au/C exhibits maximum electrochemical activity towards ORR. Powder X-ray diffraction pattern and transmission electron micrograph suggest Pt–Au alloy nanoparticles to be well dispersed onto the carbon-support. Energy dispersive X-ray analysis and inductively coupled plasma-optical emission spectroscopy data suggest that the atomic ratios of the alloying elements match well with the expected values. A polymer electrolyte fuel cell (PEFC) operating at 0.6 V with (3:1) Pt–Au/C cathode delivers a maximum power-density of 0.65 W/cm2 in relation to 0.53 W/cm2 delivered by the PEFC with pristine carbon-supported Pt cathode.

    • Influence of polymer additive molecular weight on surface and microstructural characteristics of electrodeposited copper

      R Manu Sobha Jayakrishnan

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      Electrodeposition of copper was done with different molecular weight (MW) polyethylene glycol (PEG) as an additive in the plating bath. The adsorbed layer formed of PEG and chloride ion (Cl) in the presence of copper ions has a definite role in controlling the deposition mechanism and the coating characteristics. The adsorption behaviour and suppressor nature of PEG with different MW (200–20000) on the physicochemical and the surface morphological features of the copper deposit were characterized. The results reveal that depending on the adsorption capacity of the intermediate complex, the deposit properties show gradation. There is a range of morphology with particular grain structure for different MW PEG addition. Grain size and the roughness decreased with increase in PEG MW. The concentration of Cl ion in the plating bath is also significant in determining the deposit mechanism of the bath as revealed from the shift in cathodic potential. The adsorbing power of the complex depends not only on PEG MW but also on Cl ion concentration. XRD analysis of the copper deposit obtained with low MW PEG showed (220) as the major plane and with high MW PEG the prominent orientation was (111) and (200).

    • Synthesis and degradation properties of 𝛽-TCP/BG porous composite materials

      Fan Xin Chen Jian Ruan Jianming Zhou Zhongcheng Zou Jianpeng

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      𝛽-TCP/BG porous composite materials were successfully fabricated by foaming technology. X-ray diffraction was used to determine the crystal structure of powders. The pore size and distribution of the resulting materials were characterized using scanning electron microscopy. The porosity and degradation performance of materials were also investigated. The results showed that the porous composite materials possessed the pore size ranging from 100 to 500 𝜇m in diameter, whereas the interconnection among macrospores was poor. The porosity in materials increased from 58.7% to 63.47% with BG content ranging from 0 to 3 wt%, further increasing of BG content results in a decrease in porosity. The degradation rate of composite materials can be adjusted by varying the BG content.

    • Modeling of thermally stimulated depolarization current (TSDC) using dipole–dipole interaction concept

      A E Kotp

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      The study of thermally stimulated depolarization current (TSDC) using the dipole–dipole interaction model is described in this work. The dipole–dipole interactionmodel (DDIM) determines the TSDC peak successfully since it gives significant peak parameters (i.e. activation energy (𝐸) and pre-exponential factor ($\tau_{0}$)) in addition to the dipole–dipole interaction strength parameter ($d_{i}$). Application of this model to study the peak parameters of some polymeric systems is presented.

    • Lattice dynamical investigations on Zn diffusion in zinc oxide

      P Vinotha Boorana Lakshmi K Ramachandran

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      Zinc self diffusion in bulk zinc oxide is studied by lattice dynamical approach here to get more insight into the diffusion in nano ZnO. The results reveal that only cationic self diffusion is dominant over anionic self diffusion and that too by single vacancy mechanism. The results are compared with the available experiments and discussed.

    • Growth of strontium oxalate crystals in agar–agar gel

      P V Dalal K B Saraf

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      Single crystals of strontium oxalate have been grown by using strontium chloride and oxalic acid in agar–agar gel media at ambient temperature. Different methods for growing crystals were adopted. The optimum conditions were employed in each method by varying concentration of gel and reactants, and gel setting time etc. Transparent prismatic bi-pyramidal platy-shaped and spherulite crystals were obtained in various methods. The grown crystals were characterized with the help of FT–IR studies and monoclinic system of crystals were supported with lattice parameters 𝑎 = 9.67628 Å, 𝑏 = 6.7175 Å, 𝑐 = 8.6812 Å, 𝛽 = 113.566°, and 𝑉 = 521.84 Å3 calculated from X-ray diffractogram.

    • Photonic crystal waveguides by direct writing of e-beam on self-assembled photonic crystals

      Sunita Kedia R Vijaya

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      Direct electron beam lithography technique is used for writing a variety of waveguide structures on thin films of polymethyl methacrylate (PMMA) and self-assembled three-dimensionally ordered photonic crystals made up of PMMA colloidal spheres. The waveguide structures fabricated on both these type of samples are characterized by scanning electron microscope and optical microscope images.

    • Formation of hydroxyapatite coating on titanium at 200°C through pulsed laser deposition followed by hydrothermal treatment

      Manoj Komath P Rajesh C V Muraleedharan H K Varma R Reshmi M K Jayaraj

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      Pulsed laser deposition (PLD) has emerged as an acceptable technique to coat hydroxyapatite on titanium-based permanent implants for the use in orthopedics and dentistry. It requires substrate temperature higher than 400°C to form coatings of good adhesion and crystallinity. As this range of temperatures is likely to affect the bulk mechanical properties of the implant, lowering the substrate temperature during the coating process is crucial for the long-term performance of the implant. In the present study, hydroxyapatite target was ablated using a pulsed Nd:YAG laser (355 nm) onto commercially pure titanium substrates kept at 200°C. The coating thus obtained has been subjected to hydrothermal treatment at 200°C in an alkaline medium. The coatings were analysed using microscratch test, optical profilometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and infrared spectroscopy (FTIR). XRD, EDS and FTIR showed that the as-deposited coating contained amorphous calcium phosphate and the hydrothermal treatment converted it into crystalline hydroxyapatite. The micro-morphology was granular, with an average size of 1 micron. In the microscratch test, a remarkable increase in adhesion with the substrate was seen as a result of the treatment. The plasma plume during the deposition has been analysed using optical emission spectroscopy, which revealed atomic and ionic species of calcium, phosphorous and oxygen. The outcomes demonstrate the possibility of obtaining adherent and crystalline hydroxyapatite on titanium substrate at 200°C through pulsed laser deposition and subsequent hydrothermal treatment.

    • Applicability of four parameter formalisms in interpreting thermodynamic properties of binary systems

      S Acharya J P Hajra

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      The four parameter functions are generally considered to be adequate for representation of the thermodynamic properties for the strongly interacting binary systems. The present study involves a critical comparison in terms of applicability of the three well known four-parameter formalisms for the representation of the thermodynamic properties of binary systems. The study indicates that the derived values of the infinite dilution parameters based on the formalisms compare favourably with the computed data available in the literature. The standard deviations in terms of the partial and integral excess functions of all the models lie well within the experimental scatter of the computed data and coincide exactly with each other. The formalisms are useful in representation of the thermodynamic properties of most of the binary systems except for the Mg–Bi and Mg–In systems. In such systems, it appears that the additional compositional terms may be necessary for the formalisms for adequate description of behaviour of the systems. Since the derived values of the thermodynamic properties of all the formalisms match favourably over the entire compositional range for the systems as studied in the present research, any one of them may be used for adequate representation of the properties of the systems.

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