• Volume 32, Issue 6

December 2009,   pages  563-670

• Preparation of diamond like carbon thin film on stainless steel and its SEM characterization

We report the formation of a very smooth, continuous and homogeneous diamond-like carbon DLC thin coating over a bare stainless steel surface without the need for a thin Si/Cr/Ni/Mo/W/TiN/TiC interfacial layer. As confirmed by the field-emission scanning electron microscopy, good adhesion is achieved as characterized by

1. the formation of a smooth, continuous film with no pores,

2. a significant reduction of oxygen in the interfacial layer, and

3. the development of rich carbon content at the top surface.

Thickness measurements by cross-sectional secondary-emission microscopy showed that the DLC coating is essentially a 2-dimensional material.

• Swift heavy ion irradiation effect on Cu-doped CdS nanocrystals embedded in PMMA

Semiconductor nanocrystals (NCs) have received much interest for their optical and electronic properties. When these NCs dispersed in polymer matrix, brightness of the light emission is enhanced due to their quantum dot size. The CdCuS NCs have been synthesized by chemical route method and then dispersed in PMMA matrix. These nanocomposite polymer films were irradiated by swift heavy ion (SHI) (100 MeV, Si+7 ions beam) at different fluences of 1 × 1010 and 1 × 1012 ions/cm2 and then compared their structural and optical properties by XRD, atomic force microscopy, photoluminescence, and UV-Vis spectroscopy before and after irradiation. The XRD spectra showed a broad hump around 2𝜃 ≈ 11.83° due to amorphous PMMA and other peaks corresponding to hexagonal structure of CdS nanocrystals in PMMA matrix. The photoluminescence spectra shows a broad peak at 530 nm corresponding to green emission due to Cu impurities in CdS. The UV-Vis measurement showed red shift in optical absorption and bandgap changed from 4.38–3.60 eV as the irradiation fluency increased with respect to pristine CdCuS nanocomposite polymer film.

• Dielectric properties of Al-substituted Co ferrite nanoparticles

A series of polycrystalline spinel ferrites with composition, CoFe2–𝑥Al𝑥O4 (0 ≤ 𝑥 ≤ 1), have been synthesized by sol–gel method. The effect of Al-substitution on structural and dielectric properties is reported in this paper. X-ray diffraction analysis revealed the nanocrystalline nature in the prepared ferrite samples. The particle size, 𝐷, decreases with increase in Al-content. The lattice parameter, 𝑎 and X-ray density, 𝑑x, decreased with increase in Al-content. The dielectric properties for all the samples have been studied as a function of frequency in the range 100 Hz–10 MHz. Dielectric properties such as dielectric constant, 𝜀′, dielectric loss, 𝜀″ and dielectric loss tangent, tan 𝛿, have been studied for nanocrystalline ferrite samples as a function of frequency. The dielectric constant and dielectric loss obtained for the nanocrystalline ferrites proposed by this technique possess lower value than that of the ferrites prepared by other methods for the same composition. The low dielectric behaviour makes ferrite materials useful in high frequency applications.

• High rate performance of LiFePO4 cathode materials co-doped with C and Ti4+ by microwave synthesis

Nanostructured LiFePO4 powder with a narrow particle size (ca. 100 nm) for high rate lithium-ion battery cathode application was obtained by microwave heating and using citric acid as carbon source. The microstructures and morphologies of the synthesized materials were investigated by X-ray diffraction and scanning electron microscope while the electrochemical performances were evaluated by galvanostatic charge–discharge. The carbon coating and Ti4+ could improve the conductivity both between the LiFePO4 particles and the intrinsic electronic conductivity. The LiFePO4 doped with 5% C and 1% Ti4+ resulted in a specific capacity of 114.95 mAh.g-1 and 102.4 mAh.g-1 at discharge rates of 0.3C and 1C, respectively, and the cycle performance is very good.

• Synthesis of nanocrystalline mixed metal fluorides in nonaqueous medium

Synthesis of mixed metal fluorides of the general formula, KMF3 (M = Mg, Mn, Co, Ni, Cu and Zn), possessing perovskite structure was investigated in non-aqueous medium. The fluorides were characterized by powder X-ray diffraction, FT–IR spectroscopy, thermal analysis, SEM and TEM. Monophasic cubic phases were obtained for the central metal ions such as Mg, Mn, Co, Ni, and Zn and a tetragonally distorted phase was observed for Cu. The usage of non-aqueous medium is advantageous for the bulk synthesis of these fluorides, since it eliminated the generation and handling of the hazardous HF that has usually been encountered during aqueous preparations. The average crystallite size of the fluorides obtained by this approach was estimated to be in the range of 9–30 nm. SEM micrographs of KZnF3 showed cubic morphology of perovskite phases. TEM studies on KCuF3 confirmed the presence of tetragonal distortion. The fluoride content was determined by titrimetry and found to be nearly stoichiometric. Some of these fluorides were found to be thermally stable up to 225°C in air. These fluorides were employed as fluorinating agents in organic fluorination reactions, thereby suggesting their possible utilization for selective fluorination of aliphatic and aromatic hydrofluorocarbons (HFCs) that are industrially relevant.

• Continuous jute fibre reinforced laminated paper composite and reinforcement-fibre free paper laminate

Plastic bags create a serious environmental problem. The proposed jute fibre reinforced laminated paper composite and reinforcement-fibre free paper laminate may help to combat the war against this pollutant to certain extent. The paper laminate, without reinforcement fibre, exhibited a few fold superiority in tensile properties than single paper strip. The studies further show that an appreciable improvement in tensile properties can be achieved by introducing continuous jute fibre in paper laminates.

• Elastic properties of Na2O–ZnO–ZnF2–B2O3 oxyfluoride glasses

Elastic properties of Na2O–ZnO–ZnF2–B2O3 oxyfluoride glasses with different ZnF2 concentrations have been investigated using ultrasonic velocity measurements at room temperature, at a frequency of 10 MHz. Glasses prepared by melt quenching method were suitably polished for the ultrasonic velocity measurements using pulse-echo superposition method. Various elastic moduli have been calculated and their compositional dependence has been examined. The compositional dependence of elastic moduli with the concentration of ZnF2 shows decrease in the moduli initially, with further increase in ZnF2 the moduli sharply increases and then again tend to decrease when ZnF2 concentration is 20 mol%. The values of Poisson’s ratio lie in the range of 0.24–0.30, which is typical to covalent bonded network. The variation of 𝜃D with ZnF2 indicates complex behaviour of the glass network. The results have been analysed in view of the modified borate glass network. Addition of ZnF2 into the pure glass seems to influence the borate network by replacement of B–O–B linkages with B–O–Zn.

• Heat capacity measurements on Yb𝑥Gd2–𝑥Zr2O7 (𝑥 = 0, 1, 2) ceramics by differential scanning calorimetry

Yb𝑥Gd2–𝑥Zr2O7 (𝑥 = 0, 1, 2) ceramics were pressureless-sintered using ceramic powders acquired by chemical-coprecipitation and calcination methods. Heat capacities of Yb𝑥Gd2–𝑥Zr2O7 were measured with a heat flux-type differential scanning calorimetry in the temperature range of 298–1200 K. At 298 K, the heat capacities of Gd2Zr2O7, YbGdZr2O7 and Yb2Zr2O7 were 214, 221 and 230 J.K-1 mol-1, respectively.

• Cracking cone fracture after cold compaction of argillaceous particles

Cold uniaxial pressing of powder into a green body is a common forming process used in ceramic and pharmaceutical industries. Argillaceous particles are used as a model system to investigate granule failure during compaction. Indeed, the volume enclosed between the die and punches is reduced and the powder consolidates until a final height is obtained or a prescribed compacting pressure is reached. Desired properties of the green body are high strength, uniform density, no defects and fracture. In this work an experimental investigation has been focused on the `cracking cone’ fracture in powder compacts. This includes studies of crack propagation and determination of operating conditions to avoid the green body fracture. The numerical modelling is implemented using a finite element method based on the Von Mises criterion. A case of simulation is presented to demonstrate the ability of the model to compute the distribution of the relative stresses.

• Phase diagram of the system Ca–Ti–O at 1200 K

Phase relations in the system Ca–Ti–O have been established by equilibration of several samples at 1200 K for prolonged periods and identification of phases in quenched samples by optical and scanning electron microscopy, XRD and EDS. Samples representing 20 compositions in the ternary system were analyzed. There was negligible solid solubility of Ca in the phases along the binary Ti–O, and of Ti in CaO. Four ternary oxides were identified: CaTiO3, Ca4Ti3O10 and Ca3Ti2O7 containing tetravalent titanium, and CaTi2O4 containing trivalent titanium. Tie-lines link calcium titanite (CaTi2O4) with the three calcium titanates (CaTiO3, Ca4Ti3O10 and Ca3Ti2O7), CaO, oxygen excess TiO1+𝛿 and stoichiometric TiO. Tie-lines connect CaTiO3 with TiO2–𝑥, Magneli phases Ti$_{n}$O$_{2n–1}$ (28 ≥ 𝑛 ≥ 4), Ti3O5, Ti2O3 and TiO1+𝛿. CaO was found to coexist with TiO, and Ti–O solid solutions 𝛼 and 𝛽. The phase diagram is useful for understanding the mechanisms and kinetics of direct calciothermic reduction of TiO2 to metal and electrochemical reduction of TiO2 using graphite anode and molten CaCl2 electrolyte.

• Study on hardness and microstructural characteristics of sand cast Al–Si–Cu alloys

In this study, the influence of Cu content on the hardness and microstructural characteristics of sand cast Al–Si–Cu alloys have been investigated. Al–Si alloys with 2% and 5% Cu have been utilized for this purpose. Solidification of Al–Si–Cu alloys have been realized by melting in a gas furnace with a crucible and casting in green sand molds at 690°C. The solution treatment has been performed at 500°C for 7 h and then specimens were quenched in water. The samples have been aged at 190°C for 15 h to observe the effect of aging on mechanical properties.

• Anisotropy in elastic properties of lithium sodium sulphate hexahydrate single crystal—An ultrasonic study

The double sulfate family (ABSO4), where A and B are alkali metal cations, is the object of great interest owing to the complexity and richness of its sequence of phase transition induced by temperature variation. A new sulfate salt characterized by the presence of water molecule in the unit cell with the chemical formula, Li2Na3(SO4)2.6H2O (LSSW), was obtained. The ultrasonic velocity measurement was done with pulse echo overlap technique [PEO]. All the six second order elastic stiffness constants, 𝐶11 = 𝐶22, 𝐶33, 𝐶44 = 𝐶55, 𝐶12, 𝐶14 and 𝐶13 = 𝐶23 are reported for the first time. The anisotropy in the elastic properties of the crystal are well explained by the pictorial representation of the polar plots of phase velocity, slowness, Young’s modulus and linear compressibility in 𝑎–𝑏 and 𝑎–𝑐 planes.

• Ionic transport in P(VdF–HFP)–PEO based novel microporous polymer electrolytes

A novel microporous polymer electrolyte (MPE) comprising blends of poly(vinylidene fluoride-cohexafluoropropylene) [P(VdF–HFP)] and polyethylene oxide (PEO) was prepared by phase inversion technique. It was observed that addition of PEO improved the pore configuration, such as pore size, pore connectivity and porosity of P(VdF–HFP) based membranes. The room temperature ionic conductivity was significantly enhanced. The highest porosity of about 65% and ionic conductivity of about 7 × 10-4 S cm-1 was obtained when the weight ratio of PEO was 40%. The liquid electrolyte uptake was found to increase with increase in porosity and pore size. However, at higher weight ratio of PEO (&gt; 40%) porosity, pore size and ionic conductivity was decreased. This descending trend with further increase of PEO weight ratio was attributed to conglomeration effect of PEO at the pores.

• Synthesis of crosslinked poly(styrene-𝑐𝑜-divinylbenzene-𝑐𝑜-sulfopropyl methacrylate) nanoparticles by emulsion polymerization: Tuning the particle size and surface charge density

We have synthesized highly charged, crosslinked poly (styrene-𝑐𝑜-divinylbenzene-𝑐𝑜-sulfopropyl methacrylate) copolymer colloidal particles using emulsion polymerization. The effects of concentration of the emulsifier and the initiator on the particle size and the charge density of the colloidal particles are studied. Colloidal particle size is highly dependent upon the concentration of the emulsifier and the initiator. The colloidal particle diameter decreases with increasing concentration of the emulsifier and increases with increasing concentration of the initiator in the polymerization mixture. Number of particles, surface charge density and charges per particle are also functions of both the emulsifier and the initiator concentration. The surface charge density and the number of charges per sphere increase with increasing particle diameter. These copolymer colloid particles self assemble readily and diffract visible light. Polymer hydrogel imbibed with these colloids shows the light diffraction.

• A comprehensive study on the effect of Ru addition to Pt electrodes for direct ethanol fuel cell

The electro-oxidation of ethanol was studied over nanosized Pt and different compositions of PtRu catalysts synthesized by the borohydride reduction method. Physicochemical characterizations of the catalyst material were made by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with EDX analysis and transmission electron microscopy (TEM). XRD patterns showed that Ru induces a contraction of the Pt lattice. EDX provided the composition of binary catalysts while TEM images indicated uniform distribution of discrete nanoparticle of the catalysts with narrow range. The electro-catalytic activities of the materials towards ethanol oxidation were investigated through electrochemical techniques, viz. cyclic voltammetry (CV), potentiodynamic polarization, chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) at room temperature. The onset potential of ethanol electro-oxidation is lowered on bimetallic PtRu catalysts compared to that on Pt alone. Of the investigated catalyst compositions the one with the highest electrocatalytic activity was found to be Pt82Ru18. This enhancement towards ethanol oxidation is explained on the basis of a structural effect and modified bi-functional mechanism.

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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019