• Volume 36, Issue 3

June 2013,   pages  345-504

• Exploring a novel approach to fabricate vanadium carbide encapsulated into carbon nanotube (VC@C) with large specific surface area

A novel approach to the fabrication of vanadium carbide encapsulated into carbon nanotube (VC@C) core-shell structured composite by thermal treatment with the precursor V3O7.H2O@C was developed for the first time. The as-obtained VC@C were characterized by X-ray powder diffraction (XRD), Raman spectrum, energydispersive X-ray spectrometer (EDX), elemental analysis (EA), Fourier transform infrared spectroscopy (FT)–(IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET). The results showed that VC@C with core-shell structures could be successfully synthesized at 1000 °C for 2 h. The specific surface area, average pore size and measured pore volume of VC@C were 135.46 m2/g, 4.443 nm and 0.180 cm3/g, respectively indicating that the as-obtained VC@C composite could be used as a mesoporous material. Furthermore, thermal behaviour of the as-obtained VC@C composite in air was investigated by thermogravimetric/differential thermal analyser (TG/DTA). The experimental result revealed that the carbon coated on the surface of VC has high activity with O2 in air atmosphere.

• Pt–Ru decorated self-assembled TiO2–carbon hybrid nanostructure for enhanced methanol electrooxidation

Porous titanium oxide–carbon hybrid nanostructure (TiO2–C) with a specific surface area of 350 m2/g and an average pore-radius of 21.8 Å is synthesized via supramolecular self-assembly with an in situ crystallization process. Subsequently, TiO2–C supported Pt–Ru electro-catalyst (Pt–Ru/TiO2–C) is obtained and investigated as an anode catalyst for direct methanol fuel cells (DMFCs). X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM) have been employed to evaluate the crystalline nature and the structural properties of TiO2–C. TEM images reveal uniform distribution of Pt–Ru nanoparticles (𝑑Pt−Ru = 1.5–3.5 nm) on TiO2–C. Methanol oxidation and accelerated durability studies on Pt–Ru/TiO2–C exhibit enhanced catalytic activity and durability compared to carbon-supported Pt–Ru. DMFC employing Pt–Ru/TiO2–C as an anode catalyst delivers a peak-power density of 91 mW/cm2 at 65 °C as compared to the peak-power density of 60 mW/cm2 obtained for the DMFC with carbon-supported Pt–Ru anode catalyst operating under similar conditions.

• Preparation of polystyrene–clay nanocomposite by solution intercalation technique

Polymer–clay nanocomposites of commercial polystyrene (PS) and clay laponite were prepared via solution intercalation technique. Laponite was modified suitably with the well known cationic surfactant cetyltrimethyl ammonium bromide by ion-exchange reaction to render laponite miscible with hydrophobic PS. X-ray diffraction analysis in combination with scanning electron microscopy gives an idea of structural and morphological information of PS–laponite nanocomposite for different varying organo-laponite contents. Intercalation of PS chain occurs into the interlayer spacings of laponite for low organo-laponite concentration in the PS–O-laponite mixture. However, aggregation and agglomeration occur at higher clay concentration. The molecular bond vibrational profile of laponite as well as PS–laponite nanocomposite have been explored by Fourier transform infrared spectroscopy. Thermogravimetric analysis along with differential scanning calorimetry results reveal the enhancement of both thermal stability and glass transition temperature of PS due to the incorporation of clay platelets.

• Facile synthesis of Au/ZnO nanoparticles and their enhanced photocatalytic activity for hydroxylation of benzene

Au/ZnO nanocomposites have been prepared by a simple chemical method. For the first time, the nanocomposites were directly used as photocatalysts for hydroxylation of aromatic hydrocarbons under UV and visible light irradiation. The results show that the as-prepared photocatalysts display high photocatalytic activity for UV and visible catalytic hydroxylation of benzene. Without the assistance of any solvent or additive, high selectivity and high conversion efficiency were still obtained. Different photocatalytic mechanisms were proposed depending on whether excitation happens on ZnO semiconductor or on the surface plasmon band of Au. The former is Au nanoparticles act as electron buffer due to irradiation by UV light and ZnO nanoparticles as reactive sites for hydroxylation of benzene, the latter is that Au nanoparticles act as light harvesters and inject electrons into ZnO conduction band and as photocatalytic sites under visible light irradiation.

• Multifunctional CNTs nanohybrids decorated with magnetic and fluorescent nanoparticles layer-by-layer

Fe3O4/CNTs nanocomposites, which were prepared by polyol-medium in situ high-temperature decomposition of Fe(𝑎𝑐𝑎𝑐)3 using PVP as stabilizing agent andmodified with SDS, were further decorated with high-quality ZnS nanocrystal via a wet technique in glycol solution. The obtained ZnS/Fe3O4/CNTs nanohybrids were characterized by XRD, FT–IR, Raman microscope, TEM, EDS, XPS, VSM and fluorophotometers. Results indicated that magnetic Fe3O4 nanoparticles and fluorescent ZnS nanocrystal were uniformly dispersed on the surface of CNTs layer-by-layer with PVP and SDS as stabilizing agent and ion-capture agent, respectively. The novel multi-functional nanohybrids exhibit super-paramagnetic properties with a saturation magnetization about 6.795 emu g-1 at room temperature and show a strong emission band at 367 nm with a broad shoulder around 342–483 nm due to the interactions and/or background emissions of Fe3O4 and CNTs. The superparamagnetic and fluorescent properties of obtained products are promising for potential applications in magnetically guided and fluorescence tracing drug delivery systems.

• Oxidation of ZnO thin films during pulsed laser deposition process

Pulsed laser deposition of ZnO thin films, using KrF laser, is analysed. The films were deposited on (001) sapphire substrates at 400 °C, at two different oxygen pressures (0.3 and 0.4 mbar) and two different target–substrate distances (30 and 40 mm). It is observed that in order to obtain good quality in the photoluminescence of the films, associated with oxygen stoichiometry, it is needed to maximize the time during which the plasma remains in contact with the growing film (plasma residence time), which is achieved by selecting suitable combinations of oxygen pressures and target to substrate distances. It is also discussed that for the growth parameters used, the higher probability for ZnO films growth results from the oxidation of Zn deposited on the substrate and such process takes place during the time that the plasma is in contact with the substrate. Moreover, it is observed that maximizing the plasma residence time over the growing film reduces the rate of material deposition, favouring the surface diffusion of adatoms, which favours both Zn–O reaction and grain growth.

• Effects of Bi doping on dielectric and ferroelectric properties of PLBZT ferroelectric thin films synthesized by sol–gel processing

[Pb0.95(La1−𝑦Bi𝑦)0.05][Zr0.53Ti0.47]O3 (PLBZT) ferroelectric thin films have been synthesized on indium tin oxide (ITO)-coated glass by sol–gel processing. PLBZT thin films were annealed at a relatively low temperature of 550 °C in oxygen ambient. Effects of Bi doping on structure, dielectric and ferroelectric properties of PLBZT were investigated. Bi doping is useful in crystallization of PLBZT films and promoting grain growth. When the Bi-doping content 𝑦 is not more than 0.4, an obvious improvement in dielectric properties and leakage current of PLBZT was confirmed. However, when the Bi-doping content is more than 0.6, the pyrochlore phase appears and the remnant polarization 𝑃r of PLBZT thin films is smaller than that of (Pb1−𝑥La𝑥)(Zr1−𝑦 Ti𝑦)O3 (PLZT) thin films without Bi doping. PLBZT thin films with excessive Bi-doping content are easier to fatigue than PLZT thin films.

• Electrical conductivity and chemical stability of BaCe0.8−𝑥A𝑥Gd0.2O3−𝛿 (A = In, Zr, Ta; 𝑥 = 0, 0.1) ceramics

BaCe0.8−𝑥A𝑥Gd0.2O3−𝛿 (A = In, Zr, Ta; 𝑥 = 0, 0.1) ceramics were synthesized by solid-state reaction method. Microstructure and electrical properties of BaCe0.8−𝑥A𝑥Gd0.2O3−𝛿 ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis at intermediate temperatures of 573–1073 K in different atmospheres. BaCe0.8Gd0.2O3−𝛿, BaCe0.7In0.1Gd0.2O3−𝛿 and BaCe0.7Zr0.1Gd0.2O3−𝛿 ceramics exhibit a single cubic perovskite structure. BaCe0.7In0.1Gd0.2O3−𝛿 ceramic has the highest conductivity of 4.6 × 10-2 S.cm-1 in air at 1073 K. BaCe0.7In0.1Gd0.2O3−𝛿 and BaCe0.7Zr0.1Gd0.2O3−𝛿 ceramics exhibit an excellent chemical stability against boiling water. Indium is a suitable doping element to promote the sintering densification and to enhance both electrical conductivity and chemical stability of Gd-doped BaCeO3 at operating temperatures.

• Effect of power variation on wettability and optical properties of co-sputtered titanium and zirconium oxynitride films

The present paper deals with deposition of titanium and zirconium oxynitride films prepared from cosputtering titanium and zirconium targets by reactive RF magnetron sputtering. The effect of power variation on various properties of the deposited films is analysed. The film gets transformed from amorphous to well crystalline oxynitride films with gradual increase of target powers as observed from XRD graphs. The films exhibit hydrophilic and hydrophobic behaviours depending upon the presence of various phases. Surface energy decreases as the film properties change from hydrophilic to hydrophobic due to greater contact angle values. The optical properties were measured by UV–Vis–NIR spectrophotometer, transmission spectra and bandgap values show variation with respect to change in elemental composition as determined from EDS analysis.

• Effect of Zn doping on optical properties and photoconductivity of SnS2 nanocrystalline thin films

Zn-doped SnS2 thin films have been deposited simply by spray pyrolysis technique. The doping level was changed from [Zn/Sn] = 0 to 7.5 at%. The films were characterized by means of X-ray diffraction, scanning tunneling microscopy (STM), energy dispersive X-ray analysis (EDX), photoluminescence and UV-Vis spectroscopy. XRD patterns of the films with different zinc contents show that all samples have polycrystalline structure with Berndtite dominant phase and preferred orientation of (001) growth plane. Zn insertion causes a significant decrease in grain size. Optical bandgap of the films have been calculated for different dopant concentrations and they lie in the region of 2.3–2.7 eV. Surprisingly, regardless of doping level, the luminescent properties of films are related to the fundamental bandgap energy and deep levels inside the bandgap. Photoconductivity of the films have been measured under visible light. Sensitivity to the light increases by zinc incorporation, which was a large amount for SnS2:Zn of 7.5%.

• Synthesis, non-isothermal crystallization and magnetic properties of Co0.75Zn0.25Fe2O4/poly(ethylene-co-vinyl alcohol) nanocomposite

The synthesis of Co0.75Zn0.25Fe2O4/poly(vinyl alcohol-co-ethylene) (ferrite/PEVA) nanocomposite was carried out through two steps: impregnation of the ferrite particules by PEVA and then mixing the ferrite/PEVA impregnated with PEVA solution. A non-isothermal study of the crystallization kinetic of ferrite/PEVA nanocomposite was carried out by differential scanning calorimetry (DSC), scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. It was observed that the Ozawa equation describes perfectly the primary process of non-isothermal crystallization of ferrite/PEVA system. There is a strong dependence of the ferrite/PEVA composition on the crystallization parameters. The crystallization activation energy (𝐸a) calculated from the Xu and Uhlmann model increased by increasing the ferrite content in ferrite/PEVA nanocomposites between 3 and 7wt% and decreased dramatically beyond these values. The results revealed that the ferrite nanoparticles were uniformly distributed throughout the PEVA matrix. The percentage of magnetization of the composite decreases as the concentration of the ferrite increases.

• Effect of bias voltage on microstructure and mechanical properties of arc evaporated (Ti, Al)N hard coatings

In the present study, authors report on the effect that substrate bias voltage has on the microstructure and mechanical properties of (Ti, Al)N hard coatings deposited with cathodic arc evaporation (CAE) technique. The coatings were deposited from a Ti0.5Al0.5 powder metallurgical target in a reactive nitrogen atmosphere at three different bias voltages: UB = −25, −50 and −100 V. The coatings were characterized in terms of compositional, microstructural and mechanical properties. Microstructure of the coatings was investigated with the aid of X-ray diffraction in glancing angle mode, which revealed information on phase composition, crystallite size, stress-free lattice parameter and residual stress. Mechanical properties were deduced from nano-indentation measurements. The residual stress in all the coatings was compressive and increased with increasing bias voltage in a manner similar to that reported in literature for Ti–Al–N coatings deposited with CAE. The bias voltage was also found to significantly influence the phase composition and crystallite size. At −25 V bias voltage the coating was found in single phase fcc-(Ti, Al)N and with relatively large crystallites of ∼9 nm. At higher bias voltages (−50 and −100 V), the coatings were found in dual phase fcc-(Ti, Al)N and fcc-AlN and the size of crystallites reduced to approximately 5 nm. The reduction of crystallite size and the increase of compressive residual stress with increasing bias voltage both contributed to an increase in hardness of the coatings.

• Microstructures and mechanical properties of Mg–Zn–Zr–Dy wrought magnesium alloys

Microstructures and phase compositions of as-cast and extruded ZK60–𝑥Dy (𝑥 = 0–5) alloys were analysed by optical microscope, scanning electron microscope, X-ray diffraction and differential scanning calorimetry. Meanwhile, the tensile mechanical property was tested.With increasing Dy content, Mg–Zn–Dy new phase increases gradually, while MgZn2 phase decreases gradually to disappear. As-cast microstructure is refined gradually; meanwhile extruded one is refined further with decreasing average grain size to 1 𝜇m for ZK60–4.32Dy alloy. Second phase, tending to distribute along grain boundary by continuous network in as-cast state, breaks and distributes dispersedly in extrusion state. As-cast tensile mechanical property remains almost unchanged at ambient temperature; however, extruded ones are enhanced significantly at ambient and elevated temperatures, respectively. Tensile strength at 298 and 473 K increases gradually from 355 and 120 MPa for ZK60 alloy to 395 and 171 MPa for ZK60–4.32Dy alloy, respectively. Extruded tensile fractures exhibit a typical character of ductile fracture.

• An investigation on microwave sintering of Fe, Fe–Cu and Fe–Cu–C alloys

The powder characteristics of metallic powders play a key role during sintering. Densification and mechanical properties were also influenced by it. The current study examines the effect of heating mode on densification, microstructure, phase compositions and properties of Fe, Fe–2Cu and Fe–2Cu–0.8C systems. The compacts were heated in 2.45 GHz microwave sintering furnaces under forming gas (95%N2–5%H2) at 1120 °C for 60 min. Results of densification, mechanical properties and microstructural development of the microwave-sintered samples were reported and critically analysed in terms of various powder processing steps.

• Thermodynamic and relative approach to compute glass-forming ability of oxides

This study deals with the evaluation of glass-forming ability (GFA) of oxides and is a critical reading of Sun and Rawson thermodynamic approach to quantify this aptitude. Both approaches are adequate but ambiguous regarding the behaviour of some oxides (tendency to amorphization or crystallization). Indeed, ZrO2 and Al2O3 were inappropriately listed by Sun and Rawson to be glassformer oxides while being intermediate ones.We present a non-dimensional approach to value GFA of single oxide by affecting to each one of the coefficients (without measuring units). Obeying to the non-dimensional analysis rules, we introduce a neglected (in all prior thermodynamic models) characteristic: the isobaric heat capacity (𝐶p) of oxides, and execute a mathematical treatment of oxides thermodynamic data.We note this coefficient as thermodynamical relative glass-forming ability (ThRGFA) and formulate a model to compute it. Computed values of 2nd, 3rd, 4th and 5th period metal oxides reveal a clear differentiation between them. Indeed, all glass former oxides are characterized by ThRGFA values over 1.709. Moreover, the value intervals confirm the oxides classification into three groups (forming, intermediate and modifier) and sorting of the former ones in distinctive strong and fragile oxides.

• Synthesis, IR, crystallization and dielectric study of (Pb, Sr)TiO3 borosilicate glass–ceramics

Eleven glass compositions were prepared by melt and quench method with progressive substitution of SrO for PbO (0 ≤ 𝑥 ≤ 1.0) with a step-wise increment of 0.10 in the glass [(Pb𝑥Sr1−𝑥)OTiO2]–[(2SiO2B2O3)]–[BaO.K2O].Nb2O5 (mol percentage) system. The infrared spectra (IR) of various glass compositions in the above mentioned glass system was recorded over a continuous spectral range 400–4000 cm-1 to study their different oxides structure systematically. Differential thermal analysis (DTA) was recorded from room temperature (∼27 °C) to 1400 °C employing a heating rate of 10 °C/min to determine glass transition temperature, 𝑇g and crystallization temperature, 𝑇c. The melting temperature, 𝑇m, of these glass compositions was found to be in the range 597–1060 °C depending on the composition under normal atmospheric conditions. 𝑇g and 𝑇m of glasses were found to increase with increasing SrO content. X-ray diffraction analysis of these glass–ceramic samples shows that major crystalline phase of the glass–ceramic sample with 𝑥 ≤ 0.5 was found to have cubic structure similar to SrTiO3 ceramic. Scanning electron microscopy has been carried out to see the surface morphology of the crystallites dispersed in the glassy matrix.

• Microhardness studies on nonlinear optical 𝐿-alanine single crystals

Vickers and Knoop microhardness tests were carried out on grown 𝐿-alanine single crystals by slow evaporation technique over a load range of 10–50 g on selected broad (2 0 3) plane. Vickers (𝐻v) and Knoop (𝐻k) microhardness for the above loads were found to be in the range of 60–71 kg/mm2 and 35–47 kg/mm2, respectively. Vickers microhardness number (𝐻v) and Knoop microhardness number (𝐻k) were found to increase with increasing load. Meyer’s index number (𝑛) calculated from 𝐻v shows that the material belongs to the soft material category. Using Wooster’s empirical relation, the elastic stiffness constant (𝑐11) was calculated from Vickers hardness values. Young’s modulus was calculated using Knoop hardness values. Hardness anisotropy has been observed in accordance with the orientation of the crystal.

• Electrodeposition of dicalcium phosphate dihydrate coatings on stainless steel substrates

Cathodic reduction of an aqueous solution containing dissolved calcium and phosphate ions results in the deposition of micrometer thick CaHPO4.2H2O (dicalcium phosphate dihydrate) coatings on stainless steel substrates. The coating obtained at a low deposition current (8 mA cm-2) comprises lath-like crystallites oriented along 020. The 020 crystal planes are non-polar and have a low surface energy. At a high deposition current (12 mA cm-2), platelets oriented along 12$\bar{1}$ are deposited. CaHPO4.2H2O is an important precursor to the nucleation of hydroxyapatite, the inorganic component of bones. Differently oriented CaHPO4.2H2Ocoatings transform to hydroxyapatite with different kinetics, the transformation being more facile when the coating is oriented along 12$\bar{1}$. These observations have implications for the development of electrodeposited biocompatible coatings for metal endoprostheses for medical applications.

• Optimization of process parameter for synthesis of silicon quantum dots using low pressure chemical vapour deposition

Si quantum dots-based structures are studied recently for performance enhancement in electronic devices. This paper presents an attempt to get high density quantum dots (QDs) by low pressure chemical vapour deposition (LPCVD) on SiO2 substrate. Surface treatment, annealing and rapid thermal processing (RTP) are performed to study their effect on size and density of QDs. The samples are also studied using Fourier transformation infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and photoluminescence study (PL). The influence of Si–OH bonds formed due to surface treatment on the density of QDs is discussed. Present study also discusses the influence of surface treatment and annealing on QD formation.

• Synthesis, characterization and oxide ionic conductivity of 𝛽-type solid solution in bismuth oxide doped with ytterbium oxide binary system

In this study, after doping Yb2O3 substance to 𝛼-Bi2O3 substance in the range of 1% ≤ 𝑛 ≤ 8% in a series of different mole ratios, heat treatment was performed by applying a cascade temperature rise in the range of 700–790 °C for 48 and 120 h and new phases were obtained in the (Bi2O3)1−𝑥 (Yb2O3)𝑥 system. After 48 h of heat treatment at 750 °C and 120 h of heat treatment at 790 °C, mixtures containing 1–8% mole Yb2O3 formed a tetragonal phase. With the help of XRD, crystal systems and lattice parameters of the solid solutions were obtained and their characterization was carried out. Thermal measurements were made by using a simultaneous DTA/TG system. The total conductivity (𝜎T) in the 𝛽-Bi2O3 doped with Yb2O3 system was measured using four-probe d.c. method.

• GITT studies on oxide cathode LiNi1/3Co1/3Mn1/3O2 synthesized by citric acid assisted high-energy ball milling

Layered LiNi1/3Co1/3Mn1/3O2 was synthesized by a citric acid assisted solid-state method. The structure and electrochemical properties of the LiNi1/3Co1/3Mn1/3O2 materials were investigated. XRD analysis indicated the as-synthesized LiNi1/3Co1/3Mn1/3O2 was with the layered 𝛼-NaFeO2 structure. The discharge capacity was about 154 m.Ahg-1 at 0.1 °C rate in the range of 2.0–4.5 V. The kinetics of the LiNi1/3Co1/3Mn1/3O2 materials was investigated by the galvanostatic intermittent titration technique (GITT) method. The lithium ion diffusion coefficient of the LiNi1/3Co1/3Mn1/3O2 was determined in the range of 10-8−10-9 cm2.s-1 as a function of voltage of 3.7−4.5 V.

• Red-emitting alkaline-earth rare-earth pentaoxometallates powders prepared by metal carboxylates solution

Moisture-insensitive metal carboxylates that are mostly liquids at room temperature have been first applied to the preparation of strontium europium aluminate (Sr2EuAlO5) powders for red-emitting phosphor under near ultraviolet radiation. Strontium naphthenate, aluminium-2-ethylhexanoate and europium-2-ethylhexanoate were dissolved with toluene to prepare starting solution. Precursor pyrolyzed at 500 °C for 240 min was finally annealed at 900–1200 °C for 240 min in Ar. X-ray diffraction analysis, field emission–scanning electron microscope and fluorescent spectrophotometer were used to evaluate structural and optical properties. For the 1000 °C-annealed powders with regular shape and narrow size distribution confirmed by FE–SEM observation, strong red emission at 615nm under the excitation of 395nm maximum was reached, then the higher annealed samples at above 1100 °C gave the lower emission intensities.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019