• Volume 36, Issue 6

November 2013,   pages  945-1132

• Self-assembling behaviour of Pt nanoparticles onto surface of TiO2 and their resulting photocatalytic activity

In the present study, self-assembling behaviour of guest nanoparticles (platinum) onto the surface of host support (titanium dioxide) during photodeposition process as a function of solution pH has been explored in detail by means of transmission electron microscope (TEM). The photocatalytic activity of the resulting bimetallic nanoassembly (Pt/TiO2) was evaluated by studying the degradation of two organic pollutants viz. triclopyr and methyl orange. Microscopic studies revealed that the deposition and/or distribution of Pt nanoparticles onto the surface of TiO2 were strongly guided by the ionization state of support which in turn was regulated by the solution pH of photodeposition process. A direct relationship between the solution pH of deposition process and the photocatalytic activity of resulting bimetallic catalyst has been observed. A mechanism based on the interparticle interaction between TiO2 and hydrolytic products of metal ions has been proposed for the differences in the photocatalytic activity of the resulting nanocomposite.

• A novel method for massive synthesis of SnO2 nanowires

This paper reports a simple, inexpensive and fast method to prepare SnO2 nanowires. A large amount of ultra-long high purity single-crystalline SnO2 nanowires with rutile structure, that is over hundreds of micrometers in length and 20–100 nm in diameter, have been synthesized through a one-step typical thermite reaction at 200 °C in O2 atmosphere, with a gas pressure of 0.9 atm. These SnO2 nanowires do not grow in one direction as those synthesized by other methods do, and are perfect single crystals without any dislocation or point defects detected in TEM images. The optoelectronic properties of these smooth and uniform nanowires have been characterized by means of X-ray photoelectron spectra, laser Raman spectrum and Fourier transform infrared spectrum. The result of X-ray photoelectron spectra analysis shows that some oxygen vacancies exist in these SnO2 nanowires. In addition, possible growth mechanism of the SnO2 nanowires has been described in detail by the studies of comparative experiments, which is quite different from that of SnO2 nanowires synthesized by some other methods.

• Pinning enhancement in MgB2 superconducting thin films by magnetic nanoparticles of Fe2O3

MgB2 thin films were fabricated on 𝑟-plane Al2O3 (1$\bar{1}$02) substrates. First, deposition of boron was performed by rf magnetron sputtering on Al2O3 substrates and followed by a post-deposition annealing at 850 °C in magnesium vapour. In order to investigate the effect of Fe2O3 nanoparticles on the structural and magnetic properties of films, MgB2 films were coated with different concentrations of Fe2O3 nanoparticles by spin coating process. The magnetic field dependence of the critical current density 𝐽c was calculated from the M–H loops and magnetic field dependence of the pinning force density, 𝑓p(𝑏), was investigated for the films containing different concentrations of Fe2O3 nanoparticles. The critical current densities, 𝐽c, in 3Tmagnetic field at 5 K were found to be around 2.7 × 104 A/cm2, 4.3 × 104 A/cm2, 1.3 × 105 A/cm2 and 5.2 × 104 A/cm2 for films with concentrations of 0, 25, 50 and 100% Fe2O3, respectively. It was found that the films coated with Fe2O3 nanoparticles have significantly enhanced the critical current density. It can be noted that especially the films coated by Fe2O3 became stronger in the magnetic field and at higher temperatures. It was believed that coated films indicated the presence of artificial pinning centres created by Fe2O3 nanoparticles. The results of AFM indicate that surface roughness of the films significantly decreased with increase in concentration of coating material.

• Detection of H2S gas at lower operating temperature using sprayed nanostructured In2O3 thin films

Nanostructured indium oxide (In2O3) thin films were prepared by spray pyrolysis (SP) technique. X-ray diffraction (XRD) was used to investigate the structural properties and field emission scanning electron microscopy (FESEM) was used to confirm surface morphology of In2O3 films. Measurement of electrical conductivity and gas sensing performance were conducted using static gas sensing system. Gas sensing performance was studied at different operating temperature in the range of 25–150°C for the gas concentration of 500 ppm. Themaximum sensitivity (𝑆 = 79%) to H2S was found at lower temperature of 50 °C. The quick response (4 s) and fast recovery (8 s) are the main features of this film.

• X-ray determination of crystallite size and effect of lattice strain on Debye–Waller factors of platinum nano powders

In the present study, nano platinum particles were produced by ball milling process. The lattice strains in platinum (Pt) powders produced by milling have been analysed by X-ray powder diffraction. The lattice strain (𝜀) and Debye-Waller factor (𝐵) are determined from the half-widths and integrated intensities of the Bragg reflections. In Pt, the Debye–Waller factor is found to increase with lattice strain. From the correlation between the strain and effective Debye–Waller factor, the Debye–Waller factors for zero strain have been estimated for Pt. The variation of energy of vacancy formation as a function of lattice strain has been studied.

• Electrostatic model of semiconductor nanoparticles trapped in polymer electrolytes

A simple electrostatic model is applied to study the solvation energy and localization energy to inorganic semiconductor nanocrystallites trapped in polymer and ion conducting polymer electrolytes. The effective mass approximation has been applied to the system. In the single charge configuration, the dielectric constant of the medium has been identified as the selection criteria for hosting the nanoparticles. Solvation energy has been shown to depend on the host medium and the size of the crystallite.

• Green chemical incorporation of sulphate into polyoxoanions of molybdenum to nano level

Synthesis of sulphomolybdate (SMO) nanospheres was carried out by using sodium molybdate and a structure directing cationic surfactant, dodecyl pyridinium chloride (DPC) at room temperature by applying green chemistry principles. The composition and morphology of the nanospheres were established by Fourier transform infrared spectroscopy (FT–IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA) and inductively coupled plasma atomic emission spectroscopic (ICP–AES) techniques. Nanospheres in the diameter range of 10–100 nm, having the highest population within 50 nm were obtained. The effects of reaction parameters such as concentration of surfactant, temperature and pH of solution on the synthesis of nanospheres were investigated. The mechanism of agglomeration of nanoparticles are also discussed.

• Preparation and properties of polyrotaxane from 𝛼-cyclodextrin and poly(ethylene glycol) with poly(vinyl alcohol)

𝛼–Cyclodextrin (𝛼-CD) was found to form inclusion complexes with poly(ethylene glycol) (PEG) having a crystalline state in high yields, which have been investigated extensively in the past. Formation of an inclusion complex depends strongly on structure, molecular weight and geometry of the polymer. Development of a dicomponent inclusion complex (DIC) of PEG and 𝛼-CD in the presence of poly(vinyl alcohol) (PVA) and initiation of hexagonal crystals upon sonication have exhibited various microstructures. Formation of the new inclusion complex in PVA heavily depends on the concentration of PVA, temperature and sonication time. The complexes produced are characterized by FTIR, HNMR spectra and powder X-ray. 1HNMR of the complexes demonstrate that their stoichiometric ratio is 2:1 (two ethylene glycol units and one 𝛼-CD). X-ray patterns of PEG–𝛼-CD complex indicate that the 𝛼-CD forms channels whereas PEG/𝛼-CD/PVA creates cage-type structures.

• Optical, magnetic and structural characterization of Zn1−𝑥Co𝑥O nanoparticles synthesized by solvothermal method

Nanoparticles of Co-doped ZnO with 3.8, 7.2 and 11.5 wt% were synthesized by solvothermal method through oxalate precursor route. X-ray diffraction studies showed the formation of hexagonal ZnO structure for 𝑥 = 0.038, however, secondary phase of Co3O4 arises on increasing the Co content up to 11.5%. Transmission electron microscopic studies showed that particles are in the nano-metric regime and the grain size decreases on increasing the Co concentration. Optical reflectance measurements showed an energy bandgap, which decreases on increasing Co concentration. Specific surface area of these nanoparticles was found to be very high and comes out to be 97.6, 112.1 and 603.8 m2g-1, respectively. All the solid solutions showed paramagnetism with weak antiferromagnetic interactions. It is seen that the antiferromagnetic interaction increases on increasing Co concentration.

• Influence of conductive electroactive polymer polyaniline on electrochemical performance of LiMn1.95Al0.05O4 cathode for lithium ion batteries

Conductive electroactive polymer polyaniline is utilized to substitute conductive additive acetylene black in the LiMn1.95Al0.05O4 cathode for lithium ion batteries. Results show that LiMn1.95Al0.05O4 possesses stable structure and good performance. Percolation theory is used to optimize the content of conductive additive in cathode. It shows that the conductivity of cathode reaches its maximum value when the content of conductive additives is 15 wt%. This is in agreement with the results of charge and discharge experiments. The application of polyaniline can evidently enhance the electrochemical performance of cathode. The discharge capacity of cathode using 15 wt% polyaniline is 95.9 mAh g-1 at the current density of 170 mA g-1. The charge transfer resistance under different depths of discharge of cathode is much lower compared with the use of acetylene black. It can be concluded that the application of polyaniline in cathode can greatly improve the electrochemical performances of LiMn1.95Al0.05O4 cathode.

• Adhesion enhancement for liquid silicone rubber and different surface by organosilane and Pt catalyst at room temperature

Surface modification of aluminum, glass, epoxy resin, polypropylene and polyethylene via corona discharge pretreatment and platinum catalyst addition to promote their adhesion with liquid silicone rubber is reported. The corona-pretreated substrate surface was silanized with vinyltrimethoxysilane to generate vinyl groups on the surface, which could be initiated by platinum catalyst to form vinyl radicals. Then, the vinyltrimethoxysilane modified substrate was dipped into platinum catalyst solution to introduce platinum on the vinyltrimethoxysilane surface. The modified aluminum surface was characterized by X-ray photoelectron spectroscopy (XPS). The strong adhesion property between liquid silicone rubber and different surface was achieved by introducing a small amount of vinyltrimethoxysilane and platinum catalyst, followed by curing at low temperature. XPS result indicated the formation of vinyltrimethoxysilane coating on aluminum surface. Peel strength for liquid silicone rubber/vinyltrimethoxysilane–platinum surface was over 3.2 kN/m compared to only 1.1 kN/m for liquid silicone rubber/vinyltrimethoxysilane–aluminum. The cohesive failure in the bulk of liquid silicone rubber was observed for liquid silicone rubber/vinyltrimethoxysilane–platinum surface. It is assumed that the cross-linking reactions between vinyl groups in the vinyltrimethoxysilane coating and unsaturated terminal group of liquid silicone rubber occur due to the existence of platinum catalyst.

• High temperature impedance spectroscopy of barium stannate, BaSnO3

Polycrystalline powder of BaSnO3 was prepared at 1300 °C using a high-temperature solid-state reaction technique. X-ray diffraction analysis indicated the formation of a single-phase cubic structure with lattice parameter: 𝑎 = (4.1158 ± 0.0003) Å. The synthesized powder was characterized using X-ray diffraction (XRD) scanning electron micrographs, energy dispersive X-ray analysis, differential thermal analysis, thermogravimetric analysis and Fourier transform infrared techniques. Electrical properties were studied using a.c. impedance spectroscopy technique in the temperature range of 50–650 °C and frequency range of 10 Hz–13 MHz. The complex impedance plots at temperature ≥ 300 °C show that total impedance is due to the contributions of grains, grain boundaries and electrode. Resistance of these contributions has been determined. Variation of these resistances with temperature shows the presence of two different regions with different slopes. The nature of variation for the above three resistances, in both the temperature regions confirms that conducting species (phases) responsible for grain, grain boundaries and electrode are the same. Based on the value of activation energy, it is proposed that conduction via hopping of doubly ionized oxygen vacancies ($V^{\bullet \bullet}_{o}$) is taking place in the temperature region of 300–450 °C, whereas in the temperature region of 450–650 °C, hopping of proton, i.e. OH$^{\bullet}$ ions occurs.

• Aluminum alloy nanosecond vs femtosecond laser marking

Based on the lack of consistent literature publications that analyse the effects of laser marking for traceability on various materials, the present paper proposes a study of the influence of such radiation processing on an aluminum alloy, a vastly used material base within several industry fields. For the novelty impact, femtolaser marking has been carried out, besides the standard commercial nanosecond engraving. All the marks have been analysed using profilometry, overhead and cross-section SEM microscopy, respectively and EDAX measurements.

• Zirconium influence on microstructure of aluminide coatings deposited on nickel substrate by CVD method

Influence of Zr on the microstructure and phase characteristics of aluminide diffusion coatings deposited on the nickel substrate has been investigated in this study. The coatings with and without zirconium were deposited by CVD method. The cross-section chemical composition investigations revealed that during the coatings formation, there is an inward aluminum diffusion and outward nickel diffusion in both types of coatings (with and without zirconium), whereas zirconium is located far below the coating surface, at a depth of ∼17 𝜇m, between 𝛽-NiAl phase and 𝛾'-Ni3Al phase. XRD examinations showed that 𝛽-NiAl, 𝛾-NiAl and 𝛾'-Ni3Al were the main components of the deposited coatings. 𝛽-NiAl phase is on the surface of the coatings, whereas 𝛾-NiAl and 𝛾'-Ni3Al form deeper parts of the coatings. Zirconium is dissolved in NiAl on the border between 𝛽-NiAl and 𝛾'-Ni3Al.

• Nucleus geometry and mechanical properties of resistance spot welded coated–uncoated DP automotive steels

In this study, mechanical properties of resistance spot welding of DP450 and DP600, galvanized and ungalvanized automotive sheets have been investigated. The specimens have been joined by resistance spot welding at different weld currents and times. Welded specimens have been examined for their mechanical, macrostructure and microstructure properties. Depending on the weld current and time, effects of zinc coating on tensile properties, microhardness values as well as microstructure nugget geometry and nucleus size ratio have been investigated. X-ray diffraction analysis has been used to investigate the phase that formed at the joint interface. Result of the experiment show that nugget diameter, indentation depth and tensile load-bearing capacity are affected by weld parameters. Coating prevents full joining at low parameters. Microhardness increased in heat-affected zone and weld metal.

• Effect of TiN particulate reinforcement on corrosive behaviour of aluminium 6061 composites in chloride medium

In the present investigation, the corrosive behaviour of Al 6061–TiN particulate composites prepared by liquidmetallurgy has been studied in chloride medium using electroanalytical techniques such as Tafel, cyclic polarization and electrochemical impedance spectroscopy (EIS). Surface morphology of the sample electrodes was examined using scanning electron micrography and energy dispersive X-ray methods. X-ray diffraction technique was used to confirm inclusion of TiN particulates in the matrix alloy and identify the alloying elements and intermetallic compounds in the Al 6061 composites. Polarization studies indicate an increase in the corrosion resistance in composites compared to the matrix alloy. EIS study reveals that the polarization resistance (𝑅p) increases with increase in TiN content in composites, thus confirming improved corrosion resistance in composites. The observed decrease in corrosion rate in the case of composites is due to decoupling between TiN particles and Al 6061 alloy. It is understood that after the initiation of corrosion, interfacial corrosion products may have decoupled the conducting ceramic TiN from Al 6061 matrix alloy thus eliminating the galvanic effect between them.

• Chemical shift of Mn and Cr K-edges in X-ray absorption spectroscopy with synchrotron radiation

Mn and Cr K X-ray absorption edges were measured in various compounds containing Mn in Mn2+, Mn3+ and Mn4+ oxidation states and Cr in Cr3+ and Cr6+ oxidation states. Few compounds possess tetrahedral coordination in the 1st shell surrounding the cation while others possess octahedral coordination. Measurements have been carried out at the energy dispersive EXAFS beamline at INDUS-2 Synchrotron Radiation Source at Raja Ramanna Centre for Advanced Technology, Indore. Energy shifts of ∼8–16 eV were observed for Mn K edge in the Mn-compounds while a shift of 13–20 eV was observed for Cr K edge in Cr-compounds compared to values in elementalMn and Cr, respectively. The different chemical shifts observed for compounds having the same oxidation state of the cation but different anions or ligands show the effect of different chemical environments surrounding the cations in determining their X-ray absorption edges in the above compounds. The above chemical effect has been quantitatively described by determining the effective charges on Mn and Cr cations in the above compounds.

• Intrinsic structure and friction properties of graphene and graphene oxide nanosheets studied by scanning probe microscopy

In this paper, atomic structure of single-layered graphene oxide (GO) and chemically reduced graphene oxide (CRGO) nanosheets was investigated using atomic force microscopy and scanning tunnelingmicroscopy (AFM and STM). Furthermore, friction properties of the graphene and GO nanosheets were studied by frictional force microscopy (FFM). STM imaging provided direct evidence and the morphology was influenced by oxygen-containing groups and defects. The atomic scale structural disorder in a hexagonal two-dimensional network of carbon atoms changes the surface condition, which also caused the frictional property variations of the samples.

• Yellow phosphors doping with Gd3+, Tb3+ and Lu3+ in MTiO3 (M = Mg and Sr) luminescence properties

This paper reports Gd3+, Tb3+ and Lu3+ doped MTiO3 (M = Mg and Sr)-based phosphors which were synthesized by the conventional solid-state reaction method, their crystal structures and luminescence properties were investigated. X-ray diffraction patterns (XRD) showed that phosphors sintered at 1000 °C for 2 h were the pure SrTiO3 and MgTiO3 phases. The optimization of reaction conditions was carried out by thermogravimetry and differential thermal analysis (DTA/TG) methods. Surface and elemental analyses were performed by using SEM instrument. The excitation and emission spectra were recorded by a photoluminescence spectrophotometer (PL). The thermoluminescence (TL) properties of MgTiO3:RE (RE = Gd3+, Tb3+, Lu3+) and SrTiO3:RE (RE = Gd3+, Tb3+, Lu3+) were investigated.

• Identification of 𝛽-SiC surrounded by relatable surrounding diamond medium using weak Raman surface phonons

It is difficult to detect 𝛽-SiC using micro-Raman scattering, if it is surrounded by carbon medium. Here, 𝛽-SiC is identified in the presence of a relatable surrounding diamond medium using subtle, but discernible Raman surface phonons. In this study, diamond/𝛽-SiC nanocomposite thin film system is considered in which nanosized 𝛽-SiC crystallites are surrounded by a relatable nanodiamond medium that leads to the appearance of a weak Raman surface phonon band at about 855 cm-1. Change in the nature of the surrounding material structure and its volume content when relatable, will affect the resultant Raman response of 𝛽-SiC phase as seen in the present case of diamond/𝛽-SiC nanocomposite thin films.

• Facile preparation of superhydrophobic surface with high adhesive forces based carbon/silica composite films

Glass substrates modified by carbon/silica composites are fabricated through a two-step process for the preparation of a superhydrophobic surface (water contact angle ≥ 150°). Carbon nanoparticles were first prepared through a deposition process on glass using a hydrothermal synthesis route, then the glass was modified by SiO2 using the hydrolysis reaction of tetraethylorthosilicate at room temperature. It is not only a facile method to create a superhydrophobic surface, but also helps to form a multi-functional surface with high adhesive forces.

• An efficient method combining thermal annealing and acid leaching for impurities removal from silica intended for photovoltaic application

This work investigates the photothermal treatment of silica sand to reduce impurities to a low level suitable for the production of acceptable solar grade silicon for photovoltaic application. It describes experiment carried out by using a tungsten lamp furnace to purify silica under controlled atmosphere. This process enables to attract impurities to the surface of silica grains where they can be easily extracted by partial dissolution in an acid mixture. Thus obtained silica was investigated by inductively coupled plasma atomic emission spectrometry (ICP–AES) method. Major impurities present in silica sand were Al, K, Fe, Na, Ca, Mg and B. Among the new products, almost major impurities were removed effectively. Indeed purity degree, given by characterization of ICP–AES, passes from 99.76 to 99.96% and the average impurity removal efficiency is 83.33%.

• Thermal characteristics and corrosion behaviour of Mg–𝑥Zn alloys for biomedical applications

The thermal parameters of Mg–𝑥Zn cast alloys with 0.5–9 wt% Zn were evaluated by using computer aided cooling curve thermal analysis (CA–CCTA), whereas the corrosion behaviour was investigated by potentiodynamic polarization and immersion tests. Thermal analysis results revealed that the dendrite coherency temperature (𝑇DCP) decreased from 642.2 to 600 °C with the addition of Zn from 0.5 to 9 wt%. The liquid fraction at coherency point ($f^{\text{DCP}}_{\text{L}}$) increased by 72% when Zn was increased up to 9 wt%. MgZn intermetallic phase was observed in samples with &lt;3 wt% Zn. At higher percentages of Zn, the Mg51Zn20 intermetallic phase was also detected in addition to 𝛼-Mg and MgZn by first derivative cooling curves under non-equilibrium solidification. All these phases were observed along the grain boundary when Zn was rejected from the solid/liquid interface and enriched in the triple conjunction of grain boundary. The grain size decreased from 185.2 to 71.5 𝜇m when Zn content was increased. The addition of Zn content had a significant effect on the corrosion rate and the corresponding mechanisms. The corrosion rate decreased from 2.1 to 1.81 mmpy as Zn content increased from 0.5 to 3 wt%; afterwards, however, this value increased with further increase of Zn. Mg–3Zn also had the lowest degradation rate and highest corrosion resistance which can be fully utilized for biodegradable orthopedic applications.

• Evidence for high ionic conductivity in lithium–lanthanum titanate, Li0.29La0.57TiO3

Lithium–lanthanum titanate, Li0.29La0.57TiO3, is prepared by solid-state reaction method and it is furnace-cooled to room temperature. X-ray diffraction results indicated that the compound has tetragonal perovskite-like structure and the lattice parameters are determined as 𝑎 = 3.8714 Å and 𝑐 = 7.7370 Å. The average grain size is found to be 5 𝜇m from SEM micrograph. The analysis of FTIR and Raman spectra of the sample supported tetragonal structure inferred from XRD data. The impedance spectrum of the sample is separated into bulk and grain boundary parts by analysing the impedance data. The high bulk ionic conductivity is reported as 1.12 × 10-3 S cm-1 at room temperature. D.C. conductivity measurements indicate that the compound is a good ionic conductor.

• Ion exchange synthesis and thermal characteristics of some $[\text{N}^{+}_{2222}]$ based ionic liquids

Eight salts were obtained by reacting tetraethylammonium cation $[\text{N}^{+}_{2222}]$ with inorganic anions like BF$^{-}_{4}$, NO$^{-}_{3}$, NO$^{-}_{2}$, SCN-, BrO$^{-}_{3}$, IO$^{-}_{3}$, PF$^{-}_{6}$ and HCO$^{-}_{3}$ using ion exchange method. These ionic liquids (ILs) were characterized using thermal methods, infrared spectroscopy and densitometry. Thermophysical properties such as density, coefficient of volume expansion, heat of fusion, heat capacity and thermal energy storage capacity were determined. Thermal conductivity of the samples was determined both in solid and liquid phases. Owing to high values of thermal energy storage capacity coupled with handsome liquid phase thermal conductivity, ILs under investigation were recommended as materials for thermal energy storage (TES) as well as heat transfer applications.

• Comparison of in vivo biocompatibilities between parylene-C and polydimethylsiloxane for implantable microelectronic devices

Implantable devices are often composed of or coated with different biologically compatible materials based on their requirements. Selecting a surface material for an implantable device is not an easy task, and it is necessary to compare the biocompatibilities of the available surface materials. In this study, we perform a comparison of the in vivo biocompatibilities of polydimethylsiloxane (PDMS) and para-xylyene polymer (parylene-C) as they are considered to be candidates for a coating material for implantable microelectronic devices. For in vivo biocompatibility testing, fifty four male Sprague-Dawley rats were used for testing, and they were divided into three groups (PDMS, parylene-C and a positive control). At one, four and twelve weeks after implantation of the test object, the density of inflammatory cells and the granulation layer thickness were recorded for each group and compared with other groups using visible light and fluorescence microscopy. The thickness of the granulation layer tended to decrease over time for all of the experimental groups, whereas the granulation layer thickness remained constant in the positive control group. The thinnest capsular layer was observed for the parylene-C group and fewest inflammatory cells were observed in this group during the entire experimental period. Macrophage infiltration was minimal, even at one week, and was not observed thereafter. The parylene-C group showed better biocompatibility than the PDMS groups, both for acute and chronic implantation. Thus, parylene-C is the best candidate of the tested materials for applications involving permanent implantable micro-devices.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 5
October 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019