• Volume 37, Issue 2

April 2014,   pages  167-369

• Characterization of composite materials based on Fe powder (core) and phenol–formaldehyde resin (shell) modified with nanometer-sized SiO2

Soft magnetic composites based on Fe powder and phenol–formaldehyde resin (PFR) modified with tetraethylorthosilicate are investigated in detail. The chemical synthesis of PFR, its modification with nanometer-sized SiO2 particles created by sol–gel method and subsequent coating, enables a preparation of insulating PFR–SiO2 (PFRT) layer on the surface of Fe particles. Thermal degradation and FTIR analysis of PFR and PFRT with different amount of SiO2 was examined. Mechanical hardness and flexural strength of FePFRT composites was studied depending on the amount of nanosized-SiO2 in the coating. SEM serves in evidence of a defectless microstructure if the coating contains at least 2% of silica particles. The morphology of Fe particles implies uniform coating without any visible exfoliation. A presence of fine SiO2 particles was verified by TEM. The best magnetic properties were found in Fe–PFRT composite with 2% of SiO2 in the insulating layer on behalf of its uniform arrangement and homogeneity.

• Influence of deposition rate on PL spectrum and surface morphology of ZnO nanolayers deposited on Si (100) substrate

Zinc oxide (ZnO) thin films were deposited on Si (100) substrate through sputtering of zinc by DC magnetron, followed by thermal oxidation. Different deposition rates were used in coating films with 100 nm thickness (0.6–4.5 nm/s). Photoluminescence spectra of the produced samples were obtained and it was found that the violet emission peak intensity increases with deposition rate. Scanning electron microscopy (SEM) micrograph and atomic force microscopy (AFM) images for the zinc oxide films were obtained. Morphological changes due to various deposition rate are discussed in the light of changes observed in the ZnO crystals. Low coating rates produced smooth surface with small grains while higher deposition rates increased the surface roughness and larger grain size. AFM and SEM results are in good agreement and support the PL results.

• Self-assembled nanofilm of 1,2-dihydro-3-(octadecylthio)benzotriazine on copper for corrosion protection

The self-assembled nanofilm of 1,2-dihydro-3-(octadecylthio)benzotriazine (DOTBT) was formed on fresh copper surface obtained by etching with 7 N nitric acid at a room temperature of 30°C. The conditions for formation of the DOTBT nanofilm have been optimized by electrochemical impedance and electrochemical quartz crystal nanobalance (EQCN) studies. The DOTBT nanofilm on copper surface was characterized by contact-angle measurement, X-ray photoelectron spectra (XPS), reflection absorption FTIR spectra and atomic force micrographs (AFM). It is inferred that formation of DOTBT film is due to chemisorption of DOTBT on copper surface through nitrogen and subsequent complex formation between DOTBT and Cu+ ions. Corrosion protection ability of DOTBT nanofilm was evaluated in dilute aqueous NaCl solution using electrochemical impedance, potentiodynamic polarization, weight-loss and XPS studies. These studies inferred that the DOTBT film protects effectively copper from corrosion. Potentiodynamic polarization studies revealed that the DOTBT film inhibits corrosion by controlling the cathodic reaction. The mechanism of corrosion protection of copper by DOTBT nanofilm is discussed in this paper.

• Ciprofloxacin conjugated zinc oxide nanoparticle: A camouflage towards multidrug resistant bacteria

Gradual development of antibiotic resistant bacteria is producing severe global threat. Newer strategies are now being employed in order to control the microbial infections and to reduce the mortality as well as infection rates. Herein we describe successful synthesis of ZnO nanoparticles (ZNP) under microwave assisted condition followed by functionalization with ciprofloxacin, an antibiotic, using EDC/NHS chemistry. Successful conjugation of ciprofloxacin was confirmed by FTIR spectra. Ciprofloxacin-conjugated ZnO nanoparticles (ZN-CIP) exhibited excellent antibacterial activity against clinically isolated multidrug resistant bacterial strains of Escherichia coli, Staphylococcus aureus and Klebsiella sp. ZNP were small in size with particle size distribution 18–20 nm as obtained from transmission electron microscope (TEM). Surface topology was obtained from atomic force microscopic (AFM) image and x-ray diffraction confirmed that ZNP possessed hexagonal crystal structure. A concentration of 10 𝜇g/mL of ZN-CIP was a benchmark concentration. During evaluation of minimum inhibitory concentration (MIC) values, similar concentration of antibiotic was incapable of producing antibacterial activity.

• Bioactive nanocrystalline wollastonite synthesized by sol–gel combustion method by using eggshell waste as calcium source

The sol–gel combustion method was employed to synthesize the nanocrystalline wollastonite by taking the raw eggshell powder as a calcium source and TEOS as a source of silicate. Glycine was used as a reductant or fuel and nitrate ions present in metal nitrate acts as an oxidizer. The phase purity of the wollastonite was analysed by powder XRD and the product is found to contain single-phasic wollastonite. FT–IR spectrum shows the characteristic peaks of the functional groups present in the wollastonite. SEM images show that particles are agglomerated and the particle size is found to be in the nanoregime. The calcination temperature was optimized based on the thermal analysis of the precursor. The bioactivity of wollastonite was investigated by immersing the scaffold in a simulated body fluid for 15 days at 37°C and intermediate analysis of the surface by XRD shows the deposition of hydroxyapatite layer after 5 days.

• One-pot synthesis of hydroxyapatite–silica nanopowder composite for hardness enhancement of glass ionomer cement (GIC)

Hydroxyapatite–silica nanopowder composite was prepared using one-pot sol–gel technique. The morphology of the powder consists of a mixture of spherical silica particles (∼ 30 nm) embedded within the elongated hydroxyapatite (∼ 103 nm). The synthesized nanoparticles were incorporated into commercial glass ionomer cement (GIC) and Vickers hardness was evaluated. Results shown that the addition of the nanopowder composite gave ∼ 73% increment in the hardness compared to the pure GIC. Higher content of hydroxyapatite–silica nanopowder resulted in dense cement and produced a stronger GIC and the application of this material with improved hardness property might lead to extend the clinical indications, especially in stress bearing areas.

• Role of iron oxide impurities in electrocatalysis by multiwall carbon nanotubes: An investigation using a novel magnetically modified ITO electrodes

The role of iron oxide impurities in the electrocatalytic properties of multiwall carbon nanotubes (MWCNTs) prepared by catalytic chemical vapour decomposition method (CCVD) is studied in detail. A novel magnetically modified electrodes have been developed by which MWCNTs were immobilized on indium-tin oxide (ITO) electrodes, without any chemical binders. The electro-catalytic oxidation of dopamine, and reduction of hydrogen peroxide have been studied by cyclic voltammetry on magnetically modified electrodes with (i) MWCNTs with occluded iron oxide impurities (Fe-MWCNTs), (ii) MWCNTs grown on iron oxide nanoparticle particulate films (Io-MWCNTs) and (iii) pristine iron oxide nanoparticle particulate film (Io-NPs). A shift towards less positive potentials for the oxidation of dopamine was observed which is in the order of Fe-MWCNTs &lt; Io-MWCNTs &lt; Io-NPs. Similarly, trend towards less negative potentials for the reduction of hydrogen peroxide was observed. Thus, the electrocatalytic activities displayed by MWCNTs have been attributed to the iron oxide impurities associated with it. The systematic variation was related to the nature of interaction of iron oxide nanoparticles with MWCNT surface.

• Processing and properties of Cu based micro- and nano-composites

Nano-composites of 1, 3, 5 and 7 vol% Al2O3 (average size &lt; 50 nm) and microcomposites having compositions 5, 10, 15, 20 vol% of Al2O3 (average size ∼ 10 𝜇m) reinforced in copper matrix were fabricated by powder metallurgy route. All the specimens were sintered at different sintering temperatures (850, 900 and 1000°C) to study the effect of temperature on the process and progress of sinterability of the reinforced micro- and nanoparticles in the matrix. These micro- and nano-composites were characterized using X-ray diffraction and scanning electron microscopy followed by density, microhardness and wear measurements. The compression and flexural tests were also carried out in order to investigate the mechanical behaviour of the micro- and nano-composites for a fixed optimum sintering temperature. Fractography of the 3-point bend specimens was performed to investigate the fracture behaviour of the micro- and nano-composites. The flexural test results showed that the ultimate flexural strength decreases and flexural modulus increases with the increase in reinforcement content.

• Macro-scale complexity of nano- to micro-scale architecture of olivine crystals through an iodine vapour transport mechanism

The production of nano- to micro-scale olivine (magnesium and iron silicate) crystals has been achieved at relatively low temperatures through an iodine vapour transport of the metal onto amorphous silicon dioxide. The process occurs down a temperature gradient from 800 to 600°C yielding high quality crystals with long range crystallinity, highly complex interconnectivity and intricate macroscale architecture. Scanning electron microscopy (SEM) imaging of the substrate before and after the reaction reveals that the amorphous silicon oxide species is mobile, due to the lack of correlation between the silicon oxide layer and the final olivine particles, leading to a vapour–liquid–solid or vapour–solid growth mechanism. This technique demonstrates a facile, low temperature synthetic route towards olivine crystals with nano- to micro-scale dimensions.

• Chemical bath deposition of CdS thin films doped with Zn and Cu

Zn- and Cu-doped CdS thin films were deposited onto glass substrates by the chemical bath technique. ZnCl2 and CuCl2 were incorporated as dopant agents into the conventional CdS chemical bath in order to promote the CdS doping process. The effect of the deposition time and the doping concentration on the physical properties of CdS films were investigated. The morphology, thickness, bandgap energy, crystalline structure and elemental composition of Zn- and Cu-doped CdS films were investigated and compared to the undoped CdS films properties. Both Zn- and Cu-doped CdS films presented a cubic crystalline structure with (1 1 1) as the preferential orientation. Lower values of the bandgap energy were observed for the doped CdS films as compared to those of the undoped CdS films. Zn-doped CdS films presented higher thickness and roughness values than those of Cu-doped CdS films. From the photoluminescence results, it is suggested that the inclusion of Zn and Cu into CdS crystalline structure promotes the formation of acceptor levels above the CdS valence band, resulting in lower bandgap energy values for the doped CdS films.

• A comparative study regarding effects of interfacial ferroelectric Bi4Ti3O12 (BTO) layer on electrical characteristics of Au/𝑛-Si structures

Present study focuses on the effects of interfacial ferroelectric BTO layer on the electrical characteristics of Au/𝑛-Si structures, hence Au/𝑛-Si (MS) and Au/BTO/𝑛-Si (MFS) structures were fabricated and admittance measurements (capacitance–voltage: 𝐶-𝑉 and conductance–voltage: G/𝜔-𝑉) of both structures were conducted between 10 kHz and 1 MHz at room temperature. Results showed that 𝐶-𝑉 and G/𝜔-𝑉 characteristics were affected not only by frequency but also through deposition of BTO layer. Some effects can be listed as sharper peaks in 𝐶-𝑉 plots, higher capacitance and conductance values. Structure’s series resistance (𝑅s) also decreased due to BTO layer. Interface states (𝑁ss) profiles of the structures were obtained using Hill–Coleman and high-low frequency capacitance (𝐶HF - 𝐶LF). Some of the main electrical parameters were extracted from 𝐶-2-𝑉 plots using depletion capacitance approach. Furthermore, current–voltage characteristics of MS and MFS structures were presented.

• Electrical properties of Ba0.7Bi0.3Fe0.9Sn0.1O3–BaCo$_{0.02}^{II}$ Co$_{0.04}^{III}$Bi0.94O3 thick film thermistors with wide-range adjustable parameters

A novel (1−𝑥)Ba0.7Bi0.3Fe0.9Sn0.1O3-𝑥BaCo$_{0.02}^{II}$ Co$_{0.04}^{III}$Bi0.94O3 (0.2 ≤ 𝑥 ≤ 0.9) negative temperature coefficient (NTC) thick film thermistors with high thermistor constant was prepared by screen printing. The values of room-temperature resistivity, thermistor constant and activation energy of the thick film thermistors, increasing with the addition of Ba0.7Bi0.3Fe0.9Sn0.1O3, are in the range of 35.5 𝛺cm-1.34 M𝛺 cm, 2067–6139 K and 0.177-0.527 eV, respectively. This means that the electrical properties of the thick films are adjustable at a wide range, depending on the compositions. Impedance analysis shows that the magnitude of thick film bulk resistance is mainly attributed to the contribution of grain boundary.

• Study of electrical properties of polyvinylpyrrolidone/polyacrylamide blend thin films

Electrical properties of polyvinylpyrrolidone, polyacrylamide and their blend thin films have been investigated as a function of temperature and frequency. The films were prepared using solution casting method and the measurements on films were carried out at different temperatures ranging from 305 to 345 K covering a frequency range from 102 to 105 Hz. The conductivity of film samples was found to increase upon increasing the temperature. Lowering of activation energy by increasing the polyvinylpyrrolidone percentage may be due to the predominance of ion conduction mechanism caused by polyvinylpyrrolidone in the blend. The permittivity (𝜖r) and dielectric loss (𝜖i) were found to decrease upon increasing frequency. Temperature and frequency dependence of impedance, relaxation time and electric modulus of thin film samples have also been studied. From electric modulus formalism, polarization and conduction relaxation behaviour in the film samples have been discussed.

• Optical properties of zinc–vanadium glasses doped with samarium trioxide

Zinc–vanadium glasses doped with samarium oxide having the chemical composition Sm2O3(𝑥) ZnO(40-𝑥)V2O5(60) (where 𝑥 = 0.1–0.5 mol%) were prepared by melt quenching method. The density of these glasses was measured by Archimedes method; the corresponding molar volumes have also been calculated. The values of density range from 3.7512 to 5.0535 gm/cm3 and those of molar volume range from 28.3004 to 37.6415 cm-3. The optical absorbance studies were carried out on these glasses to measure their energy bandgaps. The absorption spectra of these glasses were recorded in UV–Visible region. No sharp edges were found in the optical spectra, which verify the amorphous nature of these glasses. The calculated optical bandgap energies of these glasses were found to be in the range of 0.3173–0.6640 eV. The refractive index and polarizability of oxide ion have been calculated by using Lorentz–Lorentz relations. The values of refractive index range from 1.1762 to 1.2901 and those of polarizability of oxide ion range from 1.6906 × 10-24 to 2.2379 × 10-24 cm3.

• Structural and optoelectronic properties of cubic perovskite RbPbF3

The structural and optoelectronic properties of cubic perovskite RbPbF 3 are calculated using all electrons full potential linearized augmented plane wave (FP-LAPW) method. The calculated lattice constant is in good agreement with the experimental result. The calculated band structure shows a direct band gap of 3.07 eV. The contribution of different bands is analysed from the total and partial density of state curves. We identified hybridization of Pb 𝑠, Pb 𝑝 states with F 𝑝 states in the valence bonding region. Calculations of the optical spectra, viz., the dielectric function, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss are performed for the energy range of 0-30 eV. Based on the direct bandgap, as well as other optical properties of the compound, it is predicted that this material is useful for vacuum-ultraviolet-transparent (VUV-transparent) applications.

• Ultraviolet sensing properties of polyvinyl alcohol-coated aluminium-doped zinc oxide nanorods

Undoped and aluminium (Al)-doped zinc oxide (ZnO) nanorods have been synthesized by electrochemical route. The synthesized materials have been characterized by X-ray diffraction, UV–visible spectrometer and scanning electron microscope. The Al-doped ZnO nanorods have been coated with polyvinyl alcohol. Current–voltage characteristics have been investigated in dark and under UV-light illumination. Aluminium doping in ZnO increase its electrical conductivity and further polyvinyl alcohol coating on Al-doped ZnO increase UV sensitivity of the material. Response and recovery time of Al-doped ZnO and PVA-coated Al-doped ZnO nanorods have been recorded. PVA-coated Al-doped ZnO nanorods shows very fast response and recovery time of 10 s in comparison to uncoated ZnO (20 min) nanorods.

• Properties of poly(vinyl alcohol)–borax gel doped with neodymium and praseodymium

Neodymium and praseodymium ions, singly and in combination, have been doped into a poly(vinyl alcohol)–borax matrix. X-ray diffraction shows structural correlations from 2 to 6 Å and 15 Å, while small angle neutron scattering indicates that the rare-earth ions do not affect the nanoscale structures of the gels. Differential scanning calorimetry shows the glass transition temperature to increase with concentration of Pr in the gel. Excitation in the ultraviolet region leads to luminescent emission in the visible region. Simultaneous absorption in the visible region then leads to luminescent emission in the near infra-red region. The spectral qualities of the emission bands can be varied by choosing appropriate relative ratios of rare-earth species.

• Preparation and characterization of PEG–Mg(CH3COO)2–CeO2 composite polymer electrolytes for battery application

Composite polymer electrolytes based on poly(ethylene glycol) (PEG), magnesium acetate [Mg(CH3COO)2], and 𝑥 wt% of cerium oxide (CeO2) ceramic fillers (where 𝑥 = 0, 5, 10, 15 and 20, respectively) have been prepared using solution casting technique. X-ray diffraction patterns of PEG–Mg(CH3COO)2 with CeO2 ceramic filler indicated the decrease in the degree of crystallinity with increasing concentration of the filler. DSC measurements of PEG–Mg(CH3COO)2-CeO2 composite polymer electrolyte system showed that the melting temperature is shifted towards the lower temperature with increase of the filler concentration. The conductivity results indicate that the incorporation of ceramic filler up to a certain concentration (i.e. 15 wt%) increases the ionic conductivity and upon further addition the conductivity decreases. The transference number data indicated the dominance of ion-type charge transport in these specimens. Using this (PEG–Mg(CH3COO)2-CeO2) (85-15-15) electrolyte, solid-state electrochemical cell was fabricated and their discharge profiles were studied under a constant load of 100 k𝛺.

• Effect of carbides on erosion resistance of 23-8-N steel

Microstructure is one of the most important parameters influencing erosion behaviour of materials. The role of carbides in the matrix is very complicated in controlling the erosion rate of the materials. Conflicting results have been reported in the literature about the effect of carbides on erosion resistance. Carbides are of great importance especially as obstacles against the penetration of erosive particles into the material surface. However, they are susceptible to cracking and causing matrix decohesion which may increase the overall erosion rate. In 23-8-N nitronic steel, carbides present in the form of bands are observed to accelerate the erosion rate. Coarse carbides cause depletion of carbon in the austenite matrix which adversely affects the strain hardening tendency thus causing deterioration in erosion resistance of the bulk material. The dissolution of carbides in the austenitic matrix after solution annealing is observed to improve the erosion resistance of 23-8-N nitronic steel.

• Effect of chemical composition and alumina content on structure and properties of ceramic insulators

In the present work, six electrical porcelain compositions with different amount of alumina and silica have been prepared and fired in an industrial furnace at 1300°C. Density, porosity, bending strength and electrical strength were measured in the samples. In order to find a relationship between properties and sample microstructures, samples were analyzed by scanning electron microscope (SEM) and x-ray diffraction (XRD) techniques. The results showed that, with chemical composition of 53.5 wt.% SiO2 and 37.5 wt.% alumina, highest electrical strength of 21.97 kV/mm was achieved in fabricated electrical porcelains. Increasing amount of alumina up to 30 wt.% decreases quartz and cristobalite phases, but increases corundum phase 3 to 5 times. SEM observation revealed that dense particles and uniform distribution of long and thin needle shaped mullite are predominant in sample microstructures with highest electrical strength.

• Effect of tempering after cryogenic treatment of tungsten carbide–cobalt bounded inserts

Cryogenic treatment is a recent advancement in the field of machining to improve the properties of cutting tool materials. Tungsten carbide is the most commonly used cutting tool material in the industry and the technique can also be extended to it. Although the importance of tempering after cryogenic treatment has been discussed by many researchers, very little information is available in published literature about the effect of multi-tempering after cryogenic treatment. In this study, an attempt has been made to understand effect of the number of post-tempering cycles during cryogenic treatment on tungsten carbide–cobalt inserts. Metallurgical investigations have been performed to observe the effect of such post-tempering on the inserts by analysing microhardness and microstructural changes. The crystal structure and morphology were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. Metallurgical investigations revealed a significant improvement in tungsten carbide inserts having three tempering cycles, after cryogenic treatment, with marginal differences for two cycles of tempered inserts, established by the study of wear behaviour in turning.

• Solvothermal growth of single-crystal CdS nanowires

Cadmium sulfide (CdS) nanowires (NWs) were prepared by the solvothermal method using ethylenedi-amine as a solvent. Two sets of CdS NWs were synthesized at 160 and 200° C for various reaction durations (3.5, 7 and 24 h). Scanning/tunneling electron microscopy was used to examine the surface morphology of the grown NWs. Their dimensions are found to depend on the reaction temperature and duration. The CdS NWs grown at 200° C for all durations are longer than those prepared at 160° C, with diameters ranging from 15 to 40 nm. A three-armed structure is exhibited by all the samples. The grown CdS NWs display a hexagonal wurtzite phase and grows along the 001 direction. The optical absorption of the grown NWs shows a sharp absorption edge with a blueshift, which indicates an expansion of the optical band gap. All prepared samples show two emission peaks in their photoluminescence spectra. The emission peak location depends on the reaction temperature and duration. The CdS NWs prepared at 160° C show a sharp band–band emission compared with those prepared at 200° C. Raman analysis indicates that the optical properties of the grown NWs are enhanced with increased temperature and reaction duration.

• Influence of MWCNTs and gamma irradiation on thermal characteristics of medical grade UHMWPE

Several techniques are available to characterize the influence of 𝛾-irradiation on structural parameters of polymers; among which thermal characterization is more often used. The present work is aimed to study the influence of multi walled carbon nanotubes (MWCNTs) and 𝛾-irradiation on polymer crystallinity, lamellar thickness, coefficient of thermal expansion (CTE) and thermal stability of UHMWPE. The chemically treated MWCNTs were homogenously dispersed in UHMWPE using a ball milling machine and compression moulded to make the nanocomposites with different concentration of MWCNTs. The nanocomposites were then 𝛾-irradiated at a dose rate of 2.5 kGy/h up to 25, 50, 75, 100 kGy irradiation doses. The results obtained from TGA studies revealed that the presence of MWCNTs improved the thermal stability and onset temperature of degradation of nanocomposites. The CTE of nanocomposites was decreased with an increase of MWCNTs concentration and irradiation dose. The reduction of thermal expansion of nanocomposites aids in minimizing the dimensional fluctuation of them. It is concluded that irradiation and the presence of MWCNTs in UHMWPE not only improved the thermal stability of the composites but also enhanced their crystallinity and lamellar thickness.

• Conductive biodegradable film of 𝑁-octyloxyphenyl-𝑁ʼ- (4-methylbenzoyl)thiourea

Thiourea derivatives are versatile family of ligands which provides wide range of electronic properties since they consist of rigid 𝜋-systems on their structures. In this work, a new type of thiourea compound with general formula Me-C6H4C(O)NHC(S)NHC6H4-OC8H17 of 𝑁ʼ-(4-methylbenzoyl)thiourea (MBTU) was successfully synthesised and characterized by using NMR, FTIR and UV–vis analysis. The development of new conductive biodegradable film based on MBTU has been accomplished by incorporating chitosan to the polymer-dopant system via solution-cast technique. The impedance measurement technique was employed to determine conductivity of biodegradable film. It shows that, with the addition of MBTU, the increasing of conductivity is from 10−9 to 10−8 Scm−1. TNM results show that the conductivity of biodegradable film is governed by electronic conducting species. It is proven that MBTU compound exhibits promise and has great potential to be explored and used as doping system in conductive materials applicationin the future.

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