• Volume 34, Issue 7

December 2011,   pages  1285-1801

• Structural and optical properties of zinc sulphide–polyvinyl alcohol (ZnS–PVA) nanocomposite thin films: effect of Zn source concentration

ZnS–PVA nanocomposite thin films are grown by chemical bath deposition (CBD) method by varying the concentration of zinc source. Formation of nanocrystalline hexagonal ZnS is confirmed by X-ray diffraction. Hexagonal form is predominant at some lower concentration. The morphological properties of the films are determined by transmission electron microscope (TEM). The particle size as given by TEM indicates increase in particle size. Bandgap measured from UV-Visible transmission spectra shows a decreasing trend with decrease of Zn source concentration. Photoluminescence (PL) measurement showed blue emission centred at 417 nm and that the intensity decreases with decrease in Zn source concentration.

• Preparation of novel polymer–metal oxide nanocomposites with nanophase separated hierarchical structure

This article deals with preparation of nanocomposite which comprised of nanophase separated structure of polymer chains and metal oxide. By grafting poly(hydroxyethyl methacrylate), poly(HEMA) on the surface of titanium which is covered by passive titanium oxide by atom transfer radical polymerization (ATRP) and executing anodic polarization, hierarchy nanophase separated structure with controlled thickness can be obtained. The titanium ions would be cationically charged and completely filled up the unoccupied binding sites of the polymer chains via electrochemical reaction, eventually covering the polymer chains with titanium oxide. However, this structure can be obtained when the anodic polarization is executed at initial applied voltage exceeding 10 VSCE. The control of thickness is possible by controlling the initial applied voltage. These results prove that the conventional polymer can form composite structure with metal oxide without using fillers or special polymers designed for composite.

• Morphology, thermal, electrical and electrochemical stability of nano aluminium-oxide-filled polyvinyl alcohol composite gel electrolyte

In the present work, an attempt has been made to develop nano aluminium oxide (Al2O3)-filled polyvinyl alcohol (PVA) composite gel electrolytes. Surface morphological studies, thermal behaviour, electrochemical stability and electrical characterization of these composite gel electrolytes have been performed. An increase in the concentration of Al2O3 in composite gel electrolytes increases the amorphous characteristics of pure PVA. Bulk conductivity of composite gel electrolytes increases by an order of magnitude on addition of a nano filler. Maximum conductivity of 5.81 × 10-2 S/cm is observed for 6 wt% Al2O3-filled polymer gel composite electrolytes. Temperature dependence of electrical conductivity shows a combination of Arrhenius and Vogel–Tamman–Fulcher (VTF) nature. Maximum current stability during oxidation and reduction cycle is noticed for 6 wt% Al2O3-filled PVA composite electrolyte, viz. ±1.65 V.

• Dielectric behaviour of nano-crystalline spinel Ni0.2Ca0.8Fe2O4 and their nano-composite with polypyrrole

The spinel ferrite nano-particles of chemical composition Ni0.2Ca0.8Fe2O4 have been prepared by sol–gel method. Subsequently, the nanoparticles are encapsulated with the intrinsically conducting polymer shell of polypyrrole. The X-ray diffraction patterns confirm the single phase cubic spinel structure of the materials. To understand the dielectric properties of the materials, frequency-dependent dielectric measurement has been performed at 300 K in the range of 100 mHz to 2 MHz. On polymerization, both the dielectric strength as well the dielectric loss is significantly increased. Also, the dielectric conductivity, which arises from the electron hopping mechanism, is considerably increased on polymerization.

• Fabrication and characterization of Ti3SiC2–SiC nanocomposite by in situ reaction synthesis of TiC/Si/Al powders

The microstructure and mechanical properties of Ti3SiC2–SiC nanocomposite fabricated by in situ hot pressing (HP) synthesis process were studied. The results show that dense Ti3SiC2–SiC composite contained minor TiSi2 obtained by hot sintering at 1350°C for 1 h. The average grain size of Ti3SiC2 was 4 𝜇m in length, and the size of SiC grains is about 100 nm. With its fine microstructure, the Ti3SiC2–SiC nanocomposite shows good mechanical properties.

• Solvothermal synthesis and characterization of acicular 𝛼-Fe2O3 nanoparticles

Nanometer-sized 𝛼-Fe2O3 particles have been prepared by a simple solvothermal method using ferric acetylacetonate as a precursor. The products were characterized by X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDAX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transition electron microscopy (TEM), infrared spectroscopy (IR) and thermal analysis (TG–DTA). XRD indicates that the product is single-phase 𝛼-Fe2O3 with rhombohedral structure. Bundles of acicular shaped nanoparticles are seen in TEM images with an aspect ratio ∼ 12; typically 8–12 nm wide and over 150 nm long. The 𝛼-Fe2O3 nanoparticles posses a high thermal stability, as observed on thermal analysis traces.

• Barium ferrite nanoparticles prepared by self-propagating low-temperature combustion method and its characterization

The barium ferrite particles were prepared using a self-propagating low-temperature combustion method using polyethylene glycol (PEG) as a fuel. The process was investigated with simultaneous thermogravimetric-differential thermal analysis (TG–DTA). The crystalline structure, morphology and the magnetic properties of the barium ferrite particles were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and SQUID susceptometer. The results show that the ignition temperature of PEG is lower compared with other combustion methods and gives nanocrystalline barium ferrite.

• Synthesis and characterization of zinc ferrite nanoparticles obtained by self-propagating low-temperature combustion method

The self-propagating low-temperature combustion method was used to produce nanocrystalline particles of zinc ferrite. The products were characterized for chemical and phase composition, morphology and magnetic properties. The results obtained showed the formation of single-phase zinc ferrite nanoparticles with an average particle size of about 40 nm. As-synthesized powder displayed good magnetic property. Due to the simplicity and low cost of this process, it could also become a valuable starting point for the generation of other mixed and complex ferrites.

• Synthesis of one-dimensional N-doped Ga2O3 nanostructures: different morphologies and different mechanisms

N-doped monoclinic Ga2O3 nanostructures of different morphologies have been synthesized by heating Ga metal in ambient air at 1150°C to 1350°C for 1 to 5 h duration. Neither catalyst nor any gas flow has been used for the synthesis of N-doped Ga2O3 nanostructures. The morphology was controlled by monitoring the curvature of the Ga droplet. Plausible growth mechanisms are discussed to explain the different morphology of the nanostructures. Elemental mapping by electron energy loss spectroscopy of the nanostructures indicate uniform distribution of Ga, O and N. It is interesting to note that we have used neither nitride source nor any gas flow but the synthesis was carried out in ambient air. We believe that ambient nitrogen acts as the source of nitrogen. Unintentional nitrogen doping of the Ga2O3 nanostructures is a straightforward method and such nanostructures could be promising candidates for white light emission.

• Synthesis and characterization of mixture of nanozirconia and nanosilica obtained from commercially available zircon flour by sol–gel method

In this paper we present the results of our patented (application filed in India) process for synthesizing a mixture of nanozirconia and nanosilica, obtained by the sol–gel method from commercially available zircon flour and hydrofluoric acid at low temperatures (∼ 100°C). Within the scope of this study, 99.2% dissolution of zircon was obtained by using 40% HF for a solid–liquid (S/L) ratio of 0.05 for a digestion period of 120 h. The nanoparticles, characterized by XRD, SEM and TEM techniques, were found to be largely spherical in shape and the average size of the particles was found to be less than 5 nm. Within the product, zirconiarich and silica-rich regions were found to exist.

• Influence of preparation method on structural and magnetic properties of nickel ferrite nanoparticles

Nickel ferrite nanoparticles of very small size were prepared by sol–gel combustion and co-precipitation techniques. At the same annealing temperature sol–gel derived particles had bigger crystallite size. In both methods, crystallite size of the particles increased with annealing temperature. Sol–gel derived nickel ferrite particles were found to be of almost spherical shape and moderate particle size with a narrow size distribution; while co-precipitation derived particles had irregular shape and very small particle size with a wide size distribution. Nickel ferrite particles produced by sol–gel method exhibited more purity. Sol–gel synthesized nanoparticles were found to be of high saturation magnetization and hysteresis. Co-precipitation derived nickel ferrite particles, annealed at 400°C exhibited superparamagnetic nature with small saturation magnetization. Saturation magnetization increased with annealing temperature in both the methods. At the annealing temperature of 600°C, co-precipitation derived particles also became ferrimagnetic.

• Photoconductivity and high-field effects in amorphous Se83Te15Zn2 thin film

The glassy alloy of Se83Te15Zn2 has been prepared by conventional rapid melt-quenching technique. The glassy nature of the prepared alloy is confirmed through X-ray diffraction (XRD) technique. A thin film of the aforesaid material was prepared by thermal evaporation technique. Coplanar indium electrode was used. Current–voltage (𝐼–𝑉) characteristics and photoconductivity measurements were obtained. At low electric field, ohmic, and at high electric fields (𝐸 ∼ 104 V/cm), non-ohmic behaviour was observed. An analysis of the experimental data confirms the presence of space charge limited conduction (SCLC) in the glassy material studied in the present case. From the fitting of the data to the theory of SCLC, the density of defect states (DOS) near the Fermi level was calculated. Temperature dependence of conductivity in dark as well as in the presence of light shows that conduction is through a thermally activated process in both the cases. The activation energy is found to decrease with the increase in light intensity. This indicates the shift of the Fermi level with intensity. Transient photoconductivity measurements at different temperatures indicate that the decay of photoconductivity is quite slow, which is found to be non-exponential in the present case, indicating the presence of a continuous distribution of defect states in the aforesaid glassy alloy.

• Using speciation diagrams to improve synthesis of magnetic nanosorbents for environmental applications

This work addresses environmental applications of magnetic nanoparticles. We highlight the chemical design of filtration aids based on magnetic nanoferrites coated with specific ligands potentially used in magnetic separation of pollutants from water. From electrochemical measurements, we determined the concentration of the surface sites in function of pH for the precursor magnetic nanoparticles. Then, coupling the speciation diagrams of the precursor nanoferrite particle surface with that of the specific ligand, it was possible to provide a theoretical prediction of the optimal pH for particle surface–ligand complexation, leading to advances in nanosorbents developing.

• Effect of aging on copper nanoparticles synthesized by pulsed laser ablation in water: structural and optical characterizations

Effect of aging on copper nanoparticles synthesized by pulsed laser ablation of copper plate in water was studied. By characterization studies of the aged nanoparticles, it is found that copper nanoparticles converted into Cu@Cu2O nanostructure. The synthesized nanomaterial is characterized with UV-Visible absorption, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman and photoluminescence (PL) spectroscopic techniques. TEM image shows that the aged nanoparticles get assembled into cactus like structure and are spherical in shape with average diameter 7 nm and dispersion 2 nm. XRD and FTIR spectrum confirm the formation of Cu@Cu2O in the aged sample. Raman spectrum also confirms the presence of Cu2O nanoparticles. PL spectrum of the aged nanoparticles shows a direct allowed transition with bandgap energy of 2.24 eV. The mechanism for synthesis of core-shell nanoparticles and formation of self-assembly of nanoparticles is also discussed.

• Hydrothermal synthesis of NaEuF4 spindle-like nanocrystals

NaEuF4 spindle-like nanocrystals have been synthesized through a simple hydrothermal method. The nanocrystals were well crystallized and exhibited fine morphology, as indicated by X-ray diffraction, transmission electron microscope and selected area electron diffractometer. The luminescence properties of these NaEuF4 products were investigated.

• Laser annealing of sputter-deposited 𝑎-SiC and 𝑎-SiC𝑥N𝑦 films

This work describes the laser annealing of 𝑎-SiC and 𝑎-SiC𝑥N𝑦 films deposited on (100) Si and quartz substrates by RF magnetron sputtering. Two samples of 𝑎-SiC𝑥N𝑦 thin films were produced under different N2/Ar flow ratios. Rutherford backscattering spectroscopy (RBS), Raman analysis and Fourier transform infrared spectrometry (FTIR) techniques were used to investigate the composition and bonding structure of as-deposited and laser annealed SiC and SiC𝑥N𝑦 films.

• Preparation and characterization of LaNiO3 films grown by metal–organic deposition

We have investigated the synthesis and characterization of LaNiO3 (LNO) layers deposited on YSZ (100) substrate by metal–organic deposition (MOD). Texture, morphology and electrical properties of the LaNiO3 films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and electrical resistivity measurement. It has been found that the formation of (ℎ00) orientation depends on pyrolysis temperature, annealing temperature and thickness of LaNiO3 layers. The LaNiO3 films prepared under optimal condition indicate highly (ℎ00) orientation and a rather smooth surface. The LaNiO3 films show a metallic behaviour in the measured temperature range.

• Effect of Mn doping on electrical properties and accelerated ageing behaviours of ternary ZVM varistors

The electrical properties and d.c. accelerated ageing behaviour of ZVM (Zn–V–Mn) ceramics were investigated with different valences and contents of Mn. The incorporation of Mn into the ZV ceramics was found to restrict the abnormal grain growth of ZnO. The nonlinear properties and stability against the d.c. accelerated ageing stress are significantly affected by different valences and contents of Mn. The high valence of Mn (Mn4+) in the ZVM ceramics resulted in better nonlinear properties than low valence of Mn (Mn2.66+). Furthermore, an increase in doping level of MnO2 greatly improved its nonlinear properties. The ZVM ceramics doped with 2 mol% MnO2 exhibited not only a high nonlinearity, in which the nonlinear coefficient is 27 and the leakage current density is 0.042 mA/cm2, but also a good stability, in which %𝛥 𝐸1\ mA = –2.1%, %𝛥 𝛼 = –25.9% for the d.c. accelerated ageing stress of 0.85 𝐸1\ mA/85°C/24 h.

• Dielectric and impedance spectroscopic studies of (Sr1–𝑥Pb𝑥)TiO2 glass ceramics with addition of Nb2O5

Glasses were made by melt-quench method in the system [(Sr1–𝑥Pb𝑥)O.TiO2]–[2SiO2.B2O3]–5[K2O–BaO] (0.0 ≤ 𝑥 ≤ 0.4) with addition of 1 mol% Nb2O5. Perovskite strontium lead titanate in solid solution phase has been crystallized in borosilicate glassy matrix with suitable choice of composition and heat treatment schedule. Addition of 1 mol% of Nb2O5 enhances the crystallization of lead strontium titanate phase in the glassy matrix. Scanning electron microscopy (SEM) is performed to study the surface morphology of the crystallites and crystalline interface to the glass. Dielectric properties of these glass ceramics were studied by measuring capacitance and dissipation factor as a function of temperature at a few selected frequencies. Nb2O5 doped strontium lead titanate glass ceramic shows a high value of dielectric constant. It is of the order of 10,000 while the dielectric constant of undoped glass ceramic sample is of the order of 500. Complex impedance and modulus spectroscopic techniques were used to find out the contributions of polarization of crystallites and glass crystal interfaces to the resulting dielectric behaviour.

• Dielectric behaviour of Pb-substituted BZT ceramics

Material series with compositional formula Ba1.0–𝑥Pb𝑥Ti0.90Zr0.10O3 (0 ≤ 𝑥 ≤ 0.20, in steps of 0.05) were prepared by conventional solid state method. All the samples were subjected to X-ray diffraction (XRD) studies and found to be single phase with perovskite structure. SEM measurements were done in order to collect micro-structural information. Different transition temperatures were found to depend on the Pb content. Tetragonality (𝑐/𝑎) and Curie temperature (𝑇c) increase with increase in lead content 𝑥. Dielectric properties were studied as a function of temperature and frequencies.

• High performance of low cost soft magnetic materials

The consistent interest in supporting research and development of magnetic materials during the last century is revealed in their steadily increasing market. In this work, the soft magnetic nanocrystalline FINEMET alloy was prepared with commercial purity raw materials and compared for the first time with the generally studied high purity one. The exhaustive characterization covers several diverse techniques: X-ray diffraction, Mössbauer spectroscopy, differential scanning calorimetry, differential thermal analysis and magnetic properties. In addition, a brief economic analysis is presented. For the alloys annealed at 813 K, the value of the grain size was 16 nm with 19.5% of Si, the coercivity was 0.30 A m-1 while the saturation was 1.2 T. These results prove that structural, magnetic and thermal properties of this material are very close to the expensive high purity FINEMET alloy, while a cost reduction of almost 98% seems highly attractive for laboratories and industry. The analysis should be useful not only for the production of FINEMETs, but for other type of systems with similar constitutive elements as well, including soft and hard magnetic materials.

• Influence of temperature on structural and magnetic properties of Co0.5Mn0.5Fe2O4 ferrites

Co0.5Mn0.5Fe2O4 ferrites have been synthesized using a single-step sol–gel auto-combustion method in which the metal nitrate (MN)-to-citric acid (CA) ratio was adjusted to 0.5 : 1 and pH to 7, respectively. The structural and magnetic properties of as-burnt and annealed samples were studied as a function of temperature. The inverse spinel structure was confirmed by X-ray diffraction (XRD) and crystallite size was estimated by the most intense peak (311) using Scherrer’s formula. Contrary to earlier studies reported in the literature, both as-burnt and annealed samples exhibit crystalline behaviour. Room temperature magnetic properties were studied using vibrating sample magnetometer (VSM) with field strengths up to ± 10 kOe. Lattice constant and crystallite size increased as the annealing temperature was increased. However, the coercivity (𝐻c) initially increased and then decreased with the increase of crystallite size. The variation in coercivity is ascribed to the transition from a multi-domain to a single-domain configuration.

• Effect of thermomechanical processing on evolution of various phases in Ti–Nb alloys

This paper deals with the effect of thermomechanical processing on microstructural evolution of three alloys, viz. Ti–8Nb, Ti–12Nb and Ti–16Nb. The alloys were hot rolled at 800°C and then subjected to various heat treatments. Samples from hot-rolled alloys were given solution-treatment in 𝛽 and 𝛼 + 𝛽 phase fields, respectively followed by water quenching and furnace cooling. The solution-treated alloys were subsequently aged at different temperatures for 24 h. Phases evolved after various heat treatments were studied using X-ray diffractometer, optical, scanning and transmission electron microscopes. The alloy Ti–8Nb exhibits 𝛼 and 𝛽 phases while the alloys Ti–12Nb and Ti–16Nb show the presence of 𝛼'', 𝛽 and 𝜔 phases in the as-cast and hot-rolled conditions. The 𝛽 solution treated and water quenched specimen of the alloy Ti–8Nb displays 𝛼'' phase while the alloys Ti–12Nb and Ti–16Nb exhibit 𝛼'', 𝛽 and 𝜔 phases. The alloy Ti–8Nb shows the presence of 𝛼, 𝛽 and 𝜔 phases while those of Ti–12Nb and Ti–16Nb display the presence of 𝛼, 𝛼'', 𝛽 and 𝜔 in 𝛼 + 𝛽 solution treated and water quenched condition. The observation of 𝜔 phase in solution treated condition depends on the cooling rate and the Nb content while in the aged specimens, it is governed by aging temperature as well as the Nb content.

• Annealing twins in a multifunctional beta Ti–Nb–Ta–Zr–O alloy

The grain boundary character distribution and annealing twins in a multifunctional 𝛽-type Ti–23Nb–0.7Ta–2Zr–O alloy having a stable bcc phase structure are investigated by electron backscattering diffraction (EBSD). The results show that the coincident site lattice (CSL) boundaries, including 𝛴 3 and 𝛴 11 twin boundaries mainly form at the early stage of recrystallization. {112}$\langle$111$\rangle$ and {332} $\langle$113$\rangle$ annealing twins are observed to occur in the completely recrystallized Ti–23Nb–0.7Ta–2Zr–O alloy.

• Heat treatment and effects of Cr and Ni in low alloy steel

The effects of Cr and Ni on low carbon steel was observed. Undissolved carbide particles refine the austenite grain size. In the presence of nickel, chromium carbide is less effective in austenite grain refinement than chromium carbide in absence of nickel at temperature below 975°C. Nickel does not produce any austenite grain refinement but presence of nickel promotes the formation of acicular ferrites. It was also found that Ni and Cr as chromium carbide also refines the ferrite grain size and morphology. Cr as chromium carbide is more effective in refining ferrite grain size than nickel.

• Low temperature enhanced ductility of friction stir processed 5083 aluminum alloy

Commercial 5083 Al rolled plates were subjected to friction stir processing (FSP) with two different processing parameters, having 430 and 850 rpm tool rotational speed with a single traverse feed rate of 90 mm/min. These FSP conditions resulted in two fine grained microstructures of 0.95 𝜇m (430 rpm) and 2.6 𝜇m (850 rpm). Tensile elongations were measured at a relatively low temperature of 250°C at three strain rates, and demonstrated that a decrease in grain size resulted in significantly enhanced ductility and lower forming loads. The occurrence of a relatively high value of strain rate sensitivity, 𝑚 of 0.45 for a grain size of 0.95 𝜇m, suggests the operation of superplastic deformation under these present experimental conditions.

• Small-angle scattering from GP zones in Al–Cu alloy

It is well known that Guinier Preston (GP) zones form in Al–Cu alloys upon solutionizing and artificial aging, which are extensively used in commercial practice. It is well established that GP zones are discshaped precipitates, i.e. disks of clusters of copper atoms in the FCC aluminium matrix. These disks have coherency strain fields in aluminium that give the alloy its high yield strength. The formation of GP zones in the supersaturated aluminium matrix is thought to be heterogeneous nucleation and growth. Some authors have believed that the formation of GP zones is by spinodal decomposition of the supersaturated Al–Cu solid solution. The main objective of the present work is to test whether spinodal decomposition is responsible for the formation of GP zones in Al–Cu alloy. The experimental alloy AA2219 was selected for its high copper content (Al–6%Cu–0.2%Zr). After solutionizing and artificial aging, the aging curve was plotted and smallangle scattering experiments were carried on the powdered samples as a function of time during artificial aging. Small-angle scattering data were analysed, and evidence has been obtained for the occurrence of spinodal decomposition as the mechanism responsible in the early stages of formation of GP zones.

• Calorimetric studies of non-isothermal crystallization in amorphous Cu𝑥Ti100–𝑥 alloys

The present paper reports the composition dependence of pre-exponential factor and activation energy of non-isothermal crystallization in amorphous alloys of Cu𝑥Ti100–𝑥 system using differential scanning calorimeter (DSC) technique. The applicability of Meyer–Neldel relation between the pre-exponential factor and activation energy of non-isothermal crystallization for amorphous alloys of Cu–Ti system was verified.

• Effect of ageing treatment on wear properties and electrical conductivity of Cu–Cr–Zr alloy

In this study, the effect of ageing processes on the wear behaviour and electrical conductivity was investigated. Prior to solid solution heat treatment at 920°C and ageing at 470°C, 500°C and 530°C for 1 h, 2 h and 3 h, respectively, the prepared samples were homogenized at 920°C for 1 h. After the ageing processes, all samples were characterized in terms of electrical conductivity, scanning electron microscope (with energy dispersive X-ray spectrum (EDS)) and hardness (HV5). In wear tests, pin-on-disc type standard wearing unit was used. As a result, starting from 1 h aged specimens, orderly increase of electrical conductivity was defined. From EDS analyses it was observed that Cr rate increases as precipitates grow. With increase of Cr rate there was also a defined rise of electrical conductivity. From the wear tests, it was observed that the least wear loss was in Cu–Cr–Zr alloy aged at 500°C for 2 h and the most wear loss was in specimens aged at 530°C for 2 h. Furthermore, it was observed that the friction coefficient values resulting from wear rate were overlapped with hardness results and there is a decrease tendency of friction coefficient as wear distance increases.

• Effect of grain boundary misorientation on discontinuous precipitation in an AZ91 alloy

A scanning electron microscopy (SEM)-based electron backscatter diffraction (EBSD) analysis showed that the discontinuous precipitation (DP) reaction rate was dependent on the geometry of the grain boundary in Mg–9Al–1Zn (wt.%) alloys. DP converted a supersaturated solid solution, 𝛿0 (magnesium (Mg)-rich solid solution), into a two-phase 𝛿 + 𝛾 aggregate, with 𝛿 being a precipitated Mg17Al12 (intermetallic phase) behind a migrating reaction front. The near-special grain boundary was rather inactive, whereas most of the random high-angle boundaries promoted the reaction. Prior deformation (hot rolling to achieve up to 80% thickness reduction) had no effect on the frequency of special-grain boundaries.

• Rapid heating effects on grain-size, texture and magnetic properties of 3% Si non-oriented electrical steel

The rapid heating effects on the microstructure, texture and magnetic properties of 3% Si nonoriented electrical steel has been investigated through optical microscopy, X-ray diffraction and Epstein frame. The results show that recrystallized grains were refined with increased heating rate, caused by the nucleation rate increase, which is faster than the growth rate due to rapid hearting. With the heating rate increase, the characteristic {111} recrystallization fibre of cold-rolled steel was depressed, but the beneficial $\langle$001$\rangle$//RD and $\langle$001$\rangle$//ND fibres were significantly strengthened. Although the grain-size decreases with heating rate increasing, the optimal magnetic properties can also be obtained through the recrystallized grain-size and texture optimization by rapid heating. In this research, we find the magnetic properties optimization can be obtained when annealed with 100°C/s heating rate: the core loss ($P_{1.5/50}$) decrease 13% and the magnetic induction ($B_{50}$) increase 3%.

• Effect of Zr on dielectric, ferroelectric and impedance properties of BaTiO3 ceramic

A polycrystalline sample of Zr-doped barium titanate (BaTiO3) was prepared by conventional solid state reaction method. The effect of Zr (0.15) on the structural and microstructural properties of BaTiO3 was investigated by XRD and SEM. The electrical properties (dielectric, ferroelectric and impedance spectroscopy) were measured in wide range of frequency and temperature. With substitutions of Zr, the structure of BaTiO3 changes from tetragonal to rhombohedral. Lattice parameters were found to increase with substitution. The room temperature dielectric constant increases from ∼ 1675 to ∼ 10586 and peak dielectric constant value increases from ∼ 13626 to ∼ 21023 with diffuse phase transition. Impedance spectroscopy reveals the formation of grain and grain boundary in the material and found to decrease with increase in temperature.

• Effect of substitution of titanium by magnesium and niobium on structure and piezoelectric properties in (Bi1/2Na1/2)TiO3 ceramics

To develop new (Bi1/2Na1/2)TiO3-based ceramics with excellent piezoelectric properties, the similarities and the differences between PZT and (Bi1/2Na1/2)TiO3 ceramics were analysed. Based on the analysis, a new (Bi1/2Na1/2)TiO3-based piezoelectric ceramic of B-site substitution of complex ions (Mg1/3Nb2/3)4+ for Ti4+ was prepared by a conventional ceramic technique, and the effect of complex ions (Mg1/3Nb2/3)4+ addition on the microstructure, dielectric and piezoelectric properties was investigated. The research results show that all compositions are mono-perovskite phase and the grain size increases with increasing content of (Mg1/3Nb2/3)4+. The piezoelectric constant $d_{33}$ first increases and then decreases, and electromechanical coupling factor $k_{p}$ varies insignificantly with increasing content of (Mg1/3Nb2/3)4+.

• Mathematical aspects of Rietveld refinement and crystal structure studies on PbTiO3 ceramics

The core mathematics, goodness-of-fit parameters of Rietveld refinement technique is introduced for structural analysis of crystalline materials not available as single crystals. X-ray diffraction (XRD) patterns of PbTiO3 compound prepared by following solid-state route, suggests it to be in single crystal form. All the observed peaks could be indexed to $P4mm$ space group with tetragonal symmetry. XRD pattern is analysed by employing Rietveld method. The unit cell parameters are found to be 𝑎 = 𝑏 = 3.8987 (0.0008) Å and 𝑐 = 4.1380 (0.0009) Å. The axial ratio 𝑐/𝑎 and unit cell volume are found to be 1.0614 and 62.896 (0.023) Å3. Bond lengths and angles are calculated using the cell parameters. Using the Rietveld refinement parameters a stable PbTiO3 structure is suggested.

• Ce-doped LCMO CMR manganites: a consequence of enhanced $T_{c}$ and $T_{\text{IM}}$

A series of Ce-doped (1–20 mol%) La0.67Ca0.33MnO3 (LCMO) sintered (1400°C) ceramic samples were prepared by the solid-state reaction route. The significant enhancement of metal insulator transition temperature ($T_{\text{IM}} \approx$ 280 K) and Curie transition temperature ($T_{c} \approx$ 270 K) associated with LCMO system by the addition of 10 mol% of Ce has been observed. Further interesting observation showed that both low (≈ 1 mol%) and high (≥ 15 and 20 mol%) level of Ce-doping in LCMO reduced the $T_{\text{IM}}$ appreciably from 280 K to 220 K, and from 100 to 160 K, respectively exhibiting the signature of a unique spin glass transitions at around 30 K. Structural and spectroscopic studies revealed that unreacted CeO2 and MnO2 phases are found to be present in 1, 15, 20 mol% Ce-doped LCMO samples, which is one of the reasons why they show spin glass transition at low temperature. Our present results on bulk Ce-doped (10 mol%) LCMO are found to be encouraging as far as $T_{\text{IM}}$ of epitaxial La0.7Ce0.3MnO3 thin film ($T_{\text{IM}} \approx$ 250 K) is concerned. This finding suggests that single-phase materials of Ce-doped (10 mol%) LCMO can be prepared with enhanced $T_{\text{IM}}$ effectively using solid-state reaction route.

• Formation of ternary Mg–Cu–Dy bulk metallic glasses

The glass-forming ability (GFA) of ternary Mg–Cu–Dy alloys was systematically investigated by using differential scanning calorimetry (DSC) and X-ray diffractometry (XRD) techniques. The results showed that a series of ternary Mg–Cu–Dy bulk metallic glasses (BGMs) with a diameter of 4–8 mm were successfully fabricated in the system with conventional Cu-mold casting method. Mg55Cu32Dy13, Mg60Cu27Dy13, Mg65Cu25Dy10 and Mg70Cu17Dy13 BMGs exhibit a clear glass transition, a broad supercooled liquid region and different crystallization and melting behaviours. They have supercooled liquid region ($\Delta T_{x}$) from 41 K to 65 K, reduced glass transition temperature ($T_{rg}$) from 0.5363 to 0.5974 and 𝛾 parameter from 0.4038 to 0.4136. The 𝛾 shows a relatively good agreement with the GFA of the BGMs. On the other hand, a high fracture compressive strength of 624 MPa was obtained for Mg60Cu27Dy13 BMG.

• Effects of MO (M = Mg, Ca, Ba) on crystallization and flexural strength of semi-transparent lithium disilicate glass–ceramics

In this study, semitransparent lithium disilicate glass–ceramics in the Li2O–K2O–Al2O3–Y2O3–La2O3–SiO2 system was investigated by incorporation of P2O5 as nucleation agent and alkaline earth oxides as additive. The influence of alkaline earth oxides on the structure of glasses network, crystalline phases, microstructure and mechanical properties were investigated by means of Raman spectra, differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The mechanical strength was measured corresponding to norm ISO 6872. The Raman spectra predominantly showed that small additions of alkaline earth oxides not only form asymmetrical vibrations of the M–Si–O bonds, but also enhance the intensities of symmetrical vibrations of the P–O bonds, making the glass network more stable. And the small additions of CaO or BaO has more influence on the crystallization behaviour, crystalline phase, microstructure and mechanical properties of the glass–ceramics than the addition of MgO. The additions of alkaline earth oxides enhanced the first exothermic peak temperature but decreased the flexural strength of lithium disilicate glass–ceramics.

• Superconducting state parameters of ternary metallic glasses

The well-known empty core (EMC) model potential of Ashcroft was used to study the theoretical investigation of the superconducting state parameters (SSP) viz. electron–phonon coupling strength 𝜆, Coulomb pseudopotential $\mu^{\ast}$, transition temperature $T_{C}$, isotope effect exponent 𝛼 and effective interaction strength $N_{O}V$ of some ternary metallic glasses. Most recent local field correction function due to Sarkar et al is used to study the screening influence on the aforesaid properties. Quadratic $T_{C}$ equations have been proposed and found successful. Also, the present findings are found to be in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the ternary superconductors. The pseudo-alloy-atom (PAA) model was applied for the first time instead of Vegard’s law.

• Effect of complexing salt on conductivity of PVC/PEO polymer blend electrolytes

Solid polymer electrolyte membrane comprising poly(vinyl chloride) (PVC), poly(ehylene oxide) (PEO) and different lithium salts (LiClO4, LiBF4 and LiCF3SO3) were prepared by the solution casting technique. The effect of complexing salt on the ionic conductivity of the PVC/PEO host polymer is discussed. Solid polymer electrolyte films were characterized by X-ray diffraction, FTIR spectroscopy, TG/DTA and ac impedance spectroscopic studies. The conductivity studies of these solid polymer electrolyte (SPE) films are carried out as a function of frequency at various temperatures ranging from 302 K to 353 K. The maximum room temperature ionic conductivity is found to be 0.079 × 10-4 S cm-1 for the film containing LiBF4 as the complexing salt. The temperature dependence of the conductivity of polymer electrolyte films seems to obey the Vogel–Tamman–Fulcher (VTF) relation.

• Preparation of semi-IPN(BA–VAc–VAE) by emulsion polymerization and its properties investigation

A semi-interpenetrating polymer network (semi-IPN) combining vinyl acetate–ethylene (VAE) and butyl acrylate (BA), as well as vinyl acetate (VAc), was prepared through emulsion polymerization with the help of self-made dispersant and diethylene glycol diacrylate (DEGDA), the cross-linking agent. Both the dispersant and DEGDA had significant contribution on the preparation of semi-IPN(BA–VAc–VAE). And, the DEGDA had a strong influence on the conversion of polymerization system. The effects of emulsifiers and their amounts on the stability of obtained emulsions have been determined, and the best choices have been made after series experiments. The optical microscopy (OM), FTIR and DSC methods were adopted to characterize the structure and composition, morphology, and Tg of the prepared emulsions, respectively. Various comparisons have been made between the semi-IPN and VAE emulsions, and the experimental results indicated that the semi-IPN(BA–VAc–VAE) had been developed with improved properties in both water resistance and adhesion.

• Synthesis and characterization of polycaprolactone/acrylic acid (PCL/AA) hydrogel for controlled drug delivery

In the present work biodegradable pH-sensitive polycaprolactone/acrylic acid (PCL/AA) hydrogels have been developed using ethylene glycol dimethacrylate (EGDMA) as a cross-linker and benzoyl peroxide as initiator. For these prepared hydrogels swelling studies, sol–gel fraction analysis and porosity measurements were performed. Results show that swelling of the hydrogels decreases on increasing the concentration of PCL and EGDMA, however swelling of hydrogels increases on increasing the concentration of AA. Results of sol–gel fraction analysis show that gel fraction increases on increasing concentration of monomer AA, polymer PCL as well as cross-linker EGDMA. As far as porosity is concerned, it increases on increasing the concentration of AA and PCL while porosity decreases on increasing the concentration of EGDMA. Hydrogels were characterized by measuring diffusion coefficient (𝐷) and equilibrium water content (EWC). Network formation, morphology and crystallinity of PCL/AA hydrogels were investigated using FTIR, SEM and XRD, respectively. Tramadol hydrochloride was loaded as model drug and its release pattern was analysed using various kinetic models like zero order, first order, Higuchi and Peppas. Results indicated that most of the samples followed non-Fickian release mechanism.

• Tribological effects of polymer surface modification through plastic deformation

The efficacy of using polymers in cylindrical applications depends closely on its surface friction and wear characteristics. In this regard, a surface modification technique through plastic deformation has been implemented. Roller burnishing is commonly used to improve the surface quality of non-ferrous surfaces, but no work showed concern about roller burnishing as a polymer surface treatment process. The objective of the present work is to investigate the influence of burnishing force and burnishing speed on the friction and wear performance of acetal homopolymer and polyurethane under dry and lubricated sliding conditions. The results reveal that the coefficient of friction and wear rate decreased to a minimum value and then increased as higher burnishing force and speed were applied. It was shown that roller burnishing had favourable prospective to be utilized as a valuable polymer surface treatment technique.

• Synthesis, characterization and magnetic properties of polyaniline/𝛾-Fe2O3 composites

Conducting polyaniline/𝛾-Fe2O3 (PANI/FE) composites have been synthesized using an in situ deposition technique by placing fine-graded 𝛾-Fe2O3 in a polymerization mixture of aniline. The composites are characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and infrared (IR) spectroscopy. The electrical properties such as d.c. and a.c. conductivities are studied by sandwitching the pellets of these composites between the silver electrodes. It is observed that the conductivity increases up to a composition of 20 wt.% of 𝛾-Fe2O3 in polyaniline and decreases thereafter. The initial increase in conductivity is attributed to the extended chain length of polyaniline, where polarons possess sufficient energy to hop between favourable sites. Beyond 20 wt.% of 𝛾-Fe2O3 in polyaniline, the blocking of charge carrier hop occurs, reducing conductivity values. The magnetic properties such as hysteresis characteristics and normalized a.c. susceptibility are also measured, which show a strong dependence on content of 𝛾-Fe2O3 in polyaniline. Because of superparamagnetic behaviour of these composites, they may find extensive technological applications, especially for absorbing and shielding applications in microwave frequencies.

• Drilling analysis of coir–fibre-reinforced polyester composites

An investigation has been carried out to make use of coir, a natural fibre abundantly available in India. Coir–polyester composites were prepared and their mechanical and machinability characteristics were studied. The short coir–fibre-reinforced composites exhibited the tensile, flexural and impact strength of 16.1709 MPa, 29.2611 MPa and 46.1740 J/m, respectively. The regression equations were developed and optimized for studying drilling characteristics of coir–polyester composites using the Taguchi approach. A drill bit diameter of 6 mm, spindle speed of 600 rpm and feed rate of 0.3 mm/rev gave the minimum value of thrust force, torque and tool wear in drilling analysis.

• Effect of ZnO loading technique on textural characteristic and methyl blue removal capacity of exfoliated graphite/ZnO composites

Two exfoliated graphite/ZnO composites, marked as EG/ZnO-1 and EG/ZnO-2, were prepared by heating a mixture of expandable graphite and Zn(OH)2 or a mixture of expanded graphite (EG) and Zn(OH)2, respectively. The composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and nitrogen adsorption. Under UV irradiation, the composites were used for removing methyl blue (MB) from aqueous solution. For the composites made from expandable graphite (EG/ZnO-1), the micronsized ZnO particle agglomerates (1–20 𝜇m) heterogeneously distributed at the surface of graphite flakes, while for the composites made from EG (EG/ZnO-2), the submicron-sized ZnO particle masses (0.2–0.5 𝜇m) almost homogeneously located both at the surface and interior of graphite flakes. In the presence of UV irradiation, the composites had the adsorption capacity of EG and the photocatalysis capacity of ZnO at the same time. Compared with EG/ZnO-1, EG/ZnO-2 was more effective in removing MB. After 2 h of UV irradiation, MB could be completely removed by using the EG/ZnO-2 containing 45% ZnO, and the decomposition efficiency of the ZnO was the primary cause for the removal of MB.

• Effect of fibre content and alkali treatment on mechanical properties of Roystonea regia-reinforced epoxy partially biodegradable composites

The present paper investigates the effect of fibre content and alkali treatment on tensile, flexural and impact properties of unidirectional Roystonea regia natural-fibre-reinforced epoxy composites which are partially biodegradable. The reinforcement Roystonea regia (royal palm) fibre was collected from the foliage of locally available royal palm tree through the process of water retting and mechanical extraction. The poor adhesion between fibre and matrix is commonly encountered problem in natural-fibre-reinforced composites. To overcome this problem, specific physical and chemical treatments were suggested for surface modification of fibres by investigators. Alkali treatment is one of the simple and effective surface modification techniques which is widely used in natural fibre composites. In the present study both untreated and alkali-treated fibres were used as reinforcement in Roystonea regia epoxy composites and the tensile, flexural and impact properties were determined at different fibre contents. The alkali treatment found to be effective in improving the tensile and flexural properties while the impact strength decreased.

• Changes in microstructural parameters of NB4D2 silk fibres due to electron irradiation: X-ray line profile analysis

The present study is concerned with changes of microcrystalline parameters in NB4D2 (Bombyx mori) silk fibres, due to electron irradiation. The irradiation process was performed in air at room temperature using 8 MeV electron beam at different dose rates: 0, 25, 50 and 75 kGy, respectively. X-ray recording of these irradiated samples and the line profile analysis were carried out. The crystal imperfection parameters such as crystallite size $\langle N \rangle$, lattice strain (g in %) and surface weighted crystallite size ($D_{s}$) were computed and compared with other physical parameters in order to asertain the changes that have crept into these irradiated fibres. Exponential, lognormal and Reinhold functions for the column length distributions have been used for the determination of these parameters.

• Hot pressing effect on (Bi0.25Sb0.75)2Te3 mechanical and thermoelectric properties

(Bi0.25Sb0.75)2Te3 thermoelectric material is a well known 𝑝 type of compound that has higher figure of merit than other stoichiometries. The crystal of this compound was prepared, pulverized in a particle size ratio of 64% with a mesh of 80 (200 𝜇m2) and 36% with a mesh of 60 (250 𝜇m2). The powder was sintered in a heat up to 350–500°C under pressure of 500 MPa (hot pressing). To find out the temperature effects on thermal conductivity of the sample it was systematically investigated in nano-scale intrinsic structures by systems of X-ray diffraction, scanning electron microscopy and, for only once successful attempt, atomic force microscopy. The acquired images ensured to show homogeneous structures for hot pressed samples. In terms of thermal conductivity and with regard to the figure of merit (𝑍), optimum sintering temperature hovers at around 500°C, which leads to a maximum 𝑍 value of around 1.53 K-1.

• Synthesis and in situ mechanism of nuclei growth of layered double hydroxides

A host–guest material such as layered double hydroxide (LDH) has generated immense interest in current research due to its technological importance, whereby its dimension significantly affect its mechanical and other physical properties. The purpose of this study was to prepare Mg/Al-LDHs by systematically varying the molar concentration of cations, aging time and pH. The prepared LDHs were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis and transmission electron microscopy to confirm their formation and morphology. We qualitatively observed a new growth route for LDH system which is dissimilar to the existing growth mechanism. The rate of growth is shown to be slower than the well known Ostwald ripening process. This unusual behaviour is due to the formation of effective passivation layer by Na+ ions around the generated LDHs nuclei. This suggested growth mechanism will be helpful in further controlling the particle size of other LDH, which may be useful for various future applications.

• Synthesis, characterization and catalytic performance of a novel zeolite ITQ-2-like by treating MCM-22 precursor with H2O2

A novel zeolite material denoted as ITQ-2-like was synthesized by treating MCM-22 precursor with H2O2 and characterized by various physicochemical techniques (X-ray powder diffraction, transmission electron microscopy, thermogravimetric-differential thermal analyses, Fourier transform infrared spectroscopy and nitrogen adsorption–desorption). It was found that not only the organic template could be completely removed but also the morphology and topology structure of MCM-22 precursor was well preserved after H2O2 treatment. Novel zeolite material ITQ-2-like presented relatively ordered cascaded layers in a faceto-face orientation along the 𝑐-axis and exhibited different physicochemical properties in comparison with ITQ-2 and MCM-22 prepared from the same precursor. Moreover, the catalytic behaviour and pore roles of three kinds of Mo-containing catalysts of ITQ-2-like, MCM-22 and ITQ-2 were investigated in the reaction of methane aromatization.

• Effect of thin Mo2C layer on thermal stability of Si/SiO2/Ti/Cu system

The effect of introducing a thin Mo2C (30 nm) layer between Ti and Cu on the thermal stability of Si/SiO2/Ti/Cu system was studied using four-point probe (FPP), scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDAX) and X-ray diffraction (XRD) techniques. The measured value of the sheet resistance in the bi-layered diffusion barrier structure does not show any change up to an annealing temperature of 750°C. The sheet resistance when measured after annealing at 800°C marginally increases but less than twice its value at room temperature. The XRD analysis indicated no copper diffusion and the formation of Cu3Si phase up to 800°C. The bi-layered barrier structure annealed at elevated temperature shows copper-depleted and agglomerated regions. The sheet resistance measurement, study of surface morphology and the XRD analysis confirm that the insertion of thin Mo2C layer increases the thermal stability of the system from 400°C to 750°C. The increased thermal stability of the system is ascribed to longer diffusion path length in the bi-layered system probably because of grain boundaries mismatch at Ti–Mo2C interface.

• Structural, elastic and thermodynamic properties of Ti2SC

The structural parameters, elastic constants and thermodynamic properties of Ti2SC were investigated under pressure and temperature by using first-principles plane-wave pseudopotential density functional theory within the generalized gradient approximation. The obtained results are in agreement with the available experimental data. The bulk moduli along the 𝑎- and 𝑐-axes, $B_{a}$ and $B_{c}$, almost linearly increase with pressure, and the former is always smaller than the latter. The ratio of $B_{c}/B_{a}$ has a trend of gradual increase as the pressure increases. It is found that the elastic constants, anisotropy and Debye temperature of Ti2SC increase with pressure, while axial compressibility along the 𝑎- and 𝑐-axes decreases with pressure. The thermal properties including the equation of state, the Grüneisen parameter 𝛾, the anisotropies $\Delta_{p}, \Delta_{S1}$ and $\Delta_{S2}$, and the heat capacity are estimated at various pressures and temperatures.

• DLTS study of annihilation of oxidation induced deep-level defects in Ni/SiO2/𝑛-Si MOS structures

This paper describes the fabrication of MOS capacitor and DLTS study of annihilation of deeplevel defects upon thermal annealing. Ni/SiO2/𝑛-Si MOS structures fabricated on 𝑛-type Si wafers were investigated for process-induced deep-level defects. The deep-level traps in Si substrates induced during the processing of Ni/SiO2/𝑛-Si have been investigated using deep-level transient spectroscopy (DLTS). A characteristic deep-level defect at 𝐸C = 0.49 eV which was introduced during high-temperature thermal oxidation process was detected. The trap position was found to shift to different energy levels (𝐸C = 0.43, 0.46 and 0.34 eV) during thermal annealing process. The deep-level trap completely anneals at 350°C. Significant reduction in trap density with an increase in recombination life time and substrate doping concentration as a function of isochronal annealing were observed.

• Estimation of vapour pressure and partial pressure of subliming compounds by low-pressure thermogravimetry

A method for the estimation of vapour pressure and partial pressure of subliming compounds under reduced pressure, using rising temperature thermogravimetry, is described in this paper. The method is based on our recently developed procedure to estimate the vapour pressure from ambient pressure thermogravimetric data using Langmuir equation. Using benzoic acid as the calibration standard, vapour pressure–temperature curves are calculated at 80, 160 and 1000 mbar for salicylic acid and vanadyl bis-2,4-pentanedionate, a precursor used for chemical vapour deposition of vanadium oxides. Using a modification of the Langmuir equation, the partial pressure of these materials at different total pressures is also determined as a function of temperature. Such data can be useful for the deposition of multi-metal oxide thin films or doped thin films by chemical vapour deposition (CVD).

• Solid-state titania-based gas sensor for liquefied petroleum gas detection at room temperature

This paper reports the liquefied petroleum gas (LPG) sensing of titanium dioxide (Qualigens, India). Scanning electron micrographs and X-ray diffraction studies of samples were done. SEM shows that the material is porous and has grapes-like morphology before exposure to the LPG. XRD patterns reveal the crystalline nature of the material. The crystallites sizes of the TiO2 were found in the range of 30–75 nm. Variations in resistance with exposure of LPG to the sensing element were observed. The average sensitivity for different volume percentages of gas was estimated. The maximum value of average sensitivity was 1.7 for higher vol.% of LPG. Percentage sensor response (%SR) as a function of time was calculated and its maximum value was 45%. Response time of the sensor was 70 s. The sensor was quite sensitive to LPG and results were found reproducible.

• Fermi-edge singularity in photoluminescence spectra of modulation-doped AlGaAs/InGaAs/GaAs quantum wells

The photoluminescence study of Fermi-edge singularity (FES) in modulation-doped pseudomorphic Al𝑥Ga1–𝑥As/In𝑦Ga1–𝑦As/GaAs quantum well (QW) heterostructures is presented. In the above QW structures the optical transitions between 𝑛 = 1 and 𝑛 = 2 electronic subband to the 𝑛 = 1 heavy hole subband (𝐸11 and 𝐸21 transitions, respectively) are observed with FES appearing as a lower energy shoulder to the 𝐸21 transition. The observed FES is attributed to the Fermi wave vector in the first electronic subband under the conditions of population of the second electronic subband. The FES appears at about 10 meV below 𝐸21 transition around 4.2 K. Initially it gets stronger with increasing temperature and becomes a distinct peak at about 20 K. Further increase in temperature quenches FES and reaches the base line at around 40 K.

• Blue-shifted photoluminescence of Alq3 dispersed in PMMA

Alq3 is known to emit bright green light under UV excitation. Blue shift of the emission was reported in recent literature. This was ascribed to the presence of various isomers/crystallographic modifications obtained through train sublimation. Here a blue shift was reported for Alq3 dispersed in PMMA. No isomers/phases, which were reponsible for blue-shift, separated and yet the emission maxima shift to shorter wavelengths as the concentration of Alq3 in PMMA decreases. The results were interpreted on the basis of cross relaxation between interacting Alq3 molecules.

• Spray-drying of alumina powder for APS: effect of slurry properties and drying conditions upon particle size and morphology of feedstock

In this paper, effects of variables concerning slurry properties and drying conditions on the particle size and morphology of feedstock were discussed. The results indicated that, the increase of powder loading increased 𝐷50 and volume content but reduced recovery rate slightly. Other variables, such as inlet temperature, showed a maximum on the desired property. The particle size of resulting feedstock increased with the rise of feeding rate of slurry, however, decreased with the increase of atomization pressure based on the premise that atomization pressure was enough to force slurry to form the liquid membrane. For preparation of spherical feedstock, optimized variables were as follows: 60 wt.% powder in slurry, 2 wt.% PVA in slurry, inlet temperature of 60°C, atomization pressure of 13 × 103 KPa and feeding rate of 12 ml min-1. The volume content of feedstocks with 10–45 𝜇m was above 65% and for 𝐷50 it was 15.42 𝜇m. In addition, according to the heat and mass transfer equation, the drying mechanism was established, which was well in agreement with the experimental results.

• Effect of size of fly ash particle on enhancement of mullite content and glass formation

Quartz is widely replaced by fly ash in traditional porcelain composite. Increased strength and stability of the fly ash-mixed composite depends on the quantity and crystallinity of the mullite phase in the fly ash. Our aim in this investigation is to increase the formation of mullite in nanocrystalline form and study the effect of temperature. Quantitative estimation of mullite and residual quartz content were done by Xray diffraction (XRD) and nanostructure and crystallization were studied using differential thermal analysis (DTA), field effect scanning electron microscopy (FESEM), XRD and Fourier transform infrared (FTIR) spectroscopy. The results show that fly ash sieved through 250 holes/cm2 mesh contain more mullite initially and growth of mullite as well as glass formation was faster in this sample compared to coarse fly ash. The maximum mullite in these samples was formed at 1600°C. Transformation of quartz and cristobalite phases into glassy phase was also faster for smaller particle sizes of fly ash.

• Kaliophilite from fly ash: synthesis, characterization and stability

Kaliophilite was synthesized by fusion method using fly ash as starting material. In this method, at first, alkaline fusion of fly ash with KOH occurs, followed by hydrothermal treatment in KOH medium. Scanning electron microscopy (SEM) observations revealed that the synthesized kaliophilite (S-KAL) was a plate-like crystal. X-ray diffraction (XRD) results showed three characteristic diffraction peaks located at 2𝜃 = 19.56°, 20.78° and 28.71°, respectively. The thermal analysis indicated that the S-KAL had remarkable thermal stability when heated to 1000°C. Leaching test confirmed the high retention rate of potassium for S-KAL in boiling water for 10 h.

• Uptake of permanganate from aqueous environment by surfactant modified montmorillonite batch and fixed bed studies

Organo-clay was prepared by incorporating different amounts (in terms of CEC, ranging from 134–840 mg of quaternary ammonium cation (QACs) such as hexadecytrimethylammonium bromide ([C19H42N]Br) into the montmorillonite clay. Prepared organo-clays are characterized by CHN analyser and XRD to measure the amount of elemental content and interlayer spacing of surfactant modified clay. The batch experiments of sorption of permanganate from aqueous media by organo-clays was studied at different acidic strengths (pH 1–7). The experimental results show that the rate and amount of adsorption of permanganate was higher at lower pH compared to raw montmorillonite. Laboratory fixed bed experiments were conducted to evaluate the breakthrough time and nature of breakthrough curves. The shape of the breakthrough curves shows that the initial cationic surfactant loadings at 1.0 CEC of the clay is enough to enter the permanganate ions in to the interlamellar region of the surfactant modified smectile clays. These fixed bed studies were also applied to quantify the effect of bed-depth and breakthrough time during the uptake of permanganate. Calculation of thermodynamic parameters shows that the sorption of permanganate is spontaneous and follows the first order kinetics.

• Preparation of an efficient humidity indicating silica gel from rice husk ash

An efficient humidity indicating silica gel was prepared using rice husk ash as a raw material via sodium silicate extraction and acid neutralization method. Cobalt chloride was impregnated into the silica gel as a colour indicating material. A low concentration of cobalt chloride solution (0.0005 mol dm-3) was used for the impregnation. The effect of pH of the impregnating solution on the colour development behaviour of the gel was investigated. The specific surface area of the gel was determined by Brunauer–Emmett–Teller method. The gel has been characterized using X-ray diffraction, scanning electron microscopy and visible spectroscopy. The moisture adsorption and desorption kinetics of the desiccant were evaluated using simultaneous thermogravimetry and differential scanning calorimetry.

• Improvement of multicrystalline silicon wafer solar cells by post-fabrication wet-chemical etching in phosphoric acid

In this study, we have improved electrical characteristics such as the efficiency (𝜂) and the fill factor (FF) of finished multicrystalline silicon (𝑚𝑐-Si) solar cells by using a new chemical treatment with a hot phosphoric (H3PO4) acidic solution. These 𝑚𝑐-Si solar cells were made by a standard industrial process with screen-printed contacts and a silicon nitride (SiN) antireflection coating. We have deposited SiN thin layer (80 nm) on 𝑝-type 𝑚𝑐-Si substrate by the mean of plasma enhanced chemical vapour deposition (PECVD) technique. The reactive gases used as precursors inside PECVD chamber are a mixture of silane (SiH4) and ammonia (NH3) at a temperature of 380°C. The developed H3PO4 chemical surface treatment has improved 𝜂 from 5.4 to 7.7% and FF from 50.4 to 70.8%, this means a relative increase of up to 40% from the initial values of 𝜂 and FF. In order to explain these improvements, physical (AFM, EDX), chemical (FTIR) and optical (spectrophotometer) analyses were done.

• Nitrates–melt synthesized LiNi0.8Co0.2O2 and its performance as cathode in Li-ion cells

Layered LiNi0.8Co0.2O2 crystallizing in 𝑅$\bar{3}$𝑚 space group is synthesized by decomposing the constituent metal–nitrate precursors. Oxidizing nature of metal nitrates stabilizes nickel in +3 oxidation state, enabling a high degree of cation ordering in the layered LiNi0.8Co0.2O2. The powder sample characterized by XRD Rietveld refinement reveals &lt; 2% Li–Ni site exchange in the layers. Scanning electron microscopic studies on the as-synthesized LiNi0.8Co0.2O2 sample reflect well defined particles of cubic morphology with particle size ranging between 200 and 250 nm. Cyclic voltammograms suggest that LiNi0.8Co0.2O2 undergoes phase transformation on first charge with resultant phase being completely reversible in subsequent cycles. The first-charge-cycle phase transition is further supported by impedance spectroscopy that shows substantial reduction in resistance during initial de-intercalation. Galvanostatic charge–discharge cycles reflect a firstdischarge capacity of 184 mAh g-1 which is stabilized at 170 mAh g-1 over 50 cycles.

• Corrosion resistant Zn–Co alloy coatings deposited using saw-tooth current pulse

Micro/nanostructured multilayer coatings of Zn–Co alloy were developed periodically on mild steel from acid chloride bath. Composition modulated multilayer alloy (CMMA) coatings, having gradual change in composition (in each layer) were developed galvanostatically using saw-tooth pulses through single bath technique (SBT). CMMA coatings were developed under different conditions of cyclic cathode current densities (CCCDs) and number of layers, and their corrosion resistances were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) method. Optimal configuration, represented as (Zn–Co)2.0/4.0/300 was found to exhibit ∼ 89 times better corrosion resistance compared to monolithic (Zn–Co)3.0 alloy deposited for same time, from same bath. The better corrosion resistance of CMMA coatings was attributed to changed interfacial dielectric properties, evidenced by dielectric spectroscopy. Improved corrosion resistance was attributed to formation of 𝑛-type semiconductor film at the interface, supported by the Mott–Schottky plot. Further, the formation of multilayer and corrosion mechanism was analysed using scanning electron microscopy (SEM).

• Effect of heat treatment temperature on microstructure and electrochemical properties of hollow carbon spheres prepared in high-pressure argon

Heat treatment was carried out between 800 and 1200°C to investigate its effects on the microstructure and electrochemical properties of the hollow carbon spheres (HCSs) prepared in high-pressure argon. Samples were characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and N2 adsorption–desorption isotherms. The graphitization of the HCSs was improved with increase of heat treatment temperature. Mesopores of 𝑐𝑎. 4 nm in diameter were created on the HCSs after the heat treatment. The results of electrochemical performance measurements for the HCSs as anode material for lithium ion batteries indicate that the discharge capacity of the HCSs is improved after heat treatment at 800°C compared with the as-prepared HCSs and have a maximum value of 357 mAh/g and still retains 303 mAh/g after 40 cycles. However, the discharge capacity of the HCSs decreases and the cycling performance is improved with the increase of heat treatment temperature.

• Biodegradable poly(lactic acid) microspheres containing total alkaloids of Caulis sinomenii

The fabrication of biodegradable poly(lactic acid) (PLA) microspheres containing total alkaloids of Caulis sinomenii was investigated. The formation, diameter, morphology and properties of the microspheres were characterized using Fourier transform infrared spectroscopy (FT–IR), laser particle size analyser and scanning electron microscopy (SEM), etc. In vitro releasing behaviour was also investigated using UV-Vis spectrometer. As a result, the drug-loaded microspheres with a narrower distributive, rounder and smoother surface were prepared. Drug-releasing behaviour from microspheres was affected by the concentration of emulsifier and the stirring rate. The results demonstrated that a medicated system, which can be potentially applied within a drug delivery system, was designed. This system acts in a systematic manner for the treatment of rheumatoid arthritis.

• Tissue-engineered triphasic ceramic coated hydroxyapatite induced bone formation and vascularization at an extraskeletal site in a rat model

Tissue-engineered bone regeneration has attracted much attention because of its high clinical demand for restoration of injured tissues. In the present study, we have evaluated the capability of bare (without cells) and tissue-engineered (with osteogenic-induced rat Mesenchymal Stem Cells (MSCs)) bioactive ceramics such as hydroxyapatite (HA) and triphasic ceramic-coated hydroxyapatite (HASi) to mediate vascularisation and osteoinduction at an extraskeletal site of rat model. The viability, proliferation and osteogenic differentiation of MSCs on the scaffolds were assessed in vitro and thereby established the capability of HASi in providing a better structural habitat than HA. The vascular invasion was relatively low in bare and tissueengineered HA at 2 and 4 weeks. Interestingly, the implantation site was well vascularised with profuse ingrowth of blood capillaries in HASi groups, with preference for tissue-engineered HASi groups. Similarly, neo-osteogenesis studies were shown only by tissue-engineered HASi groups. The ingrowth of numerous osteoblast-like cells was seen around and within the pores of the material in bare HASi and tissue-engineered HASi groups (very low cellular infiltration in bare HA groups), but there was no osteoid deposition. The positive impact in forming bone in tissue-engineered HASi groups is attributable to the scaffold and to the cells, with the first choice for scaffold because both HA and HASi were engineered simultaneously with the cells from same source and same passage. Thus, highly porous interconnected porous structure and appropriate chemistry provided by HASi in combination with osteogenic-induced MSCs facilitated better vascularisation that lead to neo-osteogenesis.

• Influence of preparation method on hydroxyapatite porous scaffolds

Hydroxyapatite (HA) is extensively used in medical applications as an artificial bone because of its similarity to the natural components of human bones and for its excellent biocompatibility. The porous structure of HA ceramics is more generally used as a scaffold. Many techniques, which are performed under fluid system, have been applied to fabricate HA porous scaffolds. In this work, polymeric sponge technique was employed in the preparation of HA slurry appropriated for porous ceramic fabrication. Effort for strength improvement was made on porous HA ceramic in several aspects. The effect of HA/water, binder/plasticizer ratios and dispersant content on the rheological properties of HA suspension in combination with the addition of SiC and SiO2 on the compressive strength of porous bodies were investigated and discussed.

• Evaluation of starch based cryogels as potential biomaterials for controlled release of antibiotic drugs

In the present study starch has been blended with poly(vinyl alcohol) to design macroporous architectures following a repeated freeze-thaw method. These macroporous cryogels were loaded with an antibiotic drug, ciprofloxacin hydrochloride (Cfx), and evaluated for its in vitro delivery in a completely controlled manner thus exploring possibilities to use it as a biomaterial in burn or wound healing applications. The key advantage of the present system is that cryogels formed do not contain any chemical crosslinking agent which is often harmful to organic compounds. These Cfx loaded cryogels were characterized by infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques. The controlled release of Cfx drug from cryogels was investigated under varying experimental conditions such as percent loading of the antibiotic drug, chemical architecture of the cryogels and pH, temperature, and nature of the release media. The prepared cryogels show promise to provide a possible pathway for controlling delivery of antibiotic drug thus minimizing the known side effects and improving efficacy also.

• Synthesis of hydroxyapatite nanopowders by sol–gel emulsion technique

Hydroxyapatite nanopowders were synthesized by a sol–gel emulsion technique by varying the concentration of a non-ionic surfactant in the organic phases (oil phase) of water-in-oil (w/o) emulsion. Calcium acetate dissolved in distilled water and phosphorous pentoxide dissolved in 2-butanol were used as starting precursors. The prepared sol was emulsified in a support solvent (cyclohexane) containing 2, 4 and 5 volume% of surfactant (Span 80), followed by the addition of triethylamine, for gelation. The gel powders thus obtained were calcined at different temperatures up to 750°C. Characterization was done using XRD, SEM and TEM. Pellets were made from the developed HAP powders and tested for its biocompatibility after their immersion in the simulated body fluid.

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• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019