• Volume 33, Issue 1

February 2010,   pages  1-88

• Effect of fuel characteristics on synthesis of calcium hydroxyapatite by solution combustion route

The effect of fuel characteristics on the processing of nano sized calcium hydroxyapatite (HA) fine powders by the solution combustion technique is reported. Urea, glycine and glucose were used as fuels in this study. By using different combinations of urea and glycine fuels and occasional addition of small amounts of highly water-soluble glucose, the flame temperature (𝑇f) of the process as well as product characteristics could be controlled easily. The powders obtained by this modified solution combustion technique were characterized by XRD, FTIR spectroscopy, SEM, FESEM–EDX, particle size analyser (PSD) and specific surface area (SSA) measurements. The particle size of phase pure HA powder was found to be &lt; 20 nm in this investigation. The effects of glucose addition with stoichiometric (𝜇 = 1) and fuel excess (𝜇 &gt; 1) urea and glycine precursor batches were investigated separately.

• Synthesis of CuO nanoflower and its application as a H2O2 sensor

CuO three-dimensional (3D) flower-like nanostructures were successfully synthesized by a simple method at 100°C with Cu(NO3)2.3H2O and NH3.H2O for 6 h in the absence of any additives. We found that NH3.H2O amount was critical for CuO morphology evolution. The phase analysis was carried out using X-ray diffraction (XRD) and the result confirmed that the CuO nanoflowers were single-phase. The morphological investigations by field emission scanning electron microscope (FESEM) revealed that the CuO nanoflowers were mono-dispersed in a large quantity and consisted of nanosheets. And then, CuO nanoflowers were successfully used to modify a gold electrode to detect H2O2 with cyclic voltammetry (CV) and amperometric (AC). It was found that CuO nanoflowers may be of great potential for H2O2 electrochemical sensing.

• Zn/ZnO core/shell nanoparticles synthesized by laser ablation in aqueous environment: Optical and structural characterizations

Zn/ZnO core/shell nanoparticles are synthesized by pulsed laser ablation (PLA) of Zn metal plate in the aqueous environment of sodium dodacyl sulfate (SDS). Solution of nanoparticles is found stable in the colloidal form for a long time, and is characterized by UV-visible absorption, transmission electron microscopy (TEM), photoluminescence (PL) and Raman spectroscopic techniques. UV-visible absorption spectrum has four peaks at 231, 275, 356, and 520 nm, which provides primary information about the synthesis of core-shell and elongated nanoparticles. TEM micrographs reveal that synthesized nanoparticles are monodispersed with three different average sizes and size distributions. Colloidal solution of nanoparticles has significant absorption in the green region, therefore, it absorbs 514.7 nm light of Ar+ laser and emits in the blue region centred at 350 and 375 nm, violet at 457 nm and green at 550 nm regions. Raman shift is observed at 300 cm-1 with PL spectrum, which corresponds to ${}^{3}$𝐸2N and 𝐸3L mode of vibrations of ZnO shell layer. Synthesis mechanism of Zn/ZnO core/shell nanoparticles is discussed.

• Dispersion and reinforcing mechanism of carbon nanotubes in epoxy nanocomposites

Carbon nanotube based epoxy composites have been fabricated at room temperature and refrigeration process using sonication principle. Flexural moduli, electrical conductivity, glass transition temperature of epoxy resin as well as nanocomposite samples have been determined. Distribution behaviour of carbon nanotubes in the epoxy matrix was examined through scanning electron microscopy. Composite samples showed better properties than resin samples due to strengthening effect of the filled nanotubes. Refrigerated nanocomposites obtained increasing mechanical property because of better dispersion due to low temperature settlement of polymers. Improvement of electrical conductivity was due to the fact that aggregated phases form a conductive three-dimensional network throughout the whole sample. The increasing glass transition temperature was indicative of restricting movement of polymer chains that ascribe strong interaction presented between carbon nanotubes and epoxy chains that was again supplemented by Raman study and SEM.

• Effects of SiO2 and TiO2 fillers on thermal and dielectric properties of eco-friendly bismuth glass microcomposites of plasma display panels

The effects of SiO2 (amorphous) and TiO2 (crystalline, rutile) fillers on softening point (𝑇s), glass transition temperature (𝑇g), coefficient of thermal expansion (CTE), and dielectric constant (𝜀) of zinc bismuth borate, ZnO–Bi2O3–B2O3 (ZBIB) glass microcomposites have been investigated with a view to its use as the white back (rear glass dielectric layer) of plasma display panels (PDPs). The experimentally measured properties have also been compared with those of theoretically predicted values. Both the experimental and theoretical trends of these properties with added filler contents correlate very well. The interaction of fillers with glass which occurred during sintering at 560°C has also been monitored by XRD and FTIR spectroscopic analyses. The microstructures and distribution of fillers in the glass matrix have been analyzed by SEM images. It is observed that the fillers have partially dissolved in the glass at the firing temperature leaving some unreacted filler as residue which results in ceramic–glass microcomposites. In consideration of the desired properties of white back of PDPs, the addition of TiO2 filler to ZBIB glass is found to be more preferable than SiO2 filler. The addition of 10 wt% TiO2 filler yielded 𝑇s, 𝑇g, CTE and 𝜀 values of 560°C, 480°C, 82 × 10-7/K and 14.6 which are found to meet the desired values of &lt; 580°C, &lt; 500°C, &lt; 83 × 10-7/K and &lt; 15, respectively with respect to use of PD200 glass as substrate in PDP technology.

• Microstructure and mechanical properties of Mg–HAP composites

In the present study, it has been attempted to develop biodegradable Mg–HAP (magnesium–hydroxyapatite) composite materials for bone replacement. At first the HAP powders were prepared by chemical synthesis process and synthesized powders were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Synthesized powders contain HAP as a major phase with tricalcium phosphate (𝛽-TCP) as a minor phase. The Mg–HAP composites were prepared by adding different amounts of HAP powders to Mg melts and finally the billets were extruded. The microstructure of Mg–HAP composite was examined by optical microscope (OM). The presence of HAP in Mg matrix results in decrease of grain size of Mg–HAP composites. The theoretical and experimental hardness of the composites are compared with the addition of HAP. The tensile strength of composites is found to decrease with the addition of HAP, whereas compressive strength increases with HAP.

• Effect of heat treatment on strength and abrasive wear behaviour of Al6061–SiCp composites

In recent years, aluminum alloy based metal matrix composites (MMC) are gaining importance in several aerospace and automobile applications. Aluminum 6061 has been used as matrix material owing to its excellent mechanical properties coupled with good formability and its wide applications in industrial sector. Addition of SiCp as reinforcement in Al6061 alloy system improves its hardness, tensile strength and wear resistance. In the present investigation Al6061–SiCp composites was fabricated by liquid metallurgy route with percentages of SiCp varying from 4 wt% to 10 wt% in steps of 2 wt%. The cast matrix alloy and its composites have been subjected to solutionizing treatment at a temperature of 530°C for 1 h followed by quenching in different media such as air, water and ice. The quenched samples are then subjected to both natural and artificial ageing. Microstructural studies have been carried out to understand the nature of structure. Mechanical properties such as microhardness, tensile strength, and abrasive wear tests have been conducted both on matrix Al6061 and Al6061–SiCp composites before and after heat treatment. However, under identical heat treatment conditions, adopted Al6061–SiCp composites exhibited better microhardness and tensile strength reduced wear loss when compared with Al matrix alloy.

• Function of magnesium aluminate hydrate and magnesium nitrate as MgO addition in crystal structure and grain size control of 𝛼-Al2O3 during sintering

Chemically pure reactive alumina (𝛼-Al2O3) which is commercially available was used for densification study in presence of widely accepted dopant MgO as additive. MgO was added both as spinel (MgAl2O4) forming precursor i.e. magnesium aluminate hydrate, and magnesium nitrate. Sintering investigations were conducted in the temperature range 1500–1600°C with 2 h soaking. Structural study of sintered pellets was carried out by extensive XRD analysis. Scanning electron mode SEM images of the specimens were considered to understand the effect of both types of additions. Addition of MgO within and beyond optimum amount had some effect on development of microstructure of sintered bodies. Densification, around 99% ρth, with fine grain microstructure was achieved. These different types of additions caused two distinct changes in crystal structure of alumina-one small contraction and the other expansion of unit cell parameters.

• Structure, optical and thermal decomposition characters of LDPE graft copolymers synthesized by gamma irradiation

Methyl methacrylate (MMA) monomer was grafted onto low density polyethylene by the direct method of radiation grafting. The effect of cohesive energy density of different organic solvents on the degree of grafting was investigated. It was found that the extent of grafting depends largely on the kind of solvent, in which the highest degree of grafting was achieved in the presence of dioxane, whereas the lowest degree of grafting occurred in the presence of methanol. This behaviour was attributed to the solubility parameters of the solvent, monomer and polymer. The change in structure of the LDPE graft copolymer films was characterized by scanning electron microscopy, X-ray diffraction, UV/vis absorption and thermogravimetric analysis. The X-ray diffraction results showed a decrease in the crystallinity of LDPE graft copolymer matrix at high degree of grafting. Studies were made on the UV-absorption edge, and indirect allowed transitions with their optical energy gaps are determined. At the same time the Urbach energy was evaluated. The activation energy of the thermal decomposition was calculated according to Horowitz and Metzger method.

• Low temperature synthesis of Ba1–𝑥Sr𝑥SnO3 (𝑥 = 0–1) from molten alkali hydroxide flux

Perovskite structured stannates (Ba1–𝑥Sr𝑥SnO3, 𝑥 = 0.0–1.0) powders have been synthesized for the first time by molten salt synthesis (MSS) method using KOH as the flux at lower temperature (400°C) compared to other methods. The phase formation was confirmed by FT–IR spectroscopy, powder X-ray diffraction (XRD) and the microstructure was analysed by scanning electron microscopy. XRD patterns reveal the formation of single phasic products for parent and substituted products with good crystallinity throughout the range (𝑥 = 0.0–1.0). The morphology of the particles of BaSnO3 and SrSnO3 is spherical and rod shaped, respectively. Effect of soaking periods on the grain growth is observed clearly in SrSnO3. Ba0.5Sr0.5SnO3 (BSS5) crystallizes in flake like morphology.

• Sol–gel synthesis and photoluminescence of CaTi1–𝑥Zr𝑥O3 : Pr3+ phosphors

CaTi1–𝑥Zr𝑥O3 : Pr3+ phosphors have been synthesized by sol–gel and solid state methods, with 𝑥 = 1/300, 2/300, 3/300, 4/300, 5/300, 6/300, 7/300, respectively. Powder X-ray diffraction (XRD), UV-visible absorption spectra, photoluminescent spectra (PL), and scanning electron microscopy (SEM) images are used to characterize the powder samples. The inverse absorption at 610 nm appearing in the UV-visible absorption spectra is due to the ${}^{1}D_{2} \rightarrow {}^{3}H_{4}$ characteristic emission of Pr3+. Changes in the emission spectra at 610 nm were agreed with those in UV-visible absorption spectra. The strongest red excitation obtained from CaTi1–𝑥Zr𝑥O3 : Pr3+ (𝑥 = 4/300) and CaTi1–𝑥Zr𝑥O3 : Pr3+ (𝑥 = 5/300) possesses the strongest emission at 610 nm, similar to the intensities of Ca(Ti1–𝑥Zr𝑥)O3 : Pr3+ (𝑥 = 3/300, 4/300, 6/300), which may be corresponded to the cell parameters of CaTi1–𝑥Zr𝑥O3 : Pr3+.

• Solar photocatalytic generation of hydrogen under ultraviolet-visible light irradiation on (CdS/ZnS)/Ag2S + (RuO2/TiO2) photocatalysts

In order to efficiently use the UV-vis light in the photocatalytic reaction, a novel (CdS/ZnS)/ Ag2S + RuO2/TiO2 was synthesized by chemical coprecipitation and metal ion implantation. The composition and structure of this composite were characterized by BET, UV-vis spectroscopy, SEM, XRD and EDX. This composite exhibited much higher photocatalytic activity for the generation of hydrogen (H2).

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