• Volume 31, Issue 7

December 2008,   pages  919-1041

• Facile hydrothermal route to the controlled synthesis of 𝛼-Fe2O3 1-D nanostructures

Single-crystalline 𝛼-Fe2O3 1-D nanostructures can be obtained via a facile one-step hydrothermal synthetic route. It was found that the introduction of SnCl4 played a key role in determining the composition and morphology of 𝛼-Fe2O3. The addition of SnCl4 favours the formation of Fe2O3 rather than FeOOH, and the morphology can be tuned from nanorod to double-shuttle as the increase of SnCl4 concentration. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selectedarea electron diffraction (SAED). This simple method does not need any seed, catalyst, or template, thus is promising for large-scale and low-cost production.

• Photoelectrochemical studies on colloidal copper (I) oxide/modified with some organic semiconductors: Incentive for use of nanoparticle systems

Colloidal Cu2O solutions were used to explore photonic activities at the semiconductor/electrolyte interface. Fluorescence spectroscopic studies were performed on Cu2O colloidal particles modified with some conjugated organic monomers such as 2-amino-phenyl pyrrole (2-APPy), tri-phenyl amine (TPA), or 2-thionyl pyrrole (2-Th-Py) to investigate the quantum absorbance efficiency at this inorganic/organic interface (IOI). Our study shows that colloidal 𝑝-type Cu2O possesses a bandgap with direct transition of ≈ 2.2 eV and indirect transition of 1.85 eV. The recorded rates of charge injection into colloidal Cu2O, 𝑘ct, were 2.31 × 109 s-1, 5.05 × 108 s-1, and 7.22 × 108 s-1 for 2-APPy, TPA and 2-Th-Py, respectively. The studied systems show more stability in colloidal form than in thin solid form. Results were interpreted using the optical and electrical parameters of the organic monomer such as ionization potential (IP), electron affinity (EA) and energy bandgap (Eg), and the barrier height at the IOI interface. Stability of the colloidal system is attributed to the physical dimensions of the photoactive system. The nano-colloidal particle offers a condition where its size is less than √𝐷𝑡.

• Synthesis of hierarchical CuS flower-like submicrospheres via an ionic liquid-assisted route

A facile, ionic liquid-assisted route was developed to synthesize hierarchical CuS flower-like submicrospheres at 80°C for 24 h. The method was based on a reaction between CuCl2 and thioacetamide (TAA) in aqueous solution with using ionic liquid 1-𝑛-butyl-3-methylimidazolium chloride ([BMIM]Cl) as an assisted agent. The chemical composition, morphology and size of CuS product were characterized by XRD, SEM and TEM. The result shows that the as-prepared CuS consists of flowery spheres with a diameter of 0.6 ∼ 1.0 𝜇m, and these submicrospheres are, in fact, built by numerous nanoflakes with a thickness of 10 ∼ 20 nm. The optical property of CuS product was examined by UV-Vis. In general, we suggested an ecologically and environmentally friendly route for the syntheses of hierarchical metal chalcogenides structures in this paper.

• Microwave assisted template synthesis of silver nanoparticles

Easier, less time consuming, green processes, which yield silver nanoparticles of uniform size, shape and morphology are of interest. Various methods for synthesis, such as conventional temperature assisted process, controlled reaction at elevated temperatures, and microwave assisted process have been evaluated for the kind of silver nanoparticles synthesized. Starch has been employed as a template and reducing agent. Electron microscopy, photon correlation spectroscopy and surface plasmon resonance have been employed to characterize the silver nanoparticles synthesized. Compared to conventional methods, microwave assisted synthesis was faster and provided particles with an average particle size of 12 nm. Further, the starch functions as template, preventing the aggregation of silver nanoparticles.

• Prospects of microwave processing: An overview

Microwave processing has been emerging as an innovative sintering method for many traditional ceramics, advanced ceramics, specialty ceramics and ceramic composites as well as polymer and polymer composites. Development of functionally gradient materials, joining, melting, fibre drawing, reaction synthesis of ceramics, synthesis of ceramic powder, phosphor materials, whiskers, microtubes and nanotubes, sintering of zinc oxide varistors, glazing of coating surface and coating development have been performed using microwave heating. In addition, microwave energy is being explored for the sintering of metal powders also. Ceramic and metal nanopowders have been sintered in microwave. Furthermore, initiatives have been taken to process the amorphous materials (e.g. glass) by microwave heating. Besides this, an attempt has been made to study the heating behaviour of materials in the electric and magnetic fields at microwave frequencies. The research is now focused on the use of microwave processing for industrial applications.

• A new ion-selective electrode based on aluminium tungstate for Fe(III) determination in rock sample, pharmaceutical sample and water sample

An inorganic cation exchanger, aluminum tungstate (AT), has been synthesized by adding 0.1 M sodium tungstate gradually into 0.1 M aluminium nitrate at pH 1.2 with continuous stirring. The ion exchange capacity for Na+ ion and distribution coefficients of various metal ions was determined on the column of aluminium tungstate. The distribution studies of various metal ions showed the selectivity of Fe(III) ions by this cation exchange material. So, a Fe(III) ion-selective membrane electrode was prepared by using this cation exchange material as an electroactive material. The effect of plasticizers viz. dibutyl phthalate (DBP), dioctylphthalate (DOP), di-(butyl) butyl phosphate (DBBP) and tris-(2-ethylhexylphosphate) (TEHP), has also been studied on the performance of membrane sensor. It was observed that the membrane containing the composition AT: PVC: DBP in the ratio 2 : 20 : 15 displayed a useful analytical response with excellent reproducibility, low detection limit, wide working pH range (1–3.5), quick response time (15 s) and applicability over a wide concentration range of Fe(III) ions from 1 × 10-7 M to 1 × 10-1 M with a slope of 20 ± 1 mV per decade. The selectivity coefficients were determined by the mixed solution method and revealed that the electrode was selective for Fe(III) ions in the presence of interfering ions. The electrode was used for atleast 5 months without any considerable divergence in response characteristics. The constructed sensor was used as indicator electrode in the potentiometric titration of Fe(III) ions against EDTA and Fe(III) determination in rock sample, pharmaceutical sample and water sample. The results are found to be in good agreement with those obtained by using conventional methods.

• Preparation, characterization and luminescent properties of europium oxide doped nano LaMn0.9Zn0.1O3+𝑑 by sol–gel processing

New compounds of rare earth complex oxides with perovskite structure in a combination of La with Eu ions and Mn with Zn ions, La1–𝑥Eu𝑥Mn0.9Zn0.1O3+𝑑 (LEMZ) (0.0 ≤ 𝑥 ≤ 0.32) in A and B sites, respectively were synthesized. X-ray powder diffraction (XRD), fourier transform infrared spectroscopy (FT–IR) and photoluminescence spectra (PL) were used to characterize the resulting nanoparticles. The powder X-ray diffraction peaks could be indexed as a rhombohedral cell. The results of FT–IR spectra were in agreement with those of XRD. High-quality nanopowders with controlled stoichiometry and microstructure were prepared at a temperature range of 700–800°C for 6 h, with mean particle sizes of ∼ 17.5 nm. Photoluminescence measurements showed Eu3+ ions characteristic red emission in crystalline LEMZ powders due to the ${}^{5}D_{0} \rightarrow {}^{7}F_{J}$ (𝐽 = 0–6) transitions of the 4𝑓 electrons of Eu3+ ions. The structure, homogeneity and particle size of the obtained compounds during different stages were investigated by scanning electron microscopy (SEM).

• In vitro studies on crystallization of SeMHP and strategies for nucleation reduction

Naturally many types of crystals grow in our human body. Especially different crystals or minerals are deposited in human urinary tracts. These crystals are named as octacalcium phosphate (OCP), calcium hydrogen phosphate (CHP), hydroxyapatite (HAP), magnesium hydrogen phosphate (MHP) etc. The SeMg-HPO4 crystals are also known as Selenio–Newberryite crystals. The main reasons for the formation of crystals are due to the increased concentration of magnesium and phosphate ions in the human urine. In the present study, SeMHP crystals are grown in silica gel medium at various concentrations and different pH values in sun light medium and laser exposed medium. It has been observed that the nucleation rate was partially and completely reduced in sunlight and laser exposed medium, respectively. During the growth period, Liesegang rings were observed. Characteristic studies of SeMHP crystals such as FTIR, AAS, SEM, XRD, TGA/DTA and etching were done. The results are compared with the reported values and discussed in detail.

• In vitro studies of calcium mixed minerals growth in different growth faces and semiconductor laser induced suppression of nuclei strategy

Kidney stone consists of various organic, inorganic and semi organic compounds. Mineral oxalate monohydrate and di-hydrate are the main organic constituents of kidney stones. However, mechanisms leading to the formation of mineral oxalate kidney stones are not clearly understood. The effect of some urinary stone constituents such as ammonium oxalate, calcium citrate, proteins and trace elements were reported by us. The calcium magnesium hydrogen phosphate (CaMHP) crystals were grown in SMS gel medium which provides the necessary kidney stimuli growth medium. The growth processes were done by single diffusion method for different physical and chemical parameters. The pH range in which HPO$^{2-}_{4}$ ions dominates were considered which in turn is necessary for the growth of CaMHP crystals. In the present study, calcium magnesium hydrogen phosphate (CaMHP) crystals are grown in three different growth faces to attain the total nucleation reduction. As an extension of this research, many characterization studies have been carried out like XRD, FTIR, TGA, SEM and etching and the results are reported.

• Metathesis synthesis and characterization of complex metal fluoride, KMF3 (M = Mg, Zn, Mn, Ni, Cu and Co) using mechanochemical activation

Metathesis synthesis of complex metal fluorides using mechanochemical activation has been reported. The high lattice energy of the byproduct KCl helps the reaction towards product formation in under 20 min. The proposed process, in contrast to the available methods of synthesis, is very rapid, economical and results in products with controlled morphology. The structural, optical and chemical properties of synthesized powders are determined by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, magnetization measurements and diffused reflectance spectra in the UV–VIS range.

• Effect of bauxite addition on densification and mullitization behaviour of West Bengal clay

The effect of bauxite addition on the densification and mullitization of reaction sintered bauxite–clay mixture had been studied in the temperature range 1400–1500°C. The maximum bulk density (2.89 g/cc) and minimum apparent porosity (0.58%) was achieved by addition of 50 wt% bauxite. The impurities present in bauxite and clay formed liquid phase which helped in particle diffusion to aid densification. The X-ray diffraction of sample fired at 1500°C showed cristoballite phase gradually disappearing and at the same time mullite and 𝛼-Al2O3 phase appearing at a higher level of bauxite addition. The in situ nascent alumina formed was reactive that facilitated the formation of secondary mullite by solution precipitation mechanism. The presence of bauxite also changed the morphology of the mullite particles. Two types of mullite were distinctly observed in the SEM photographs: elongated primary mullite and equiaxed secondary mullite.

• Effect of increased manganese addition and mould type on the slurry erosion characteristics of Cr–Mn iron systems

The wear resistance of high chromium iron is well recorded. However, the same is not the case as regards the use of manganese at higher percentages in high chromium irons and its influence on wear behaviour. Hence, this work highlights the slurry wear characteristics of chromium ($\Box$ 16–19%) iron following the introduction of manganese at two levels i.e. 5 and 10%. It is known that the wear properties are dictated by the microstructural features. To alter the structure, the cooling rate of casting has been varied by adopting two different types of moulds (i.e. sand and metal) and subsequently subjecting to thermal treatment. The as-cast and heat treated samples are examined for microstructure and then evaluated for hardness and slurry erosion properties. As the manganese content is increased from 5 to 10%, the hardness showed a decrease in value both in the as-cast and heat treated conditions. The slurry erosion loss, expectedly, showed an increase irrespective of the sample condition (i.e. mould type/heat treatment adopted). The findings are corroborated with the microstructural features obtained through optical and scanning electron microscopy.

• Nonlinear electrical properties and aging characteristics of (NiO, MgO, Cr2O3)-doped Zn–Pr–Co–R (R = Y, Er) oxide-based varistors

The electrical properties and stability of the varistors, which composed of (NiO, MgO, Cr2O3)- doped Zn–Pr–Co–R (Y, Er) oxide-based ceramics, were investigated for different additives. The breakdown voltage of the varistors increased in order of NiO$\rightarrow$undoped$\rightarrow$MgO$\rightarrow$Cr2O3: 1200$\rightarrow$1551$\rightarrow$1691$\rightarrow$1959 V/cm for ZPCY system and undoped$\rightarrow$NiO$\rightarrow$MgO$\rightarrow$Cr2O3: 1024$\rightarrow$1041$\rightarrow$1500$\rightarrow$1668 V/cm for ZPCE system, respectively. The nonlinear coefficient value increased in order of undoped$\rightarrow$NiO$\rightarrow$MgO$\rightarrow$Cr2O3: 21$\rightarrow$25$\rightarrow$38$\rightarrow$50 in ZPCY system and NiO$\rightarrow$undoped$\rightarrow$MgO$\rightarrow$Cr2O3: 27$\rightarrow$32$\rightarrow$35$\rightarrow$38 in ZPCE system, respectively. In ZPCY and ZPCE systems, the Cr2O3-additives most greatly improved the nonlinear properties. In Cr2O3-doped system, ZPCY system exhibited higher nonlinear properties than that of ZPCE system. The stability against d.c. accelerated aging stress was higher in Cr2O3-additives than in NiO- and MgO-additives for ZPCY system and was higher in NiO-additives than in MgO- and Cr2O3-additives for ZPCE system.

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• # Bulletin of Materials Science

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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019