• Issue front cover thumbnail

      Volume 34, Issue 5

      August 2011,   pages  1027-1162

    • Combustion synthesis and structural characterization of Li–Ti mixed nanoferrites

      R M Sangshetti V A Hiremath V M Jali

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      Polycrystalline samples of the mixed nanoferrites, Li0.5+0.5𝑥Ti𝑥Fe2.5−1.5xO4 (0.02 ≤ 𝑥 ≤ 0.1), were prepared by combustion method at lower temperatures compared to the conventional high temperature sintering for the first time at low temperatures, using PEG which acts as a new fuel and oxidant. XRD patterns reveal a singlephase cubic spinel structure. The as synthesized Li–Ti ferrites are in nanocrystalline phase. The crystallite size was found to be in the range 16–27 nm. SEM images reveal rod-like morphology in all the samples with a discontinuous grain growth. The B–H loops have been traced using VSM technique, for all the compositions, at room temperature and the hysteresis parameters are calculated. Saturation magnetization decreases with increase in Ti content due to the fact that the Ti4+ ion, which is a non-magnetic ion, replaces a magnetic Fe3+ ion. The hysteresis loops show clear saturation at an applied field of ±10 kOe and the loops are highly symmetric in nature. The cation distribution is known indirectly by using saturation magnetization values.

    • Synthesis of Mn-doped CeO2 nanorods and their application as humidity sensors

      C H Hu C H Xia F Wang M Zhou P F Yin X Y Han

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      Mn-doped CeO2 nanorods have been prepared from CeO2 particles through a facile compositehydroxide-mediated (CHM) approach. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The analysis from the X-ray photoelectron spectroscopy indicates that the manganese doped in CeO2 exists as Mn4+. The responses to humidity for static and dynamic testing proved dopingMn into CeO2 can improve the humidity sensitivity. For the sample with Mn% about 1.22, the resistance changes from 375.3 to 2.7M𝛺 as the relative humidity (RH) increases from 25 to 90%, indicating promising applications of the Mn-doped CeO2 nanorods in environmental monitoring.

    • Preparation and investigation of Al–4 wt% B4C nanocomposite powders using mechanical milling

      A Alizadeh E Taheri-Nassaj H R Baharvandi

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      Boron carbide nanoparticles were produced using commercially available boron carbide powder (0.8 𝜇m).Mechanical milling was used to synthesize Al nanostructured powder in a planetary ball-mill under argon atmosphere up to 20 h. The same process was applied for Al–4 wt% B4C nanocomposite powders to explore the role of nanosize reinforcements on mechanical milling stages. Scanning electron microscopy (SEM) analysis as well as apparent density measurements were used to optimize the milling time needed for completion of the mechanical milling process. The results show that the addition of boron carbide particles accelerate the milling process, leading to a faster work hardening rate and fracture of aluminum matrix. FE-SEM images show that distribution of boron carbide particles in aluminum matrix reaches a full homogeneity when steady state takes place. The better distribution of reinforcement throughout the matrix would increase hardness of the powder. To study the compressibility of milled powder, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B4C particles. For better distribution of reinforcement throughout the matrix, 𝑟, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B4C particles.

    • Helical 𝐻-type aggregation of trimeric 𝑝-phenylene vinylene with chiral ester groups

      Haiquan Zhang Ying Li Peng Wang

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      Self-assembly properties of the trimeric 𝑝-phenylene vinylene derivative containing symmetrical endgroups of 𝑅-(+)-2-methylbutyric acid ester (ChTPV) in H2O/THF mixed solvents were studied by absorption, photoluminescence and circular dichroism (CD) spectra. The results indicate that ChTPV exhibits helical 𝐻-type nano-aggregates in 80% H2O/THFmixed solvents, and the negative exciton coupling suggests that the chromophoric dipoles are oriented in a counter-clockwise direction.

    • XRD spectra of new YBaCuO superconductors

      S Sujinnapram P Udomsamuthirun T Kruaehong T Nilkamjon S Ratreng

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      XRD spectra of new YBaCuO superconductors were studied. There were 2 phases found in our samples, the superconducting phase and the non-superconducting phase. The more non-superconducting phase, the more anisotropy parameters were found. The amount of impurities have no effect on the value of 𝑐-axis which has a linear relation to the number of Cu-atoms. So the new formula of YBaCuO are the new types of superconductor in this family that have higher 𝑐-axis than the Y123.

    • Cost-effective electrostatic-sprayed SrAl2O4:Eu2+ phosphor coatings by using salted sol–gel derived solution

      Kyu-Seog Hwang Bo-An Kang Sung-Dai Kim Seung Hwangbo Jim-Tae Kim

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      3 Mol% of europium doped strontium aluminate (SrAl2O4:Eu2+) coatings on silicon substrates were prepared by electrostatic spray deposition method using a salted sol–gel derived solution as a starting material. Asdeposited films at 100°C for 5 h were heated at 1100°C for 2 h under a reducing ambient atmosphere of 95%N2 + 5%H2 . Nanocrystalline SrAl2O4 film was confirmed by surface morphological and crystallographic analyses. Monitored at 520 nm, the excitation spectrum showed a broad band from 300 ∼ 500 nm and the emission intensity showed a maximum yellow peak intensity at 512 nm with a broad band from 460 ∼ 610 nm.

    • AC impedance and dielectric spectroscopic studies of Mg2+ ion conducting PVA–PEG blended polymer electrolytes

      Anji Reddy Polu Ranveer Kumar

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      Polyvinyl alcohol (PVA)–polyethylene glycol (PEG) based solid polymer blend electrolytes with magnesium nitrate have been prepared by the solution cast technique. Impedance spectroscopic technique has been used, to characterize these polymer electrolytes. Complex impedance analysis was used to calculate bulk resistance of the polymer electrolytes. The a.c.-impedance data reveal that the ionic conductivity of PVA–PEG–Mg(NO3)2 system is changed with the concentration of magnesium nitrate, maximum conductivity of 9.63 × 10-5 S/cm at room temperature was observed for the system of PVA–PEG–Mg(NO3)2 (35–35–30). However, ionic conductivity of the above system increased with the increase of temperature, and the highest conductivity of 1.71 × 10-3 S/cm was observed at 100°C. The effect of ionic conductivity of polymer blend electrolytes was measured by varying the temperature ranging from 303 to 373 K. The variation of imaginary and real parts of dielectric constant with frequency was studied.

    • Conductivity and dielectric studies on (Na0.4Ag0.6)2PbP2O7 compound

      Haibado Mahamoud B Louati F Hlel K Guidara

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      Electrical properties of the (Na0.4Ag0.6)2PbP2O7 compound were studied using complex impedance spectroscopy in the frequency range 200 Hz–5 MHz and temperature range (484–593 K). Combined impedance and modulus plots were used to analyse the sample behaviour as a function of frequency at different temperatures. Temperature dependence of d.c. and a.c. conductivity indicates that electrical conduction in the material is a thermally activated process. The frequency dependence of the a.c. conduction activation energy was found to obey a mathematical formula.

    • Synthesis, surface characterization and optical properties of 3-thiopropionic acid capped ZnS:Cu nanocrystals

      Ashish Tiwari S A Khan R S Kher

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      3-Thiopropionic acid (TPA) capped ZnS:Cu nanocrystals have been successfully synthesized by simple aqueous method. Powder X-ray diffraction (XRD) studies revealed the particle size to be 4.2 nm. Surface characterization of the nanocrystals by FTIR spectroscopy has been done and the structure for surface bound TPA based on spectral analysis was proposed. The optical studies were done using UV-VIS spectroscopy and particle size and diameter polydispersity index (DPI) were calculated. Photoluminescence (PL) spectrum reveals emission related to the transition from conduction band of ZnS to 𝑡2 level of Cu2+. Electron microscopy was also done by scanning electron microscopy (SEM).

    • Room-temperature ferromagnetic properties of Cu-doped ZnO rod arrays

      C H Xia C G Hu C H Hu Z Ping F Wang

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      We have investigated properties of the Cu-doped ZnO crystalline film synthesized by the hydrothermal method. X-ray diffraction and X-ray photoelectron spectroscopy results provide the evidence that Cu2+ is incorporated into the ZnO lattices. Photoluminescence spectrum of the rod arrays shows that the UV emission peak shifts a little to lower energy and its intensity decreased. There are another two emission peaks centred in blue and green regions because of the incorporation of Cu2+ ions. The rod arrays have exhibited room-temperature ferromagnetic behaviour with the remanence of 0.926 × 10-3 emu/cm3. We suggest that the exchange interaction between local spin-polarized electrons (such as the electrons of Cu2+ ions) and conductive electrons is the cause of room-temperature ferromagnetism.

    • Synthesis, structure and low temperature study of electric transport and magnetic properties of GdSr2MnCrO7

      Devinder Singh Meena Sharma Sushma Sharma Rajinder Singh

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      The layered perovskite oxide, GdSr2MnCrO7, has been prepared by the standard ceramic method. The powder X-ray diffraction studies suggest that the phase crystallizes with tetragonal unit cell in the space group 𝐼4/𝑚𝑚𝑚. The electrical transport properties show that the phase is an electrical insulator and the electrical conduction in the phase occurs by a 3D variable range hopping mechanism. The magnetic properties suggest that the ferromagnetic interactions are dominant in the high temperature region.

    • Study of dependence of magnetic properties on seeding temperature in fine particles of Cu0.25Co0.25Zn0.5Fe2O4

      Hina Bhargava V D Sudheesh Snehal Jani N Lakshmi K Venugopalan

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      Using a combination of X-ray diffraction, room temperature/low temperature Mössbauer studies and d.c. magnetization, the structural and magnetic properties of nano-sized Cu0.25Co0.25Zn0.5Fe2O4, prepared using the coprecipitation method at different seeding temperatures, have been studied. Formation of 𝛼-Fe2O3 in these samples is observed to be very sensitive to the seeding temperature and is totally suppressed at a seeding temperature of 333 K. These results are explained in terms of the rate of coprecipitation of the different components as a function of temperature. Since 𝛼-Fe2O3 is antiferromagnetic, the presence and quantity of this impurity is also observed to deteriorate the overall magnetic properties of the spinel phase.

    • Influence of 1523 K annealing on phase and magnetic properties in (Gd1−𝑥Er𝑥)5Si2Ge2 compounds

      Xiang Chen Yungui Chen Yangbo Tang

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      The (Gd1−𝑥Er𝑥)5Si2Ge2 (𝑥 = 0, 0.05, 0.1, 0.15 and 0.2) compounds were prepared from the high purity Gd metal (3 N) by arc melting, and then annealed at 1523 K (3 h). The phase, microstructure, Curie temperatures, magnetic hysteresis loss, and magnetocaloric effects were investigated. All samples retain the monoclinic Gd5Si2Ge2 type structure. The temperature of magnetic transition decreases linearly from 281 K to 177 K with the increase of Er content from 𝑥 = 0–0.2. Because the (Gd1−𝑥Er𝑥)5Si2Ge2 compounds keep the typical first-order structural/magnetic transition, they display large magnetic entropy near their magnetic transition temperatures. The maximum magnetic entropy change of (Gd1−𝑥Er𝑥)Si2Ge2 compounds in the low magnetic field of 0∼2.0 T are 15.5, 16.1, 15.3 and 15.2 J/kg K for 𝑥 = 0.05, 0.1, 0.15 and 0.2, respectively.

    • Effect of particle size on microstructure and strength of porous spinel ceramics prepared by pore-forming in situ technique

      Wen Yan Nan Li Yuanyuan Li Guangping Liu Bingqiang Han Juliang Xu

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      The porous spinel ceramics were prepared from magnesite and bauxite by the pore-forming in situ technique. The characterization of porous spinel ceramics was determined by X-ray diffractometer (XRD), scanning electron microscopy(SEM), mercury porosimetry measurement etc and the effects of particle size on microstructure and strength were investigated. It was found that particle size affects strongly on the microstructure and strength. With decreasing particle size, the pore size distribution occurs from multi-peak mode to bi-peak mode, and lastly to mono-peak mode; the porosity decreases but strength increases. The most apposite mode is the specimens from the grinded powder with a particle size of 6.53 𝜇m, which has a high apparent porosity (40%), a high compressive strength (75.6MPa), a small average pore size (2.53 𝜇m) and a homogeneous pore size distribution.

    • On statistical behaviour of stress drops in Portevin–Le Chatelier effect

      A Chatterjee P Mukherjee N Gayathri P Barat Arnab Barat A Sarkar

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      The Portevin–Le Chatelier (PLC) effect is a kind of plastic instability observed in many dilute alloys when deformed at certain ranges of strain rate and temperature. In this paper we present a comprehensive statistical analysis of the observed experimental data obtained during PLC effect and establish that the occurrence probability of the stress drops in the dynamical process responsible for PLC effect is Poisson in nature.

    • Synthesis and photoluminescence characterization of Ce3+ and Dy3+ activated ALa(WO4)2(A = Na and Li) novel phosphors

      Parag Nimishe S J Dhoble

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      In this paper, we report the synthesis of Ce3+ and Dy3+ activated alkali lanthanide tungstates, ALa(WO4)2(where A = Na and Li), prepared by solid state reaction method. The prepared phosphors were characterized by X-ray diffraction and photoluminescence techniques. The NaLa(WO4)2:Dy3+ and LiLa(WO4)2:Dy3+ phosphors show two emission peaks at around 574 and 486 nm (𝜆exc = 354 nm). NaLa(WO4)2:Ce3+ and LiLa(WO4)2:Ce3+ show two emission peaks at around 378 and 425 nm (𝜆exc = 350 nm). Excitation wavelengths of Ce3+ and Dy3+ activated alkali lanthanide tungstates are in near UV region i.e. Hg free excitation. These characterizations of phosphors are applicable for solid state lighting. Accordingly, Ce3+ and Dy3+ activated NaLa(WO4)2 and LiLa(WO4)2 may be the promising materials for solid state lighting applications.

    • Catalytic oxidation of cyclohexane to cyclohexanone and cyclohexanol by tert-butyl hydroperoxide over Pt/oxide catalysts

      I Rekkab-Hammoumraoui A Choukchou-Braham L Pirault-Roy C Kappenstein

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      Heterogeneous oxidation of cyclohexane with tertiobutyl hydroperoxide was carried out on Pt/oxide (Al2O3, TiO2 and ZrO2) catalysts in the presence of different solvents (acetic acid and acetonitrile). The catalysts were prepared using Pt(NH3)2(NO2)2 as a precursor and characterized by chemical analysis using the ICP–AES method, XRD, TEM, FTIR and BET surface area determination. The oxidation reaction was carried out at 70°C under atmospheric pressure. The results showed the catalytic performance of Pt/Al2O3 as being very high in terms of turnover frequency.

    • Computation of X-ray powder diffractograms of cement components and its application to phase analysis and hydration performance of OPC cement

      Rohan Jadhav N C Debnath

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      The importance of computed X-ray diffraction patterns of various polymorphs of alite (𝑀3, 𝑇1, 𝑅), belite (𝛽, 𝛾), aluminate (cubic, orthorhombic), aluminoferrite, gypsum and hemihydrate in the quantitative phase analysis of cement and its early stage hydration performance is highlighted in this work with three OPC samples. The analysis shows that the predominant silicate phases present in all the samples are 𝑀3-alite phase and 𝛽-belite phase, respectively. Both cubic and orthorhombic phases of C3A, brownmillerite, gypsum and hemihydrates are present at different levels. Quantitative phase analysis of cement by Rietveld refinement method provides more accurate and comprehensive data of the phase composition compared to Bogue method. The comparative hydration performance of these samples was studied with 𝑤/𝑐 ratio, 0.5 and the results are interpreted in the light of difference in phase compositions viz. 𝛽-C2S/C3S ratio, fraction of finer cement particles present in the samples and theoretical modeling of C3S hydration.

    • In vitro bioactivity and cytocompatibility of tricalcium silicate

      Xiaoming Liao Hongyang Zhu Guangfu Yin Zhongbing Huang Yadong Yao Xianchun Chen

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      The in vitro bioactivity of tricalcium silicate (Ca3SiO5) ceramics was investigated by the bone-like apatite-formation ability in simulated body fluid (SBF), and the cytocompatibility was evaluated through osteoblast adhesion and proliferation assay. The results show that the Ca3SiO5 ceramics possess bone-like apatite formation ability in SBF. In vitro cytocompatible evaluation reveals that osteoblasts adhere and spread well on the Ca3SiO5 ceramics, indicating good bioactivity and cytocompatibility.

    • Preparation of SnO2/C biomorphic materials by biotemplating from ramie fibres

      Xin-Hai He Le-Hua Qi Jun-Bo Wang Ming-Qian Shen Wei Chang Chong Fu Min-Ge Yang Xiao-Lei Su

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      A new SnO2/C biomorphic material has been prepared by molding into a composite billet and carbothermal-reduction under vacuum from ramie fibres/Sn(OH)4 precursors. The phase composition and microstructure of the prepared materials were characterized. The effects of the carbonization temperature, holding time and other factors on the crystal structure, morphology and ingredients of the prepared samples were discussed. The results showed that the sintering temperature and holding time have significant effects on the final products. When the sintering temperature reached 480°C, the SnO2/C biomorphic materials were synthesized successfully.

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