• Issue front cover thumbnail

      Volume 34, Issue 4

      July 2011,   pages  595-1026

    • Thermal stability of gold-PS nanocomposites thin films

      Umananda M Bhatta Deepa Khushalani P V Satyam

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      Low-temperature transmission electron microscopy (TEM) studies were performed on polystyrene (PS, 𝑀w = 234 K) – Au nanoparticle composite thin films that were annealed up to 350°C under reduced pressure conditions. The composite thin films were prepared by wet chemical approach and the samples were then subsequently spin-coated on a carbon-coated copper grid for TEM measurements. TEM measurements were performed at liquid nitrogen temperatures to reduce the electron–beam-induced radiation damage. The results showed a marginal increase in Au nanoparticle diameter (2.3 nm–3.6 nm) and more importantly, an improved thermal stability of the polystyrene (PS) composite film much above its glass transition temperature

    • Temperature dependent grain-size and microstrain of CdO thin films prepared by spray pyrolysis method

      B G Jeyaprakash K Kesavan R Ashok Kumar S Mohan A Amalarani

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      CdO thin films on glass substrate were prepared by home built spray pyrolysis unit from aqueous solution of Cd(CH3COO)2.2H2O at different substrate temperatures. X-ray diffraction (XRD) studies indicate the formation of polycrystalline cubic CdO phase with preferential orientation along (111) plane. X-ray line broadening technique is adopted to study the effect of substrate temperature on microstructural parameters such as grain size and microstrain. Scanning electron microscopy (SEM) shows that the film prepared at 250°C consists of spherical shape grains with size in nanometer range and is comparable with the XRD studies.

    • Synthesis of nano-carbon (nanotubes, nanofibres, graphene) materials

      Kalpana Awasthi Rajesh Kumar Himanshu Raghubanshi Seema Awasthi Ratnesh Pandey Devinder Singh T P Yadav O N Srivastava

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      In the present study, we report the synthesis of carbon nanotubes (CNTs) using a new natural precursor: castor oil. The CNTs were synthesized by spray pyrolysis of castor oil–ferrocene solution at 850°C under an Ar atmosphere. We also report the synthesis of carbon nitrogen (C–N) nanotubes using castor oil–ferrocene–ammonia precursor. The as-grown CNTs and C–N nanotubes were characterized through scanning and transmission electron microscopic techniques. Graphitic nanofibres (GNFs) were synthesized by thermal decomposition of acetylene (C2H2) gas using Ni catalyst at 600°C. As-grown GNFs reveal both planar and helical morphology. We have investigated the structural and electrical properties of multi-walled CNTs (MWNTs)–polymer (polyacrylamide (PAM)) composites. The MWNTs–PAM composites were prepared using as purified, with ball milling and functionalized MWNTs by solution cast technique and characterized through SEM. A comparative study has been made on the electrical property of these MWNTs–PAM composites with different MWNTs loadings. It is shown that the ball milling and functionalization of MWNTs improves the dispersion of MWNTs into the polymer matrix. Enhanced electrical conductivity was observed for the MWNTs–PAM composites. Graphene samples were prepared by thermal exfoliation of graphite oxide. XRD analysis confirms the formation of graphene.

    • Transparent conducting film: Effect of mechanical stretching to optical and electrical properties of carbon nanotube mat

      Tsuyoshi Saotome Hansang Kim David Lashmore H Thomas Hahn

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      We describe in this paper a transparent conducting film (TCF). It is a fibrous layer of multiwalled carbon nanotubes (MWNTs), labeled a dilute CNT mat, that was prepared and unidirectionally stretched to improve both the optical and electrical properties. After stretching by 80% strain, transmittance at 550 nm wavelength was improved by 37% and sheet resistance was reduced to 71% of the original value. The improvement of the transmittance can be explained by increased area of the CNT mat after stretch, and the reduced sheet resistance can be explained by increased density of the CNT alignment in lateral direction due to contraction. Based on the microscopic observation before and after stretch, models to describe the phenomena are proposed. By further expanding on this method, it may be possible to obtain a transparent conducting carbon nanotube film which is crack-resistant for solar cell applications.

    • Transparent conducting film: Effect of vacuum filtration of carbon nanotube suspended in oleum

      Tsuyoshi Saotome Hansang Kim Zhe Wang David Lashmore H Thomas Hahn

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      Vacuum filtration process to fabricate a transparent conducting carbon nanotube (CNT) film is reported. A CNT mat, which is a fibrous sheet of long multi-walled carbon nanotubes (MWNT), was prepared and dispersed in oleum by solution-sonication. The suspension was then vacuum filtered to obtain a thin MWNT layer with improved dispersion. Sheet resistance of the obtained MWNT layer was increased despite the improved dispersion. SEM micrographs and energy dispersive spectroscopy results indicated that the increase of the sheet resistance could be attributed to degradation and oxidation of the MWNT bundles. Though the chemical approach in this study did not improve the electrical property of the CNT mat, a mechanical approach proposed in our recent work was deemed suitable to enhance optical and electrical properties of the CNT mat.

    • Preparation of cellulose fibres with antibacterial Ag-loading nano-SiO2

      Wang Shuhua Niu Runlin Jia Husheng Wei Liqiao Daijinming Liu Xuguang Xu Bingshe

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      The antibacterial cellulose fibres with acrylamide polymerization and Ag-loading SiO2 nanoantibacterial materials were successfully prepared. The chemical structures and morphologies of antibacterial cellulose fibres were characterized by Fourier transformation infrared spectrum (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that acrylamide was adsorbed on the surface of the cellulose fibres and formed a layer with thickness of 50–100 nm. The nano-SiO2 composite antibacterial materials were combined with cellulose fibres firmly by infiltrating into polyacrylamide layer about 100 nm. The antibacterial cellulose fibres with antibacterial layer owned excellent antibacterial effect.

    • Preparation of intercalated polyaniline/clay nanocomposite and its exfoliation exhibiting dendritic structure

      N Srivastava Y Singh R A Singh

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      Intercalated composite of polyaniline and clay has been reported. The composite was prepared by in situ polymerization of aniline within the layers of `illite’ clay. The composite was characterized for its structural, spectral, and microscopic properties. At higher level of loading the layered structure of composite breaks forming exfoliated composite, revealing well-defined nanosized dendritic morphology of polyaniline.

    • Synthesis and characterization of fluorophore attached silver nanoparticles

      S C G Kiruba Daniel T Anitha Sironmani V Tharmaraj K Pitchumani

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      Silver nanoparticles stabilized by soluble starch were synthesized and characterized. in vivo studies in rats showed no toxicity and revealed their distribution in various tissues and permeability across BBB. This starch stabilized silver nanoparticles have good biological characteristics to act as a potential promising vector for gene/drug delivery.

    • Synthesis of copper nanoparticles in polycarbonate by ion implantation

      Annu Sharma Suman Bahniwal Sanjeev Aggarwal S Chopra D Kanjilal

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      Copper nanoparticles have been synthesized in polycarbonate by 75 KeV Cu ion implantation with various doses ranging from 6.4 × 1015 to 1.6 × 1017 ions/cm2 with a beam current density of 800 nA/cm2. The composites formed were structurally characterized using Ultraviolet-Visible (UV-Visible) absorption spectroscopy. The appearance of particle plasmon resonance peak, characteristic of copper nanoparticles at 603 nm in absorption spectra of polycarbonate implanted to a dose of 1.6 × 1017 ions/cm2, indicates towards the formation of copper nanoparticles in polycarbonate. Transmission electron microscopy further confirms the formation of copper nanoparticles having size ∼ 3.15 nm. The formation of copper nanoparticles in the layers carbonized by Cu implantation has been discussed. The synthesized copper-polycarbonate nanocomposite has been found to be more conducting than polycarbonate as ascertained using current–voltage characteristics.

    • Emulsion-based synthesis of NaA zeolite nanocrystals and its integration towards NaA membranes

      M K Naskar A Das D Kundu M Chatterjee

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      NaA zeolite nanoparticles (seed crystals) of size 50–65 nm were synthesized using water-in-oil (w/o) type emulsions at a considerably low temperature of 65 ± 1°C in a short duration of 2 h. The emulsions were stabilized using non-ionic surfactants e.g. sorbitan monooleate (Span 80), sorbitan monolaurate (Span 20), polyoxyethylene(5)nonylphenylether with ethoxy numbers of 5 (Igepal CO-520) and polyoxyethylene sorbitan monooleate (Tween 80) of hydrophilic-lipophilic balance (HLB) values of 4.3, 8.6, 10 and 15 respectively. Among the surfactants, the intermediate HLB values of 8.6 (Span 20) and 10 (Igepal CO-520) were effective in synthesizing highly dispersible NaA nanoparticles of size 50–65 nm. The membrane prepared hydrothermally in multi-steps at 65 ± 1°C, using the Span 20-derived seed crystals deposited on porous support, showed the formation of high quality interlocked NaA coating. Single gas nitrogen (N2) permeation of the membrane exhibited a permeance value of 1.01 × 10-8 mol m-2 s-1 Pa-1 at ambient temperature (30°C).

    • Combustion synthesis and characterization of Ba2NdSbO6 nanocrystals

      V T Kavitha R Jose S Ramakrishna P R S Wariar J Koshy

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      Nanocrystalline Ba2NdSbO6, a complex cubic perovskite metal oxide, powders were synthesized by a self-sustained combustion method employing citric acid. The product was characterized by X-ray diffraction, differential thermal analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. The as-prepared powders were single phase Ba2NdSbO6 and a mixture of polycrystalline spheroidal particles and single crystalline nanorods. The Ba2NdSbO6 sample sintered at 1500°C for 4 h has high density (∼ 95% of theoretical density). Sintered nanocrystalline Ba2NdSbO6 had a dielectric constant of ∼ 21; and dielectric loss = 8 × 10-3 at 5 MHz.

    • A facile synthesis of ZnS nanocrystallites by pyrolysis of single molecule precursors, Zn (cinnamtscz)2 and ZnCl2 (cinnamtsczH)2

      Anil M Palve Shivram S Garje

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      ZnS nanocrystallites were synthesised by pyrolysis method using Zn (cinnamtscz)2 and ZnCl2 (cinnamtsczH)2 (cinnamtsczH = cinnamaldehyde thiosemicarbazone) as single source precursors. The prepared ZnS nanocrystallites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, UV-Vis and fluorescence spectroscopy. The peak broadening in XRD and emission at shorter wavelength in fluorescence spectra showed the presence of nanocrystallites. The blue shift in UV-Vis absorption spectroscopy also proved the formation of nanocrystallites. TEM images show presence of plate-like and spherical ZnS nanoparticles obtained from Zn(cinnamtscz)2 and ZnCl2 (cinnamtsczH)2 respectively.

    • Burstein Moss effect in nanocrystalline CaS : Ce

      Geeta Sharma Puja Chawla S P Lochab Nafa Singh

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      The nanocrystalline CaS : Ce nanophosphors are synthesized by wet chemical co-precipitation method. The particles possess an average size of 10 nm as calculated using Debye–Scherrer formula. The particle size and the crystalline nature of the formed nanoparticles are confirmed by TEM micrograph. The optical studies are carried out using UV–Vis absorption spectroscopy. The absorption edge is found to show blue shift with increasing cerium concentration. The shift may be attributed to Burstein Moss effect.

    • Possibilities of production of nanopowders with high power ELV electron accelerator

      Vladimir Ivanovich Lysenko Sergey Bardakhanov Alexey Korchagin Nikolay Kuksanov Alexander Lavrukhin Rustam Salimov Sergey Fadeev Vladislav Cherepkov Mikhail Veis Andrey Nomoev

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      Electron-beam evaporation of various natural and industrial materials in the atmosphere of different gases at atmospheric pressure can be used for the synthesis of nanosize powders. These powders are characterized by high purity and may exhibit unusual properties. In particular, nanopowders of silicon dioxide and oxide (SiO2, SiO), magnesia (MgO), alumina (Al2O3), titania (TiO2), gadolinium oxide (Gd2O3), various metals (tantalum, molybdenum, nickel, aluminium, copper, silver), semiconductor (Si), nitrides (AlN, TiN), and some other substances had been produced. The process of nanopowder synthesis is highly effective; in particular, the yield of oxides can exceed ten kilograms per hour.

    • Thermoluminescence properties of 𝛾-irradiated Bi doped BaS nanostructures

      Surender Singh Ankush Vij S P Lochab Ravi Kumar Nafa Singh

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      Bismuth doped barium sulphide nanocrystallities were prepared and characterized by XRD. Thermoluminescence (TL) studies of these samples after exposure to gamma radiation were carried out. The TL glow curve of the phosphors have two peaks at 403 K and 658 K while in their bulk counterparts these peaks were reported at 486 K and 570 K (Rao 1986). We noted that TL intensity increases with gamma exposure time in the range 30 min – 41 h which may be explained on the basis of track interaction model (TIM) and a high surface to volume ratio for the nanostructures. The kinetic parameters at various heating rates namely activation energy (E), order of kinetics (b) and frequency factor (s) of BaS : Bi (0.4 mol%) sample was determined using Chen’s method. The deconvolution of curve was done using the GCD function suggested by Kitis. The effect of different heating rates and different amount of dose has also been discussed.

    • Morphological and humidity sensing characteristics of SnO2–CuO, SnO2–Fe2O3 and SnO2–SbO2 nanocooxides

      B C Yadav Preeti Sharma P K Khanna

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      This paper reports the synthesis of SnO2–CuO, SnO2–Fe2O3 and SnO2–SbO2 composites of nano oxides and comparative study of humidity sensing on their electrical resistances. CuO, Fe2O3 and SbO2 were added within base material SnO2 in the ratio 1 : 0.25, 1 : 0.50 and 1 : 1. Characterizations of materials were done using SEM and XRD. SEM images show the surface morphology and X-ray diffraction reveals the nanostructure of sensing materials. The pellets were annealed at 200, 400 and 600°C respectively for 3 h and after each step of annealing, observations were carried out. It was observed that as relative humidity (%RH) increases, there was decrease in the resistance of pellet for the entire range of RH. Results were found reproducible. SnO2–SbO2 shows maximum sensitivity for humidity (12 M𝛺/%RH) among other composites.

    • Synthesis, characterization and evaluation of reflectivity of nanosized CaTiO3/epoxy resin composites in microwave bands

      M Murugan V K Kokate M S Bapat

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      Microwave absorbing materials play a major role in electromagnetic interference and compatibility measurements in anechoic chambers. Nanocrystalline calcium titanate (CT) was synthesized by hydrothermal method and further composites of CT/epoxy resin were fabricated as thin solid slabs of four different weight ratios. The composite material was analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), which reveals that CT was observed to be in the monoclinic phase with an average crystallite size of 24 nm. The reflectivity measurement of the composite materials was carried out by the transmission/reflection method using a vector network analyzer R&S: ZVA40, in the X- and Ku-bands. The effective permittivity and permeability of the samples was also computed with the help of measured transmission and reflection coefficients. The results show that CT with equal weight of epoxy resin provides –30 dB at 8.5 GHz in the X-band and –19.5 dB at 18.0 GHz in the Ku-band. Reflectivity was found to be better than –10 dB for 2.2 GHz and 1.9 GHz for X-band and Ku-band, respectively and encourages use of it as potential microwave absorber material.

    • Mechanical and tribological studies of polymer hybrid nanocomposites with nano reinforcements

      D Lingaraju K Ramji M Pramila Devi U Rajya Lakshmi

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      Developments of nanoparticle reinforced plastics are of growing interest towards the emergence of new materials which enhance optimal utilization of natural resources and particularly of renewable resources. The effects of nanoparticles as fillers in glass–epoxy composite systems on the mechanical and tribological properties have been discussed in this article. The mechanical properties such as tensile strength, impact strength, flexural strength, and hardness have been studied in accordance with ASTM standards. The composites employed in the study have been fabricated using hand lay-up technique. By varying notch radius impact strength is studied. The clay and silica used in the present system were treated with 3-aminopropyltriethoxysilane. The effect of variants in sliding speed, time and applied load on the wear behavior of polymer nanocomposites is studied by measuring the weight changes and observing the surface features using scanning electron microscope. In the experiments with wear test pin having flat face in contact with hardening rotating steel disc, sliding speed, time and loads in the range of 640–1000 RPM, 300–900 s and 5–25 N respectively was used. It is observed that wear rate increases with increasing applied load, time and sliding speeds.

    • Structure–property relationships of electroluminescent polythiophenes: role of nitrogen-based heterocycles as side chains

      S Radhakrishnan S J Ananthakrishnan N Somanathan

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      A series of conjugated polythiophenes containing nitrogen-containing heterocycles as side chain, with differing substituent nature and linkage have been studied using quantum-chemical calculations. The optical properties of synthesized polymers were compared with that of model compounds with intricate structural variations. The theoretically predicted optical characteristics are correlated with the experimentally determined parameters. Experimentally determined band gap and absorption maxima found to follow the predicted trends. Single emissive layer polymeric light emitting diodes are fabricated and the structural influence on photo- and electro-emission was studied in detail. The study shows that the nature of side chain substituent such as number/position of nitrogen atoms and mode of linking of side chain plays a crucial role in deciding the geometry which in turn controls the voltage response of the electroluminescence.

    • Effect of annealing on phase transition in poly(vinylidene fluoride) films prepared using polar solvent

      S Satapathy Santosh Pawar P K Gupta K B R Varma

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      The 𝛾-phase poly (vinylidene fluoride) (PVDF) films are usually prepared using dimethyl sulfoxide (DMSO) solvent, regardless of preparation temperature. Here we report the crystallization of both 𝛼 and 𝛾-phase PVDF films by varying preparation temperature using DMSO solvent. The 𝛾-phase PVDF films were annealed at 70, 90, 110, 130 and 160°C for five hours. The changes in the phase contents in the PVDF at different annealing conditions have been described. When thin films were annealed at 90°C for 5 h, maximum percentage of 𝛽-phase appears in PVDF thin films. The 𝛾-phase PVDF films completely converted to 𝛼-phase when they were annealed at 160°C for 5 h. From X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), differential scanning calorimetry (DSC) and Raman studies, it is confirmed that the PVDF thin films, cast from solution and annealed at 90°C for 5 h, have maximum percentage of 𝛽-phase. The 𝛽-phase PVDF shows a remnant polarization of 4.9 𝜇C/cm2 at 1400 kV/cm at 1 Hz.

    • Facile synthesis of hypercrosslinked resins via chloromethylation and continuous condensation of simple aryl molecules

      Xiaoyan Zhang Qiu Jin Libo Dai Siguo Yuan

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      A sort of non-polystyrene type hypercrosslinked resin was firstly synthesized through chloromethylation of simple aryl molecules (benzene, toluene, naphthalene, diphenyl), succedent continuous Friedel–Crafts alkylation polymerization and post-crosslinking reaction. The chemical and porous structures of these novel resins were characterized with BET, FT–IR and elementary analysis, respectively. The results showed that these novel adsorptive materials possessing abundant crosslinked networks had high specific surface areas (up to 1191.26 m2/g), large pore volumes (0.2–1.4 ml/g), narrow pore size distributions (mainly in the range of micropores and small mesopores).

    • Temperature dependent damping studies of Ni–Mn–Ga polymer composites

      R Senthur Pandi M Mahendran R Chokkalingam M Manivelraja V Chandrashekaran

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      Mechanical properties of ferromagnetic shape memory alloy (FSMA) polyurethane (PU) polymer composites are studied using dynamic mechanical analysis (DMA) at different temperatures. The sample used in the study is Ni–Mn–Ga/PU polymer composite. DMA studies reveal that the mechanical modulus decreases, when the temperature increases. The peak in internal friction (tan𝛿) appears twice due to martensite transformation of the reinforced particles and glass transition of the polymer matrix. The strain is due to the motion of twin boundaries rather than the phase transformations. Twin boundary motion is found to be the root cause for the martensite-austenite transformation and vice versa, and leads to enhanced damping mechanism. Speculations on twin boundaries of this sample to show concrete evidence on change in internal friction (tan𝛿) are still underway. This paper proposes that Ni–Mn–Ga/PU polymer composites can be used as efficient dampers.

    • Functionalization of terminal carbon atoms of hydroxyl terminated polybutadiene by polyazido nitrogen rich molecules

      Rajavelu Murali Sankar Tapta Kanchan Roy Tushar Jana

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      We report a novel synthetic approach for the attachment of the polyazido nitrogen rich molecule on to the hydroxyl terminated polybutadiene (HTPB) backbone. The terminal carbon atoms of the HTPB are functionalized by attaching cyanuric chloride (CYC) covalently on the HTPB backbone. Further reaction of this modified HTPB with sodium azide yields polyazido nitrogen rich HTPB. The unique physico-chemical properties and the microstructure of the HTPB do not get affected upon modification. IR, gel permeable chromatography (GPC) and absorption spectroscopy studies prove that the polyazido nitrogen rich molecules are covalently attached at the terminal carbon atoms of the HTPB. The π electron delocalization owing to long butadiene chain, strong electron withdrawing effect of the triazine molecules are the major driving forces for the covalent attachment of the triazine at the terminal carbon atoms of the HTPB. The disruption of the intermolecular hydrogen bonding between the terminal hydroxyl groups of the HTPB chains and the presence of hydrogen bonding between the N atoms of the triazine ring with OH group of the HTPB are observed. Theoretical study also reveals the existence of the hydrogen bonding between the OH and N. Theoretical calculation shows that the detonation performance of the polyazido nitrogen rich HTPB are very promising.

    • Nonionic emulsion-mediated synthesis of zeolite beta

      Yuguo Shen Ying Zhang Chao Jin Ying Cao Wei Gao Lishan Cui

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      Zeolite beta synthesis was first carried out in a newly developed emulsion system containing nonionic polyoxyethylated alkylphenol surfactant, which showed interesting non-conventional features. Compared to the conventional hydrothermal synthesis of zeolite beta, the reported nonionic emulsion system showed a faster nucleation rate. Furthermore, the emulsion system could stabilize the beta product and retarded its further transformation to ZSM-5 even under the high crystallization temperature at 453 K. Additionally, the beta particle size could be tuned by the adoption of different lengths of alkyl chain in the surfactant and cosurfactant. Control experiments showed each emulsion component played a crucial role in the zeolite beta growth. The approach proposed in this paper might be extended to apply for the syntheses of other types of zeolites with particle size under control.

    • Effect of surfactants in synthesis of CsH2PO4 as protonic conductive membrane

      Soraya Hosseini Wan Ramli Wan Daud Marzieh Badiei Abdul Amir Hassan Kadhum Abu Bakar Mohammad

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      Cesium dihydrogen phosphate (CDP) powders were synthesized by cetyltrimethylammoniumbromide (CTAB), polyoxyethylene-polyoxypropylene (F-68) and mixture of both surfactants F-68 : CTAB with two molar ratios 0.06 and 0.12 as surfactant solutions at room temperature. The synthesized CsH2PO4 is characterized by ICP, XRD, TEM, SEM, FT–IR, BET and IS techniques. Based on the width of the (011) XRD diffraction peak and BET measurement, the average size of nanoparticles was ∼ 10 nm in diameter, while the TEM images indicate smaller size than both techniques. The analysis reveals existence of P and Cs with mole ratio 1.02 ± 0.03 which is compatible to molar ratio CsH2PO4 formula. The experimental results show that the conductivities increase in the order of CDPCTAB > CDP(F-68 : CTAB)0.12 > CDP(F-68:CTAB)0.06 > CDPF-68. The sequence of increasing conductivity is in accordance with the ion exchange capacities of the samples that has direct proportional effect on the proton mobility of samples. Indeed CTAB as cationic surfactant shows the highest proton mobility in the as-obtained samples.

    • Crystallization and microstructures of Y–Si–Al–O–N glass–ceramics containing main crystal phase Y3Al5O12

      Xiuying Li Anxian Lu

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      A glass with the nominal composition of 28Y48Si24Al83O17N (in equal percentage) was chosen as parent glass in this paper to prepare Y3Al5O12-based glass–ceramics. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to assess the crystallization process of the parent glass. YAG as the only crystalline phase appears in all glass–ceramics produced under 1250°C. A small amount of O′-Sialon secondary phase starts to precipitate from parent glass samples as heat treatment temperature increases to 1250°C. Grain size of the dendrite crystal which corresponds to YAG phase increases and the dendrite branches get thickened as heat treatment temperature increases. Moreover, grain size of YAG phase resulting from two-stage heat treatment is much smaller than that of YAG phase obtained by one-stage heat treatment. The results are relevant to developing improved crystallization treatments for glasses with potential for crystallization to YAG-based glass–ceramics and for heat treatments of YAG/𝛽-SiAlON materials.

    • Influence of curing conditions on durability of alkali-resistant glass fibres in cement matrix

      Arabi Nourredine

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      Glass fibres in concrete material often increase the flexural strength. However, these fibres when in contact with cement are altered by alkali reactions due to the presence of portlandite. This study presents the results of investigation to show the effect of curing conditions on the durability of alkali-resistant glass fibres in cement matrix. Test results show that even alkali resistant fibres treated with zirconium oxide present the same degradation phenomenon. They also show that the nature of the cement has a large influence on the protection of the fibres: the Portland CEM II is less damaging than the CEM I. The substitutions of a part of cement by silica fume gave no substantial improvements to the mechanical strength of the glass fibre reinforced cement (GFRC). However, the observed microstructures in the samples show that the degradation is weakened with the addition of silica fumes. The analytical techniques used in this study are scanning electron microscope (SEM) and X-ray diffraction.

    • Processing–structure–property relations of chemically bonded phosphate ceramic composites

      H A Colorado C Hiel H T Hahn

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      Mechanical properties and microstructures of a chemically bonded phosphate ceramic (CBPC) and its composite with 1.0 wt% graphite nanoplatelets (GNPs) reinforcement have been investigated. Microstructure was identified by using optical and scanning electron microscopes, X-ray tomography, and X-ray diffraction. In addition, weight loss of the resin at room temperature was studied. The microstructure characterization shows that CBPC is itself a composite with several crystalline (wollastonite and brushite) and amorphous phases. SEM and micro tomography show a homogeneous distribution of crystalline phases. Bending and compression strength of the CBPC was improved by reducing bubbles via preparation in vacuum.

    • Interface-dependent resistance switching in Nd0.7Sr0.3MnO3 ceramics

      S S Chen C P Yang C L Ren R L Wang H Wang I V Medvedeva K Baerner

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      Interface-dependent electric-pulse-induced resistance switching effect (EPIR) in Nd0.7Sr0.3MnO3 ceramics was studied. The results reveal that the EPIR effect originates from the interface between the electrodes and the bulk, and the EPIR ratio as well as the high and low resistance states can be strongly influenced by applying a large electrical field on the sample for different intervals. Also, the pulse parameters have great effect on the stability of EPIR and the optimal pulse width, pulse amplitude and read bias are obtained. Based on the space charge limited current mechanism together with the theory of interfacial charge-trapped state, the interface-dependent resistance switching effect is discussed.

    • Effect of surface roughness on grain growth and sintering of alumina

      Padmaja Parameswaran Nampi Shoichi Kume Yuji Hotta Koji Watari

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      The production of ceramic bodies with less surface roughness is industrially important when one considers the aspect of final machining processes. Hence an attempt have been made to study the variation in surface roughness parameters (𝑅a, 𝑅y, 𝑅z) of alumina having three different kinds of roughness features at different sintering temperatures. Variation in surface roughness properties are also correlated with grain size. 𝑅z shows significant difference between fine and intermediate surfaces, hence predicts small difference in their microstructural features. As a general trend, average grain size increases with increase in sintering temperature, but wide distribution of grains with enhanced non-uniform grain growth is observed when the surface is coarse. Hence, creation of fine surface in the green body is necessary for homogeneously distributed grains with controlled uniform grain growth. The final roughness and grain size of the sintered alumina depend on the initial surface roughness of the green body.

    • Bonding strength of Al/Mg/Al alloy tri-metallic laminates fabricated by hot rolling

      X P Zhang M J Tan T H Yang X J Xu J T Wang

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      One of major drawbacks of magnesium alloy is its low corrosion resistance, which can be improved by using an aluminized coating. In this paper, 7075 Al/Mg–12Gd–3Y–0.5Zr/7075 Al laminated composites were produced by a hot roll bonding method. The rolling temperature was determined based on the flow stresses of Mg–12Gd–3Y–0.5Zr magnesium alloy and 7075 Al alloy at elevated temperature. The bonding strength of the laminate composites and their mechanism were studied. The effects of the reduction ratio (single pass), the rolling temperature, and the subsequent annealing on the bonding strength were also investigated. It was observed that the bonding strength increased rapidly with the reduction ratio and slightly with the rolling temperature. The bonding strength increases with the annealing time until the annealing time reaches 2 h and then decreases. The mechanical bond plays a major role in the bonding strength.

    • High temperature oxidation of Ti–48Al–8Cr–2Ag alloy with sputtered coating at 1000°C in air

      Y J Xi Y J Liu

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      Magnetron-sputter deposition was used to produce a Ti–48Al–8Cr–2Ag (at.%) coating on a cast alloy substrate with the same composition. The oxidation behaviour of the cast Ti–48Al–8Cr–2Ag alloy and its sputtered coating was investigated in air at 1000°C. The resulting scale structures were analyzed in great detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanocrystalline coating showed higher oxidation rate than the cast alloy, because an outer TiO2 layer formed over a finegrain Al2O3 scale on the coating. The oxidation mechanism was discussed.

    • Determination of optimum welding parameters in connecting high alloyed X53CrMnNiN219 and X45CrSi93 steels by friction welding

      Mehmet Uzkut Bekir Sadik Ünlü Mustafa Akdağ

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      In this study, different welding parameters were applied to two different steels with high alloys and mechanical and metallographical investigations are performed. Thus, the optimum welding parameters were determined for these materials and working conditions. 12.30 diameter steel bars made up of 1.4871 (X53CrMnNiN219) and 1.4718 (X45CrSi93) steel were used as experimental material. The material loss increased with increase in friction and rotating pressure. No fracture at the welding region was observed and the highest fracture energy was identified in B5 group. Based on micro hardness investigation; the hardness profile reached its minimum value at the welding region.

    • Magnetocaloric effect of Gd5Si2Ge2 alloys in low magnetic field

      Hong Zeng Chunjiang Kuang Jiuxing Zhang Ming Yue

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      The magnetocaloric effect of Gd5Si2Ge2 alloys under heat treatment conditions are investigated in low magnetic fields. The magnetocaloric effect (MCE) is studied by measuring magnetic entropy change (𝛥 𝑆M) and adiabatic temperature change (𝛥 𝑇ad) in a magnetic field of 1.5 T using a vibrating sample magnetometer (VSM) and a home-made magnetocaloric effect measuring apparatus, respectively. The maximum 𝛥 𝑆M of the alloys increases by 200% from 4.38 to 13.32 J kg-1 K-1, the maximum 𝛥 𝑇ad increases by 105% from 1.9 to 3.9 K when compared to the as-cast due to the homogeneous composition distribution and microstructure, while the magnetic ordering temperature is slightly reduced. These results indicate that the annealed Gd5Si2Ge2 compounds are promising as high-performance magnetic refrigerants working room temperature in relatively low magnetic fields.

    • Effect of annealing process of iron powder on magnetic properties and losses of motor cores

      Fuzheng Yin Haibo Yang Jianjun Tian De-An Pan Jian Wang Shengen Zhang

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      Iron powder magnetic cores are used as soft magnetic rotors, in micro special motors such as BS brake motors, refrigerator compressor motors and brushless servo motors. Heat treatment of iron powder played an important role in the magnetic properties and loss of the motor cores. After the annealing process, the cracks and the pores on the surface of the powder decreased which in turn decreased the micro-hardness. The Vickers-hardness of the powder decreased from 50–42, while the resistance of the cores increased by 87% after annealing at 400°C for 30 min. The amplitude permeability and magnetic loss of the cores reached the maximum and minimum values, respectively. The magnetic loss of the cores was separated into hysteresis loss and eddy current loss by Stoppels Method which were decreased by the annealing process.

    • Fabrication and performances of MWCNT/TiO2 composites derived from MWCNTs and titanium (IV) alkoxide precursors

      Mingliang Chen Fengjun Zhang Wonchun Oh

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      Multi-walled carbon nanotubes (MWCNTs)/TiO2 composites were synthesized by sol–gel technique using titanium (IV) 𝑛-butoxide (TNB), titanium (IV) isopropoxide (TIP) and titanium (IV) propoxide (TPP) as different titanium alkoxide precursors. The as-prepared composites were comprehensively characterized by BET surface area, SEM, XRD, EDX and UV-Vis absorption spectroscopy. The samples were evaluated for their photocatalytic activity towards the degradation of methylene blue (MB) under UV irradiation. The results indicated that the sample MPB had best excellent photocatalytic activity among the three kinds of samples. Furthermore, we also used piggery waste to determine the photocatalytic activity for the MWCNT/TiO2 composites by using a chemical oxygen demand (COD) method. It seemed all of the samples have an excellent removal effect of COD. From the results of the bactericidal test, MWCNT/TiO2 composites with sunlight had a greater effect on E. coli than any other experimental conditions.

    • Synthesis and characterization of composites of mixed oxides of iron and neodymium in polymer matrix of aniline–formaldehyde

      Sajdha H N Sheikh B L Kalsotra N Kumar S Kumar

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      Nanocomposites of mixed oxides of iron and neodymium in polymer matrix of anilineformaldehyde are reported. The composites have been obtained by treating the aqueous solution of aniline, hydrochloric acid and formaldehyde with halide of iron and neodymium oxide. The infra-red spectra show broad peaks at ∼ 590 cm-1 and at ∼ 610 cm-1 due to the presence of oxides of both iron and neodymium. In heated samples, the absorption peaks due to metal oxides are better resolved. A broad and strong peak in XRD spectra at 2𝜃 value of 35.69920 corresponds to spinel 𝛾-Fe2O3. 57Fe Mössbauer spectrum for unheated sample gives Mössbauer parameters, i.e. isomer shift (𝛿), quadrupole splitting (𝛥 𝐸) and effective magnetic field (Heff). Transmission electron microscopy (TEM) micrographs reveal well dispersed particles at different magnifications. Vibrating sample magnetometry (VSM) studies indicate that the ferrite nanoparticles exhibit characteristics of ferromagnetism.

    • Unusual route for preparation of manganese(II), cobalt(II), zinc(II) and cadmium(II) carbonate compounds: synthesis and spectroscopic characterizations

      Moamen S Refat Mohsen M Al-Qahtani

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      The manganese(II) carbonate, MnCO3.H2O, cobalt(II) carbonate, CoCO3.4H2O, zinc(II) carbonate, ZnCO3 and cadmium(II) carbonate, CdCO3, respectively, were synthesis by a new simple unusual route during the reaction of aqueous solutions of MnX2, CoX2, ZnX2 and CdX2, where (X = Br- and ClO$^{-}_{4}$) with urea at high temperature within ∼ 90°C for 6 h. The infrared spectra of the reaction products clearly indicate the absence of the bands of urea, but show the characteristic bands of ionic carbonate, CO$^{2-}_{3}$. A general mechanism describing the preparation of manganese(II), cobalt(II), zinc(II) and cadmium(II) carbonate compounds are discussed.

    • MgAl2O4–𝛾-Al2O3 solid solution interaction: mathematical framework and phase separation of 𝛼-Al2O3 at high temperature

      Soumen Pal A K Bandyopadhyay S Mukherjee B N Samaddar P G Pal

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      Although existence of MgAl2O4–𝛾-Al2O3 solid solution has been reported in the past, the detailed interactions have not been explored completely. For the first time, we report here a mathematical framework for the detailed solid solution interactions of 𝛾-Al2O3 in MgAl2O4 (spinel). To investigate the solid solubility of 𝛾-Al2O3 in MgAl2O4, Mg–Al spinel (MgO–𝑛Al2O3; 𝑛 = 1, 1.5, 3, 4.5 and an arbitrary high value 30) precursors have been heat treated at 1000°C. Presence of only non-stoichiometric MgAl2O4 phase up to 𝑛 = 4.5 at 1000°C indicates that alumina (as 𝛾-Al2O3) present beyond stoichiometry gets completely accommodated in MgAl2O4 in the form of solid solution. 𝛾 → 𝛼 alumina phase transformation and its subsequent separation from MgAl2O4 has been observed in the Mg–Al spinel powders (𝑛 > 1) when the 1000°C heat treated materials are calcined at 1200°C. In the mathematical framework, unit cell of MgAl2O4 (Mg8Al16O32) has been considered for the solid solution interactions (substitution of Mg2+ ions by Al3+ ions) with 𝛾-Al2O3. It is suggested that combination of unit cells of MgAl2O4 takes part in the interactions when 𝑛 > 5 (MgO–𝑛Al2O3).

    • Enhancement of MgAl2O4 spinel formation from coprecipitated precursor by powder processing

      Soumen Pal A K Bandyopadhyay S Mukherjee B N Samaddar P G Pal

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      Although low temperature fast coprecipitation technique has been used to synthesize stoichiometric (MgO–nAl2O3, 𝑛 = 1) MgAl2O4 spinel forming precursor, delayed spinellization has always been the concern in this process. In this article, the precursor of this ‘fast technique’ has been used for bulk production by further processing by high speed mixing with solvents and mechanical activation by attrition milling in terms of superior spinellization. At 1000°C, MgAl2O4 – 𝛾-Al2O3 solid solution and MgO phases are formed (spinel formed by 1000°C is regarded as primary spinel). At higher temperatures, due to large agglomerate size, MgO can not properly interact with the exsolved 𝛼-Al2O3 from spinel solid solution to form secondary spinel; and consequently spinellization gets affected. Solvent treatment and attrition milling of the coprecipitated precursor disintegrate the larger agglomerates into smaller size (effect is more in attrition). Then MgO comes in proper contact with exsolved alumina, and therefore total spinel formation (primary + secondary) is enhanced. Extent of spinellization, for processed calcined samples where some alumina exists as solid solution with spinel, can be determined from the percentage conversion of MgO. Analysis of the processed powders suggests that the 4 h attrited precursor is most effective in terms of nano size (< 25 nm) stoichiometric spinel crystallite formation at ≤ 1100°C.

    • Infrared spectra, Raman laser, XRD, DSC/TGA and SEM investigations on the preparations of selenium metal, (Sb2O3, Ga2O3, SnO and HgO) oxides and lead carbonate with pure grade using acetamide precursors

      Moamen S Refat Khaled M Elsabawy

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      Ga2O3, Se metal, SnO, Sb2O3, HgO and PbCO3 are formed upon the reaction of acetamide aqueous solutions with Ga(NO3)3, SeO2, SnCl2, SbCl3, HgCl2 and Pb(NO3)2, respectively, at 90°C. Different amorphous or crystalline phases can be obtained depending upon the experimental conditions (molar ratios, metal salts and temperature). The chemical mechanisms for the formations of this metal, oxides or carbonate are discussed and the X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscope (AFM) are described. The type of metal ions plays an important role in the decomposition of acetamide, leading to the formation of solid stable (metal, oxides or carbonate), soluble and gases species. These new precursors are more stable preventing the rapid precipitation of metal, oxides or carbonate. Furthermore, this route allows the formation of pure compounds in solutions.

    • Preparation of titanium diboride powders from titanium alkoxide and boron carbide powder

      Hamed Sinaei Pour Fard Hamidreza Baharvandi

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      Titanium diboride powders were prepared through a sol–gel and boron carbide reduction route by using TTIP and B4C as titanium and boron sources. The influence of TTIP concentration, reaction temperature and molar ratio of precursors on the synthesis of titanium diboride was investigated. Three different concentrations of TTIP solution, 0.033/0.05/0.1, were prepared and the molar ratio of B4C to TTIP varied from 1.3 to 2.5. The results indicated that as the TTIP concentration had an important role in gel formation, the reaction temperature and B4C to TTIP molar ratio showed obvious effects on the formation of TiB2. Pure TiB2 was prepared using molar composition of Ti : B4C = 1 : 2.3 and the optimum synthesis temperature was 1200°C.

    • Synthesis and nonlinear optical characterization of new 1,3,4-oxadiazoles

      B Chandrakantha Arun M Isloor Reji Philip M Mohesh Prakash Shetty A M Vijesh

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      A new series of 1,3,4-oxadiazole derivatives containing 2-fluoro-4-methoxy phenyl were synthesized by refluxing mixture of acid hydrazide 3 with different aromatic carboxylic acids (a–e) in phosphorous oxychloride. These newly synthesized compounds were characterized by NMR, mass spectral, and IR spectral studies, and also by C, H, N analyses. The open-aperture z-scan experiment was employed to measure the optical nonlinearity of the samples at 532 nm, using 5 ns laser pulses. The measurements indicate that compound 4a, which contains Bromine, behaves as an optical limiter at this wavelength, with potential applications in optoelectronics.

    • Hyperpolarizability studies of some nonconjugated twin donor–acceptor molecules

      Elizabeth Chirackal Varkey Krishnapillai Sreekumar

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      Extensive theoretical calculation on the effects of spacer length enhancement on the second-order NLO properties of twin donor acceptor molecules having two amide units bridged by the CH2 spacers was performed. The role of such aliphatic bridges on the Donor–Acceptor groups was computed by ZINDO/CV quantum chemical formalism. The odd-even effects were observed in twin donor acceptor systems (with two aliphatic units) linked by an alkyl spacer of varying length from 𝑛 = 1 to 𝑛 = 12. The system considered for the present study was 𝑁,𝑁'-alkane-(1, 𝑛) diyl bis-4-hydroxy hexanamides. For an odd number of CH2 spacers, the 𝛽 value was an order of magnitude higher than that for the even number of CH2 spacers. The origin for such oscillation is attributed to the similar oscillations in the dipole moment difference between the ground state and the dipole allowed state and to some extent on the variation in the oscillator strength.

    • Structural, dielectric and multiferroic properties of Er and La substituted BiFeO3 ceramics

      Pragya Pandit S Satapathy Poorva Sharma P K Gupta S M Yusuf V G Sathe

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      Erbium (Er) and lanthanum (La) substituted BiFeO3 (BFO) ceramics have been prepared through conventional solid solution route. X-ray diffraction data indicated a gradual phase transition from rhombohedral to monoclinic structure in Bi0.9–𝑥 La0.1Er𝑥 FeO3 (𝑥 = 0.05, 0.07 and 0.1) (BLEFO𝑥 = 0.05, 0.07,0.1) ceramics. Differential thermal analysis (DTA) measurements of BFO samples showed a ferroelectric transition at 835°C, whereas it is shifted to 792°C for BLEFO𝑥 = 0.1. The Raman spectra of BLEFO𝑥 = 0.05,0.07,0.1 samples showed the shift of Raman modes to higher wavenumbers and suppression of A1 modes indicating decrease in ferroelectricity. The Raman spectra also indicated the structural transformation due to Er and La substitution in BFO. On subsequent erbium doping, the intrinsic dielectric constant is found to decrease from 68 (for pure BFO) to 52 for BLEFO𝑥 = 0.05 to 43 for BLEFO𝑥 = 0.07 but increased to 89 for BLEFO𝑥 = 0.1 when compared to pure BFO. The increase in Er content resulted in the increase in spontaneous magnetization (0.1178 emu/g at 8T for BLEFO𝑥 = 0.1) due to collapse of spin cycloid structure. Ferroelectric remnant polarization of BLEFO𝑥 = 0.05 and BLEFO𝑥 = 0.07 decreases when compared to pure BFO while small remnant polarization (close to paraelectric behaviour) is evident for BLEFO𝑥 = 0.1.

    • Structural, dielectric and electrical properties of CaBa4SmTi3Nb7O30 ferroelectric ceramic

      Prasun Ganguly A K Jha

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      The polycrystalline sample of CaBa4SmTi3Nb7O30, a member of tungsten bronze family, was prepared by solid-state reaction method. X-ray diffraction analysis shows the formation of single-phase compound with an orthorhombic structure at room temperature. Scanning electron micrograph of the material shows uniform distribution of grains. Detailed studies of dielectric properties of the compound as a function of temperature at different frequencies suggest that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 198°C, and exhibits non-relaxor kind of diffuse phase transition. The ferroelectric nature of the compound has been confirmed by recording polarization–electric field hysteresis loop. Piezoelectric and pyroelectric studies of the compound have been discussed in this paper. Electrical properties of the material have been analyzed using complex impedance technique. The Nyquist plots manifest the contribution of grain boundaries (at higher temperature), in addition to granular contribution (at all temperatures) to the overall impedance. The temperature dependence of dc conductivity suggests that the compound has negative temperature coefficient of resistance (NTCR) behaviour. The frequency dependence of ac conductivity is found to obey Jonscher’s universal power law. The observed properties have been compared with calcium free Ba5SmTi3Nb7O30 compound.

    • Dielectric relaxation and ionic conductivity studies of Na2ZnP2O7

      S Chouaib A Ben Rhaiem K Guidara

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      The Na2ZnP2O7 compound was obtained by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction, infrared analysis and electrical impedance spectroscopy. The impedance plots show semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance 𝑅p and constant phase elements CPE. Dielectric data were analyzed using complex electrical modulus 𝑀* for the sample at various temperatures. The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The conductivity 𝜎d.c. follows the Arrhenius relation. The near value of activation energies obtained from the analysis of 𝑀'' and conductivity data confirms that the transport is through ion hopping mechanism, dominated by the motion of the Na+ ions in the structure of the investigated materials.

    • Microstructure and microwave dielectric properties of (Zn1–𝑥Mg𝑥)2SiO4 ceramics

      Bo Li Ying Yuan Shuren Zhang Hongmei Jiang

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      (ZnMg)2SiO4 powders was prepared by the sol–gel process, and the microstructure and dielectric properties of (Zn1–𝑥Mg𝑥)2SiO4 microwave materials were investigated systematically. TG-DSC and XRD analyzes for gels indicate that the (ZnMg)2SiO4 with pure willemite phase could be obtained at low temperature of 850°C. Further, XRD illustrates that just small amounts of Mg can be incorporated into Zn2SiO4 lattice, and the solid solution limit of Mg in Zn2SiO4 is about 𝑥 = 0.1. By appropriate Mg substitution for Zn, the sintering range is widened and the sintering temperature of Zn2SiO4 ceramics can be lowered effectively. SEM shows that Mg-substitution for Zn can promote the grain growth of Zn2SiO4. Moreover, the microwave dielectric properties strongly depended on the substitution content of Mg and sintering temperatures. (Zn0.8Mg0.2)2SiO4 dielectrics sintered at 1170°C show the condense microstructure with small uniform grains and best microwave properties: 𝜀r = 6.3, 𝑄 × 𝑓 = 189800 GHz and 𝜏f = –63 ppm/°C.

    • Phase transition and dielectric study in Ba0.95Dy0.05TiO3 ceramic

      M R Panigrahi S Panigrahi

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      Temperature and frequency dependence dielectric permittivity of Ba0.95Dy0.05TiO3 ceramic has been studied in the temperature range of 100–350 K at the frequencies, 1 kHz, 10 kHz, 100 kHz and 1 mHz. Diffuse phase transition and frequency dispersion is observed in the permittivity-vs-temperature plots. This has been attributed to the occurrence of relaxor ferroelectric behaviour. The observed relaxor behaviour has been quantitatively characterized based on phenomenological parameters. A comparison with the Zr doped BaTiO3 has also been presented. The microstructure of as-sintered samples shows a dense and almost uniform micrograph without any impurity phases; the grains are almost spherical with random orientation.

    • Dielectric and piezoelectric properties of Bi0.5(Na0.82K0.18)0.5 TiO3–LiSbO3 lead-free piezoelectric ceramics

      Zhou Chong-Rong Chai Li-Yuan

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      The (1–𝑥)Bi0.5(Na0.82K0.18)0.5TiO3–𝑥LiSbO3 (𝑥 = 0−0.03) lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method and the effect of LiSbO3 addition on microstructure and electrical properties of the ceramics was investigated. The results of XRD measurement show that Li+ and Sb5+ diffuse into the Bi0.5(Na0.82K0.18)0.5TiO3 lattices to form a solid solution with a pure perovskite structure. The LiSbO3 addition has no remarkable effect on the crystal structure. However, a significant change in grain size took place. Simultaneously, with increasing amount of LiSbO3, the temperature for a antiferroelectric to paraelectric phase transition clearly increases. The piezoelectric constant 𝑑33 and the electromechanical coupling factor 𝑘p show an obvious improvement by adding small amount of LiSbO3, which shows optimum values of 𝑑33 = 175 pC/N and 𝑘p = 0.36 at 𝑥 = 0.01.

    • Ce and Eu activated Na2Zn5(PO4)4, a new promising novel phosphor

      K N Shinde S J Dhoble Animesh Kumar

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      A new efficient phosphor, Eu2+/Eu3+ and Ce3+ activated Na2Zn5(PO4)4 has been synthesized by solid-state reaction technique at high temperature. X-ray powder diffraction analysis confirmed the formation of Na2Zn5(PO4)4 host lattice. Scanning electron microscopy indicated that the microstructure of the phosphor consisted of irregular fine grains with a size of about 0.5–2 𝜇m. Photoluminescence excitation spectrum measurements of Ce3+ activated Na2Zn5(PO4)4 show that the phosphor can be efficiently excited by UV-Vis light from 280 to 310 nm to realize emission in the visible (blue) range due to the 5𝑑–4𝑓 transition of Ce3+ ions which is applicable for scintillation purpose, whereas Eu2+/Eu3+ activated Na2Zn5(PO4)4 phosphor emits blue, green and red emission spectrum shows at 487 nm, 546 nm with a dominant peak at 611 nm respectively, due to Eu2+/Eu3+ ions which is promising candidate for solid state lighting. Therefore, newly synthesised, by low cost and easy technique prepared, novel phosphors may be useful as RGB phosphor for solid state lighting application.

    • Hardness of metallic crystals

      Wuhui Li Fengzhang Ren Juanhua Su Zhanhong Ma Ke Cao Baohong Tian

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      This paper presents a new formula for calculating the hardness of metallic crystals, resulted from the research on the critical grain size with stable dislocations. The formula is 𝐻 = 6 𝑘𝐺/[𝜋(1 – 𝜈)𝑒𝜂], where 𝐻 is the hardness, 𝑘 the coefficient, 𝐺 the shear modulus, 𝜈 the Poisson’s ratio, 𝜂 a function of the radius of an atom (𝑟) and the electron density at the atom interface (𝑛). The formula will not only be used to testify the critical grain size with stable dislocations, but also play an important role in the understanding of mechanical properties of nanocrystalline metals.

    • 𝑃-wave velocity test for assessment of geotechnical properties of some rock materials

      Saffet Yagiz

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      𝑃-wave velocity test, a non-destructive and easy method to apply in both field and laboratory conditions, has increasingly been conducted to determine the geotechnical properties of rock materials. The aim of this study is to predict the rock properties including the uniaxial compressive strength, Schmidt hardness, modulus of elasticity, water absorption and effective porosity, slake durability index, saturated and dry density of rock using 𝑃-wave velocity (𝑉p). For this purpose geotechnical properties of nine different rock types were determined in the laboratory and their mineralogical composition examined using thin section analysis. Utilizing the generated data, sets of empirical equations were developed between 𝑉p and relevant quantified rock parameters. The validity of the obtained empirical equations was confirmed using statistical analysis. It is evident that rock texture and mineralogical compositions affect the geotechnical properties of rock materials. Therefore, the best relationship obtained between both E and UCS with 𝑉p in the correlation coefficient of 0.92 and 0.95 in that order. It is concluded that 𝑉p could be practically used for estimating the measured rock properties except dry and saturated density of rocks (𝑟 = 0.58 and 0.46 respectively).

    • Energy transfer and thermal studies of Pr3+ doped cerium oxalate crystals

      R Pragash Gijo Jose N V Unnikrishnan C Sudarsanakumar

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      Energy transfer process at room temperature for cerium (sensitizer) oxalate single crystals doped with different concentrations (10, 13, 15, 17 and 20%) of praseodymium ions (activator) grown by hydro silica gel method has been evaluated. The analysis of energy level diagrams of cerium and praseodymium ions indicates that the energy gap between the sensitizer and the activator ions varies in a small range suggesting a possible energy transfer from the Ce3+ to Pr3+. The emission and absorption spectra of these crystals were recorded. The overlapping of the absorption spectra of Pr3+ and emission spectra of Ce3+ at wavelengths 484 and 478 nm, respectively, strongly supports the possible energy transfer process in this system. From the absorption spectra, oscillator strength, electric dipole moment, branching ratio and Judd–Ofelt parameters of this system were evaluated by least square programming. The quantum efficiency, energy transfer probabilities and thermal properties have been studied.

    • Grain-size effects on thermal properties of BaTiO3 ceramics

      C J Xiao Z X Li X R Deng

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      Dense nanocrystalline BaTiO3 ceramics are successfully prepared by the high pressure assisted sintering. Microstructures are observed by scanning electronic microscopes. The grain sizes are estimated to be about 30 and 150 nm. In comparison, BaTiO3 ceramics with the grain size of 600 nm and 1.5 𝜇m are fabricated by conventional pressure-less sintering. The thermal properties of BaTiO3 ceramics with different grain sizes are investigated by differential scanning calorimetry and thermal expansion. The results suggest that the enthalpy values for the tetragonal-cubic transition decreased and the thermal expansion values increased with decreasing grain size. Furthermore, the Curie temperature shifts to lower temperature with decreasing grain size.

    • Flower-like CuO synthesized by CTAB-assisted hydrothermal method

      Yunling Zou Yan Li Nan Zhang Xiulin Liu

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      Flower-like CuO nanostructures have been synthesized by cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. Here, CuCl2.2H2O was used as copper raw material, and sodium hydroxide was used as precipitate. The resulting CuO powders were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). X-ray diffraction (XRD) pattern exhibited the nanocrystalline nature with monoclinic structure for the as-synthesized nanostructures. FESEM images indicated that the flower-like CuO nanostructures are composed of many interconnected nanosheets in size of several micrometres in length and width and 60–80 nm in thickness. The possible formation mechanism of flower-like CuO nanostructures was discussed.

    • Fabrication of hierarchical 𝛽-Co(OH)2 microspheres via hydrothermal process

      Guang Sheng Cao Xiao Juan Zhang Ling Su

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      Hierarchical 𝛽-Co(OH)2 microspheres with 20–50 𝜇m diameter assembled from nanoplate building blocks were successfully fabricated via a hydrothermal process in the presence of a cation surfactant cetyltrimethylammonium bromide (CTAB). The products are characterized in detail by multiform techniques: X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis. The effect of CTAB and pH value on the 𝛽-Co(OH)2 morphology was also investigated. When pH value is maintained at 9, an appropriate added amount of CTAB (3 g) is the crucial prerequisite for the formation of this interesting morphology. In this experiment, pH value of the solution and the cation surfactant CTAB together results in the formation of hierarchical 𝛽-Co(OH)2 microsphere structures assembled from nanoplates.

    • Synthesis and characterization of super-microporous material with enhanced hydrothermal stability

      Shujie Wu Ke Song Jingqi Guan Qiubin Kan

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      Super-microporouos silicon material with high hydrothermal stability denoted as MCM-41-T has been prepared from mesoporous MCM-41 by high temperature treatment. The structural and chemical property of MCM-41-T has been characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption, infrared spectroscopy and 29Si MAS NMR. The characteristic results show that Si–OH groups are forced to condense by high temperature treatment, and the pore size of MCM-41-T is around 1.5 nm in the super-microporous range. Compared with the original material MCM-41, the hydrothermal stability of MCM-41-T has been significantly enhanced.

    • An investigation on surface roughness of granite machined by abrasive waterjet

      Gokhan Aydin Izzet Karakurt Kerim Aydiner

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      Abrasive waterjet (AWJ) cutting is an emerging technology which enables the shaping of practically all engineering materials. However, AWJ cutting may cause roughness and waviness on the cut surface. This significantly affects the dimensional accuracy of the machined part and the quality of surface finish. In this study, the surface roughness of three granites is experimentally investigated for varying process parameters in abrasive waterjet. The philosophy of the Taguchi design is followed in the experimental study. Effects of the control (process) factors on the surface roughness are presented in terms of the mean of means responses. Additionally, the data obtained are evaluated statistically using the analysis of variance (ANOVA) to determine significant process parameters affecting the surface roughness. Furthermore, effects of the material properties on the surface roughness are assessed. It was statistically found that the water pressure and the abrasive flow rate are the most significant factors influencing the surface roughness of granites. Additionally, a consistent relationship between the material grain size and surface roughness of the granites was observed.

    • Surface morphology and corrosion resistance of electrodeposited composite coatings containing polyethylene or polythiophene in Ni–Mo base

      J Niedbała

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      Ni–Mo + PENi and Ni–Mo + PTh composite coatings have been prepared by nickel-molybdenum deposition from a bath containing a suspension of PENi or Th. These coatings were obtained at galvanostatic conditions, at a current density of 𝑗dep = – 0.100 A cm-2 and temperature of 293 K. A scanning electron microscope was used for surface morphology characterization of the coatings. The chemical composition of the coatings was determined by EDS. Electrochemical corrosion resistance investigations were carried out in 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. On the basis of these investigations it was found, that the composite coatings containing thiophene are more corrosion resistant in alkaline solution than the Ni–Mo + PENi coatings. This is caused by presence of the polymer on the coatings surface and decrease of corrosion active surface area of the coatings.

    • Electrolytic deposition and corrosion resistance of Zn–Ni coatings obtained from sulphate-chloride bath

      Katarzyna Wykpis Magdalena Popczyk Antoni Budniok

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      Zn–Ni coatings were deposited under galvanostatic conditions on steel substrate (OH18N9). The influence of current density of deposition on the surface morphology, chemical and phase composition was investigated. The corrosion resistance of Zn–Ni coatings obtained at current density 10–25 mA cm-2 are measured, and are compared with that of metallic cadmium coating. Structural investigations were performed by the X-ray diffraction (XRD) method. The surface morphology and chemical composition of deposited coatings were studied using a scanning electron microscope (JEOL JSM-6480) with EDS attachment. Studies of electrochemical corrosion resistance were carried out in the 5% NaCl, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. On the ground of these research, the possibility of deposition of Zn–Ni coatings contained 24–26% at. Ni was exhibited. It was stated, that surface morphology, chemical and phase composition of these coatings are practically independent on current density of deposition. On the basis of electrochemical investigations it was found that corrosion resistance of these Zn–Ni coatings is also independent of current density. These coatings are more corrosion resistant in 5% NaCl solution than metallic cadmium. It was suggested that the Zn–Ni coating may be used as a substitute for toxic cadmium.

    • Effect of oil and oil with graphite on tribological properties of glass filled PTFE polymer composites

      Y R Kharde K V Saisrinadh

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      Present work deals with the experimental investigation of tribological properties of GF-filled polymer composites considering three velocities, i.e. 0.5, 1 and 2.0 m/s and loads ranging from 15.7 N to 45.13 N keeping rest of the parameters constant. The test has been carried out for three materials, PTFE + 15% GF, PTFE + 25% GF and PTFE + 35% GF in wet (oil) and adding additive as graphite (5% wt) in oil. SAE 20W40 oil is used for the test. Friction and wear tests of PTFE composite against a counter surface of EN8 with surface finish of 0.56 𝜇m are carried out at ambient conditions using pin-on-disc tribometre (TR-20), Ducom make, Bangalore. The results are tabulated and graphs are plotted. It has been found that load and wet conditions have significant effect on coefficient of friction and specific wear rate of the materials. Where as sliding velocity also plays little role in wear mechanism of the material. It is concluded from the experimental study that the specific wear rate in wet condition as well as by adding additives in lubricating oil with 5% (by wt.) has been declined. Also the specific wear rate decreases with normal load and sliding velocity. Wear of PTFE + GF composite decreases with increase in glass percentage. Microscopic analysis of pin and disc surface is made with optical microscope. The mathematical models has been developed by using regression analysis and found to be valid for the above tested parameters.

    • Method for increasing 𝛽-SiC yield on solid state reaction of coal fly ash and activated carbon powder

      Sulardjaka Jamasri M W Wildan Kusnanto

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      A novel process for increasing 𝛽-SiC yield on solid state reaction of coal fly ash and micro powder activated carbon powder has been proposed. 𝛽-SiC powder was synthesized at temperature 1300°C for 2 h under vacuum condition with 1 l/min argon flow. Cycling synthesis process has been developed for increasing 𝛽-SiC yield on solid state reaction of coal fly ash and activated carbon powder. Synthesized products were analyzed by XRD with Cu-K𝛼 radiation, FTIR spectrometer and SEM fitted with EDAX. The results show that the amount of relative 𝛽-SiC is increased with the number of cycling synthesis.

    • Biomimetic synthesis and characterization of semiconducting hybrid organic–inorganic composite materials based on polyaniline–polyethylene glycol–CdS system

      A Singh N P Singh R A Singh

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      Triple hybrid materials based on polyaniline-polyethylene glycol and cadmium sulphide have been prepared by the duffusion–limited biomimetic route and characterized by a number of spectroscopic, XRD, SEM, thermal and electrical measurements. These hybrid materials have been prepared by controlled precipitation of cadmium sulphide by passing H2S gas and mixing the resultant colloid with the acidic solution of aniline. in situ polymerization of adsorbed anilinium ions on anionic surface of CdS resulted in hybrids. Water–soluble polyethylene glycol led to diffusion–limited growth of polyaniline and CdS resulting in a nanosized hybrid material as indicated by UV-visible spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM). AC impedance spectroscopic studies on binary and ternary nanocomposites of polyaniline with polyethylene glycol and cadmium sulphide separately and triple hybrid system have been reported. Equivalent circuits were determined and discussed in the light of contributions made from different sources such as grain, grain boundary and electrode.

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