Sol-Gel Template Synthesis, Structural Characterization and Growth Mechanism of Barium Zirconate Nanotubes

In this paper, we report the synthesis of barium zirconate, BaZrO3, (BZ) nanotubes fabricated by the modified sol-gel method within the nanochannels of anodic aluminum oxide (AAO) templates. The morphology, structure, and composition of as prepared nanotubes were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), selected-area electron diffraction ( SAED), high resolution TEM (HRTEM) and energy-dispersive X-ray spectroscopy (EDX). The results of XRD and SAED indicated that postannealed (at 650 degrees C for 1 h) BZ nanotubes (BZNTs) exhibited a polycrystalline cubic perovskite crystal structure. SEM and TEM analysis revealed that BZNTs possessed a uniform length and diameter (similar to 200 nm) and the thickness of the wall of the BZNTs was about 20 nm. Y-junctions, multiple branching and typical T-junctions were also observed in some BZNTs. EDX analysis demonstrated that stoichiometric BaZrO3 was formed. HRTEM image confirmed that the obtained BZNTs were composed of nanoparticles in the range of 5-10 nm. The possible formation mechanism of BZNTs was discussed.

Fabrication and Phase Transformation in Crystalline Nanoparticles of PbZrO3 Derived By Sol-Gel

In this research fabrication of crystalline PbZrO3 (PZ) nanoparticles and their phase transformation behavior is investigated. A novel sol-gel method was used for the synthesis of air-stable and precipitate-free diol-based sol of PZ, which was dried at 150 degrees C and then calcined at 300-700 degrees C for 1 h. The morphology, crystallinity and phase formation of as synthesized nanoparticles were studied by the selected-area electron diffraction (SAED), X-ray diffraction (XRD), thermal gravimetric analysis/differential scanning calorimetry (TGA-DSC), and high resolution transmission electron microscope (HRTEM). The XRD, SAED, and TGA-DSC analyses confirmed the tetragonal lead rich zirconia phase (t-Z phase) and monoclinic zirconia phase (m-Z phase) as the intermediate phases during the calcinations process followed by crystallization of single orthorhombic PZ phase at about 700 degrees C. The average PZ particle size was observed about 20 nm as confirmed by TEM study. Energy-dispersive X-ray spectroscopy (EDX) analysis demonstrated that stoichiometric PbZrO3 was formed.

Preparation temperature effect on the synthesis of various carbon nanostructures

Various carbon nanostructures (CNs) have been prepared by a simple deposition technique based on the pyrolysis of a new carbon source material tetrahydrofuran (THF) mixed with ferrocene using quartz tube reactor in the temperature range 700-1100 degrees C. A detailed study of how the synthesis parameter such as growth temperature affects the morphology of the carbon nanostructures is presented. The obtained CNs are investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), electron dispersive scattering (EDS)thermogravimetry analysis (TGA), Raman and transmission electron microscope (TEM). It is observed that at 700 degrees C. normal CNTs are formed. Iron filled multi-walled carbon nanotubes (MWCNTs) and carbon nanoribbons (CNRs) are formed at 950 degrees C. Magnetic characterization of iron filled MWCNTs and CNRs studied at 300 K by superconducting quantum interference device (SQUID) reveals that these nanostructures have an enhanced coercivity (Hc = 1049 Oe) higher than that of bulk Fe. The large shape anisotropy of MWCNTs, which act on the encapsulated material (Fe), is attributed for the contribution of the higher coercivity. Coiled carbon nanotubes (CCNTs) were obtained as main products in large quantities at temperature 1100 degrees C.

EPR Evidence for Premonitory Charge-Ordering Fluctuations in Hydrothermally Grown Pr0.57Ca0.41Ba0.02MnO3 Nanowires

Electron paramagnetic resonance (EPR) and magnetic properties of nanowires of Pr0.57Ca0.41Ba0.02MnO3 (PCBMO) are studied and compared with those of the bulk material. PCBMO nanowires with diameter of 80-90 nm and length of similar to 3.5 mu m were synthesized by a low reaction temperature hydrothermal method and the bulk sample was prepared following a solid-state reaction route. The samples were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The bulk PCBMO manganite exhibits charge order at 230 K along with a ferromagnetic transition at 110 K. However, superconducting quantum interference device measurements on the PCBMO nanowires show a complete `melting' of charge ordering and a ferromagnetic transition at 115 K. This result is confirmed by the EPR intensity behavior as well. However, the EPR line width, which is reflective of the spin dynamics, shows a shallow minimum for nanowires at the temperature corresponding to the charge-ordering transition, i.e., 230 K. We interpret this result as an indication of the presence of charge-ordering fluctuations in the nanowires even though the static charge order is absent, thus heralding the occurrence of charge order in the bulk sample.

Low temperature molten-salt synthesis of nanocrystalline cubic Sr2SbMnO6

Sr2SbMnO6 (SSM) powders were successfully synthesized at reasonably low temperatures via molten-salt synthesis (MSS) method using eutectic composition of 0.635 Li2SO4-0.365 Na2SO4 (flux). High-temperature cubic phase SSM was stabilized at room temperature by calcining the as-synthesized powders at 900 degrees C/10 h. The phase formation and morphology of these powders were characterized via X-ray powder diffraction and scanning electron microscopy, respectively. The SSM phase formation associated with similar to 60 nm sized crystallites was also confirmed by transmission electron microscopy. The activation energy associated with the particle growth was found to be 95 +/- 5 kJ mol(-1). The dielectric constant of the tetragonal phase of the ceramic (fabricated using this cubic phase powder) with and without the flux (sulphates) has been monitored as a function of frequency (100 Hz-1 MHz) at room temperature. Internal barrier layer capacitance (IBLC) model was invoked to rationalize the dielectric properties.

Microwave absorption studies of iron encapsulating carbon-polymer nanocomposite films

Iron encapsulated carbon nanoparticle polyvinyl chloride composite films have been prepared by solvent mixing and drying method. The films were characterized by scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM). A 5 nm thin graphitic carbon coating is observed on cubic Fe nanoparticles. The microwave absorption studies by wave guide technique in the Ka band range showed highest electromagnetic interference shielding efficiency of 18dB on a 300 micron thick film. The shielding efficiency depends on weight % of the filler in the composite. The data obtained for different films indicate that these lightweight materials are good candidates for potential electromagnetic interference shielding applications.

Bi4Ti3O12-5BiFeO(3) Aurivillius intergrowth: Structural and ferroelectric properties

Aurivillus intergrowth Bi4Ti3O12-5BiFeO(3) was demonstrated to be ferroelectric that evoked the possibility of achieving high temperature magnetoelectric property in this family of compounds. X-ray diffraction studies confirmed its structure to be orthorhombic [Fmm2; a=5.5061(11) A degrees, b=5.4857(7) A degrees, c=65.742(12) A degrees]. However, transmission electron microscopy established the random incidence of intergrowth at nanoscale corresponding to n=6 and n=7 members of the Aurivillius family. Diffuse ferroelectric orthorhombic to paraelectric tetragonal phase transition around 857 K was confirmed by dielectric and high temperature x-ray diffraction studies. Polarization versus electric field hysteresis loops associated with 2P(r) of 5.2 mu C/cm(2) and coercive field of 42 kV/cm were obtained at 300 K.

Aminoglycoside-Resistance Mechanisms in Multidrug-Resistant Staphylococcus aureus Clinical Isolates

Aminoglycoside resistance in six clinically isolated Staphylococcus aureus was evaluated. Genotypical examination revealed that three isolates (HLGR-10, HLGR-12, and MSSA-21) have aminoglycoside-modifying enzyme (AME) coding genes and another three (GRSA-2, GRSA-4, and GRSA-6) lacked these genes in their genome. Whereas isolates HLGR-10 and HLGR-14 possessed bifunctional AME coding gene aac(6′)-aph(2′′), and aph(3′)-III and showed high-level resistance to gentamycin and streptomycin, MSSA-21 possessed aph(3′)-III and exhibited low resistance to gentamycin, streptomycin, and kanamycin. The remaining three isolates (GRSA-2, GRSA-4, and GRSA-6) exhibited low resistance to all the aminoglycosides because they lack aminoglycoside-modifying enzyme coding genes in their genome. The transmission electron microscopy of the three isolates revealed changes in cell size, shape, and septa formation, supporting the view that the phenomenon of adaptive resistance is operative in these isolates.

A one-step technique to prepare aligned arrays of carbon nanotubes

A simple effective pyrolysis technique has been developed to synthesize aligned arrays of multi-walled carbon nanotubes (MWCNTs) without using any carrier gas in a single-stage furnace at 700 °C. This technique eliminates nearly the entire complex and expensive machinery associated with other extensively used methods for preparation of CNTs such as chemical vapour deposition (CVD) and pyrolysis. Carbon source materials such as xylene, cyclohexane, camphor, hexane, toluene, pyridine and benzene have been pyrolyzed separately with the catalyst source material ferrocene to obtain aligned arrays of MWCNTs. The synthesized CNTs have been characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy. In this technique, the need for the tedious and time-consuming preparation of metal catalysts and continuously fed carbon source material containing carrier gas can be avoided. This method is a single-step process where not many parameters are required to be monitored in order to prepare aligned MWCNTs. For the production of CNTs, the technique has great advantages such as low cost and easy operation.

Implantation Induced Hardening of Nanocrystalline Titanium Thin Films

Formation of nanocrystalline TiN at low temperatures was demonstrated by combining Pulsed Laser Deposition (PLD) and ion implantation techniques. The Ti films of nominal thickness similar to 250 nm were deposited at a substrate temperature of 200 degrees C by ablating a high pure titanium target in UHV conditions using a nanosecond pulsed Nd:YAG laser operating at 1064 nm. These films were implanted with 100 keV N+ ions with fluence ranging from 1.0 x 10(16) ions/cm(2) to 1.0 x 10(17) ions/cm(2). The structural, compositional and morphological evolutions were tracked using Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectrometry (SIMS) and Atomic Force Microscopy (AFM), respectively. TEM analysis revealed that the as-deposited titanium film is an fcc phase. With increasing ion fluence, its structure becomes amorphous phase before precipitation of nanocrystalline fcc TiN phase. Compositional depth profiles obtained from SIMS have shown the extent of nitrogen concentration gradient in the implantation zone. Both as-deposited and ion implanted films showed much higher hardness as compared to the bulk titanium. AFM studies revealed a gradual increase in surface roughness leading to surface patterning with increase in ion fluence.

Evolution of nanocrystalline BaBi2Nb2O9 in Li2B4O7 BaO-Bi(2)O3-Nb2O5 glass system

Transparent glasses and glass nano crystal composites (GNCs) of various compositions in the system (100 - x)Li2B4O7-x (BaO-Bi2O3-Nb2O5) (where x = 10, 20, and 30 in molar ratio) were fabricated via splat-quenching technique. The glassy nature of the as quenched samples was established by differential thermal analyses. X-ray powder diffraction and transmission electron microscopic (TEM) studies confirmed the formation of layered perovskite BBN via a fluorite like phase. TEM studies revealed the presence of 10 nm sized spherical crystallites of fluorite like BaBi2Nb2O9 phase in the glassy matrix of Li2B4O7 (LBO). The influence of composition on the dielectric and the optical properties (transmission, optical band gap) of these samples has been investigated. (c) 2007 Elsevier B.V. All rights reserved.

Process variables in biomimetic synthesis of silver nanoparticles by aqueous extract of Azadirachta indica (Neem) leaves

Owing to widespread applications, synthesis and characterization of silver nanoparticles is recently attracting considerable attention. Increasing environmental concerns over chemical synthesis routes have resulted in attempts to develop biomimetic approaches. One of them is synthesis using plant parts, which eliminates the elaborate process of maintaining the microbial culture and often found to be kinetically favourable than other bioprocesses. The present study deals with investigating the effect of process variables like reductant concentrations, reaction pH, mixing ratio of the reactants and interaction time on the morphology and size of silver nanoparticles synthesized using aqueous extract of Azadirachta indica (Neem) leaves. The formation of crystalline silver nanoparticles was confirmed using X-ray diffraction analysis. By means of UV spectroscopy, Scanning and Transmission Electron Microscopy techniques, it was observed that the morphology and size of the nanoparticles were strongly dependent on the process parameters. Within 4 h interaction period, nanoparticles below 20-nm-size with nearly spherical shape were produced. On increasing interaction time (ageing) to 66 days, both aggregation and shape anisotropy (ellipsoidal, polyhedral and capsular) of the particles increased. In alkaline pH range, the stability of cluster distribution increased with a declined tendency for aggregation of the particles. It can be inferred from the study that fine tuning the bioprocess parameters will enhance possibilities of desired nano-product tailor made for particular applications.

Formation of ω-Al7Cu2Fe phase during laser processing of quasicrystal-forming Al-Cu-Fe alloy

The formation of an ω-Al7Cu2Fe phase during laser cladding of quasicrystal-forming Al65Cu23.3Fe11.7 alloy on a pure aluminium substrate is reported. This phase is found to nucleate at the periphery of primary icosahedral-phase particles. A large number of ω-phase particles form an envelope around the icosahedral phase. On the outer side, they form an interface with an agr-Al solid solution. Detailed transmission electron microscopic observations show that the ω phase exhibits an orientation relationship with the icosahedral phase. Analysis of experimental results suggests that the ω phase forms by precipitation on an icosahedral phase by heterogeneous nucleation and grows into the aluminium-rich melt until supersaturation is exhausted. The microstructural observations are explained in terms of available models of phase transformations.

Synthesis of multiwall carbon nanotubes by chemical vapor deposition of ferrocene alone

Multiwall carbon nanotubes (MWNTs) filled with Fe nanoparticles (NPs) have been synthesized by thermal chemical vapor deposition of ferrocene alone as the precursor. The MWNTs were grown at different temperatures: 980 and 800 degrees C. Characterization of as-prepared MWNTs was done by scanning and transmission electron microscopy, and X-ray diffraction. The transmission electron microscopy study revealed that Fe NPs encapsulated in MWNTs grown at 980 and 800 degrees C are spherical and rod shaped, respectively. Room-temperature vibrating sample magnetometer studies were done on the two samples up to a field of 1T. The magnetization versus magnetic field loop reveals that the saturation magnetization for the two samples varies considerably, almost by a factor of 4.6. This indicates that Fe is present in different amounts in the MWNTs grown at the two different temperatures. (C) 2009 Elsevier Ltd. All rights reserved.

Synthesis of BaSO4 nanoparticles by precipitation method using sodium hexa metaphosphate as a stabilizer

We describe the synthesis and structure of Barium sulfate nanoparticles by precipitation method in the presence of water soluble inorganic stabilizing agent, sodium hexametaphosphate, (NaPO3)(6). The structural parameters were refined by the Rietveld refinement method using powder X-ray diffraction data. Barium sulfate nanoparticles were crystallized in the orthorhombic structure with space group Pbnm (No. 62) having the lattice parameters a = 7.215(1) (angstrom), b = 8.949(1) (angstrom) and c = 5.501 (1) (angstrom) respectively. Transmission electron microscopy study reveals that the nanoparticles are size range, 30-50 nm. Fourier transform infrared spectra showed distinct absorption due to the SO42- moiety at 1115 and 1084 cm(-1) indicating formation of barium sulfate nanoparticles free from the phosphate group from the stabilizer used in the synthesis. (C) 2009 Elsevier Ltd. All rights reserved.