V. L. Mathe

Synthesis and characterization of Nd2O3 nanoparticles in a radiofrequency thermal plasma reactor

The synthesis of nanocrystalline Nd2O3 through an inductively coupled radiofrequency thermal plasma route is reported. Unlike in conventional synthesis processes, plasma-synthesized nanoparticles are directly obtained in a stable hexagonal crystal structure with a faceted morphology. The synthesized nanoparticles are highly uniform with an average size around 20 nm. The nanoparticles are characterized in terms of phase formation, crystallinity, morphology, size distribution, nature of chemical bonds and post-synthesis environmental effects using standard characterization techniques. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy are used for structural and morphological studies. The thermo-gravimetric technique, using a differential scanning calorimeter, is used to investigate the purity of phase. Fourier transform infrared spectroscopy is used to investigate the nature of existing bonds. The optical response of the nanoparticles is investigated through the electronic transition of Nd(3+) ions in its crystalline structure via UV-visible spectroscopy. The presence of defect states and corresponding activation energies in the nanocrystalline Nd2O3 compared to those of the precursors are studied using thermoluminescence.

Si nanotubes and nanospheres with two-dimensional polycrystalline walls

We report on the characteristics of a new class of Si-based nanotubes and spherical nanoparticles synthesized by the dc-arc plasma method in a mixture of argon and hydrogen. These two nanostructures share common properties: they are hollow and possess very thin, highly polycrystalline and mainly oxidized walls. In particular, we get several hints indicating that their walls could constitute only one single Si oxidized layer. Moreover, we find that only the less oxidized nanotubes exhibit locally atomic ordered, snakeskin-like areas which possess a hexagonal arrangement which can be interpreted either as an sp(2) or sp(3) hybridized Si or Si-H layer. Their ability to not react with oxygen seems to suggest the presence of sp(2) configuration or the formation of silicon-hydrogen bonding.

Ultrasound assisted synthesis of WO 3 -ZnO nanocomposites for brilliant blue dye degradation

The present work deals with the preparation of WO3 and WO3-ZnO nanocomposites in presence of ultrasonic irradiation, and its use in the sonocatalytic degradation of brilliant blue dye. WO3-ZnO nanocomposite is prepared using one step in-situ ultrasound assisted method. The successfully prepared WO3 and WO3-ZnO nanocomposites were characterized using different characterization techniques such as XRD, Raman, BET, FE-SEM and EDS. The XRD pattern reveals that the formation of monoclinic and hexagonal crystal structures of WO3 and ZnO respectively. BET study shows that WO3-ZnO nanocomposite have maximum surface area than that of the WO3. EDS study confirms the formation of WO3-ZnO nanocomposites. Further the use of the prepared WO3 and WO3-ZnO nanocomposites as a sonocatalyst for the degradation of brilliant blue dye. The rate constant (k) was evaluated as a function of the initial concentration of brilliant blue dye. It is found that WO3-ZnO nanocomposites exhibits maximum sonocatalytic activity as compared to WO3 photocatalyst.

Phase controlled structure formation of the nanocrystalline zirconia using thermal plasma technique

Nanocrystalline ZrO2 powder was synthesized by dc transferred arc thermal plasma reactor by homogeneous gas phase condensation mechanism. ZrO2 is an oxide ceramic with a high melting point, good chemical resistance and high mechanical strength. When doped with certain oxides, ZrO2 shows high ionic conductivity. ZrO2 is also recognized as a superior thermal barrier material. Thermal plasma synthesis of oxide nano materials shows pressure dependent crystalline phase and crystallite size. The X-ray diffraction analysis clearly shows that as the ambient oxygen gas pressure increases from 100 Torr to 1000 Torr the abundance of tetragonal phase goes on increasing. The morphology of the as synthesized ZrO2 powder was found to be spherical and independent on the ambient gas pressure as seen from the Scanning Electron Microscopy studies. The specific surface area of powder was calculated using the nitrogen gas adsorption Brunauer, Emmett, Teller surface area analysis technique and found no much variation.

Magnetodielectric properties of La0.67Sr0.33MnO3 and Ba0.7Sr0.3TiO3 thin film heterostructures

The paper discuses synthesis and magnetodielectric properties of La0.67Sr0.33MnO3 (LSMO), Ba0.7Sr0.3TiO3 (BST), and BST/LSMO thin film heterostructures. The XRD spectra are determined for confirmation of the crystal structure of LSMO, BST and formation of a pure bi-phase composite. The paper presents variation of Cp and tanδ as a function of frequency between 100 Hz to 1 MHz and applied magnetic field up to 0.6 T. The observed variation of Cp, tanδ, magnetocapacitance and impedance spectra are analyzed in terms of a possible equivalent circuit model. The present analysis shows that the method of impedance spectra could be used to separate out the possible contributions.

Surface chemical bonds, surface-enhanced Raman scattering, and dielectric constant of SiO2 nanospheres in-situ decorated with Ag-nanoparticles by electron-irradiation

Nanostructures of dielectric materials decorated with metal nanoparticles are of great scientific interest; however, the involved synthesis methods are complicated and require multistep chemical processing, including functionalization of the dielectric surfaces. In the present work, without chemical processes, silver nanoparticles of average sizes in the range of 11 to 15 nm were in-situ synthesized and decorated on SiO2 nanospheres in a single step process by irradiating a solution (AgNO3–polyvinylpyrrolidone (PVP)–SiO2 nanospheres) with 6 MeV electrons at 1.5 × 1015 e−/cm2, 3.0 × 1015 e−/cm2, and 4.5 × 1015 e−/cm2 fluences. The electron irradiated solutions were characterized with different surface and other techniques. The results revealed that the SiO2 nanospheres were uniformly decorated with Ag nanoparticles, and the prominent chemical bonds involved were Ag–O, Si–O–Ag, and Si–Ag. Moreover, the sizes and the decoration density of Ag nanoparticles could be tailored by varying electron fluence. The Su...

Arc plasma synthesized Si nanotubes: A promising low turn on field emission source

Here, the authors report the field emission investigations of silicon nanotubes (SiNTs) synthesized by vapor phase condensation method in DC arc plasma reactor. The SiNTs have diameters in the range of 10–15 nm and length of a few 100 nm. A maximum current density of 4.2 mA/cm2 has been attained. The turn on field, defined for obtaining a current density of 10 μA/cm2, is found to be 1.9 V/μm. The specimen exhibits a good emission current stability at 1 μA over a period of 3 h. The field enhancement factor, β, is estimated to be ∼5534. The current stability is quantified in terms of standard deviation and its magnitude has been measured to be only 9.7% with respect to the average value.

Synthesis of nanocrystalline Y2O3 in a specially designed atmospheric pressure radio frequency thermal plasma reactor

Synthesis of yttrium oxide nanoparticles in a specially designed radio frequency thermal plasma reactor is reported. Good crystallinity, narrow size distribution, low defect state concentration, high purity, good production rate, single-step synthesis, and simultaneous formation of nanocrystalline monoclinic and cubic phases are some of the interesting features observed. Synthesized particles are characterized through X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, thermo-luminescence (TL), and Brunauer–Emmett–Teller surface area analysis. Polymorphism of the nanocrystalline yttria is addressed in detail. Synthesis mechanism is explored through in-situ emission spectroscopy. Post-synthesis environmental effects and possible methods to eliminate the undesired phases are probed. Defect states are investigated through the study of TL spectra.

Electrokinetic properties of PMAA functionalized NiFe2O4 nanoparticles synthesized by thermal plasma route

The magnetic nickel ferrite (NiFe2O4) nanoparticles with an average size of 30nm were synthesised by Transferred arc DC Thermal Plasma route. The synthesized nickel ferrite nanoparticles were characterized by TEM and FTIR techniques. The synthesized nickel ferrite nanoparticles were further functionalized with PMAA (polymethacrylic acid) by self emulsion polymerization method and subsequently were characterized by FTIR and Zeta Analyzer. The variation of zeta potential with pH was systematically studied for both PMAA functionalized (PNFO) and uncoated nickel ferrite nanoparticles (NFO). The IEP (isoelectric points) for PNFO and NFO was determined from the graph of zeta potential vs pH. It was observed that the IEP for NFO was at 7.20 and for PNFO it was 2.52. The decrease in IEP of PNFO was attributed to the COOH functional group of PMAA.

Thermal plasma processed ferro-magnetically ordered face-centered cubic iron at room temperature

Here, we report tailor made phase of iron nanoparticles using homogeneous gas phase condensation process via thermal plasma route. It was observed that crystal lattice of nano-crystalline iron changes as a function of operating parameters of the plasma reactor. In the present investigation iron nanoparticles have been synthesized in presence of argon at operating pressures of 125–1000 Torr and fixed plasma input DC power of 6 kW. It was possible to obtain pure fcc, pure bcc as well as the mixed phases for iron nanoparticles in powder form as a function of operating pressure. The as synthesized product was characterized for understanding the structural and magnetic properties by using X-ray diffraction, vibrating sample magnetometer, and Mossbauer spectroscopy. The data reveal that fcc phase is ferromagnetically ordered with high spin state, which is unusual whereas bcc phase is found to be ferromagnetic as usual. Finally, the structural and magnetic properties are co-related.