Search

The simple, reliable, and economical process of combustion is used to synthesize carbon loaded cobalt oxide (C–Co3O4) for hydrogen generation via NaBH4 hydrolysis. The effect of NaBH4 concentration, pH, and temperature of the solution on hydrogen generation is investigated in detail. C–Co3O4 exhibits zero order reaction kinetics with respect to NaBH4 concentration. A stable Hydrogen Generation Rate (HGR) is observed throughout the reaction in the temperature range of 300–315 K using C–Co3O4. It is found that 0.01 g of C–Co3O4 exhibited high reaction activity with a maximum HGR of 5430 ml min−1 g−1 for the optimal solution at 320 K. The activation energy is calculated to be 55.9 kJ mol−1 for hydrolysis of NaBH4 using C–Co3O4. The present study provides an economical method for the large-scale production of C–Co3O4 for hydrogen generation from NaBH4 hydrolysis, which can pave the way to commercialize hydrogen as a main source of fuel.

Present article discusses the role of plasma parameters on the morphology of nanocrystalline powders of lanthanum hexaboride (LaB6) synthesized by arc plasma gas-phase condensation method. The nanocrystalline powders so obtained were used to fabricate pellet-shaped cathodes of 5 mm diameter and thickness of 1 mm. Moreover, thermal plasma plume was used for sintering the cathodes and achieve desired densification. Prior to fabrication of cathodes, the synthesized powders of LaB6 were characterized using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy to investigate phase purity and morphological properties. Finally, an indigenously developed thermionic emission experimental set-up was used to record thermionic emission current obtained from LaB6 cathode at different temperatures. Richardson Dushman equation was used to find out the work function of the cathode under investigation.

Erosion studies of polyimide, exposed to high energy electrons and atomic oxygen, is necessary in view of its application in space vehicles. Here we present the erosion studies and degradation characteristics of polyimide after its sequential exposure to 1 MeV pulsed electron beam from Microtron accelerator and ~12 eV oxygen ions from a plasma reactor in the laboratory. The fluence of electrons was varied from 5 × 1014 to 2.0 × 1015 electrons/cm2 and that of oxygen ions from ~5 × 1016 to 2 × 1017 ions cm−2. The post irradiated and virgin polyimide samples were characterized by gravimetric analysis and contact-angle measurements. The morphological and spectroscopic information were obtained with Scanning Electron Microscopy, Fourier Transform Infra-Red spectroscopy, and photo-absorption spectroscopy. The erosion yield, surface wettability and the surface roughness were seen to be much higher when exposed to both the radiations as compared to either of them, reflecting the synergetic effects.

Nanocrystalline Al2O3:C has been synthesized by thermal plasma method. The sample was annealed at 1300 °C in air and vacuum. XRD studies show phase change from γ-Al2O3:C to α-Al2O3:C. Average particle sizes estimated from XRD peaks and TEM images show increase in the particle size from ~30 nm to ~ 67 nm. The UV–visible spectrum of the as-synthesized Al2O3:C shows absorption peaks at 209 and 255 nm confirming the formation of F and F+ centers. XPS analysis reveals that the concentration of carbon impurity remains intact in Al2O3 lattice. The TL glow curves were fitted by CGCD method. The glow curve of as-synthesized Al2O3:C found to have six peaks and that of annealed sample have four peaks. The changes in the glow curve structures of the as-synthesized and annealed phosphor may be attributed to the phase change of the crystal structure and/or different kinds of defects formed on annealing in air/vacuum.

The work presented involves the generation of oxygen plasma species at low pressure utilizing an Electron Cyclotron Resonance (ECR) plasma reactor, and their interactions with micron- and nano-sized iron films (M-Fe and N-Fe film respectively) prepared using ethyl cellulose processed at high temperature. A specially designed radiation heater (RH) was used to raise the surface temperature of the film rapidly, exactly at the film interface, where the plasma species interact with the surface. As a result of the interaction of oxygen plasma species and temperature, iron is oxidized to different polymorphs depending on the operating pressure and hence oxygen gas flow rate. The phase, as well as the morphology of the film was controlled by monitoring the oxygen flow rate using the unique Plasma-Assisted Thermal Oxidation (PATO) process. Different polymorphs, viz., Fe3O4, γ-Fe2O3, α-Fe2O3 and different morphologies, such as polygonal, compact facets, wire-like (1D) nanostructures at the surface were obtained for the films processed using PATO. The selected PATO-processed films were investigated for Field Electron Emission (FEE) properties. The 1D-grown surface of iron oxide obtained from the M-Fe film showed a turn-on field of 3 MV m−1 and emission current of 337 μA cm−2, whereas the pyramidal surface morphology obtained using N-Fe film gives a turn-on field of 3.3 MV m−1 with an emission current of 578 μA cm−2.

This paper reports an increase in the optical reflectivity of two kinds of copolymers used in contact lenses, with different proportions of silicon and fluorine derivatives, when irradiated with 4.1 MeV alpha particles from an 241Am source. The fiber-optic reflectance technique showed that the lens with a higher proportion of silicon and fluorine content and a lower proportion of methyl-methacrylate is more susceptible to alpha radiation. X-Ray photoelectron spectroscopy and Raman spectroscopy have revealed the formation of silicon oxide and carbide species as a result of chain scission and recombination in the 20 μm thick irradiated regions of lens materials. It is presumed that the high (260 eV/nm) linear energy transfer of alpha particles in polymers creates trapped gas “Bubbles”, and the observed increase in the optical reflectivity with increased irradiation time is explained on the basis of diffuse reflectance caused by the scattering of light from the hard surfaces of these “Bubbles”.

Electron emission properties of lanthanum hexaboride are dependent on the crystal structure as well as stoichiometric ratio of boron and lanthanum. Present research deals with the influence of carbon diffusion on the stoichiometric LaB6 synthesized using arc plasma gas phase condensation process. Noncrystalline LaB6 has been synthesized using arc plasma at different plasma powers viz 2–3.4 kW. Further, an inclusion of carbonaceous species from the graphite anode with increasing plasma power and its correlation with stoichiometry has been elucidated. X-ray photo-electron spectroscopic technique has been used for the identification of surface chemistry of the synthesized powders and more effectively to infer the stoichiometry i. e. ratio of B:La in the samples synthesized with increasing plasma in put power. The influence of plasma parameters on the work function of the synthesized nanoparticles has also been elucidated using Ultraviolet Photoelectron Spectroscopy (UPS).

Silicon ions, of energy 150 MeV and fluence ∼1012 ions/cm2, were used to register latent tracks in 40 µm thick polyimide samples. Different sizes of tracks were obtained by etching the ion irradiat...

Electrophoretic deposition is the only technique available to fabricate nanoparticle thin films offering control on size distributions of nanoparticles on them. We describe the extensive efforts to understand this complex electrophoretic deposition process. One of the gaps in this research involves the size distributions achieved in the process. We address this particular issue by performing a lab scale experiment and providing a phenomenological model for size distributions. Nanocrystalline iron oxide particles were electrophoretically deposited from a stirred sedimenting suspension using different applied voltages onto silicon substrates. The as-deposited particles were further characterized by X-Ray diffraction and Transmission Electron Microscopy. For understanding the size distributions of these deposited particles, a phenomenological (lumped) model has been proposed. Two parameters have been considered in this model viz. applied electric field during deposition and effective viscosity of the medium in which particles were dispersed. There is good agreement between experiments and theory proposed through the model for a range of voltages.

In this paper we report single step large scale synthesis of highly crystalline iron oxide nanoparticles viz. magnetite (Fe3O4) and maghemite (γ-Fe2O3) via gas phase condensation process, where micron sized iron metal powder was used as a precursor. Selective phases of iron oxide were obtained by variation of gas flow rate of oxygen and hence partial pressure of oxygen inside the plasma reactor. Most of the particles were found to possesses average crystallite size of about 20–30 nm. The DC magnetization curves recorded indicate almost super-paramagnetic nature of the iron oxide magnetic nanoparticles. Further, iron oxide nanoparticles were analyzed using Raman spectroscopy, X-ray photoelectron spectroscopy and Mossbauer spectroscopy. In order to explore the feasibility of these nanoparticles for magnetic damper application, rheological studies have been carried out and compared with commercially available Carbonyl Iron (CI) particles. The nanoparticles obtained by thermal plasma route show improved dispersion which is useful for rheological applications.

The paper emphasizes the morphological and microstructural analysis of SiC nanostructures grown by thermal plasma assisted gas phase condensation process. High Resolution Transmission Electron Microscopic and Selected Area Electron Diffraction studies are used to analyze the growth directions and the polytypic arrangement with stacking faults in the as synthesized SiC nanoparticles. The results help in understanding the hierarchical poly-types related to the observed geometries and showed the presence of both α- and β-SiC polytypes. The microstructural study is supported by X-Ray diffraction and UV–Visible absorption spectroscopic studies.

In the present study, we report the morphological tuning of carbonaceous nanocrystalline lanthanum hexaboride (LaB6) using an arc plasma route. It was possible to obtain different morphologies, namely: pebbles, rods and sheets, on a nano-scale by means of plasma assisted vapour phase growth and by varying the plasma current. At elevated plasma currents, as a consequence of graphite electrodes being used in the arc geometry, the synthesized product was obtained in the form of carbonaceous LaB6 having a high degree of crystallinity. Detailed morphological analysis using electron microscopy has revealed that nanorods and nanosheets of carbonaceous LaB6 can be grown by elevating the plasma currents. The field emission (FE) current was found to be enhanced from 200 μA cm−2 to 660 μA cm−2 for the hierarchical structure of nanosheets as compared to that of nanopebbles at a much reduced turn-on potential. A stable FE current is an important feature exhibited by all these LaB6 nanostructures.

High temperature synthesis process of microcrystalline and nanocrystalline (LaCe)B6 by Self-propagating High temperature Synthesis (SHS) and arc plasma gas phase condensation method respectively have been investigated in the present work. These are rapid and economically viable processes used for the synthesis of technologically important refractory hexaborides. Microcrystalline powders of (LaCe)B6 were synthesized using SHS process, starting from oxide precursors of lanthanum, cerium, and boron. The powders so obtained were used as a precursor to obtain nanocrystalline (LaCe)B6 using thermal plasma route. The thermal plasma synthesis was carried out using nitrogen and argon plasmas, respectively. In-situ plasma diagnostics was used to identify evaporated species and to determine plasma temperature during formation of nanocrystalline (LaCe)B6 using optical emission spectroscopy. Further, an effect of plasma temperature on the structural and optical properties of as synthesized nanocrystalline (LaCe)B6 was investigated using XRD analysis, Raman spectroscopy and X-ray Photoelectron spectroscopy. Thorough investigation of morphological and structural properties of synthesized nanocrystalline (LaCe)6 has been carried out using transmission electron microscopy. Finally, field effect electron emission properties of the microcrystalline and nanocrystalline product were investigated and current density, turn on field, stability of emission performance were determined.

Magnetic nanoparticles of nickel substituted cobalt ferrites, Ni x Co 1−x Fe 2 O 4 , (x=0 to 1 in the step of 0.2) were successfully synthesized by gas phase nucleation and growth process. For the first time, we report feasibility of synthesizing such mixed ferrite system using thermal plasma route. Further, effect of change in molar ratio of Co:Ni on the structural, optical and magnetic properties has been investigated in detail. The structural and phase formation analysis of the samples under investigation have been carried out using powder X-ray diffraction and Raman spectroscopy. The surface morphology of these particles has been studied using scanning electron microscopy and the micrographs so obtained were used to find out average gain size and size distribution. The optical and magnetic properties of the as synthesized samples were finally correlated with the magnetic moment of substituted species such as Ni for Co and cation distribution, analyzed using Mossbauer spectroscopy. Special modification in Thermo Gravimetric Analyzer was used to determine magnetic transition temperature.

The paper addresses the issue of phase formation in the nano-crystalline binary alloys of FeNi and AlNi, synthesized by plasma assisted vapor phase condensation process. In depth experimental analysis of the crystal structure, for the alloy nanoparticles with different compositions, is presented. The observed crystalline phases of the products have been compared with those expected from the standard phase diagram of the respective alloys. Crystalline phases of FeNi system showed no deviation, whereas, those of AlNi showed considerable deviation. Differences in the thermo-physical properties of Al and Ni are shown to be responsible for such a deviation. The results are supported by a computational model, which accounts for the supersaturation of the species in gas phase, leading to nucleation and growth. Keywords: Thermal plasma, Binary nano-alloys, Super-saturation, Crystallographic phase

In this paper we report single step synthesis of ZnO - ZnWO4 nanocomposites using thermal plasma route, where thermal plasma plume having sufficiently high thermal flux was impinged onto zinc -tungsten precursor and the species so evaporated were made to interact with oxygen in gas phase to get the final product. X-ray diffraction and Raman spectroscopic techniques were used to ascertain the composite phases. X-Ray Diffraction and Raman Spectroscopic analysis witnessed the formation of ZnO-ZnWO4 nano-composites, with monoclinic wolframite structure of tungstate while wurtzite structure of ZnO. Optical properties of the as synthesized product were recorded and analyzed using UV–vis and Photo-luminescence spectroscopic techniques. Retarding field diode method was used to determine work function of the ZnO-ZnWO4 composites under investigation, where gold sample was used as a reference. Subsequently, the photocatalytic efficiency of such ZnO-ZnWO4 nano-composites was analyzed by assessing the degradation of Crystal Violet dye. Experimentally measured values of surface work-function of the composites were analyzed and corelated with photocatalytic response. The degradation of Crystal Violet up to 82.07 % was achieved for 5 wt. % of W in the composite as compared to a value of 25.14 % for the pure ZnO nanoparticles under the exposure to sunlight radiations.

In the present work spinel structured cobalt ferrites with aluminum substitution having composition CoAl x Fe 2− x O 4 ( x =0.0, 0.1, 0.2 and 0.3) have been synthesized using chemical co-precipitation method. Their microstructural, magnetic, magnetostriction and magnetoimpedance properties have been investigated. The piezomagnetic coefficient (d λ /dH) obtained from magnetostriction data is found to enhance with 0.1 Al substitutions in place of iron which decreases with further increase of Al content. It is noticed that 0.3 Al substitutions in place of Fe introduces domain wall pinning as evidenced from magnetostriction, magnetoimpedance and dc magnetization data. It is noted that ferrites so prepared using a simple procedure are magnetostrictive in good measure and with the addition of very small amount of non-magnetic aluminum their magnetostriction has shown saturation at relatively low magnetic fields. Such magnetostrictive ferrites find their applications in magnetic sensors and actuators.

Structural and magnetic properties of thermal plasma synthesized Fe 1− x Ni x ( x = 0.25, 0.33, 0.50, 0.67 and 0.75) alloy nanoparticles have been investigated using x-ray diffraction, neutron diffraction, transmission electron microscopy, scanning electron microscopy, dc magnetization, and Mossbauer spectroscopy techniques. High temperature gas phase nucleation and growth environment inside thermal plasma reactor facilitate stabilization of the disordered γ-FeNi ( fcc ) phase throughout (except for x = 0.25) the composition range under investigation. For x = 0.25 composition, a small (∼8%) amount of the disordered bcc phase along with prominent fcc (∼92%) phase is present, as inferred from the neutron diffraction data analysis. The spherical shaped nanoparticles possess high crystallinity. The average crystallite size (in 30–40 nm range) as well as particle size distribution show insignificant change as a function of composition. The observed value of the saturation magnetic moment for these nanoparticles are very close to that for their bulk counterparts, indicate highly crystalline nature of the thermal plasma synthesized nanoparticles. Room temperature Mossbauer spectroscopic data reveals that the alloy nanoparticles contain two different sites for Fe corresponding to high moment/low moment states. The neutron diffraction data indicates ferromagnetic ordering for all the compositions of the series. The average magnetic moments/f.u., derived from neutron diffraction and dc magnetization, are found to match with each other as well as with the values reported in the literature for bulk Fe 1− x Ni x alloys. The highest ordered magnetic moment was found to be 1.4 μ B per f.u. for Fe 0.50 Ni 0.50 composition. Overall, thermal plasma based synthesis is found to be an excellent route to produce high-quality nanoparticles of the binary metallic alloys.

Here, we report synthesis and in situ passivation of aluminum nanoparticles using thermal plasma reactor. Both air and palmitc acid passivation was carried out during the synthesis in the thermal plasma reactor. The passivated nanoparticles have been characterized for their structural and morphological properties using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. In order to understand nature of passivation vibrational spectroscopic analysis have been carried out. The enhancement in active aluminum content and shelf life for a palmitic acid passivated nano-aluminum particles in comparison to the air passivated samples and commercially available nano Al powder (ALEX) has been observed. Thermo-gravimetric analysis was used to estimate active aluminum content of all the samples under investigation. In addition cerimetric back titration method was also used to estimate AAC and the shelf life of passivated aluminum particles. Structural, microstructural and thermogravomateric analysis of four year aged passivated sample also depicts effectiveness of palmitic acid passivation.

Looking at the increasing scope of plasma processing of materials surface, here we present the development and diagnostics of a microwave assisted Electron Cyclotron Resonance (ECR) plasma system suitable for surface modification of polymers. Prior to the surface-treatment, a detailed diagnostic mapping of the plasma parameters throughout the reactor chamber was carried out by using single and double Langmuir probe measurements in Ar plasma. Conventional analysis of I-V curves as well as the elucidation form of the Electron Energy Distribution Function (EEDF) has become the source of calibration of plasma parameters in the reaction chamber. The high energy tail in the EEDF of electron temperature is seen to extend beyond 60 eV, at much larger distances from the ECR zone. This proves the suitability of the rector for plasma processing, since the electron energy is much beyond the threshold energy of bond breaking in most of the polymers. Nylon 6 is used as a representative candidate for surface processing in the presence of Ar, H

Here we report synthesis of Fe-Ni nanoparticles using thermal plasma route. In thermal plasma, gas phase nucleation and growth at sufficiently higher temperature is observed. The synthesized Fe-Ni nanoparticles are examined by X-ray Diffraction, Raman Spectroscopy, Vibrating Sample Magnetometer and Thermo gravimetric Analysis. Formation of 16-21 nm sized Fe-Ni nanoparticles having surface oxidation show maximum value of magnetization of ∼107 emu/g. The sample synthesized at relatively low power (4kW) show presence of carbonaceous species whereas the high power (6 kW) synthesis does not depicts carbonaceous species. The presence of carbonaceous species protects oxidation of the nanoparticles significantly as evidenced from TGA data.Here we report synthesis of Fe-Ni nanoparticles using thermal plasma route. In thermal plasma, gas phase nucleation and growth at sufficiently higher temperature is observed. The synthesized Fe-Ni nanoparticles are examined by X-ray Diffraction, Raman Spectroscopy, Vibrating Sample Magnetometer and Thermo gravimetric Analysis. Formation of 16-21 nm sized Fe-Ni nanoparticles having surface oxidation show maximum value of magnetization of ∼107 emu/g. The sample synthesized at relatively low power (4kW) show presence of carbonaceous species whereas the high power (6 kW) synthesis does not depicts carbonaceous species. The presence of carbonaceous species protects oxidation of the nanoparticles significantly as evidenced from TGA data.

Thermal Protecting System (TPS) material, consisted of silica reinforced fibres and coated with transtion metal complex was exposed to atomic oxygen produced in Electron Cyclotron Resonance (ECR) plasma reactor. The choice of atomic oxygen is based on the necessity of investigating its inteaction with transition metal complex during the re-entry of the space vehicle. The experiments were carried out at different temperature in the range of 30-500°C. The surface morphology of the tile material was investigated with and without exposure to oxygen plasma as a function of temperature using scanning electron microscopy technique, whereas structural analysis of the same samples was carried out using x-ray diffraction technique. Prior to this, ECR plasma reactor was charectorised for electron energy and plasma density using Langmuir probe so as to know the plasma parameter during the interaction.

Indigenously available natural dyes have been used as natural sensitisers for dye-sensitised solar cells (DSSCs) in this study. The chlorophyll extract from Azadirachta indica (Neem) leaves and anthocyanin extract from poinsettia bracts were obtained using ethanol. Nanoparticles of TiO2 having an average size of 80 nm were deposited on fluorine-doped tin oxide (FTO) coated glass using the electrophoretic deposition method. Counter electrode was prepared by spraying conductive graphite over FTO glass substrates. A sandwich-type cell was assembled, and the fill factor and the power conversion efficiency were measured under a light source simulating AM 1.5 with an intensity of 100 mW/cm2. DSSCs containing chlorophyll and anthocyanin exhibited open circuit voltages of 404 and 406 mV with fill factors of 40.1% and 45.8%, respectively. The mixture of the two natural dyes as sensitiser for DSSCs gave the best photovoltaic conversion efficiency of approximately 1%.

The paper presents an improved method of depositing nanocrystalline thin films of Fe-doped TiO2 to be used as a reusable cyclic photocatalyst for degrading the organic pollutants. The technique of electron cyclotron resonance plasma-enhanced chemical vapor deposition was employed with titanium tetra-isopropoxide (C12H28O4Ti) and ferrocene (C10H10Fe) as precursors of Ti and Fe, respectively. Optical emission spectroscopy was used to identify the reactive species, to determine the electron temperature and the ion density during deposition. The films were characterized using optical absorption and photoluminescence spectra, whereas the morphological analysis was carried out with scanning electron microscopy. Strong adhesion of the deposited films with the substrate ruled out any possibility of TiO2 particles being leached out. It was confirmed by observing the degradation rate of the same film repeatedly. Cyclic use of the film for the catalytic reactions thus makes the process much user friendly for the water treatment. Copyright © 2014 John Wiley & Sons, Ltd.

Silicon nanoparticles (Si-NPs) were synthesized using thermal plasma assisted gas phase condensation at different compositions of argon and hydrogen. The content of hydrogen in argon was varied from 0 to 15 mole percent. Synthesized nanoparticles were characterized by Transmission Electron Microscopy (TEM) and Fourier Transform Infrared spectroscopy (FTIR). Noticeable change in the morphology of nanostructures was observed with changing hydrogen content. Si-NPs synthesized in the presence of argon consisted of flake like structures, mostly amorphous. With increase in hydrogen concentration, flake like structures disappeared and prominent spherical structures and nanowires were observed. On further increasing hydrogen content spherical crystalline nanostructures with a tail of nanowire were formed and then nanoplatelets of SiC along with silicon nanostructures were observed. Different parameters that changed owing to different hydrogen concentration, were calculated and it is attempted to predict the cause of changing morphology.

Influence of manganese substitution on the magnetoimpedance ratio and magnetostrictive constant of cobalt ferrite samples has been studied in the present investigation. Magnetoimpedance was found to vary with manganese content and frequency under the action of applied axial magnetic field. Maximum value of magnetoimpedance ratio was obtained for the composition Co1.1Mn0.1Fe1.8O4 at a low frequency of 102 Hz. In order to understand magnetoimpedance behavior of the samples Cole–Cole plot of Mn substituted cobalt ferrites was studied. It was also noted that magnetostrictive constant under applied dc magnetic field changes with manganese content. The magnetic field required for maximum magnetostriction decreases with substitution of cobalt by manganese in Co1.2−xMnxFe1.8O4. The strain sensitivity ratio dλ/dH was maximum for Co1.1Mn0.1Fe1.8O4, whereas value of magnetostriction was maximum for CoMn0.2Fe1.8O4 sample.

Nanophase alumina is synthesized in an atmospheric pressure radio frequency (RF) plasma reactor through melting, evaporation, and vapor phase nucleation technique. A specially designed high-pressure RF plasma reactor fitted with an indigenously built RF plasma torch converts commercially available micrometer size alumina chunks into spherical nanophase alumina in a single step under ambient quenching conditions without use of any additional quenching gas. Obtained powder contains mixed phases of α and δ -alumina as revealed by X-ray diffraction studies. Transmission Electron Microscopy analyses exhibit very small particle size (peak at 15 nm), narrow size distribution (half width ~ 24 nm), zero agglomeration, and good crystallinity. Obtained particle characteristics together with the high purity owing to inherent electrode-less feature of the RF discharge are suitable for important technological applications including fabrication of high-power ceramic laser gain media like Y3Al5O12 (YAG) from composites of Al2O3 and Y2O3. Characteristics of the synthesized alumina are compared with that of nanoalumina synthesized in atmospheric arcs.

Synthetic graphite is one of the best thermal shock resistant materials and is generally believed to remain unaffected by a thermal shock alone. However, subject to a cold thermal shock, under a pool-boiling heat transfer process, micron size synthetic graphite may become noticeably fragile and can readily convert, to a significant fraction, into rotationally misoriented few-layer graphene (FLG) near the Leidenfrost point. Here we report, for the first time, how such FLG, with precisely controlled number of layers (N), can be obtained from an isostatically compacted synthetic graphite and analyzed the mechanism behind such transformation by a theoretical modeling. In a nutshell, we suggest how one can optimize this technique for producing such FLG with precisely controlled N with minimal cost and instrumental facility with an unbelievably high production-rate.

We report the generation and properties of few-layer graphene (FLG) in an external magnetic field modulated DC carbon arc in different non-reactive buffer gases. The effects of buffer gases on the anode erosion rate and the cathode deposit (CD) formation rate have been investigated during the synthesis of FLG. The constituents of the as-synthesized CDs were investigated using transmission electron microscopy, selected area electron diffraction, Raman spectroscopy, scanning tunneling microscopy and X-ray diffraction analysis. A plausible growth mechanism of such FLG is predicted. The results indicate that, under a parametrically optimized condition, an electric-arc of this kind can efficiently introduce rotational stacking faults to the as-synthesized flat FLG, which exhibits superior electron transport property than bulk graphite. A guideline for controlling the number of layers of such FLG has also been suggested.

Silica-coated, silicon nanotubes (SCSNTs) and silica-coated, silicon nanoparticles (SCSNPs) have been synthesized by catalyst-free single-step gas phase condensation using the arc plasma process. Transmission electron microscopy and scanning tunneling microscopy showed that SCSNTs exhibited a wall thickness of less than 1 nm, with an average diameter of 14 nm and a length of several 100 nm. Both nano-structures had a high specific surface area. The present study has demonstrated cheaper, resistance-free and effective antibacterial activity in silica-coated silicon nano-structures, each for two Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration (MIC) was estimated, using the optical densitometric technique, and by determining colony-forming units. The MIC was found to range in the order of micrograms, which is comparable to the reported MIC of metal oxides for these bacteria. SCSNTs were found to be more effective in limiting the growth of multidrug-resistant Staphylococcus aureus over SCSNPs at 10 μg/ml (IC 50 = 100 μg/ml).

The paper reports the large scale synthesis of nanoparticles of CoFe 2 O 4 using thermal plasma reactor by gas phase condensation method. The yield of formation was found to be around 15 g h −1 . The magnetic properties of CoFe 2 O 4 , synthesized at different reactor powers, were investigated in view of studying the effect of operating parameters of plasma reactor on the structural reorganization leading to the different cation distribution. The values of saturation magnetization, coercivity and remanent magnetization were found to be influenced by input power in thermal plasma. Although the increase in saturation magnetization was marginal (61 emu g −1 to 70 emu g −1 ) with increasing plasma power; a significant increase in the coercivity (552 Oe to 849 Oe) and remanent magnetization (16 emu g −1 to 26 emu g −1 ) were also noticed. The Mossbauer spectra showed mixed spinel structure and canted spin order for the as synthesized nanoparticles. The detailed analysis of cation distribution using the Mossbauer spectroscopy and X-ray photoelectron spectroscopy leads to the conclusion that the sample synthesized at an optimized power shows the different site selective states.

The photocatalytic activity of pure ZrO 2 samples, prepared by a thermal plasma route, and characterized by X-ray diffraction technique was tested for the degradation of methylene blue, which is known to be a hazardous dye. Although, all these samples synthesized at different operating pressures of the thermal plasma reactor showed the photocatalytic activity; the sample synthesized at 1.33 bar of operating pressure showed the highest photocatalytic activity. The blue shift in the band gap of monoclinic phase, as observed from the photo-absorption spectroscopy, may be attributed to the enhanced photocatalytic activity. The existence of different defect states and their concentration as, inferred from the photo-absorption measurements were also found to be responsible for the enhanced photocatalytic activity of the as synthesized samples.

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.

Composites of polymers with aluminium were formed by swift high energy ions of 150 MeV, which are used as low thermal emissivity materials for infrared wavelengths between 8–14 μm. Emissivity and dielectric constants were studied for these structures. A semi-empirical model has been established to obtain the relation between emissivity and dielectric constant.

The present work reports the application of micron-particulate crystalline hexagonal aluminium nitride/aluminium as a novel, mild acidic and reusable solid heterogeneous catalyst in organic synthesis. The catalyst was synthesized by thermal plasma technique and characterized using X-ray diffractometer and scanning electron microscopy. It catalyzes efficiently many organic transformations such as the synthesis of heterocyclic compounds 2,4,5-triaryl-substituted imidazoles and 2-aryl benzimidazoles.

The microwave-synthesized zinc-oxide (ZnO) nanonorods of average length of ∼ 1500 nm and diameter ∼ 100 nm were irradiated with 6.5 meV electrons. From sample to sample, the electron fluence was varied over the range 5×1014 to 2.5×1015 e-cm−2. The pre- and post-electron-irradiated ZnO nanorods were characterized by X-ray diffraction, UV–VIS, EDAX, scanning electron microscopy, transmission electron microscopy, and BET methods. The results show that after electron irradiation, the ZnO nanorods could retain the hexagonal phase with the wurtzite structure; however, the average length of the ZnO nanorods reduced to ∼ 800 nm. Moreover, the oxygen atoms from a fraction of ZnO molecules were dislodged, and the process contributed to the formation of Zn–ZnO mixed phase, with increased zinc to oxygen ratio. In the photo-degradation of Rhodamine-B, a significant enhancement in the photocatalytic activity of the electron-irradiated ZnO nanorods was observed. This could be attributed to the induced defects, reduced d...

We, herein, report the antimicrobial properties of uncapped silver nanoparticles for a Gram positive model organism, Bacillus subtilis. Uncapped silver nanoparticles have been prepared using less-explored DC arc thermal plasma technique by considering its large scale generation capability. It is observed that the resultant nanoparticles show size as well as optical property dependent antimicrobial effect.

The paper emphasizes the effect of electric field on photocatalytic efficiency of nanoparticles of TiO 2 (nano TiO 2 ). The effect was observed by applying electric field to nano TiO 2 during the photocatalytic degradation process of methylene blue. Porous silicon was used as a template to immobilize the nano TiO 2 and to facilitate the application of electric field. Nano TiO 2 , having an average particle size of 15 nm, was synthesized by thermal plasma assisted gas phase condensation. A critically selected negative bias potential, applied on the catalyst with reference to the solution, is shown to enhance the photocatalytic efficiency by 18%. The observed effect is explained on the basis of band movements at the TiO 2 /solution interface. Band movement influences the oxidation and reduction reactions at the interface and thus controls the photocatalytic degradation.

The paper deals with the comparative study of nanocrystalline Lanthanum hexaboride (LaB6) thin films grown on various substrates by Pulsed laser deposition and Arc plasma method. Field emission studies were carried out on LaB6 films deposited on various substrates show metallic behavior of the emitters. The high value of field enhancement factors, indicating that the electron emission from LaB6 nanoscale protrusions deposited on emitter surface. The post field emission surface morphology of the emitters showed no significant erosion of the films during continuous operation. The observed behavior indicates that it is linked with the growth of LaB6 films on substrate crystal structure. The LaB6 nanocrystallites/nanowires films were synthesized using arc plasma method shows good emission current stability. The LaB6 micro/nanocrystallites were also obtained by picosecond laser irradiation which gives high enhancement β factor, and good emission current stability along with high current density. The results reveal that nanocrystalline LaB6 films, exhibit high resistance to ion bombardment and excellent structural stability and are more promising emitters for practical applications in field emission based new generation devices.

We report the low thermal-emissive surface properties of composites of ZnO–polyimide. The composites were synthesized by depositing ZnO on polyimide surface by pulsed laser deposition technique. ZnO target was ablated at different incident energy densities and the substrate (polyimide) was held at elevated temperature. This facilitated the c-axis oriented growth of ZnO, which was inferred from the X-ray diffraction analysis. The composites consisted of multilayers having different electrical resistivities. The values of which are also estimated from Hagen–Rubens relation. The reduced infrared emissivities of the composite films, as compared to polyimide, were correlated to the increased carrier concentration and reduced surface resistivity estimated from the Hall measurements.

This article addresses the growth of hollow nanocrystalline particles of γ-alumina by the post-oxidation of nano-aluminium particles in air. The nanoparticles of aluminium were synthesized in a DC-transferred arc thermal plasma reactor. The as-synthesized nano-aluminium particles were oxidized, in air, at different temperatures. The as-synthesized parent nano aluminium and their daughter nanoparticles of aluminium oxide were thoroughly characterized with the help of X-ray diffraction analysis, high resolution transmission electron microscopy and thermogravimetric analysis. Two-step oxidation behaviours, unique in nanoparticles, are found to be the main driving force behind the formation of hollow spherical structures. The entire phenomenon is compared with the oxidation behaviour of coarse grain aluminium. The content of γ-alumina, identified by X-ray diffraction, relative to that of unreacted aluminium, has increased almost exponentially with the oxidation temperature in the case of nano aluminium. Similar behaviour is not observed in the case of coarse grain aluminium. The crystalline features of alumina, forming the walls of the hollow sphere, were confirmed by high resolution transmission electron microscopy.

Measurements of axial temperature and electron density have been carried out for Ar-H2 dc transferred arc-plasma columns under varying ambient-pressure conditions (100-760 torr). Optical emission spectroscopy has been used as the diagnostic tool. Temperature was determined by the relative intensity method using atomic hydrogen lines. The electron-density measurements were obtained from the Stark width of the Hs (486.13 nm) line. Possible deviation from local thermodynamic equilibrium (LTE) has been studied by using Hs transitions and by measuring the population factor using ArI (696.5 nm) transition. The nonideality along the plasma column has been studied using the electron-density data. The plasma approaches weakly nonideal conditions near substrate. The maximum deviation from LTE conditions also arises near the transferred anode substrate. With an increase in pressure, the volume of plasma approaches LTE.

The paper has addressed the problem of controlling the thermal emissivities from metal/polymer composites prepared by solution method. Aluminium is used as a filler and polystyrene as a polymer–matrix. Aluminium particles, with micrometer and nanometer dimensions having different morphologies, were employed. The values of emissivities were reduced when the coarse grains and flakes of aluminium were used as fillers, whereas, no significant change was observed when nano-aluminium was used in the composite. Dielectric dispersion for the composites was measured and the results are analysed in view of Fresnel relation. The differences in the values of dielectric constants, between the experimentally measured and those which can be predicted theoretically, are thought to arise from the interfacial polarization.

Lanthanum hexaboride (LaB6) nanocrystallites/nanowires have been successfully synthesized using gas phase condensation in arc plasma. Our results show that the LaB6 nanowires have ~20 nm diameter and length of several micrometers. The as-synthesized LaB6 nanocrystallites and nanowires are crystalline in nature. Field emission studies were carried out on as synthesized LaB6 nano-powder deposited on W and Re tips and foils, and also on Si foil substrates under ultra high vacuum. The Fowler–Nordheim plots obtained from the current–voltage characteristics are found to be linear in accordance with the quantum mechanical tunneling phenomenon. High value of field enhancement factor (8177) is observed for LaB6 on Re substrate, indicating that the electron emission is from the nanometric features of the LaB6. Our results show that the arc plasma synthesized LaB6 nanocrystalline film exhibits good emission stability as emitter without severe deviations from the initial set value and also a strong ability to withstand the ion bombardment, which is useful for low operation voltage vacuum micro/nano electronic devices.

The synthesis of nanoparticles of titanium dioxide (TiO2) with varying percentages of anatase and rutile phases is reported. This was achieved by controlling the operating pressure in a transferred-arc, direct current thermal plasma reactor in which titanium vapors are evaporated, and then exposed to ambient oxygen. The average particle size remained around 15 nm in each case. The crystalline structure of the as-synthesized nanoparticles of TiO2 was studied with X-ray diffraction analysis; whereas the particle morphology was investigated with the help of transmission electron microscopy. The precursor species responsible for the growth of these nanoparticles was studied with the help of optical emission spectroscopy. As inferred from the X-ray diffraction analysis, the relative abundance of anatase TiO2 was found to be dominant when synthesized at 760 Torr, and the same showed a decreasing trend with decreasing chamber pressure. The study also reveals that anatase TiO2 is a more effective photocatalytic agent in degrading methylene blue by comparison to its rutile phase.

The paper presents the experimental results showing that the crystalline phase of the nano-particles, synthesized in a DC transferred arc thermal plasma reactor, critically depend on the operating pressure in the reaction zone. The paper reports about the changes in crystalline phases of three different compounds namely: aluminium oxide (Al2O3), aluminium nitride (AlN) and iron oxide (FexOy) synthesized at 760 Torr and 500 Torr of operating pressures. The major outcome of the present work is that the phases having higher defect densities are more probable to form at the sub-atmospheric operating pressures. The variations in the crystalline structures are discussed on the basis of the change in the temperature during the nucleation process, prevailing at the boundary of the plasma, on account of the ambient pressures. The as-synthesized nano-particles were examined by X-ray diffraction analysis and transmission electron microscopy. In addition, the confirmatory analysis of the crystalline phases of iron oxides was carried out with the help of Mossbauer spectroscopy.

A composite film fabricated by plasma treated poly(etherimide) with subsequent deposition of gold nanoparticles and lysine using layer by layer assembly has been demonstrated to be good for cell attachment and proliferation making it an attractive strategy for tissue engineering applications. As compared to the other methods the decrease in contact angle obtained here does not depend much on the plasma treatment thus affecting the polymer structure minimally. A combination of surface roughness provided by the gold nanoparticles and the presence of amine groups of lysine is hypothesized to be the reason for the features observed.

Deposits of one dimensional nanowires of zinc with diameters of 90–120 nm have been obtained by means of dc sputtering within an electron cyclotron resonance plasma reactor. The sputtering has been made effective by using a negatively biased cylindrical target. The structure of the nanocrystalline wires deposited on glass substrates were investigated with scanning electron microscopy, transmission electron microscopy and scanning tunneling microscopy. STM revealed that the structure of the one dimensional nanowires are ensemble of nanoclusters and nanowires with diameter of 4–5 nm. The crystalline nature of the metallic nanowires was studied with X-ray and electron diffraction analysis. The native oxide present on the metallic wires was revealed by photoluminescent spectroscopy. Theoretical modeling has been used to explain the possible mechanisms operative inside the plasma which lead into deposition of zinc on the substrate starting from the precursor species.