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In the present work, graphene nanoflakes (GNFs) were grown at both low and high levels of nitrogen functionalization and subsequently put through a wet-chemical method to add iron functionalities to the surface and create active catalyst centers. No mechanical treatments are used in order to minimize the formation of defects on the GNFs and evaluate if iron-nitrogen-GNF edges or surface sites can generate catalytic activity rather than the macropore structures holding these functionalities on porous carbon black. The catalysts produced under various synthesis routes were characterized and screened for their performance as an oxygen reduction reaction (ORR) catalyst. Characterization included an electrochemical study, an examination of the carbon and nitrogen content and bonding structure, in addition to Raman analysis and the calculation of the BET surface areas. It was found that samples that were both treated with iron acetate and put through pyrolysis produced the most active samples. These samples were composed of graphitic carbon and contained a large amount of pyridinic nitrogen. Additionally, when working with GNFs generated with high levels of nitrogen, no extra nitrogen source was needed during the iron incorporation step. This study further develops the GNF-based catalyst already seen to be a suitable ORR catalyst for the polymer electrolyte membrane fuel cell.

Graphene nanoflakes (GNFs) are a stack of 5–20 layers of highly crystalline graphene sheets having a planar size of approximately 100 by 100 nm and low defect concentration. They are produced here through homogeneous nucleation following the plasma decomposition of a carbon source in an inductively coupled thermal plasma reactor. Following synthesis within the plasma reactor, the GNFs are functionalized downstream in the plasma recombination zone with the addition of oxygen to the main plasma stream. Tunable oxygen functionalization is obtained and values up to 14.2 atomic percent are reached on the surface of the particles. While the non-functionalized GNFs are hydrophobic, the oxygen-functionalized GNFs (O-GNFs) show full stability of all the produced powders when directly dispersed in water or ethanol without any surfactant. The O-GNFs keep their structural integrity even after the implementation of the hydrophilic groups on the surface of the nanoparticles, and maintain their dispersion stability in water and ethanol over a long period of time.

Emerging nanofluid-based technologies for cooling, transport, and storage applications have previously been enhanced through the use of graphene nanoflake (GNF) nanofluids. Many of the beneficial effects of GNFs have now been documented, though little work has yet been completed to characterize the morphological behaviour of GNF nanofluids both during and after the phase change process. In this study, the crystallization behaviour of sessile water droplets was evaluated for two plasma-functionalized, hydrophilic GNF concentrations (20 and 100 ppm) at three driving force temperatures (-5 °C, -10 °C, and -20 °C). At low driving forces, the GNFs were wholly expelled from the solid matrix due to low crystallization velocities. At high driving forces, more rapid crystallization rates resulted in the entrapment of GNFs within the air bubbles and inter-dendritic spaces of the solid droplet. However, individual particle dispersion was not achieved within the solid matrix at any driving force. Furthermore, for all experimental conditions, the functionalized GNF clusters which formed during freezing did not disperse spontaneously upon melting as drying-like effects may have altered the attraction properties of their surfaces and destabilized the suspension. Compared to previous studies using multi-walled carbon nanotubes, the GNFs were found to have higher liquid mobility at the solid front, provide less resistance to that front as it ascended, and be better dispersed after melting. These effects may have been geometrical; the square nanoflake geometry does not result in any physical particle entanglement.

In this paper we present a template-based table structure matching using association graphs for handwritten/printed historical documents. The recognition of the table structure consisting of column and header information is the prerequisite for the subsequent row detection and handwritten text recognition used for information extraction. The table matching is done by detecting the maximum clique in an association graph, which represents the matching of the line information of the template and a document of interest. This allows for variations of widths and heights of rows and columns. The presented methodology is evaluated on historical register books (death records) of the Archive of the Diocese of Passau. The method shows a reliable detection of the structure of handwritten/printed tables with a mean cell match of 88.28%.

Modified glassy carbon RDE method is introduced in this work for the determination of heterogeneous reaction rate constant of H2O2 decomposition. This method is based on the analysis of RDE voltammograms of H2O2 reduction on a glassy carbon electrode covered with a catalyst layer. As a case study, the rate constant of H2O2 decomposition on nitrogen doped graphene is determined by using both glassy carbon and gold RDE methods. A good agreement is observed between the results of these two methods indicating the reliability of the glassy carbon method. Moreover, advantages and limitations of the glassy carbon method are discussed.

Fe–N-doped graphene containing 0.3 at% of Fe and 1.9 of N with an active specific surface area of 77.5 ± 4 m2 g−1 is synthesized in two steps: first N-doped graphene is produced by thermal dissociation of methane in an inductively coupled thermal plasma (ICP) reactor and subsequently the product is converted to Fe–N-doped graphene by a wet chemical method. The catalytic activity of this catalyst toward H2O2 reduction reaction (HPRR) is studied by rotating disk electrode for fuel cell applications. Although the mechanism of HPRR on Fe–N-doped graphene, N-doped graphene and graphene is similar, Fe–N-doped graphene shows the highest catalytic activity toward HPRR. The exchange current density based on the active surface area (j0A) of Fe–N-doped graphene in Na2SO4 solution is (4.4 ± 0.2) × 10−8 A cm−2, which is 5 times greater than j0A of the N-doped graphene. Direct reduction of H2O2, H2O2 decomposition, O2 reduction, and O2 desorption are predicted as the reactions involved in the HPRR while O2 reduction and O2 desorption are negligible at low and high overpotentials, respectively. Investigation of the effect of the electrolyte and catalyst loading reveals that HPRR on Fe–N-doped graphene suffers from kinetic limitations especially at low catalyst lodgings, fast rotation rates, and strong acidic and basic solutions.

Colloidal suspensions of functionalized carbon nanotubes (CNT nanofluids) have the potential to be used in a variety of applications, many of which require operation at elevated temperatures. In this study, we examine what effect exposure to an argon/oxygen/ethane RF glow discharge plasma has on the surface chemistry and structure of CNTs and what happens to the plasma-generated functionalities at high temperatures. An analysis performed using X-ray photoelectron spectroscopy and Raman spectroscopy indicates that longer and higher power plasma treatments decrease the sp2 graphitic nature of the CNTs without increasing the degree of oxygen functional groups. Heating of the functionalized-CNTs up to 350 °C in air and 600 °C in argon, both lead to a substantial decrease in the surface oxygen concentration, which can be attributed to the decomposition of carboxylic functionalities at low temperatures (< 350 °C).

The catalytic activity of LaNiO 3 toward H 2 O 2 reduction reaction (HPRR), with a potential application in the cathode side of fuel cells, is studied in alkaline, neutral and acidic solutions by rotating disk electrode. The LaNiO 3 particles synthesised by citrate-based sol–gel method have sizes between 30 and 70 nm with an active specific surface area of 1.26 ± 0.05 m 2 g −1 . LaNiO 3 shows high catalytic activity toward HPRR in 0.1 M KOH solution with an exchange current density based on the active surface area ( j 0 A ) of (7.4 ± 1) × 10 −6 A cm −2 which is noticeably higher than the j 0 A of N-doped graphene. The analysis of kinetic parameters suggests that the direct reduction of H 2 O 2 , H 2 O 2 decomposition, O 2 reduction and O 2 desorption occur through HPRR on this catalyst. In order to control and minimize oxygen evolution from the electrode surface, the effects of catalyst loading, bulk concentration of H 2 O 2 , and using a mixture of LaNiO 3 and N-doped graphene are studied. Although the mechanism of HPRR is independent of the aforementioned operating conditions, gas evolution decreases by increasing the catalyst loading, decreasing the bulk concentration of H 2 O 2 , and addition of N-doped graphene to LaNiO 3 .

H2O2 reduction reaction (HPRR) is studied on both graphene (GNF) and nitrogen doped graphene nanoflakes in 0.1 M Na2SO4 solution by rotating disk electrode. The XPS results indicate that N-doped graphene nanoflakes with high nitrogen content, 32 at%N (N-GNF32), are synthesised successfully by an inductively-coupled thermal plasma (ICP) reactor. Pyridinic, pyrrolic and graphitic N species contribute up to 67% of the total nitrogen. Kinetic parameters such as Tafel slope and stoichiometric number suggest that HPRR occurs by the same mechanism on both GNF and N-GNF32. Although nitrogen does not change the mechanism of HPRR, the results indicate that the reaction rate of H2O2 reduction is enhanced on N-GNF32. The exchange current density of H2O2 reduction based on the active surface area of N-GNF32 is (8.3 ± 0.3) × 10−9 A cm−2, which is 6 times higher than the value determined for GNF. The apparent number of electrons involved in the process suggests that H2O2 decomposition competes with H2O2 reduction on both catalysts. Evaluation of the apparent heterogeneous reaction rate constant and the Tafel slope indicate that simultaneous reduction of O2 and H2O2 is negligible on the N-GNF32. On the other hand, the reduction of O2 and H2O2 occurs simultaneously on the GNF surface.

The control of nanoparticle synthesis using thermal plasmas is difficult and often leads to problems of chemical and structural purity, and poor process robustness in terms of consistency of product from run to run. Good reactor design allowed to overcome these issues and to develop a new material based on graphene with a flake-like structure (labeled graphene nanoflakes, GNF) supporting nitrogen for catalytic applications, for example as platinum replacement in fuel cells. These structures showed not only to be active, but also stable in polymer electrolyte fuel cell operation. Characterization of these structures, in situ fuel cell studies and modeling analysis all indicate that achievement of stability relates on the crystalline two-dimensional graphene structure. This paper first reviews the basic aspects behind the structural objectives, describes the synthesis process design leading to this crystalline structure, and provides a two-dimensional analysis on the graphitic growth based on fundamental theory and CFD calculations. These calculations indicate that an independent control of the graphene structure thickness (number of atomic planes) and sheet lengths is possible in a thermal plasma reactor.

This work presents a methodology to analyze hydrogen peroxide reduction reaction (HPRR) studied by rotating disk electrode (RDE). Generally the Koutecky–Levich equation is used to determine the kinetic parameters of an electrochemical reaction. This equation is not applicable to electrochemical reactions with a complex reaction mechanism. The HPRR is an example of these complex reactions because the H2O2 reduction, H2O2 decomposition and O2 reduction may take place simultaneously on the electrode surface. In the current work the mass transport equations of H2O2 in the electrolyte and the reaction equations on the electrode surface are solved simultaneously under the steady state conditions to derive a specific equation for HPRR. The new equation shows the same linear relationship between the inverse of the current density (j−1) and the inverse square root of the rotation frequency (ω−1/2), but the slopes and the intercepts of the lines are shown to be functions of the reaction rate constants involved in the HPRR. One of the most important results of the work is the possibility to determine the hydrogen peroxide decomposition rate constant directly from RDE data. Prediction of simultaneous reduction of H2O2 and O2 on the electrode and suggestion a mechanism for HPRR are other advantages of the derived equation when compared with Koutecky–Levich equation.

This work presents a simple, inexpensive and scalable method to grow multi-walled carbon nanotubes (CNTs), using chemical vapor deposition, directly from stainless steel 316 mesh, without any pretreatment or the use of an external catalyst. A growth method is proposed based on the generation of particle-like growth sites, which are created as a result of chromium migration to the surface during heating. Acetylene concentrations were modeled within the reactor at various flow conditions and compared to experimental results to show that carbon input can be used as a way of controlling the diameter of the CNTs. All CNTs produced were strongly rooted to the SS substrate, however the larger diameter CNTs were more difficult to break and remove by means of ultrasonication.

Two of the major challenges for the commercialization of automotive fuel cells are cost and durability. Cost estimations indicate that at a large production rate, the majority of the stack component cost comes from the catalyst ink. Decreasing this cost depends on finding a durable cost-effective platinum-free electrocatalyst. In this work, pure graphene nano-flake (GNFs) powders are produced by plasma decomposition. The GNFs are composed of 5–20 layers of stacked graphene sheets, a structure that appears to be closely associated to catalyst stability and durability. Additionally, the large number of attachment sites for nitrogen and atomic iron functionalization provide an avenue for improving activity. The GNFs were nitrogen functionalized and then used to support atomic iron to create the active sites for a non-noble catalyst. Iron was successfully incorporated at a value of 0.28 at% on the surface of the catalyst structure. The catalyst was used on the cathode side of a polymer electrolyte membrane fuel cell (PEMFC) and showed stability over 100 h. The performance of the catalyst demonstrates, to our knowledge, the first proof of a stable strictly iron-based fuel cell catalyst.

A study has been undertaken of the degradation of carbon nanotube (CNT)-covered stainless steel mesh cathodes during exposure to low-pressure oxygen glow discharges. Emission spectroscopy and molecular absorption spectroscopy in DC glow discharge and in RF afterglow experiments, as well as morphological evidence, mass spectrometry spectra of condensed oxidation products, and molecular structure models have shown that plasma oxidation favors the production of 2,3 naphthalic anhydride. Absorption spectra taken during plasma oxidation match both literature sources for 2,3 naphthalic anhydride, as well as spectra of a chemical standard. MS data indicate that the only heavy compounds produced during plasma oxidation are poly-cyclic aromatics that can be attributed either directly to 2,3 naphthalic anhydride or to toluene, its major plasma decomposition product. Morphological observations using the scanning electron microscope support the conclusion that the reaction is facilitated by the field enhancement effect that accelerates oxygen ions to the tips of CNTs, where the oxidation takes place. Tests using water vapor show that oxidation is anhydrous, even in the presence of hydrogen.

Graphene nanoflakes (GNF), a stack of 5 to 20 layers of graphene sheets with typically 100 nm side lengths, are the product of methane decomposition using an argon ICP thermal plasma. GNFs are good candidates to support non-noble catalytic sites for the oxygen reduction reaction. This material has a high crystallinity allowing the graphene to be acid resistant, together with a high electrical conductivity, these properties providing a good basis for a stable catalyst material in fuel cells. The GNFs are functionalized with nitrogen to support iron atoms and create catalytic sites dispersed at the atomic level on the nano-structured powders. The iron functionalization step is realized in situ as a post-processing step within the synthesis reactor through the vaporization of two different Fe precursors in the core of the plasma. The first consists of pure iron powders carried by a nitrogen flow; this method having the advantage of avoiding impurities during the functionalization step. The second precursor is an iron(II) acetate solution also carried by a nitrogen flow, with the iron already in atomic form once dissociated in the thermal plasma core. The effects of the type of precursor, the power of the plasma, and the reactor chamber pressure on the iron functionalization are studied in the present contribution. The structure, composition, and activity of the resulting catalyst are also fully characterized.

Carbon black nanopowders were produced using two thermal plasma processes based on DC, respectively ICP plasma torches. Although the produced particles were in the nanometer size range, the values obtained for the surface area of the particles using a Brunauer Emmett Teller technique were very small. This indicated the presence of contaminants in the experimental powders, as confirmed by Raman spectroscopy and thermogravimetric Analysis. A thermal treatment process was developed in order to extract these volatile compounds, which were then identified using a Gas Chromatography–Mass Spectrometry method. The experimental powders were analyzed using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy before and after the thermal treatment in order to determine the effect of the heat treatment on the powder structural properties.

The mechanism of formation of carbon nanotubes (CNTs) produced from the dissociation of tetrachloroethylene (TCE) and the co-injection of tungsten vapour in the nozzle of a DC thermal plasma torch is discussed. Tungsten and the dissociation of TCE form nanoparticles of tungsten carbide (WC), which provide the catalyst activity for the formation of CNTs. A new route for the mechanisms of formation is discussed following thermodynamic equilibrium calculations of the plasma torch system, energy dispersive spectroscopy and nano-diffraction analyses of the WC nanoparticles formed. These analyses provide an understanding of the dissociation pattern of TCE, evaluate the carbon concentration in the catalyst nanoparticles and determine the phase structure of these nanoparticles. We propose from these results a new mechanism of formation for CNT occurring above the peritectic temperature of the stoichiometric WC alloy.

Carbon material was produced using an inductively coupled thermal plasma torch system of 35 kW and a conical shape reactor. The carbon nanopowders were obtained by plasma decomposition of methane at various flow rates and show a uniform microstructure throughout the reactor. The product has a crystalline graphitic structure, with a stacking of between 6 and 16 planes and a nano-flake morphology with particles dimensions of approximately 100 nm long, 50 nm wide and 5 nm thick. Nitrogen was also introduced in some synthesis experiments along with the methane precursor using flow rates of 0.1 and 0.2 slpm. The resulting product has the same structural properties and the nitrogen is incorporated into the graphitic structure through pyridinic type bonds.

Carbon nanotubes are synthesized directly on stainless steel (SS) 304 particles (o70 μm) by chemical vapor deposition (CVD) in a fluidized bed system (FBCVD) without the addition of an external catalyst. The direct growth method was originally developed for a fixed thermal CVD furnace, it is shown here it can be extended to FBCVD in a demonstration of the ease of scale up of the direct growth method. The growth method is compliant with SS particles substrate microstructures in the form of dendrites. It is also shown the SS particles can be successfully recycled for a second growth sequence without having to repeat the particle pre-treatment.

Carbon black (CB) nanopowders were obtained by plasma decomposition of methane at various flow rates using inductively coupled thermal plasma torch system of 35 kW. Nitrogen was also introduced in some experiments along with the methane. Using a cylindrical shape reactor the obtained powders were composed mainly of spherical particles, non-uniform in terms of particles size with diameters between 30 and 150 nm. The shape and size of this reactor resulted in the presence of recirculation areas enabling the formation of large CB particles and other secondary volatile compounds. Changing the reactor to a conical geometry resulted in the production of CB powders showing a crystalline and flake-like morphology made of sheets having 6–16 graphitic planes. The conical shape avoids the presence of recirculation areas and promotes the formation of a uniform powder morphology throughout the reactor.

This article reports a method for surface modification of multi-walled carbon nanotubes (MWNTs) using a low-pressure capacitively coupled RF glow-discharge. Ar/C2H6 and Ar/C2H6/O2 gaseous mixtures were used to produce non-polar (np-) and polar (p-) coatings, respectively, onto MWNTs. After 5 min of plasma treatment at 20 W and 20 torr, strongly hydrophobic and non-electrically conductive np-MWNTs were produced. The p-MWNTs were strongly hydrophilic and showed no measurable hydrophobic recovery 2 weeks after treatment. Aqueous suspensions of p-MWNTs remained stable and free of agglomerates after being boiled. The ζ-potential of p-MWNT nanofluids was −40.3 mV, indicating a highly stable dispersion.

We present a method for structuring a document according to the information present in its different organizational tables: table of contents, tables of figures, etc. This method is based on a two-step approach that leverages functional and formal (layout-based) kinds of knowledge. The functional definition of organizational table, based on five properties, is used to provide a first solution, which is improved in a second step by automatically learning the form of the table of contents. We also report on the robustness and performance of the method and we illustrate its use in a real conversion case.

A method is described to synthesize carbon nanotubes (CNTs) by thermal chemical vapour deposition (th-CVD) directly on stainless steel substrates of various geometries. This method allows the bulk metal surface to act as both the catalyst and support for the CNT growth, thus enhancing the contact and adherence of the tubes to the substrate and eliminating the requirement of adding an additional catalyst in the process. The procedure was optimized to obtain a uniform layer of CNTs on the substrate.

A numerical investigation of the topographic field-enhancement factor for structures including individual vertically aligned carbon nanotubes (VACNTs) and arrays of VACNT is presented. Some previously reported results for simple structures are reviewed first. Then, the extent of the zones of field enhancement and significant screening effects surrounding a given structure is discussed. The investigation with combined VACNT confirms the criterion that the spacing between identical CNT should be about twice their height to minimize screening effects. This statement is generalized to structures having different height ratios. The possibility of combining patterns of different height VACNT to minimize screening effects while allowing a larger surface density of such emitters is then investigated. The results show that height anisotropies in VACNT arrays can significantly reduce the field-emission current for a given applied field. A subsequent study that takes into account Joule heating and radiation losses during field emission demonstrates that, for height anisotropies larger than 5%, the VACNT tips reach temperatures above the onset temperature for selective field-assisted evaporation. This phenomenon occurs before the field-emission current from the nonideal films matches the targeted current value deduced from ideal VACNT arrays.

In this study we produce carbon nanotubes (CNT) using a DC non-transferred plasma torch operated at a power of 30 kW in argon and producing a supersonic jet. Tetrachloroethylene (TCE) is used as the carbon raw material. As an initial demonstration of the supersonic plasma jet approach and in an attempt to simplify the flow/nucleation fields of metal catalyst nanoparticles, the erosion of the torch tungsten electrodes is used as a source of metal vapours nucleating in situ into catalytic nanoparticles within the plasma jet. CNT mass yield values are based on thermogravimetry analysis correlated using electron microscopy and Raman spectroscopy. A parametric study is made to evaluate the influence of the different operating parameters on the yields of carbon nanotubes. The rapid quench generated by the supersonic jet, the high vapour pressures of carbon and a control of the temperature profile within the torch nozzle enable the rapid growth of CNT. Decreasing the reactor pressure from 0.66 to 0.26 atm leads to a CNT yield increase by 22%. High vapour pressure of carbon is obtained by increasing the TCE feed rate. From 0.05 to 0.15 mol/min, the yield of CNT is improved from 38.6 to 53.7 wt%. Beyond 0.15 mol TCE/min, the yield of CNT levels to around 50 wt%. In the start-up phase, the time of operation controls the temperature profile, which in turn drastically increases the yield of CNT from 0 to 8.2 wt% between the 3rd and the 4th minute of operation and to 53.7 wt% after the 5th minute.

Multi-walled carbon nanotubes (MWCNTs) were produced by chemical vapor decomposition using acetylene gas in the presence of Ferrocene catalyst at 800 degrees C, and then oxidized with concentrated nitric acid at 150 degrees C. Both (as-produced and oxidized) CNTs were characterized by TEM, Boehm titration, N2-BET and cation exchange capacity techniques. The adsorption capacity for nickel ions from aqueous solutions increased significantly onto the surface of the oxidized CNTs compared to that on the as-produced CNTs. The effects of adsorption time, solution pH and initial nickel ions concentrations on the adsorption uptake of Ni2+ for both the as-produced and oxidized CNTs were investigated at room temperature. Both Langmuir and Freundlich isotherm models match the experimental data very well. According to the Langmuir model the maximum nickel ions adsorption uptake onto the as-produced and oxidized CNTs were determined as 18.083 and 49.261 mg/g, respectively. Our results showed that CNTs can be used as an effective Ni2+ adsorbent due to the high adsorption capacity as well as the short adsorption time needed to achieve equilibrium.

Arc velocity and erosion rate measurements were performed on nanostructured pure Cu cathodes in 10?5?Torr vacuum (1.3324?m?Pa), in an external magnetic field of 0.04?T. Five different kinds of nanostructured cathodes were produced by spraying pure Cu powders of three different sizes, on Cu coupons by atmospheric pressure plasma spraying and high velocity oxygen fuel spraying techniques. The erosion rates of these electrodes were obtained by measuring the weight loss of the electrode after igniting as many as 135 arc pulses, each of which was 500??s long at an arc current of 125?A. The arc erosion values measured on three kinds of nanostructured coatings were 50% lower than the conventional pure massive Cu cathodes. Microscopic analyses of the arc traces on these nanostructured coatings show that the craters formed on these coatings were smaller than those formed on conventional Cu (

Machine Translation (MT) has advanced in recent years to produce better translations for clients’ specific domains, and sophisticated tools allow professional translators to obtain translations according to their prior edits. We suggest that MT should be further personalized to the end-user level ‐ the receiver or the author of the text ‐ as done in other applications. As a step in that direction, we propose a method based on a recommender systems approach where the user’s preferred translation is predicted based on preferences of similar users. In our experiments, this method outperforms a set of non-personalized methods, suggesting that user preference information can be employed to provide better-suited translations for each user.

Recently, direct solar collection through the use of broadly absorbing nanoparticle suspensions (known as nanofluids) has been shown as a promising method to improve efficiencies in solar thermal devices. By utilizing a volatile base fluid, this concept could also be applied to the development of a direct absorption heat pipe for an evacuated tube solar collector. However, for this to happen or for any other light-induced vapor production applications, the nanofluid must remain stable over extended periods of time at high temperatures and throughout repetitive evaporation/condensation cycles. In this work, we report for the first time a nanofluid consisting of plasma-functionalized multiwalled carbon nanotubes (MWCNTs) suspended in denatured alcohol, which achieves this required stability. In addition, optical characterization of the nanofluid demonstrates that close to 100% of solar irradiation can be absorbed over a relatively small nanofluid thickness.

A simple method of growing carbon nanotubes directly on nickel substrate without chemical pretreatment is reported. It is demonstrated that carbon nanotubes growth is directly affected by the roughness on the surface. Carbon nanotubes density is large in each growth zone observed on the surface; these zones being spread sparsely for coarse roughness of the surface. The density of carbon nanotubes decreases and the number of growth zones increases as the roughness on the surface is reduced. The above trend was not affected with C 2 H 2 flow time changing from 10 to 2 min. A similar result was obtained using a Ni alloy as substrate, but the effect of surface roughness on the growth of CNTs was less pronounced. The CNTs grown on the Ni alloy were free of amorphous carbon and uniformly distributed.

Steady-state modelling and experimental results are given on the electric arc attachment on cold carbon cathodes working at low pressure. The modelling results are compared with the case of copper cathodes and with experimental data on vacuum arc erosion characteristics for graphite materials. A region of existence of a physically meaningful solution for self-sustained operation of the steady-state cathode spot is given in the electron temperature?cathode spot plasma pressure space. A solution domain comprised between Te ? 1.2?1.5?eV and p? 2?45?atm corresponding to carbon surface temperatures in the range 4200?4900?K is found. Values of the local heat flux to the cathode surface are evaluated in the range 1?20 ? 1010?W?m?2, and ratios of the various contributions to this flux and current density are given. Also given are the cathode spot radii and upper/lower limits for the erosion rate through vapourization, these being compared with experimental data. It is shown that the cathode spot pressure conditions can provide a mechanism for the control of macroparticle emission on carbon. This effect is used experimentally through cathode spot plasma confinement for the reduction of the microdroplet emission in arc sources used for diamondlike film deposition. Experimental data obtained on graphite materials are in agreement with the model-based design guidelines.

This communication reports on a new method for the collection of nanoparticles using carbon nanotubes (CNT) as collecting surfaces, by which the problem of agglomeration of nanoparticles can be circumvented. CNT (10–50 nm in diameter, 1–10 μm in length) were grown by thermal CVD at 923 K in a 7 v/v% C2H2 in N2 mixture on electroless nickel-plated copper transmission electron microscopy (TEM) grids and Monel coupons. These samples were then placed downstream of an arc plasma reactor to collect individual copper nanoparticles (5–30 nm in diameter). It was observed that the Cu nanoparticles preferentially adhere onto CNT and that the macro-particles (diameter >1 μm), a usual co-product obtained with metal nanoparticles in the arc plasma synthesis, are not collected. Cu–Ni nanoparticles, a catalyst for CNT growth, were deposited on CNT to grow multibranched CNT. CNT-embedded thin films were produced by re-melting the deposited nanoparticles.

Satellite solar array discharges are studied experimentally on samples made of copper and zinc and on real solar cell samples. Secondary discharge currents up to 4 A and discharge voltages around 20 V were measured. Spectroscopic analysis of the emission spectrum indicates that the discharge plasma is composed of eroded metal vapors from the cell electrodes. Scanning electron microscope analysis confirms the important local degradation of the cathode electrode and metallization of the gap between adjacent cells. The results indicate clearly that the secondary discharges have the characteristics of vacuum arc discharges sustained by the power of the solar array.

Carbon nanotubes (CNTs) are produced using a 100 kW dc non-transferred plasma torch and C2Cl4 as the carbon precursor. Catalytic metallic nanoparticles are generated in situ using the tungsten metal vapours emitted by the electrode erosion process. Large quantities of multi-walled carbon nanotubes (MWNTs) and spherical (onion-like) carbon structures are observed under FE-SEM and TEM. Preliminary results are given here on the effect of the type and pressure of the gas in the reactor on the zone of CNT nucleation. A large amount of CNTs, over 50 µm in length, is observed to grow within the torch nozzle at 0.26 atm pressure in helium and argon. Increasing the pressure to 0.66 atm in both gases has the effect of pushing the CNT production downstream in the gas phase within the main reactor.

In order to optimize the fullerene synthesis process based on an electric arc with graphite electrodes, an experimental study using a reactor geometry optimized for plasma spectroscopy is performed to correlate the arc properties with the fullerene formation. Emission spectroscopy studies based on the use of the Swan C2(0,0) rotational system emission spectra were carried out to determine the plasma temperature. The self-absorption effect in the d3Πg, v' = 0 → a3Πu, v'' = 0 C2 band was used for column density determination of C2 molecules and temperatures under various arc discharge conditions. Discharge parameters (pressure, arc current, electrode gap length) are optimized with respect both to the anode erosion rate and the weight percentage of toluene extractable fullerenes in the soot. Local plasma discharge conditions (temperature and density fields) are evaluated and correlated with the C60 yield. Steep temperature gradients around the arc fringes are shown to provide optimal conditions for C60 production.

Cross-sections of erosion craters formed by vacuum arc discharges on graphite cathodes are examined using electron microscopy. These reveal erosion craters that are covered with a growth layer forming a continuous film on the arced surface. The film surface is composed of sphere-like structures similar to cauliflower diamond and to the emitted macro-particles (MPs) observed in coating experiments using graphite vacuum arc sources. The film thickness within the cathode erosion craters evolves with the mean values of the MP diameter and mean crater depth for four graphite material morphologies. These two parameters increase with a decrease in arc spot velocity. The growth layer shows a relatively porous columnar structure, with micro-Raman spectroscopy indicating an evolution from amorphous carbon (cathode base), to graphitic (middle), to diamond dominating the top layer.

In a RF induction thermal plasma chemical vapour deposition system the substrate is used as an electrical probe to monitor the diamond film evolution in situ. The evolving electron emission current allows us to identify the transition from the initial nucleation stage to the diamond growth stage. A direct-current bias voltage is applied to the substrate, and the polarity is adjusted in situ according to the changing growth requirements, providing a tool for controlling the diamond formation independent of the plasma source.

Substrate biasing is an emerging technique extensively used in diamond and cBN chemical vapor deposition (CVD) processes. Direct current bias voltages between -400 V and +500 V are here applied to a diamond deposition surface in an RF induction thermal plasma CVD system. This is made possible by introducing a high-impedance filter network, eliminating the time-varying voltage drop across the plasma-substrate junction and suppressing the radio-frequency interference. A traditional limitation of thermal RF systems is thereby overcome. Negative. bias conditions enhance the initial diamond nucleation density. Positive bias improves the diamond quality and augments the film growth rate. A threefold increase in linear growth rate is attained at +500 V as compared to the unbiased case. In conjunction with optical emission spectroscopic diagnostics, the substrate is used as an electrical and thermal probe. Contrary to do arcjet CVD, there is no secondary discharge created in the RF system at positive bias voltage. Also, the role of ion bombardment at negative bias is shown to be of little importance. It is inferred that the predominant mechanism leading here to changes in the diamond deposit under bias conditions is the promotion and suppression of electron emission from the growing diamond.

Carbon nanofibers (CNF) are useful for many applications such as polymer reinforcement, electrochemical devices like sensors, batteries, and supercapacitors. The most common method of producing them is by catalytic chemical vapor deposition (CVD) or by electrospinning. CNF growth using CVD is a single step process, unlike electro spinning which requires an additional carbonization step at higher temperatures. In CVD the catalyst is either incorporated directly onto the substrate or introduced with the feed gases. This adds extra cost and set limits to the design of the systems used for the CNF growth process, particularly in cases where porous structures are envisioned. In supercapacitors, the electrode material is most often painted or deposited with an ink of carbon particles. Directly growing the carbon nanomaterial from the supporting surface would eliminate this step and allow complex geometries. It would also help in achieving a higher capacitance by removing the requirement of a binder material and eliminate the occurrence of agglomeration of the active material inherent in the ink deposition process. Another advantage is the higher conductivity of CNF compared to the commonly used active carbon material. With CNF growing directly of the current collector, the addition of conductive carbon black can possibly be eliminated. Finally, an increase access of the electrolyte to the electrode can be expected due to the natural 3-D nano-architecture formed by the CNF. On the other hand, the micro-scale 3-D structure of nickel foams have been the most sought after substrates (current collectors) in the battery and supercapacitor research as they offer more surface area for the deposition of the required active material, together with being non-corrosive in alkali medium. CNF grown directly on Ni-foams are thus expected to extend the performances of supercapacitor electrodes. In this work, we have found a novel method of growing dense CNF on nickel foam. Cyclic voltammetry, galvanotactic charge discharge, and electrochemical impedance spectroscopy was made to electrochemically characterize these CNF/Ni-foam supercapacitor electrodes. When tested as a supercapacitor electrode in 6M KOH, our directly grown CNF gives a good aerial capacitance of about 60 mF/cm2 and an energy density of 16 mWh/m2. We believe this nickel foam with CNF to be very useful in supercapacitors and batteries in decreasing the resistance of the electrochemical device and provide additional surface area.

In this paper, we propose a novel kind of network that uses people instead of wires (or other communication media) to carry message packets between devices and between physical places. We will describe how this movement of people can be harnessed to allow the communication of electronic messages, albeit in a way that is relatively unreliable and unpredictable compared with traditional networks. This new kind of network infrastructure has a number of advantages, such as low cost and scalability, and opens the way for numerous new kinds of application scenarios.

A novel titanium nitride (TiN)/carbon nanotube (CNT) nanocomposite is produced with the purpose to mechanically, structurally and chemically stabilize a 'felt-like' CNT growth structure. The CNTs are grown on stainless steel (SS) 304 by chemical vapor deposition using the direct growth method previously developed, which does not require the use of an additional catalyst precursor. The TiN coating is achieved by physical vapor deposition and is shown here to generate a nanocomposite with a porous three-dimensional architecture. The contact stiffness is evaluated using nanoindentation, and wetting properties of the TiN/CNT nanocomposites are determined from contact angle measurements. An increase in contact stiffness and effective elastic modulus with TiN coating time was observed. The TiN coating on the non-wetting CNT felt results in a wetting nanocomposite surface. The wetting property is found to be a function of the TiN coating thickness on the CNT structure.

Based on the results of a cold cathode spot model assuming that a high local metallic plasma pressure generated by the erosion process is necessary for self-sustained operation of the arc, the time scales needed by the cathode to reach its melting temperature are evaluated. The predicted heating times typically fall below 10 µs, values that are compatible with experimental observations of the very rapid melting in the cathode spot area. Predictions of the time-dependent liquid mass formation (mliq) and maximum erosion rate by cathode material liquid ejection from the arc attachment region (Emax,liq) are given. Both values of mliq and Emax,liq are predicted for copper cathode spot currents of 5 and 10 A, bulk surface temperatures from 300 to 700 K, and spot lifetimes up to 10 µs. The results for a copper cathode bulk temperature of 300 K yield a maximum possible liquid erosion of, typically, around 100-200 µg liq C-1 for a 10 A cathode spot current if all the liquid volume is ejected. This erosion is attained after a 5 µs lifetime of the spot and stabilizes for longer spot burning times. By comparison, the same condition applied to a 5 A cathode spot yields around 10 µg liq C-1 attained after 8 µs burning time. The maximum liquid erosion rate is finally added to the maximum erosion rate due to vaporization, as predicted by the plasma model, to yield a general picture of the non-thermionic `cold cathode' erosion phenomena.

his study is related to the fundamental aspects of the arc-cathode interactions in atmospheric and higher-pressure arc systems. The primary objective of this paper is to demonstrate that, evm though the arc attachment on bdh refr;zctory and wn-refractory cathcdes appear substantially mereat, they follow the same physics and therefore the same model can be applied to describe both situations. Indeed, it is shown that the two situations are actually representing the two extremes of a unique descriptian; the self-suStaintng opemtion of an arc discharge on a reffadory (hot) cathode is achieved without the need of vaporization of the cathode surface while for non-refhctory (cold) cathodes, a strong vaporization resulbng in a pressure build up in the cathode region is necessary for self-whined arc operation.

A numerical model describing the attachment of an electric arc on a vaporizing non-refractory cathode is developed and applied to a Cu cathode. The model describes the arc - cathode interaction zone by a combination of a quasi-stationary vacuum arc cathode spot model with a collisionless cathode sheath model for the current transfer in the cathode region. The conditions of pressure and electron temperature within the cathode spot plasma necessary to account for current densities ranging from A (upper limit for non-vaporizing cathode models) to A are presented. Results show that current densities higher than A can only be accounted for with metallic plasma pressures exceeding 35 atm and electron temperatures ranging from 1 to 2 eV within the cathode spots. The current transfer to the cathode is mainly assumed by the ions at low current densities ( A ) and by the thermo-field electrons for higher current densities. The heat flux to the cathode surface under the spots is mainly due to the flux of returning ions and ranges from to W for current densities ranging from to A . At low current densities (), the main heat loss is by conduction through the cathode while at high current densities, the Nottingham cooling associated with the thermo-field emission of electrons dominates. The model allowed us to define the upper and lower limits for the vacuum erosion rate by vaporization of the cathode. It is shown that the experimentally obtained vacuum erosion rate value for Cu falls between both limits for an electron temperature within the cathode spot of 1 to 2 eV.

The predictions of a numerical model of the cathode-sheath region of high-pressure arcs using three different equations for the cathodic electron-emission current density are compared for two typical arc - cathode systems. These equations for cathodic electron emission include: (i) the field-enhanced thermionic emission (FEE) equation representative of the electron emission for high temperatures and moderate electric field strengths ; (ii) the Murphy and Good (MG) equation for thermo-field (T-F) emission valid for high temperatures and high surface electric field strengths in the range about - ; and (iii) the Murphy and Good equation for T-F emission enhanced by the presence of a high density of slowly moving ions in the cathode region (the MG+I equation). Results show that, in the case of a metal vapour arc (representative of vacuum arcs and high-pressure arcs on non-refractory cathodes) the use of the MG+I equation is always prescribed due to the formation of the high-local-pressure cathode-spot plasma. For high-pressure arcs on refractory cathodes the results show that, at atmospheric pressure, the generally used FEE equation introduces an underestimation by at least around 20% of the cathodic electron current density compared with the MG+I equation. The same comparison but for an ambient pressure of 50 atm shows that this underestimation becomes considerable.

A mathematical model is developed for the simulation of the PyroGenesis thermal plasma reactor used for the synthesis of fullerenes ( and others) via the dissociation of . The reactor studied is a spherical, water-cooled chamber equipped with a non-transferred d.c. plasma torch. is introduced into the plasma jet. The equation of continuity is solved, along with the equations of conservation of axial and radial momentum and energy. The K - model is used for the consideration of turbulence effects. The radiation term is represented by the net emission coefficient method. The equation of transport for is solved in order to estimate the quality of the mixing with the hot jet, not taking into account chemical reactions. Fields of the flow, temperature and concentration patterns are presented. Experimentally obtained deposition rates and wall temperatures are compared with the results of the model.

This paper describes WebFlow, an environment that supports distributed coordination services on the World Wide Web. WebFlow leverages the HTTP Web transport protocol and consists of a number of tools for the development of applications that require the coordination of multiple, distributed servers. Typical applications of WebFlow include distributed document workspaces, inter/intra-enterprise workflow, and electronic commerce. In this paper we describe the general WebFlow architecture for distributed coordination, and then focus on the environment for distributed workflow.

Thermo-field emission current densities calculated by the commonly used Richardson - Dushman equation corrected for the Schottky effect are compared with those calculated using the more accurate treatment of Murphy and Good for a wide range of temperatures (1000 - 5000 K), electric field strengths () and work functions (2 - 5 eV) encountered in numerical modelling of the thermal arc-cathode interactions. Results show that the emission current densities predicted by the Richardson - Dushman equation are always lower than those predicted by the more accurate treatment. The disagreement between the two predictions is in the range 20 - 30% for the conditions encountered in numerical modelling of the attachment of a thermal arc to a hot tungsten cathode whereas it is much larger when a cold copper cathode is considered (>175%). It is suggested that the more accurate treatment of Murphy and Good should be used in order to increase the accuracy of prediction of the numerical models.