Graphite Atomizer Research Articles

Phase transitions and critical phenomena of tiny grains carbon films synthesized in microwave‐based vapor deposition system

Different peak trends of tiny grains carbon film have been observed under the investigations of the Raman spectroscopy and energy loss spectroscopy. Carbon films known in nanocrystalline and ultrananocrystalline diamond films are synthesized by employing microwave‐based vapor deposition system. Carbon atoms exhibit several state behaviors depending on the incurred positions of their electrons. Different morphology of tiny grains under different chamber pressure is related to different rate of arriving typical energies at/near substrate surface. Those tiny grains of carbon film, which evolved in graphitic state atoms are converted to structure of smooth elements where elongation of atoms of one‐dimensional arrays is as per exerting surface format forces along opposite poles from their centers. Such tiny grains in the film are the cause of v1 peak under the investigation of the Raman spectrum because of the enhanced propagation of input laser signals through channelized inter‐state electron gaps of elongated graphitic state atoms. Those tiny grains of carbon film, which evolved in fullerene state are the cause of v2 peak. The tiny grains related to v1 peak possess a low intensity as compared with the ones which comprised atoms having state behaviors known in their exceptional hardness. Tiny grains representing v1 peak in the Raman spectrum are also the cause of field emission characteristic of a carbon film. Different peak recordings were made for the Raman at defined positions indicating a different state of carbon atoms for a different phase of deposited tiny grains, which is in line to their energy loss spectroscopy.

Essential and toxic elements in honeys consumed in Italy

ABSTRACTThe aim of this study was to determine the levels of iron (Fe), manganese (Mn), chromium (Cr), copper (Cu), zinc (Zn), mercury (Hg), cadmium (Cd) and lead (Pb) in several types of honey purchased from the local consumer markets in Central Italy by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Lead and Cd were also determined by Atomic Absorption Spectrometry with graphite tube atomization (AAS-GTA). The degree of humidity, sugar content, pH, free acidity, combined acidity (lactones) and total acidity were also measured. These elements were found to be present in honeys in various proportions depending upon (1) area foraged by bees, (2) flower type visited for the collection of nectar, and (3) quality of water in the vicinity of the hive. The honeys consumed in Italy were of good quality, but not completely free of heavy metal contamination. Compared with established recommended daily intakes, heavy metals or trace element concentrations in samples investigated, however, do not pose any serious concern to human health.

Work function, carrier type, and conductivity of nitrogen-doped single-walled carbon nanotube catalysts prepared by annealing via defluorination and efficient oxygen reduction reaction

Pyridinic and graphitic nitrogen atoms can be doped into carbon nanomaterials to create intrinsic structural defects and improve catalytic activity for the oxygen reduction reaction (ORR). An understanding of the relationship between the electronic properties and ORR activity of nitrogen-doped carbon nanomaterials could help design catalysts with better ORR performance. Here we report on the synthesis of nitrogen-doped single-walled carbon nanotubes (SWCNTs) by a combination of defluorination-assisted nanotube-substitution reaction and high-temperature annealing treatment using edge-free highly crystalline SWCNTs. The electronic properties of the prepared samples, such as the work function, carrier type, and conductivity were measured and correlated with their ORR activity in an acid electrolyte. Graphitic nitrogen-rich SWCNTs with n-type carrier, low work function, and high conductivity exhibited efficient ORR activity. The work function, carrier type, conductivity, and O2 dissociative adsorption sites are dependent on both the species/number of doping nitrogen atoms and the structural defects. The tuning of these two structural factors is necessary for achieving high ORR activity.

Catalytic performance of semi-coke on hydrogen iodide decomposition in sulfur-iodine thermochemical cycle for carbon dioxide-free hydrogen production

Sulfur-iodine thermochemical water splitting cycle is a promising and carbon dioxide-free method for hydrogen production. Among the reactions in this cycle, hydrogen iodide catalytic decomposition is the rate-determining step. In this study, catalytic reactivity test combined with characterizations of nitrogen physisorption, X-Ray diffraction, and Raman spectroscopy provide evidences that hydrofluoric acid modified semi-coke is a promising catalyst candidate for hydrogen iodide decomposition because of its high active and low cost. The raw semi-coke enhanced the hydrogen iodide conversion rate. After modification of hydrofluoric acid, the catalytic activity of semi-coke increased largely. Semi-coke modified by 40 wt% hydrofluoric acid showed better performance than commercial activated carbon catalyst. Combine the characterization results and catalytic reactivity, the graphitic edge carbon atoms in semi-coke are the active sites for hydrogen iodide decomposition. This finding pointed out the direction of carbon material catalyst design for hydrogen iodide decomposition.

Enhancement of Electrical Property of Thermally-Annealed Nano Carbon Based Polymer Composite By High Frequency Induction Heating

It has been said that CNT and Graphene have especially excellent electrical, thermally and mechanical property. Also it has been expected as fillers for polymer composite instead of conventional carbon fiber. Recently large amount of research has been done about Nanocarbon, so we can get easily a lot of kind of Nanocarbon. There is not the universal standard for Nanocarbon materials especially CNT and Graphene. Therefore, it causes a large problem for prediction of property of composites that their qualities and size are not uniform because property and structure of CNTs are changed by production method. CNTs has different names and property depending on the number of layers such as Single-wall carbon nanotube (SWCNT) and Multi-wall carbon nanotube (MWCNT). So the purpose in this study is to clarify the effect of Nano carbon materials quality on the properties of polymer based Nanocarbon composite and to develop polymer matrix Nanocarbon composite which have excellent properties. We improve the quality by heating the Nanocarbon materials in the inert atmosphere by high frequency induction heating. Also we compared filler properties of Nanocarbon composite polymer. First, the sample of CNT and Graphite was set into a carbon crucible and heated in the inert atmosphere for 10 to 30 minutes by high frequency induction heating. Thereafter, the qualities of the annealed samples were analyzed by Raman spectroscopy. In Raman spectroscopy can analyze crystal integrity, diameter and other. In the Raman scattering spectrum of CNT appear characteristic waveforms. Specifically, it are appeared near 1590 cm⁻¹ called G band and near 1350 cm⁻¹ called D band. Since the G band is derived from the in-plane stretching motion of the 6-membered ring structure of carbon atoms in graphite and the D band is derived from its defect structure, the crystal integrity (G / D ratio) is determined by the ratio of the peaks of the G band and the D band . In general, the larger the G / D ratio is, the higher the crystalline perfection is. For example, when graphene is thermally annealed at 1500 ° C for 15 minutes, the Full Width at Half Maximum (FWHM) is larger than that of without thermally annealing. It showed that impurities in graphite were removed by thermal annealing. But, there was not large change in G/D ratio. Second, the shapes of samples were analyzed for example diameter and length by using a scanning electron microscope. In SEM observation, the shape and size of Nanocarbon was mainly observed. TEM mainly observed the diameter, size and layers of CNT. Next, the nanocarbon samples were mechanical mixing with the polymer. This matrix used polypropylene (PP).The mixer used was of an elliptical blade. The temperature was 200 to 250 ° C. for 30 to 60 minutes, and the rotation speed was 80 to 100 rpm. Finally, the volume resistivity of the prepared composite material was measured using a resistivity meter. In general, the volume resistivity of PP is about 10 ^ 16 to 10 ^ 17 Ωcm, and the boundary through which electricity passes is said to be 10 ^ 6 Ωcm. Also, we think that annealed high quality Nanocarbon property in comparison with no thermal annealed Nanocarbon. So, we will be able to improve property of Nanocarbon composite.

Fluorination of nuclear graphite IG-110 in molten 2LiF-BeF2 (FLiBe) salt at 700 ºC

It is important for the development of advanced nuclear reactors to understand if the exposure to molten fluoride salts changes physical properties of graphite and its ability to absorb tritium. This paper demonstrated that the interaction between high purity nuclear grade graphite IG-110 and molten salt mixture 2LiF-BeF2 (FLiBe) at 700 °C for twelve hours in argon envirnoment resulted in graphite fluorination and changes in graphite microstructure. XPS C1s spectra analysis shows an increase in F functionalization (from 3.5% to 9.0–19.3%), an increase in the sp3/sp2 ratio (from 0.1496 to 0.1798), and F1s spectrum analysis confirms appearance of CF bonds. Raman spectra show an increase in ID/IG ratio from 0.35 to 0.69 and an appearance of peak shoulders characteristic of CF bond formation. GDMS depth analysis from the surface to 5 μm depth shows a higher depth penetration of F compared to that of Li and Be, indicative of surface salt reduction and bulk graphite fluorination. FLiBe reduction by graphite fluorination is not thermodynamically favorable, but certain carbon sites in the graphite are more reactive than the majority of carbon atoms in graphite. We argue that graphite fluorination occurred at these reactive sites, leading to the reduction of salt at the graphite surface. XRD and Raman confirmed microstructural changes. This indicates that the fluorination process may introduce new active sites as existing active sites are consumed, which could be advantageous for tritium chemisorption from FLiBe.

Graphite furnace atomic absorption spectrometric determination of vanadium after cloud point extraction in the presence of graphene oxide

Vanadium (V) and vanadium (IV) in the presence of a small concentration of graphene oxide (0.05mgmL−1) are quantitatively transferred to the coacervate obtained with Triton X-114 in a cloud point microextraction process. The surfactant-rich phase is directly injected into the graphite atomizer of an atomic absorption spectrometer. Using a 10-mL aliquot sample and 150μL of a 15% Triton X-114 solution, the enrichment factor for the analyte is 103, which results in a detection limit of 0.02μgL−1 vanadium. The separation of V(V) and V(IV) using an ion-exchanger allows speciation of the element at low concentrations. Data for seven reference water samples with certified vanadium contents confirm the reliability of the procedure. Several beer samples are also analyzed, those supplied as canned drinks showing low levels of tetravalent vanadium.

气体吸附对暴露/覆盖的石墨原子台阶边缘摩擦力的影响

气体吸附对暴露/覆盖的石墨原子台阶边缘摩擦力的影响

Detection of Sodium in Highly Pure Graphite via High-Resolution Electrothermal Atomic Absorption Spectrometry with a Continuous Spectrum Source

This study is dedicated to elucidating the analytical abilities of electrothermal atomic absorption spectrometry with a continuous spectrum source (ETAAS-CSS) to detect the presence of sodium in highly pure graphite powder. In order to plot the calibration dependence for sodium detection, a special technique based on argon dilution of the atomic vapor obtained by introducing the aqueous reference solution in the atomizer is applied. The conditions for thermal pretreatment of highly pure graphite powder and atomization of sodium are established, and the sodium detection threshold is evaluated via ETAAS-CSS (2.6 × 10–4 ng) as well. The validity of the results is confirmed via the sample variation method.

Hexagonal rotator order of bound ionic surfactants and temperature triggered dispersion of carbon nanotubes

Oxidized Carbon Nanotubes (CNT) form stable adducts with ammonium ions exhibiting long alkyl chains. Outer surfaces of CNT adducts are completely covered by hydrocarbon tails, which spontaneously organize in hexagonal rotator order, with 1 hydrocarbon tail per 8 graphitic carbon atoms of the external CNT wall. Order-disorder transitions, which involve loss of packing and of zig-zag planar conformation of the bound hydrocarbon tails, occur by heating at temperatures not far from room temperature and lead to temperature-triggered dispersion in organic media of the CNT adducts. CNT adduct formation is reversible with pH changes, as clearly shown by reversible moving of CNT between apolar and polar immiscible phases.

Low-temperature annealing of radiation-induced defects in carbon nanotube bundles

The annealing of radiation-induced defects in carbon nanotube bundles below room temperature has been investigated experimentally. Significant feature of this study is that electron irradiation (with an energy 1MeV and fluence up to 1016el/cm2) was carried out at liquid helium temperature. A detailed analysis of the resistance change over a wide temperature range (7–300K) enables us to prove partial annealing of irradiation-induced defects at moderate temperatures. It is shown that such an annealing follows a first-order reaction in whole investigated temperature range. While at temperatures below 40K, annealing is nonactivation, tunneling process; at higher temperatures (100−300K) it becomes activated, with activation energy of ~0.05eV. The value of discovered activation energy is close to the migration energy of interstitial carbon atom in graphite. Probably, observed annealing of radiation-induced defects in carbon nanotube bundles is also caused by the migration of interstitial carbon atoms between single nanotubes below room temperature.

Selective Etching of Nitrogen‐Doped Carbon by Steam for Enhanced Electrochemical CO2 Reduction

AbstractNitrogen‐doped carbon structures have recently been demonstrated as a promising candidate for electrocatalytic CO2 reduction, while in the meantime the pyridinic and graphitic nitrogen atoms also present high activities for electroreduction of water. Here, an etching strategy that uses hot water steam to preferentially bind to pyridinic and graphitic nitrogen atoms and subsequently etch them in carbon frameworks is reported. As a result, pyrrolic nitrogen atoms with low water affinity are retained after the steam etching, with a much increased level of among all nitrogen species from 22.1 to 55.9%. The steam‐etched nitrogen‐doped carbon catalyst enables excellent electrocatalytic CO2 reduction performance but low hydrogen evolution reaction activity, suggesting a new approach for tuning electrocatalyst activity.

An improved model for N2 adsorption on graphitic adsorbents and graphitized thermal carbon black—The importance of the anisotropy of graphene

Computer simulations of N2 adsorption on graphite frequently use the 10-4-3 equation with Steele’s molecular parameters to describe the dispersive-repulsive interaction between a molecule and graphite. This model assumes that graphite is a uniformly homogeneous continuum solid, and its derivation implies the following assumptions: (1) the solid is built from stacked, equally spaced graphene layers, (2) there is an infinite number of layers, and (3) the carbon atom molecular parameters are invariant for all layers (collision diameter of 0.34 nm and reduced well depth of interaction energy of 28 K). Despite the fact that this model can give an acceptable description of experimental data for this system, there are experimental observations that simulation results fail to account for. First, the isotherm does not exhibit a step in the sub-monolayer coverage region at 77 K, which is attributed to a transition from the supercritical state of the adsorbate to the commensurate state, and therefore fails to reproduce the cusp and heat spike in the experimental isosteric heat curve versus loading at close to monolayer coverage. Second, the simulation results overpredict the experimental data in the multilayer region. These discrepancies suggest that (1) the absence of lateral corrugation in the 10-4-3 potential misses the commensurate to incommensurate transition and (2) the long-range solid-fluid potential, experienced by the second and higher layers onwards, is too strong. Here we examine a revised graphite potential model that incorporates three features absent from the 10-4-3 model: (1) an energetic corrugation of the potential arising from the discrete atom structure of the adsorbent, (2) the unequal spacing of the graphene layers due to the anisotropic force field acting on graphene layers at the surface, and (3) the different polarizabilities of carbon atoms in graphite, parallel and normal to the graphene surface. These features are corroborated by a number of experimental measurements and quantum-mechanical calculations: (1) the Low-Energy Electron Diffraction (LEED) and Surface-Extended X-ray Absorption Fine Structure (SEXAFS) experiments show that the first adsorbate layer is smaller than predicted by the 10-4-3 model with the traditional molecular parameters suggested by Steele, and (2) the potential well depth for atoms in graphene is stronger than for C-atoms in graphite. The simulation results using this revised graphite model give an improved description of the fine features of adsorption of N2 on graphite: the sub-step in the first layer of the isotherm, the spike in the isosteric heat curve versus loading, and the coverage at higher loadings.

Nitrogen doped nanographene structures; study on the adsorption of nucleobases, nucleotides, and their triphosphate derivatives using mixed docking, MD, and QM/MM approaches.

The interactions of the nucleobases, nucleotides, and their triphosphate derivatives in both neutral and anionic forms with the nitrogen doped graphenes (NG) were studied using docking and molecular dynamic simulation methods. In docking studies, based on binding energy results, the anionic species and nucleobases were showing the most and the least tendency toward the surface of the NG, respectively. The molecular mechanic/Poisson-Boltzmann surface area results revealed similar results, except for the anionic species; in these studies, the anionic species showed a lesser affinity toward the NG. The time-dependent density functional theory studies were carried out to investigate the effects of the NG on the electronic nature of the investigated ligands; a red-shift in all of the cases was observed. The results of binding energy decomposition and atoms in molecules studies showed that the interactions are van der Waals in nature. The graphitic, pyridinic, and pyrrolic nitrogen atoms which were considered in this study behaved similar to each other.

On the effect of carbon content for achieving a high performing Na3V2(PO4)3/C nanocomposite as cathode for sodium-ion batteries

An in-situ generated carbon matrix has demonstrated to be essential to provide electrical conducting properties to Na3V2(PO4)3 as cathode materials for sodium-ion cells. Na3V2(PO4)3/C nanocomposites are synthesized by varying their eventual carbon content in order to determine the influence in the electrochemical behavior. X-ray diffraction patterns evidence the crystallinity and purity of Na3V2(PO4)3, while Raman spectroscopy reveals the disordered character of the carbon phase. The determination of the chemical state of the carbonaceous phase unveils that an increase of the carbon content involves a decrease of carboxyl groups and a slight increase of graphitic carbon atoms, in agreement with the Raman results. The electrochemical characterization of these composites in sodium half cells reveals that carbon contents close to 7% are preferred to provide cycling stability, while the best rate performance is achieved for the sample with carbon content close to 11%. A full sodium-ion cell delivers an energy density of 320Whkg−1 at 2C.

Solid sampling determination of magnesium in lithium niobate crystals by graphite furnace atomic absorption spectrometry

The vaporization/atomization processes of Mg in high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS) were investigated by evaporating solid (powder) samples of lithium niobate (LiNbO3) optical single crystals doped with various amounts of Mg in a transversally heated graphite atomizer (THGA). Optimal analytical conditions were attained by using the Mg I 215.4353nm secondary spectral line. An optimal pyrolysis temperature of 1500°C was found for Mg, while the compromise atomization temperature in THGAs (2400°C) was applied for analyte vaporization. The calibration was performed against solid (powered) lithium niobate crystal standards. The standards were prepared with exactly known Mg content via solid state fusion of the oxide components of the matrix and analyte. The correlation coefficient (R value) of the linear calibration was not worse than 0.9992. The calibration curves were linear in the dopant concentration range of interest (0.74–7.25mg/gMg), when dosing 3–10mg of the powder samples into the graphite sample insertion boats. The Mg content of the studied 19 samples was in the range of 1.69–4.13mg/g. The precision of the method was better than 6.3%. The accuracy of the results was verified by means of flame atomic absorption spectrometry with solution sample introduction after digestion of several crystal samples.

Characterization and Catalytic Activity of Different Carbon Supported Pd Nanocomposites

In our experiments, high nitrogen content N-doped multiwall carbon nanotubes (N-CNTs) were synthetized by chemical vapour deposition (CVD) method, after these nanotubes were used as dehydrogenation catalyst support. The chemical nature of the nitrogen atoms in graphitic lattice of N doped CNT was characterized with X-ray photoelectron spectroscopy (XPS) analysis, the pyridinic and graphitic nitrogen atoms were located in nanotube wall. The lattice defects of N-CNT structure were checked with Raman spectroscopy, according to which many defect were present in structure of N-CNTs, owing to the incorporated nitrogen atoms. The formed oxidized N-doped CNT samples were studied by Fourier transform infrared (FT-IR) spectroscopy, according to the test, many oxygen content surface functional groups were identified (COOH, OH and C=O). Palladium nanoparticle morphology and surface on the catalyst substrates were characterized by high resolution transmission electron microscopy (HRTEM) and X-Ray diffraction (XRD) methods. The diameters of palladium particles were slightest in case of carbon nanotube supported catalyst (2 nm), smaller than case of activated carbon, due to absence of microporosity and presence of functional groups on the N-CNT surface. The catalytic activity of the CNT supported catalysts was compared to an active carbon and norit supported samples. The dehydrogenation of C2H6 has been investigated on Pd deposited on various carbon supported catalysts at 573–973 K. On the Pd/CNT catalyst the highest selectivity was reached to ethene (85 %) at 973 K. The most active Pd/Ac achieved 64 % conversion at 973 K.

Density functional theory investigation of oxygen interaction with boron-doped graphite

Boron inserted as impurity by substitution of carbon atoms in graphite is known to change (improve or deteriorate) oxidation resistance of nuclear graphite, but the reason for both catalytic and inhibiting oxidation is still uncertain. As a first step, this work is more specially devoted to the adsorption and diffusion of oxygen atoms on the surface and related to the problem of oxygen retention on the pure and boron-containing graphite surfaces. Adsorption energies and energy barriers associated to the diffusion for molecular oxygen recombination are calculated in the density functional theory framework. The existence of boron modifies the electronic structure of the surface, which results in an increase of the adsorption energy for O. However, low boron loading makes it easier for the recombination into molecular oxygen. For high boron concentration, it induces a better O retention capability in graphite because the presence of B-B bonds decreases recombination of the adsorbed oxygen atoms. A possible explanation for both catalytic and inhibiting effects of boron in graphite is proposed.

Plasma-aminothiols status and inverse correlation of total homocysteine with B-vitamins in arsenic exposed population of West Bengal, India

ABSTRACTChronic arsenic toxicity is a serious environmental health problem across the world. Bangladesh and India (particularly the state of West Bengal) are the worst affected countries with such problem. The present study reports plasma-aminothiols (p-aminothiols) like L-cysteine (L-Cys), cysteinyl glycine (Cys-gly), total homocysteine (t-Hcy) and glutathione (GSH) status, and the inverse relationship of t-Hcy with B-vitamins (B1, B6, B9 and B12) in arsenic exposed population of West Bengal, India. Reverse phase HPLC was used to measure p-aminothiols and serum B-vitamins in different arsenic exposed population. Arsenic in drinking water and urine were measured by flow injection analysis system – Atomic Absorption Spectrometry (FIAS-AAS) and Transversely heated graphite atomizer (THGA-AAS) techniques, respectively. Water arsenic exposure was >50 µg/L in 50% population, of which majority (33.58%) belong to the range of >50–500 µg/L and more than 8% were even >1000 µg/L. Urine arsenic (µg/g creatinine) levels increased with arsenic exposure. The variability among p-aminothiols was also observed with higher exposure to arsenic in drinking water. A significant difference between exposed and control population was noticed for plasma L-Cys. The difference of B-vitamins between the population exposed to <50 and >50 µg/L arsenic in drinking water was also found to be significant. B9 and B12 deficiency with increased consumption of arsenic in water corroborates the anemic conditions commonly observed among arsenic exposed population. The aminothiol status indicated oxidative stress in exposed population. This study demonstrated progressive increase in plasma t-Hcy as well as inverse relationships of serum B-vitamins with increased water arsenic concentration.

A Nanopore-Structured Nitrogen-Doped Biocarbon Electrocatalyst for Oxygen Reduction from Two-Step Carbonization of Lemna minor Biomass.

So far, the development of highly active and stable carbon-based electrocatalysts for oxygen reduction reaction (ORR) to replace commercial Pt/C catalyst is a hot topic. In this study, a new nanoporous nitrogen-doped carbon material was facilely designed by two-step pyrolysis of the renewable Lemna minor enriched in crude protein under a nitrogen atmosphere. Electrochemical measurements show that the onset potential for ORR on this carbon material is around 0.93 V (versus reversible hydrogen electrode), slightly lower than that on the Pt/C catalyst, but its cycling stability is higher compared to the Pt/C catalyst in an alkaline medium. Besides, the ORR at this catalyst approaches to a four-electron transfer pathway. The obtained ORR performance can be basically attributed to the formation of high contents of pyridinic and graphitic nitrogen atoms inside this catalyst. Thus, this work opens up the path in the ORR catalysis for the design of nitrogen-doped carbon materials utilizing aquatic plants as starting precursors.