Concentration Of Carbon Atoms Research Articles

Honeycomb-like hierarchical porous carbon derived from kapok fiber for supercapacitors

The fine structural engineering of biomass-derived porous carbon is the key to maximize the specific capacitance and rate performance of capacitive carbon. Herein, a hierarchical porous carbon (HPC) has been fabricated from kapok fiber via oxalic acid hydrothermal coupled chemical activation strategy. Moderate concentration of oxalic acid hydrothermal treatment is beneficial to increase the concentration of concentration of CO, CO, and sp2 hybrid carbon atoms on fiber surface, and chemical activation accelerate the growth of integrated honeycomb microstructures and hierarchical pores, especially 1.0–2.0 nm micropores. The optimized HPC shows a high specific surface area of 2045 m2 g−1, moderate meso-macropore volume of 0.13 cm3 g−1, low ID/IG of 0.95, and well-developed honeycomb structure, which endows HPC with high ions adsorption capacity and fast kinetic behavior. The optimized HPC exhibits a high specific capacitance of 305.5 F g−1 at 0.5 A g−1 and 194.0 F g−1 at 50 A g−1 in 6 M KOH electrolyte, with a high capacitance retention of 63.5 %. The assembled supercapacitor based on HPC delivers a higher energy density of 10.2 Wh kg−1 at power density of 150 W kg−1 in KOH electrolyte and 27.7 Wh kg−1 at 225 W kg−1 in Na2SO4/PVA gel electrolyte, and superb capacitance retention of 95 % for 20,000 cycles. This will also provide a potential strategy for biomass micro-composition modulation and hierarchical porous carbon structural regulation toward high performance electrode materials.

A new strategy for preparing carbide coatings on easily oxidized tantalum by non-vacuum carburizing: Fe-coating-mediated carburization

A new strategy for preparing TaC coatings on easily oxidized tantalum by non-vacuum carburizing is proposed, which is called Fe-coating-mediated carburization. Fe-coating-mediated carburization is the carburization of Ta substrate with a pre-electroplated Fe coating. During carburization, the electroplated Fe coating was transformed into a carbon steel coating, while a high concentration of interstitial carbon atoms in the carbon steel coating diffused into tantalum, forming a TaC coating. The Fe coating isolated the tantalum from oxygen and changed the state of active carbon atoms in contact with the tantalum surface. The TaC coatings are nonporous, have fine grains with grain size gradients, and combine high hardness (32 GPa) and excellent coating-substrate adhesion strength (>100 N). The Fe-coating-mediated carburization realizes the carburization of oxidizable carbide-forming metals under non-vacuum conditions, providing a new strategy to prepare protective coatings with both high hardness and high coating-substrate adhesion for carbide-forming metals.

Evaluation of UV photofunctionalization effect on ultrastructural properties of SLA titanium disks: An in vitro study.

The success rate of dental implants diminishes over time; the lack of osseointegration and infection are the major causes of most implant failures. One of the effective methods to improve the surface properties is to irradiate ultraviolet (UV) light. This study investigated the effect of UV photofunctionalization on the ultrasuperficial properties of sandblasted, large-grit, acid-etched (SLA) titanium discs. In this in vitro study, 24 sandblasted and acid-etched titanium discs, with a lifespan of more than four weeks, were categorized into three groups (n=8): control, ultraviolet C (UVC), and ultraviolet B (UVB). Then, they were exposed to a UV light source for 48 hours at a 1-cm distance. In addition to measuring the contact angle between the liquid and the disc surface in each of the three groups, the atomic concentrations of carbon, oxygen, and nitrogen atoms were measured at three different sites on each disc. One-way ANOVA and post hoc Tukey tests were used to analyze data. The mean concentration of carbon atoms significantly differed in the control, UVC, and UVB groups (P<0.001). The mean concentrations of nitrogen atoms differed significantly between the three groups (P<0.001). However, the mean concentrations of oxygen atoms were not significantly different between the three groups. In examining the contact angle, wettability was higher in the UVC group than in the UVB group and higher in the UBV group than in the control group. Photofunctionalization with UV light significantly decreased carbon and nitrogen concentrations on the surface of titanium implants, indicating that the implant's superficial hydrocarbons were eliminated. It was observed that UVC photofunctionalization was more effective than UVB photofunctionalization in reducing superficial contamination and improving wettability.

Effect of Nitrogen Arc Discharge Plasma Treatment on Physicochemical Properties and Biocompatibility of PLA-Based Scaffolds.

The effect of low-temperature arc discharge plasma treatment in a nitrogen atmosphere on the modification of the physicochemical properties of PLA-based scaffolds was studied. In addition, the cellular-mediated immune response when macrophages of three donors interact with the modified surfaces of PLA-based scaffolds was investigated. PLA surface carbonization, accompanied by a carbon atomic concentration increase, was revealed to occur because of plasma treatment. Nitrogen plasma significantly influenced the PLA wettability characteristics, namely, the hydrophilicity and lipophilicity were improved, as well as the surface energy being raised. The viability of cells in the presence of the plasma-modified PLA scaffolds was evaluated to be higher than that of the initial cells.

Sampling of Gas-Phase Intermediate Pyrolytic Species at Various Temperatures and Residence Times during Pyrolysis of Methane, Ethane, and Butane in a High-Temperature Flow Reactor

Air pollution in many major cities is endangering public health and is causing deterioration of the environment. Particulate emissions (PM) contribute to air pollution as they carry toxic polyaromatic hydrocarbons (PAHs) on their surface. Abatement of PM requires continuous strict emission regulation and, in parallel, the development of fuels with reduced formation of PM. Key processes in the formation of PM are the decomposition of hydrocarbon fuels and the synthesis of potential precursors that lead to the formation of benzene rings and thereafter growth to PAHs and eventually PM. Methane, ethane and butane are important components of natural gas and liquefied petroleum gas, and are also widely used in transportation, industrial processes and power generation. This paper reports on a quantitative investigation of the intermediate gaseous species present during pyrolysis of methane, ethane and butane in a laminar flow reactor. The investigation aimed to further the understanding of the decomposition process of these fuels and the subsequent formation of aromatic rings. The pyrolysis of methane, ethane and butane were carried out in a tube reactor under laminar flow conditions and within a temperature range of 869–1213 °C. The fuels were premixed in nitrogen carrier gas at a fixed carbon atom concentration of 10,000 ppm, and were pyrolysed under oxygen-free conditions. Intermediate gaseous species were collected from within the tube reactor at different residence times using a specially designed high-temperature ceramic sampling probe with arrangements to quench and freeze the reactions at entry to the probe. Identification and quantification of intermediate species were carried out using a gas chromatography-flame ionization detector (GC-FID). During methane pyrolysis, it was observed that as the concentration of acetylene increased, the concentration of benzene also increased, suggesting that the benzene ring is formed via the cyclo trimerisation of acetylene. With all three fuels, all intermediate species disappeared at higher temperatures and residence times, suggesting that those species converted into species higher than benzene, for example naphthalene. It was observed that increasing carbon chain length lowered the temperature at which fuel breakdown occurred and also affected the relative abundance of intermediate species.

Influence of ordering phenomena on carbon segregation in tungsten screw dislocation

Concentration profiles on the different sites of tungsten screw dislocation are calculated as a function of the nominal carbon atom concentration, temperature and dislocation density. Rigid lattice Monte Carlo simulations and associated mean-field modelling are performed based on interaction energies from ab initio calculations. We show that the repulsive interactions induce ordering phenomena that drastically change the concentration in the core of the dislocation and leads to ordered structures among the octahedral sites. We detail the domains of short-range ordering (SRO) and long-range ordering (LRO).

Nano-Fe/SiO2 catalysts prepared by facile colloidal deposition: Enhanced durability in Fischer-Tropsch synthesis

Nano-iron catalysts exhibit good performances in the Fischer–Tropsch synthesis to lower olefins (FTO), however, there is still a lack of simple methods for their preparation. In this work, we introduced a facile colloidal deposition (CD) method to fabricate silica-supported Fe2O3 nanoparticles using a colloidal solution readily prepared from ferric hydroxide. With increasing the Fe loading from 16.3 % to 31.6 %, the Fe2O3 particle size increased from 1.3 to 6.1 nm. The catalytic performances in FTO were tested at a H2/CO molar ratio of 1. At a Fe loading of 30.4 %, the catalyst having a particle size of 4.7 nm showed the highest lower olefin selectivity and the lowest CO2 selectivity, outperforming analogs prepared by impregnation method. Furthermore, this catalyst showed good stability in a 200-hour durability test, while the impregnated analogue quickly deactivated due to serious coking. Presumably, the effective contact areas between the nanoparticles and the generated carbon sheets are geometrically small, which results in weak van der Waals forces between them, preventing the former from being heavily covered by the latter. Besides, from the point of view of the carbide decomposition mechanism of coking, due to the relatively low volume to surface area ratios of the intermediate carbide nanoparticles, the surface concentrations of carbon atoms released from them are low, which delays the coke formation. This study may provide a simple method to fabricate supported nano-iron catalysts, and cast some light on understanding catalyst durability in FTO.

Low-Temperature Barrier Discharge Plasma Modification of Scaffolds Based on Polylactic Acid.

We have explored the effect of low-temperature barrier discharge plasma treatment in oxygen, nitrogen, and argon on modification of the physicochemical properties of polylactic acid (PLA)-based scaffolds. The cellular-mediated immune response to the interaction of macrophages of three donors with the modified surface of PLA-based scaffolds was also investigated. Carbonization of the PLA surface accompanied by a carbon atomic concentration increase is shown to occur following plasma treatment. Argon plasma significantly affects the wettability characteristics of PLA; the hydrophilicity and lipophilicity are improved, and the surface energy is increased. The viability of cells in the presence of plasma-modified PLA scaffolds is lower than that for unmodified PLA but remains greater than that for the negative control. We find that PLA scaffolds do not cause increased expression of the proinflammatory (TNFα, IL-6, IL-1β) cytokines after 6 days of cell cultivation. At the same time, PLA scaffolds do not affect the increased production of anti-inflammatory cytokines (IL-10).

Nondestructive analysis of solute carbon in the ferrite phase in dual-phase steels containing Mn or Si by mechanical loss measurements

As a development of an earlier attempt to determine the concentration of mobile carbon atoms in the ferrite phase in dual-phase (DP, ferrite + martensite) steels by means of mechanical loss measurements, which was made on binary Fe-C alloys [Honda et al., Solid State Phenom. 184 (2012) 87–91], we have investigated effects of Mn and Si on the mechanical loss profiles, aiming at establishing a method for quantitatively evaluating the distribution of carbon in practical DP steels. First we re-examined the effects of Mn and Si on the relation between the strength of the Snoek relaxation and the concentration of carbon in iron by measuring the mechanical loss of solution-treated, single-phase ferrite samples of dilute Fe-Mn-C and Fe-Si-C alloys. We then measured mechanical loss of ferrite + martensite two-phase alloys of various carbon contents, after equilibrating at a temperature where the material consists of ferrite and austenite, and then quenching. The concentrations of carbon in solution in the ferrite phase can be estimated from the observed magnitude of the Snoek relaxation peak, using the linear relation obtained in the first set of experiments, and correcting for the volume fraction of the ferrite phase. These estimates agree reasonably well with those expected from the compositions expected from the ternary phase diagrams, as in the previous case of simple Fe-C alloys. This renders the basis for determining the carbon concentration in the ferrite phase by measuring mechanical loss of DP steels with alloying elements. As another development, the properties of the characteristic mechanical loss due to the martensite phase have been studied. The mechanical loss, which steadily increase above room temperature, turned out to exhibit a maximum at 480–500 K. It is found to be a thermally activated relaxation, with the following parameters of the relaxation time: pre-exponential factor τ0 ≃ 10−14 s and activation energy E ≃ 1.2 eV. However, its magnitude does not show a simple linear relation with the carbon content, unlike the case of the Snoek relaxation in ferrite.

Atomic coordination dictates vibrational characteristics and thermal conductivity in amorphous carbon

We discuss the role of atomic coordination in dictating the vibrational characteristics and thermal conductivity in amorphous carbon. Our systematic atomistic simulations on amorphous carbon structures at varying mass densities show the significant role played by the ratio of sp2 to sp3 hybridized bonds in dictating the contributions from propagating (phonon-like) and non-propagating vibrational modes and their influence on the overall thermal conductivities of the structures. Specifically, our results show that as the concentration of sp3-bonded carbon atoms increases, the thermal conductivity can be increased by four fold, which is attributed to enhanced contributions from propagating modes in these amorphous structures. Our results shed more light into the role of atomic coordination on dictating heat transfer mechanisms in amorphous materials, and also provide a deeper understanding of the ability to tune the thermal conductivity of amorphous carbon structures through the control of the local atomic coordination.

Effect of carbon concentration on optical and structural properties in the transition from Silicon Rich Oxide to SiCxOy films formation

The role of carbon atomic concentration on the transition from Silicon Rich Oxide (SRO) to Silicon Oxicarbide films (SiCxOy) is reported. For this, optical and structural properties were analyzed by Photoluminescence (PL), Micro-Raman, Fourier Transform Infrared (FTIR) and X-Ray Photoelectron Spectroscopy (XPS) measurements. An SRO film with 16.6 at.% of Si-excess and SiCxOy films with carbon concentration from 1.3 to 7.2 at.% were grown by Hot Filament Chemical Vapor Deposition Technique (HFCVD). The SRO film (C = 0 at.%) and SiCxOy films with low carbon atomic concentration (C = 1.3 at.%) exhibited a very low PL emission in the red-infrared region (1.5–1.7 eV) manly attributed to SiO defects which are reduced or annihilated by incorporation of carbon. An increase in carbon atomic concentration greater than 1.3 produces a strong PL emission at white region (3.35–1.72 eV) characteristic of SiCxOy films attributed to radiative defects such as defects associated to Si-related oxygen vacancies (Si-NOVs), Si-related oxygen deficiency centers (Si-ODC) and C-related oxygen vacancies (C-NOVs). In this work it was found that a carbon atomic concentration greater that 1.3 is required to have a high density of these radiative defects. Also, due to the high growth temperature (900 °C) and Si-excess (from 16.6 to 3.9 at.%), we propose the presence of Si nanocrystals (Si–NCs) embedded in both SRO and SiCxOy films with low carbon concentration (SiO2-Like characteristics). Whereas an increase in carbon concentration of 7.2 at. %, Si–NCs precipitation was inhibited in the SiCxOy films.

INFLUENCE OF MECHANICAL POLISHING ON THE PHYSICAL-MECHANICAL PROPERTIES OF MONOCRYSTALLINE p-SiGe SUBSTRATES

The effect of mechanical polishing on the structural-sensitive physical properties of the monocrystalline p-SiGe substrates has been investigated. Non-monotonic changes in the electrical characteristics, optical absorption spectra of infrared radiation, internal friction and shear modulus values on the (111) surfaces of SiGe substrates treated with a polishing compound containing different dispersions diamond particles have been shown. Defects formed in the polishing process interact with boron and technological origin oxygen and carbon atoms. Defects of deformation origin are formed in the mechanical processing at room temperature. In the absorption spectra of infrared irradiation a decrease of the concentration of carbon and oxygen atoms and Ci-Cs, Ci-Oi, V-O defects have been revealed. It is supposed that the non-monotonic changes in the electrophysical and physical-mechanical properties on the (111) surfaces of SiGe substrates are caused by changes in the electrical activity of defects and mechanisms of the dislocation-defect associations interaction, formed in the polishing processes.

Features of silicon carbide synthesis by cold implantation of carbon recoil atoms

The Auger electron spectroscopy method confirmed a high concentration of carbon atoms (~ 85 at.%) introduced into silicon by cold implantation of recoil atoms. Carbon atoms are concentrated in a thin (~ 5 nm) near-surface region of silicon. Annealing of such a structure did not reveal a noticeable diffusion of carbon, which prevents obtaining a layer of SiC with a thickness of more than a few nm. This problem was solved by using radiation-enhanced diffusion. This made it possible to control the distribution profiles of carbon atoms in a wide range. Annealing at 1150oC allowed obtaining layers of amorphous-crystalline SiC with a thickness of 50-150 nm. Higher annealing temperatures are required to obtain a single-crystal SiC film. Keywords: cold implantation, radiation-enhanced diffusion, silicon carbide, recoil atom, thin films.

Особенности синтеза карбида кремния методом холодной имплантации атомов отдачи углерода

The Auger electron spectroscopy method confirmed a high concentration of carbon atoms (~ 85 at. % ), introduced into silicon by cold implantation of recoil atoms. Carbon atoms are concentrated in a thin (~ 5 nm) near-surface region of silicon. Annealing of such a structure did not reveal a noticeable diffusion of carbon, which does not allow obtaining a layer of SiC with a thickness of more than a few nm. The solution to this problem was carried out by the use of radiation-stimulated diffusion. This made it possible to control the distribution profiles of carbon atoms in a wide range. Annealing at 1150 oC allowed to obtain layers of amorphous crystalline SiC with a thickness of 50-150 nm. Higher annealing temperatures are required to obtain a single-crystal SiC film.

Measurement of soot mass and PAHs during the pyrolysis of C2[sbnd]C4 alcohols at high temperatures

Particulate matter (PM) is emitted from a range of combustion sources, can vary greatly in properties, and is able to penetrate deep into the human lungs, conveying carcinogenic PAHs present on the particle surface. Alcohol based biofuels have been shown to potentially reduce PM emissions when displacing fossil fuels. To improve understanding of the influence of fuel bound oxygen on and the relative toxicity of PM, this paper investigates quantitatively the soot mass and PAHs produced from the pyrolysis of ethanol, 1-propanol, 2-propanol,1-butanol, and 2-butanol in a laminar flow reactor. The pyrolysis of alcohol fuels and collection of soot-bound and gas-phase PAH was carried out between 1323 and 1623 K at a fixed carbon atom concentration in nitrogen. Accelerated solvent extraction (ASE) was used to extract soot bound PAH and gaseous species captured on XAD resin, with speciation and quantification of PAHs undertaken using GCMS. Of the primary alcohols, the highest and lowest masses of soot were observed for 1-butanol and ethanol respectively, while secondary alcohols generated more soot mass than corresponding primary alcohols. An effect of hydroxyl group position on the total PAH distribution in the gas and particulate-bound phases was observed within the temperature range of 1323 to 1423 K. At 1323 K, 1-propanol produced approximately three times more particle phase (PP) PAH concentration than 2-propanol. Amongst the fuels tested, 1-propanol produced the highest level of carcinogenic PAHs at 1323 K, while for all C3 and C4 fuels the toxicity equivalence factor decreased with increasing pyrolysis temperature.

The Concentration of C(sp3) Atoms and Properties of an Activated Carbon with over 3000 m2/g BET Surface Area.

The alkaline activation of a carbonized graphene oxide/dextrin mixture yielded a carbon-based nanoscale material (AC-TR) with a unique highly porous structure. The BET-estimated specific surface area of the material is 3167 m2/g, which is higher than the specific surface area of a graphene layer. The material has a density of 0.34 g/cm3 and electrical resistivity of 0.25 Ω·cm and its properties were studied using the elemental analysis, transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (XAES), and electron energy loss spectroscopy (EELS) in the plasmon excitation range. From these data, we derive an integral understanding of the structure of this material. The concentration of sp3 carbon atoms was found to be relatively low with an absolute value that depends on the measurement method. It was shown that there is no graphite-like (002) peak in the electron and X-ray diffraction pattern. The characteristic size of a sp2-domain in the basal plane estimated from the Raman spectra was 7 nm. It was also found that plasmon peaks in the EELS spectrum of AC-TR are downshifted compared to those of graphite.

Study of diamond like carbon coatings formed by pulsed hydrocarbon ions irradiations over different substrate materials using plasma focus device

Pulsed hydrocarbon ions produced in a plasma focus device were used to irradiate different substrate materials (Si, Ti, Mo and W) and to deposit thin films of carbon material over it. High energetic and high intensity pulsed hydrocarbon ions were produced when plasma focus device was filled with 0.5 mbar of acetylene gas and operated at 2 kJ. Effects of substrate materials properties, its thermal evolution under pulsed irradiation of energetic ions and plasma streams on the deposited films have been studied. Visible Raman spectroscopic measurements confirmed that deposited films were of diamond-like-carbon. Fraction of sp3 bonded carbon in films on different substrate materials (16%, 8.7%, 13% and 18.9% on Si, Ti, Mo and W respectively) was found to be correlated to substrate materials thermal properties i.e. high fraction of sp3 bonded carbon was observed over substrate materials having high thermal conductivity. Carbon atom concentrations were measured to be different (22.46 at. %, 22.7 at. %, 10.4 at. % and 32 at. % on Si, Ti, Mo and W respectively) over different substrates. Surface morphologies of DLC were also observed to be different for different substrates. On inserting graphite at anode tip, fraction of sp3 bonded carbon in DLC coating over Si substrate increased to 19.5%.

Surface Activation of Titanium Dental Implants by Using UVC-LED Irradiation.

Organic contaminants significantly limit the bioactivity of titanium implants, resulting in the degradation known as the ageing of titanium. To reactivate the surfaces, they can be photofunctionalized, i.e., irradiated with C-range ultraviolet (UVC) light. This descriptive in vitro study compares the effectiveness of novel light-emitting diode (LED) technology to remove contaminant hydrocarbons from three different commercially available titanium dental implants: THD, TiUnite, and SLA. The surface topography and morphology were characterized by scanning electron microscopy (SEM). The chemical compositions were analyzed by X-ray photoelectron spectroscopy (XPS), before and after the lighting treatment, by a pair of closely placed UVC (λ = 278 nm) and LED devices for 24 h. SEM analysis showed morphological differences at the macro- and micro-scopic level. XPS analysis showed a remarkable reduction in the carbon contents after the UVC treatment: from 25.6 to 19.5 C at. % (carbon atomic concentration) in the THD; from 30.2 to 20.2 C at. % in the TiUnite; from 26.1 to 19.2 C at. % in the SLA surface. Simultaneously, the concentration of oxygen and titanium increased. Therefore, LED-based UVC irradiation decontaminated titanium surfaces and improved the chemical features of them, regardless of the kind of surface.

Features of the formation of a diffusion layer and the mechanism of diffusion during boronizing of steels

The paper presents the results of studies on the formation of a diffusion layer during the boriding of steel with a carbon content of 0.38 wt%. The study of diffusion coatings by SEM and TEM methods allows one to more clearly determine the mechanisms of diffusion of boron atoms and the formation of diffusion boride coatings. Diffusion of boron in the processes of diffusion boriding of iron-carbon alloys proceeds by a mixed mechanism: the delivery of active boron atoms to the diffusion front proceeds along the grain and phase boundaries. The reaction mechanism is realized by a gradual substitution of carbon with boron in iron carbides. Due to the continuous diffusion of boron, the reaction boundary is constantly moving in the direction from the surface to the core of the saturated material. In this case, as the diffusion proceeds, the concentration of carbon atoms under the boride layer constantly increases. This provides resistance to diffusion of boron atoms by the atomic mechanism and provokes diffusion by the reaction mechanism.

Surface Modification Features of Tool Steels by Laser Radiation

In this paper, we present the study results of the surface layers of carbon steels U8 and U10 performed by X-ray photoelectron spectroscopy after laser exposure. The thicknesses of oxidized surface layers were determined to be 43 nm and 108 nm for U8 and U10 steels, respectively. Both the total thickness of the formed oxide film and its phase composition (FeO, Fe2O3, Fe3O4) with depth were found to change depending on the concentration of iron, oxygen, and carbon atoms in the considered steels. The “layer” structure effect of the oxides of the layer modified by laser irradiation on the frictional characteristics of steels is shown. In particular, the presence of FeO oxide on the U8 steel surface increases the wear characteristics, while the presence of Fe2O3 and Fe3O4 oxides provides a higher wear resistance of steel U10 compared to an unirradiated steel surface.