Formation Of Carbon Phases Research Articles

Effect of Nitrogen on Growth and Optical Properties of Single-Crystal Diamond Synthesized by Chemical Vapor Deposition.

Concurrently achieving high growth rate and high quality in single-crystal diamonds (SCDs) is significantly challenging. The growth rate of SCDs synthesized by microwave plasma chemical vapor deposition (MPCVD) was enhanced by introducing N2 into the typical CH4-H2 gas mixtures. The impact of nitrogen vacancy (NV) center concentration on growth rate, surface morphology, and lattice binding structure was investigated. The SCDs were characterized through Raman spectroscopy, photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy. It was found that the saturation growth rate was increased up to 45 μm/h by incorporating 0.8-1.2% N2 into the gas atmosphere, which is 4.5 times higher than the case without nitrogen addition. Nitrogen addition altered the growth mode from step-flow to bidimensional nucleation, leading to clustered steps and a rough surface morphology, followed by macroscopically pyramidal hillock formation. The elevation of nitrogen content results in a simultaneous escalation of internal stress and defects. XPS analysis confirmed chemical bonding between nitrogen and carbon, as well as non-diamond carbon phase formation at 0.8% of nitrogen doping. Furthermore, the emission intensity of NV-related defects from PL spectra changed synchronously with N2 concentrations (0-1.5%) during diamond growth, indicating that the formation of NV centers activated the diamond lattice and facilitated nitrogen incorporation into it, thereby accelerating chemical reaction rates for achieving high-growth-rate SCDs.

Influence of supercritical carbon dioxide (scCO2) curing on carbonation and strength development of brucite recovered from desalination reject brine

Brucite is a potentially sustainable alternative to reactive magnesium oxide (MgO) cement (RMC) with no calcination requirement. This study investigated the effect of elevated CO2 curing concentrations on CO2 sequestration, the formation of carbonate phases, and the compressive strength of compacted pellets of brucite nanopowders synthesized from reject brine. It was revealed that the compressive strength of the compacted brucite pellets with optimum water-to-binder ratio (w/b) enhanced by 45% within 4 h under supercritical CO2 (scCO2) conditions compared to the maximum strength observed under 20% CO2 and 80% relative humidity (RH) at 30 ºC conditions. The scCO2 curing enabled the formation of a high-density nesquehonite phase primarily responsible for the strength development of the brucite pellets. In addition, the CO2 sequestration in the scCO2-cured brucite pellets reached up to 66% of their maximum storage capacity, indicating their excellent CO2 absorption capability.

Near Surface Studies on the Role of Graphene Oxide in the Carbon Species Activities in IT-SOFC Cathode Materials

Active roles of carbon species in solid oxide fuel cell (SOFC) cathode was simulated by adding graphene oxide (GO) into Ba0.5Sr0.5Co0.2Fe0.8 (BSCF) materials prepared by sol-gel method. The mixture was heated up to intermediate temperature SOFC range (650 - 850°C) for a period of 5 hours. A depth-profiling measurement by x-ray photoelectron spectroscopy (XPS) technique was carried out to analyse the carbon species activities at near surface of BSCF cathode. A depth-profiling analysis indicated that the graphene oxide bond components are retained under the cathode surface and does not affected the formation of carbonate phases in BSCF cathode.

Alkali metal bifunctional catalyst-sorbents enabled biomass pyrolysis for enhanced hydrogen production

Alkali ceramics are well-known high temperature CO2 sorbents in forms of zirconates or orthosilicates with catalytic tar cracking ability prior to or after carbonation. In this study, Li2ZrO3, Li4SiO4, and Na2ZrO3 were selected as catalyst-sorbent bifunctional materials to enhance the pyrolysis of sawdust. This study investigated the synergy between the alkali metal bifunctional materials under pyrolytic conditions. The weight loss data and gas yield trends in the temperature between 200 and 800 °C demonstrated a combined catalytic process and gas-solid reaction. A metal carbonate phase was formed after the reaction of capturing CO2. The CO2 capture promoted H2 production because of Le Chatelier principle and the formation of carbonate phase assisted tar cracking reactions. H2 production increased from 5.73 mmol g−1 to 8.87 mmol g−1, 15.85 mmol g−1, and 13.67 mmol g−1 in the presence of Li2ZrO3, Li4SiO4, and Na2ZrO3, respectively. At temperatures around 700 °C, CO was released due to secondary cracking reaction and the Boudouard reaction of CO2 released from the sorbents. Overall, the alkali ceramics present the catalyst-sorbent bifunctional activity for enhancing H2 production during biomass pyrolysis.

Study on carbon contamination and carboxylate group formation in Y2O3-MgO nanocomposites fabricated by spark plasma sintering

For Y2O3-MgO nanocomposites fabricated by spark plasma sintering (SPS), the strong absorption peaks, which are assigned to the stretching vibrations of carboxylate group (OCO), are commonly observed in IR spectra. These absorption peaks can negatively affect military applications such as IR windows or domes. In order to suppress the formation of these absorption peaks, therefore, it is important to understand how the carboxylate group in the SPSed Y2O3-MgO nanocomposite originated. In this study, it is demonstrated that the formation of the carboxylate group is related to the carbon contamination during SPS processing. The carbon phase transforms into CO2 gas by annealing and this leads to a reaction with metal oxide phases, resulting in the formation of carbonate phase. This carbonate phase contributes to the absorption peaks of the carboxylate group.

Formation of carbonate phases and their effect on the performance of reactive MgO cement formulations

This study investigated the formation of different phases and their influence on the microstructural and mechanical development of carbonated reactive MgO cement formulations. Hydrated magnesium carbonates (HMCs) were identified and quantified via XRD, TG-DTG and SEM. Visual observations of the 3D internal structure at different depths were performed by X-ray computed tomography and confocal Raman microscopy. Elastic modulus of different components was obtained by nano-indentation. The expansive formation of HMCs led to dense microstructures composed of well-connected carbonate networks. The transition of artinite to hydromagnesite/nesquehonite was observed over time. The initial formation of a dense carbonate layer on sample surface inhibited continuous diffusion of CO2, resulting in a slower strength development at later ages. Despite this limitation, the continuation of hydration and evolution of carbonate morphology led to 28-day strengths of 60 MPa in concrete samples, supported by the higher elastic modulus of HMCs than brucite (19.4 vs. 2.5 GPa).

Improving the Properties of Filled Gypsum Composites by Carbonization

Carbonization of modified composites based on gypsum binder has been proposed as a promising method for producing gypsum materials with high technical properties. To reduce costs and improve manufacturability, mineral modifiers are used in gypsum composites. Together with gypsum and lime the waste of basalt production is used. In contrast to other methods, the proposed carbonization during the formation of gypsum forms a gypsum stone, which has a reduced porosity. Of particular interest is the clogging of external pores, which communicate with the external environment. It is these pores that reduce the water resistance of gypsum composites. The formation of carbonate phases in the structure of gypsum stone will help improve the performance of the material. At the same time, the problem of preserving the natural environment for future generations is being solved. It also increases the economic and environmental attractiveness of the project

Evidence of diamond-like carbon phase formation due to 80 keV Xe+ ion impact on pencil-lead graphitic systems with oblique angle incidence

We report on the effect of 80 keV Xe+ ion irradiation on the commercially available, sectioned 10B pencil-graphite specimens subjected to normal and oblique angle incidence of ions (θi = 0°–70°) and considering a fixed ion fluence of . The pristine and irradiated samples were characterized by powder x-ray diffraction, atomic force microscopy and Raman spectroscopy studies. Unlike pristine graphite and normal incidence cases, several ripple patterns can be visualized in the atomic force micrographs of the specimens irradiated with an oblique angle incidence. Moreover, apart from conventional G-band located at , a distinct diamond-like carbon (DLC) phase has been witnessed at in the Raman spectra of the graphitic specimens subjected to ion impact and for values of 50° and 70°. The formation of the DLC phase along with surface ripple formation would find numerous scopes while dealing with properties such as surface transport, field emission and mechanically hard coating in miniaturized devices.

Water as a cosolvent – Effective tool to avoid phase separation in bimetallic Ni-Cu catalysts obtained via supercritical antisolvent approach

A series of Ni-Cu metal catalysts were synthesized using supercritical antisolvent (SAS) approach under conditions of controlled water content in the initial solution of precursors. It is shown that low content of water in methanol (up to 9 vol.%) helps to adjust the structure, texture and morphology of the obtained materials. The water additives promote the formation of carbonate phase that during further decomposition and reduction steps allows obtaining the solid Ni1‐xCux solution without phase separation. In particular the addition of 7 and more vol.% of water leads to the complete introduction of Cu into the Ni crystal lattice without formation of separate enriched phases of Ni or Cu.

Formation of carbon phases under hydrothermal conditions

The formation of carbon phases by reacting formaldehyde with sulfuric acid under hydrothermal conditions was studied. The final products of the reaction were found to be amorphous carbon, diamond-like carbon, α- and β-graphite phases, fullerenes C60 and C70, fullerites, carbolite, and chaoite. Hydrocarbons of various compositions were detected in reaction products, namely cyclic hydrocarbons, including aromatic ones, and naphthene hydrocarbons. A formation scheme is suggested for carbon structures.

Preparation of new titanium nitride-carbon nanocomposites in supercritical benzene and their oxygen reduction activity in alkaline medium

Titanium nitride-carbon nanocomposites are synthesized by the reaction of TiCl4 and NaN3 in supercritical benzene medium that also serves as a carbon source. The as-prepared precursors (SI, SII) are subjected to several heat treatments (SIII–SV). The synthesized nanoparticles are characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The samples are tested as electrocatalyst for oxygen reduction reaction in an alkaline electrolyte. It is shown that the electrocatalytic properties of the synthesized nanoparticles are highly dependent on the heat treatment atmosphere and duration. The heat treatment under ammonia atmosphere at 1000°C for 10h (SIV) increased the ORR mass activity from −0.64 (SI) to −1.28mAmg−1 (SIV) at −0.6V vs. SCE. Moreover, the heat treated sample (SIV) shows almost twice ORR mass activity as commercial TiN. Rotating disk electrode (RDE) measurements exhibit ORR on commercial TiN proceeds via two parallel pathways including two and four electrons, resulting in almost 60% H2O2 production, while SIV sample improves ORR by reducing H2O2 formation to almost 16%. The high ORR activity and stability of the sample SIV are mainly due to (i) random layer structure of carbon that combines through a hybrid state with TiN nanoparticles, (ii) unstoichiometric nitrogen and oxygen doped into TiN lattice, and (iii) higher electrochemical surface area. Moreover, the possible pathways of carbon phase formation in vicinity of supercritical reaction are discussed.

Selforganization in Fischer–Tropsch synthesis with iron- and cobalt catalysts

Unsteady initial regimes of Fischer–Tropsch synthesis with iron and cobalt catalysts have been investigated for changes in rate and selectivity, applying own-developed methods for temporal resolution of product composition. Using the kinetic model of non-trivial surface-polymerization, probabilities of reactions of chemisorbed intermediates are calculated as function of time and carbon number of species, at several sets of reaction parameters and different catalyst properties. Results are used to elucidate principles of selforganization.The rules of iron catalyst selforganization are dominated by alkali promoting, as controlling iron phase composition and the relative rate of reaction of on-site-carbon for FT-monomer formation, Fe-carbide formation and carbon-phase formation—these as in relation to primary and secondary formation of olefins and paraffins.With cobalt as catalyst, selforganization for creating different kinds of active sites for primary and secondary reactions appears essential, and is explained via the observed selectivity changes. A dynamic structure of active sites is proposed. Probability of linear chain prolongation is merely carbon number dependent, but probability of growth with chain branching declines exponentially with carbon number, indicating increasing spatial constraints on the reaction. Selectivity changes are mechanistically understood from the ordered complexity of product composition.

Bis(trimethylsilyl)Ethylamine: Synthesis, Properties and its use as CVD Precursor

Abstract Bis(trimethylsilyl)ethylamine (BTMSEA) was synthesized and characterized as CVD precursor for silicon carbonitride SiCxNy films synthesis (vapor pressure, thermodynamic modeling). SiCxNy films were deposited by PECVD from BTMSEA.in.the.temperature.range.of.100-700 oC.using.two.additional.gases.(He.or.NH3)..FT-IR,.Raman spectroscopy, ellipsometry, EDX, SEM, UV-Visible spectroscopy and nanoindentation tests were used for film characterization. FT-IR analysis showed that temperature increase lead to the transition from a low-temperature polymeric-like films to the high-temperature inorganic material. It was also shown that the high-temperature films content predominantly Si-C bonds independently on the additional gas type. As it was confirmed by Raman spectroscopy, high- temperature SiCxNy films content carbon phase. Ammonia addition into the reaction mixture resulted in the shift of the temperature boundary of carbon phase-free region. The transmittance of SiCxNy.films obtained using BTMSEA + He mixture in the deposition temperature range of 100-500 oC was 85-95% and decreased significantly in the case of carbon phase formation at Tdep more than 500 oC. Optical band gap estimated from UV-Vis spectra varied in the range of 1.9-4.4 eV depending on the deposition temperature. NH3 addition to initial mixture led to the film transmittance decrease to 80-90%, the optical band gap changed in the range of 2.0-5.1 eV. Nanoindentation tests showed that hardness of the films synthesized at high temperature was 18.5-21.5 GPa.

Carbon Nanostructures Synthesize from Coconut Coir Dust Mediated by Layered Clays through Hydrothermal Process

Brazil has a large potential for energy generation and development of new materials from renewable resources through eco-friendly routes, which presents an alternative for construction of an eco-technological platform, where the entire lifecycle of the material or industrial product be sustainable. The proposal of the present work was synthesize carbon nanostructures from coconut coir dust and via template synthesis mediated by layered clays through hydrothermal process. The obtained materials were characterized by Raman Spectroscopy, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscope (SEM). Carbon phase formation was indicated by infrared results with bands at 1444 cm-1and 1512 cm-1assigned to C=C of aromatic groups. Raman spectroscopy results showed presence of carbonaceous species by the appearance of D and G bands assigned to disordered and graphitic crystallites, respectively. SEM results showed overlapping sheets and plates formation. High Resolution Transmission Electron Microscopy measures are in progress.

Catalytic formation of carbon phases in metal modified, porous polymer derived SiCN ceramics

A novel method for the simultaneous formation of catalytic active metal nanoparticles, multiwall carbon nanotubes (MWCNTs) and/or turbostratic carbon and porous M@SiCN (M = Fe, Co, Pt, Cu, Ag, Au) ceramics during pyrolysis of metal modified polysilazanes and polyethylene (PE) particles as sacrificial filler is described. The thermal decomposition of the polyethylene leads not only to the generation of the porosity but also to an in situ reduction of the metal compounds to the metal nanoparticles, due to the reductive atmosphere. Depending on the metal, carbon nanotubes as well as turbostratic carbon were formed in different amounts, due to the chemical vapor deposition (CVD) like conditions. The resulting carbon phases, ceramics and metal nanoparticles were investigated using the combination of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) measurements, giving evidence for the presence of the carbon phases and the metal particles.

Physico-Chemical Characterization of Steel Slag. Study of its Behavior under Simulated Environmental Conditions

The chemical and mineralogical composition of steel slag produced in two ArcelorMittal steel plants located in the North of Spain, as well as the study of the influence of simulated environmental conditions on the properties of the slag stored in disposal areas, was carried out by elemental chemical analysis, XRF, X-ray diffraction, thermal analysis, and scanning electron microscopy with EDS analyzer. Spectroscopic characterization of the slag was also performed by using FTIR spectroscopy. Due to the potential uses of the slag as low cost adsorbent for water treatment and pollutants removal, its detailed textural characterization was carried out by nitrogen adsorption-desorption at 77 K and mercury intrusion porosimetry. The results show that the slag is a crystalline heterogeneous material whose main components are iron oxides, calcium (magnesium) compounds (hydroxide, oxide, silicates, and carbonate), elemental iron, and quartz. The slags are porous materials with specific surface area of 11 m(2)g(-1), containing both mesopores and macropores. Slag exposure to simulated environmental conditions lead to the formation of carbonate phases. Carbonation reduces the leaching of alkaline earth elements as well as the release of the harmful trace elements Cr (VI) and V. Steel slags with high contents of portlandite and calcium silicates are potential raw materials for CO(2) long-term storage.

Hydrothermal synthesis of sp3 bonded carbon from β-SiC–organic compound system

Synthesis of carbon polymorphs through the decomposition of metal carbides was studied employing hydrothermal technique in the pressure and temperature ranges of 100–200 MPa and 350–800°C respectively. It was observed that dissociation of β-SiC into SiO2 occurred in the presence of organic compounds and controlled free elemental carbon phase formation. The organic compounds are known to dissociate at low temperature to C–O–H supercritical fluids under supercritical hydrothermal condition which have great influence on the decomposition of metal carbides. The scanning electron microscopic (SEM) studies of β-SiC–organic compounds system reveal that the bulk of the carbon particles formed are spherical or ovoid shaped particles and in some runs, the authors find the formation of nanosized octahedral crystallites at the inner walls of the hallow spherical carbon particles exhibiting sp3 hybridisation. The microRaman spectral studies of carbon crystallites reveal that they have typical spectra of sp3 hybridisation, which clearly demonstrates the formation of nanosized diamond crystallites. The X-ray diffraction studies of the silicon carbide–water experimental run products shows only the lines of silica which are either quartz or cristobalite phase and no traces of carbon were seen.

The carbon phases formed during pyrolysis of gaseous hydrocarbons in reaction volume of a fluidized bed apparatus

In view of the kinetic laws of hydrocarbon pyrolysis, three mechanisms of the carbon phase formation are considered: the mechanism of individual atoms, the two-stage model of growth, and the mechanism of agglomerate. The macrostructure is investigated by means of optical and scanning electron microscopy, and the microstructure of carbon deposits is investigated with the help of transmission electron microscopy. The parameters of crystal structure are determined as well: the parameter of lattice (a), the interlayer distance (d002), and the coherent dispersion areas La and Lc. The radiation stability of pyrocarbon is investigated under irradiation with a stream of high-energy electrons. The fact of a noncatalytic growth of the carbon fibers on the outfit walls of a fluidized bed apparatus (above the level of the particles) forming owing to interfacing globular deposits in the pores is established.

Hydrothermal synthesis and characterization of micro to nano sized carbon particles

Experiments under hydrothermal conditions were carried out to study the formation of elemental carbon through the decomposition of β-Silicon carbide (β-SiC) in the presence of organic compounds. The organic compounds were known to dissociate at low P-T conditions and produce the C–O–H supercritical fluids, which will have great influence on the decomposition of β-SiC. These hydrothermal runs under the influence of supercritical fluids will not only help in dissociating the silicon carbide into SiO2 and free elemental carbon but also control the type of carbon phase formation. The Scanning Electron Microscopic (SEM) studies of the run products indicate the formation of the micron sized carbon particles having characteristic shapes like spherical/ovoid, scaly with metallic lustre and in some runs we find the formation of nano sized octahedral crystallites. Micro Raman study of these carbon particles reveals that bulk of the carbon formed in these runs were disordered / sp2–hybridized carbon but we also noticed the formation of black scales over the spherical particles and the octahedral crystallites which exhibits the sp3-hybridization having the characteristic sharp band at 1332 cm-1, comparable to that of diamond powder. The octahedral crystallites are formed at the inner walls of the hollow spherical carbon particles. In any of the experimental runs we haven't used either the metal catalysts or the diamond seed with the charge material. Thus, the nucleation and formation of nano sized octahedral crystallites of diamond (sp3-hybridized carbon) in the present study at lower P-T conditions compared to that of its formation in nature is a significant breakthrough in the study of diamond synthesis.

Resonant nuclear reaction analysis study of carbon phase formation during carbon ion-implantation into silver substrates

High fluence (10 16 to 3 × 10 17 ions cm −2) carbon ( 13C + or 12C +) ion-implantations were performed into silver substrates held at high temperature (400–700 °C) to produce carbon onions. The carbon concentration profiles were determined by using the 13C(p,γ) 14N resonant nuclear reaction at the proton energy of 1748 keV. Implanted carbon atoms mainly precipitated inside the bulk of the silver matrix contributing to the formation of carbon onions. Carbon also precipitates onto the surface at the beginning of the implantation process, a phenomenon that concerns at maximum 1% of the implanted carbon atoms. Resonant nuclear reactions analysis characterizations reveal that there is no preferential carbon diffusion towards the surface during the implantation process. Furthermore, sputtering and evaporation of silver are proposed to be the key mechanisms that control the carbon concentration in the near surface region.