Formation Of Amorphous Carbon Research Articles

The effect of constant electric field on zirconium oxidation by supercritical CO2

The oxidation of zirconium by supercritical CO2 (20.2 and 14.1 MPa, and 823 K) results in the formation of a layer of the monoclinic ZrO2 and amorphous carbon. In the constant electric field (E = 293 kV/m) when a sample of zirconium is the anode, the formation of amorphous carbon leads to a growth of leakage current and a twelve-fold increase in the rate of zirconium oxidation.

Optical properties of carbon nanostructures produced by laser irradiation on chemically modified multi-walled carbon nanotubes

This research focused on the nanosecond (Nd: YAG-1064nm) laser pulse effect on the optical and morphological properties of chemically modified multi-walled carbon nanotubes (MWCNT). Two suspensions of MWCNT in tetrahydrofuran (THF) were prepared, one was submitted to laser pulses for 10min while the other (blank) was only mechanically homogenized during the same time. Following the laser irradiation, the suspension acquired a yellow-amber color, in contrast to the black translucent appearance of the blank. UV-vis spectroscopy confirmed this observation, showing the blank a higher absorption. Additionally, photoluminescence measurements exhibited a broad blue-green emission band both in the blank and irradiated suspension when excited at 369nm, showing the blank a lower intensity. However, a modification in the excitation wavelength produced a violet to green tuning in the irradiated suspension, which did not occur in the blank. Lastly, the electron microscopy analysis of the treated nanotubes showed the abundant formation of amorphous carbon, nanocages, and nanotube unzipping, exhibiting the intense surface modification produced by the laser pulse. Nanotube surface modification and the coexistence with the new carbon nanostructures were considered as the conductive conditions for optical properties modification.

Analysis of the Formation of Multi-Layer Carbon Nanotubes in the Process of Mechanical Activation of the Pyrolysis Products of Vegetable Raw Materials

The carbon nanotubes are formed by pyrolytic and mechanochemical technology. Amorphous carbon is produced at 950°C and then subjected to mechanochemical treatment in a planetary mill for 1–46 h. Analysis ofinfluence of duration of mechanical activation of amorphous carbon on the morphology of moldable multilayer carbon nanotubes. It is demonstrated that prolonged mechanical activation of carbon composite in a vario-planetary mill promotes to formation of aggregates and amorphous carbon and to loss of thermal stability of nanotubeswith furtherconduct of vacuum annealing.

Characteristics of local atomic configurations in ball‐milled fullerenes

Structural changes occurring in C60 fullerenes after ball‐milling processing were studied. The quantitative characteristics of the local atomic configurations were reconstructed by the reverse Monte Carlo method in the structure of pristine and ball‐milled fullerenes C60, respectively. It is shown that 3‐fold atomic rings, indicating complete amorphization of crystalline fullerenes, are dominant in the structure of material after 14 h treatment. The behavior of the distribution of the sphericity coefficient of Voronoi polyhedra validates a gradual structural disordering of molecular crystal of C60 and, respectively, the formation of amorphous carbon with randomly arranged close‐packed structure after continuous ball‐milling treatment.

Investigation into the morphology, composition, structure and dry tribological behavior of rice husk ceramic particles

To expand the application of rice husk (RH) resource, this study developed carbon-based RH ceramic (RHC) particles using a common high-temperature carbonization method. The morphology, composition, and structure of the RHC particles were characterized with a series of modern analysis technologies and were then compared with those of the initial RH powder and carbonized RH (CRH) particles. The dry tribological behavior of RHC particle adobes (RHAs) was also investigated. Results showed the sheet-shaped morphology of the RHC particles. The graphitization degree of the RHC particles was lower than that of the CRH particles possibly because the phenolic resin (PR) filled the micro-pores of the RH particles, thereby prompting the formation of amorphous carbon in the RHC particles as a result of high-temperature carbonization. The appearance of a hydroxy function group (OH) on the surface of the RHC particles was ascribed to the decomposition of PR at 900°C. The friction coefficients and mass loss rates of the RHAs almost increased with the rise in load and velocity. In addition, the friction coefficients of the RHAs decreased at high load (5N) and velocity (0.261m/s) conditions. Such outcome indicated that the variation of contact area between steel ball and RHA at high load and velocity conditions resulted in the abrasive wear or catastrophic wear.

Synthesis of SnO2 pillared carbon using long chain alkylamine grafted graphene oxide: an efficient anode material for lithium ion batteries.

With the objective of developing new advanced composite materials that can be used as anodes for lithium ion batteries (LIBs), herein we describe the synthesis of SnO2 pillared carbon using various alkylamine (hexylamine; dodecylamine and octadecylamine) grafted graphene oxides and butyl trichlorotin precursors followed by its calcination at 500 °C for 2 h. While the grafted alkylamine induces crystalline growth of SnO2 pillars, thermal annealing of alkylamine grafted graphene oxide results in the formation of amorphous carbon coated graphene. Field emission scanning electron microscopy (FE-SEM) results reveal the successful formation of SnO2 pillared carbon on the graphene surface. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy characterization corroborates the formation of rutile SnO2 crystals on the graphene surface. A significant rise in the BET surface area is observed for SnO2 pillared carbon, when compared to pristine GO. Electrochemical characterization studies of SnO2 pillared carbon based anode materials showed an enhanced lithium storage capacity and fine cyclic performance in comparison with pristine GO. The initial specific capacities of SnO2 pillared carbon are observed to be 1379 mA h g(-1), 1255 mA h g(-1) and 1360 mA h g(-1) that decrease to 750 mA h g(-1), 643 mA h g(-1) and 560 mA h g(-1) depending upon the chain length of grafted alkylamine on the graphene surface respectively. Electrochemical impedance spectral analysis reveals that the exchange current density of SnO2 pillared carbon based electrodes is higher, corroborating its enhanced electrochemical activity in comparison with GO based electrodes.

Quality and wear behavior of graded polycrystalline diamond compact cutters

The wear behavior of conventional and graded polycrystalline diamond compact cutters was studied using a vertical lathe with mortar counterfaces. Different cutters were considered regarding to their diamond grain size and the high pressure and the high temperature conditions of the manufacturing process (HPHT). On the base of these cutters, a cobalt graduation process was performed on the WC–Co substrates by reactive imbibition. A quality factor developed in previous studies was calculated to evaluate cutters wear performances. The results showed that a controlled HPHT process can act on the wear resistance certainly by improving the diamond grain boundary cohesion. Unexpectedly, the diamond granulometry appeared to be a secondary factor influencing the wear resistance. The reactive imbibition clearly increased the wear resistance, even for cutters with coarse diamond grains (i.e. potentially impact resistant). Finally, a third body approach describes that the quartz particles detached from the mortar rock realizes abrasive scratches on the cutters wear flat. When the wear flat reaches the substrate, the formation of voids in the contact, associated with the trapping of abrasive particles, rises the wear kinetic. As a secondary mechanism, Raman spectroscopy measurements highlighted tribological transformed structures by the formation of graphite and amorphous carbon on the diamond worn surfaces.

Treatment of TNT red water by chemical-modified carbon adsorbent prepared from cheap raw materials of pine tree wood

This work reports the treatment of trinitrotoluene (TNT) red water by chemical-modified carbon adsorbent. The pine wood was used for preparation of carbon particles. The chemical modification by solutions of HNO3, ZnCl2, and NaOH was made for activation of carbon adsorbent. The activated carbon particles were characterized by X-ray diffraction (XRD) pattern, FT-IR spectra, scanning electron microscope (SEM) images, BET, and CHNS analyses. The formation of amorphous carbon was confirmed by XRD pattern. The variation of pores of carbon particles before and after the treatment of TNT red water was seen from SEM images. The area and pores volume of activated carbon were obtained 197–211 m2/g and 0.149–0.157 cm3/g, respectively. The considerable decrease of chemical oxygen demand amount was obtained after the treatment of TNT red water samples with activated carbon by HNO3 solution. Treatment experiments were carried out using batch method. The treatment efficiency of 90% was obtained in optimized parameters of pH value of 3, adsorbent dose of 40 g/L, and contact time of 300 min. Adsorption process followed the pseudo-second-order kinetic model. Thermodynamic studies revealed that the adsorption process is spontaneous (−ΔG = 10.4–12.5 kJ/mol) and endothermic (ΔH = 10.7 kJ/mol) at temperature range of 25–55°C. The sorption isotherm was in good agreement with the Freundlich isotherm for TNT red water diluted in range of 100–500 times. Desorption process using sodium hydroxide and boiling water for reuse of the adsorbent were studied and the removal efficiency of 48–72% was obtained in three times of reuse of carbon adsorbent.

Near-Ambient-Pressure X-ray Photoelectron Spectroscopy Study of Methane-Induced Carbon Deposition on Clean and Copper-Modified Polycrystalline Nickel Materials.

In order to simulate solid-oxide fuel cell (SOFC)-related coking mechanisms of Ni, methane-induced surface carbide and carbon growth was studied under close-to-real conditions by synchrotron-based near-ambient-pressure (NAP) X-ray photoelectron spectroscopy (XPS) in the temperature region between 250 and 600 °C. Two complementary polycrystalline Ni samples were used, namely, Ni foam—serving as a model structure for bulk Ni in cermet materials such as Ni/YSZ—and Ni foil. The growth mechanism of graphene/graphite species was found to be closely related to that previously described for ethylene-induced graphene growth on Ni(111). After a sufficiently long “incubation” period of the Ni foam in methane at 0.2 mbar and temperatures around 400 °C, cooling down to ∼250 °C, and keeping the sample at this temperature for 50–60 min, initial formation of a near-surface carbide phase was observed, which exhibited the same spectroscopic fingerprint as the C2H4 induced Ni2C phase on Ni(111). Only in the presence of this carbidic species, subsequent graphene/graphite nucleation and growth was observed. Vice versa, the absence of this species excluded further graphene/graphite formation. At temperatures above 400 °C, decomposition/bulk dissolution of the graphene/graphite phase was observed on the rather “open” surface of the Ni foam. In contrast, Ni foil showed—under otherwise identical conditions—predominant formation of unreactive amorphous carbon, which can only be removed at ≥500 °C by oxidative clean-off. Moreover, the complete suppression of carbide and subsequent graphene/graphite formation by Cu-alloying of the Ni foam and by addition of water to the methane atmosphere was verified.

Fast-moving dislocations trigger flash weakening in carbonate-bearing faults during earthquakes.

Rupture fronts can cause fault displacement, reaching speeds up to several ms−1 within a few milliseconds, at any distance away from the earthquake nucleation area. In the case of silicate-bearing rocks the abrupt slip acceleration results in melting at asperity contacts causing a large reduction in fault frictional strength (i.e., flash weakening). Flash weakening is also observed in experiments performed in carbonate-bearing rocks but evidence for melting is lacking. To unravel the micro-physical mechanisms associated with flash weakening in carbonates, experiments were conducted on pre-cut Carrara marble cylinders using a rotary shear apparatus at conditions relevant to earthquakes propagation. In the first 5 mm of slip the shear stress was reduced up to 30% and CO2 was released. Focused ion beam, scanning and transmission electron microscopy investigations of the slipping zones reveal the presence of calcite nanograins and amorphous carbon. We interpret the CO2 release, the formation of nanograins and amorphous carbon to be the result of a shock-like stress release associated with the migration of fast-moving dislocations. Amorphous carbon, given its low friction coefficient, is responsible for flash weakening and promotes the propagation of the seismic rupture in carbonate-bearing fault patches.

Sonochemical synthesis of Pt, Ru doped TiO2 for methane reforming

Platinum group materials (Pt, Ru, Rh) are highly active materials for reforming. In the present study, bimetallic Pt and Ru substituted TiO2 catalysts were synthesized by sonochemical method. The bimetallic 2% Pt 2% Ru/TiO2 showed high surface area of 66m2/g compared with the other catalysts. The prepared catalysts were characterized by XRD, XPS, TEM, TPR and BET. Dry reforming, partial oxidation and combined reforming (CR) with CO2 were studied on these materials. Synthesized catalysts were found to be highly active for dry reforming reaction. 26% and 95% of methane conversions were obtained with Ru substituted TiO2 (4% Ru/TiO2) at 400°C and at 700°C. The H2/CO ratio was close to unity with both Pt and Ru substituted catalysts after 650°C. The apparent activation energies found to be 51 and 56kJmol−1 with respect to methane for 4% Ru/TiO2 and 4% Pt/TiO2, respectively. High oxygen storage capacity of 4% Pt/TiO2 further showed the good activity for dry reforming. The bimetallic catalyst 2% Pt 2% Ru/TiO2 sintered under time on stream condition and also resulted in the formation of amorphous carbon on to the surface of catalysts, which made them an inactive catalyst for reforming process. The surface intermediates during these reactions were found by in situ FTIR at different temperatures for reforming processes. The peaks corresponding to CO2 adsorption were not observed in case of 4% Ru/TiO2 and 2% Pt 2% Ru/TiO2 for dry reforming and this indicates the Eley-Rideal mechanism on both catalysts. A kinetic model was developed by considering CH4 dissociation as rate determining step (RDS) and the model was validated to the obtained experimental data.

Quenching of liquid carbon under intensive heat transfer to the cold diamond substrate: Molecular-dynamic simulation

Quenching of liquid carbon (T = 6600 K) on a cold diamond substrate at T = 300 K in conditions close to the experimental laser melting of dispersed graphite on the substrate of natural diamond is investigated using molecular dynamics (MD) simulations. Quenching was carried out for two types of boundary conditions on the side opposite to the diamond substrate. The simulations confirmed the experimental result of the formation of amorphous carbon under such conditions. The calculations showed that the destruction of the diamond substrate did not take place because of its very high thermal conductivity. The estimation of the cooling rate of liquid carbon was done, the result is 1015 K/s. Temperature profiles in different layers of liquid carbon were restored to reproduce the detailed picture of the quenching process. We evaluated the radial distribution functions (RDF), the distribution of carbon atom bond fractions sp1-sp2-sp3, the average bond length and the azimuthal angles distributions for amorphous carbon atoms. This analysis confirmed that the amorphous carbon obtained by quenching in MD-simulations had a graphite-like structure.

Nitrogen Incorporated Ultrananocrystalline Diamond Microstructures From Bias‐Enhanced Microwave N2/CH4‐Plasma Chemical Vapor Deposition

Microstructural evolution as a function of film thickness of nitrogen incorporated ultrananocrystalline diamond (NUNCD) films, grown using bias‐enhanced microwave plasma chemical vapor deposition with gas mixtures of N2/CH4, is systematically investigated. It is observed that by controlling the growth time, the morphology, the microstructure, and the electrical properties of NUNCD films can be manipulated. The growth of NUNCD films starts with the formation of amorphous carbon on Si surface prior to the nucleation of diamond. In the growth time of 10 min, the films retain rod‐shaped diamond grains, whereas in the films grown for 30 min, needle‐like diamond grains are formed, which comprises a diamond core encased in a sheath of sp2‐bonded graphite phase. On increasing the growth time to 60 min, the growth of acicular grains ceases and large proportion of graphite clusters or defective diamond clusters (n‐diamond) is formed. The salient features of such materials with unique granular structure are that their electrical properties can be tuned in wide range such that they are especially useful in practical applications.

Characterization of carbon ion implantation induced graded microstructure and phase transformation in stainless steel

Austenitic stainless steel 316L is ion implanted by carbon with implantation fluences of 1.2×1017ions-cm−2, 2.4×1017ions-cm−2, and 4.8×1017ions-cm−2. The ion implantation induced graded microstructure and phase transformation in stainless steel is investigated by X-ray diffraction, X-ray photoelectron spectroscopy and high resolution transmission electron microscopy. The corrosion resistance is evaluated by potentiodynamic test. It is found that the initial phase is austenite with a small amount of ferrite. After low fluence carbon ion implantation, an amorphous layer and ferrite phase enriched region underneath are formed. Nanophase particles precipitate from the amorphous layer due to energy minimization and irradiation at larger ion implantation fluence. The morphology of the precipitated nanophase particles changes from circular to dumbbell-like with increasing implantation fluence. The corrosion resistance of stainless steel is enhanced by the formation of amorphous layer and graphitic solid state carbon after carbon ion implantation.

Si-doped nano- and microcrystalline diamond films with controlled bright photoluminescence of silicon-vacancy color centers

Nanocrystalline diamond (NCD) and microcrystalline diamond (MCD) films with bright photoluminescence (PL) of silicon-vacancy (SiV) color centers at 738nm have been grown using a microwave plasma CVD technique. The films were doped with Si via adding silane to CH4–H2 reaction gas mixture in the course of the deposition process. The dependence of SiV PL intensity on silane concentration in gas shows a maximum at SiH4/CH4 ratios of 0.2% and 0.6% for NCD and MCD films, respectively, the maximum intensity for MCD being an order of magnitude stronger compared with that for NCD. The PL quenching at higher CH4 addition occurs, however, no significant degradation of the film structure, such as Si-induced amorphous carbon formation, was observed within the SiH4 concentration range studied (0%–0.9%). The higher PL efficiency of the MCD films is related to their less defective structure, as deduced from Raman spectroscopy analysis.

A novel Mo-W interlayer approach for CVD diamond deposition on steel

Steel is the most widely used material in engineering for its cost/performance ratio and coatings are routinely applied on its surface to further improve its properties. Diamond coated steel parts are an option for many demanding industrial applications through prolonging the lifetime of steel parts, enhancement of tool performance as well as the reduction of wear rates. Direct deposition of diamond on steel using conventional chemical vapour deposition (CVD) processes is known to give poor results due to the preferential formation of amorphous carbon on iron, nickel and other elements as well as stresses induced from the significant difference in the thermal expansion coefficients of those materials. This article reports a novel approach of deposition of nanocrystalline diamond coatings on high-speed steel (M42) substrates using a multi-structured molybdenum (Mo) – tungsten (W) interlayer to form steel/Mo/Mo-W/W/diamond sandwich structures which overcome the adhesion problem related to direct magnetron sputtering deposition of pure tungsten. Surface, interface and tribology properties were evaluated to understand the role of such an interlayer structure. The multi-structured Mo-W interlayer has been proven to improve the adhesion between diamond films and steel substrates by acting as an effective diffusion barrier during the CVD diamond deposition.

Synthesis of stable heterogeneous catalysts by supporting carbon-stabilized palladium nanoparticles on MOFs.

Cycling instability of catalysts is a persisting challenge in heterogeneous catalysis. In this work, we reported an effective in situ strategy for preparing ZIF-8 supported carbon-stabilized Pd nanoparticles (C@Pd/ZIF-8). The original ZIF-8 structure was well-preserved after the formation of Pd nanoparticles and amorphous carbon. Here, the Pd nanoparticles were encapsulated in the carbon matrix with a good dispersion. The as-prepared catalysts showed a better activity and cycling stability for the hydrogenation of C[double bond, length as m-dash]C containing substrates. C@Pd/ZIF-8 catalysts are reusable without significant loss of activity after 5 cycles, exhibiting higher cycling stability than those prepared from directly supported Pd nanoparticles on ZIF-8 (Pd/ZIF-8).

Layered Perovskite Nanofibers via Electrospinning for Overall Water Splitting

The (111)-layered perovskite materials Ba5 Ta4 O15 , Ba5 Ta2 Nb2 O15 and Ba5 Nb4 O15 are prepared with nanofiber morphology via electrospinning for the first time. The nanofibers are built up from small single crystals, with up to several micrometers length even after calcination. The formation mechanism is investigated in detail, revealing an intermediate formation of amorphous barium carbonate strengthening the nanofiber morphology for high temperature treatment. All nanofiber compounds are able to generate hydrogen without any co-catalyst in photocatalytic reformation of methanol. After photodeposition of Rh-Cr2 O3 co-catalysts, the nanofibers show better activity in overall water splitting compared to sol-gel-derived powders.

The application of inelastic neutron scattering to investigate a hydrogen pre-treatment stage of an iron Fischer–Tropsch catalyst

The effect of a hydrogen pre-treatment step on an iron based Fischer–Tropsch catalyst applied to the CO hydrogenation reaction at 623 and 723K has been investigated by inelastic neutron scattering (INS). The catalyst cannot support methane production over a 6h period of reaction at 623K but it is active at 723K. The INS spectrum indicates the presence of a predominantly aliphatic hydrocarbonaceous overlayer for the post-reaction 623K sample, whereas the spectrum for the 723K sample is assigned to an overlayer comprising partially hydrogenated polycyclic aromatic compounds. The hydrocarbonaceous overlayer associated with the active phase of the catalyst is modified by the hydrogen pre-treatment step. The INS spectra are interpreted with reference to microreactor studies, powder X-ray diffraction, temperature-programmed oxidation and transmission electron microscopy. The hydrogen pre-treatment stage favours the formation of amorphous carbon and is deemed not to convey any advantage with respect to CO hydrogenation activity.

Enhanced catalytic stability through non-conventional synthesis of Ni/SBA-15 for methane dry reforming at low temperatures

A non-conventional synthesis route for the preparation of Ni/SBA-15 catalyst for methane dry reforming (MDR), comprising the addition of ascorbic acid as reducing agent, was considered and compared to impregnation and precipitation conventional preparation methods. The catalyst prepared following this novel route evidenced successful confinement of Ni-species inside the pores of SBA-15, both NiO and Ni-phyllosilicates. Due to its particular characteristics, this catalyst showed enhanced activity, selectivity and stability in MDR experiments. Concretely, deactivation of the catalyst was substantially hindered, due to improved selectivity, preferential carbon growth on the external surface of the catalyst, and special ability of the catalyst to favor the formation of amorphous carbon.