Carbon Carbide Research Articles

Luminescence induced in diamond by He+ ion implantation into SiC/C composites with an inverse opal structure

The photoluminescence induced in diamond by helium ion implantation into SiC/C nanocomposite samples and their structure revealed by high-resolution transmission electron microscopy have been investigated. It has been found that, apart from crystallites of silicon carbide, graphite, and amorphous carbon, in the structure of the composites there are spherical carbon particles containing concentric graphite-like shells (onion-like particles). It has been established that onion-like particles are formed during high-temperature treatment of SiC/C nanocomposites in the course of their preparation. It has been shown that, after the implantation with the subsequent thermal treatment, nanocomposite samples exhibit a luminescence characteristic of N-V centers in diamonds. The assumption has been made that the diamond crystallites are formed at the center of onion-like particles during high-temperature treatment of the composite.

Titanium–aluminum–polytetrafluoroethylene coated stainless steel micromold via co-sputtering deposition: Replication performance and limitation in hot-embossing

Stainless steel micromold is an alternative of silicon (Si) micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti–Al–PTFE coatings, which affected the bonding structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti–Al–PTFE coatings were a mixture of carbide, PTFE-like material and amorphous carbon. The surface roughness of coated micromolds decreased with the increase in the PTFE concentration. The Ti–Al–PTFE coating deposited with 50W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1×10−3N/m, respectively. The coated stainless steel micromolds showed a better replication performance compared to the bare stainless steel micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the micromold channels and the limitations of the Ti–Al–PTFE coatings for application in hot-embossing.

Electrocatalytic Performance of Tungsten Carbide and Vulcan XC-72 Carbon Supported Pd Catalyst for Formic Acid Oxidation

This work investigated the elecrocatalytic performance of tungsten carbide(WC) and Vulcan XC-72 carbon(XC) supported Pd(Pd/WC-XC) catalysts for formic acid oxidation.It is found that the electrocatalytic performance of the Pd/WC-XC catalysts for formic acid oxidation is better than that of the Pd/XC catalyst.Furthermore,the electrocatalytic performance of the Pd/WC-XC catalyst is related to the mass ratio of WC and XC.When the mass ratio of WC and XC is 3∶ 1,the electrocatalytic activity of the catalyst is best.When the mass ratio of WC and XC is 2∶ 1,the electrocatalytic stability of the catalyst is best.

Long-term Adhesion Studies of Polyimide to Inorganic and Metallic Layers

ABSTRACTDelamination between thin-film metal and substrate is a major cause of failure in polyimide based neural microelectrode arrays. Chemical adhesion is the only way to establish a long-term bond that will allow two materials to stick to each other even in a wet environment, given that the materials do not deteriorate in the presence of water. This study assesses, by means of peel and shear tests, a long-term quantitative and comparative study of the adhesion of polyimide to various metallic and other inorganic layers of interest. Polyimide (BPDA-PPD) was cured on the layers, which involve platinum, gold and tungsten-titanium as commonly used implant metals and diamond-like carbon (DLC), silicon carbide (SiC), silicon dioxide (SiO2) and silicone nitride (SiN) as potential adhesion promoters to be used later as intermediate layers between metal and polyimide. The adhesion was observed over one year under accelerated-aging conditions by storing the specimens in 60°C saline (corresponding to 40000 hrs at 37°C). Only silicon carbide and amorphous carbon showed almost unaffected adhesion to polyimide over the testing period. No water intrusion at the interface was observed and the strong bond is almost fully maintained.

Investigation of iron oxide reduction by ethanol as a potential route to produce hydrogen

In this work, a novel way to indirectly store and produce H2 from ethanol was investigated using a two-step process based on the reduction of iron oxide followed by oxidation with H2O. The reduction of different iron oxides, i.e., Fe2O3, Fe3O4 and FeOOH, with ethanol to produce Feo was investigated. TPRe (Temperature Programmed Reactions) and Mössbauer and XRD analyses showed that ethanol reduces Fe2O3 sequentially to Fe3O4 at 350–500°C, to Fe3O4/FeO at 500–600°C and finally to Feo at 700°C. The formed Feo can then be oxidized by H2O to produce H2 and Fe3O4, as shown by Mössbauer and XRD analyses. Cyclic experiments showed that iron could be consecutively reduced/oxidized at least 5 times without any significant decrease in H2 production after the second cycle. However, reactions of Fe2O3 with ethanol at higher temperatures, i.e., 800 and 900°C, led to the formation of iron carbide and significant carbon deposition. XPS, SEM, TEM, Raman and TG showed 24–28wt% carbon content, particularly on the surface as nanofibers and as amorphous and graphitic carbon.

Effect of the introduction of niobium carbide on non-oxidative dehydro-aromatization of methane over MoMCM-22

The effect of the introduction of niobium carbide was studied on the dehydro-aromatization of methane over a molybdenum containing HMCM-22 zeolite at 973 K. The introduction of niobium decreased Bronsted acidity, affecting catalyst behavior on the dehydro-aromatization of methane. Niobium carbide containing zeolite showed lower activity, lower coke deposition and predominant formation of naphthalene, in the expenses of benzene, the major product observed for Mo containing zeolite. Besides carbidic carbon, two other types of coke were observed: one associated to molybdenum and the other associated to Bronsted acid sites located both on the catalyst surface and inside zeolite pores.

Experimental determination of carbon isotope fractionation between iron carbide melt and carbon: 12C-enriched carbon in the Earth's core?

We report here new experimental data on equilibrium carbon isotope fractionation between graphite/diamond and iron carbide melt at 5 and 10 GPa and in the temperature range between 1200 and 2000 °C. Carbon isotope equilibrium was tested using morphological features of graphite and also by performing a longer duration experiment, both of which suggested that equilibrium carbon isotope fractionation is present. The results suggest that iron carbide melt will preferentially accumulate 12C rather than 13C. An equilibrium temperature dependent fractionation between iron carbide melt and graphite/diamond is proposed based on the relation Δ 13 C ( gr / dia – iron carbide melt ) = 8 . 85 1 0 6 / T 2 K + 0. 99 . Our results are consistent with the carbon isotope distribution between graphite and cohenite (Fe 3C) observed in iron meteorites. We propose that temperature-dependent fractionation of carbon isotopes between iron carbide melt and graphite/diamond might have created a “ 12C-enriched core” with a significant difference in the distribution of carbon isotopes between the carbon in the metallic core and bulk silicate Earth during the accretion and differentiation of early Earth. Recent findings of low δ 13C carbonados and diamonds of deep mantle origin supports the presence of a 12C enriched source. The possible presence of a reservoir of 12C-enriched carbon in the Earth's core implies that it can generate large perturbations in the surface and shallow carbon-isotope system by the flux of lighter carbon from the core–mantle boundary.

Steel-Bonded Cemented Carbide Cladding Prepared by Technological Combination of Powder Explosive Compaction and Liquid Sintering

Steel-bonded cemented carbide sheet considered as cladding was successfully bonded with carbon steel plate by a technological combination of powder explosive compaction and liquid sintering. The microstructural interface between steel-bonded cemented carbide cladding and carbon steel plate was characterized by SEM, EDS analysis and hardness testing. The results showed that the gradient distributions of the elements Fe, C and W were found in the normal direction of the interface. The element W permeated about 100μm in depth through the side of carbon steel. The improved hardness of about 600～700HV of cladding was attributed to multiple carbides.

Carbon in oxide layers formed under electric discharge conditions

The presence of carbon on the surface and in deep layers of oxide coatings produced by plasmaelectrolytic oxidation is studied. Graphite is found in the coatings formed on titanium under the conditions of cathodic polarization in an organic electrolyte. Carbon in the amount of 16–40 at % is present on the surface of coatings produced on aluminum at the anodic polarization in aqueous electrolytes. Compounds with C-O (oxidized carbon), C-C or C-H (aliphatic carbon), and C-M (carbide carbon) bonds are determined. The carbon content decreases to a few atomic percents upon etching the surface with a high-energy argon beam and removing a nearly 3-nm layer. Aliphatic and metal-oxide carbon is present at this depth. The carbon content on either the surface or in deep layers of the coatings is the same, regardless of the stage of the coating formation, namely, prespark, spark, or microarc anodizing.

Friction and Wear Behavior of Structural Ceramics Sliding against Bearing Steel under Vacuum Condition

The friction and wear behavior of Si3N4, SiC and ZrO2 sliding against M50 bearing steel under vacuum condition at various applied load were investigated. The results showed that the properties of different ceramic materials cause the difference in wear behaviors. The coefficient of friction was lowest in SiC and M50 bearing steel couple than other cases for graphitic carbon replaced carbidic carbon at the worn layer of SiC. The specific wear rate of ZrO2 was highest and the lowest was Si3N4. The ceramic ball materials have transferred on M50 bearing steel surfaces and tribofilm consistently formed on the ceramic balls wearing surfaces. Dominant wear behaviors for three structural ceramics were adhesion abrasion, plastic deformation and brittle fracture. The couple with Si3N4 and M50 showed the best operating conditions for friction and wear resistance under higher applied load.

Carbon Nanotubes with Uniform Wall Thickness Synthesized Via a Solid-Liquid Reaction

Carbon nanotubes(CNTs) with uniform wall thickness were synthesized by a solid-liquid reaction route. Calcium carbide block and carbon tetrachloride as double carbon sources were enclosed in a 100ml stainless steel autoclave at 400°C for 8 hours. The fabricated products were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and Transmission electron microscope (TEM). The research results indicate that the synthesized CNTs have lengths on the order of 10μm and external diameters in the range of 120-200nm. The nanotubes are typically the uniform inner diameters of 70nm and grow in the same direction. The growth mechanism is simply discussed.

Surface transformations of carbon (graphene, graphite, diamond, carbide), deposited on polycrystalline nickel by hot filaments chemical vapour deposition

The deposition of carbon has been studied at high temperature on polycrystalline nickel by hot filaments activated chemical vapor deposition (HFCVD). The sequences of carbon deposition are studied by surface analyses: Auger electron spectroscopy (AES), electron loss spectroscopy (ELS), X-ray photoelectron spectroscopy (XPS) in a chamber directly connected to the growth chamber. A general scale law of the (C/Ni) intensity lines is obtained with a reduced time. Both, shape analysis of the AES C KVV line and the C1s relative intensity suggest a three-step process: first formation of graphene and a highly graphitic layer, then multiphase formation with graphitic, carbidic and diamond-like carbon and finally at a critical temperature that strongly depends on the pretreatment of the polycrystalline nickel surface, a rapid transition to diamond island formation. Whatever the substrate diamond is always the final product and some graphene layers the initial product. Moreover it is possible to stabilize a few graphene layers at the initial sequences of carbon deposition. The duration of this stabilization step is strongly depending however on the pre-treatment of the Ni surface.

Co-Deposition of Binary Particles during Slip Casting Process

Co-deposition of silicon carbide particles and carbon (or carbon sources) particles is essential for preparation of reaction bonded silicon carbide (RBSC) products by slip casting. The way of co-depositing of silicon carbide particles and carbon particles during slip casting process, and the influence of composition of raw particles on particle co-depositing in green bodies were studied. The experiment results show: 1.Co-deposition of binary particles is greatly affected by particle size distribution, and large proportion of rigid SiC particles increases the difficulty in demoulding procedure because of small shrinkage; 2. Dispersants in deposited cake trend to enrich at the surface in contact with mould wall, while this enrichment of dispersant has little effect on mechanical performance of RBSC products; 3. Sharp edges on surface of raw particles could result to friction among particles, which afford strength to green bodies but prevent particles packing more closely.

Preparation and characterization of one-dimensional SiC–CNT composite nanotubes

One-dimensional silicon carbide–carbon nanotube composite was fabricated using a direct solid reaction process between pure silicon powders and carbon nanotubes at temperatures ranging from 1300 to 1400 °C. Scanning electron microscopy, X-ray diffraction, Raman scattering, and cathodoluminescence techniques were used to characterize their structures. The as-prepared composite products have shown pronounced luminescent properties with two emission bands centered at 2.3 eV and 2.9 eV by room-temperature cathodoluminescence.

Experimental determination of carbon isotope fractionation between iron carbide melt and carbon: 12C-enriched carbon in the Earths core?

Experimental determination of carbon isotope fractionation between iron carbide melt and carbon: 12C-enriched carbon in the Earths core?

Morphological Studies on CNT Reinforced SiC/SiOC Composites

Carbon nanotubes (CNTs) have been grown on commercially available silicon carbide (SiC) fabric by the catalytic chemical vapour deposition (CCVD) technique. These CNT coated SiC fabrics were used to develop Silicon Carbide–Carbon Nanotube–Silicon oxy Carbide matrix composites (SiC/CNTs/SiOC) by sol gel technique. Silicon oxy Carbide refers to carbon containing silicates wherein oxygen and carbon atoms share bonds with silicon in the amorphous network structure. In this approach, alkyl-substituted silicon alkoxides, which are molecular precursors containing oxygen and carbon functionalities on the silicon, are hydrolyzed and condensed in the presence of sucrose, which provides excess of carbon to bond into the silicon alkoxide network during hydrolysis. A low-temperature (1000 °C) heat-treatment of the gel creates a glassy silicate material whose molecular structure consists of an oxygen/carbon anionic network. The microstructures of these hybrid materials and their composites have been studied using scanning electron microscope (SEM), transmission electron microscope (TEM) and Raman spectroscope.

Spark plasma sintered tantalum carbide–carbon nanotube composite: Effect of pressure, carbon nanotube length and dispersion technique on microstructure and mechanical properties

TaC–4wt.% CNT composites were synthesized using spark plasma sintering. Two kinds of CNTs, having long (10–20μm) and short (1–3μm) length, were dispersed by wet chemistry and spray drying techniques respectively. Spark plasma sintering was carried out at 1850°C at pressures of 100, 255 and 363MPa. Addition of CNTs leads to an increase in the density of 100MPa sample from 89% to 95%. Short CNTs are more effective in increasing the density of the composites whereas long CNTs are more effective grain growth inhibitors. The longer CNTs are more effective in increasing the fracture toughness and an increase up to 60% was observed for 363MPa sample. Hardness and elastic modulus are found to increase by 22% and 18% respectively for 100MPa samples by addition of long CNTs. Raman spectroscopy, SEM and TEM images indicated that the CNTs were getting transformed into flaky graphitic structures at pressure higher than 100MPa.

Parametric studies on iron–carbon composite nanoparticles synthesized by laser pyrolysis for increased passivation and high iron content

Iron/iron carbide core and carbon shell nanoparticles with improved magnetic properties were successfully synthesized by laser pyrolysis. As iron and carbon precursors, iron pentacarbonyl and pure or argon-diluted acetylene/ethylene mixtures, respectively, were used. The aim of the present optimization is the improvement of the magnetic properties of the nanomaterials by the increase of the iron percent in powders simultaneously to the maintaining of the protective character of the carbon coverage of nanoparticles. The chemical content and the crystalline structure were monitored by EDX, XRD and TEM techniques. In the first study, the content of acetylene as carbon source was diminished from 75% to 0%. Consequently the percent iron increased from 10 at.% to 28 at.% while oxygen remained relatively constant (around 5 at.%). In the second step, only diluted ethylene was used (maximum 87.5 vol.% Ar). In this case, an increase of iron to 46 at.% is observed. An optimum 50% carbon source dilution was found. Above this value, the carbon content increases and below it, superficial oxidation increases through the diminishing of the carbon shell. The magnetic properties and the Fe phase composition of the Fe–C samples were analyzed by temperature dependent Mössbauer spectroscopy.

Titanium carbide/carbon composite nanofibers prepared by a plasma process

The incorporation of metal or metal carbide nanoparticles into carbon nanofibers modifiestheir properties and enlarges their field of application. The purpose of this work is to reporta new non-catalytic and easy method to prepare organized metal carbide–carbon compositenanofibers on nanopatterned silicon substrates prepared by laser interference lithographycoupled with deep reactive ion etching. Titanium carbide–carbon composite nanofiberswere grown on the top of the silicon lines parallel to the substrate by a hybrid plasmaprocess combining physical vapor deposition and plasma enhanced chemical vapordeposition. The prepared nanofibers were analyzed by scanning electron microscopy,x-ray photoelectron spectroscopy, Raman spectroscopy and transmission electronmicroscopy. We demonstrate that the shape, microstructure and the chemicalcomposition of the as-grown nanofibers can be tuned by changing the plasma conditions.

Optical and structural properties of silicon carbon nitride thin films deposited by reactive pulsed laser ablation

Silicon carbide and silicon carbon nitride thin films were grown by pulsed laser ablation of SiC targets in vacuum or in the presence of a controlled N2 atmosphere. The influence of the substrate temperature and of the N2 partial pressure on the optical and structural properties of the samples were investigated by means of Fourier transform infrared (FTIR), Raman, X-ray photoelectron and ellipsometric spectroscopies. Samples deposited in vacuum showed a nearly 1:1 stoichiometry, thus preserving the target composition. In vacuum, by increasing the substrate temperature, a better crystalline quality of the films was observed from both FTIR and Raman spectroscopy. A nitrogen content up to about 20.8% was achieved performing the deposition process in the presence of an N2 atmosphere of 54 Pa. A widening of the optical band gap as a function of the nitrogen content was observed, together with a progressive decrease in the absorption coefficient and in the index of refraction values.