Showing papers on "Carbide published in 2013"

Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide

Abstract: The intercalation of ions into layered compounds has long been exploited in energy storage devices such as batteries and electrochemical capacitors However, few host materials are known for ions much larger than lithium We demonstrate the spontaneous intercalation of cations from aqueous salt solutions between two-dimensional (2D) Ti3C2 MXene layers MXenes combine 2D conductive carbide layers with a hydrophilic, primarily hydroxyl-terminated surface A variety of cations, including Na+, K+, NH4+, Mg2+, and Al3+, can also be intercalated electrochemically, offering capacitance in excess of 300 farads per cubic centimeter (much higher than that of porous carbons) This study provides a basis for exploring a large family of 2D carbides and carbonitrides in electrochemical energy storage applications using single- and multivalent ions

Organic light emitting diode

Abstract: An organic light-emitting diode comprising a first (102) and second barrier coating (110),wherein the barrier coating is selected from (i) amorphous silicon carbide, (ii) an amorphous silicon carbide alloy comprising at least one element selected from F, N, B, and P, (iii) hydrogenated silicon oxycarbide, (iv) a coating prepared by (a) curing a hydrogen silsesquioxane resin with an electron beam or (b) reacting a hydrogen silsesquioxane resin using a chemical vapor deposition process; and (v) a mutilayer combination of at least two of (i), (ii), (iii), and (iv).

Experimental and theoretical investigation of molybdenum carbide and nitride as catalysts for ammonia decomposition.

Abstract: Constant CO(x)-free H2 production from the catalytic decomposition of ammonia could be achieved over a high-surface-area molybdenum carbide catalyst prepared by a temperature-programmed reduction-carburization method. The fresh and used catalyst was characterized by N2 adsorption/desorption, powder X-ray diffraction, scanning and transmission electron microscopy, and electron energy-loss spectroscopy at different stages. Observed deactivation (in the first 15 h) of the high-surface-area carbide during the reaction was ascribed to considerable reduction of the specific surface area due to nitridation of the carbide under the reaction conditions. Theoretical calculations confirm that the N atoms tend to occupy subsurface sites, leading to the formation of nitride under an NH3 atmosphere. The relatively high rate of reaction (30 mmol/((g of cat.) min)) observed for the catalytic decomposition of NH3 is ascribed to highly energetic sites (twin boundaries, stacking faults, steps, and defects) which are observed in both the molybdenum carbide and nitride samples. The prevalence of such sites in the as-synthesized material results in a much higher H2 production rate in comparison with that for previously reported Mo-based catalysts.

Carbon Nanofiber Supported Transition‐Metal Carbide Catalysts for the Hydrodeoxygenation of Guaiacol

Abstract: Hydrodeoxygenation (HDO) studies over carbon nanofiber-supported (CNF) W2C and Mo2C catalysts were performed on guaiacol, a prototypical substrate to evaluate the potential of a catalyst for valorization of depolymerized lignin streams. Typical reactions were executed at 55 bar hydrogen pressure over a temperature range of 300–375?°C for 4 h in dodecane, using a batch autoclave system. Combined selectivities of up to 87 and 69?% to phenol and methylated phenolics were obtained at 375?°C for W2C/CNF and Mo2C/CNF at >99?% conversion, respectively. The molybdenum carbide-based catalyst showed a higher activity than W2C/CNF and yielded more completely deoxygenated aromatic products, such as benzene and toluene. Catalyst recycling experiments, performed with and without regeneration of the carbide phase, showed that the Mo2C/CNF catalyst was stable during reusability experiments. The most promising results were obtained with the Mo2C/CNF catalyst, as it showed a much higher activity and higher selectivity to phenolics compared to W2C/CNF.

Tungsten Carbide Nanoparticles as Efficient Cocatalysts for Photocatalytic Overall Water Splitting

Abstract: Tungsten carbide exhibits platinum-like behavior, which makes it an interesting potential substitute for noble metals in catalytic applications. Tungsten carbide nanocrystals (≈5 nm) are directly synthesized through the reaction of tungsten precursors with mesoporous graphitic C(3)N(4) (mpg-C(3)N(4)) as the reactive template in a flow of inert gas at high temperatures. Systematic experiments that vary the precursor compositions and temperatures used in the synthesis selectively generate different compositions and structures for the final nanocarbide (W(2)C or WC) products. Electrochemical measurements demonstrate that the WC phase with a high surface area exhibits both high activity and stability in hydrogen evolution over a wide pH range. The WC sample also shows excellent hydrogen oxidation activity, whereas its activity in oxygen reduction is poor. These tungsten carbides are successful cocatalysts for overall water splitting and give H(2) and O(2) in a stoichiometric ratio from H(2)O decomposition when supported on a Na-doped SrTiO(3) photocatalyst. Herein, we present tungsten carbide (on a small scale) as a promising and durable catalyst substitute for platinum and other scarce noble-metal catalysts in catalytic reaction systems used for renewable energy generation.

Structure and Electrochemical Performance of Carbide‐Derived Carbon Nanopowders

Abstract: Microporous carbon materials are widely used in gas storage, sorbents, supercapacitor electrodes, water desalination, and catalyst supports. While these microporous carbons usually have a particle size in the 1–100 μm range, here the synthesis of porous carbide‐derived carbon (CDC) with particle diameters around 30 nm by extraction of titanium from nanometer‐sized titanium carbide (TiC) powder at temperatures of 200 °C and above is reported. Nanometer‐sized CDCs prepared at 200–400 °C show a disordered structure and the presence of CN sp1 bonds. Above 400 °C, the CN bond disappears with the structure transition to disordered carbon similar to that observed after synthesis from carbide micropowders. Compared to CDCs produced from micrometer‐sized TiC, nano‐CDC has a broader pore size distribution due to interparticle porosity and a large contribution from the surface layers. The material shows excellent electrochemical performance due to its easily accessible pores and a large specific surface area.

Comparison of Tungsten and Molybdenum Carbide Catalysts for the Hydrodeoxygenation of Oleic Acid

Abstract: Group 6 (W, Mo) metal carbide catalysts are promising alternatives to hydrodesulfurization (NiMo, CoMo) catalysts and group 10 (Pd) type catalysts in the deoxygenation of vegetable fats/oils. Herein, we report a comparison of carbon nanofiber-supported W2C and Mo2C catalysts on activity, selectivity, and stability for the hydrodeoxygenation of oleic acid to evaluate the catalytic potential for the upgrading of fat/oil feeds. W2C/CNF was more selective toward olefins, whereas Mo2C/CNF was more selective toward paraffins. This was related to the hydrogenation activities of the respective metal carbides. Mo2C/CNF showed higher activity and stability compared with W2C/CNF.

Metal Oxide/Carbide/Carbon Nanocomposites: In Situ Synthesis, Characterization, Calculation, and their Application as an Efficient Counter Electrode Catalyst for Dye-Sensitized Solar Cells

Abstract: This paper describes the metal oxide/carbide/carbon nanocomposites and in situ synthesis, characterization, calcn. and their application as efficient counter electrode catalyst for dye-sensitized solar cells. The poor adhesion between carbon-based materials and fluorine-doped tin oxide (FTO) substrate limits the application of counter electrode (CEs) in dye-sensitized solar cells (DSC).

Method for forming conformal carbon films, structures and devices including a conformal carbon film, and system of forming same

Abstract: Methods of forming carbon films, structures and devices including the carbon films, and systems for forming the carbon films are disclosed. A method includes depositing a metal carbide film using atomic layer deposition (ALD). Metal from the metal carbide film is removed from the metal carbide film to form a carbon film. Because the films are formed using ALD, the films can be relatively conformal and can have relatively uniform thickness over the surface of a substrate.

Silane and borane treatments for titanium carbide films

Abstract: Methods of treating metal-containing thin films, such as films comprising titanium carbide, with a silane/borane agent are provided. In some embodiments a film comprising titanium carbide is deposited on a substrate by an atomic layer deposition (ALD) process. The process may include a plurality of deposition cycles involving alternating and sequential pulses of a first source chemical that comprises titanium and at least one halide ligand, a second source chemical comprising metal and carbon, wherein the metal and the carbon from the second source chemical are incorporated into the thin film, and a third source chemical, wherein the third source chemical is a silane or borane that at least partially reduces oxidized portions of the titanium carbide layer formed by the first and second source chemicals. In some embodiments treatment forms a capping layer on the metal carbide film.

Low-cost industrially available molybdenum boride and carbide as “platinum-like” catalysts for the hydrogen evolution reaction in biphasic liquid systems

Abstract: Rarely reported low-cost molybdenum boride and carbide microparticles, both of which are available in abundant quantities due to their widespread use in industry, adsorb at aqueous acid–1,2-dichloroethane interfaces and efficiently catalyse the hydrogen evolution reaction in the presence of the organic electron donor – decamethylferrocene. Kinetic studies monitoring biphasic reactions by UV/vis spectroscopy, and further evidence provided by gas chromatography, highlight (a) their superior rates of catalysis relative to other industrially significant transition metal carbides and silicides, as well as a main group refractory compound, and (b) their highly comparable rates of catalysis to Pt microparticles of similar dimensions. Insight into the catalytic processes occurring for each adsorbed microparticle was obtained by voltammetry at the liquid–liquid interface.

Tungsten Carbides: Structure, Properties and Application in Hardmetals

Abstract: Introduction.- Phases and Equilibria in the W - C and W - Co - C Systems.- Ordering of Tungsten Carbides.- Nanocrystalline Tungsten Carbide.- Hardmetals WC - Co Based on Nanocrystalline Powders of Tungsten Carbide WC.

New insight on the solidification path of an alloy 625 weld overlay

Abstract: Ni-based alloys are a special class of engineering material with excellent corrosion resistance in harsh environments. However, microstructural changes due to the solidification, may result in solidification cracks and reduction in the corrosion resistance. Knowing the microchemical and microstructural evolutions during the solidification of these alloys is essential for the understanding of the relationship between the metallurgical aspects and the properties. This research presents a new insight on the solidification path of alloy 625 weld metals deposited by the TIG cold wire process on the C–Mn steel plates. After the welding, samples having been extracted and evaluated by the scanning electron microscope, transmission electron microscopy and energy dispersive X-ray spectroscopy techniques. The results showed the presence of two types of secondary phases, identified as Laves phase and complex nitride/carbide particles. Due to the presence of nitrides particles, stable in the solid state during the melting of the alloy, during the solidification it is noted the occurrence of a complex nitride/carbide precipitation. This implies in a new route to explain the solidification of the aforementioned alloy.

Relationships between feedstock structure, particle parameter, coating deposition, microstructure and properties for thermally sprayed conventional and nanostructured WC–Co

Abstract: Thermal spray cermet based on tungsten carbide has been widely used due to its excellent wear resistance. The features of both carbide and binder phases are essential factors which determine the performance of cermet coating. The thermal cycling of WC–Co spray particles up to a temperature over the melting point of binder phase during thermal spraying involves the decarburization of carbide. The decarburization of carbide becomes severe with the decrease of carbide particle size, which makes it difficult yet to deposit a dense nanostructured WC–Co with a limited decarburization by thermal spraying. The decarburization not only reduces the wear-resistant phase but also leads to the formation of brittle Co–W–C ternary binder phase. Moreover, the limited decarburization involves the deposition of spray particle at a solid–liquid two-phase state with carbides at a solid state and metal binder in a molten state during spraying. High velocity impact of two-phase droplets as in high velocity oxy-fuel spraying (HVOF) results in the formation of a dense cermet coating and on the other hand leads to the possibility of rebounding of wear-resistant solid carbide particles. In this review article, the microstructural features of thermal spray WC–Co are examined based on the effect of the decarburization of tungsten carbide. The decarburization mechanisms of tungsten carbide are discussed for the control of decarburization of carbide. The effects of carbide particle size on the deposition process, adhesion of HVOF coating and wear performance of WC–Co coating as well are examined based on a solid–liquid two-phase deposition process. It is demonstrated that WC–Co cermet with different sizes of WC particles should be deposited by different processes. Moreover, the deposition of nanostructured WC–Co by thermal spraying and recent advances on the cold spraying of nanostructured WC–Co are introduced. The cold spraying with the proper design of spray powders will become promising process to deposit nanostructured WC–Co with pure cobalt binder with the hardness comparable to a sintered bulk and even high toughness of 18.9 MPa m1/2. The pure metastable metal binder phase evolved in the deposit makes it possible to deposit hard cermet through healing the non-bonded interfaces in the coating by post-spray annealing.

Microscopic View on a Chemical Vapor Deposition Route to Boron-Doped Graphene Nanostructures

Abstract: Single layer boron-doped graphene layers have been grown on polycrystalline copper foils by chemical vapor deposition using methane and diborane as carbon and boron sources, respectively. Any attempt to deposit doped layers in one-step has been fruitless, the reason being the formation of very reactive boron species as a consequence of diborane decomposition on the Cu surface, which leads to disordered nonstoichiometric carbides. However, a two-step procedure has been optimized: as a first step, the surface is seeded with pure graphene islands, while the boron source is activated only in a second stage. In this case, the nonstochiometric boron carbides formed on the bare copper areas between preseeded graphene patches can be exploited to easily release boron, which diffuses from the peripheral areas inward of graphene islands. The effective substitutional doping (of the order of about 1%) has been demonstrated by Raman and photoemission experiments. The electronic properties of doped layers have been char...

A review of cemented carbides for rock drilling: An old but still tough challenge in geo-engineering

Abstract: Cemented carbide is an old and well-known WC-based hardmetal, which has been widely applied in geo-engineering as drill buttons and various wear-resistant parts. In order to extend the service life of cemented carbide components and enhance their efficiency for rock drilling under various conditions, the recent research efforts have focused on their failure mechanisms and developing nanostructured, functionally graded and Co-free cemented carbides. With the advance in synthesizing nanosized powders and advent of electric field assisted fast sintering techniques, the consolidation of nanostructured and Co-free cemented carbides and even pure WC materials has been possible; and because of their high hardness and wear resistance, they are much promising in geo-engineering drilling. Functionally graded cemented carbide provides a combination of high wear resistance and toughness in a single component, which is also much favorable for geo-engineering drillers. In addition, by replacing the binder phase Co with Ni or carbide binder, and even without binder phase, the corrosion and oxidation of the resultant materials can be significantly improved without considerable deterioration of fracture toughness.

Microstructure and mechanical behavior of metal injection molded Ti–Nb binary alloys as biomedical material

Abstract: The application of titanium (Ti) based biomedical materials which are widely used at present, such as commercially pure titanium (CP-Ti) and Ti-6Al-4V, are limited by the mismatch of Young's modulus between the implant and the bones, the high costs of products, and the difficulty of producing complex shapes of materials by conventional methods. Niobium (Nb) is a non-toxic element with strong β stabilizing effect in Ti alloys, which makes Ti-Nb based alloys attractive for implant application. Metal injection molding (MIM) is a cost-efficient near-net shape process. Thus, it attracts growing interest for the processing of Ti and Ti alloys as biomaterial. In this investigation, metal injection molding was applied to the fabrication of a series of Ti-Nb binary alloys with niobium content ranging from 10wt% to 22wt%, and CP-Ti for comparison. Specimens were characterized by melt extraction, optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Titanium carbide formation was observed in all the as-sintered Ti-Nb binary alloys but not in the as-sintered CP-Ti. Selected area electron diffraction (SAED) patterns revealed that the carbides are Ti2C. It was found that with increasing niobium content from 0% to 22%, the porosity increased from about 1.6% to 5.8%, and the carbide area fraction increased from 0% to about 1.8% in the as-sintered samples. The effects of niobium content, porosity and titanium carbides on mechanical properties have been discussed. The as-sintered Ti-Nb specimens exhibited an excellent combination of high tensile strength and low Young's modulus, but relatively low ductility.