Showing papers on "Carbide published in 2016"

Highly Conductive Optical Quality Solution-Processed Films of 2D Titanium Carbide

Abstract: MXenes comprise a new class of solution-dispersable, 2D nanomaterials formed from transition metal carbides and nitrides such as Ti3C2. Here, it is shown that 2D Ti3C2 can be assembled from aqueous solutions into optical quality, nanometer thin films that, at 6500 S cm−1, surpass the conductivity of other solution-processed 2D materials, while simultaneously transmitting >97% of visible light per-nanometer thickness. It is shown that this high conductivity is due to a metal-like free-electron density as well as a high degree of coplanar alignment of individual nanosheets achieved through spincasting. Consequently, the spincast films exhibit conductivity over a macroscopic scale that is comparable to the intrinsic conductivity of the constituent 2D sheets. Additionally, optical characterization over the ultraviolet-to-near-infrared range reveals the onset of free-electron plasma oscillations above 1130 nm. Ti3C2 is therefore a potential building block for plasmonic applications at near-infrared wavelengths and constitutes the first example of a new class of solution-processed, carbide-based 2D optoelectronic materials.

Self-assembly of noble metal monolayers on transition metal carbide nanoparticle catalysts

Abstract: One approach for increasing the activity of precious metals in catalysis is to coat them onto less expensive earth-abundant transition metal cores such as nickel, but often these structures alloy and deactivate during reactions. Hunt et al. synthesized several types of transition metal carbide nanoparticles coated with atomically thin precious-metal shells. Titanium-doped tungsten carbide nanoparticles with platinum-ruthenium shells were highly active for methanol electrooxidation, stable over 10,000 cycles, and resistant to CO deactivation. Science , this issue p. [974][1] [1]: /lookup/doi/10.1126/science.aad8471

Porous Two‐Dimensional Transition Metal Carbide (MXene) Flakes for High‐Performance Li‐Ion Storage

Abstract: Herein we develop a chemical etching method to produce porous two-dimensional (2D) Ti3C2Tx MXenes at room temperature in aqueous solutions. The as-produced porous Ti3C2Tx (p-Ti3C2Tx) have larger sp ...

A Two-Dimensional Zirconium Carbide by Selective Etching of Al3C3 from Nanolaminated Zr3Al3C5.

Abstract: The room-temperature synthesis of a new two-dimensional (2D) zirconium-containing carbide, Zr3C2Tz MXene is presented. In contrast to traditional preparation of MXene, the layered ternary Zr3Al3C5 material instead of MAX phases is used as source under hydrofluoric acid treatment. The structural, mechanical, and electronic properties of the synthesized 2D carbide are investigated, combined with first-principles density functional calculations. A comparative study on the structrual stability of our obtained 2D Zr3C2Tz and Ti3C2Tz MXenes at elevated temperatures is performed. The obtained 2D Zr3C2Tz exhibits relatively better ability to maintain 2D nature and strucural integrity compared to Ti-based Mxene. The difference in structural stability under high temperature condition is explained by a theoretical investigation on binding energy.

Ultrasmall and phase-pure W 2 C nanoparticles for efficient electrocatalytic and photoelectrochemical hydrogen evolution

Abstract: Earlier research has been primarily focused on WC as one of the most promising earth-abundant electrocatalysts for hydrogen evolution reaction (HER), whereas the other compound in this carbide family—W2C—has received far less attention. Our theoretical calculations suggest that such a focus is misplaced and W2C is potentially more HER-active than WC. Nevertheless, the preparation of phase pure and sintering-free W2C nanostructures represents a formidable challenge. Here we develop an improved carburization method and successfully prepare ultrasmall and phase-pure W2C nanoparticles. When evaluated for HER electrocatalysis, W2C nanoparticles exhibit a small onset overpotential of 50 mV, a Tafel slope of 45 mV dec−1 and outstanding long-term cycling stability, which are dramatically improved over all existing WC-based materials. In addition, the integration of W2C nanoparticles with p-type Si nanowires enables highly active and sustainable solar-driven hydrogen production. Our results highlight the great potential of this traditionally non-popular material in HER electrocatalysis. Tungsten carbide has yet to live up to its long-believed potential as a replacement for precious metal electrocatalysts. Here, Li and co-workers demonstrate that ditungsten carbide in the form of ultrasmall, phase-pure nanoparticles is a better candidate for the hydrogen evolution reaction.

A dual-metal–organic-framework derived electrocatalyst for oxygen reduction

Abstract: High-performance electrocatalysts for the oxygen reduction reaction are indispensable in many electrochemical energy storage and conversion technologies. However, the lack of efficient and inexpensive catalysts or catalyst systems that can compete with noble metal catalysts hinders their large-scale industrial applications. As an important class of porous materials, metal–organic frameworks (MOFs) with systematically tailored structures and compositions have recently been suggested as promising precursors for the preparation of diverse functional materials. Here we report a dual-MOF confined-pyrolysis approach for the preparation of iron carbide nanoparticle-embedded carbon nanotube assemblies. Starting from a novel MOF-in-MOF precursor consisting of a Zn-based MOF polyhedron host and many engulfed Fe-based MOF nanorods, a complex structured composite material constructed from iron carbide nanocrystallite-embedded carbon nanotubes encapsulated in a porous carbon matrix is successfully prepared. We further demonstrate that the as-derived composite material manifests remarkable electrocatalytic performance for the oxygen reduction reaction in an alkaline electrolyte. The present strategy significantly expands the toolbox for the design and synthesis of MOF-derived functional materials for a wide range of applications.

3D Metal Carbide@Mesoporous Carbon Hybrid Architecture as a New Polysulfide Reservoir for Lithium-Sulfur Batteries

Abstract: 3D metal carbide@mesoporous carbon hybrid architecture (Ti3C2Tx@Meso-C, TX ≈ FxOy) is synthesised and applied as cathode material hosts for lithium-sulfur batteries Exfoliated-metal carbide (Ti3C2Tx) nanosheets have high electronic conductivity and contain rich functional groups for effective trapping of polysulfides Mesoporous carbon with a robust porous structure provides sufficient spaces for loading sulfur and effectively cushion the volumetric expansion of sulfur cathodes Theoretical calculations have confirmed that metal carbide can absorb sulfur and polysulfides, therefore extending the cycling performance The Ti3C2Tx@Meso-C/S cathodes have achieved a high capacity of 12258 mAh g−1 and more than 300 cycles at the C/2 current rate The Ti3C2Tx@Meso-C hybrid architecture is a promising cathode host material for lithium-sulfur batteries

Transition metal carbide-based materials: synthesis and applications in electrochemical energy storage

Abstract: Transition metal carbides have attracted vast interest over the past years due to their appealing properties such as high conductivity, high chemical stability and thermal stability. With the rapid development of nanotechnology, more and more novel transition metal carbide structures have been prepared and investigated in various areas. In the present review, we summarize the current very recent progress in the synthesis and applications of transition metal carbides in the fields of capacitors and batteries. We also present critical issues, challenges, and perspectives with the hope of providing a fuller understanding of the associated electrochemical processes. Such an understanding is critical for tailoring and designing transition metal carbides with desired activity and stability.

Two-Dimensional Phosphorus Carbide: Competition between sp2 and sp3 Bonding

Abstract: We propose previously unknown allotropes of phosphorus carbide (PC) in the stable shape of an atomically thin layer. Different stable geometries, which result from the competition between sp2 bonding found in graphitic C and sp3 bonding found in black P, may be mapped onto 2D tiling patterns that simplify categorizing of the structures. Depending on the category, we identify 2D-PC structures that can be metallic, semimetallic with an anisotropic Dirac cone, or direct-gap semiconductors with their gap tunable by in-layer strain.

Activating earth-abundant electrocatalysts for efficient, low-cost hydrogen evolution/oxidation: sub-monolayer platinum coatings on titanium tungsten carbide nanoparticles

Abstract: Most earth-abundant electrocatalysts suffer from negligible activity for the hydrogen oxidation reaction (HOR) and significant overpotentials for the hydrogen evolution reaction (HER) in acidic media. We designed earth-abundant, carbon-supported titanium tungsten carbide (TixW1−xC) nanoparticles decorated with surface Pt coatings ranging from the “single-atom” to the two-monolayer regime. Reactivity studies demonstrated that sub-monolayer Pt coverages are optimal and could activate the exposed metal carbide sites for both HER and HOR at low overpotentials. Specifically, a 0.25 monolayer coverage of Pt improved the exchange current density of Ti0.2W0.8C by more than three orders of magnitude. This catalyst outperformed traditional Pt/C by a factor of 13 on a Pt mass basis, allowing for over a 96% reduction in Pt loadings. Deactivation was not observed after 10 000 cycles between −50 and +600 mV vs. RHE in 1.0 M HClO4, and activity was maintained after 140 000 catalytic turnovers. A technoeconomic analysis revealed that over the catalyst lifetime, this new architecture could reduce materials and energy costs by a factor of 6 compared to state-of-the-art earth-abundant catalysts and a factor of 12 compared to Pt/C.

Influence of B4C particle reinforcement on mechanical and machining properties of Al6061/B4C composites

Abstract: This study investigates the mechanical and machinability properties of the aluminum 6061 reinforced with boron carbide (B4C). Four aluminum 6061 composite specimens reinforced with 5 wt%, 10 wt%, 15 wt%, and 20 wt% B4C were fabricated using a powder metallurgy and hot-extrusion method. The composite samples were investigated to elucidate the influence of different weight fractions of B4C reinforcement content on the hardness, fracture toughness, tensile strength, transverse rupture strength (TRS) and milling properties of the resulting composites. The milling tests were performed based on the Taguchi mixed-orthogonal-array for experiments, L16 (44 × 21), to determine the effect of B4C content on surface quality and energy consumption for different cutting parameters under dry- and compressed-air cooling and using an uncoated carbide insert. The results reveal that the B4C particles are uniformly distributed in the matrix and that the fracture toughness decreases and the hardness increases as the weight fraction of the reinforcement increases. The highest tensile and transverse rupture strength are for Al6061/5 wt% B4C and Al6061 reinforced with 10 wt% B4C composite material has the best fracture toughness from among the specimens measured. At higher milling speed and lower cutting feed and under dry machining conditions, an excellent surface quality is obtained after milling all composites materials and the surface finish improves with increasing B4C content in the matrix. The power consumption and surface roughness increases when cooling with compressed air.

Highly active Au/δ-MoC and Cu/δ-MoC catalysts for the conversion of CO2: The metal/C ratio as a key factor defining activity, selectivity, and stability

Abstract: The ever growing increase of CO2 concentration in the atmosphere is one of the main causes of global warming. Thus, CO2 activation and conversion toward valuable added compounds is a major scientific challenge. A new set of Au/δ-MoC and Cu/δ-MoC catalysts exhibits high activity, selectivity, and stability for the reduction of CO2 to CO with some subsequent selective hydrogenation toward methanol. Sophisticated experiments under controlled conditions and calculations based on density functional theory have been used to study the unique behavior of these systems. A detailed comparison of the behavior of Au/β-Mo2C and Au/δ-MoC catalysts provides evidence of the impact of the metal/carbon ratio in the carbide on the performance of the catalysts. The present results show that this ratio governs the chemical behavior of the carbide and the properties of the admetal, up to the point of being able to switch the rate and mechanism of the process for CO2 conversion. A control of the metal/carbon ratio paves the roa...

Boron carbide reinforced aluminium matrix composite: Physical, mechanical characterization and mathematical modelling

Abstract: This paper investigates the manufacturing of aluminium-boron carbide composites using the stir casting method. Mechanical and physical properties tests to obtain hardness, ultimate tensile strength (UTS) and density are performed after solidification of specimens. The results show that hardness and tensile strength of aluminium based composite are higher than monolithic metal. Increasing the volume fraction of B4C, enhances the tensile strength and hardness of the composite; however over-loading of B4C caused particle agglomeration, rejection from molten metal and migration to slag. This phenomenon decreases the tensile strength and hardness of the aluminium based composite samples cast at 800 °C. For Al-15 vol% B4C samples, the ultimate tensile strength and Vickers hardness of the samples that were cast at 1000 °C, are the highest among all composites. To predict the mechanical properties of aluminium matrix composites, two key prediction modelling methods including Neural Network learned by Levenberg-Marquardt Algorithm (NN-LMA) and Thin Plate Spline (TPS) models are constructed based on experimental data. Although the results revealed that both mathematical models of mechanical properties of Al-B4C are reliable with a high level of accuracy, the TPS models predict the hardness and tensile strength values with less error compared to NN-LMA models.

Magnetically Induced Continuous CO2 Hydrogenation Using Composite Iron Carbide Nanoparticles of Exceptionally High Heating Power

Abstract: The use of magnetic nanoparticles to convert electromagnetic energy into heat is known to be a key strategy for numerous biomedical applications but is also an approach of growing interest in the field of catalysis. The heating efficiency of magnetic nanoparticles is limited by the poor magnetic properties of most of them. Here we show that the new generation of iron carbide nanoparticles of controlled size and with over 80 % crystalline Fe2.2 C leads to exceptional heating properties, which are much better than the heating properties of currently available nanoparticles. Associated to catalytic metals (Ni, Ru), iron carbide nanoparticles submitted to magnetic excitation very efficiently catalyze CO2 hydrogenation in a dedicated continuous-flow reactor. Hence, we demonstrate that the concept of magnetically induced heterogeneous catalysis can be successfully applied to methanation of CO2 and represents an approach of strategic interest in the context of intermittent energy storage and CO2 recovery.

First-principles investigation of hydrogen interaction with TiC precipitates in α -Fe

Abstract: A correct description of hydrogen diffusion and trapping is the prerequisite for an understanding of the phenomenon of hydrogen embrittlement. In this study, we carried out extensive first-principles calculations based on density functional theory to investigate the interaction of H with TiC precipitates that are assumed to be efficient trapping agents mitigating HE in advanced high-strength steels. We found that there exists a large variety of possible trapping sites for H associated with different types of interfaces between the TiC particle and the Fe matrix, with misfit dislocations and other defects at these interfaces, and with carbon vacancies in TiC. The most efficient trapping by more than 1 eV occurs at carbon vacancies in the interior of TiC particles. However, these traps are difficult to populate at ambient temperatures since the energy barrier for H entering the particles is high. H trapping at the semicoherent interfaces between the TiC particles and the Fe matrix is moderate, ranging from 0.3 to 0.5 eV. However, a sufficiently large concentration of the carbide particles can significantly reduce the amount of H segregated at dislocation cores in the Fe matrix. A systematic comparison of the obtained theoretical results with available experimental observations reveals a consistent picture of hydrogen trapping at the TiC particles that is expected to be qualitatively valid also for other carbide precipitates with the rock-salt crystal structure.

Graphene-reinforced aluminum matrix composites prepared by spark plasma sintering

Abstract: Graphene-reinforced 7055 aluminum alloy composites with different contents of graphene were prepared by spark plasma sintering (SPS). The structure and mechanical properties of the composites were investigated. Testing results show that the hardness, compressive strength, and yield strength of the composites are improved with the addition of 1wt% graphene. A clean, strong interface is formed between the metal matrix and graphene via metallurgical bonding on atomic scale. Harmful aluminum carbide (Al4C3) is not formed during SPS processing. Further addition of graphene (above 1wt%) results in the deterioration in mechanical properties of the composites. The agglomeration of graphene plates is exacerbated with increasing graphene content, which is the main reason for this deterioration.

Modes of failure of cemented tungsten carbide tool bits (WC/Co): A study of wear parts

Abstract: Cemented tungsten carbide (WC/Co) holds a successful past as abrasion and wear-resistant components in mining industries for their wonderful combination of very high hardness and good fracture toughness as well as comparatively extraordinary wear resistance. Generally, the tungsten carbide drill bits/blades are used in rock drilling, mineral cutting, gas oil drilling and even tunneling industries. The service environments of the WC/Co tool bits are terribly complicated because of totally different hardness of the drilling objectives at different working conditions, consequence various movement patterns of the WC/Co drill bits. As a result, the failure mechanism of the tool bits is quite different. The mechanism of hole drilling and different mining operation and processes, a tool-bit gradually degrades till it breaks at the end of its life. Replacing a drill-bit once its breakage is often expensive in certain special applications. At the same time an early tool replacement decision could lead to cause of lower tools life. This type of claims is marking the ways that modify the accurate prediction of tool failures. In circumstances, where degradation signals using the appropriate features are utilized to make the tool replacement decision. Intensive investigation of the performance of tungsten carbide tools in hard metal industries and tool industries is being conducted worldwide. Tungsten carbide alloyed with cobalt (WC/Co) shows unique characteristics like high strength at elevated temperature and high mechanical and chemical resistance that makes carbide tools appropriate for cutting, drilling, mining and machining operation. A whole failure study is revealed within the paper. This study also discusses the failure mode of a tungsten carbide tools, its prediction and remedies.

The effects of cryogenic-treated carbide tools on tool wear and surface roughness of turning of Hastelloy C22 based on Taguchi method

Abstract: In this study, Taguchi method has been applied to evaluate the effect of cryogenically treated tools in turning of Hastelloy C22 super alloy on surface roughness. The optimum parameters (cryogenic treatment, cutting speed, and feed rate) of turning were determined by using the Taguchi experimental design method. In Taguchi method, L9 orthogonal array has been used to determine the signal noise (S/N) ratio. Analysis of ANOVA was carried out to identify the significant factors affecting surface roughness. The statistical analysis indicated that feed rate, with a contribution percentage as high as 87.64 %, had the most dominant effect on machining performance, followed by the cryo-treated tools treatment and cutting speed, respectively. The confirmation tests indicated that it is possible to improve surface roughness significantly by using the Taguchi method. Surface roughness was improved by 28.3 and 72.3 % by shallow (CT1) cryogenic treatment and deep cryogenic treatment (CT2) applied on cementite carbide tools (UT). It found that wear resistance of tungsten carbide insert was increased by shallow and deep cryogenic treatments.

Biomass-Derived Porous Fe3C/Tungsten Carbide/Graphitic Carbon Nanocomposite for Efficient Electrocatalysis of Oxygen Reduction

Abstract: The oxygen-reduction reaction (ORR) draws an extensive attention in many applications, and there is a growing interest to develop effective ORR electrocatalysts. Iron carbide (Fe3C) is a promising alternative to noble metals (e.g., platinum), but its performances need further improvement, and the real role of the Fe3C phase remains unclear. In this study, we synthesize Fe3C/tungsten carbide/graphitic carbon (Fe3C/WC/GC) nanocomposites, with waste biomass (i.e., pomelo peel) serving as carbon source, using a facile, one-step carbon thermal-reduction method. The nanocomposite is characterized by a porous structure consisting of uniform Fe3C nanoparticles encased by graphitic carbon (GC) layers with highly dispersed nanosized WC. The Fe3C provides the active sites for ORR, while the graphitic layers and WC nanoparticles can stibilize the Fe3C surface, preventing it from dissociation in the electrolyte. The Fe3C/WC/GC nanocomposite is highly active, selective, and stable toward four-electron ORR in pH-neutral...

Ceramic coating for corrosion resistance of nuclear fuel cladding

Abstract: Coating used for radioactive fuel or a structural component in radioactive fuel reactors, e.g., nuclear fuel cladding alloys, can include a ternary monolithic coating or multiple layers of one or more layers of TiAlN TiZrN, TiCrN, TiNbN and/or CrN, ZrN, NbN, TiN, TaN, HfN. TiHfN, TaHfN, TaNbN, or mixed combinations and/or CrN, ZrN, NbN, TiN, TaN, Si3N4, and/or HfN. In addition, one or more layers can be comprised of a nitride, oxide, or carbide or mixed combination (i.e., carbonides, oxynitrides, oxycarbides, etc.) from Ti, Al, Zr, Cr, Si, Nb, Hf, or mixed combination (i.e., TiAlC 1-x N x ). The multilayer coating can be doped with a dopant.