Showing papers on "Carbide published in 2020"
Book•
08 Jul 2020
TL;DR: In this article, the authors provide a thorough treatment of ultra-high temperature materials with melting (sublimation or decomposition) points around or over 2500 °C, including binary, ternary and multi-component systems.
Abstract: The series of books represents a thorough treatment of ultra-high temperature materials with melting (sublimation or decomposition) points around or over 2500 °C. In the third volume are included physical (structural, thermal, electromagnetic, optical, mechanical, nuclear) and chemical (more than 1100 binary, ternary and multi-component systems, including those used for materials design, data on solid-state diffusion, wettability, interaction with chemicals, gases and aqueous solutions) properties of titanium monocarbide TiC1–x, vanadium monocarbide VC1–x and related 2D-molecular (graphene-like) carbide MXenes, discovered and developed only in the last decade. TiC1–x and VC1–x are also widely applied in the general technological and engineering practice in a wide range of temperatures as parts of highly hard materials (alloys) and special steels. This book will be of interest to researchers, engineers, postgraduate, graduate and undergraduate students alike. For the named materials, readers/users are provided with the full qualitative and quantitative assessment, which is based on the latest updates in the field of fundamental physics, chemistry, nanotechnology, materials science, design and engineering.
111 citations
TL;DR: It is demonstrated that atomically thin Pt shells stabilize titanium tungsten carbide cores, even at highly oxidizing potentials.
Abstract: Core–shell particles with earth-abundant cores represent an effective design strategy for improving the performance of noble metal catalysts, while simultaneously reducing the content of expensive noble metals1–4. However, the structural and catalytic stabilities of these materials often suffer during the harsh conditions encountered in important reactions, such as the oxygen reduction reaction (ORR)3–5. Here, we demonstrate that atomically thin Pt shells stabilize titanium tungsten carbide cores, even at highly oxidizing potentials. In situ, time-resolved experiments showed how the Pt coating protects the normally labile core against oxidation and dissolution, and detailed microscopy studies revealed the dynamics of partially and fully coated core–shell nanoparticles during potential cycling. Particles with complete Pt coverage precisely maintained their core–shell structure and atomic composition during accelerated electrochemical ageing studies consisting of over 10,000 potential cycles. The exceptional durability of fully coated materials highlights the potential of core–shell architectures using earth-abundant transition metal carbide (TMC) and nitride (TMN) cores for future catalytic applications. Using core–shell particles represents an effective design strategy for improving the performance of noble metal catalysts, but their stabilities can suffer during reactions. Atomically thin Pt shells are shown to stabilize titanium tungsten carbide cores, even at highly oxidizing potentials.
108 citations
TL;DR: In this article, a high-entropy carbide ceramics (HECC) with a single-phase rock-salt structure was synthesized by spark plasma sintering, which was irradiated by 3-MeV Zr ions to 20 dpa at 25, 300, and 500°C.
104 citations
TL;DR: This work provides a feasible strategy to fabricate bimetallic carbides and explores their possibility as bifunctional catalysts toward overall water splitting through a facile metal-organic framework (MOF) derived method.
Abstract: Carbides are commonly regarded as efficient hydrogen evolution reaction (HER) catalysts, but their poor oxygen evolution reaction (OER) catalytic activities seriously limit their practical application in overall water splitting. Here, vertically aligned porous cobalt tungsten carbide nanosheet embedded in N-doped carbon matrix (Co6 W6 C@NC) is successfully constructed on flexible carbon cloth (CC) as an efficient bifunctional electrocatalyst for overall water splitting via a facile metal-organic framework (MOF) derived method. The synergistic effect of Co and W atoms effectively tailors the electron state of carbide, optimizing the hydrogen-binding energy. Thus Co6 W6 C@NC shows an enhanced HER performance with an overpotential of 59 mV at a current density of -10 mA cm-2 . Besides, Co6 W6 C@NC easily in situ transforms into tungsten actived cobalt oxide/hydroxide during the OER process, serving as OER active species, which provides an excellent OER activity with an overpotential of 286 mV at a current density of -10 mA cm-2 . The water splitting device, by applying Co6 W6 C@NC as both the cathode and anode, requires a low cell voltage of 1.585 V at 10 mA cm-2 with the great stability in alkaline solution. This work provides a feasible strategy to fabricate bimetallic carbides and explores their possibility as bifunctional catalysts toward overall water splitting.
103 citations
TL;DR: In this paper, a high-entropy (TiZrNbTaMo) ceramic has been successfully fabricated by hot pressing the newly-synthesized quinary carbide powder to investigate its microstructure and mechanical properties.
100 citations
TL;DR: It is found that the weight ratio of DCA to AM can regulate chemical composition of tungsten carbide/carbon composites, while less impact on the average size of WC 1− x nanoparticles.
Abstract: Carbides/carbon composites are emerging as a new kind of binary dielectric systems with good microwave absorption performance. Herein, we obtain a series of tungsten carbide/carbon composites through a simple solvent-free strategy, where the solid mixture of dicyandiamide (DCA) and ammonium metatungstate (AM) is employed as the precursor. Ultrafine cubic WC1−x nanoparticles (3–4 nm) are in situ generated and uniformly dispersed on carbon nanosheets. This configuration overcomes some disadvantages of conventional carbides/carbon composites and is greatly helpful for electromagnetic dissipation. It is found that the weight ratio of DCA to AM can regulate chemical composition of these composites, while less impact on the average size of WC1−x nanoparticles. With the increase in carbon nanosheets, the relative complex permittivity and dielectric loss ability are constantly enhanced through conductive loss and polarization relaxation. The different dielectric properties endow these composites with distinguishable attenuation ability and impedance matching. When DCA/AM weight ratio is 6.0, the optimized composite can produce good microwave absorption performance, whose strongest reflection loss intensity reaches up to − 55.6 dB at 17.5 GHz and qualified absorption bandwidth covers 3.6–18.0 GHz by manipulating the thickness from 1.0 to 5.0 mm. Such a performance is superior to many conventional carbides/carbon composites.
87 citations
TL;DR: In this paper, the development of efficient light-harvesting for converting CO2 into fuels via solar energy would be a promising strategy to reduce CO2 emissions and produce value-added carbon compounds.
Abstract: Conversion of CO2 into fuels via solar energy would be a promising strategy to reduce CO2 emissions and produce value-added carbon compounds. However, the development of efficient light-harvesting ...
85 citations
TL;DR: The relationship between microstructures and mechanical properties, especially strength and toughness of high-entropy carbide based ceramics are reported in this paper, and the main toughening mechanism is considered to be crack deflection by SiC particles.
Abstract: The relationships between microstructures and mechanical properties especially strength and toughness of high-entropy carbide based ceramics are reported in this article. Dense (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C (HEC) and its composite containing 20 vol.% SiC (HEC-20SiC) were prepared by spark plasma sintering. The addition of SiC phase enhanced the densification process, resulting in the promotion of the formation of the single-phase high-entropy carbide during sintering. The high-entropy carbide phase demonstrated a fast grain coarsening but SiC particles remarkably inhibited this phenomena. Dense HEC and HEC-20SiC ceramics sintered at 1900 °C exhibits four-point bending strength of 332 ± 24 MPa and 554 ± 73 MPa, and fracture toughness of 4.51 ± 0.61 MPa·m1/2 and 5.24 ± 0.41 MPa·m1/2, respectively. The main toughening mechanism is considered to be crack deflection by the SiC particles.
81 citations
TL;DR: Monodisperse nanoparticles (NPs) of CoFe2O4 were synthesized as efficient catalyst precursors for CO2 hydrogenation to produce high value-added C2-C4 olefin products.
Abstract: Monodisperse nanoparticles (NPs) of CoFe2O4 were synthesized as efficient catalyst precursors for CO2 hydrogenation to produce high value-added C2–C4 olefin products, which are important building b...
75 citations
TL;DR: In this article, a cylindrical sample consisting of a titanium carbide was investigated numerically and the governing equations of heat diffusion and electricity distribution in the whole device was solved using finite element method.
72 citations
TL;DR: In this article, the MAX phases have been extended to include carbides and/or nitrides, and the MAX phase has been used for the first time to include p-block elements.
Abstract: Conventional MAX phases (M is an early transition metal, A represents a p-block element or Cd, and X is carbon or nitrogen) have so far been limited to carbides and/or nitrides. In the present work...
TL;DR: In this paper, the chemical bonding in high-entropy carbide ceramics is primary covalent with secondary metallic bonding, which makes HECs promising candidate materials for high-temperature applications.
Abstract: Compared to the extensively studied metallic high-entropy alloys (HEAs), high-entropy ceramics including oxide, borides, and carbides are less investigated. They are characterized by multiple metal elements in equal atomic concentrations in the cation position, while a nonmetal element (such as O, B, or C) occupies the anion position. It is noted, however, that the chemical bonding in high-entropy carbide ceramics is primary covalent with secondary metallic bonding.1,2 High-entropy ceramic materials have shown special physical properties. For example, the recent research on high-entropy carbides (HECs)3-5 has revealed low thermal conductivity,6 high hardness,7-9 and an improved oxidation resistance.10-12 These properties make HECs as promising candidate materials for high-temperature applications such Received: 24 October 2019 | Revised: 5 February 2020 | Accepted: 2 March 2020 DOI: 10.1111/jace.17103
TL;DR: In this article, a series of dual-phase high-entropy ultra-high temperature ceramics (DPHE-UHTCs) are fabricated starting from N binary borides and (5-N) binary carbides powders.
Abstract: A series of dual-phase high-entropy ultra-high temperature ceramics (DPHE-UHTCs) are fabricated starting from N binary borides and (5-N) binary carbides powders. > ∼99 % relative densities have been achieved with virtually no native oxides. These DPHE-UHTCs consist of a hexagonal high-entropy boride (HEB) phase and a cubic high-entropy carbide (HEC) phase. A thermodynamic relation that governs the compositions of the HEB and HEC phases in equilibrium is discovered and a thermodynamic model is proposed. These DPHE-UHTCs exhibit tunable grain size, Vickers microhardness, Young’s and shear moduli, and thermal conductivity. The DPHE-UHTCs have higher hardness than the weighted linear average of the two single-phase HEB and HEC, which are already harder than the rule-of-mixture averages of individual binary borides and carbides. This study extends the state of the art by introducing dual-phase high-entropy ceramics (DPHECs), which provide a new platform to tailor various properties via changing the phase fraction and microstructure.
TL;DR: ZrB2-SiC-graphite composites with 0-35vol% graphite flakes were densified via hot-pressing route at the temperature of 1800°C under the uniaxial pressure of 40MPa for 1h.
TL;DR: The present strategies can be applied to various carbide and Mo-based catalysts, and the established Mo valence and HER relations can guide development of highly active HER electrocatalysts.
Abstract: To overcome inherent limitations of molybdenum carbide (MoxC) for hydrogen evolution reaction (HER), i.e., low density of active site and nonideal hydrogen binding strength, we report the synthesis of valence-controlled mesoporous MoxC as a highly efficient HER electrocatalyst. The synthesis procedure uses an interaction mediator (IM), which significantly increases the density of active site by mediating interaction between PEO-b-PS template and Mo source. The valence state of Mo is tuned by systematic control of the environment around Mo by controlled heat treatment under air before thermal treatment at 1100 °C. Theoretical calculations reveal that the hydrogen binding is strongly influenced by Mo valence. Consequently, MoxC achieves a significant increase in HER activity (exceeding that of Pt/C at high current density ∼35 mA/cm2 in alkaline solution). In addition, a volcano-type correlation between HER activity and Mo valence is identified with various experimental indicators. The present strategies can be applied to various carbide and Mo-based catalysts, and the established Mo valence and HER relations can guide development of highly active HER electrocatalysts.
TL;DR: In this article, the authors report on the APT analysis of hydrogen and deuterium within the nanostructure of an ultra-high strength steel with high resistance to hydrogen embrittlement.
TL;DR: In this article, the phase formation and composition uniformity of high entropy carbides are analyzed using XRD, EDS, and SEM, and the phase composition for samples sintered at 1600℃ includes TaC, NbC, WC, MoC and VC according to XRD peak fitting and deconvolution.
Abstract: (VNbTaMoW)C high entropy carbide was fabricated by reaction synthesis using the constituent metal and graphite powders as raw materials. Phase formation and composition uniformity are analyzed using XRD, EDS and SEM. The phase composition for samples sintered at 1600℃ includes TaC, NbC, WC, MoC and VC according to XRD peak fitting and deconvolution. Samples sintered at 1850℃ form a single phase high entropy carbides, which exhibit high microhardness and relatively lower thermal conductivity of 9.2 W/m.K-1 at room temperature compared with binary carbides. Severe lattice distortion and high concentration of point defects are responsible for the low thermal conductivity of the high entropy (VNbTaMoW)C.
TL;DR: This work succeeds in stabilizing pure-phase ε-Fe2C nanocrystals by confining them into graphene layers and obtaining an iron-time yield of 1258 μmolCO gFe−1s−1 under realistic FT synthesis conditions, one order of magnitude higher than that of the conventional carbon-supported Fe catalyst.
Abstract: The development of efficient catalysts for Fischer–Tropsch (FT) synthesis, a core reaction in the utilization of non-petroleum carbon resources to supply energy and chemicals, has attracted much recent attention. e-Iron carbide (e-Fe2C) was proposed as the most active iron phase for FT synthesis, but this phase is generally unstable under realistic FT reaction conditions (> 523 K). Here, we succeed in stabilizing pure-phase e-Fe2C nanocrystals by confining them into graphene layers and obtain an iron-time yield of 1258 μmolCO gFe−1s−1 under realistic FT synthesis conditions, one order of magnitude higher than that of the conventional carbon-supported Fe catalyst. The e-Fe2C@graphene catalyst is stable at least for 400 h under high-temperature conditions. Density functional theory (DFT) calculations reveal the feasible formation of e-Fe2C by carburization of α-Fe precursor through interfacial interactions of e-Fe2C@graphene. This work provides a promising strategy to design highly active and stable Fe-based FT catalysts. e-Fe2C has been identified as the highly active phase for Fischer-Tropsch synthesis (FTS), but is stable only at low-temperature. Here, the authors show that e-Fe2C phase can be stabilized even at ~ 573 K by being encapsulated inside graphene layers, and retains high activity in FTS.
20 Apr 2020-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, quantitative crystallographic and microstructural analyses of carbide phases are performed on wrought samples, samples fabricated via additive manufacturing (AM), and samples that underwent hot isostatic pressing (HIP) after AM of alloy Inconel 718 (IN718).
Abstract: In this work, quantitative crystallographic and microstructural analyses of γ, γ′, γ″, δ, and MC carbide phases are performed on wrought samples, samples fabricated via additive manufacturing (AM), and samples that underwent hot isostatic pressing (HIP) after AM of alloy Inconel 718 (IN718). In doing so, an advanced neutron diffraction-based procedure is developed facilitating the determination of volume fractions of every detectable phase in the alloy. To supplement the diffraction procedure, precipitate sizes are measured by scanning electron microscopy. Moreover, semi-quantitative elemental analyses are performed by energy dispersive spectroscopy. Finally, image thresholding is carried out on micrographs of samples that underwent cathodic dissolution to create secondary electron contrast between phases to verify the phase fractions determined from the neutron diffraction datasets. The study reveals a significantly higher volume fraction of δ phase and a significantly lower volume fraction of γ″ phase governing a higher strength of the AM material relative to the lower strength AM + HIP and wrought materials. Furthermore, γ′ and MC volume fractions are found similar in the materials despite the differences in MC morphology, elemental composition and distribution controlling the dispersion strengthening. These results are presented and discussed in this paper along with the procedure developed for determining volume fractions of all detectable phases present in the alloy.
TL;DR: Tungsten carbide (WC) with imperfect structures determined by phase engineering and heteroatom doping has attracted a great deal of attention with respect to hydrogen evolution reaction (HER).
Abstract: Tungsten carbide (WC) with imperfect structures determined by phase engineering and heteroatom doping has attracted a great deal of attention with respect to hydrogen evolution reaction (HER). Howe...
TL;DR: In this article, high-entropy (Zr,Ti,Hf,Nb,Ta) carbides exhibit high oxidation resistance with a small mass gain per unit area of 6.6
TL;DR: In this article, the authors show that carbon vacancies determine the catalytic behavior of vanadium carbides in the CO2 conversion to CO via the Reverse Water Gas Shift (RWGS) reaction.
Abstract: Experimental and theoretical evidences show that carbon vacancies determine the catalytic behavior of vanadium carbides in the CO2 conversion to CO via the Reverse Water Gas Shift (RWGS) reaction. Two VCx samples, one mostly containing stoichiometric VC and the other being C deficient, mainly V8C7, were synthesized, characterized, and studied. The samples show different CO2 adsorption heats, which correlate with those calculated using Density Functional Theory (DFT) on suitable models. The sample containing more V8C7 shows a higher CO2 conversion and CO selectivity and a lower apparent activation energy, being a stable catalyst over long-time tests. DFT calculations confirm that C vacancies in V8C7 are responsible for the observed catalytic behavior, allowing reactants to adsorb more strongly and lowering the energy barrier for both H2 and CO2 dissociation steps. The present work highlights the importance of such native point defects in the transition metal carbides surface chemistry and catalytic properties.
TL;DR: In this article, the design and synthesis of high-performance nonprecious metal catalysts for the hydrogen evolution reaction was discussed, which is a promising technique to produce high-quality hydrogen.
Abstract: Water electrolysis is a promising technique to produce high-quality hydrogen. However, the design and synthesis of high-performance nonprecious metal catalysts for the hydrogen evolution reaction a...
TL;DR: In this paper, a novel nitrogen-doped carbon-hosted TMC catalyst with dual transition metals to modulate the electronic structures of tungsten carbide is reported, enabling implementation by introducing copper from a prefabricated core-shell CuWO4@ZIF-67 precursor and subsequently with an annealing treatment, which not only maximize the active Co and W sites, but also enable the construction of a good interconnected conductive network.
Abstract: Developing transition metal carbides (TMCs) as multifunctional electrocatalysts to catalyze the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) has been attracting increasing attention. Unlike traditional single-source modification, a novel nitrogen-doped carbon-hosted TMC catalyst with dual transition metals to modulate the electronic structures of tungsten carbide is reported here. It enables implementation by introducing copper from a prefabricated core–shell CuWO4@ZIF-67 precursor and subsequently with an annealing treatment, which not only maximize the active Co and W sites, but also enable the construction of a good interconnected conductive network. Consequently, the optimized nitrogen-doped carbon-supported polymetallic carbide catalyst synthesized at 700 °C (denoted as S-2) with a suitable structure and composition configuration exhibits decent activities with ultralow overpotentials (η) of 238 mV and 98 mV at 10 mA cm−2 for OER and HER, respectively, along with good overall water splitting performances, surpassing that of majority of TMCs. This work paves viable ways for the rational design and regulation of the local electron structures of metallic carbides by introducing appropriate transition metals.
TL;DR: In this paper, the formation of the nanolayer structure of the Ti-TiN-(Ti,Cr,Al)N coating and its influence on the thickness of coatings, their resistance to fracture in scratch testing, and the wear resistance of coated tools in turning 1045 steel.
Abstract: The paper presents the results of the investigation into the formation of the nanolayer structure of the Ti-TiN-(Ti,Cr,Al)N coating and its influence on the thickness of coatings, their resistance to fracture in scratch testing, and the wear resistance of coated tools in turning 1045 steel. The structure of the coatings with the nanolayer thicknesses of 302, 160, 70, 53, 38, 24, 16, and 10 nm was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution (HR) TEM. It is shown that the grain sizes in the nanolayers decrease to certain values with an increase in the thickness of the nanolayers, and then, with a further decrease in the nanolayer thickness, the grain sizes of the nanolayer grow as the interlayer interfaces cease to produce a restraining effect on the growth of the grains. The study found that the nanolayer thickness influenced the wear of carbide cutting tools and the pattern of fracture for the Ti-TiN-(Ti,Cr,Al)N coatings.
01 Jan 2020
TL;DR: In this article, a study on preparation of copper-Graphite-Silicon-Carbide hybrid metal matrix composite by stir casting technique is presented. And it is spontaneously expected that present composite will be highly beneficial in structural and mechanical applications.
TL;DR: In this paper, the potentials of bimetal compounds, which have been well recognized in other environmental catalysis, are also extended to Li-S batteries and a simple cathode (S/Super P composite) can deliver high sulfur utilization, high rate performance, and excellent cycle stability with a low capacity decay rate of ∼ 0.034% per cycle at 1 C up to 1000 cycles.
Abstract: The polysulfide shuttling and sluggish redox kinetics, due to the notorious adsorption-catalysis underperformance, are the ultimate obstacles of the practical application of lithium-sulfur (Li-S) batteries. Conventional carbon-based and transition metal compound-based material solutions generally suffer from poor catalysis and adsorption, respectively, despite the performance gain in terms of the other. Herein, we have enhanced polysulfide adsorption-catalytic capability and protected the Li anode using a complementary bimetallic carbide electrocatalyst, Co3Mo3C, modified commercial separator. With this demonstration, the potentials of bimetal compounds, which have been well recognized in other environmental catalysis, are also extended to Li-S batteries. Coupled with this modified separator, a simple cathode (S/Super P composite) can deliver high sulfur utilization, high rate performance, and excellent cycle stability with a low capacity decay rate of ∼0.034% per cycle at 1 C up to 1000 cycles. Even at a high S-loading of 8.0 mg cm−2 with electrolyte/sulfur ratio=6 mL g−1, the cathode still exhibits high areal capacity of ∼6.8 mA h cm−2. The experimental analysis and the first principles calculations proved that the bimetallic carbide Co3Mo3C provides more binding sites for adsorbing polysulfides and catalyzing the multiphase conversion of sulfur/polysulfide/sulfide than monometallic carbide Mo2C. Moreover, the modified separator can be reutilized with comparable electrochemical performance. We also showed other bimetallic carbides with similar catalytic effects on Li S batteries and this material family has great promise in different energy electrocatalytic systems.
TL;DR: In this article, a medium-entropy alloys with chemical compositions of Co17.5Cr12.5Ni10Mo4C1 and Co 17.5Fe55Ni 10Mo3C2 (at%) exhibiting excellent tensile properties at both room and liquid nitrogen temperatures have been developed.
TL;DR: In this article, the authors provide an experimental complement to a companion publication, which outlines analytical and computational thermodynamic approaches that are envisioned to aid the design of refractory high entropy materials containing group IV (Hf, Zr, Ti) and group V (Ta, Nb) constituents.