Showing papers on "Carbide published in 2019"

Cemented carbide microstructures: a review

Abstract: Cemented carbides cover a wide range of applications in many relevant industries, i.e. as cutting tools (turning, milling, drilling) for machining of metal components in the automotive and/or aerospace industry, as components of drill bits or road headers in the rock tools and mining area or as wear parts in wire drawing dies or punch tools. In this review selected cemented carbide and cermet microstructures are presented. The focus is on microstructures, both those that are already established in the cemented carbide industry and those which have drawn scientific attention due to new potential applications. Cemented carbides are here divided in four groups based on microstructure and chemistry: WC morphology and chemistry, cubic carbide containing cemented carbide and cermets, functionally graded cemented carbides, and binder design of cemented carbides. Furthermore, this review covers some historical background that motivated the microstructure design as well as the status of each class of materials nowadays. The paper aims at categorising cemented carbides in a structured way and to serve as an introduction to cemented carbide microstructures for engineers, researchers and scientists.

Ultrafine Dual-Phased Carbide Nanocrystals Confined in Porous Nitrogen-Doped Carbon Dodecahedrons for Efficient Hydrogen Evolution Reaction

Abstract: Designing novel non-noble electrocatalysts with controlled structures and composition remains a great challenge for efficient hydrogen evolution reaction (HER). Herein, a rational synthesis of ultrafine carbide nanocrystals confined in porous nitrogen-doped carbon dodecahedrons (PNCDs) by annealing functional zeolitic imidazolate framework (ZIF-8) with molybdate or tungstate is reported. By controlling the substitution amount of MO4 units (M = Mo or W) in the ZIF-8 framework, dual-phase carbide nanocrystals confined in PNCDs (denoted as MC-M2 C/PNCDs) can be obtained, which exhibit superior activity toward the HER to the single-phased MC/PNCDs and M2 C/PNCDs. The evenly distributed ultrafine nanocrystals favor the exposure of active sites. PNCDs as the support facilitate charge transfer and protect the nanocrystals from aggregation during the HER process. Moreover, the strong coupling interactions between MC and M2 C provide beneficial sites for both water dissociation and hydrogen desorption. This work highlights a new feasible strategy to explore efficient electrocatalysts via engineering on nanostructure and composition.

Overview of the synthesis of MXenes and other ultrathin 2D transition metal carbides and nitrides

Abstract: In 2011, a new family of two dimensional (2D) carbides, carbonitrides and nitrides – labeled MXenes – was discovered. Since then the number of papers on these materials has increased exponentially for several reasons amongst them: their hydrophilic nature, excellent electronic conductivities and ease of synthesizing large quantities in water. This unique combination of properties and ease of processing has positioned them as enabling materials for a large, and quite varied, host of applications from energy storage to electromagnetic shielding, transparent conductive electrodes, electrocatalysis, to name a few. Since the initial synthesis of Ti3C2 in hydrofluoric acid, many more compositions were discovered, and different synthesis pathways were explored. Most of the work done so far has been conducted on top-down synthesis where a layered parent compound is etched and then exfoliated. Three bottom-up synthesis methods, chemical vapor deposition, a template method and plasma enhanced pulsed laser deposition have been reported. The latter methods enable the synthesis of not only high-quality ultrathin 2D transition metal carbide and nitride films, but also those that could not be synthesized by selective etching. This article reviews and summarizes the most important breakthroughs in the synthesis of MXenes and high-quality ultrathin 2D transition metal carbide and nitride films.

High-Temperature Behavior and Surface Chemistry of Carbide MXenes Studied by Thermal Analysis

Abstract: Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) have attracted significant attention due to their electronic, electrochemical, chemical, and optical properties. However, understanding of their thermal stability is still lacking. To date, MXenes are synthesized via top-down wet chemical etching, which intrinsically results in surface terminations. Here, we provide detailed insight into the surface terminations of three carbide MXenes (Ti3C2Tx, Mo2CTx, and Nb2CTx) by performing thermal gravimetric analysis with mass spectrometry analysis (TA–MS) up to 1500 °C under a He atmosphere. This specific technique enables probing surface terminations including hydroxyl (−OH), oxy (═O), and fluoride (−F) and intercalated species, such as salts and structural water. The MXene hydrophilicity depends on the type of etching (hydrofluoric acid concentration and/or mixed acid composition) and subsequent delamination conditions. We show that the amount of structural water in Ti3C2Tx increases with decre...

Single Site Cobalt Substitution in 2D Molybdenum Carbide (MXene) Enhances Catalytic Activity in the Hydrogen Evolution Reaction.

Abstract: Two-dimensional (2D) carbides, nitrides, and carbonitrides known as MXenes are emerging materials with a wealth of useful applications. However, the range of metals capable of forming stable MXenes...

One-pot synthesized molybdenum dioxide–molybdenum carbide heterostructures coupled with 3D holey carbon nanosheets for highly efficient and ultrastable cycling lithium-ion storage

Abstract: The molybdenum dioxide (MoO2)–molybdenum carbide (Mo2C) heterostructures were built by in situ forming the (100) plane of Mo2C nanoparticles along the (101) plane of MoO2 nanoparticles and were simultaneously anchored on a 3D holey carbon substrate via optimized annealing of the bio-inspired ammonium molybdate tetrahydrate-agar gel. Both experimental results and theoretical simulations demonstrated the important roles of wide interfaces between MoO2 and Mo2C in improving the electrochemical performance of MoO2-based electrodes. These uniquely prepared MoO2/Mo2C/C electrodes delivered a capacity of 845.2 mA h g−1 at 0.1 A g−1 after 200 cycles, with a capacity change rate of 2.3%, overcoming the key obstacle for commercial application of transition metal oxides caused by capacity changes during the cycling process. Meanwhile, the electrodes displayed ultrastable long cycling performance with a capacity of 507.3 mA h g−1 at a high current density of 1.0 A g−1 after 2400 cycles, still far higher than the theoretical capacity of carbon materials. Both a local in-built driving force in the electrodes and synergistically induced more efficient mass transport across the interface were predicted by the Density Functional Theory (DFT) and Density of States (DOS) calculations from the formed interfacial electric field, yielding the fast reaction kinetics and outstanding lithium storage ability. This work highlights an efficient strategy to obtain ultrastable long cycling performance and also excellent electrochemical performance of MoO2-based materials and other transition metal oxides as anodes for lithium ion batteries. In addition, the full batteries based on MoO2/Mo2C/C anodes and a commercial LiCoO2 cathode present stable cycling performance.

Discovery of hexagonal ternary phase Ti2InB2 and its evolution to layered boride TiB

Abstract: Mn+1AXn phases are a large family of compounds that have been limited, so far, to carbides and nitrides. Here we report the prediction of a compound, Ti2InB2, a stable boron-based ternary phase in the Ti-In-B system, using a computational structure search strategy. This predicted Ti2InB2 compound is successfully synthesized using a solid-state reaction route and its space group is confirmed as P $$\bar 6$$ m2 (No. 187), which is in fact a hexagonal subgroup of P63/mmc (No. 194), the symmetry group of conventional Mn+1AXn phases. Moreover, a strategy for the synthesis of MXenes from Mn+1AXn phases is applied, and a layered boride, TiB, is obtained by the removal of the indium layer through dealloying of the parent Ti2InB2 at high temperature under a high vacuum. We theoretically demonstrate that the TiB single layer exhibits superior potential as an anode material for Li/Na ion batteries than conventional carbide MXenes such as Ti3C2. Two-dimensional materials are promising for electrochemical storage and conversion, but are somewhat limited in composition. Here the authors use a computational strategy to predict the existence of a layered boride material, which they synthesize and demonstrate prospective for use as an anode material.

Transition metal carbide catalysts for biomass conversion: A review

Abstract: The increasing demand for sustainable energy resources has initiated the investigation of biomass conversion over a wide range of catalysts. Among those, transition metal carbides have been extensively studied which demonstrated distinct reactivity and/or selectivity from transition or noble metals in a variety of chemical reactions. In this review, we summarize recent advances in the synthesis of transition metal carbides and their applications in biomass conversion, particularly focusing on the catalytic conversions of (hemi)cellulose, lignin and some typical platform chemicals to fuels or fine chemicals involving C C, C O C and C O H bonds cleavages. Perspectives regarding the future research directions on the improvement of transition metal carbide catalysts and detailed reaction mechanism studies are also presented.

High entropy carbide ceramics from different starting materials

Abstract: Three typical ceramic processing were respectively used to synthesize (Ti0.2Zr0.2Nb0.2Ta0.2W0.2)C high-entropy carbide (HEC) ceramics by spark plasma sintering. Although single-phase composition characterized by X-ray diffraction were obtained by the three processes, the microstructures and elemental distributions are different. The reasons for the formation of these features are preliminarily discussed. The results demonstrate that the particle sizes of the starting metallic powders was a key factor for obtaining a homogeneous distribution of each elements in the HEC. Carbide process with relatively finer starting carbide powders compared to the above metallic starting powders resulted in an HEC with homogeneous distribution of elements, but the obtained ceramics showed the lowest relative density. For oxide process, it is considered that the obviously higher reaction temperature between ZrO2 and graphite resulted in a two-phase structure of an HEC and a zirconium-rich phase, but the obtained HEC showed the highest relative density.

N-Butyllithium-Treated Ti3C2Tx MXene with Excellent Pseudocapacitor Performance.

Abstract: MXenes, a family of two-dimensional (2D) transition-metal carbide and nitride materials, are supposed to be promising pseudocapacitive materials because of their high electronic conductivity and hy...

Molten salt shielded synthesis of oxidation prone materials in air.

Abstract: To prevent spontaneous oxidation during the high-temperature synthesis of non-oxide ceramics, an inert atmosphere is conventionally required1,2. This, however, results in high energy demand and high production costs. Here, we present a process for the synthesis and consolidation of oxidation-prone materials, the ‘molten salt shielded synthesis/sintering’ process (MS3), which uses molten salts as a reaction medium and also to protect the ceramic powders from oxidation during high-temperature processing in air. Synthesis temperatures are also reduced, and the final product is a highly pure, fine and loose powder that does not require additional milling steps. MS3 has been used for the synthesis of different ternary transition metal compounds (MAX phases, such as Ti3SiC23, Ti2AlN4, MoAlB5), binary carbides (TiC) and for the sintering of titanium. The availability of high-quality powders, combined with energy and cost savings, may remove one of the bottlenecks for the industrial application of these materials. Molten salts are used as a reaction medium to protect carbide, nitride and boride powders from oxidation during high-temperature synthesis in air, thus avoiding the need to carry out these processes in a vacuum or inert environment.

Ultra-High Temperature Materials II: Refractory Carbides I (Ta, Hf, NB and Zr Carbides)

Abstract: The work represents a thorough treatment of ultra-high temperature materials with melting points around or over 2500 °C. The second volume included physical (structural, thermal, electromagnetic, optical, mechanical and nuclear) and chemical (binary, ternary and multicomponent systems, solid-state diffusion, wettability, interaction with chemicals, gases and aqueous solutions) properties of refractory carbide materials: tantalum carbides (monocarbide TaC1–x and semicarbide a/b-Ta2±xC), hafnium monocarbide HfC1–x, niobium carbides (monocarbide NbC1–x and semicarbide a/b/c-Nb2±xC) and zirconium monocarbide ZrC1–x. It will be of interest to researchers, engineers, postgraduate, graduate and undergraduate students alike. The reader/user is provided with the full qualitative and quantitative assessment for the materials, which could be applied in various engineering devices and environmental conditions in the wide range from cryogenic to ultra-high temperatures, on the basis of the latest updates in the field of physics, chemistry, nanotechnology, materials science and engineering.

Additive manufacturing of high-strength crack-free Ni-based Hastelloy X superalloy

Abstract: Laser powder bed fusion (LPBF) is a proven additive manufacturing (AM) technology for producing metallic components with complex shapes using layer-by-layer manufacture principle. However, the fabrication of crack-free high-performance Ni-based superalloys such as Hastelloy X (HX) using LPBF technology remains a challenge because of these materials’ susceptibility to hot cracking. This paper addresses the above problem by proposing a novel method of introducing 1 wt.% titanium carbide (TiC) nanoparticles. The findings reveal that the addition of TiC nanoparticles results in the elimination of microcracks in the LPBF-fabricated enhanced HX samples; i.e. the 0.65% microcracks that were formed in the as-fabricated original HX were eliminated in the as-fabricated enhanced HX, despite the 0.14% residual pores formed. It also contributes to a 21.8% increase in low-angle grain boundaries (LAGBs) and a 98 MPa increase in yield strength. The study revealed that segregated carbides were unable to trigger hot cracking without sufficient thermal residual stresses; the significantly increased subgrains and low-angle grain boundaries played a key role in the hot cracking elimination. These findings offer a new perspective on the elimination of hot cracking of nickel-based superalloys and other industrially relevant crack-susceptible alloys. The findings also have significant implications for the design of new alloys, particularly for high-temperature industrial applications.

Carbon-Encapsulated Metal/Metal Carbide/Metal Oxide Core–Shell Nanostructures Generated by Laser Ablation of Metals in Organic Solvents

Abstract: Laser ablation of metal in organic solvents (LAMOS) has been proven to be an efficient technique for one-step synthesis of carbon-encapsulated metal/metal carbide/metal oxide core–shell nanostructures. However, the correlation between the influential factors and the final products, such as composition of the core and crystalline structure of the carbon shell, is still unclear to date; moreover, the precise control of this is full of challenges. Herein, comparative experiments of 16 transition metals (Cu, Ag, Au, Pt, Pd, Ti, V, Nb, Cr, Mo, W, Ni, Zr, Mn, Fe, and Zn) were performed to clarify the panorama of LAMOS, including metal atomization and liquid decomposition into carbon and reductive gases, subsequent metal carbonization, surface precipitation, and metal-catalyzed graphitization to form amorphous and graphitic carbon shells. Importantly, it is found that the carbon solubility in metals and the affinity of metals to oxygen are the critical factors in determining the core composition: (1) inert metal...

Calcium-Based Sustainable Chemical Technologies for Total Carbon Recycling

Abstract: Calcium carbide, a stable solid compound composed of two atoms of carbon and one of calcium, has proven its effectiveness in chemical synthesis, due to the safety and convenience of handling the C≡C acetylenic units. The areas of CaC2 application are very diverse, and the development of calcium-mediated approaches resolves several important challenges. This Review aims to discuss the laboratory chemistry of calcium carbide, and to go beyond its frontiers to organic synthesis, life sciences, materials and construction, carbon dioxide capturing, alloy manufacturing, and agriculture. The recyclability of calcium carbide and the availability of large-scale industrial production facilities, as well as the future possibility of fossil-resource-independent manufacturing, position this compound as a key chemical platform for sustainable development. Easy regeneration and reuse of the carbide highlight calcium-based sustainable chemical technologies as promising instruments for total carbon recycling.

Hydrothermal Synthesis of Ruthenium Nanoparticles with a Metallic Core and a Ruthenium Carbide Shell for Low-Temperature Activation of CO2 to Methane.

Abstract: Ruthenium nanoparticles with a core–shell structure formed by a core of metallic ruthenium and a shell of ruthenium carbide have been synthesized by a mild and easy hydrothermal treatment. The dual...

Laser-sculptured ultrathin transition metal carbide layers for energy storage and energy harvesting applications

Abstract: Ultrathin transition metal carbides with high capacity, high surface area, and high conductivity are a promising family of materials for applications from energy storage to catalysis. However, large-scale, cost-effective, and precursor-free methods to prepare ultrathin carbides are lacking. Here, we demonstrate a direct pattern method to manufacture ultrathin carbides (MoCx, WCx, and CoCx) on versatile substrates using a CO2 laser. The laser-sculptured polycrystalline carbides (macroporous, ~10–20 nm wall thickness, ~10 nm crystallinity) show high energy storage capability, hierarchical porous structure, and higher thermal resilience than MXenes and other laser-ablated carbon materials. A flexible supercapacitor made of MoCx demonstrates a wide temperature range (−50 to 300 °C). Furthermore, the sculptured microstructures endow the carbide network with enhanced visible light absorption, providing high solar energy harvesting efficiency (~72 %) for steam generation. The laser-based, scalable, resilient, and low-cost manufacturing process presents an approach for construction of carbides and their subsequent applications. Transition metal carbides are attractive for electrochemical energy storage and catalysis, but cost effective preparation on a large scale is challenging. Here the authors use a direct pattern method to fabricate transition metal carbides for supercapacitors and solar energy harvesting for steam generation.

The effect of oxide, carbide, nitride and boride additives on properties of pressureless sintered SiC: A review

Abstract: Properties such as high hardness, low density, and high elastic modulus have made SiC ceramics proper choices for a variety of industrial applications. However, disadvantages such as low sinterability, and low fracture toughness have limited the fabrication of these ceramics. Past researches show that the use of Al2O3-Y2O3 additives play an important role in improving the sinterability and the properties of the composites. The use of oxide, carbide, nitride and boride additives results in improved sinterability, physical and mechanical properties. The investigations show that the microstructure, porosities, amount of additives, reaction of additives with the matrix, grain size and, finally, the sintering temperature are the most important factors affecting the properties of SiC ceramics. In this paper, the effect of using various additives, the sintering temperature and the annealing heat treatment on sinterability, microstructure and properties of the SiC matrix composites fabricated by pressureless sintering method have been investigated.

Wear analysis of Al 5052 alloy with varying percentage of tungsten carbide

Abstract: Aluminium 5052 have its various applications in aerospace, fencing, hydraulic tubes and marine components due to their high dimensional stability, light in weight, high strength to weight ratio, economic and elevated stiffness. Since Aluminium alloy (Al 5052) has its application in aerospace and marine industries, its wear properties have to be improved further for better life of the components in its applications. Literature study reveals that studies were not carried out for Al 5052 alloy for improving its wear behaviour. Tungsten carbide (WC) normally used for manufacturing wear-resistant tools, cutting tools, protective coatings and carbide steel because of its wear resistance properties. In this research the wear behaviour of Al 5052 alloy analysed by reinforcing with varying weight percentage of tungsten carbide (1%, 3 %, 5%) fabricated using stir casting process. Taguchi L27 orthogonal array were used to conduct the experiment. Dry sliding wear behaviour is performed by means of Pin-on-disc wear testing apparatus. The process parameters are composition, Speed, Load, Sliding distance and the responses are Coefficient of Friction (CoF) and specific wear rate. Taguchi Signal-to-Noise ratio was carried out to determine best optimal combination to minimize the Coefficient of Friction (CoF) and specific wear rate. From the result it is seen that 5% of tungsten carbide reinforcement gives lower Coefficient of Friction (CoF) and specific wear rate at various parametric condition. To identify the wear track Scanning Electron Microscopic analysis were made and it is analysed that the lesser wear is seen in Al5052 reinforced with 5% of tungsten carbide with constant input parameter. From experiment, the Tungsten carbide improves wear resistance property of Al 5052 alloy with the increase in weight percentage of reinforcement.