Showing papers on "Carbide published in 2022"

In Situ Growth of Three‐Dimensional MXene/Metal‐Organic Framework Composites for High‐Performance Supercapacitors

Abstract: In this study, we propose a versatile method for synthesizing uniform three-dimensional (3D) metal carbides, nitrides, and carbonitrides (MXenes)/metal–organic frameworks (MOFs) composites (Ti3C2TX/Cu-BTC, Ti3C2TX/Fe,Co-PBA, Ti3C2TX/ZIF-8, and Ti3C2TX/ZIF-67) that combine the advantages of MOFs and MXenes to enhance stability and improve conductivity. Subsequently, 3D hollow Ti3C2TX/ZIF-67/CoV2O6 composites with excellent electron- and ion-transport properties derived from Ti3C2TX/ZIF-67 were synthesized. The specific capacitance of the Ti3C2TX/ZIF-67/CoV2O6 electrode was 285.5 F g−1, which is much higher than that of the ZIF-67 and Ti3C2TX/ZIF-67 electrode. This study opens a new avenue for the design and synthesis of MXene/MOF composites and complex hollow structures with tailorable structures and compositions for various applications.

In Situ Growth of Three‐Dimensional MXene/Metal–Organic Framework Composites for High‐Performance Supercapacitors

Abstract: In this study, we propose a versatile method for synthesizing uniform three-dimensional (3D) metal carbides, nitrides, and carbonitrides (MXenes)/metal-organic frameworks (MOFs) composites (Ti3 C2 TX /Cu-BTC, Ti3 C2 TX /Fe,Co-PBA, Ti3 C2 TX /ZIF-8, and Ti3 C2 TX /ZIF-67) that combine the advantages of MOFs and MXenes to enhance stability and improve conductivity. Subsequently, 3D hollow Ti3 C2 TX /ZIF-67/CoV2 O6 composites with excellent electron- and ion-transport properties derived from Ti3 C2 TX /ZIF-67 were synthesized. The specific capacitance of the Ti3 C2 TX /ZIF-67/CoV2 O6 electrode was 285.5 F g-1 , which is much higher than that of the ZIF-67 and Ti3 C2 TX /ZIF-67 electrode. This study opens a new avenue for the design and synthesis of MXene/MOF composites and complex hollow structures with tailorable structures and compositions for various applications.

Recent Advances in Oxidation Stable Chemistry of 2D MXenes

Abstract: As an emerging star of 2D nanomaterials, 2D transition metal carbides and nitrides, named MXenes, present a large potential in various research areas owing to their intrinsic multilayer structure and intriguing physico-chemical properties. However, the fabrication and application of functional MXene-based devices still remain challenging as they are prone to oxidative degradation under ambient environment. Within this review, the preparation methods of MXenes focusing on the recent investigations on their thermal structure-stability relationships in inert, oxidizing, and aqueous environments are systematically introduced. Moreover, the key factors that affect the oxidation of MXenes, such as, atmosphere, temperature, composition, microstructure, and aqueous environment, are reviewed. Based on different scenarios, strategies for avoiding or delaying the oxidation of MXenes are proposed to encourage the utilization of MXenes in complicated environments, especially at high temperature. Furthermore, the chemistry of MXene-derived oxides is analyzed, which can offer perspectives on the further design and fabrication of novel 2D composites with the unique structures of MXenes being preserved.

Additive-mediated intercalation and surface modification of MXenes.

Abstract: 2D carbides and nitrides of transition metals, also known as MXenes, are an emerging class of 2D nanomaterials that have shown excellent performances and broad application prospects in the fields of energy storage, catalysis, sensing, electromagnetic shielding, electronics and photonics, and life sciences. This unusual diversity of applications is due to their superior hydrophilicity and conductivity, high carrier concentration, ultra-high volumetric capacitance, rich surface chemistry, and large specific surface area. However, it is difficult to make MXenes with the desired surface functional groups that deliver high reactivity and high stability, because most MXenes are extracted from ceramics (MAX phase) by an etching process, where a large number of metal atoms are inevitably exposed on the surface, with other anions and cations embedded uncontrollably. The exposed metal atoms and implanted ions are thermodynamically unstable and readily react with trace oxygen or oxygen-containing groups to form the corresponding metal oxides or degrade chemically, resulting in a sharp decline in activity and loss of excellent physicochemical properties. The addition of certain synergistic additives during the intercalation and chemical modification of surface functional groups under non-hazardous conditions can result in stable and efficient MXene-based materials with exceptional optical, electrical, and magnetic properties. This review discusses several such methods, mainly additive-mediated intercalation and chemical modification of the surface functional groups of MXene-based materials, followed by their potential applications. Finally, perspectives are given to discuss the future challenges and promising opportunities of this exciting field.

Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO2 hydrogenation

Abstract: Identifying the dynamic structure of heterogeneous catalysts is crucial for the rational design of new ones. In this contribution, the structural evolution of Fe(0) catalysts during CO2 hydrogenation to hydrocarbons has been investigated by using several (quasi) in situ techniques. Upon initial reduction, Fe species are carburized to Fe3C and then to Fe5C2. The by-product of CO2 hydrogenation, H2O, oxidizes the iron carbide to Fe3O4. The formation of Fe3O4@(Fe5C2+Fe3O4) core-shell structure was observed at steady state, and the surface composition depends on the balance of oxidation and carburization, where water plays a key role in the oxidation. The performance of CO2 hydrogenation was also correlated with the dynamic surface structure. Theoretical calculations and controll experiments reveal the interdependence between the phase transition and reactive environment. We also suggest a practical way to tune the competitive reactions to maintain an Fe5C2-rich surface for a desired C2+ productivity.

Processing of Aluminium-Silicon Alloy with Metal Carbide as Reinforcement through Powder-Based Additive Manufacturing: A Critical Study

Abstract: Powder-based additive manufacturing (PAM) is a potential fabrication approach in advancing state-of-the-art research to produce intricate components with high precision and accuracy in near-net form. In PAM, the raw materials are used in powder form, deposited on the surface layer by layer, and fused to produce the final product. PAM composite fabrication for biomedical implants, aircraft structure panels, and automotive brake rotary components is gaining popularity. In PAM composite fabrication, the aluminium cast alloy is widely preferred as a metal matrix for its unique properties, and different reinforcements are employed in the form of oxides, carbides, and nitrides. However, for enhancing the mechanical properties, the carbide form is predominantly considered. This comprehensive study focuses on contemporary research and reveals the effect of metal carbide's (MCs) addition to the aluminium matrix processed through various PAM processes, challenges involved, and potential scopes to advance the research.

Multiphase Molybdenum Carbide Doped Carbon Hollow Sphere Engineering: The Superiority of Unique Double-Shell Structure in Microwave Absorption.

Abstract: In order to achieve excellent electromagnetic wave (EMW) absorption properties, the microstructure design and component control of the absorber are critical. In this study, three different structures made of Mo2 C/C hollow spheres are prepared and their microwave absorption behavior is investigated. The Mo2 C/C double-shell hollow spheres consisting of an outer thin shell and an inner rough thick shell with multiple EMW loss mechanisms exhibit good microwave absorption properties. In order to further improve the microwave absorption properties, MoC1-x /C double-shell hollow spheres with different crystalline phases of molybdenum carbide are prepared to further optimize the EMW loss capability of the materials. Finally, MoC1-x /C double-shell hollow spheres with α-phase molybdenum carbide have the best microwave absorption properties. When the filling is 20 wt.%, the minimum reflection loss at 1.8 mm is -50.55 dB and the effective absorption bandwidth at 2 mm is 5.36 GHz, which is expected to be a microwave absorber with the characteristics of "thin, light, wide, and strong".

Tool wear, surface roughness, cutting temperature and chips morphology evaluation of Al/TiN coated carbide cutting tools in milling of Cu–B–CrC based ceramic matrix composites

Abstract: Ceramics-based composites are a special class of materials carrying combined properties that belongs to alloys and metals according to market demands. This makes composites completely different and paves the way for new applications that requires the utmost properties. Machining of such composites is of great importance to finalize the fabrication process with improved part quality; however, the process implies several challenges due to the complexity of the cutting processes and random material structure. The current study aims to examine the machinability characteristics when milling novel material, Cu–B–CrC composites using Al/TiN coated carbide tools. Further, the influence of machining parameters along with the different weight ratios of the powders amounts used to fabricate the machined reinforced samples on output parameters namely surface roughness, tool wear, chip morphology and cutting temperatures was investigated. One of the key findings of the study is the dominant effect of reinforcement ratio (Cu, B, CrC) on machinability, which showed that 5% additive (2% B, 3% CrC) provides improved properties such as surface roughness, tool wear and cutting temperature. Cutting speed alterations play an important role in the machinability characteristics, i.e., increasing value increases flank wear and cutting temperatures and reduces surface roughness. Increasing feed rate increases the surface roughness meanwhile its effect shows changing behavior on the flank wear and cutting temperatures according to cutting speed and reinforcement ratio.

Ambient-pressure hydrogenation of CO2 into long-chain olefins

Abstract: Abstract The conversion of CO 2 by renewable power-generated hydrogen is a promising approach to a sustainable production of long-chain olefins (C 4+ = ) which are currently produced from petroleum resources. The decentralized small-scale electrolysis for hydrogen generation requires the operation of CO 2 hydrogenation in ambient-pressure units to match the manufacturing scales and flexible on-demand production. Herein, we report a Cu-Fe catalyst which is operated under ambient pressure with comparable C 4+ = selectivity (66.9%) to that of the state-of-the-art catalysts (66.8%) optimized under high pressure (35 bar). The catalyst is composed of copper, iron oxides, and iron carbides. Iron oxides enable reverse-water-gas-shift to produce CO. The synergy of carbide path over iron carbides and CO insertion path over interfacial sites between copper and iron carbides leads to efficient C-C coupling into C 4+ = . This work contributes to the development of small-scale low-pressure devices for CO 2 hydrogenation compatible with sustainable hydrogen production.

Key properties of inorganic thermoelectric materials—tables (version 1)

Abstract: This paper presents tables of key thermoelectric properties, which define thermoelectric conversion efficiency, for a wide range of inorganic materials. The twelve families of materials included in these tables are primarily selected on the basis of well established, internationally-recognized performance and promise for current and future applications: tellurides, skutterudites, half Heuslers, Zintls, Mg–Sb antimonides, clathrates, FeGa3-type materials, actinides and lanthanides, oxides, sulfides, selenides, silicides, borides and carbides. As thermoelectric properties vary with temperature, data are presented at room temperature to enable ready comparison, and also at a higher temperature appropriate to peak performance. An individual table of data and commentary are provided for each family of materials plus source references for all the data.

CO2 capture and conversion to value-added products promoted by MXene-based materials

Abstract: Carbon dioxide (CO2) capture and conversion is the key route for the mitigation of the greenhouse effect and utilization of carbon sources to obtain value-added products or fuels. Much attention is paid to the development of novel materials with high CO2 adsorption capacity and conversion rate. MXene is the graphene-like two-dimensional metal carbide/nitride/carbonitride owning favorable structure, morphology, high surface–bulk ratio, and physicochemical properties. Here, we review the CO2 capture, sensing, and conversion by MXene and MXene-based materials. Furthermore, the underlying mechanism involved the capture, sensing, and conversion of CO2 is summarized. This review would open a new horizon for CO2 valorization with high efficiency and promising widespread applications.

Carbide-based thermal spray coatings: A review on performance characteristics and post-treatment

Abstract: Components working under harsh environments in power generation, marine, and aerospace sectors are subjected to severe surface degradation because of wear, corrosion, and erosion by solid particles, slurry, silt, and cavitation. Carbide-based materials exhibit high resistance to degradation under such conditions because of their high hardness and chemical stability. These carbides can be effectively deposited as coatings on the components using advanced thermal spray techniques such as plasma spraying, HVOF, and HVAF. The carbide-based thermal spray coatings are majorly based on either WC or Cr3C2 or a combination of these materials. However, the composition of the carbides, the type and percentage of binders, and process parameters significantly affect the performance of these coated components. In this article, the degradation behavior and performance of the different carbide-based coatings as a function of carbide grain size and type of metallic binders, spray process parameters, and working conditions have been critically reviewed. On the other hand, the post-processing of carbide coatings is also emerging as a promising strategy to enhance the performance by modifying and refining the structure of coatings. Hence, a comprehensive summary of the post-processing techniques such as heat treatment, laser treatment, and cryogenic treatment of the carbide coatings is also provided.

Understanding the nanostructure evolution and the mechanical strengthening of the M50 bearing steel during ultrasonic shot peening

Abstract: Ultrasonic shot peening (USP) is a surface engineering technology used to enhance the mechanical properties of the components during manufacturing. M50 steel is one of the commonly used materials for aerospace bearings. In this study, surface nanocrystallization of the high-strength M50 bearing steel is performed at room temperature via USP technology. The materials characterizations show that the thickness of the lath martensite in the M50 bearing steel has been refined down to 10 nm. The extremely fine nanostructured M50 martensite increases the mechanical strength significantly at the nanoscale. Nanoindentation tests show that the nanohardness of the nanostructured M50 is 12.43 GPa, which is 38% higher than that of the as-received matrix materials with a value of 9.03 GPa. Additionally, the microstructure evolution of the M50 during the USP process is investigated and the grain refinement mechanism for M50 is revealed. EBSD characterization results confirm the transformation of the low angle grain boundaries to high angle grain boundaries and the formation of the equiaxed ultrafine grains. The decomposition of the carbides in the M50 during grain refinement is observed. This indicates that in addition to the diffusion of C, the decomposition of the carbides is also influenced by carbide-forming elements. This work deepens the current understanding of the grain refinement of the M50 bearing steel during the USP process and its mechanical strengthening at the nanoscale.

Achieving ultra-broadband electromagnetic wave absorption in high-entropy transition metal carbides (HE TMCs)

Abstract: Abstract Electronic devices pervade everyday life, which has triggered severe electromagnetic (EM) wave pollution. To face this challenge, developing EM wave absorbers with ultra-broadband absorption capacity is critically required. Currently, nano-composite construction has been widely utilized to realize impedance match and broadband absorption. However, complex experimental procedures, limited thermal stability, and interior oxidation resistance are still unneglectable issues. Therefore, it is appealing to realize ultra-broadband EM wave absorption in single-phase materials with good stability. Aiming at this target, two high-entropy transition metal carbides (HE TMCs) including (Zr,Hf,Nb,Ta)C (HE TMC-2) and (Cr,Zr,Hf,Nb,Ta)C (HE TMC-3) are designed and synthesized, of which the microwave absorption performance is investigated in comparison with previously reported (Ti,Zr,Hf,Nb,Ta)C (HE TMC-1). Due to the synergistic effects of dielectric and magnetic losses, HE TMC-2 and HE TMC-3 exhibit better impedance match and wider effective absorption bandwidth (EAB). In specific, the exclusion of Ti element in HE TMC-2 endows it optimal minimum reflection loss (RL min ) and EAB of −41.7 dB (2.11 mm, 10.52 GHz) and 3.5 GHz (at 3.0 mm), respectively. Remarkably, the incorporation of Cr element in HE TMC-3 significantly improves the impedance match, thus realizing EAB of 10.5, 9.2, and 13.9 GHz at 2, 3, and 4 mm, respectively. The significance of this study lays on realizing ultra-broadband capacity in HE TMC-3 (Cr, Zr, Hf, Nb, Ta), demonstrating the effectiveness of high-entropy component design in tailoring the impedance match.

Perspectives of 2D MXene Tribology

Abstract: The large and rapidly growing family of 2D early transition metal carbides, nitrides, and carbonitrides (MXenes) raises significant interest in the materials science and chemistry of materials communities. Discovered a little more than a decade ago, MXenes have already demonstrated outstanding potential in various applications ranging from energy storage to biology and medicine. The past two years have witnessed increased experimental and theoretical efforts toward studying MXenes’ mechanical and tribological properties when used as lubricant additives, reinforcement phases in composites, or solid lubricant coatings. Although research on the understanding of the friction and wear performance of MXenes under dry and lubricated conditions is still in its early stages, it has experienced rapid growth due to the excellent mechanical properties and chemical reactivities offered by MXenes that make them adaptable to being combined with other materials, thus boosting their tribological performance. In this perspective, the most promising results in the area of MXene tribology are summarized, future important problems to be pursued further are outlined, and methodological recommendations that could be useful for experts as well as newcomers to MXenes research, in particular, to the emerging area of MXene tribology, are provided.

Recent Advances in Growth of Transition Metal Carbides and Nitrides (MXenes) Crystals

Abstract: As a novel family of 2D materials, MXenes have drawn intensive interests owing to its fascinating property profile. The ability to grow high‐quality MXenes in a controllable way would in turn further promote the development of fabrication techniques and expand wide advanced applications. Then 2D MXenes crystals are highly desirable and many approaches have been explored to realize the mass production. Chemical vapor deposition (CVD) provides compelling benefits over other alternatives in controllability, uniformity and scalability. In this review, the recent advances in growth of MXenes crystals by CVD method will comprehensively present. Several typical kinds of MXenes crystals are demonstrated to be fabricated with a precise control in terms of size, morphology and thickness. Further, a series of MXenes heterostructures are constructed including vertical and lateral spatial orientations. Then, the properties and applications of MXenes crystals are exhibited, of which superconductivity and electrochemical catalysts will be mainly emphasized. Finally, the authors put forward views on the future development in the synthesis of MXenes. With continuous efforts devoted, a bright future of MXenes crystals prepared by CVD is expected.

Phase controlled synthesis of transition metal carbide nanocrystals by ultrafast flash Joule heating

Abstract: Abstract Nanoscale carbides enhance ultra-strong ceramics and show activity as high-performance catalysts. Traditional lengthy carburization methods for carbide syntheses usually result in coked surface, large particle size, and uncontrolled phase. Here, a flash Joule heating process is developed for ultrafast synthesis of carbide nanocrystals within 1 s. Various interstitial transition metal carbides (TiC, ZrC, HfC, VC, NbC, TaC, Cr 2 C 3 , MoC, and W 2 C) and covalent carbides (B 4 C and SiC) are produced using low-cost precursors. By controlling pulse voltages, phase-pure molybdenum carbides including β-Mo 2 C and metastable α-MoC 1-x and η-MoC 1-x are selectively synthesized, demonstrating the excellent phase engineering ability of the flash Joule heating by broadly tunable energy input that can exceed 3000 K coupled with kinetically controlled ultrafast cooling (>10 4 K s −1 ). Theoretical calculation reveals carbon vacancies as the driving factor for topotactic transition of carbide phases. The phase-dependent hydrogen evolution capability of molybdenum carbides is investigated with β-Mo 2 C showing the best performance.