A step forward in metal nitride and carbide synthesis: from pure nanopowders to nanocomposites

Transition metal nitrides and carbides (MN/MC) are intriguing materials due to their combination of properties that place them between high-performance ceramics and pure metals. Recent progress in easier synthetic routes toward their production as bulk or nanostructured materials explains the current surge in sustained attention such progress has been receiving. After progressing toward easier syntheses of MN/MC nanosystems as pure phases, coupling MN/MC with a second phase for the production of hybrids and nanocomposites is considered a next important step in the development of these nanosystems. The coupled phase can simply be a different nitride or carbide; it also can be a polymer, a poly(ionic liquid) or a carbon phase, just to give a few examples. The combination of these phases with MN/MC nanoparticles could lead to multifunctional materials. The aim of the present review is to show how far the research concerning the production of MN/MC-based nanocomposites has progressed, especially in terms of controlled composition, morphology and properties. We discuss the most intensely investigated systems and related motivations, as well as partially unexplored yet appealing alternative materials.     

铈对M2高速钢凝固组织的作用

研究了Ｃｅ对Ｍ２高速钢凝固组织的影响及其作用机制。发现Ｃｅ在高速钢中可减轻Ｗ,Ｍｏ等合金元素的偏析,使共晶碳化物量减少并细化;Ｃｅ主要偏聚在晶界共晶碳化物与奥氏体的界面上,并有部分Ｃｅ参与形成含Ｃｅ的Ｍ２Ｃ碳化物;Ｃｅ促进共晶碳化物在高温加热时的断网和团球化。     

Formation and spectroscopy of carbides

We review the evidence for carbides in space both from infrared spectroscopy and direct measurements on presolar grains extracted from primitive meteorites. The paper includes a discussion of the structural properties of silicon carbide and metal carbides and their formation routes from the gas phase. In addition, we present spectroscopic data in the infrared, which are required for a better understanding of astronomical spectra.     

A new class of electrocatalysts for hydrogen production from water electrolysis: metal monolayers supported on low-cost transition metal carbides

This work explores the opportunity to substantially reduce the cost of hydrogen evolution reaction (HER) catalysts by supporting monolayer (ML) amounts of precious metals on transition metal carbide substrates. The metal component includes platinum (Pt), palladium (Pd), and gold (Au); the low-cost carbide substrate includes tungsten carbides (WC and W(2)C) and molybdenum carbide (Mo(2)C). As a platform for these studies, single-phase carbide thin films with well-characterized surfaces have been synthesized, allowing for a direct comparison of the intrinsic HER activity of bare and Pt-modified carbide surfaces. It is found that WC and W(2)C are both excellent cathode support materials for ML Pt, exhibiting HER activities that are comparable to bulk Pt while displaying stable HER activity during chronopotentiometric HER measurements. The findings of excellent stability and HER activity of the ML Pt-WC and Pt-W(2)C surfaces may be explained by the similar bulk electronic properties of tungsten carbides to Pt, as is supported by density functional theory calculations. These results are further extended to other metal overlayers (Pd and Au) and supports (Mo(2)C), which demonstrate that the metal ML-supported transition metal carbide surfaces exhibit HER activity that is consistent with the well-known volcano relationship between activity and hydrogen binding energy. This work highlights the potential of using carbide materials to reduce the costs of hydrogen production from water electrolysis by serving as stable, low-cost supports for ML amounts of precious metals.     

Compositional and structural characterization of alloyed carbide by 3D atom probe and high‐resolution TEM

During tempering of solute supersaturated ferrous martensite, the face‐centered cubic MC‐type carbides (M is alloy elements) such as VC and NbC phases usually co‐precipitate on crystal defects such as dislocation and take on plate‐like morphology. Over‐tempering makes the plate‐like shape change to spherical shape because of Ostwald coarsening. The coarsening process strongly correlates to the diffusion behaviors of the carbon and carbide‐forming elements, and consequently inhomogeneous compositional and structural distribution in the carbides is formed. Three‐dimensional atom probe and high‐resolution transmission electron microscopy have been proved useful methods to characterize the composition, morphology and nanostructure of the carbides that precipitate in a quench‐tempered micro‐alloyed steel. Depending on the actual affinity with C and the diffusion behavior, Si and Al are rejected from the alloy carbide, whereas Mn, V and Nb are inhomogeneously enriched in it. The morphology and structure change with the compositional redistribution. During the coarsening process of the pre‐existing plate‐like carbide, transition carbide that is semi‐coherent with ferritic matrix is formed because of the disparity in diffusion ratio of different solutes. A core–shell complex nanostructure is consequently formed in the coarsening carbide, and the core and shell are identified as V₈C₇ enriched in Mn, Mo and Mo₂C, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Structural stability and phase transition in OsC and RuC

The structural stability and phase transition of osmium and ruthenium carbides (OsC and RuC) were investigated by first principles. Nine structures were considered for each carbide. Zinc blende structure has the lowest energy among the considered structures at ambient conditions for both carbides. For OsC at elevated pressures, the most stable phase is zinc blende structure from 0 to 10 GPa, FeSi from 10 to 32 GPa. In these two structures, Os atom is fourfold coordinated. From 32 to 40 GPa, tungsten carbide (WC) and NiAs are energetically competitive with Os atom sixfold coordinated. NiAs becomes energetically the most stable structure above 40 GPa. For RuC, zinc blende structure is the most stable from 0 to 20 GPa. From 20 to 100 GPa, WC structure is the most stable.     

过渡金属碳化物的研究进展

过渡金属碳化物作为一种催化新材料显示了其独特的性能,在石油馏份的HDS、HDN、加氢和脱氢反应、烃的异构化和芳构化、甲烷转化、F-T合成和电催化等反应中都表现出了优良的催化性能.本文综述了国内外关于钼、钨碳化物的制备方法以及在上述反应中的应用研究进展。     

DTA-EGA determination of carbides chemically extracted from steel

Differential thermal analysis-effluent gas analysis (DTA-EGA) techniques have been applied to the determination of specific metal carbides in residues which are isolated from steels by chemical methods. In this method, a weighed portion of sample residue is transferred to the DTA sample-holder and subjected to programmed heating in a dynamic oxygen atmosphere. When combustion of the carbide occurs, a differential temperature response is recorded over a specific temperature range. The temperature range is used as an aid in identifying the specific carbide present. The thermal conductivity of the effluent gas is recorded and the signal resulting from the presence of carbon dioxide in the effluent gas is then used for the quantitative determination of the carbide. The DTA-EGA method has been applied to several experimental steels for determination of the carbides of zirconium, vanadium or titanium individually and for the determination of vanadium and zirconium carbides in mixtures of the two. Results for these metal carbides obtained by DTA-EGA agreed within 15% with those obtained by the lengthy chemical methods. The lower limits of detection, based on the original steel sample weight, were 0.02% for the vanadium and titanium carbides and 0.01% for zirconium carbide.     

Superconductivity and Chemistry

The microscopic theory of superconductivity worked out by Bardeen, Cooper, and Schrieffer led to a fundamental understanding of the phenomenon. However, this theory does not provide a materials aspect. Starting from the special situation of chemical bonding in carbides and carbide halides of the rare earth metals a general view of the origin of superconductivity is developed, based on a tendency for (pairwise) localization of conduction electrons. This approach is tested in terms of special features in the electronic band structure and compared with existing physical models of electron pairing in real space. Its applicability to high-temperature superconductors discovered during the last decade is discussed.     

Interlayer Space Engineering of MXenes for Electrochemical Energy Storage Applications

The increasing demand for high-performance rechargeable energy storage systems has stimulated the exploration of advanced electrode materials. MXenes are a class of two-dimensional (2D) inorganic transition metal carbides/nitrides, which are promising candidates in electrodes. The layered structure facilitates ion insertion/extraction, which offers promising electrochemical characteristics for electrochemical energy storage. However, the low capacity accompanied by sluggish electrochemical kinetics of electrodes as well as interlayer restacking and collapse significantly impede their practical applications. Recently, interlayer space engineering of MXenes by different chemical strategies have been widely investigated in designing functional materials for various applications. In this review, an overview of the most recent progress of 2D MXenes engineering by intercalation, surface modification as well as heterostructures design is provided. Moreover, some critical challenges in future research on MXene-based electrodes have been also proposed.     

Application of graphite tubes modified with high-melting carbides in electrothermal atomic absorption spectrometry. I. General approach

The principal processes taking place in graphite tubes modified with high-melting carbides are critically discussed. Analysis of the published data supports the idea that these processes depend largely on the tube treatment procedure applied and on the properties of the corresponding carbide. Therefore, the most commonly used methods of tube treatment and some properties of high-melting carbides are described. Depending on the composition and structure of the carbide layer, the reactivity of graphite may increase or decrease. For both situations, the reasons for changes in the sensitivity and lifetime of the graphite tube are discussed. The major processes taking place in carbide-modified graphite tubes seem to be of a catalytic nature. For further research, a wider application of ideas and methods from other fields of science seems to be most promising.     

MXenes材料的光学特性及相关研究进展

过渡金属碳化物、 氮化物或碳氮化物(MXenes)具有丰富的元素组成和结构可调性, 显示出丰富的物理化学性质和巨大的应用潜力. 本文以此类材料的基本光学特性为基础, 从光子发射、 透明导电及储能、 非线性光学、 表面等离激元及拉曼增强、 光热转化、 光催化及光响应等光学相关领域展开分析和综述. 并对此二维材料相关应用的未来发展及机遇作了简单评述, 以期为进一步的研究提供参考.     

Principles and Latest Developments in the Field of Metallic and Nonmetallic Hard Materials

A survey of some fundamental aspects of the theory of hardness is followed by a discussion of recent developments in the field of sintered hard metal alloys. For example, good results have been obtained by the addition of hafnium carbide to hard metals. Niobium carbide can sometimes replace the more expensive tantalum carbide; vanadium carbide can be used to inhibit grain growth, especially in the case of ultrafine carbides. A brief outline is given of the results of investigations on ternary and quaternary systems with the components TiC, HfC, NbC, TaC, and WC. The utilization of sintered nitride and carbonitride hard metals in the field of machining appears feasible. Recently developed high-pressure/high-temperature autoclaves permit work on nitride systems under a high nitrogen pressure. The authors comment on the latest work in the field of non-metallic hard materials and on diamond synthesis.     

Superconductivity—a source of surprises

Superconductivity is ascribed to a tendency of pairwise localization of conduction electrons. As a necessary condition in k space bands with very small as well as large dispersion need to be present at the Fermi level (“flat band/steep band”). The sufficient condition is a strong enough coupling of the flat band states to specific phonons in case of phonon-mediated superconductivity. The electron–phonon coupling parameter λ reveals a peak structure in the phonon q-space. These aspects are discussed for actual examples, e.g., rare earth carbides and carbide halides as well as MgB₂.     

碳化钼催化材料的制备、表征及CO加氢反应性能的研究

以MoO3为前驱体,CH4/4H2为碳化介质,通过程序升温反应法(TPRe)制备了不同晶型碳化钼 (β-Mo2C和α-MoC1-x) 催化材料,并通过XRD、BET、TEM、SEM和XPS等表征手段对碳化钼材料的晶体结构、比表面积、形貌及电子特征进行了研究;同时考察了不同晶型碳化钼的CO加氢反应性能。结果表明,其具有很高CO加氢活性,产物主要为烷烃,同时有少量低碳醇生成。因此,碳化钼有望成为新型F T合成或低碳醇合成的催化剂。     

Boride-based nano-laminates with MAX-phase-like behaviour

MAX-phases being usually composed of transition metals, group A elements and carbon/nitrogen are considered interesting materials for many applications because of their tremendous bulk modulus, “reversible” plasticity, and machinability. This is mainly due to their unique kind of bonding comprising covalent, ionic as well as metallic bonds providing “easy” planes of rupture and deformability due to the layered crystal structures.In transition metal boride systems, similar types of bonding are available. In particular the W₂B₅-structure type and its stacking variations allow the synthesis of strongly layered crystal structures exhibiting unique delamination phenomena.The paper presents ab initio calculations showing the similarities of bonding between the ternary carbides and the corresponding ternary or quaternary borides. Formation of boride-based nano-laminates from auxiliary liquid phases, from the melt as well as during sintering and precipitation from supersaturated solid solutions will be discussed by means of SEM and TEM studies. The role of impurities weakening the interlayer bonding will be addressed in particular. The pronounced cleavage parallel to the basal plane gives rise for crack deflection and pull-out mechanisms if the laminates are dispersed in brittle matrices such as boron carbide, silicon carbide or other transition metal borides.     

In Situ Transformation of Prussian-Blue Analogue-Derived Bimetallic Carbide Nanocubes by Water Oxidation: Applications for Energy Storage and Conversion

Using bimetallic Prussian blue analogue (PBA) as a precursor is effective for preparing electrocatalysts for the oxygen evolution reaction (OER); however, the role of these PBA-derived catalysts in the OER is still ambiguous. Herein, by simply controlling synthesis temperature, a bimetallic PBA-derived O,N-codoped Ni–Fe carbide, can be well tuned to optimize structure and OER performance. Importantly, by a series of ex situ and in situ investigations, real active species of NiFeO_xH_y are in situ formed on the surface during the OER, which reveals a “pre-catalyst” role of O,N-codoped Ni–Fe carbides. Furthermore, it has been successfully applied to highly efficient Zn–air batteries and outplays its RuO₂ counterpart. When applied to photoelectrocatalytic water oxidation as the co-catalyst, it improves the performance of the BiVO₄ photoanode by enhancing hole collecting and transporting ability. We believe this research not only provides a highly efficient and low-cost electrocatalyst for the OER, but also unveils the “pre-catalyst” role of PBA-derived materials in energy-storage and conversion devices.     

V2AlC, V4AlC3-x (x approximately 0.31), and V12Al3C8: synthesis, crystal growth, structure, and superstructure

Single crystals of V2AlC and the new carbides V4AlC3-x and V12Al3C8 were synthesized from metallic melts. V2AlC was formed with an excess of Al, while V4AlC3-x (x approximately 0.31) and V12Al3C8 require the addition of cobalt to the melt. All compounds were characterized by XRD, EDX, and WDX measurements. Crystal structures were refined on the basis of single-crystal data. The crystal structures can be explained with a building-block system consisting of two types of partial structures. The intermetallic part with a composition VAl is a two-layer cutting of the hexagonal closest packing. The carbide partial structure is a fragment of the binary carbide VC1-x containing one or three layers. V2AlC is a H-phase (211-phase) with space group P63/mmc, Z=2, and lattice parameters of a=2.9107(6) A, and c=13.101(4) A. V4AlC3-x (x approximately 0.31) represents a 413-phase with space group P63/mmc, Z=2, a=2.9302(4) A, and c=22.745(5) A. The C-deficit is limited to the carbon site of the central layer. V12Al3C8 is obtained at lower temperatures. In the superstructure (P63/mcm, Z=2, a=5.0882(7) A, and c=22.983(5) A) the vacancies on the carbon sites are ordered. The ordering is combined to a small shift of the V atoms. This ordered structure can serve as a structure model for the binary carbides TMC1-x as well. V4AlC3-x (x approximately 0.31) and V12Al3C8 are the first examples of the so-called MAX-phases (MX)nMM' (n=1, 2, 3), where a deficit of X and its ordered distribution in a superstructure is proven, (MX1-x)nMM'.     

High activity carbide supported catalysts for water gas shift

Nanostructured carbides are refractory materials with high surface areas that could be used as alternatives to the oxide materials that are widely used as support materials for heterogeneous catalysts. Carbides are also catalytically active for a variety of reactions, offering additional opportunities to tune the overall performance of the catalyst. In this paper we describe the synthesis of molybdenum carbide supported platinum (Pt/Mo(2)C) catalysts and their rates for the water gas shift reaction. The synthesis method allowed interaction of the metal precursor with the native, unpassivated support. The resulting materials possessed very high WGS rates and atypical Pt particle morphologies. Under differential conditions, rates for these catalysts were higher than those for the most active oxide-supported Pt catalysts and a commercial Cu-Zn-Al catalyst. Experimental and computational results suggested that active sites on the Pt/Mo(2)C catalysts were located on the perimeter of the Pt particles and that strong interactions between Pt and the Mo(2)C surface gave rise to raft-like particles.     

Hydrogenation of CO over carbides of tungsten

CO hydrogenation on tungsten carbides has been investigated.The methanation activitiesof tungsten carbides are comparable to that of supported Group VIII metal catalysts.Temperature-programmed thermal desorption spectra of CO on tungsten carbide show that CO is adsorbed non-dissociatively,and the surface—CO bond appears to be rather weak.