Carbide

About: Carbide is a research topic. Over the lifetime, 36331 publications have been published within this topic receiving 503586 citations.

Carbothermal reduction synthesis of nanocrystalline zirconium carbide and hafnium carbide powders using solution-derived precursors

Abstract: Zirconium carbide (ZrC) and hafnium carbide (HfC) powders were produced by the carbothermal reduction reaction of carbon and the corresponding metal oxide (ZrO2 and HfO2, respectively). Solution-based processing was used to achieve a fine-scale (i.e., nanometer-level) mixing of the reactants. The reactions were substantially completed at relatively low temperatures (<1500°C) and the resulting products had small average crystallite sizes (∼50–130 nm). However, these products contained some dissolved oxygen in the metal carbide lattice and higher temperatures were required to complete the carbothermal reduction reactions. Dry-pressed compacts prepared using ZrC-based powders with ∼100 nm crystallite size could be pressurelessly sintered to ∼99% relative density at 1950°C.

Tungsten Carbide Nanoparticles as Efficient Cocatalysts for Photocatalytic Overall Water Splitting

Abstract: Tungsten carbide exhibits platinum-like behavior, which makes it an interesting potential substitute for noble metals in catalytic applications. Tungsten carbide nanocrystals (≈5 nm) are directly synthesized through the reaction of tungsten precursors with mesoporous graphitic C(3)N(4) (mpg-C(3)N(4)) as the reactive template in a flow of inert gas at high temperatures. Systematic experiments that vary the precursor compositions and temperatures used in the synthesis selectively generate different compositions and structures for the final nanocarbide (W(2)C or WC) products. Electrochemical measurements demonstrate that the WC phase with a high surface area exhibits both high activity and stability in hydrogen evolution over a wide pH range. The WC sample also shows excellent hydrogen oxidation activity, whereas its activity in oxygen reduction is poor. These tungsten carbides are successful cocatalysts for overall water splitting and give H(2) and O(2) in a stoichiometric ratio from H(2)O decomposition when supported on a Na-doped SrTiO(3) photocatalyst. Herein, we present tungsten carbide (on a small scale) as a promising and durable catalyst substitute for platinum and other scarce noble-metal catalysts in catalytic reaction systems used for renewable energy generation.

Relationship between Iron Carbide Phases (ε-Fe2C, Fe7C3, and χ-Fe5C2) and Catalytic Performances of Fe/SiO2 Fischer–Tropsch Catalysts

Abstract: The influence of different iron carbides on the activity and selectivity of iron-based Fischer–Tropsch catalysts has been studied. Different iron carbide phases are obtained by the pretreatment of a binary Fe/SiO2 model catalyst (prepared by coprecipitation method) to different gas atmospheres (syngas, CO, or H2). The phase structures, compositions, and particle sizes of the catalysts are characterized systematically by XRD, XAFS, MES, and TEM. It is found that in the syngas-treated catalyst only χ-Fe5C2 carbide is formed. In the CO-treated catalyst, Fe7C3 and χ-Fe5C2 with a bimodal particle size distribution are formed, while the H2-treated catalyst exhibits the bimodal size distributed e-Fe2C and χ-Fe5C2 after a Fischer–Tropsch synthesis (FTS) reaction. The intrinsic FTS activity is calculated and assigned to each corresponding iron carbide based on the phase composition and the particle size. It is identified that Fe7C3 has the highest intrinsic activity (TOF = 4.59 × 10–2 s–1) among the three candidat...

Influence of doping on the structural and optoelectronic properties of amorphous and microcrystalline silicon carbide

Abstract: Amorphous and microcrystalline silicon carbide, undoped and doped, has attracted a great attention for its optical and electrical properties. The introduction of dopant atoms in the network of amorphous films permits the control of electrical properties but it gives rise to a decreasing of the optical gap. Microcrystalline SiC:H films seem to provide films having a wide range of electrical conductivities without drastic change in the optical gap. This paper presents the results of a detailed study on the effects of boron and phosphorus doping on structural, optical, and electrical properties of a‐SiC:H and μc‐SiC:H films. An optical gap as high as 2.1 eV, together with a conductivity of 10−3 Ω−1 cm−1, are shown by doped μc‐SiC:H.