Vanadium Carbide Nanopowders Research Articles

Synthesis of Vanadium Carbide Nanopowders via Mechanical Alloying and Microwave Heating Methods

A simple and fast method of preparation of vanadium carbide (V8C7) nanopowders using mechanical alloying assisted microwave heating method was demonstrated. The micron-sized V2O5 and nano-sized carbon black were used as starting materials. The as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric and differential scanning calorimetry (TG-DSC), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. The experimental results show that the V8C7 powders can be obtained by microwave heating at 1 100 °C for 1 h (34wt% C). The synthesized powders show good dispersion and are mainly composed of spherical or near-spherical particles with a mean diameter of about 30 nm. The XPS spectra show that the surface of the specimen mainly consists of V, C, and O three species elements.

Nanocrystalline VC y powders in the homogeneity range of a disordered cubic phase

Nonstoichiometric vanadium carbide nanopowders ranging in average particle size from 20 to 40 nm have been prepared by high-energy milling and then vacuum-annealed at temperatures from 600 to 1200°C. The crystal structure, microstructure, morphology, and particle size distribution of the starting, milled, and annealed vanadium carbide powders have been studied by X-ray diffraction, laser diffraction, and scanning electron microscopy. The results demonstrate that vacuum annealing of the VCy nanopowders at temperatures from 600 to 800°C leads to partial carbon loss, compositional changes within the homogeneity range of the disordered cubic phase, and a slight increase in nanoparticle size. Vacuum annealing of the nanopowders at t ≥ 1000°C leads to a considerable carbon loss, the formation of the hexagonal phase V2C along with the cubic carbide VCy, and an appreciable increase in VCy particle size. Thus, vacuum annealing of the nanopowders at 800°C or a lower temperature allows one to vary their composition from VC0.70 to VC0.81, while maintaining the average particle size in the range 50 to 20 nm.

Fast synthesis of VC and V2C nanopowders by the mechanochemical combustion method

VC and V2C nanopowders were synthesized by the mechanochemical combustion method in a high-energy ball mill. The synthesized powders were studied by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). According to X-ray diffraction the product predominantly consists of VC and V2C phases after 80min milling without further heat treatment. The TEM results show that vanadium carbide nanopowders are mainly composed of nearly spherical particles with a mean diameter of about 40nm. Thermodynamic calculations show the reaction to be a mechanically induced self-sustaining one (MSR).

Tungsten Carbide and Vanadium Carbide Nanopowders Synthesis in DC Plasma Reactor

Air–methane and nitrogen–hydrogen DC thermal plasma confined flows were used to synthesize tungsten carbide and vanadium carbide nanopowders. The influence of input process parameters such as C/W and C/V molar ratio, plasma jet chemical composition, plasma jet enthalpy, and reactants flow rates on the average nanoparticle size, chemical and crystallographic phase compositions were investigated. During post heat treatment, the synthesized MeC1−x nanopowders were fully carburized to monocarbides WC and VC with particles size less than 80 and 40 nm correspondently.

Effect of Carbon Content on Preparation of Vanadium Carbide Nanopowders by the Carbonization of the Precursor

Vanadiunm carbide (V8C7) nanopowders were prepared by the solution-derived precursor method, ammonium vanadate (NH4VO3) and glucose (C6H12O6) were used as raw materials. The samples were characterized by TG-DTA, XRD and SEM. The results show that the weight of the sample reduces rapidly before 600°C (about 25 wt.%), but it changes very slowly (about 1.0 wt.%) after 600°C. The DTA curve mainly includes 5 endothermic peaks and an exothermic peak which are corresponding to the peaks of 110°C, 300°C, 348°C, 677°C, 1000°C and 509°C, respectively. When the carbon content between 24 wt.% and 30 wt.%, the samples mainly consist of V2O3 and VC1−X (1−X = 0.66–0.88). When the carbon content is 32 wt.%, the sample includes a main phase (V8C7) and a second phase (V2O3). When the carbon content reaches to 36 wt.%, the single-phase V8C7 powder can be obtained. The SEM results show that major powders exhibit good dispersion and are mainly composed of particles with a mean diameter of ~200 nm.

Synthesis of vanadium carbide nanopowders by thermal processing and their characterization

Vanadium carbide (V 8C 7) nanopowders were successfully prepared by thermal processing the precursor which originated from the mixture of ammonium vanadate (NH 4VO 3) and nanometer carbon black. The products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) methods. The single phase V 8C 7 powders can be prepared at ∼ 1100 °C for 1 h with the average crystallite size of 32.6 nm and the powders show good dispersion and are mainly composed of uniformly-sized spherical particles with a mean diameter of ∼ 100 nm.