WC Nanoparticles Research Articles

Diamond tools in metal bonds dispersion-strengthened with nanosized particles for cutting highly reinforced concrete

The paper describes two bonds dispersion-strengthened with WC and ZrO2 nanoparticles, which are used in the manufacture of diamond tools for cutting reinforced concrete. The pattern of nano-particles distribution in the metal matrix is studied. Physical-mechanical and tribological properties of the bonds have been determined. The use of dispersion-strengthened bonds is demonstrated to ensure a 60% longer tool life without reducing the cutting speed.

On the development of nanostructured WC-Co hard alloys

A dimensional region of the existence of WC nanoparticles and nanostructured WC-Co hard alloys has been substantiated. It has been shown that the existing technologies do not allow to obtain pore- free WC-Co hard alloys with carbide particles of size 5–40 nm to be produced. A method of the formation of nanostructured hard alloys has been proposed.

Tungsten carbide on the subnanoscale level: Atomic structure, electronic states, and mechanical properties

Density functional theory and pseudopotential methods are used to study the atomic structure, electronic states, and mechanical properties of WC nanoparticles 1 nm in size and smaller. It is found that the smallest particles (containing less than 15 atomic pairs of WC) have a cubelike NaCl-type structure. In the range of 10 to 20 pairs, WC particles with cubic and trigonal structures have approximately equal energies; however, their internal atomic structure preserves the alternation pattern of W and C atoms that is inherent in NaCl. A trigonal WC15 particle is used to study the tensile strength and resistance to compression. It is found that the strength of the nanoparticle is much higher than the strength of the bulk material. Tungsten and carbon vacancies decrease the strength of the particles; however, cobalt atoms penetrating into the vacancy positions can restore the strength of the nanoparticles and their resistance to compression almost to values characteristic of a defect-free case. The density of electronic states of WC nanoparticles has a form close to the density of states of the bulk cubic phase of tungsten carbide exhibiting a metallic nature with a high density near the Fermi level.

Novel Synthesis of Hierarchical Tungsten Carbide Micro‐/Nanocrystals from a Single‐Source Precursor

Hierarchical tungsten carbide (WC) micro‐/nanocrystals were synthesized by thermal treating a single‐source precursor of the tungstate‐based inorganic–organic hybrid compound in a sealed quartz tube at 1000°–1050°C. The hybrid precursor was synthesized by an acid–base reaction of H2O‐moistened H2WO4 and n‐octylamine in a nonpolar solvent. The X‐ray diffraction results indicated that the product obtained at 1050°C for 2 h consisted of a hexagonal WC phase, and the products obtained at temperatures lower than 1000°C had other phases (e.g., α‐W2C, W or β‐W40.9N9.1) besides the major phase of hexagonal WC. The scanning electron microscopy observations indicated that the hexagonal WC obtained at 1050°C consisted of hierarchical microparticles with a size range of 4–18 μm, and the above microparticles were porous aggregates of WC nanoparticles with crystal sizes of 100–250 nm. The newly developed process could achieve pure WC materials at relative low temperatures using a single‐source precursor, and the porous and hierarchical WC micro‐/nanoparticles would have potential applications in catalysis and superhard composites.

Direct solid-state synthesis of tungsten carbide nanoparticles from mechanically activated tungsten oxide and graphite

Solid-state carbothermic reduction of tungsten oxide (WO 3) to nano-sized tungsten carbide (WC) particles was achieved by calcining mechanically activated mixtures of WO 3 and graphite at 1215 °C under vacuum condition. By experiments and thermodynamic calculations, the intermediate phases, WO 2.72, WO 2 and metallic tungsten (W), were observed at 741 °C, which decomposed to synthesize the final product (WC). Homogeneity increase and associated decrease in the diffusion path by mechanical milling and formation of these intermediates are mainly responsible for the successful production of WC. The process indicates that solid-state synthesis of WC nanoparticles directly from as-milled mixtures of tungsten oxide and graphite powder is possible.

Optimization of processing parameters for the synthesis of tungsten carbide (WC) nanoparticles through solvo thermal route

In order to manufacture cemented tungsten carbide nanomaterials efforts are being made to synthesize nano-WC powders by different techniques. The present work is an attempt to synthesize WC nanoparticles by thermo-chemical route where WO 3 was reduced to nano-WC. During experimentation the reaction parameters were varied to optimize the processing variables for the formation of tungsten carbide (WC) nanoparticles. The reaction time 20 h for 36 ml acetone as a carbon source gives the maximum yield of WC. Phase identification of the product phase(s) was done by X-ray diffraction and transmission electron microscope. Differential thermal analyzer and thermal gravimetric analysis were also done to study phase transformation and stability of the product phases.

Fabrication of TiC/WC ultra hard nanocomposite layers by plasma electrolysis and study of its characteristics

Ultra hard ceramic based matrix nanocomposite layers of tungsten carbide (WC) on matrix of titanium carbide were fabricated in an organic electrolyte. The dependence of WC amount in nanocomposite coatings was investigated in relation to the temperature of electrolyte, WC concentration in bath, current density and stirring rate. It was shown that volume percentage of WC in the layer can be affected by these parameters. The fabricated phases were studied with X-ray diffraction and their microhardness values were reached near to 2580 Hv 0.5. Increasing of the WC nanoparticles concentration in the electrolyte in a constant stirring rate will lead to an increase in content of nanoparticles in the nanocomposite layers. Concentration of WC nanoparticles in the bath illustrated specific level for increasing of tungsten percentage in the nanocomposite layers. Concentration of WC nanoparticles in the bath had an optimum level around 6 g l − 1 for achieving the minimum nano-roughness on the surface of nanocomposite layer. It may vary for different current densities.

Small tungsten carbide nanoparticles: Simulation of structure, energetics, and tensile strength

Ab initio methods of the density functional theory and pseudopotentials were used to study the structure, electronic states, total energy and tensile strength of WC nanoparticles. It has been found that the very small particles (having less than 15 WC atomic pairs) have a cube-like NaCl structure. Particles with trigonal and cubic structures have approximately the same energies in the region of 10–20 WC pairs; however, the local atomic structure keeps the NaCl-like alternation of W and C atoms. The WC 15 trigonal particle was used as a typical one to study the WC nanoparticle tensile strength. It has been found that W and C vacancies decrease the tensile strength, but not drastically. Electronic structure of nanoparticles looks like that of bulk fcc -WC with a large density of states at the Fermi level.

Tungsten carbide cobalt nanoparticles exert hypoxia-like effects on the gene expression level in human keratinocytes

BackgroundTungsten carbide (WC) and tungsten carbide cobalt (WC-Co) nanoparticles are of occupational health relevance because of the increasing usage in hard metal industries. Earlier studies showed an enhanced toxic potential for WC-Co compared to WC or cobalt ions alone. Therefore, we investigated the impact of these particles, compared to cobalt ions applied as CoCl2, on the global gene expression level in human keratinocytes (HaCaT) in vitro.ResultsWC nanoparticles exerted very little effects on the transcriptomic level after 3 hours and 3 days of exposure. In contrast, WC-Co nanoparticles caused significant transcriptional changes that were similar to those provoked by CoCl2. However, CoCl2 exerted even more pronounced changes in the transcription patterns. Gene set enrichment analyses revealed that the differentially expressed genes were related to hypoxia response, carbohydrate metabolism, endocrine pathways, and targets of several transcription factors. The role of the transcription factor HIF1 (hypoxia inducible factor 1) is particularly highlighted and aspects of downstream events as well as the role of other transcription factors related to cobalt toxicity are considered.ConclusionsThis study provides extensive data useful for the understanding of nanoparticle and cobalt toxicity. It shows that WC nanoparticles caused low transcriptional responses while WC-Co nanoparticles are able to exert responses similar to that of free cobalt ions, particularly the induction of hypoxia-like effects via interactions with HIF1α in human keratinocytes. However, the enhanced toxicity of WC-Co particles compared to CoCl2 could not be explained by differences in gene transcription.

Computational fluid dynamics simulation of chemical vapor synthesis of WC nanopowder from tungsten hexachloride

The chemical vapor synthesis (CVS) reactor for the preparation of WC nanopowder from tungsten hexachloride was simulated by a two-dimensional multiphase computational fluid dynamics (CFD) model. The model solves the gas-phase governing equations of overall continuity, momentum, energy, and species mass transport inside a tubular reactor system. The population balance model is coupled with the gas-phase equations to describe the formation and growth of WC nanoparticles. The model has been validated with experimental data in terms of average particle size and concentration of unreacted precursor at the outlet. The contours of temperature, velocity, species concentration and particle size distribution (PSD) inside the tubular reactor were computed.

Chitosan: a green carbon source for the synthesis of graphitic nanocarbon, tungsten carbideand graphitic nanocarbon/tungsten carbide composites

In this paper, a simple approach was proposed to fabricate graphitic carbon nanocapsules,tungsten carbide and tungsten carbides/graphitic carbon composites by using chitosan, agreen and renewable biopolymer, as a carbon source. The route includes, first,fabrication of the precursors that consist of chitosan coordinated with a certainmetal ion (or metal complex anion) followed by carbonizing the precursors underN2 atmosphere. The composition of the final products could be regulated by changing the type andratio of the metal source (cations or complex anions) combined with the chitosan in the precursors.The experimental results showed that uniform carbon nanocapsules could be obtained whenNi2+ was introducing in the precursors, while incorporating[PW12O40]3− (PW12) with chitosan led to the formation of WC nanoparticles. As theNi2+ andPW12 are simultaneously coordinated with chitosan, the composites of tungsten carbide/graphiticcarbon were successfully produced. Transmission electron microscopy (TEM) analysisrevealed that the graphitic carbon nanocapsules are about 45 nm in diameter; uniform WCnanoparticles with a average size of 40 nm are observed. Moreover, the particle size ofWC in the tungsten carbide/graphitic carbon composite is about 10 nm, which issmaller than that of the pure WC particles. Furthermore, the performance of thesample-loaded Pt nanoparticles for methanol electro-oxidation was studied in detail.The results indicated that the samples could act as good carriers for Pt in themethanol electro-oxidation reaction with high effectivity and improved stability.

Metal Nitride and Metal Carbide Nanoparticles by a Soft Urea Pathway

An easy way to produce several metal nitrides and metal carbides at relatively low temperature (800 °C) using simple and mainly nontoxic precursor is presented. The procedure has been shown to be rather general and it was possible to synthesize TiN, VN, NbN, GaN, Mo2N, W2N, CrN, NbC(N), TiC(N), WC, Mo2C, and Cr3C2 nanoparticles using urea or close derivatives as both nitrogen or carbon source and the growth controlling system. In every case, a homogeneous gel-like starting product has been formed that is converted by calcination into the corresponding metal nitride or metal carbide (including mixed species), without any preliminary treatments or further purifications. Samples were characterized by XRD, TEM, SEM, EA, and BET, and the products were shown to be well-defined and rather homogeneous.

Agglomeration of tungsten carbide nanoparticles in exposure medium does not prevent uptake and toxicity toward a rainbow trout gill cell line

Due to their increased production and use, engineered nanoparticles are expected to be released into the aquatic environment where particles may agglomerate. The aim of this study was to explore the role of agglomeration of nanoparticles in the uptake and expression of toxicity in the rainbow trout ( Oncorhynchus mykiss) gill cell line, RTgill-W1. This cell line was chosen as model because it is known to be amenable to culture in complete as well as greatly simplified exposure media. Nano-sized tungsten carbide (WC) with or without cobalt doping (WC-Co), two materials relevant in the heavy metal industry, were applied as model particles. These particles were suspended in culture media with decreasing complexity from L15 with 10% fetal bovine serum (FBS) to L15 to L15/ex, containing only salts, galactose and pyruvate of the complete medium L15. Whereas the serum supplement in L15 retained primary nanoparticle suspensions, agglomerates were formed quickly in L15 and L15/ex. Nevertheless, scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) elemental analysis revealed an uptake of both WC and WC-Co nanoparticles into RTgill-W1 cells irrespective of the state of agglomeration of nanoparticles. The localisation seemed to be restricted to the cytoplasm, as no particles were observed in the nucleus of cells. Moreover, reduction in cell viability between 10 and 50% compared to controls were observed upon particle exposure in all media although the pattern of impact varied depending on the medium and exposure time. Short-term exposure of cells led to significant cytotoxicity at the highest nominal particle concentrations, irrespective of the particle type or exposure medium. In contrast, long-term exposures led to preferential toxicity in the simplest medium, L15/ex, and an enhanced toxicity by the cobalt-containing WC nanoparticles in all exposure media. The composition of the exposure media also influenced the toxicity of the cobalt ions, which may dissolve from the WC-Co nanoparticles, with cells reacting much more sensitively toward cobalt ions in the absence of FBS. However, the toxicity observed by ionic cobalt alone did not explain the toxicity of the WC-Co nanoparticles, suggesting that the combination of metallic Co and WC is the cause of the increased particle toxicity of WC-Co. Taken together, our findings indicate that minimal exposure media can lead to rapid agglomeration of nanoparticles but that agglomeration does not prevent uptake into cells and the expression of toxicity.

Effect of WC nanoparticle size on the sintering temperature, density, and microhardness of WC-8 wt % Co alloys

Using X-ray diffraction, scanning electron microscopy, and density measurements, we have studied the effect of WC particle size (20 to 150 nm) on the optimal sintering temperature of the WC-8 wt % Co alloy and the effect of sintering temperature (800–1600°C) on its phase composition, density, and microhardness. The results indicate that, during sintering of the starting powder mixture, the first to form is the ternary carbide phase Co6W6C. At sintering temperatures of 1100°C and above, this phase reacts with carbon to form Co3W3C. Sintering above 1000°C leads to the formation of a cubic solid solution of tungsten carbide in cobalt, β-Co〈WC〉, along with the ternary carbide phases. The density and microhardness of the alloy have been measured as functions of sintering temperature. The use of WC nanopowder has been shown to reduce the optimal sintering temperature of the WC-Co alloy by about 100°C.

Synthesis of Metastable Tungsten Carbide Nanoparticles by Mechanochemical Alloying Process

Thermodynamically metastable tungsten carbide (W2C) nanoparticles have been synthesized by mechanochemical alloying (MCA) process. Mg was used as reductive agent and graphite as carbon source. The reduction reaction of WO3 and Mg gave nanometer W powders. Subsequent diffusion reaction of fresh W with carbon produced metastable W2C and a small amount of WC nanoparticles in a W rich environment. WC was then transferred to W2C during the prolonged MCA process. The mechanism of such a chemical transformation has been discussed from a point of view of thermodynamics. The subsequent self-propagation diffusion reaction of fresh W with C source controlled the rate of the whole reaction process due to its slow reaction speed. The final product of the MCA process mainly depends on the composition ratio of W to C in the raw materials. W2C nanoparticles in single phase have been finally fabricated by MCA process at a W rich environment. The structure of the final product has been determined by x-ray diffraction, while the morphology and microstructure of the as-milled W2C nanoparticles have been demonstrated by transmission electron microscopy images.

Facile route to prepare TaC, NbC and WC nanoparticles

By a novel solid-state reaction process using amorphous C3N4 (a-C3N4) and transition metal oxides as starting reagents, cubic TaC, NbC and hexagonal WC nanoparticles were successfully synthesized at 1150 °C. The products were characterized by power X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The experimental results show that a-C3N4 obtained by the reaction between C3N3Cl3 and Li3N is a highly efficient carburation reagent and the transition metal oxides are completely transformed into the corresponding metal carbide nanoparticles at 1150 °, respectively, which is significantly lower than that reported for the traditional preparation of carbides, typically >1600 °. The TaC, NbC and WC nanoparticles are found to have an average particle size of 10 nm, 15 nm and 8 nm by TEM observation, respectively.

Features of the influence of nanodispersed additions on the process of and properties of the Fe-Co-Cu-Sn sintered alloy

Features of the influence of Al2O3, ZrO2, WC, and Si3N4 nanoparticles on the process of obtainment, mechanical, and tribological properties of the 74%Fe-15%Co-9%Cu-1%Sn alloy obtained by powder metallurgy methods are investigated. Mixing nanoparticles with alloy powder was performed in a centrifugal planetary mill. It is shown that the nanoparticles uniformly distributed over the charge complicate the processes of compaction during cold pressing and sintering. The alloy (dispersion strengthened by nanoparticles), which was obtained by the technology of hot pressing, is characterized by high mechanical and tribological properties. Wear resistance increases by a factor of four, hardness is increased by 10–16 HRB, and the bending breaking point is increased by 54%.

Synthesis and characterization of laser-based direct metal deposited nano-particles reinforced surface coatings for industrial slurry erosion applications

A nano-based material system resistant to the impingement of solid and liquid particles on the solid surfaces was developed by the laser-based direct metal deposition (LBDMD) process. The nano-based materials system contains 5% tungsten carbide (WC) nano-particles that are agglomerated with nickel–tungsten carbide 60 (Ni–Tung 60) by ball mill operation for slurry erosion resistance applications. Slurry erosion tests are performed on the LBDMD processed depositions using the ceramic proppant at different impingement angles using the abrasive water jet erosion testing machine. From these tests the amount of material removed, depth of penetration, and profile of the formed crater are computed as a function of the abrasive water jet impingement angles. The nano-based materials system exhibited better performance for slurry erosion resistance than the monolithic Ni–Tung 60 depositions and 4140 steels. In order to understand the role of the WC nano-particles influence on slurry erosion resistance and to understand the characteristic features of erosion surfaces, sub-surfaces, and the erosion mechanism, different advanced characterization tools are used.

C3N4 as a Precursor for the Synthesis of NbC, TaC and WC Nanoparticles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Nanosized tungsten carbide for NO[sub x] reduction

WC nanoparticles were synthesized using a variation of pulsed laser deposition (PLD) process. In this modified PLD the ablated plume is carried away by a circulating carrier gas from the evaporation region. It is then allowed to condense heterogeneously and the condensed particles are collected on a filter. Using this technique we synthesized two different types of particles, as-prepared WC and pure W nanoparticles. Pure W nanoparticles were subsequently carburized to form WC. These nanoparticles were used to study the feasibility for the use in NOx reduction. The structural and chemical properties of these samples were analyzed using x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Catalytic activity was measured using a tube reactor. A combination of 1% NO and 99% He gas was used. Both the pure WC and carburized WC samples were found to be catalytically active with an activation temperature of about 400°C. The stability of the catalysts was studied by performing de-NOx experiments for an extended period of time. Both XRD and XPS analyses of the samples after de-NOx confirm the formation of oxide. CO addition helped to reduce the extent of oxide formation.