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Tungsten carbide (WC) is a widely used engineering material which is usually prepared at high temperature. A new mechanism for synthesizing nanoscaled WC at ultralow temperature has been discovered. This discovery opens a novel route to synthesize valuable WC and other carbides at a cost-efficient way. The novel formation mechanism is based on an i...
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... For instance, the Pt/WC catalysts have shown higher methanol oxidation activity, improved tolerance to CO poisoning, and enhanced oxygen reduction activity compared to the conventional Pt/C catalysts [6,[15][16][17], indicating a synergistic effect between WC and Pt. To further enhance the catalytic activity, WCs with Nanomaterials 2024, 14, 1024 2 of 11 various shapes and structures have been synthesized by different methods and applied in various catalytic reactions [18][19][20]. However, the inherently low surface area of WC limits its effectiveness as a support. ...
... indicating a synergistic effect between WC and Pt. To further enhance the catalytic a ity, WCs with various shapes and structures have been synthesized by different met and applied in various catalytic reactions [18][19][20]. However, the inherently low su area of WC limits its effectiveness as a support. ...
A composite material of tungsten carbide and mesoporous carbon was synthesized by the sol-gel polycondensation of resorcinol and formaldehyde, using cetyltrimethylammonium bromide as a surfactant and Ludox HS-40 as a porogen, and served as a support for Pd-based electrodes. Phosphorus-modified Pd particles were deposited onto the support using an NH3-mediated polyol reduction method facilitated by sodium hypophosphite. Remarkably small Pd nanoparticles with a diameter of ca. 4 nm were formed by the phosphorus modification. Owing to the high dispersion of Pd and its strong interaction with tungsten carbide, the Pd nanoparticles embedded in the tungsten carbide/mesoporous carbon composite exhibited a hydrogen oxidation activity approximately twice as high as that of the commercial Pt/C catalyst under the anode reaction conditions of proton exchange membrane fuel cells.
... These methods fail to produce pure carbide materials with particle sizes under 100 nm. To attain nanosized tungsten carbide powders, plasma-enhanced chemical, mechanochemical, detonation, self-propagating, high-temperature, and electrochemical synthesis in melts and electrical explosion of metal conductors are employed [13][14][15][16][17][18][19][20][21][22]. ...
Abstract: High-temperature electrochemical synthesis (HTES) in molten salts is highly promising among the up-to-date methods for the production of carbide powders. Ultrafine composite powders of tungsten carbides (WC|C, WC|C|Pt, W2C|WC, and W2C|W) were synthesized using the HTES method in electrolytic baths with different chemical compositions under various synthesis conditions (cathode current density, CO2 pressure in the electrolyzer, temperature, and cathode material). Composite powders (up to 3 wt.% free carbon) with a WC particle size of 20–30 nm were prepared using Na, K|Cl (1 : 1)–Na2W2O7 (6.4 wt.%)–CO2 (1.25 MPa) and Na, K|Cl (1 : 1)–Na2WO4 (12.0 wt.%)– NaPO3 (0.7 wt. %)–CO2 (1.25 MPa) electrolytic baths at a temperature of 750°C. When the CO2 pressure was reduced to 0.75 MPa, composite W2C|WC powders formed at the cathode. The ratio of carbide phases in the composites depended on the initial concentration of tungsten salts in the electrolyte and on the CO2 gas pressure in the electrolyzer. The addition of Li2CO3 (4.5 wt.%) to the electrolytic salt mixture decreased the tungsten carbide particles to 10 nm, changed their morphology, and increased the free carbon content in the composite up to 5 wt.%. The specific surface area of the powder increased by a factor of 4 to 7 (from 20–35 to 140 m2/g). The resulting products were modified with fine platinum particles through the use of platinum cathodes. The HTES method demonstrated its potential for producing tungsten carbide powders with the properties allowing their use as electrocatalysts in the hydrogen evolution reaction. For the WC|C composite powders synthesized in the Na, K|Cl–Na2W2O7–Li2CO3–CO2 system, the hydrogen evolution potential was – 0.02 V relative to the normal hydrogen electrode, the overpotential at a current density of 10 mA/cm2 was –110 mV, the exchange current was 7.0 10–4 A/cm2, and the Tafel slope was –85 mV/dec.
Keywords: electrochemical synthesis, molten salts, nanosized powders, tungsten carbides, surface morphology
... The MWCNTs have great conductance and they can swiftly conduct the photogenerated charge carriers away from the titania surfaces which resulted in lowering the E g of MWCNTs-TiO 2 nanocomposite [37]. Besides the superior photocatalytic performance of WC and its potential usage as a replacement for Pt catalyst [44,[73][74][75], it also has a wide bandgap (~ 3.3 eV) which caused the enlargement of WC-TiO 2 nanocomposite's E g [76]. Content courtesy of Springer Nature, terms of use apply. ...
In this paper, a comparative study about the photocatalytic performance of pure Anatase/Rutile mixed-phase Titania (AR-TiO2) nanoparticles and their nanocomposites with multi-walled Carbon Nanotubes (MWCNTs) & ‘Platinum-like’ Tungsten Carbide (WC) has been carried out. Nanostructured amorphous-titania was synthesized through the Sol–gel route followed by its crystallization through calcination at ~ 550 °C, while the MWCNTs-TiO2 and WC-TiO2 nanocomposites were produced by the Bath Ultrasonication of their individual aqueous mixtures with the AR-TiO2 nanoparticles. These nanocatalysts were further characterized using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), UV–Visible Spectrophotometry, and Photocatalytic decomposition testing using Methylene Blue (MB) dye. The XRD-based structural examinations determined the occurrence of anatase/rutile mixed phases of titania in all nanocatalysts alongside the MWCNTs and WC in their relevant nanocomposites having connected through physical means only. The chemical analysis was conducted through the FT-IR which also confirmed that there are no chemical interactions in-between the constituents of nanocomposites. The SEM-based morphological studies revealed that the AR-TiO2 nanoparticles were spherical in shape, having average sizes of ≈ 20 nm which were forming flower-like structures around the ends of MWCNTs and were making agglomerates in MWCNTs-TiO2 and WC-TiO2 nanocomposites, respectively. The Optical bandgaps (Eg) were measured through UV–Visible spectrophotometry where the Eg of AR-TiO2 nanoparticles (~ 2.69 eV) was decreased by the mixing of MWCNTs (~ 2.56 eV) while an increasing trend was found with the WC addition (~ 2.75 eV). Finally, the photocatalytic studies showed that MWCNTs-TiO2 and WC-TiO2 nanocomposites have higher efficiencies than the pure AR-TiO2 nanoparticles in the visible and UV-A (λ ~ 366 nm) ranges, respectively.
... Tungsten carbide has been widely used in various fields for decades due to its unique physical and mechanical properties. Significant experience has been accumulated in obtaining, analyzing the properties (especially physical-mechanical), and applying carbide tungsten-based materials [1][2][3][4][5]. Nevertheless, the determining factor when applying nanoscale materials is the chemical and phase composition. ...
–Studies of tungsten-carbide nanoparticles synthesized from tungsten oxide are carried out using different precursors in low-temperature plasma generated using vacuum-arc discharge. The phase content, structural features and size distribution in tungsten-carbide nanoparticles are explored using powder diffractrometry, Raman spectroscopy and the laser-scattering technique. The nanopowder X-ray diagram shows that the main phase of tungsten monocarbide WC is formed together with graphite C, tungsten W, and tungsten oxide WO3 phases. Tungsten semi-carbide W2C and cubic tungsten carbide WC1 — x are not detected which can be associated with the parameters of the electric-arc discharge and with the precursor distribution. Carbon black and glucose are used as reducing agents and carbidizers, respectively, to obtain tungsten-carbide nanopowder. Analysis of the results indicates that the use of glucose in synthesizing tungsten-carbide nanopowder dramatically increases the rate of recovering nanopowder if compared with using only graphite.
... Other examples of application of carbides in catalysts are hydrogenolysis and isomerization of hydrocarbons [22], catalytic and electrocatalytic hydrogen generation [23][24][25], hydrocarbon reforming [26,27], carbon dioxide upgrading [23,28], hydrogenation [29], and aromatization [30]. Moreover, carbides of layered structures are receiving increased attention in gas sensing [31,32] and battery applications [27,33,34]. ...
... It is characterized by high strength, fracture resistance, and resistance to high temperature and abrasion, as well as high melting (2600-2850 • C) and boiling points (6000 • C) [36]. Due to its properties, WC is widely used, among others, in the chemical, armament, and electronics industries, in the production of cutting mechanical tools, and in abrasives and surface coatings [33]. In addition, tungsten carbide exhibits catalytic properties, and the efficiency of WC as a catalyst is similar to that of platinum [34], its use being associated with much higher costs. ...
... The conversion of hydrocarbons with carbon chains longer than C 2 with carbon dioxide promotes dehydrogenation and aromatization reactions [215,221]. For propane, the oxidative dehydrogenation processes are described by Equations (29)- (33). Propane forms a surface complex with active oxygen from the oxycarbide (29). ...
Dry reforming of hydrocarbons (DRH) is a pro-environmental method for syngas production. It owes its pro-environmental character to the use of carbon dioxide, which is one of the main greenhouse gases. Currently used nickel catalysts on oxide supports suffer from rapid deactivation due to sintering of active metal particles or the deposition of carbon deposits blocking the flow of gases through the reaction tube. In this view, new alternative catalysts are highly sought after. Transition metal carbides (TMCs) can potentially replace traditional nickel catalysts due to their stability and activity in DR processes. The catalytic activity of carbides results from the synthesis-dependent structural properties of carbides. In this respect, this review presents the most important methods of titanium, molybdenum, and tungsten carbide synthesis and the influence of their properties on activity in catalyzing the reaction of methane with carbon dioxide.
... Among the hard materials, tungsten carbide (WC) has received considerable interest due to its unusual chemical and mechanical properties [46]. WC is an interstitial combination of carbon atoms filling a W crystal [46]. ...
... Among the hard materials, tungsten carbide (WC) has received considerable interest due to its unusual chemical and mechanical properties [46]. WC is an interstitial combination of carbon atoms filling a W crystal [46]. Since the early twentieth century, WC has been widely employed in the industry as cutting tool tips and wear-resistant parts. ...
... The possibility of improving mechanical properties including as hardness, elastic modulus, and fracture toughness has sparked interest in the manufacture of nanocrystalline WC ultrafine powders. Numerous methods, including chemical synthesis [46], mechanically induced solid state reduction [53], plasma-chemical interaction [54], and chemical vapor deposition (CVD), can be employed to synthesize polycrystalline superfine WC powders with an average grain size of 300-40 nm. However, mechanical milling (MM) is believed to be the most potent approach for generating nanocrystalline WC ultrafine powders on an industrial scale at near room temperature [51,53]. ...
Throughout human history, any society’s capacity to fabricate and refine new materials to satisfy its demands has resulted in advances to its performance and worldwide standing. Life in the twenty-first century cannot be predicated on tiny groupings of materials; rather, it must be predicated on huge families of novel elements dubbed “advanced materials”. While there are several approaches and strategies for fabricating advanced materials, mechanical milling (MM) and mechanochemistry have garnered much interest and consideration as novel ways for synthesizing a diverse range of new materials that cannot be synthesized by conventional means. Equilibrium, nonequilibrium, and nanocomposite materials can be easily obtained by MM. This review article has been addressed in part to present a brief history of ball milling’s application in the manufacture of a diverse variety of complex and innovative materials during the last 50 years. Furthermore, the mechanism of the MM process will be discussed, as well as the factors affecting the milling process. Typical examples of some systems developed at the Nanotechnology and Applications Program of the Kuwait Institute for Scientific Research during the last five years will be presented in this articles. Nanodiamonds, nanocrystalline hard materials (e.g., WC), metal-matrix and ceramic matrix nanocomposites, and nanocrystalline titanium nitride will be presented and discussed. The authors hope that the article will benefit readers and act as a primer for engineers and researchers beginning on material production projects using mechanical milling.
... Interestingly, at the higher heating rates of 4 and 8 K/min, the TEM observations clearly confirm sequential formation of e-W 2 C followed by a-WC layer as the mechanism for the evolution of core-shell nanoparticles. Previous reports on solid-gas and solid-solid reduction reactions followed by carburization process demonstrated that W 2 C is a metastable phase, which could only stabilize in the presence of WC or metallic element for example platinum [43][44][45][46][47]. Upon prolong heat treatment the metastable W 2 C gradually transform to ground state a-WC phase below the eutectoid temperature of 1523 K [48,49]. ...
The structure, morphology and growth mechanism of nanostructured W-C phases during its synthesis by thermo-chemical processing at different heating rates was investigated. Higher heating rates of 8 and 4 K/min led to the formation of core–shell type nanoparticles via sequential formation of the trigonal ε-W2C (Space group:Pm1) followed by the hexagonal α-WC layer (Space group: Pm2). It appears that the formation of the core–shell possibly initiates by the nucleation of metastable W2C to form octahedral core, which subsequently act as the nucleation site for the growth of the lower order α-WC from the surface layer. The surface layer encapsulating the metastable phase possibly restricts the coarsening of the particles to a size less than 100 nm. Slow heating rate of 1 K/min, on the other hand, leads to the formation of single phase ε-W2C with abnormal particle size growth and epitaxial morphology along (0 0 1) crystallographic plane. This observation confirms that the anisotropic lattice volume expansion in the crystalline ε-W2C induced diffusion of carbon leading to abnormal particle coarsening.
... Research has also shown that tungsten carbides possess catalytic properties. Tungsten carbides have been shown to have catalytic abilities that are comparable to precious metal catalysts such as platinum and palladium, making carbides a more economical option for the catalysis of numerous chemical reactions [7]- [10]. ...
... where the rate of adsorption with respect to time is represented by dn/dt, k6 represents the equilibrium constant for Equation (7), and K represents the combined equilibrium constants for the forward and reverse reactions presented in Equations (7), (8), and (9) (K = k7k8k9/k7'k8'k9'). ...
... Regardless of the type of tungsten oxide used, it has been accepted that reduction to metallic tungsten must occur before carburization to WC can take place [7], [19], [20], [23]- [25], [66]. ...
Carbide ceramics rank high among the hardest and most chemically resistant materials. Their ability to resist physical and chemical attack under conditions where more traditional materials fail make them very desirable for a number of industrial applications. Their use is limited, however, due to the expensive and energy-intensive methods required to produce them commercially. A more versatile and energy-efficient process for commercial carbide production has been developed by synthesizing micron/sub-micron carbide ceramic particles through the adsorption and subsequent carburization of anions on an activated carbon matrix. Oxyanion solutions containing sodium tungstate, sodium molybdate, or sodium metasilicate are adsorbed onto activated carbon to produce anion-loaded precursors. These precursors are carburized in the presence of a reducing atmosphere consisting of hydrogen, carbon monoxide, and methane to produce carbide crystals on the activated carbon surface. In this study, tungstate (WO42-), molybdate (MoO42-), and silicate (SiO32-) anions were evaluated. Silicon carbide (SiC) whiskers and mixed crystals of tungsten carbide (WC), tungsten semicarbide (W2C), and tungsten (W) were formed via carbothermal reduction using inert and reducing gas atmospheres at temperatures much lower than current commercial practice. Mixed crystals of WC, W2C, and W were synthesized at 950 °C under an atmosphere of 80% CH4, 10% H2, and 10% CO. Molybdenum carbide (Mo2C) was synthesized at temperatures as low as 850oC under an atmosphere consisting of 80% CH4, 10% CO, and 10% H2. Under optimal conditions, conversion to Mo2C and WC exceeded 90%. SiC was synthesized at temperatures as low as 1200 °C under H2. Separation of the WC/W2C/W crystals from the activated carbon matrix has been demonstrated using surfactant-aided density separation methods. Response surface modeling was used to determine optimal conditions for tungstate, molybdate, and silicate adsorption as well as the optimal carburization conditions for the W-loaded and Mo-loaded precursors. Results show that the carburization process is feasible and that it is possible to mathematically model and statistically optimize the production and carburization of the activated carbon precursors.
... Recently, ultrafine WC powder has critical applications since the grain refinement could significantly alter the physical, mechanical, and chemical properties of their bulk materials [8][9][10]. It has been reported that the use of ultrafine tungsten carbide powder could dramatically improve the mechanical properties such as strength, hardness, wear resistance and toughness [11][12][13][14][15][16][17][18][19]. Therefore, the preparation of ultrafine WC powder has become a hot research topic. ...
... Pandey et al. [15] synthesized nano-WC by the method of thermo-chemical reaction. Yan et al. [17] synthesized nanosized tungsten carbide by using an ion-exchange resin as carbon source to locally anchor the W and Fe species, which is beneficial to the formation of FeWO 4 and the conversion into WC. Other methods such as solid state metathesis [18], sol-gel [19] and mechanical alloying [20] were also developed to prepare ultrafine and nanosized tungsten carbide powder. ...
In the present work, ultrafine tungsten carbide (WC) powder with a high purity has been prepared by first roasting yellow tungsten trioxide (WO3) and carbon black powder under argon atmosphere followed by the further carbonization reaction with CH4-H2 mixed gases. The effects of C/WO3 molar ratio, CH4 percentage in the CH4-H2 mixed gases on the phase composition, morphology and particle size of the products were discussed. The results revealed that when the C/WO3 molar ratios were 2.5 and 2.6, nano tungsten carbide powder with the average particle sizes of 93 nm and 77 nm could be prepared. Whereas, when the C/WO3 molar ratio was in the range of 2.7–3.5, the finally prepared WC has the particle size of 446–192 nm, and became smaller with the increase of C/WO3 molar ratio. The percentage of CH4 should be <15% to prepare WC with a low free carbon content. From the results of thermodynamic calculation, X-ray diffraction (XRD), FE-SEM, and infrared carbon‑sulfur analyzer, it was concluded that ultrafine tungsten carbide powders with a high purity could be successfully prepared by this method.
... On average, there are only about 2 rods in every 100 μm 2 . One can suggest that the W content of the coating coupled with the high temperatures inherent to the PLD process might have favoured the formation of these rods [16][17][18][19][20]. However, their formation mechanism is not fully understood yet, mainly because of the way in which they melt under proton irradiation. ...
... Thermal excitation has been reported to favour the growth of nanorods in the presence of Zinc [26] and Tungsten [16] as catalysts. Furthermore, WC nanorods were reported to be synthesised in processes where WO 3 nanorods and thermal treatment played a key role [17][18][19][20]. ...
