Tungsten Loading Research Articles

Control of tungsten-epoxy composite porosity prepared using a high-energy ball milling method: An engineering aspect of backing layer fabrication

Tungsten-epoxy composite is commonly used as a backing layer substrate of piezoelectric-based ultrasonic transducers. The physical properties of this composite, such as porosity, play a significant role in controlling the behavior and specifications of transducer fabrication. Therefore, this study aimed to investigate the effects of tungsten content in epoxy to control porosity and determine the engineering aspects of ultrasonic transducer fabrication. The experiment was conducted using a shaker-type high-energy ball milling method, where non-spherical and faceted tungsten particles with a mean size of 1 μm were composited into epoxy resin as a matrix at various tungsten-epoxy weight ratios of 0:1 to 10:1. The prepared composite surface morphological and elemental, tungsten loading, particles, and epoxy bonding were examined and analyzed. Furthermore, analysis was carried out on the relationship between tungsten content and the parameters corresponding to the composite acoustic characteristics, such as sound velocity, acoustic attenuation, and acoustic impedance. The results showed that composite porosity increased in the range of 12.40–31.87%, corresponding to acoustic impedance from 3.04 to 9.37 Mrayl (below 10 Mrayl for biomedical ultrasonic transducers) when the tungsten-epoxy weight ratio varied from 0:1 to 10:1. This showed the significant influence of tungsten particle loading on controlling porosity of tungsten-epoxy composite by precisely tuning the weight ratio, contributing to engineering process in the fabrication. In conclusion, porosity was adjusted by controlling the tungsten loading content in epoxy.

Effect of vanadium and tungsten loading order on the denitration performance of F-doped V2O5-WO3/TiO2 catalysts.

F-doped V2O5-WO3/TiO2 catalyst has been confirmed to have excellent denitration activity at low temperatures. Since the V2O5-WO3/TiO2 catalyst is a structure-sensitive catalyst, the loading order of V2O5 and WO3 may affect its denitration performance. In this paper, a series of F-doped V2O5-WO3/TiO2 catalysts with different V2O5 and WO3 loading orders were synthesized to investigate the effect of denitration performance at low temperatures. It was found that the loading orders led to significant gaps in denitration performance in the range of 120-240 °C. The results indicated loading WO3 first better utilized the oxygen vacancies on the TiF carrier promoting the generation of reduced vanadium species. In addition, loading WO3 first facilitated the dispersion of V2O5 thus enhanced the NH3 adsorption capacity of VWTiF. In situ DRIFT verified the rapid reaction between NO2, nitrate, and nitrite species and adsorbed NH3 over the VWTiF, confirming that the NH3 selective catalytic reduction (NH3-SCR) reaction over VWTiF at 240 °C proceeded by the Langmuir-Hinshelwood (L-H) mechanism. This research established the constitutive relationship between the loading order of V2O5 and WO3 and the denitration performance of the F-doped VWTi catalyst providing insights into the catalyst design process.

Broadening active temperature window for NH3-SCR on tungsten-promoted MnCeOx nanorod catalysts

xW/MnCe nanorod catalysts with various tungsten contents were synthesised using the incipient wetness impregnation method for selective catalytic reduction (SCR) of nitrogen oxides with NH3 (i.e. NH3-SCR reaction). Tungsten addition considerably widened the active temperature window and enhanced the SO2/H2O tolerance of the catalysts. The optimum catalytic performance was achieved when the tungsten content was 15 wt% with NOx conversion being ≥ 80% in the range of 175–450 °C. The MnCe nanorods approximately retained their morphology after tungsten loading. Microcrystalline WO3 formed when the W content was 15%, resulting in increments in the amount of Ce3+ and Mn4+, which is in favour of the NH3-SCR reaction on the catalyst surface. Moreover, the broad active temperature windows of the tungsten-modified MnCe nanorod catalysts were related to the balance between the redox and acidic properties. Tungsten addition enhanced the acidity of the MnCe catalyst while suppressing its reducibility. Both the Brønsted and Lewis acid sites are active, and the formation of reactive bridging nitrate species promote the performance of 15 W/MnCe catalyst. Overall, this study provided an easy method of adjusting the active temperature window of Mn–Ce nanorod catalysts through W modification.

Nickel‑tungsten co-doped carbon-based catalyst for high selective production of ethylene glycol from cellulose hydrogenolysis

Nickel‑tungsten co-doped spherical carbon-based catalysts (m%Ni-n%W-GCT) are prepared by one-pot hydrothermal‑carbonization using glucose as carbon host. Structural composition of tungsten transforms from WOx → W → WCx when increasing carbonization temperature and tungsten loading content at the presence of Ni during hydrogen reduction, attributed to the occurrence of carburizing reaction. The carbon-based catalysts exhibit developed porous structures with weak and moderately strong acidity, and the Brønsted acid and total acid contents increase with promoting tungsten loading content. Investigation of m%Ni-n%W-GCT activity on catalyzing cellulose hydrogenolysis shows that the porous structure provides abundant reaction sites and facilitates reactant transportation, where the Brønsted acid sites promote hydrolyzing cellulose, and WCx is beneficial for hydrogenolysis of glucose other than direct hydrogenation and then Retro-Aldol condensation for ethylene glycol (EG). The optimized reaction condition (2 h at 230 °C and 5 MPa with 9%Ni-13.5%W-GC850 as the catalyst) delivers a cellulose conversion of 100%, with 69.2% selectivity for EG. The study provides an effective method for preparing EG from cellulose employing biomass-based carbon as the catalyst support.

Promoting effect exerted by WOx on Pt/ZrO2 catalysts during NOx reduction using H2 in the excess of O2

This work addresses the reduction of NOx by H2 under O2-rich conditions below 200 °C using Pt/W/ZrO2 catalysts with tungsten loadings from 0 to 14 wt%. Samples were thoroughly characterized by N2 physisorption, temperature-programmed desorption of CO, X-ray diffraction, laser Raman spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with CO as probe molecule. Catalytic investigations showed the highest efficiency for the sample with 5 wt% W providing NOx conversion of 94 % and N2O selectivity of 15 %. The effect of W promoter is mostly attributed to structural promotion by isolated WO6 entities stabilizing the ZrO2 surface and leading to a high number of active Pt sites. By contrast, negligible electronic interaction between the promoter and Pt sites appears. Moreover, DRIFTS studies suggest that, in addition to the predominate NOx reduction by H2 on Pt sites, a side reaction occurs including NHx species formed at the interface of Pt and WOx/ZrO2.

COx -free H2 Production via Catalytic Decomposition of CH4 over Fe Supported on Tungsten oxide-activated Carbon Catalyst: Effect of Tungsten Loading

Production of COx-free H2 from CH4 (a major global warming contributor) over cheap catalysts is a dominant task for the scientific community to accomplish environmental-friendly clean H2 energy sources. Herein, a tungsten oxide-activated carbon-supported Fe catalyst is prepared by impregnation method, characterized by X-ray diffraction, surface area-porosity measurement, temperature programmed reduction/oxidation and thermogravimetry analysis. 30wt.%Fe supported tungsten oxide incorporated activated carbon catalyst is found superior to 30 wt% Fe supported on activated carbon incorporated tungsten oxide due to higher surface area and high concentration of reducible catalytic active sites. 30wt.%Fe impregnated over 25 wt%WO3-75 wt%activated carbon support catalyst has the highest concentration of reducible surface-active species and it had excellent performance among other tungsten oxide incorporated catalysts. The catalyst showed 66.04% CH4 conversion, 63.12% H2 yield and YH2 /CCH4 > 0.9 initially which didn’t fall below 35 % up to 160-minutes. Improper matching between the rate of carbon formation and the rate of diffusion over a highly crystalline 30Fe50W50Ac catalyst resulted in rapid deactivation.

Microstructure and tribological properties of sputtered MoSx-W composite films supported by porous alumina aperture array

Aluminum alloys are widely used in the aerospace and automotive industries due to their high strength and low density but also suffer from poor wear resistance. The employment of stable solid lubricants on aluminum alloys will be beneficial for their service life under load-bearing conditions. In this paper, MoSx-W composite coatings were deposited on porous anodic aluminum oxide (AAO)/Al substrates. The effects of tungsten content on the film structure and friction properties were systematically investigated. It is found that tungsten exists as metallic particles within the MoSx matrix, forming a system of hardness phase reinforced soft matrix. With the increase of W content, the film morphology transforms from nano-flower-like to ball-like, associated with an obvious enhancement of film density as well as hardness. The latter prolongs the service life of MoSx films from 10 min only in untreated specimen to 88.8 min in composite sample. Finally, the improvement of wear performance upon tungsten loading was discussed in detail.

Flame synthesis of tungsten‐doped titanium‐dioxide nanoparticles using novel precursor combination of liquid titanium tetra‐isopropoxide and solid tungsten mesh

AbstractTungsten‐doped titanium‐dioxide (W‐TiO2) nanoparticles are successfully synthesized using a multiple‐diffusion‐flame burner with a separate center tube. Vaporized titanium tetra‐isopropoxide (TTIP) precursor issues from a center tube to produce TiO2 nanoparticles, while a tungsten mesh, suspended above the surrounding multiple over‐ventilated hydrogen diffusion flames, serves as the solid‐phase metal doping source. At a lower tungsten loading rate, W‐TiO2 nanoparticles are generated, as indicated by an obvious angle shift of 0.15° for the entire x‐ray diffraction spectrum. However, at a higher tungsten loading rate, homogenous nucleation of WOx occurs before or concurrently with TiO2 nucleation, producing mixed nanopowders, permitting fewer tungsten ions to be doped into TiO2. Ultraviolet–visible spectroscopic characterization reveals that the as‐synthesized W‐TiO2 nanoparticles possess augmented absorbing ability in the visible‐light wavelength range, where the band gap is reduced from 3.20 to 3.05 eV, compared with that for the nondoped TiO2 nanoparticles.

γ-Valerolactone Production from Levulinic Acid Hydrogenation Using Ni Supported Nanoparticles: Influence of Tungsten Loading and pH of Synthesis.

γ-Valerolactone (GVL) has been considered an alternative as biofuel in the production of carbon-based chemicals; however, the use of noble metals and corrosive solvents has been a problem. In this work, Ni supported nanocatalysts were prepared to produce γ-Valerolactone from levulinic acid using methanol as solvent at a temperature of 170 °C utilizing 4 MPa of H2. Supports were modified at pH 3 using acetic acid (CH3COOH) and pH 9 using ammonium hydroxide (NH4OH) with different tungsten (W) loadings (1%, 3%, and 5%) by the Sol-gel method. Ni was deposited by the suspension impregnation method. The catalysts were characterized by various techniques including XRD, N2 physisorption, UV-Vis, SEM, TEM, XPS, H2-TPR, and Pyridine FTIR. Based on the study of acidity and activity relation, Ni dispersion due to the Lewis acid sites contributed by W at pH 9, producing nanoparticles smaller than 10 nm of Ni, and could be responsible for the high esterification activity of levulinic acid (LA) to Methyl levulinate being more selective to catalytic hydrogenation. Products and by-products were analyzed by 1H NMR. Optimum catalytic activity was obtained with 5% W at pH 9, with 80% yield after 24 h of reaction. The higher catalytic activity was attributed to the particle size and the amount of Lewis acid sites generated by modifying the pH of synthesis and the amount of W in the support due to the spillover effect.

Modified Mesoporous HMS Supported V/W for Oxidative Desulfurization of Dibenzothiophene

Two V/W-HMS (hexagonal mesoporous silica) nanostructures were synthesized with various vanadium and tungsten loadings. And their catalytic activities were investigated in oxidative desulphurization of dibenzothiophene (DBT) in model diesel fuel. The catalysts were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and N_2 physical adsorption-desorption (BET/BJH) techniques. The best V/W-HMS catalyst exhibited high catalytic activity, capable of converting more than 95% of DBT in the model diesel fuel under the optimum reaction condition (0.05 gr 1:4 of catalyst, T=60°C, t=2h). After doping of vanadium with tungsten, it was found that bandgap of the catalyst was reduced and its catalytic performance was improved effectively. The catalytic activity remained unchanged even after 6 recycling processes. The reaction kinetics, mechanism, and bandgap energy of the catalysts were also investigated.

NH3-Selective Catalytic Reduction of NOx to N2 over Ceria Supported WOx Based Catalysts: Influence of Tungsten Content

A series of HPW/CeO2 catalysts generated from 12-tungstophosphoric acid, H3PW12O40 (HPW), supported on ceria and presenting different tungsten loadings (2, 4.5, 9, 16, and 40 wt% W) were prepared and characterized by N2 physisorption, XRD, IR, Raman, and UV-Vis. The different characterization techniques suggested that low loading of tungsten resulted in mainly isolated sites, while high tungsten loading produced polymeric or tungsten clusters. Those materials exhibited high activity in NH3-SCR of NOx into N2. Moreover, the series of experiments indicated that low loading in tungsten (2% HPW/CeO2) displayed the highest activity with a remarkable N2 selectivity (99%) at medium-high temperature (300–515 °C), owing to the high amount of monomeric tungstate coverage on the catalyst surface.

Effect of small amounts of Al on the surface silanol structure and their correlation to the improved catalytic performances of WOx/SiO2–Al2O3 in the propene self-metathesis

Surface silanol structures, acid properties, and tungsten dispersion of the sol-gel-derived 7W/SiO2–xAl2O3 (x = 0.2–23 wt%) were investigated by means of 29Si, 27Al, and 1H MAS NMR, NH3-TPD, in-situ NH3-IR spectroscopy, XRD, and Raman spectroscopy. The surface silanol structure changed upon Al and tungsten loadings; however, loading of 1 wt% Al2O3 appeared to be the threshold for preserving the Si(OH)Al with isolated bridge after impregnation of 7 wt% W. The 7W/SiO2–1Al2O3 (1 wt% Al2O3) was also found to exhibit the lowest ratio of Bronsted to Lewis acid with the highest amount of Lewis acid sites and the best catalyst performances in propene self-metathesis at 550 °C in terms of both propene conversion and ethylene/butene selectivity. Despite its low tungsten dispersion, the metathesis activity was correlated well with the higher amount of tungsten carbene species, which were formed on the catalysts containing higher isolated bridge silanol and the presence of higher Lewis acid sites.

Computational analysis of the evolution of the brittle-to-ductile transition of tungsten under fusion conditions

Tungsten components inside fusion reactors are subjected to extreme conditions, including an exceptionally high heat flux. This loading induces high stress levels, that may lead to brittle fracture. The current work aims to provide novel insights by relating the risk for brittle fracture to the tungsten microstructure and loadings conditions. To this end, a crystal plasticity framework is adopted with a temperature dependent slip resistance. The required parameters are obtained from experimental data in the literature. The risk for brittle fracture is assessed by means of Beremin’s weakest-link theory. The brittle-to-ductile transition temperature (BDTT) found in literature can be accurately described with the presented framework. The simulation results reveal that the BDTT decreases linearly with the volume fraction of recrystallized grains in the microstructure. It is also shown that a sharp interface between rolled and recrystallized microscopic grains is more favourable in terms of risk for brittle fracture.

Thermal Properties of Nano Tungsten - Ethylene Vinyl Acetate (EVA) Composites

Ethylene vinyl acetate (EVA) with different percentage of nano tungsten powder (0wt%, 30/wt %, 45/wt %, 60/wt%, and 70/wt %) composites (EVA/W nano-composites) were prepared by melt blending in a twin-screw brabender. The structural, morphological, thermal and mechanical properties of the prepared nano-composites were investigated using powder X-ray diffraction (PXRD), Scanning Electron Microscopy (SEM), thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA). It was found that the EVA composites show a higher thermal stability at high levels of tungsten loading.

Nitrogen Monoxide and Soot Oxidation in Diesel Emissions with Platinum–Tungsten/Titanium Dioxide Catalysts: Tungsten Loading Effect

Compared with Pt/TiO2, tungsten-loaded Pt–W/TiO2 catalysts exhibit improved activity for NO and soot oxidation. Using catalysts prepared by an incipient wetness method, the tungsten loading effect was investigated using Brunauer–Emmett–Teller surface areas, X-ray diffraction, transmission electron microscopy (TEM), CO pulse chemisorption, H2 temperature-programmed reduction, NH3 temperature-programmed desorption (NH3-TPD), and pyridine Fourier transform infrared (FT-IR) spectroscopy. Loading tungsten on the Pt/TiO2 catalyst reduced the platinum particle size, as revealed in TEM images. CO pulse chemisorption showed that platinum was covered with tungsten and the dispersion of platinum decreased when 5 wt.% or more of tungsten was loaded. The NH3-TPD and pyridine-FT-IR results demonstrated that the number of strong acid sites and Brønsted acid sites in the catalyst were increased by the presence of tungsten. Therefore, a catalyst containing an appropriate amount of tungsten increased the dispersion of platinum, thereby increasing the number of active sites for NO and soot oxidation, and increased the acidity of the catalyst, thereby increasing the activity of soot oxidation by NO2

Synthesis, Characterization, and Hydrotreating Activity of NiW Presulfurized Catalysts Prepared via a Tetrathiotungstate-Intercalated NiAl LDH.

A tetrathiotungstate-intercalated NiAl layered double hydroxide (LDH) was synthesized and then calcined under N2 at various temperatures to prepare a series of NiW presulfurized hydrotreating catalysts. Upon calcination, WS42– in the interlayer decomposes into WS3 and then WS2, releasing sulfur to sulfurize nickel in the sheets. The property and activities of catalysts for hydrodesulfurization (HDS) of dibenzothiophene and hydrodearomatization (HDA) of tetralin are dependent on the calcination temperature. At 300 °C, WS3 can be well maintained, offering highly active hydrogenation sites S22– and superior HDA activity. As the temperature increases up to 500 °C, WS3 converts into WS2, while nickel sulfides migrate to the edge of WS2 to form NiWS phases with high HDS activity. LDH-based presulfurized catalysts can achieve fully sulfurized and well-dispersed tungsten species even at high tungsten loadings and can retain more WS3 even at high temperatures because of the peculiar properties of LDHs. Therefore, they show better HDS and superior HDA activities over an oxidic NiW LDH-based catalyst (LDO) and an alumina-supported NiWS presulfurized catalyst (NiWS/Al2O3). The optimized catalyst shows 1.59 and 1.05 times higher HDS activity than LDO and NiWS/Al2O3 while 2.05 and 1.77 times higher HDA activity than LDO and NiWS/Al2O3, respectively. It also shows better HDS and HDA activity for a real diesel than a NiCoMoW/Al2O3 commercial catalyst.

Gamma-ray shielding characteristics of flexible silicone tungsten composites

Silicone being a hybrid elastomer is well known for its excellent thermal and mechanical properties, chemical resistance, compatibility with organic and inorganic fillers, nontoxicity, and flexibility. As the reported literature on silicone tungsten composite is rare, thus, a complete possible spectrum of silicone tungsten composites series with tungsten loading of 0–88.1 %wt has been fabricated by RTV method and studied as a flexible gamma shielding material. Flexible silicone/tungsten composite formulations containing different weight percentages of tungsten powder (0, 30.1, 47.8, 59.8, 68.1, and 88.1 wt %) were developed by the room-temperature vulcanization route. Two lead collimators with diameters of 0.6 cm were used to make a narrow beam geometry for gamma rays emitted from a137Cs (gamma-ray energy of 662 keV) point source. Uncollided flux was measured with a NaI(Tl) scintillation detector enclosed in lead shielding to reduce the background radiation level. The measured mass attenuation coefficient for our composites with 88.1 wt % tungsten was 0.1035 cm2/g, which is nearly 3.5% higher than that of commercially available silicone/tungsten composites named T-Flex (nearly 0.095 cm2/g) containing the same tungsten loading. Similarly, superior half value layers (HVL) of our composites with 88.1 % wt loading of tungsten i.e 1.01 cm versus 1.27 cm for the reported T-Flex counterpart with additional advantage of insitu fabrication on complex geometries. It was also found that the effectiveness of gamma-ray shielding increases with increase in density of the composites, which is due to the increase in the weight percent of tungsten powder. Our material will have applications as shielding material for both mobile and stationary radiation sources and it can also be used as fabrication material for gloves, safety shoes, coats, etc. to protect workers in a radiation environment.

Influence of acidity on the performance of silica supported tungsten oxide catalysts assessed by in situ and Operando DRIFTS

The types of acidity on WOx/SiO2 catalysts prepared with different tungsten loadings (5 and 9 wt.% W) and pretreatment atmospheres (N2 and H2) were clarified by using the in situ diffuse reflectance infrared Fourier transform spectroscopy with temperature-programmed desorption (in situ DRIFTS-TPD) technique. Ammonia (NH3) acted as probe molecules that could block Lewis acid site type II (1620 cm−1) on the studied catalysts. The reactant feed containing 2% trans-2-butene or mixed feed of 2% trans-2-butene and 4% ethylene were used to investigate the reaction pathway on the WOx/SiO2 catalysts. Combining the Operando DRIFTS with gas chromatography-flame ionization detector (Operando DRIFTS-GC-FID) technique and in situ DRIFTS-TPD led to more deeply understanding of the correlation of acid sites and the primary cross metathesis reaction as the main reaction with isomerization of trans-2-butene as the side reaction. The adsorption energy of pulse chemisorption of 1-butene on catalyst by in situ DSC, confirmed the presence of the Lewis acid site type II related to the opportunity of 1-butene adsorption. The results confirmed that the Lewis acid site at 1620 cm−1 was crucial for the secondary metathesis reaction of 1-butene.

W–modified Ni/Al2O3 catalysts for the dry reforming of methane: Effect of W loading

Abstract W-modified Ni/Al2O3 catalysts were investigated for the dry reforming of methane. xW-Ni/Al2O3 catalysts (10 wt% Ni and tungsten loading in the range of x = 0–26.2 wt% W) were synthesized by wet co-impregnation. Textural and structural characteristics were studied by N2 adsorption- desorption, XRD, UV–vis DRS, Raman, TPR, NH3-TPD and HR-TEM. Catalytic behaviour was evaluated using a feed of 50% CH4 and 50% CO2, at 973 K and atmospheric pressure. Qualitative and quantitative analyses of the amount and the structure of carbonaceous deposits on the used catalysts were performed by TPH, TPO, XRD and HR-TEM. Modification with tungsten loading up to 11.9 wt% causes a slight decrease in activity but results in significant reduction of carbonaceous deposits. As tungsten loading increases further, catalytic activity decreases significantly. The suppression of carbon formation was attributed to the double role of tungsten: a) Ni-W alloys, formed during reduction, hinder carbon diffusion in their lattice; b) carbon remaining at the surface is removed through a carbon formation-gasification mechanism involving tungsten carbides. The catalyst doped with 11.9 wt% W exhibited catalytic performance comparable to that of the undoped Ni/γ–Al2O3 catalyst but forms 76% less carbon.

Influence of tungsten loading on CO2 /O2 reforming of methane over Co-W-promoted NiO-Al2 O3 nanocatalyst designed by sol-gel-plasma

Co-W–promoted NiAl2O4 nanocatalyst with various amount of tungsten (0, 1, 3, and 7 wt.%) was fabricated via hybrid sol-gel-plasma method. The nanocatalysts were evaluated by XRD, FESEM, EDX, BET, and FTIR analyses. The samples were utilized in CO2/O2 reforming of methane to syngas. EDX results proved the existence of all the applied elements in synthesis. FESEM and BET results illustrated that tungsten addition led to lower surface area, larger particle size, and roughly worse particles scattering. Therefore, Co-NiAl2O4 (NCW0A) presented higher yield; however, yields were reduced for the other samples due to the covering impact of tungsten. As a result of time on streams performance (2880 minutes and at 750°C), the 7 wt.% tungsten promoted sample exhibited stable but lower yield (YH2 = 64%). Moreover, NCW1A exhibited more stable and higher yield than NCW0A. Optimum operating parameters were obtained as GHSV = 24 l/gcat.h, CH4/CO2 = 1, and CH4/CO2/O2 = 1/1/0.08. TG-DTG, EDX, and FESEM analyses were applied for the used samples. TG-DTG graphs demonstrated that by rising of tungsten loading, lighter and lower amount of coke was formed. Some agglomerations were observed in the EDX images of NCW0A and NCW1A while lower agglomeration was found for the tungsten-rich sample. Carbon fiber formation was detected in the FESEM images of the used NCW0A while for the others, amount of the deposited coke and carbon fibers decreased.