Tungsten Metal Research Articles

Development of dispersion layers for dental drills with reduced nickel release

ObjectivesWithout rotating instruments, for example diamond-coated drills with a core made of stainless steel, the dental routine would be unimaginable, since these are used in almost every dental activity and are thus indispensable for the professional practice. Unfortunately, such drills release Nickel particles to a high content into the cooling water of the drill. Values up to 1.3 mg/l Nickel were found by ICP – OES in the cooling water of the drillers which is of course also transferred into the patient's oral cavity with possible severe negative effects. Therefore, novel plating procedures have to be developed to increase the patients (and dentists) safety during treatment. MethodsDispersion layers with the hard metal Tungsten carbide (WC) particles on stainless steel blanks were deposited following two synthesis routines (i) Plasma-Electrolytic Oxidation (PEO) and (ii) galvanic plating out of a Watts bath. Both were accomplished using water-based electrolytes. ResultsIn order to verify the dental applicability of the developed coatings, tests-drills were accomplished under defined conditions on plastic teeth for the sake of reproducibility.Commercially produced drills were compared with the newly plated ones by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and the drilling cooling water was examined for heavy metal residues using Inductively Coupled Plasma (ICP) analytics. The resulting grinding patterns in the plastic teeth were investigated by light microscopy and SEM.It could be shown that dispersion layers plated by a galvanic procedure showed a reduced Nickel release compared to a commercial driller by factor 7.6 and 13.4 compared to PEO plated ones during dental treatments. ConclusionsFollowing the clinical significance the Watts bath plated drillers showed a better WC particle distribution on the surface and better abrasive properties during the drilling experiments compared to PEO plated drillers. In addition the Nickel release during dental use is much less from the galvanic treated ones. By optimising the plating condition from the Watts dispersion bath further novel drilling devices with significantly reduced release of Nickel particles can be developed for the benefit of the patients.

Robust monazite U-Pb and molybdenite Re-Os ages reveal the magmatic and metallogenic history of a highly evolved granitic system in the Xianghualing deposit, South China

Tin, tungsten, and rare metals are key strategic metals and are regarded as having potentially relationship with highly evolved granites. However, excessive U accumulation with magmatic evolution, complex melt-fluid interaction, and late hydrothermal alteration make it difficult to obtain accurate age information from the highly evolved granitic system. The Xianghualing deposit, located in southern Hunan Province, China, is a giant Sn-Nb-Ta-polymetallic deposit with various types of mineralization spatially associated with the Laiziling and Jianfengling highly evolved granite plutons, and is an ideal target to investigate the magmatic-hydrothermal process of highly evolved magmas and related Sn-Nb-Ta-polymetallic mineralization. Previous studies have reported a relatively wide range of intrusion ages and multi-stage mineralization ranging from Triassic to Cretaceous. However, the timing and genetic link between magma emplacement and Sn-Nb-Ta-polymetallic mineralization remain controversial. Here we employ multiple dating methods, including SHRIMP zircon U-Pb analysis, LA-ICP-MS zircon and monazite U-Pb analysis, and molybdenite Re-Os dating analysis with a view to obtain a precise geochronological framework of the Xianghualing deposit. The SHRIMP zircon U-Pb data from the Laiziling protolithonite granite yielded a weighted 206Pb/238U age of 156.4 ± 1.5 Ma, whereas the LA-ICP-MS monazite U-Pb age for the Laiziling albite granite and the greisenized granite show 207Pb-corrected lower intercept 206Pb/238U ages of 155.5 ± 0.7 and 155.3 ± 0.5 Ma, respectively, which represent the emplacement ages of the Laiziling granite stock. Compared with the scattered SHRIMP and LA-ICP-MS zircon U-Pb age, monazite from the albite granite and greisenized granite yields more precise age information. Our study shows that monazite can be used as a robust tool for dating highly evolved granites. Molybdenite from the Laiziling pegmatite yields a Re-Os isochron age of 157.8 ± 4.2 Ma, which is consistent with the emplacement age of the Laiziling pluton. This result, integrated with previously reported metallogenic age, suggests a temporal and genetic link between the Laiziling granite and Sn-Nb-Ta polymetallic mineralization. Although multi-stage Sn-W metallogenic events have been identified in Nanling Region, it is suggested that the Xianghualing Sn-Nb-Ta mineralization formed during the Late Jurassic within a short duration coeval with the regional large-scale W-Sn mineralization at 160–150 Ma.

Electrospun Tungsten‐Polyurethane Composite Nanofiber Mats for Medical Radiation‐Shielding Applications

AbstractElectrospun composite nanofiber mats consisting of polyurethane (PU) and nontoxic tungsten powder are manufactured via electrospinning for use as X‐ray shielding materials. Upon systematical formation of tungsten‐PU composite nanofiber layers, heat and pressure are simultaneously treated to design light‐weight mats containing various amount of tungsten metals. After examining their structural and physical properties, the X‐ray mass attenuation coefficient, nitrogen permeability, and flexibility of the resulting mats are compared to conventional film‐type shielding mats. While the nanofiber‐based composite mats still exhibit a comparable X‐ray mass attenuation coefficient (9.64 cm2/g), their gas permeability (8.56 L/min) and flexibility (bending angle of 28.8°) are almost two and five times higher than those of conventional mats, respectively. This work clearly demonstrates the preparation of effective composite mats with controlled properties for the development of nontoxic shielding suits that can replace conventional lead‐based materials possessing environmental and health concerns.

Design of Grating Type GaAs Solar Absorber and Investigation of Its Photoelectric Characteristics

In recent years, as a renewable clean energy with many excellent characteristics, solar energy has been widely concerned. In this paper, we propose an ultra-broadband solar absorber based on metal tungsten and semiconductor GaAs structure. A multilayer metal semiconductor composite structure composed of W-Ti-GaAs three-layer films and GaAs gratings is proposed. The finite difference time domain method is used to simulate the performance of the proposed model. High efficiency surface plasmon resonance is excited by adjusting the geometric parameters, and the broadband absorption of up to 2,350 nm in 500–2850 nm is realized. The spectrum of the structure can be changed by adjusting the geometric parameters to meet different needs. The proposed absorber has good oblique incidence characteristics (0–60°) and high short-circuit current characteristics. The geometry of the absorber is clear, easy to manufacture, and has good photoelectric performance. It can realize solar energy collection, light heat conversion, high sensitive sensing and other functions.

Preparation of nano-crystalline tungsten powders from gaseous WO2(OH)2

The industrial production of tungsten powder is carried out by the reduction of tungsten oxide powder via hydrogen. In this process, the size of the W particles is limited to particle sizes larger than 100 nm. To get below this limit, alternative processes are needed. In the current work, the possibility of preparing W powder below 100 nm via a vapour phase reduction of volatile WO2(OH)2 by hydrogen was investigated. The process consists of two stages. In the first stag,e WO2(OH)2 is formed by reacting WO3 with water vapour at temperatures of 1000–1100 °C. In the second stage, WO2(OH)2 is reduced by hydrogen at about 1000 °C to form metallic tungsten. The influence of process parameters such as furnace temperature, humidity and gas flow on the WO2(OH)2 evaporation and formation of tungsten powder was investigated. The characterization of the resulting powders was performed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). By optimization of the reaction conditions, powder with a metallic tungsten content of about 70 at% besides tungsten oxides was produced with metal particle sizes down to 5 nm. Further optimization should lead to a high tungsten content and a high product yield. Due to the small particle size, applications in catalysis might be possible, although an industrial realization of the process seems unrealistic at moment.

Electron Collision Rate in Ultrashort Laser – Metal Interaction Inferred from Reflectivity Measurements

We study optical laser coupling of four metals (aluminum, copper, nickel and tungsten) upon single ultrashort 30-fs laser irradiation. Using dedicated experimental methodology, we carefully monitor the evolution of the material reflectivity integrated over the femtosecond pulse duration. We further apply the Drude-Lorentz formalism to infer the evolution of the effective electron collision rate eff as a function of applied fluence. The knowledge of this parameter is of paramount importance in any lasermatter interaction situation because of its immediate impact on laser energy coupling in material and on its subsequent macroscopic transformation.

Extending the absorption band from infrared to ultraviolet using the ITO transition from reflection to transparence

A numerical simulation based on the finite-element method shows that a metamaterial absorber using Tungsten (W) and Indium tin oxide (ITO) plasmonic metals can be ultra-broadband and show high-performance. Conventional broadband absorbers usually consist of multiple metal-dielectric layers or multi-resonators and have a bulky shape. The present work investigates the possibility to reach optimal characteristics with a simple design by combining two plasmonic materials (W/ITO) within a single resonator. Involving the ITO transition from reflection to transparence dramatically increases the absorption bandwidth, which is extended from infrared to ultraviolet, with up to 99.92% absorption. The design is polarization-insensitive under oblique incidence, up to 75° and 80°, for TE and TM polarization waves, respectively.

Towards pressureless sintering of nanocrystalline tungsten

The challenge of sintering ultrafine-grained tungsten to >99% density and towards nanocrystallinity is hereby addressed by optimized pressureless two-step sintering. It successfully produced tungsten samples with 99.3% theoretical density and 290 nm average grain size, with a uniform grain structure, good grain boundary cohesion, and 7.8 GPa hardness that is the highest in all pressurelessly sintered tungsten. The critical role of initial powders and the resultant green bodies was noted, which greatly affects later-on sintering kinetics and microstructural uniformity. Several key questions concerning two-step sintering of metallic tungsten were addressed, including the selection of the first- and second-step sintering temperatures, the thermodynamically required critical density to start the second-step sintering, and grain growth kinetics during sintering. The lessons learned here should be directly transferable to other refractory metals and their alloys and would help address the ultimate task of pressureless sintering of bulk nanocrystalline refractory metals/alloys.

Simultaneous Observation of Tungsten Spectra of W0 to W46+ Ions in Visible, VUV and EUV Wavelength Ranges in the Large Helical Device

Spectroscopic studies for emissions released from tungsten ions have been conducted in the Large Helical Device (LHD) for contribution to the tungsten transport study in tungsten divertor fusion devices and for expansion of the experimental database of tungsten line emissions. Tungsten ions are distributed in the LHD plasma by injecting a pellet consisting of a small piece of tungsten metal wire enclosed by a carbon tube. Line emissions from W0, W5+, W6+, W24+–W28+, W37+, W38+, and W41+–W46+ are observed simultaneously in the visible (3200–3550 Å), vacuum ultraviolet (250–1050 Å), and extreme ultraviolet (5–300 Å) wavelength ranges and the wavelengths are summarized. Temporal evolutions of line emissions from these charge states are compared for comprehensive understanding of tungsten impurity behavior in a single discharge. The charge distribution of tungsten ions strongly depends on the electron temperature. Measurements of emissions from W10+ to W20+ are still insufficient, which is addressed as a future task.

Inhalation of Tungsten Metal Particulates Alters the Lung and Bone Microenvironments Following Acute Exposure.

Inhalation of tungsten particulates is a relevant route of exposure in occupational and military settings. Exposure to tungsten alloys is associated with increased incidence of lung pathologies, including interstitial lung disease and cancer. We have demonstrated, oral exposure to soluble tungsten enhances breast cancer metastasis to the lungs through changes in the surrounding microenvironment. However, more research is required to investigate if changes in the lung microenvironment, following tungsten particulate exposure, can drive tumorigenesis or metastasis to the lung niche. This study examined if inhalation to environmentally relevant concentrations of tungsten particulates caused acute damage to the microenvironment in the lungs and/or systemically using a whole-body inhalation system. Twenty-four female BALB/c mice were exposed to Filtered Air, 0.60 mg/m3, or 1.7 mg/m3 tungsten particulates (<1 µm) for 4 h. Tissue samples were collected at days 1 and 7 post-exposure. Tungsten accumulation in the lungs persisted up to 7 days post-exposure and produced acute changes to the lung microenvironment including increased macrophage and neutrophil infiltration, increased levels of proinflammatory cytokines interleukin 1 beta and C-X-C motif chemokine ligand 1, and an increased percentage of activated fibroblasts (alpha-smooth muscle actin+). Exposure to tungsten also resulted in systemic effects on the bone, including tungsten deposition and transient increases in gene expression of proinflammatory cytokines. Taken together, acute whole-body inhalation of tungsten particulates, at levels commonly observed in occupational and military settings, resulted in changes to the lung and bone microenvironments that may promote tumorigenesis or metastasis and be important molecular drivers of other tungsten-associated lung pathologies such as interstitial lung disease.

Упрочнение FeCrMoWCBSi аморфных электроискровых покрытий карбидом вольфрама

A new direction in the development of metal-matrix coatings are composites based on an amorphous matrix with reinforcing ceramic additives. In this work, composite coatings were prepared by electrospark treatment of AISI 1045 in a mixture of iron granules with a multicomponent composition CrMoWCBSi and the addition of tungsten carbide powder. According to X-ray analysis, with an increase in the concentration of WC in the mixture of granules up to 1.2 vol.%, the content of the WC phase in the coating composition increased. In addition, the X-ray analysis showed metallic tungsten, which is a product of the partial dissolution of WC particles in the iron melt. In the microstructure of the coatings, inclusions of tungsten carbide with a diameter of 1.8 ± 0.9 μm were observed. The oxidation resistance of the coatings at a temperature of 700°C decreased monotonically with an increase of WC additive in the mixture of granules. The microhardness of the coatings with tungsten carbide was in the range from 814 to 1118 HV, which is higher compared to a completely amorphous sample (743 HV). The average values of the coating friction coefficient with WC ranged from 0.60 to 0.67, which is 30 % lower than that of an amorphous coating. The wear rate of coatings with tungsten carbide was in the range of 0.5 –1.1×10−5 mm3 / Nm, which is lower than that of the sample without WC (1.8 ×10−5 mm3 / Nm). The optimal value of the addition of WC powder in the mixture of granules during the deposition of the coatings for tribotechnical applications is 1.2 vol.%. Thus, the use of amorphous coatings reinforced with tungsten carbide makes it possible to reduce the wear of steel 45 by up to 8 times.

Investigation on structural and opto-electronic properties of substitutional Sn doped WS2 by co-sputtering technique

The doping of two-dimensional materials provides them with tunable physical properties and broadens their application. In this study, the doping of tungsten disulfide with metallic Sn atoms via a co-sputtering technique was demonstrated. In particular, WS2 was deposited by radio frequency (RF) magnetron sputtering, while Sn atoms deposited by DC sputtering become substitutional dopants. It was revealed that the metallic tungsten atom, and in some cases sulfur vacancies, in the WS2 atomic layer created by RF magnetron sputtering were partially filled/substituted by metallic Sn atoms. The Sn-doped WS2 layers exhibited n-type doping behavior with remarkable opto-electronic properties (bandgap 2.09 eV, mobility 7.84 cm2/V·s and resistivity 2.81 × 103 Ω-cm for 1 min Sn doping) suitable for photovoltaic applications. Overall, this technique facilitates better control of the dopant distribution than the traditional approach.

Customizing MRI-Compatible Multifunctional Neural Interfaces through Fiber Drawing.

Fiber drawing enables scalable fabrication of multifunctional flexible fibers that integrate electrical, optical and microfluidic modalities to record and modulate neural activity. Constraints on thermomechanical properties of materials, however, have prevented integrated drawing of metal electrodes with low-loss polymer waveguides for concurrent electrical recording and optical neuromodulation. Here we introduce two fabrication approaches: (1) an iterative thermal drawing with a soft, low melting temperature (Tm) metal indium, and (2) a metal convergence drawing with traditionally non-drawable high Tm metal tungsten. Both approaches deliver multifunctional flexible neural interfaces with low-impedance metallic electrodes and low-loss waveguides, capable of recording optically-evoked and spontaneous neural activity in mice over several weeks. We couple these fibers with a light-weight mechanical microdrive (1g) that enables depth-specific interrogation of neural circuits in mice following chronic implantation. Finally, we demonstrate the compatibility of these fibers with magnetic resonance imaging (MRI) and apply them to visualize the delivery of chemical payloads through the integrated channels in real time. Together, these advances expand the domains of application of the fiber-based neural probes in neuroscience and neuroengineering.

Formation and Properties of Oxide Coatings with Immobilized Zeolites Obtained by Plasma Electrolytic Oxidation of Aluminum

In this paper, we employed plasma electrolytic oxidation (PEO) of aluminum in a water solution of sodium tungstate (Na2WO4∙2H2O) with the addition of the pure and Ce-loaded zeolites clinoptilolite and 13 X for the preparation of oxide coatings. The obtained coatings were characterized with respect to their morphologies and chemical and phase compositions using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, and X-ray diffraction. The prepared coatings contained γ-alumina, WO3, and metallic tungsten. The surface morphologies of the obtained coatings strongly depended on the PEO processing time; the roughness of all coatings increased with PEO time, while porosity decreased with PEO processing time as a result of microdischarge coalescence and growth. All coatings contained elements originating from the substrate and from the electrolytes. Coatings containing zeolites with Ce showed higher photoactivity than those with immobilized pure zeolites. The highest photocatalytic activity levels were observed for coatings containing immobilized Ce-exchanged clinoptilolite processed for 10 min. It was observed that both clinoptilolite and 13X zeolites improved the features of the PEO coatings in a similar manner, making natural and abundant clinoptilolite an excellent candidate for various applications.

Zircon Hf‐isotope constraints on the formation of metallic mineral deposits in Thailand

AbstractThe effects of the Sibumasu–Indochina Terranes collision created several kinds of mineral deposits in Thailand, which include porphyry–skarn copper–gold, epithermal gold and antimony, orogenic gold–antimony–tungsten and tin‐tungsten mineralization among others. The deposits show a distinct spatial zonal distribution and occur in specific tectonic terranes. Combining regional geological data and ore deposit distribution data with Hf‐isotopic data of zircons in igneous rocks can be used to investigate the relationship between crustal construction processes and metallogeny. In this study, we investigated the Sukhothai Fold Belt, which is composed of quartz monzodiorite, granodiorite, syenogranite, and monzogranite of I‐ and S‐type affinities. All granitoids were analyzed for zircon U–Pb geochronology and Lu–Hf isotopic analysis. The granitoids of the Sukhothai Fold Belt yielded U–Pb zircon ages ranging from ~243 to 202 Ma, which mark the timing of subduction to the syn‐collisional stage between the Sibumasu–Indochina terranes at ~243–237 Ma and the timing of post‐collision between the Sibumasu–Indochina terranes during 230–202 Ma. In addition, an age of ~43 Ma in the south of the Sukhothai Fold Belt may indicate intrusion during the sinistral movement of the Klaeng and Mae Ping fault zones resulted from the Indian–Eurasian plate collision. The Doi Tung quartz monzodiorite provided an age of ~350 Ma as a timing of formation of the Sukhothai Fold Belt. The negative and positive initial εHf values (−8.0 to +9.2) with two‐stage depleted mantle model ages (TDMC of 2.2–0.6 Ga) of zircons from the Sukhothai Fold Belt granitoids indicate that the sources of their magma derived from partial melting of old continental crust and young oceanic crust, which probably mixed with a mantle‐derived magma. A zircon Hf‐isotope compilation including the data obtained in this study and previously reported values was used to prepare a map that allows a comparison between magmatic source and mineral deposit distribution in Thailand. The spatial distribution of Hf isotopic data reveals a distinct zonation, with initial εHf values decreasing from the east to the west, that is, from the western margin of the Indochina Terrane or the Loei Fold Belt to the Sukhothai Fold Belt, the Inthanon Zone and the Sibumasu Terrane. The magmatic source for the granitoids in the Loei Fold Belt is dominated by mantle‐derived components, as shown by positive average initial εHf values (+1.0 to +12.7), and contributed to porphyry‐related skarn copper–gold and iron and epithermal gold mineralization. In contrast, magmas in the Sibumasu Terrane and the Inthanon Zone originated from melting of old crustal materials, as indicated by mostly negative average initial εHf values (−15.1 to +0.8), and are responsible for S‐type granite‐related tin‐tungsten mineralization. The average initial εHf values (−5.0 to +11.0) from the intrusions in the Sukhothai Fold Belt suggest mixed sources, including evolved and juvenile magmatic materials, which generated the orogenic gold deposits and other vein‐type antimony, tungsten, fluorite, and base metal deposits. These results imply a close spatial correlation between the source of magmatism in each tectonic terrane of Thailand and different metal ore deposits. These isotope maps can be used as a powerful tool in the exploration for various commodities at the regional scale.

Alkali metal tungsten bronze-doped energy-saving glasses for near-infrared shielding applications

Tungsten bronze has attracted global attention for its applications in near-infrared (NIR)-shielding windows. Here, alkali metal tungsten bronze (MxWO3, M = one or two types of Li, Na, and K)-doped glasses are prepared by a simple melt-quenching method. Their structure and properties were characterized by XRD, Raman spectroscopy, XPS and UV–Vis–NIR spectrophotometry. The effects of M on their structure and the NIR shielding performance are investigated. The LiF sample has the best NIR shielding performance, but its visible transmittance is sacrificed due to its low quality. The glasses containing mixed Li+ and K+ cooperate to form a high-quality Li+/K+-codoped tungsten bronze, while the glasses containing mixed Li+ and Na+ compete for limited tungsten resources to form Li+- and Na+-doped tungsten bronzes separately. The research here is helpful for understanding the role of different alkali metal ions in bulk energy-saving glass and is hugely significant for the guidance of the future applications of energy-saving glass without films.

Structure and mechanical properties of reactive and non-reactive sputter deposited WC based coatings

During the growth of WC based thin films, carbon can be introduced by either a non-reactive or reactive deposition route. In this study, we compare the influence of the carbon origin on the coating properties, sputtering three different target materials – a ceramic WC, a ceramic WC including a conventional cobalt binder, and a metallic tungsten (W) target – in reactive (acetylene, C2H2) as well as non-reactive (pure Ar) atmospheres. The morphology changes, independently to the target type and atmosphere used, from crystalline (hex-W2C rich to pure fcc-WCx) to a nanocomposite (fcc-WCx nanometre sized grains embedded in an amorphous matrix) structure, up to amorphous coatings, only dominated by the prevalent C/W ratio. The cobalt binder however leads to a preferred amorphization of the coatings. The highest hardness is obtained for predominantly fcc structured WC0.67 (WC ceramic target), H = 40 ± 1.7 GPa, exhibiting also an excellent intrinsic fracture toughness of KIC = 3.3 ± 0.33 MPa·m1/2 obtained by micro-mechanical testing. Furthermore, the bonding nature of carbon is distinctly affected by the reactive carbon source, leading to more pronounced π-bonded carbon peak with increasing C2H2/Ar flow rates.

A Review of Tungsten Resources and Potential Extraction from Mine Waste

Tungsten is recognized as a critical metal due to its unique properties, economic importance, and limited sources of supply. It has wide applications where hardness, high density, high wear, and high-temperature resistance are required, such as in mining, construction, energy generation, electronics, aerospace, and defense sectors. The two primary tungsten minerals, and the only minerals of economic importance, are wolframite and scheelite. Secondary tungsten minerals are rare and generated by hydrothermal or supergene alteration rather than by atmospheric weathering. There are no reported concerns for tungsten toxicity. However, tungsten tailings and other residues may represent severe risks to human health and the environment. Tungsten metal scrap is the only secondary source for this metal but reprocessing of tungsten tailings may also become important in the future. Enhanced gravity separation, wet high-intensity magnetic separation, and flotation have been reported to be successful in reprocessing tungsten tailings, while bioleaching can assist with removing some toxic elements. In 2020, the world’s tungsten mine production was estimated at 84 kt of tungsten (106 kt WO3), with known tungsten reserves of 3400 kt. In addition, old tungsten tailings deposits may have great potential for exploration. The incomplete statistics indicate about 96 kt of tungsten content in those deposits, with an average grade of 0.1% WO3 (versus typical grades of 0.3–1% in primary deposits). This paper aims to provide an overview of tungsten minerals, tungsten primary and secondary resources, and tungsten mine waste, including its environmental risks and potential for reprocessing.

Preface to the special issue on diverse applications of tungsten and related metals

Preface to the special issue on diverse applications of tungsten and related metals

Consolidation and properties of tungsten by spark plasma sintering and hot isostatic pressing

The fabrication of dense tungsten was attempted with the combination process of presintering by spark plasma sintering and final hot isostatic pressing. The specimens fabricated by spark plasma sintering (1500–1600 °C) of commercial powder exhibited a relative density above 90.4%. In the case of the post hot isostatic pressing at 1650 °C for 2 h, improved relative density in the range of 96.4% to 97.2% was obtained. X-ray diffractometry and X-ray photoelectron spectroscopy analysis indicated that the sintered specimen was composed mainly of tungsten, and the trace amounts of metallic tungsten are bound with oxygen due to the surface oxidation. Strength measurement was conducted by biaxial bending test using a piston-on-three balls. Maximum flexural strength of 761 MPa were obtained for tungsten consolidated by a combined process of spark plasma sintering and hot isostatic pressing. The strength increase is explained by the increase in relative density rather than the effect of particle size.