• Journal of Powder Materials
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• v.22 no.5
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• pp.309-314
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• 2015

Tungsten trioxide thin films are successfully synthesized by a sol-gel method using tungsten hexachloride as precursors. The structural, chemical, and optical properties of the prepared films are characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-Vis spectrophotometry. The electrochemical and electrochromic properties of the films before and after heat treatment are also investigated by cyclic voltammetry, chronoamperometry, and in situ transmittance measurement system. Compared to as-prepared films, heat-treated tungsten trioxide thin films exhibit a higher electrochemical reversibility of 0.81 and superior coloration efficiency of $65.7cm^2/C$, which implies that heat treatment at an appropriate temperature is a crucial process in a sol-gel method for having a better electrochromic performance.

• Journal of Powder Materials
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• v.28 no.4
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• pp.342-351
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• 2021

Because of its unique properties, tungsten is a strategic and rare metal used in various industrial applications. However, the world's annual production of tungsten is only 84000 t. Ammonium paratungstate (APT), which is used as the main intermediate in industrial tungsten production, is usually obtained from tungsten concentrates of wolframite and scheelite by hydrometallurgical treatment. Intermediates such as tungsten trioxide, tungsten blue oxide, tungstic acid, and ammonium metatungstate can be derived from APT by thermal decomposition or chemical attack. Tungsten metal powder is produced through the hydrogen reduction of high-purity tungsten oxides, and tungsten carbide powder is produced by the reaction of tungsten powder and carbon black powder at 1300-1700℃ in a hydrogen atmosphere. Tungsten scrap can be divided into hard and soft scrap based on shape (bulk or powder). It can also be divided into new scrap generated during the production of tungsten-bearing goods and old scrap collected at the end of life. Recycling technologies for tungsten can be divided into four main groups: direct, chemical, and semi-direct recycling, and melting metallurgy. In this review, the current status of tungsten smelting and recycling technologies is discussed.

• Journal of Powder Materials
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• v.5 no.4
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• pp.329-333
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• 1998

Copper-10 wt. % tungsten alloyed powder was obtained by co-reduction of mixed tungsten-trioxide and copper oxide powders at 973 K for 7.2 Ks. In the alloy obtained by pressure-assisted sintering of this co-reduced powder, ultra fine tungsten particles (about 100nm) were dispersed uniformly in the copper matrix. At room temperature, the hardness of this alloy was Hv151 and the electrical conductivity was 85% IACS. After annealing at 1173 K for 3.6 Ks, the hardness and electrical conductivity were Hv147 and 84% IACS, respectively, and were same as before annealing. It was confirmed that the hardness and electrical conductivity of this alloy were hardly influenced by annealing condition since the microstructure of this alloy is highly stabilized.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.26 no.2
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• pp.119-138
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• 2016

Objectives: The purpose of this study is to review size, shape, and crystal structure-dependent toxicity of major metal oxide particles such as silicon dioxide, tungsten trioxide, aluminum oxide, and titanium dioxide as byproducts generated in semiconductor fabrication facility. Methods: To review the toxicity of major metal oxide particles, we used various reported research and review papers. The papers were searched by using websites such as Google Scholar and PubMed. Keyword search terms included '$SiO_2$(or $WO_3$ or $Al_2O_3$ or $TiO_2$) toxicity', 'health effects $SiO_2$(or $WO_3$ or $Al_2O_3$ or $TiO_2$). Additional papers were identified in references cited in the searched papers. Results: In various cell lines and organs of human and animals, cytotoxicity, genotoxicity, hepatoxicity, fetotoxicity, neurotoxicity, and histopathological changes were induced by silicon dioxide, tungsten trioxide, aluminium oxide, and titanium dioxide particles. Differences in toxicity were dependent on the cell lines, organs, doses, as well as the chemical composition, size, surface area, shape, and crystal structure of the particles. However, the doses used in the reported papers were higher than the possible exposure level in general work environment. Oxidative stress induced by the metal oxide particles plays a significant role in the expression of toxicity. Conclusions: The results cannot guarantee human toxicity of the metal oxide particles, because there is still a lack of available information about health effects on humans. In addition, toxicological studies under the exposure conditions in the actual work environment are needed.

• Journal of Radiation Protection and Research
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• v.48 no.4
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• pp.184-196
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• 2023

Background: Radiation protection is crucial in various fields due to the harmful effects of radiation. Shielding is used to reduce radiation exposure, but gamma radiation poses challenges due to its high energy and penetration capabilities. Materials and Methods: This work investigates the radiation shielding properties of polyvinylidene fluoride (PVDF) samples containing different weight fraction of tungsten carbide (WC), tungsten trioxide (WO₃), and tungsten disulfide (WS₂). Parameters such as the mass attenuation coefficient (MAC), half-value layer (HVL), mean free path (MFP), effective atomic number (Z_eff), and macroscopic effective removal cross-section for fast neutrons (Σ_R) were calculated using the Phy-X/PSD software. EpiXS simulations were conducted for MAC validation. Results and Discussion: Increasing the weight fraction of the additives resulted in higher MAC values, indicating improved radiation shielding. PVDF-xWC showed the highest percentage increase in MAC values. MFP results indicated that PVDF-0.20WC has the lowest values, suggesting superior shielding properties compared to PVDF-0.20WO₃ and PVDF-0.20WS₂. PVDF-0.20WC also exhibited the highest Z_eff values, while PVDF-0.20WS₂ showed a slightly higher increase in Z_eff at energies of 0.662 and 1.333 MeV. PVDF-0.20WC has demonstrated the highest Σ_R value, indicating effective shielding against fast neutrons, while PVDF-0.20WS₂ had the lowest Σ_R value. The Monte Carlo N-Particle Transport version 5 (MCNP5) simulations showed that PVDF-xWC attenuates gamma radiation more than pure PVDF, significantly decreasing the dose equivalent rate. Conclusion: Overall, this research provides insights into the radiation shielding properties of PVDF mixtures, with PVDF-xWC showing the most promising results.

• Journal of Electrochemical Science and Technology
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• v.10 no.1
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• pp.89-97
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• 2019

As a promising candidate for anode materials in lithium ion battery (LIB), tungsten trioxide ($WO_3$) and tungsten disulfide ($WS_2$) nanocrystals were synthesized, and their electrochemical properties were comprehensibly studied using a half cell. One-dimensional $WO_3$ nanowires with uniform diameter of 10 nm were synthesized by hydrothermal method, and two-dimensional (2D) $WS_2$ nanosheets by unique gas phase sulfurization of $WO_3$ using $H_2S$. $WS_2$ nanosheets exhibits uniformly 10 nm thickness. The $WO_3$ nanowires and $WS_2$ nanosheets showed maximum capacities of 552 and $633mA\;h\;g^{-1}$, respectively, after 100 cycles. Especially, the capacity of $WS_2$ is significantly larger than the theoretical capacity ($433mA\;h\;g^{-1}$). We also examined the cycling performance using a larger size $WO_3$ and $WS_2$ nanocrystals, showing that the smaller size plays an important role in enhancing the capacity of LIBs. The larger capacity of $WS_2$ nanosheets than the theoretical value is ascribed to the lower charge transfer resistance of 2D nanostructures.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.25 no.3
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• pp.294-300
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• 2015

Objectives: The aim of this study is to identify physicochemical properties such as chemical composition, size, shape and crystal structure of powder byproducts generated from a metallization process and its 1st scrubber in the semiconductor industry. Methods: Powder samples were collected from inner chambers during maintenance of the W-plug process equipment (using tungsten hexafluoride as a precursor material) and its 1st scrubber. The chemical composition, size and shape of the powder particles were determined by field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy dispersive spectroscope (EDS). The crystal structure of the powders was analyzed by X-ray diffraction (XRD). Results: From the SEM-EDS and TEM-EDS analyses, O and W were mainly detected, which indicates the powder byproducts are tungsten trioxide ($WO_3$), whereas Al, F and Ti were detected as low peaks. The powder particles were spherical and nearly spherical, and the particle size collected from the process equipment and its 1st scrubber showed 10-20 nm (agglomerates: 55-90 nm) and 16-20 nm (agglomerates: 80-120 nm) as primary particles, respectively. The XRD patterns of the yellow powder byproducts exhibit five peaks at $23.8^{\circ}$ $33.9^{\circ}$ $41.74^{\circ}$ $48.86^{\circ}$ and $54.78^{\circ}$ which correspond to the (200), (220), (222), (400), and (420) planes of cubic $WO_3$. Conclusions: We elucidated the physicochemical characteristics of the powder byproducts collected from W-plug process equipment and its 1st scrubber. This study should provide useful information for the development of alternative strategies to improve the working environment and workers' health.

• Korean Journal of Materials Research
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• v.30 no.8
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• pp.421-425
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• 2020

A transparent quantum dot (QD)-based light-emitting diode (LED) with silver nanowire (Ag NW) and indium-tin oxide (ITO) hybrid electrode is demonstrated. The device consists of an Ag NW-ITO hybrid cathode (-), zinc oxide, poly (9-vinylcarbazole) (PVK), CdSe/CdZnS QD, tungsten trioxide, and ITO anode (+). The device shows pure green-color emission peaking at 548 nm, with a narrow spectral half width of 43 nm. Devices with hybrid cathodes show better performances, including higher luminance with higher current density, and lower threshold voltage of 5 V, compared with the reference device with a pure Ag NW cathode. It is worth noting that our transparent device with hybrid cathode exhibits a lifetime 9,300 seconds longer than that of a device with Ag NW cathode. This is the reason that the ITO overlayer can protect against oxidization of Ag NW, and the Ag NW underlayer can reduce the junction resistance and spread the current efficiently. The hybrid cathode for our transparent QD LED can applicable to other quantum structure-based optical devices.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.575-578
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• 2000

In this work, all solid-state thin film supercapacitor(TFSC) was fabricated using tungsten trioxide (WO$_3$) with a structure WO$_3$/LiPON/WO$_3$/Pt/TiO$_2$/Si (substrate). After TiO$_2$ was deposited on Si(100) wafer by d.c. reactive sputtering, the Pt current collector films were grown on TiO$_2$glue layer without breaking vacuum by d.c. sputtering. Fabrication conditions of WO$_3$ thin film were such that substrate temperature, working pressure, gas ratio of $O_2$/Ar and r.f. power were room temperature, 5 mTorr, 20% (O$_2$(8sccm)/Ar(32sccm)) and 200W, respectively. LiPON electrolyte film were grown on the WO$_3$ film using r.f. magnetron sputtering at room temperature. The XRD pattern of the as-deposited WO$_3$ thin film were shown no crystalline peak (amorphous). The SEM image of as-deposited WO$_3$ thin film showed that the surface is smooth and uniform. The capacitiy of as-fabricated TFSC was 0$\times$10$^{-2}$ F/$\textrm{cm}^2$-${\mu}{\textrm}{m}$.

• Journal of Powder Materials
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• v.26 no.1
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• pp.40-44
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• 2019

Tungsten trioxide ($WO_3$) is a promising candidate as a photocatalyst because of its outstanding electrical and optical properties. In this study, we prepare $WO_3$ thin films by electrodeposition and characterize the photocatalytic degradation of methylene blue using these films. Depending on the voltage conditions (static and pulse), compact and porous $WO_3$ films are fabricated on a transparent ITO/glass substrate. The morphology and crystal structure of electrodeposited $WO_3$ thin films are investigated by scanning electron microscopy, atomic force microscopy, and X-ray diffraction. An application of static voltage during electrodeposition yields a compact layer of $WO_3$, whereas a highly porous morphology with nanoflakes is produced by a pulse voltage process. Compared to the compact film, the porous $WO_3$ thin film shows better photocatalytic activities. Furthermore, a much higher reaction rate of degradation of methylene blue can be achieved after post-annealing of $WO_3$ thin films.