• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.654-655
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• 2006

This is about the effects deoxidization, carbonization and alloying preparation on fine grain W, WC, and grade YG8 powder reduced by "yellow tungsten oxide" and "blue tungsten oxide". The result indicates that yellow tungsten has single composition and blue tungsten oxide has complex composition. With this feature, yellow tungsten oxide got better uniformity and concentration distribution on fine particle size W and WC powder than blue tungsten oxide's. The grade alloy YG8 that made of this W or WC powder has uniform alloy construction, concentrated WC grain distribution and better alloy properties.

• Journal of the Korean Chemical Society
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• v.61 no.3
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• pp.97-103
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• 2017

In this study, the functional hydrogel ophthalmic lens containing tungsten oxide nanoparticles, 2,4-dihydroxy benzophenone and 2-hydroxy-4-(methacryloyloxy) benzophenone were manufactured. HEMA (2-hydroxyethyl methacrylate), MMA (methyl methacrylate), AA(acrylic acid), the cross-linker EGDMA (ethylene glycol dimethacrylate), the initiator AIBN (azobisisobutyronitrile) and the functional additives including tungsten oxide nanoparticles, 2,4-dihydroxy benzophenone, and 2-hydroxy-4-(methacryloyloxy) benzophenone were used respectively. The measurements of water content and refractive index of the sample was decreased and increased, respectively. And also, the UV transmittance of produced lens containing 2,4-dihydroxy benzophenone, 2-hydroxy-4-(methacryloyloxy) benzophenone and tungsten oxide nanoparticles was measured. Based on the results of this study, it is judged that the performance improvement increased over time when 2-hydroxy-4-(methacryloyloxy) benzophenone was used as an additive, while the use of tungsten oxide nanoparticles influenced on blue-ray-blocking effect of the hydrophilic lens.

• Korean Journal of Materials Research
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• v.31 no.1
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• pp.23-28
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• 2021

The purpose of this study is to prepare WO3 nanopowders by high-energy milling in mixture gas (7 % H2+Ar) with various milling times (10, 30, and 60 min). The phase transformation, particle size and light absorption properties of WO3 nanopowders during reduction via high-energy milling are studied. It is found that the particle size of the WO3 decreases from about 30 ㎛ to 20 nm, and the grain size of WO3 decreases rapidly with increasing milling time. Furthermore, the surface of the particles due to the pulverization process is observed to change to an amorphous structure. UV/Vis spectrophotometry shows that WO3 powder with increasing milling times (10, 30, 60 min) effectively extends the light absorption properties to the visible region. WO3 powder changes from yellow to gray and can be seen as a phenomenon in which the progress of the color changes to blue. The characterization of WO3 is performed by high resolution X-ray diffractometry, Field emission scanning electron microscopy, Transmission electron microscopy, UV/Vis spectrophotometry and Particle size analysis.

• 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.

• Korean Journal of Materials Research
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• v.21 no.2
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• pp.83-88
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• 2011

Nano-technology is a super microscopic technology to deal with structures of 100 nm or smaller. This technology also involves the developing of $TiO_2$ materials or $TiO_2$ devices within that size. The aim of the present paper is to synthesize $WO_x$ doped nano-$TiO_2$ by the Sonochemistry method and to evaluate the effect of different percentages (0.5-5 wt%) of tungsten oxide load on $TiO_2$ in methylene blue (MB) elimination. The samples were characterized using such different techniques as X-ray diffraction (XRD), TEM, SEM, and UV-VIS absorption spectra. The photo-catalytic activity of tungsten oxide doped $TiO_2$ was evaluated through the elimination of methylene blue using UV-irradiation (315-400nm). The best result was found with 5 wt% $WO_x$ doped $TiO_2$. It has been confirmed that $WO_x-TiO_2$ could be excited by visible light (E<3.2 eV) and that the recombination rate of electrons/holes in $WO_x-TiO_2$ declined due to the existence of $WO_x$ doped in $TiO_2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.11a
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• pp.179-182
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• 1994

We have investigated the optical and electrochromic properties of molybdenum oxide(MoO$_3$) films by thermal evaporation. The MoO$_3$films deposited at substrate temperatures below 200$^{\circ}C$ are found to be amorphous and annealed films at temperature 300$^{\circ}C$ for 1 hour in air are crystalline. The optical energy gap calculated from the transmittance and reflectance spectra of MoO$_3$ films is near 2.75 eV and 3.25 eV for amorphous films and crystalline films, respectively. The MoO$_3$ thin films exhibit light blue to dark blue optical modulation on lithium intercalation and have a uniform transmittance modulation over a wavelength range of 300∼1100 nmcompared to tungsten oxide films.

• Journal of Powder Materials
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• v.8 no.1
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• pp.49-54
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• 2001

The synthesis and characteristics of W-Ni-Fe nanocomposite powder by hydrogen reduction of ball milled W-Ni-Fe oxide mixture were investigated. The ball milled oxide mixture was prepared by high energy attrition milling of W blue powder, NiO and $Fe_2O_3$ for 1 h. The structure of the oxide mixture was characteristic of nano porous agglomerate composite powder consisting of nanoscale particles and pores which act as effective removal path of water vapor during hydrogen reduction process. The reduction experiment showed that the reduction reaction starts from NiO, followed by $Fe_2O_3$ and finally W oxide. It was also found that during the reduction process rapid alloying of Ni-Fe yielded the formation of $\gamma$-Ni-Fe. After reduction at 80$0^{\circ}C$ for 1 h, the nano-composite powder of W-4.57Ni-2.34Fe comprising W and $\gamma$-Ni-Fe phases was produced, of which grain size was35nm for W and 87 nm for $\gamma$-Ni-Fe, respectively. Sinterability of the W heavy alloy nanopowder showing full density and sound microstructure under the condition of 147$0^{\circ}C$/20 min is thought to be suitable for raw material for powder injection molding of tungsten heavy alloy.

• Bulletin of the Korean Chemical Society
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• v.35 no.6
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• pp.1794-1798
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• 2014

Graphitic g-$C_3N_4-WO_3$ composite was synthesized simply by decomposing melamine in the presence of $WO_3$ at $500^{\circ}C$. The obtained material was characterized by XRD, SEM, IR and XPS. The results showed that the as-prepared composite exhibits orthorhombic $WO_3$ phase coated by g-$C_3N_4$ and the g-$C_3N_4$ decomposed completely with N-doped $WO_3$ remaining at elevated calcination temperatures. The photocatalytic activity of the composite was evaluated by the photodegradation of methylene blue under visible light. An enhancement in photocatalytic activity for the graphitic g-$C_3N_4-WO_3$ composite compared to the conventional nitrogen-doped $WO_3$ was observed, which can be attributed to the presence of g-$C_3N_4$ in the material.

• Journal of Powder Materials
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• v.24 no.6
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• pp.483-488
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• 2017

Transition-metal oxide semiconductors have various band gaps. Therefore, many studies have been conducted in various application fields. Among these, methods for the adsorption of organic dyes and utilization of photocatalytic properties have been developed using various metal oxides. In this study, the adsorption and photocatalytic effects of $WO_3$ nanomaterials prepared by hydrothermal synthesis are investigated, with citric acid added in the hydrothermal process as a structure-directing agent. The nanostructures of $WO_3$ are studied using transmission electron microscopy and scanning electron microscopy images. The crystal structure is investigated using X-ray diffraction patterns, and the changes in the dye concentrations adsorbed on $WO_3$ nanorods are measured with a UV-visible absorption spectrophotometer based on Beer-Lambert's law. The methylene blue (MB) dye solution is subjected to acid or base conditions to monitor the change in the maximum adsorption amount in relation to the pH. The maximum adsorption capacity is observed at pH 3. In addition to the dye adsorption, UV irradiation is carried out to investigate the decomposition of the MB dye as a result of photocatalytic effects. Significant photocatalytic properties are observed and compared with the adsorption effects for dye removal.

• Journal of Powder Materials
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• v.25 no.4
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• pp.316-321
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• 2018

Composites of P25 $TiO_2$ and hexagonal $WO_3$ nanorods are synthesized through ball-milling in order to study photocatalytic properties. Various composites of $TiO_2/WO_3$ are prepared by controlling the weight percentages (wt%) of $WO_3$, in the range of 1-30 wt%, and milling time to investigate the effects of the composition ratio on the photocatalytic properties. Scanning electron microscopy, x-ray diffraction, and transmission electron microscopy are performed to characterize the structure, shape and size of the synthesized composites of $TiO_2/WO_3$. Methylene blue is used as a test dye to analyze the photocatalytic properties of the synthesized composite material. The photocatalytic activity shows that the decomposition efficiency of the dye due to the photocatalytic effect is the highest in the $TiO_2/WO_3$ (3 wt%) composite, and the catalytic efficiency decreases sharply when the amount of $WO_3$ is further increased. As the amount of $WO_3$ added increases, dye-removal by adsorption occurs during centrifugation, instead of the decomposition of dyes by photocatalysts. Finally, $TiO_2/WO_3$ (3 wt%) composites are synthesized with various milling times. Experimental results show that the milling time has the best catalytic efficiency at 30 min, after which it gradually decreases. There is no significant change after 1 hour.