• Journal of the Korean Chemical Society
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• v.16 no.6
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• pp.361-368
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• 1972

The organic solvent mixture of 5 % trioctylamine and 5 % n-octyl alcohol in n-hexane could be loaded with tungsten to 62 g $WO_3$/1 whereas the amine alone could be loaded only to 37 g $WO_3$/1. Molecular interaction between amine and tungstate ion during the solvent extraction process and the synergistic effect of alcohol in enhancing the solubility of the amine-tungstate complex have been studied by NMR spectroscopy. Tungsten has been shown to be extracted as a polymeric tungstate ion into the organic phase to form a trioctyl ammonium polytungstate salt, which was more stabilized in the hydrocarbon medium by interacting with alcohol via hydrogen bonding between the tungstate ion and alcohol.

• Journal of Life Science
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• v.17 no.7 s.87
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• pp.990-995
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• 2007

We tested the effect of sodium tungstate, which disturbs the molybdenum cofactor formation, on the activities of aldehyde oxidase(AO) and the growth of maize(Zea mays) primary roots. As reported in other plants, sodium tungstate inhibited AO also in the maize root concentration-dependently. The inhibitory effect of sodium tungstate was observed only when the inhibitor was applied to the living plants. Application of tungstate to the extracted protein did not show any effect. Western analysis revealed slightly decreased level of AO protein in the presence of tungstate, indicating a positive feedback of gene regulation by the product. We also tested the effects of tungstate on the root growth. The elongation of primary root and the development of lateral roots, which are sensitive to the absolute level of auxin, were decreased in the presence of sodium tungstate. However, the gravitropic curvature of the primary root, which is dependent on the relative amount of auxin at both sides, was unaffected. These data suggested the decrease of auxin biosynthesis by the application of tungstate. However, the level of free IAA was unaffected by tungstate application. We discuss the possible explanations for the observed results.

• Resources Recycling
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• v.19 no.4
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• pp.41-50
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• 2010

A fundamental study was carried out to develop a process for recycling tungsten and cobalt from WC-Co hardmetal sludge generated in the manufacturing process of hardmetal tools. The complete extraction of cobalt and simultaneous formation of tungstic was achieved by treating the sludge using aqua regia. The effect of aqua regia concentration, reaction temperature and time, pulp density on cobalt leaching and tungstic acid formation was investigated. The complete leaching of cobalt was attained at the optimum conditions: 100 vol.% aqua regia concentration, $100^{\circ}C$ temperature, 60 min. reaction time and 400 g/L pulp density. A complete conversion of tungsten carbide of the sludge to tungstic acid was however, obtained at the pulp densities lower than 150 g/L under the above condition. The progress of reaction during the aqua regia treatment of the sludge was monitored through the XRD phase identification of the residue. The metallic impurities in the tungstic acid so produced could be further removed as insoluble residues by dissolving the tungsten values in ammonia solution. The ammonium paratungstate($(NH_4)_{10}{\cdot}H_2W_{12}O_{42}{\cdot}4H_2O$) of 99.85% purity was prepared from the ammonium polytungstate solution by the evaporation crystallization method.

• Resources Recycling
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• v.27 no.6
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• pp.3-10
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• 2018

Tungsten is a metal with high melting point and used as a raw material for the production of super alloys. Tungsten exists as $WO{_4}^{2-}$ in alkaline solution. As solution pH decreases, polymerization reaction of $WO{_4}^{2-}$ occurs to result in the precipitation of tungstic acid. The hydrometallurgical process for the recovery of tungsten from ores or secondary resources can be classified as acid and alkaline leaching. In selecting a process for the recovery of pure tungsten from secondary resources, the nature and concentration of impurities in the secondary resources and the manufactured tungsten materials should be considered.

• Journal of the Korean Chemical Society
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• v.28 no.1
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• pp.54-61
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• 1984

The species and equilibrium of molybdate and tungstate have been investigated from the elution behaviors of those in various concentrations of nitric acid and the UV spectra obtained at the various Z values. In higher concentrations than 0.05M nitric acid, the nitarte complex species of $MoO_2(NO_3)_2$ seems to form from the $MoO_2^{2+}$ ions formed by the following equation: $Mo_8O_{26}^{4-} + 20H^+$ ${\rightleftharpoons}$ $8MoO_2^{2+}$ + $10H_2O$. In the case of tungstate, the elution behaviors of tungstate in nitric acid medium are similar to those of perchloric acid, so we think the equilibrium of tungstate existed in perchloric acid could be also existed in nitric acid. These elution behaviors of tungstate are compared with the UV spectra obtained at the various Z values.

• Resources Recycling
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• v.31 no.4
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• pp.19-25
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• 2022

In this study, tungsten carbide (WC) powder was prepared using a novel recycling process for hard metal sludge that does not use ammonium paratungstate. Instead of ammonia, acid was used to remove the sodium and crystallized tungstate, resulting in the formation of tungstic acid (H₂WO₄). The WC powder was successfully synthesized by the carbothermal reduction of tungstic acid through H₂O decomposition, reduction of WO₃ to W, and formation of WC. The carbon content and holding time at the carbothermal reduction temperature were optimized to remove free carbon from the WC powder. As a result, most of the free carbon in the WC powder prepared from sludge was removed, and the content of free carbon in the synthesized WC powder was lower than that in commercial WC powder. Moreover, the crystallite size of WC prepared from H₂WO₄ was much smaller than that of commercial micron-sized WC powder produced from APT. The small crystallite size of WC induces grain growth during the sintering of the WC-Co composite; thus, a WC-Co composite with large WC grains was fabricated using the WC powder prepared from H₂WO₄. The large WC grains affected the mechanical properties of the WC-Co composite. Further, due to the large grain size, the WC-Co composite fabricated from H₂WO₄ exhibited a higher toughness than that of the WC-Co composite prepared from commercial WC powder.

• Journal of the Korean Chemical Society
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• v.19 no.4
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• pp.225-232
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• 1975

The elution behaviour of molybdate and tungstate through anion exchange column has been studied at the various pH. A discussion is made to evaluate the equilibrium constants of the polymerization of these acids comparing with the behaviour of chromate ion and dichromate ion. The eqailibrium constants found at $20^{\circ}$ are $K = 4{\times}10^{53} for 7MoO_4^{2-} + 8H^+ {\longleftrightarrow} Mo7O_{24}^{6- }+ 4H_2O$$ K = 3{\times}10^{54} for 6WO_4^{2-} + 7H^+ {\longleftrightarrow} HW6O_{21}^{5-} + 7H_2O$ referring to this results the conditions of separation of tungstate and molybdate are obtained. iThe quantitative separations of carbonate, molybdate and tungstate from the pregnant solution have been established by anion exchange chromatography, using the $22 cm{\times}44.27 cm^2$ column of Rexyn 201. The optimum eluents for the quantitative separation of those ions are as follows; 0.2M solution of sodium chloride at pH 8 for carbonate, the mixture of 0.5 M ammonium chloride and 0.05 M sodium sulfate at pH 5 for molybdate and 0.5 M solution of ammonium chloride at pH 10 for tungstate. Tungstate is directly recovered from the pregnant solution as a form of ammonium paratungstate, by eluting with ammonium chloride solution.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.221-221
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• 2016

최근에 희토류 이온이 도핑된 텅스텐산(tungstates) 형광체에 대한 연구가 재조명되고 있다. 텅스텐산 형광체는 우수한 광학적 특성과 높은 화학적 안정성을 나타내기 때문에 X-선 증강 스크린(X-ray intensifying screens), 광고판용 형광 램프, 발광 다이오드, 레이저, 섬광체(scintillator), 전계방출 디스플레이 영역에 그 응용성을 넓히고 있다. 본 연구는 모체 결정 MgWO4에 희토류 이온인 Tb3+와 융제(flux)의 몰 비를 변화 시켜 고상반응법을 사용하여 합성을 하였다. 합성한 형광체를 여기 파장 281 nm로 제어하였을 시, 545 nm의 녹색 발광 스펙트럼을 관찰 하였다. Tb3+이온이 0.10 mol일 때, 가장 발광 세기가 컸으며, 몰비가 증가 할수록 발광의 세기는 점차 커지다가 0.12 mol에서 작아졌다. 주 발광 신호 이외에도 489 nm, 586 nm, 621 nm에서 상대적으로 작은 발광 스펙트럼을 보였다. XRD를 통해 분석한 결정구조는 단사정계임을 알 수 있었으며 주 피크는 $23.9^{\circ}$에서 발생 하였고 이는 (110)면에서 발생한 회절 신호이다.

• Solar Energy
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• v.16 no.2
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• pp.87-96
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• 1996

Electochromic tungsten oxide thin films were prepared on the ITO coated glass by rf magnetron sputtering from a compressed powder tungsten oxide target in an argonoxygen atmosphere. The influence of the preparation conditions, especially the substrate temperature, on the chemical stability of film was investigated. These films were cycled in 0.6M $LiClO_4$ and 0.6M $H_2SO_4$ electrolyte respecitively, and exhibited electrochromic behavior upon the electrochemical insertion and extraction of ion. Among these tungsten oxide thin films, films prepared at a substrate temperature of $150^{\circ}C$ were found to be most stable in terms of cyclic durability.

• Proceedings of the Materials Research Society of Korea Conference
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• 2000.11a
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• pp.129-129
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• 2000