In this study, we synthesize tungsten oxide thin films by electrodeposition and characterize their electrochromic properties. Depending on the deposition modes, compact and porous tungsten oxide films are fabricated on a transparent indium tin oxide (ITO) substrate. The morphology and crystal structure of the electrodeposited tungsten oxide thin films are investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). X-ray photoelectron spectroscopy is employed to verify the chemical composition and the oxidation state of the films. Compared to the compact tungsten oxides, the porous films show superior electrochemical activities with higher reversibility during electrochemical reactions. Furthermore, they exhibit very high color contrast (97.0%) and switching speed (3.1 and 3.2 s). The outstanding electrochromic performances of the porous tungsten oxide thin films are mainly attributed to the porous structure, which facilitates ion intercalation/deintercalation during electrochemical reactions.

An optimum route to fabricate a hybrid-structured W powder composed of nano and micro size powders was investigated. The mixture of nano and micro W powders was prepared by a ball milling and hydrogen reduction process for WO3 and W powders. Microstructural observation for the ball-milled powder mixtures revealed that the nano-sized WO3 particles were homogeneously distributed on the surface of large W powders. The reduction behavior of WO3 powder was analyzed by a temperature programmed reduction method with different heating rates in Ar-10% H2 atmosphere. The activation energies for the reduction of WO3, estimated by the slope of the Kissinger plot from the amount of reaction peak shift with heating rates, were measured as 117.4 kJ/mol and 94.6 kJ/mol depending on reduction steps from WO3 to WO2 and from WO2 to W, respectively. SEM and XRD analysis for the hydrogen-reduced powder mixture showed that the nano-sized W particles were well distributed on the surface of the micro-sized W powders.

The effect of the mixing method on the characteristics of hybrid-structure W powder with nano and micro sizes is investigated. Fine WO3 powders with sizes of ~0.6 μm, prepared by ball milling for 10 h, are mixed with pure W powder with sizes of 12 μm by various mixing process. In the case of simple mixing with ball-milled WO3 and micro sized W powders, WO3 particles are locally present in the form of agglomerates in the surface of large W powders, but in the case of ball milling, a relatively uniform distribution of WO3 particles is exhibited. The microstructural observation reveals that the ball milled WO3 powder, heat-treated at 750oC for 1 h in a hydrogen atmosphere, is fine W particles of ~200 nm or less. The powder mixture prepared by simple mixing and hydrogen reduction exhibits the formation of coarse W particles with agglomeration of the micro sized W powder on the surface. Conversely, in the powder mixture fabricated by ball milling and hydrogen reduction, a uniform distribution of fine W particles forming nano-micro sized hybrid structure is observed.

This study is carried out to obtain basic data regarding oxidation and reduction reactions, originated on the recycling of waste tungsten hard scraps by oxidation and reduction processes. First, it is estimated that the theoretical Gibbs free energy for the formation reaction of WO2 and WO3 are calculated as ΔG1,000K= -407.335 kJ/mol and ΔG1,000K = -585.679 kJ/mol, from the thermodynamics data reported by Ihsan Barin. In the experiments, the oxidation of pure tungsten rod by oxygen is carried out over a temperature range of 700-1,000oC for 1 h, and it is possible to conclude that the oxidation reaction can be represented by a relatively linear relationship. Second, the reduction of WO2 and WO3 powder by hydrogen is also calculated from the same thermodynamics data, and it can be found that it was difficult for the reduction reaction to occur at 1,027oC, in the case of WO2, but it can happen for temperatures higher than 1127oC. On the other hand, WO3 reduction reaction occurs at the relatively low temperature of 827oC. Based on these results, the reduction experiments are carried out at a temperature range of 500-1,000oC for 15 min to 4 h, in the case of WO3 powder, and it is possible to conclude that the reduction at 900oC for 2h is needed for a perfect reduction reaction.

This study focuses on the development of an alkaline leaching hydrometallurgy process for the recovery of tungsten from WC/Co hardmetal sludge, and an examination of the effect of the process parameters on tungsten recovery. The alkaline leaching hydrometallurgy process has four stages, i.e., oxidation of the sludge, leaching of tungsten by NaOH, refinement of the leaching solution, and precipitation of tungsten. The WC/Co hardmetal sludge oxide consists of WO3 and CoWO4. The leaching of tungsten is most affected by the leaching temperature, followed by the NaOH concentration and the leaching time. About 99% of tungsten in the WC/Co hardmetal sludge is leached at temperatures above 90oC and a NaOH concentration above 15%. For refinement of the leaching solution, pH control of the solution using HCl is more effective than the addition of Na2S·9H2O. The tungsten is precipitated as high-purity H2WO4·H2O by pH control using HCl. With decreasing pH of the solution, the tungsten recovery rate increases and then decrease. About 93% of tungsten in the WC/Co hardmetal sludge is recovered by the alkaline leaching hydrometallurgy process.

Tungsten (W) thin film was deposited at 400 oC using pulsed chemical vapor deposition (pulsed CVD); film was then evaluated as a nucleation layer for W-plug deposition at the contact, with an ultrahigh aspect ratio of about 14~15 (top opening diameter: 240~250 nm, bottom diameter: 98~100 nm) for dynamic random access memory. The deposition stage of pulsed CVD has four steps resulting in one deposition cycle: (1) Reaction of WF6 with SiH4. (2) Inert gas purge. (3) SiH4 exposure without WF6 supply. (4) Inert gas purge while conventional CVD consists of the continuous reaction of WF6 and SiH4. The pulsed CVD-W film showed better conformality at contacts compared to that of conventional CVD-W nucleation layer. It was found that resistivities of films deposited by pulsed CVD were closely related with the phases formed and with the microstructure, as characterized by the grain size. A lower contact resistance was obtained by using pulsed CVD-W film as a nucleation layer compared to that of the conventional CVD-W nucleation layer, even though the former has a higher resistivity (~100 μΩ-cm) than that of the latter (~25 μΩ-cm). The plan-view scanning electron microscopy images after focused ion beam milling showed that the lower contact resistance of the pulsed CVD-W based W-plug fill scheme was mainly due to its better plug filling capability.

Tungsten trioxide thin films are successfully synthesized by a sol-gel method using tungsten hexachlorideas precursors. The structural, chemical, and optical properties of the prepared films are characterized by scanning elec-tron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-Vis spectrophotometry. The electrochem-ical and electrochromic properties of the films before and after heat treatment are also investigated by cyclicvoltammetry, 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 effi-ciency of 65.7 cm2/C, which implies that heat treatment at an appropriate temperature is a crucial process in a sol-gelmethod for having a better electrochromic performance.

Effect of oxygen content in the ultrafine tungsten powder fabricated by electrical explosion of wire method on the behvior of spark plasma sintering was investigated. The initial oxygen content of 6.5 wt% of as-fabricated tungsten powder was reduced to 2.3 and 0.7 wt% for the powders which were reduction-treated at 400˚C for 2 hour and at 500˚C for 1h in hydrogen atmosphere, respectively. The reduction-treated tungsten powders were spark-plasma sintered at 1200-1600˚C for 100-3600 sec. with applied pressure of 50 MPa under vacuum of 0.133 Pa. Maximun sindered density of 97% relative density was obtained under the condition of 1600˚C for 1h from the tungsten powder with 0.7 wt% oxygen. Sintering activation energy of 95.85kJ/mol-1 was obtained, which is remarkably smaller than the reported ones of 380~460kJ/mol-1 for pressureless sintering of micron-scale tungsten powders.

Due to their unique properties, tungsten borides are good candidates for the industrial applications where certain features such as high hardness, chemical inertness, resistance to high temperatures, thermal shock and corrosion. In this study, conditions were investigated for producing tungsten boride powder from tungsten oxide(WO3) by self-propagating high-temperature synthesis (SHS) followed by HCl leaching techniques. In the first stage of the study, the exothermicity of the WO3-Mg reaction was investigated by computer simulation. Based on the simulation experimental study was conducted and the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of WO3, Mg and B2O3. It was found that WO3, Mg and B2O3 reaction system produced high combustion temperature and radical reaction so that diffusion between W and B was not properly occurred. Addition of NaCl and replacement of B2O3 with B successfully solved the diffusion problem. From the optimum condition tungsten boride(W2B and WB) powders which has 0.1~0.9 um particle size were synthesized.

Cobalt coated tungsten carbide-cobalt composite powder has been prepared through wet chemical reductionmethod. The cobalt sulfate solution was converted to the cobalt chloride then the cobalt hydroxide. The tungsten carbidepowders were added in to the cobalt hydroxide, the cobalt hydroxide was reduced and coated over tungsten carbidepowder using hypo-phosphorous acid. Both the cobalt and the tungsten carbide phase peaks were evident in the tungstencarbide-cobalt composite powder by X-ray diffraction. The average particle size measured via scanning electron micro-scope, particle size analysis was around 380 nm and the thickness of coated cobalt was determined to be 30~40 nm bytransmission electron microscopy.

목적: 본 연구는 콘택트렌즈 재료로 널리 사용되는 2-hydroxyethyl methacrylate, N-vinyl-2-pyrrolidone, methyl methacrylate, ethylene glycol dimethacrylate에 titanium isopropoxide와 tungsten(VI) oxide 나노입자를 첨가하여 안의료용 렌즈 재료를 중합하였다. 방법: 안의료용 콘택트렌즈의 첨가제로 Tungsten (VI) oxide 나노입자 사용의 활용도를 조사하기 위해 tungsten(VI) oxide 나노입자를 포함한 하이드로젤 콘택트렌즈 재료의 광학적, 물리적 특성 변화를 측정하였다. 결과: 생성된 고분자에 대한 자외선 영역의 투과율은 매우 낮게 측정되어 자외선 차단 능력이 있는 것으로 나타났다. 또한 tungsten(VI) oxide 나노입자의 첨가는 함수율의 큰 변화를 나타내지 않았으나 일정비율을 첨가한 조합에서는 소량의 함수율 변화가 나타났다. 함수율의 큰 변화가 없음에도 불구하고 산소침투율의 측정 값은 tungsten(VI) oxide 나노입자의 첨가 비율이 증가할수록 계속적으로 감소하는 경향이 나타 났다. 결론: 이상의 결과를 통해 titanium isopropoxide 및 tungsten(VI) oxide 나노입자는 하이드로젤 콘택트렌즈의 기본적인 물성을 만족시키면서 기능성 콘택트렌즈 재료로 유용하게 활용될 수 있을 것으로 판단된다.

Tungsten oxide films were prepared by an electrochemical deposition method for use as the anode in rechargeable lithium batteries. Continuous potentiostatic deposition of the film led to numerous cracks of the deposits while pulsed deposition significantly suppressed crack generation and film delamination. In particular, a crack-free dense tungsten oxide film with a thickness of ca. 210 nm was successfully created by pulsed deposition. The thickness of tungsten oxide was linearly proportional to deposition time. Compositional and structural analyses revealed that the as-prepared deposit was amorphous tungsten oxide and the heat treatment transformed it into crystalline triclinic tungsten oxide. Both the as-prepared and heat-treated samples reacted reversibly with lithium as the anode for rechargeable lithium batteries. Typical peaks for the conversion processes of tungsten oxides were observed in cyclic voltammograms, and the reversibility of the heat-treated sample exceeded that of the as-prepared one. Consistently, the cycling stability of the heat-treated sample proved to be much better than that of the as-prepared one in a galvanostatic charge/discharge experiment. These results demonstrate the feasibility of using electrolytic tungsten oxide films as the anode in rechargeable lithium batteries. However, further works are still needed to make a dense film with higher thickness and improved cycling stability for its practical use.

Tungsten bronze structure Sr1-xBaxNb2O6 (SBN) single crystals were grown primarily using the Czochralski method, in which several difficulties were encountered: striation formation and diameter control. Striation formation occurred mainly because of crystal rotation in an asymmetric thermal field and unsteady melt convection driven by thermal buoyancy forces. To optimize the growth conditions, bulk SBN crystals were grown in a furnace with resistance heating elements. The zone of O2 atmosphere for crystal growth is 9.0 cm and the difference of temperature between the melt and the top is 70˚C. According to the growth conditions of the rotation rate, grown SBN became either polycrystalline or composed of single crystals. In the case of as-grown Sr1-xBaxNb2O6 (x = 0.4; 60SBN) single crystals, the color of the crystals was transparent yellowish and the growth axis was the c-axis. The facets of the crystals were of various shapes. The length and diameter of the single crystals was 50~70 mm and 5~10 mm, respectively. Tungsten bronze SBN growth is affected by the temperature profile and the atmosphere of the growing zone. The thermal expansion coefficients on heating and on cooling of the grown SBN single crystals were not matched. These coefficients were thought to influence the phase transition phenomena of SBN.

A novel chemical method was evaluated to fabricate the ultrafine tungsten heavy alloy powders with bater-base solution made from the ammonium metatungstate (AMT), iron(II) chloride tetrahydrate (), nickel(II) chloride hexahydrate () as source materials and the sodium tungstate dihydrate () as Cl-reductant. In the preparation of mixtures the amounts of the source components were chosen so as to obtain alloy of 93W-5Ni-2Fe composition(wt.%). The obtained powders were characterized by X-ray diffraction, XRF, field-emission scanning microscope (FESEM), and chemical composition was analyzed by EDX.

Tungsten nanopowders were produced by the method of wires electrical explosion in the different gases. The study of phase and dispersed composition of the powders was carried out. The influence of electrical parameters such as the value of energy input in wire and the arc stage of the explosion was discussed. The factors that make for decreasing the particles size are the lower pressure of surrounding gas and the use of addition of chemically reactive gas.

The electrochromic properties of tungsten oxide films grown by RF sputtering were investigated. Among the sputter parameters, first the Ar:O2 ratios were controlled with division into only an O2 environment, 1:1 and 4:1. The structure of each film prepared by these conditions was studied by X-ray diffraction, X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. The sputter-deposited tungsten oxide films had an amorphous structure regardless of the Ar:O2 ratios. The chemical compositions, however, were different from each other. The stoichiometric structure and low-density film was obtained at higher O2 contents. Electrochemical tests were performed by cyclic voltammetry and chronoamperometry at 0.05 M H2SO4 solutions. The current density and charge ratio was estimated during the continuous potential and pulse potential cycling at -0.5 V and 1.8 V, respectively. The film grown in a higher oxygen environment had a higher current density and a reversible charge reaction during intercalation and deintercalation. The in-situ transmittance tests were performed by He-Ne laser (633 nm). At higher oxygen contents, a big transmittance difference was observed but the response speed was too slow. This was likely caused by higher film resistivity. Furthermore, the effect of sputtering pressure was also investigated. The structure and surface morphology of each film was observed by X-ray diffraction and scanning electron microscopy. A rough surface was observed at higher sputtering pressure, and this affected the higher transmittance difference and coloration efficiency.

Porous W with controlled pore characteristics was fabricated by a freeze-drying process. WO3 powder and camphene were used as the source materials of W and sublimable vehicles, respectively. Camphene slurries with WO3 contents of 10 and 15 vol% were prepared by milling at 50˚C with a small amount of oligomeric polyester dispersant. Freezing of a slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at -25˚C while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at 800˚C for 30 min and sintered in a furnace at 900˚C for 1 h under a hydrogen atmosphere. Microstructural observation revealed that all of the sintered samples were composed of only W phase and showed large pores which were aligned parallel to the camphene growth direction. The porosity and pore size increased with increasing camphene content. The difference in the pore characteristics depending on the slurry concentration may be explained by the degree of powder rearrangement in the slurry. The results strongly suggest that a porous metal with the required pore characteristics can be successfully fabricated by a freeze-drying process using metal oxide powders.

Cemented tungsten carbide has been used in cutting tools and die materials, and is an important industrial material. When the particle size is reduced to ultrafine, the hardness and other mechanical properties are improved remarkably. Ultrafine cemented carbide with high toughness and hardness is now widely used. The objective of this study is synthesis of nanostructured WC-Co powders by liquid phase method of tungstate. The precursor powders were obtained by freezen-drying of aqueous solution of soluble salts, such as ammonium metatungstate, cobalt nitrate. the final compositions were WC-10Co. In the case of liquid phase method, it can be observed synthesis of WC-10Co. The properties of powder produced at various temperature, were estimated from the SEM, BET and C/S analyser.

Inconel 718 alloy has excellent mechanical properties at room temperature, high temperature and cryogenic conditions. UTS of base metal is about 900MPa at room temperature; this is increased up to 1300MPa after heat treatment & aging-hardening. Mechanical properties of Inconel 718 Alloy were similar to those shown in the the results for tensile test; mechanical properties of Inconel 718 alloy's GTAW were similar to those of base metal's properties at room temperature. Mechanical properties at cryogenic conditions were better than those at room temperature. Heat-treated Inconel 718, non- filler metal GTAW on Inconel 718 and GTAW used filler metal on Inconel 718's UTS was 1400MPa at cryogenic condition. As a result, the excellent mechanical properties of Inconel 718 alloy under cryogenic conditions was proved through tensile tests under cryogenic conditions. In addition, weldability of Inconel 718 alloy under cryogenic conditions was superior to that of its base-metal. In this case, UTS of hybrid joint (IS-G) at -100˚C was 900MPa. Consequently, UTS of Inconel 718 alloy is estimated to increase from -100˚C to a specific temperature below -100˚C. Therefore, Inconel 718 alloy is considered a pertinent material for the production of Lox Pipe under cryogenic conditions.