• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
• /
• pp.342-343
• /
• 2006

In order to develop the nano-sized WC powder that improved the hardness of hardmetals, carbothermal reduction of WO3 by C was examined by using the thermogravimetric analysis. At the direct carburization reaction path of $WO_3{\rightarrow}WO_{2.72}{\rightarrow}WO_2{\rightarrow}W{\rightarrow}W_2C{\rightarrow}WC$, the nano-sized grain was generated at the reaction stage $WO_{2.72}$ to $WO_2$ and W. For trial production, the intermediate products which consists of metal and carbide phases obtained by the first heating has been carburized to the final WC powder. We succeeded in the development of the WC powder of about 70nm. In addition, the nano-sized WC powder in which the vanadium of the most effective grain growth inhibitor was uniformly dispersed was developed.

• 한국분말재료학회지
• /
• 제24권5호
• /
• pp.406-413
• /
• 2017

A Nanosized $WO_3$ and CuO powder mixture is prepared using novel high-energy ball milling in a bead mill to obtain a W-Cu nanocomposite powder, and the effect of milling time on the structural characteristics of $WO_3-CuO$ powder mixtures is investigated. The results show that the ball-milled $WO_3-CuO$ powder mixture reaches at steady state after 10 h milling, characterized by the uniform and narrow particle size distribution with primary crystalline sizes below 50 nm, a specific surface area of $37m^2/g$, and powder mean particle size ($D_{50}$) of $0.57{\mu}m$. The $WO_3-CuO$ powder mixtures milled for 10 h are heat-treated at different temperatures in $H_2$ atmosphere to produce W-Cu powder. The XRD results shows that both the $WO_3$ and CuO phases can be reduced to W and Cu phases at temperatures over $700^{\circ}C$. The reduced W-Cu nanocomposite powder exhibits excellent sinterability, and the ultrafine W-Cu composite can be obtained by the Cu liquid phase sintering process.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
• /
• pp.1298-1299
• /
• 2006

In the present work, the influence of the ball-milling time, milling atmosphere and weight ratio of ball to powder on characteristics of $WO_3-CuO$ was studied. Results show that, the grain sizes of the $WO_3$ and CuO in the ball-milled powder mixture were significantly decreased with increasing the milling time. Those of each oxide ball-milled in Argon and Hexane atmosphere for 30 and 20 hour were about 98 and 84 nm, respectively. After milling of 20 hour in Hexane as PCA, the powder had a homogeneously mixed structure and the average size of $WO_3-CuO$ powders was determined to about 230nm.

• 한국분말재료학회지
• /
• 제13권3호
• /
• pp.205-210
• /
• 2006

The effect of Cu content on hydrogen reduction behavior of ball-milled $WO_3$-CuO nanocomposite powders was investigated. Hydrogen reduction behavior and reduction percent(${\alpha}$) of nanopowders were characterized by thermogravimetry (TG) and hygrometry measurements. Activation energy for hydrogen reduction of $WO_3$ nanopowders with different Cu content was calculated at each heating rate and reduction percent(${\alpha}$). The activation energy for reduction of $WO_3$ obtained in this study existed in the ranging from 129 to 139 kJ/mol, which was in accordance with the activation energy for $WO_3$ powder reduction of conventional micron-sized.

• 한국분말재료학회지
• /
• 제10권3호
• /
• pp.186-189
• /
• 2003

A chemical vapor condensation (CVC) process using the pyrolysis of metal-organic precursors was applied to produce the nanosized $WO_3$ powders. Morphology and phase changes of the synthesized $WO_3$ powder as a function of CVC parameters were investigated by XRD, BET and TEM. The agglomerated nanosized monoclinic $WO_3$ powders with nearly spherical shape and 10-38 nm in mean diameter could be obtained. Conditions to produce the $WO_3$ nanopowders are presented in this paper.

• 한국분말재료학회지
• /
• 제26권1호
• /
• pp.28-33
• /
• 2019

The gas sensor is essential to monitoring dangerous gases in our environment. Metal oxide (MO) gas sensors are primarily utilized for flammable, toxic and organic gases and $O_3$ because of their high sensitivity, high response and high stability. Tungsten oxides ($WO_3$) have versatile applications, particularly for gas sensor applications because of the wide bandgap and stability of $WO_3$. Nanosize $WO_3$ are synthesized using the hydrothermal method. As-prepared $WO_3$ nanopowders are in the form of nanorods and nanorulers. The crystal structure is hexagonal tungsten bronze ($MxWO_3$, x =< 0.33), characterized as a tunnel structure that accommodates alkali ions and the phase stabilizer. A gas detection test reveals that $WO_3$ can detect acetone, butanol, ethanol, and gasoline. This is the first study to report this capability of $WO_3$.

• 한국재료학회지
• /
• 제27권10호
• /
• pp.513-517
• /
• 2017

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 $WO_3$ and W powders. Microstructural observation for the ball-milled powder mixtures revealed that the nano-sized $WO_3$ particles were homogeneously distributed on the surface of large W powders. The reduction behavior of $WO_3$ powder was analyzed by a temperature programmed reduction method with different heating rates in Ar-10% $H_2$ atmosphere. The activation energies for the reduction of $WO_3$, 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 $WO_3$ to $WO_2$ and from $WO_2$ 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.

• 한국분말재료학회지
• /
• 제24권6호
• /
• pp.472-476
• /
• 2017

Porous W-10 wt% Ti alloys are prepared by freeze-drying a $WO_3-TiH_2$/camphene slurry, using a sintering process. X-ray diffraction analysis of the heat-treated powder in an argon atmosphere shows the $WO_3$ peak of the starting powder and reaction-phase peaks such as $WO_{2.9}$, $WO_2$, and $TiO_2$ peaks. In contrast, a powder mixture heated in a hydrogen atmosphere is composed of the W and TiW phases. The formation of reaction phases that are dependent on the atmosphere is explained by a thermodynamic consideration of the reduction behavior of $WO_3$ and the dehydrogenation reaction of $TiH_2$. To fabricate a porous W-Ti alloy, the camphene slurry is frozen at $-30^{\circ}C$, and pores are generated in the frozen specimens by the sublimation of camphene while drying in air. The green body is hydrogen-reduced and sintered at $1000^{\circ}C$ for 1 h. The sintered sample prepared by freeze-drying the camphene slurry shows large and aligned parallel pores in the camphene growth direction, and small pores in the internal walls of the large pores. The strut between large pores consists of very fine particles with partial necking between them.

• 한국분말재료학회지
• /
• 제24권5호
• /
• pp.384-388
• /
• 2017

The effect of the mixing method on the characteristics of hybrid-structure W powder with nano and micro sizes is investigated. Fine $WO_3$ powders with sizes of ${\sim}0.6{\mu}m$, prepared by ball milling for 10 h, are mixed with pure W powder with sizes of $12{\mu}m$ by various mixing process. In the case of simple mixing with ball-milled $WO_3$ and micro sized W powders, $WO_3$ 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 $WO_3$ particles is exhibited. The microstructural observation reveals that the ball milled $WO_3$ powder, heat-treated at $750^{\circ}C$ 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.

• 센서학회지
• /
• 제10권2호
• /
• pp.118-124
• /
• 2001

입자들이 용액에 녹아있을 때 pH에 따라서 다른 zeta-potential을 가지게 되며, 이것은 입자의 분산상태에 영향을 주게 된다. NO 센서에서 $WO_3$ 입자의 크기는 감도에 큰 영향을 끼치므로 Sol-Coprecipitation법에 의한 $WO_3$ 센서 제조 시에 $WO_3$ precursor 상태에서의 pH의 영향을 알아보았다. 먼저 $WO_3$ precursor의 전기적 포텐셜을 측정하여 pH가 2에서 7로 변함에 따라 mobility가 증가하여 7일 때에 가장 큰 분산도를 가진 것을 알 수 있었고, 이는 powder 제조 후 입도 분석, 감지막의 XRD peak, 표면사진으로부터 확인 할 수 있었다. 결과적으로 감도 특성에도 영향을 끼쳐 pH=7에서 제조한 센서가 다른 pH에서 제조한 센서보다 감도가 우수한 것으로 나타났다.