• 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.

• Economic and Environmental Geology
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• v.28 no.3
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• pp.287-303
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• 1995

Tungsten ore deposits in China show clearly their relationship between granitoids and orebodies. All kinds of different tungsten ore deposits, having the largest ore reserves in the world, occur in China. Major tungsten deposits in 1950'years were locally confined in three provinces such as Jiangxi, Hunan and Guangdong. However, the major tungsten ore deposits are replaced by new tungsten deposits such as Sandahozhuang, Xingluokeng, Shizhuan and Daminghsan deposit which may be larger than the previous major deposits. Tungsten ore deposits of China exhibit obviously the granitoid was the ore-bringer to form tungsten ore deposits. The wolframite-bearing quarz veins in China indicate that tungsten mineralization took place by crystallization of wolframite preferentially unless $Ca^{{+}{+}}$ was introduced from outside into the magma-origin-fluid, since it is understood that the scheelite in the Sangdong ore deposit was preferentially precipitated, because of chemical affinity, from the tungsten fluid in which Fe and Ca ions were as sufficient as to form magnetite, wolframite and scheelite. Tungsten deposits in the world are divided into two systems; W-Mo-Sn system and W-Mo system. Most of tungsten deposits in China dated to about 196-116 Ma belong to the W-Mo-Sn system, while late Cretaceous tungsten deposits such as the Sangdong deposit in Korea belongs to the W-Mo system. The genetic order of tin-tungsten-molybdenum mineralization observed in the Moping tungsten mine in China and the Sangdong in Korea may be attributed to volatile pressures in the same magma chamber. It is assumed from ages of tungsten mineralizations that ore elements such as tin, tungsten and molybdenum might be generated periodically by nuclear fission and fusion in a part of the mantle and the element generated was introduced into the magma chamber. The periodical generation of elements had determined association, depletion and enrichment of tin and molybdenum in tungsten mineralization and it results in little association of cassiterite in tungsten deposit of late Cretaceous ages. Different mechanism of emplacement of the ore-bearing magma has brought various genetic types of tungsten deposits as shown in China and the world.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.2
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• pp.68-72
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• 2004

The performance of copper-tungsten for electrodes used in an ultra high voltage interruption system was evaluated by means of an interruption test, which requires a large-scale apparatus and high cost. In this study, prior to the interruption test, the characteristics of a Cu-W electrode were estimated through the DC arc test, which is a simple, low cost procedure. The DC arc characteristics of a 20wt%Cu-80wt%W electrode were investigated with the change of tungsten powder size distribution and the addition of nickel. In specimens containing a high volume fraction of large sized tungsten particles, the relative density and hardness of sintered Cu-W electrodes increased while the electrical conductivity and the DC arc resistance decreased. Furthermore, the relative density became enhanced with the increase of the amount of nickel while the hardness and electrical conductivity diminished and the DC arc resistance worsened.

• Journal of Powder Materials
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• v.9 no.3
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• pp.174-181
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• 2002

Nanosized tungsten carbide powders were synthesized by the chemical vapor condensation(CVC) process using the pyrolysis of tungsten hexacarbonyl($W(CO)_6$). The effect of CVC parameters on the formation and the microstructural change of as-prepared powders were studied by XRD, BET and TEM. The loosely agglomerated nanosized tungsten-carbide($WC_{1-x}$) particles having the smooth rounded tetragonal shape could be obtained below $1000^{\circ}C$ in argon and air atmosphere respectively. The grain size of powders was decreased from 53 nm to 28 nm with increasing reaction temperature. The increase of particle size with reaction temperature represented that the condensation of precursor vapor dominated the powder formation in CVC reactor. The powder prepared at $1000^{\circ}C$ was consisted of the pure W and cubic tungsten-carbide ($WC_{1-x}$), and their surfaces had irregular shape because the pure W was formed on the $WC_{1-x}$ powders. The $WC_{1-x}$ and W powders having the average particles size of about 5 nm were produced in vacuum.

• Explosives and Blasting
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• v.19 no.1
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• pp.101-110
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• 2001

Depleted uranium (DU) outperforms tungsten heavy alloys (WHA) by about 10%. Because of environmental and hence, political concerns, there is a need to improve WHA performance, in order to replace the DU penetrators. A technique of metal powder compaction by the detonation of an explosive has been applied to tungsten-titanium(W-Ti) powder materials that otherwise may be difficult to fabricate conventionally or have dissimilar, nonequilibrium, or unique me1astab1e substructures. However, the engineering properties of compacted materials are not widely reported and are little known especially for the "unique" composition of W-Ti alloy. To develop high-performance tungsten composites with superior ballistic attributes, it is necessary to understand, carefully document controlled experimental results, and develop basic computational models for potential composites with controlled microstructures. A detailed understanding and engineering application of W-Ti alloy can lead to the development of new structural design for engineering components and materials.

• Journal of the Korean Ceramic Society
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• v.35 no.6
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• pp.543-550
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• 1998

A process for the preparation of spherical tungsten oxide powders by the emulsion evaporation method was developed. The characteristics of the powders thus prepared were examined by means of TGA X-ray diffraction SEM and image analysis. The emulsion was prepared by fast mixing of tungsten containing aque-ous phase and the organic phase which contained kerosene surfactant and paraffin oil. The precursor was made by evaporating the emulsion in the kerosene bath at $160^{\circ}C$ and then calcined at $650^{\circ}C$ in order to pro-duce tungsten oxide powders. The average particle size of the tungsten oxide powders was $0.5\;\mu\textrm{m}$ and their shapes were spherical. Water-in-oil type emulsion wasmore advantageous to make less agglmerated. $W_{3}$ powders than the oil-in-water type emulsion for the emulsion evaporation experiments. As the HLB value of the surfactant increased and the concentration of tungsten ions in the aqueous phase decreased the mean particle size of tungsten oxide powders decreased whereas agglomeration increased. The optimum con-centration of Span 80 was 8 percent by volume and the optimum stirring speed in the emulsion formation was 5000 rpm in order to obtain find less agglomerated $W_{3}$ powders.

• Transactions of Materials Processing
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• v.19 no.3
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• pp.191-196
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• 2010

Tungsten-carbide as typical difficult-to-cut material has excellent mechanical properties such as high thermal resistivity, mechanical strength and chemical durability. However, it is next to impossible for tungsten-carbide to be fabricated the needed parts by cutting process. In this study, for establishing the micro fabrication method of tungsten-carbide for micro injection or compression molding core, the investigation on micro cutting characteristics of tungsten-carbide green part which is made by powder injection molding process and easy to cut relatively was performed. For this, micro endmilling experiments of tungsten-carbide green part were performed according to various cutting conditions. Finally, the wear trend of micro endmill and the appearance of micro rib according to feed-rate and cutting depth per step were analyzed through SEM images of micro cutting feature and microscope images of micro tools.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.3 no.2
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• pp.107-116
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• 1993

Tungsten thin film was deposited on Si( 100) substrate by either Si substrate reduction of W$F_6$( case 1) or Si$H_4$ reduction of W$F_6$( case 2) in LPCVD system The morphology and properties of deposited films for both cases were examined. The crystal structure for both cases was determined to be bec (body centered cubic). The amount of tungsten and the grain size in thin films were increased as the film grows. From the experimental results and theoretical considerations, it can be understood that the tungsten thin film grows by the volmer-weber growth mode, that is, island growth. The detailed tungsten thin film growth mode is presented. It was also found that the initial polycrystal structure of tungsten thin film developed into single crystal structure as the film grew in thickness.

• Corrosion Science and Technology
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• v.6 no.4
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• pp.147-153
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• 2007

This study sought to investigate the reaction of Co-binder containing tungsten with molten zinc. Four kinds of Co-W alloys (pure, 10%W, 20%W, 30%W) were prepared using the powder metallurgy method. The specimens were immersion-tested in molten pure zinc baths at $460^{\circ}C$. To evaluate the corrosion property in molten zinc, the weight loss of the specimen was measured after the immersion tests at different immersion times (10~300 min.). Co-10%W alloys, compared with pure cobalt, showed no effect of tungsten addition on the reaction rate in molten zinc. The relationship between the weight loss and the square root of immersion period represents a straight line in both pure cobalt and Co-10%W alloy. The Co-Zn reaction layer in Co- 1O%W alloy consists of $\gamma2$, $\gamma1$, $\gamma$ and ($\beta1$ phases. The rate of weight loss significantly increases and the weight loss behavior is not well accord with the linear relationship as the tungsten content in the Co-W alloy increases. The $\beta1$ layer was not formed on the Co-20%W alloy and neither was a stable Co-Zn intermetallic compound layer found on the Co-30%W alloy. The main cause of increase in reaction rate with increasing tungsten content is related with the instability of the Co-Zn reaction phases as seen on micro-structural analysis.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.761-762
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• 2006

W-Cu alloy was very useful material for a heat sink, high electric contact and EDM electrode. Powder injection molding (PIM) is the optimum manufacturing technology to provide W-Cu components with low-cost and high-volume. We used various compositions of tungsten coated copper powders (W-Cu with 10 to 80 wt-% of copper) to manufacture W-Cu components by PIM. The optimum mixing, injection molding, debinding and sintering conditions to provide the high performance W-Cu components were investigated. The thermal and mechanical properties of W-Cu parts by PIM were measured. Finally, we can verify the high performance of W-Cu components by PIM with the tungsten coated copper.