• The Korean Journal of Ceramics
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• v.6 no.4
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• pp.380-384
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• 2000

Crystal structure of $Ba_5-5X$Y$_10/3$Nb$_10$O$_30$ was tried to determine by Rietveld analysis using powder X-ray diffraction data. This compound has tetragonal tungsten bronze (TTB) structure with general formula, (Al)$_2$(A2)$_4$(B1)$_2$(B2)$_8$(O1)$_8$(O2)$_8$(O3)$_4$(O4)$_2$(O5)$_4$(O6)$_4$. However, it was difficult to determine the distribution of Ba and Y in Al and A2 sites by the analysis only. Combination of Rietveld analysis and site potentials calculation as well as lattice energy calculations helped to determine the distribution. As the result, it was clarified that $Ba^2+$ cations occupy A2 (pentagonal tunnel site) and $Y^3+$ cations occupy Al (cubic site). The distribution of cations at each site coincides with the distribution estimated by the difference of ionic radii. This supports the formation condition of TTB which was proposed in our previous report. $Ba_5-5X$Y$_10X/3$Nb$_10$O$_30$ shows ferroelectric characteristics. In this compound, remanent polarization decreases slightly with the composition X. On the other hand, the result of crystal structure determination reveals that atomic positions along c-axis for A1, A2, B1 and B2 cations are also decreased with the composition X. This would suggest that the dependence of remanent polarization on composition X is derived by the dependence of atomic coordinates on composition X.

• Economic and Environmental Geology
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• v.28 no.2
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• pp.139-145
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• 1995

Tungsten skarn mineralization of the Sangdong mine is localized in the interbedded limestone layers of the Myobong Slate Formation and in the limestone of the Pungchon Limestone Formation of Cambrian age. Fluid inclusion, gas composition and Nd-Sr isotope for granites and skarns have been investigated. Gas compositions show $CO_2$ rich in the Sangdong granite and CH, rich in the Nonggeori and Eopyeong granites. The initial $^{87}Sr/^{86}Sr$ and $^{143}Nd/^{144}Nd$ ratios of the Sangdong granites have 0.714~0.716(${\varepsilon}_{Sr}$=138~162) and 0.51173~0.51178(${\varepsilon}_{Nd}$=-14.4~15.5), respectively. And their two stage model ages range from 1687 to 1764 Ma. The granite characterized by high strontium initial ratios and negative eNd value could have originated from the old continental crust source. Low homogenization temperature of the Sangdong granite having $203{\sim}296^{\circ}C$ with 1.9~9.2 NaCl equiv. wt% indicates the post-magmatic hydrothermal alteration temperature. Skarn ore fluid responsible for tungsten mineralization has been evolved from CH, rich fluid of early pyroxene garnet skarn to $CO_2$ rich later quartz-mica skarn.

• Journal of Powder Materials
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• v.14 no.2 s.61
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• pp.101-107
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• 2007

Ultrasonic-milling of metal oxide nanopowders for the preparation of tungsten heavy alloys was investigated. Milling time was selected as a major process variable. XRD results of metal oxide nanopowders ultrasonic-milled for 50 h and 100 h showed that agglomerate size reduced with increasing milling time and there was no evidence of contamination or change of composition by impurities. It was found that nanocomposite powders reduced at $800^{\circ}C$ in a hydrogen atmosphere showed a chemical composition of 93.1W-4.9Ni-2.0Fe from EDS analysis. Hardness of sintered part using 50 h and 100 h powder samples was 399 Hv and 463 Hv, respectively, which is higher than the that of commercial products (330-340 Hv).

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.185-188
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• 2002

An abrasive vitreous bonded solid mass having a vitrified abrasive structure comprising diamond grains which are held by an in inorganic bonding agent, the vitrified diamond wheel is impregnated with a composition which comprises a thermosetting synthetic resin and a surfactant. The vitrified diamond wheel is manufactured by preparing the composition including the resin and the surfactant, impregnating the abrasive structure with the composition, and curing the composition. The diamond wheel newly developed showed excellent performance in grinding carbide.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.4
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• pp.303-308
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• 2005

In this paper, the effects of oxidants on tungsten chemical mechanical polishing (CMP) process were investigated using three different oxidizers such as Fe(NO₃)₃, KIO₃ and H₂O₂. Moreover, the interaction between the tungsten film and the oxidizer was discussed by potentiodynamic polarization measurement with three different oxidizers, in order to compare the effects of W-CMP and electrochemical characteristics on the tungsten film as a function of oxidizer. As an experimental result, the tungsten removal rate reached a maximum at 5 wt％ Fe(NO₃)₃concentration, and when 5 wt％ H₂O₂was added in the slurry, the removal rate of W increased. Also, the microstructures of surface layer by atomic force microscopy(AFM) image were greatly influenced by the slurry chemical composition of oxidizers. It was shown that the surface roughness and removal rate of the polished surface were improved in Fe(NO₃)₃than KIO₃. The electrochemical results indicate that the corrosion current density of the 5 wt％ H₂O₂ and 5 wt％ H₂O/sub 2+/＋ 5 wt％ Fe(NO₃)₃was higher than the other oxidizers. Therefore, we conclude that the W-CMP characteristics are strongly dependent on the kinds of oxidizers and the amounts of oxidizer additive.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.5
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• pp.689-695
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• 2002

Film compositions are needed in semiconductor manufacturing for such diverse application as production tool qualifications and process development. Surface and interface information is generally provided with Auger electron spectroscopy(AES). In this paper, WSix films were analyzed for structural, electrical, and compositional properties of tungsten silicide thin films produced by low pressure chemical vapor deposition as a function of temperature, DCS post flow, shower head life time, and the silicon to tungsten ratios have been investigated. We find that Si/W composition ratio is increased in the surface and interface of WSix thin films by the DCS post flow process and increasing deposition temperature, respectively. The results obtained in this study are also applicable to process control of WSix deposition for memory device fabrication.

• Laser Solutions
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• v.5 no.3
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• pp.15-20
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• 2002

The principal obstacle to selection of a laser processing method in production is its relatively high equipment cost and the natural unwillingness of production supervision to try something new until it is thoroughly proven. The major objective of this work is focused on the combined features of gas tungsten arc and a low-power cold laser beam. In this work, the laser beam from a 7 watts carbon monoxide laser was combined with electrical discharges from a short-pulsed capacitive discharge GTA welding power supply. When the low power CO laser beam passes through a special composition shielding gas, the CO molecules in the gas absorbs the radiation, and ionizes through a process blown as non-equilibrium, vibration-vibration pumping. The resulting laser-induced plasma(LIP) was positioned between various configurations of electrodes. The high-voltage impulse applied to the electrodes forced rapid electrical breakdown between the electrodes. Electrical discharges between tungsten electrodes and aluminum sheet specimens followed the ionized path provided by LIP. The result was well-focused melted spots.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1325-1326
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• 2006

Tungsten-molydiside $W_xMo_{1-x}Si_2$ was synthesized by self-propagating high temperature synthesis (SHS). The SHS product with the initial composition of (0.5Mo+0.5W+2Si) contains 23.9% $MoSi_2$, 40.89% $WSi_2$ with remaining 9.11% Mo, 9.16% Si and 16.94%W. Lattice parameters of the $MoSi_2$ and $WSi_2$ determined by Rietvelt analysis were a=0.3206 nm, c=0.7841 nm and a=0.3212 nm, c=0.7822 nm, respectively.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.6
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• pp.43-49
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• 1997

Tungsten poycide has studied gate oxide reliability and dielectric strength charactristics as the composition of gate electrode which applied submicron on CMOS and MOS device for optimizing gate electrode resistivity. The gate oxide reliability has been tested using the TDDB(time dependent dielectric breakdwon) and SCTDDB (stepped current TDDB) and corelation between polysilicon and WSi$_{2}$ layer. iN the case of high intrinsic reliability and good breakdown chracteristics on polysilicon, confirmed that tungsten polycide layer is a better reliabilify properities than polysilicon layer. Also, hole trap is detected on the polysilicon structure meanwhile electron trap is detected on polycide structure. In the case of electron trap, the WSi$_{2}$ layer is larger interface trap genration than polysilicon on large POCL$_{3}$ doping time and high POCL$_{3}$ doping temperature condition. WSi$_{2}$ layer's leakage current is less than 1 order and dielectric strength is a larger than 2MV/cm.

• Journal of Powder Materials
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• v.19 no.1
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• pp.49-54
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• 2012

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.