• Explosives and Blasting
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• v.18 no.1
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• pp.53-58
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• 2000

Thermal analysis, analysis of combustion residue and combustion characteristics measure ment such as burning rate or temperature were carried out to clarify the combustion mechanism of a tungsten- potassium perchlorate-barium chromate chromate delay powder. The results obtained are as follows. The main reaction of the delay powder of tungsten-potassium perchlorate-barium chromate is the oxidation of tungsten by potassium perchlorate. Barium chromate acts as a burning rate modifier, and the smaller the larger is the burning rate. Three types of delay composition used in this study show characteristic burning behavior. A stoichiomertric or a oxidizer-rich composition has a small linear burning rate. although it is has a large heat of combustion. On the other hand, a tungsten-excess or a fuel-rich composition with a small heat of combustion has a larger linear burning rate than the former, showing a small fractional oxidation of tungeten (below 10%) contained in the delay powder. From these results, a surface combustion mechanism is proposed for the combustion mechanism of this delay powder.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.6
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• pp.515-520
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• 2005

CMP(chemical mechanical polishing) process has been attracted as an essential technology of multi-level interconnection. Also CMP process got into key process for global planarization in the chip manufacturing process. In this study, potentiodynamic polarization was carried out to investigate the influences of $H_2O_2$ concentration and metal oxide formation through the passivation on tungsten and titanium. Fortunately, the electrochemical behaviors of tungsten and titanium are similar, an one may expect. As an experimental result, electrochemical corrosion of the $5\;vol\%\;H_2O_2$ concentration of tungsten and titanium films was higher than the other concentrations. According to the analysis, the oxidation state and microstructure of surface layer were strongly influenced by different oxidizer concentration. Moreover, the oxidation kinetics and resulting chemical state of oxide layer played critical roles in determining the overall CMP performance. Therefore, we conclude that the CMP characteristics tungsten and titanium metal layer including surface roughness were strongly dependent on the amounts of hydrogen peroxide oxidizer.

• Journal of Surface Science and Engineering
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• v.41 no.4
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• pp.174-179
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• 2008

Nanosize tungsten powder was synthesized by ultrasonic spray pyrolysis method through a solution containing ammonium metatungstate hydrate $[(NH_4)_6W_{12}O_{39}{\cdot}H_2O]$ and reduction treatment. It was expected the improvement of mechanical properties due to increasing surface free energy and surface activity. Starting solutions with each concentration, reaction temperature and reduction treatment were significantly influenced on the formation of tungsten size and phase. It was found that particle size was decreased with concentration of starting solution and surface tension were decreased. The particle size was increased at thermal decomposition temperature above $600^{\circ}C$ by neck growth of interparticles. Tungsten particles were formed by reduction reaction in atmosphere of hydrogen gas at the temperature above $700^{\circ}C$.

• Resources Recycling
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• v.26 no.4
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• pp.42-49
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• 2017

As a fundamental study for the separation of vanadium and tungsten from the leaching solution obtained from the soda roasting and water leaching process of spent SCR (Selective Catalytic Reduction) catalyst was carried out. The precipitation behaviors of vanadium and tungsten using the artificial solution (V: $1g{\cdot}L^{-1}$, W: $10g{\cdot}L^{-1}$) was investigated depending on temperature, NaOH concentration and the amount of $CaCl_2$ (aq.) added. V (aq.) was selectively precipitated at lower temperature than 293 K while tungsten also was precipitated at higher temperature. Precipitation rate of V and W was decreased by the increasing concentration of NaOH. On the other hand, excess Ca addition induced the increase of precipitation rate for V and W due to the formation of $Ca(OH)_2$ following the pH decline. The response surface methodology was employed to optimize the selective precipitation. Vanadium of 99.5% and tungsten of 0.0% was precipitated at $0.5mol{\cdot}L^{-1}$ of aqueous NaOH and 1 equivalent ratio of $CaCl_2$ at 293 K.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2307-2316
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• 2024

A melting failure of W monoblock components of the upper divertor outer target in EAST occurred during the plasma campaigns in 2019. The failure characters and microstructure evolution of the failed W monoblock have been well investigated on one string (W436 string). Near the strike point region where heat flux density is highest, macroscopic cracks and severe surface damage such as dimensional change, melting and solidification are visible in several W monoblocks. At the same time, debonding, melting and migration of Cu/CuCrZr cooling tube components introduced fatal damage to the structure and function. The heat-induced microstructure evolution in the rest part has been examined via hardness tests and metallography. From the heat flux surface to the cooling tube, hardness increased gradually and the recrystallized grains could be found in the region with the highest temperature, while recrystallization grains also appear in some W monoblocks near the cooling tube area. The detailed microstructure has been investigated by metallography and EBSD. Such cases in EAST provide experiences on the extreme condition of accidental loss of coolant or higher discharge power in future devices.

• Archives of Metallurgy and Materials
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• v.66 no.3
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• pp.799-802
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• 2021

The nano-sized Y₂O₃ dispersed W composite powder is prepared by ultrasonic spray pyrolysis of a tungsten precursor using ammonium metatungstate hydrate and a polymer addition solution method using Y-nitrate. XRD analysis for calcined powder showed the formation of WO₂ phase by partial oxidation of W powder during calcination in air. The TEM and phase analysis for further hydrogen reduction of calcined powder mixture exhibited that the W powder with a uniform distribution of Y₂O₃ nanoparticles can be successfully produced. These results indicate that the wet chemical method combined with spray pyrolysis and polymer solution is a promising way to synthesis the W-based composites with homogeneous dispersion of fine oxide particles.

• Tribology and Lubricants
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• v.13 no.4
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• pp.60-65
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• 1997

The tungsten disulfide $(WS_2)$ solid lubricant was synthesized by two different reaction processes, i.e., the reaction between $CS_2$ gas phase and solid $WO_3$powder, and the vapour phase transport method of tungsten and sulfur in a high vacuum. The chemical and physical characteristics of synthesized $WS_2$powder were analyzed in terms of the average particle size, morphology, crystalline phase etc. in comparison with those of commercial $WS_2$powder. The solid $WO_3$ powder with the average size of 0.2 ${\mu}{\textrm}{m}$ was reacted with $CS_2$gas flowed with$N_2$or 96%$N_2{\times}4%H_2$forming gas for 36 h and 24 h at 90$0^{\circ}C$ respectively. $WS_2$ crystalline phase was then formed through the intermediate phase of .$W_{20}O_{58}$ In the case of vapour phase transport method, the 3.5 wt% iodine was added as a vapour transport reagent into the composition of tungsten and sulfur powders maintaining a constant molar ratio of W:S=1:2.2. The mixture was then heat treated at 85$0^{\circ}C$ for 2 weeks in vacuum. The reaction product obtained showed the average size of 12 ${\mu}{\textrm}{m}$ and the hexagonal plate shape of typical solid lubricant with 2H-$WS_2$crystalline phase.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.705-708
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• 2014

We demonstrate the blue InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) with an embedded air-gap photonic crystal (PC) which was fabricated by the lateral epitaxial overgrowth of GaN layer on the tungsten (W) nano-masks. The periodic air-gap PC was formed by the chemical reaction of hydrogen with GaN on the W nano-mask. The optical output power of LEDs with an air-gap PC was increased by 26% compared to LEDs without an air-gap PC. The enhanced optical output power was attributed to the improvement in internal quantum efficiency and light extraction efficiency by the air-gap PC embedded in GaN layer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.88-91
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• 2003

Tungsten is widely used as a plug for the multi-level interconnection structures. However, due to the poor adhesive properties of tungsten (W) on $SiO_2$ layer, the Ti/TiN barrier layer is usually deposited onto $SiO_2$ for increasing adhesion ability with W film. Generally, for the W-CMP (chemical mechanical polishing) process, the passivation layer on the tungsten surface during CMP plays an important role. In this paper, the effect of oxidants controlling the polishing selectivity of W/Ti/TiN layer were investigated. The alumina ($Al_2O_3$) abrasive containing slurry with $H_2O_2$ as the oxidizer, was studied. As our preliminary experimental results, very low removal rates were observed for the case of no-oxidant slurry. This low removal rate is only due to the mechanical abrasive force. However, for Ti and TiN with $H_2O_2$ oxidizer, different removal rate was observed. The removal mechanism of Ti during CMP is mainly due to mechanical abrasive, whereas for TiN, it is due to the formation of metastable soluble peroxide complex.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.164-170
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• 2001

The Self-propagating High-temperature Synthesis (SHS) for synthesizing ($Mo_{1-z}$ , $W_{z}$)$Si_2$was conducted experimentally with the mole fraction of Tungsten(W) from z=0.0 to z=0.5. The temperature profile was measured according to the reaction time through the thermocouple that was equipped into the center of these samples. When the reaction front is propagated around the thermocouple, the highest temperature appears and we regard this temperature as the adiabatic temperature. We found out by experimental results that the reaction velocity is in the range of 2.14~1.35mm/sec and the adiabatic temperature is in the range of 1883~1507K for the six samples. The reaction velocity and the adiabatic temperature were inclined to decrease with an increasing of the mole fraction of Tungsten (W). The SHS modeling is presented in order to predict the temperature profiles and these results are compared with the experimental results. It is predicted that in case of increasing the initial temperature of these six samples, the reaction temperature increased and that the sample of z=0.5 needs the preheating up to 800~900K in order to become reaction temperature 1900K.