• Journal of the Korean institute of surface engineering
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• v.36 no.2
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• pp.128-134
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• 2003

Alloys of Ti-43%Al-2%W-0.1%Si were oxidized isothermally and cyclically between $900^{\circ}C$ and$ 1050^{\circ}C$, and their oxidation characteristics were studied. During isothermal tests, the alloys oxidized slowly up to 100$0^{\circ}C$, but fast at $1050^{\circ}C$. Though the scale adherence was not good above $900^{\circ}C$, the alloys displayed better oxidation behavior than unalloyed TiAl alloys. The oxide scales consisted primarily of an outer $TiO_2$ layer, intermediate $Al_2$$O_3$-rich layer, and an inner mixed layer of (TiO$_2$ $+Al_2$$O_3$). Tungsten was present mainly at the lower part of the oxide scale, while Si over the whole oxide scale.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.4
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• pp.17-24
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• 2003

Chemical mechanical polishing(CMP) has been applied for planarization of topography after patterning process in semiconductor fabrication process. Tungsten CMP is necessary to build up interconnects of semiconductor device. But the tungsten dishing and the oxide erosion defects appear at end-point during tungsten CMP. It has been known that the generation of dishing and erosion is based on the over-polishing time, which is determined by pattern selectivity. Fixed abrasive pad takes advantage of decreasing the defects resulting flam reducing pattern selectivity because of the lower abrasive concentration. The manufacturing technique of fixed abrasive pad using hydrophilic polymers is introduced in this paper. For application to tungsten CMP, chemicals composed of oxidizer, catalyst, and acid were developed. In comparison of the general pad and slurry for tungsten CMP, the fixed abrasive pad and the chemicals resulted in appropriate performance in point of removal rate, uniformity, material selectivity and roughness.

• Transactions on Electrical and Electronic Materials
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• v.7 no.4
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• pp.163-166
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• 2006

The dishing and the erosion were evaluated on the tungsten CMP process with conventional and new developed slurry. The tungsten thin film was polished by orbital polishing equipment. Commercial pattern wafer was used for the evaluation. Both slurries were pre tested on the oxide region on the wafer surface and the removal rate was not different very much. At the pattern density examination, the erosion performance was increased at all processing condition due to the reduction of thickness loss in new slurry. However, the dishing thickness was not remarkably changed at high pattern density despite of the improvement at low pattern density. At the large pad area, the reduction of dishing thickness was clearly found at new tungsten slurry.

• Journal of the Korean Vacuum Society
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• v.8 no.2
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• pp.136-140
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• 1999

The stability and response time of $WO_3$ thin films for EC device are critical problems being solved. Those are affected by the species of electrolyte, preparation conditions and fabricating methods of specimen. In this paper, we compared the stabilities of three kinds of tungsten oxide film in electrolyte. Each of three films was prepared by different manufacturing conditions, that is, one is a thermal oxidation film of tungsten metal deposited on pure glass substrate, another is a $WO_3$ film made on ITO glass directly, the other is a thermally oxidized film on tungsten plate. It was observed that thermally oxidized $WO_3$ films has a remarkable stability (the lifetime was above $10^6$ cycle). From these results, we found that the stability was closely related to the stoichiometric bonding between tungsten and oxygen atoms in addition to crystallinity and density of film.

• Journal of the Korea Convergence Society
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• v.12 no.4
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• pp.87-94
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• 2021

While the shielding substances of radiation shields in medical institutions are beginning to be replaced by environmentally friendly materials, radiation protection according to the shielding properties of environmentally friendly substances is becoming an important factor rather than the existing lead shielding properties. Tungsten and barium sulfate are representative shielding materials similar to lead, and are made in sheets or fiber form with eco-friendly materials. Ytterbium is an impermeable material used as a fluorine compound in the dental radiation field. This study aims to evaluate the shielding performance in the x-ray shielding area by comparing the shielding properties of ytterbium by energy band and that of existing eco-friendly materials. When three types of shielding sheets were fabricated and tested under the same process conditions, the shielding performance of the medical radiation area was about 5 % difference from tungsten. Furthermore, shielding performance was superior to barium sulfate. In the cross-sectional structure of the shielding sheet, there was a disadvantage that the arrangement of particles was not uniform. Ytterbium oxide showed sufficient potential as a medical radiation shielding material, and it is thought that it can improve the shielding performance by controlling the particle arrangement structure and particle size.

• Korean Journal of Materials Research
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• v.2 no.1
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• pp.19-26
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• 1992

The rate of tungsten nuclei formation from $WF_6-SiH_4$ on silicon dioxide surface was measured. The nucleation rate became faster at high deposition temperature, low carrier gas flow rate and high deposition pressure. Also the rate became faster at the downstream of the oxide surface compared to the oxide surface near the inlet. Shape and cross-sectional view of the tungsten nuclei were observed with SEM and their chemical compositions were also determined.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.16.1-16.1
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• 2011

Gas sensor properties of $WO_3$ nanowire structures have been studied. The sensing layer was prepared by deposition of tungsten metal on porous single wall carbon nanotubes followed by thermal oxidation. The morphology and crystalline quality of $WO_3$ material was investigated by SEM, TEM, XRD and Raman analysis. A highly porous $WO_3$ nanowire structure with a mean diameter of 82 nm was obtained. Response to CO, $NH_3$ and $H_2$ gases diluted in air were investigated in the temperature range of $100{\sim}340^{\circ}C$ The sensor exhibited low response to CO gas and quite high response to $NH_3$ and $H_2$ gases. The highest sensitivity was observed at $250^{\circ}C$ for $NH_3$ and $300^{\circ}C$ for $H_2$. The effect of the diameters of $WO_3$ nanowires on the sensor performance was also studied. The $WO_3$ nanowires sensor with diameter of 40 nm showed quite high sensitivity, fast response and recovery times to $H_2$ diluted in dry air. The sensitivity as a function of detecting gas concentrations and gas sensing mechanism was discussed. The effect of dilution carrier gases, dry air and nitrogen, was examined.

• Journal of Electrochemical Science and Technology
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• v.7 no.2
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• pp.161-169
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• 2016

Porous tungsten oxide thin films were prepared by electrodeposition and tested as anodes of lithium secondary batteries. The synthesized films were composed of nanoparticles of 60-140 nm size, with porosities of 30-40 %. Increasing the temperature turned out to be a more effective approach to introduce porosity in the structure than increasing the electrolyte viscosity. The assessment of the synthesized films as anodes of lithium secondary batteries revealed a much higher initial discharge capacity for the porous than the dense samples. The discharge capacity retention significantly increased with increasing porosity and was further enhanced by heat treatment. In particular, a thin film composed of particles of about 140 nm in size and with a porosity of 40 % exhibited an initial discharge capacity higher than 600 mAh/g and a remaining capacity above 300 mAh/g after 30 cycles. Following heat treatment, the remaining capacity of this sample after 30 cycles increased to about 500 mA h/g.

• 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).

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1593-1601
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• 2021

Oxide dispersion strengthening (ODS) tungsten alloys are highly desirable in irradiation applications. However, how to improve the properties of ODS-tungsten alloys efficiently has been worth studying for a long time. Here we report a nanostructuring approach that achieves W-La₂O₃ alloy with a high level of flexural strength and Vickers hardness at room temperature, which have the maximum value of 581 MPa and 703 Hv, respectively. This method named solution combustion synthesis (SCS) can generate 30 nm coating structures W-La₂O₃ composite powders by using Keggin-type structural polyoxometalates as raw materials in a fast and low-cost process. The composite powder can be fabricated to W-La₂O₃ alloy with an optimal microstructure of submicrometric W grains coexisting with nanometric oxide particles in the grain interior, and a stability interface structure of grain boundaries (GBs) by forming transition zones. The method can be used to prepare new ODS alloys with excellent properties in the future.