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초음파 볼밀링 공정에 의한 용매 점도 특성에 따른 텅스텐계 합금 분쇄 거동
류근혁,소형섭,윤지석,김인호,이근재,Ryu, KeunHyuk,So, HyeongSub,Yun, JiSeok,Kim, InHo,Lee, Kun-Jae 한국분말재료학회 (*구 분말야금학회) 2019 한국분말재료학회지 (KPMI) Vol.26 No.3
Tungsten heavy alloys (W-Ni-Fe) play an important role in various industries because of their excellent mechanical properties, such as the excellent hardness of tungsten, low thermal expansion, corrosion resistance of nickel, and ductility of iron. In tungsten heavy alloys, tungsten nanoparticles allow the relatively low-temperature molding of high-melting-point tungsten and can improve densification. In this study, to improve the densification of tungsten heavy alloy, nanoparticles are manufactured by ultrasonic milling of metal oxide. The physical properties of the metal oxide and the solvent viscosity are selected as the main parameters. When the density is low and the Mohs hardness is high, the particle size distribution is relatively high. When the density is high and the Mohs hardness is low, the particle size distribution is relatively low. Additionally, the average particle size tends to decrease with increasing viscosity. Metal oxides prepared by ultrasonic milling in high-viscosity solvent show an average particle size of less than 300 nm based on the dynamic light scattering and scanning electron microscopy analysis. The effects of the physical properties of the metal oxide and the solvent viscosity on the pulverization are analyzed experimentally.
착화제 첨가에 따른 웨이퍼 세정 용액 특성 분석 및 금속 용해 거동
김명석,류근혁,이근재 한국분말야금학회 2021 한국분말재료학회지 (KPMI) Vol.28 No.1
The surface of silicon dummy wafers is contaminated with metallic impurities owing to the reaction with and adhesion of chemicals during the oxidation process. These metallic impurities negatively affect the device performance, reliability, and yield. To solve this problem, a wafer-cleaning process that removes metallic impurities is essential. RCA (Radio Corporation of America) cleaning is commonly used, but there are problems such as increased surface roughness and formation of metal hydroxides. Herein, we attempt to use a chelating agent (EDTA) to reduce the surface roughness, improve the stability of cleaning solutions, and prevent the re-adsorption of impurities. The bonding between the cleaning solution and metal powder is analyzed by referring to the Pourbaix diagram. The changes in the ionic conductivity, H2O2 decomposition behavior, and degree of dissolution are checked with a conductivity meter, and the changes in the absorbance and particle size before and after the reaction are confirmed by ultraviolet-visible spectroscopy (UV-vis) and dynamic light scattering (DLS) analyses. Thus, the addition of a chelating agent prevents the decomposition of H2O2 and improves the life of the silicon wafer cleaning solution, allowing it to react smoothly with metallic impurities.
허준형,류근혁,손은하,장재동 한국기상학회 2020 Asia-Pacific Journal of Atmospheric Sciences Vol.56 No.1
Precipitable water (PW) is a leading indicator of severe weather, such as heavy rainfall. The National Meteorological Satellite Center receives observation data directly from Low Earth Orbit (LEO) satellites, including NOAA-18, 19, MetOp-A, B, and Suomi-NPP, and generates level 2 products in near real time for the East Asia region. In this study, PWdata were retrieved from the abovementioned sources and composited to determine meteorologically significant PW fields from all available data sources considering the boundary layer (BL), middle layer (ML), high layer (HL), and total column. Cumulative distribution function (CDF) matching was performed for PWretrieved from the five satellites within specific time windows in order to integrate them and minimize their differences. The PW composite data were matched to reference PW CDF data from the Unified Model (UM) Regional Data Assimilation Prediction System (RDAPS) analysis data, which are updated according to selected time windows. PW data were composited for 03:00–09:00, 09:00–15:00, 15:00–21:00, and 21:00–03:00 UTC time windows. PW data composited during the summer and winter seasons in 2015, 2016, and 2017 were then validated. The results show improvements in composite Total Precipitable Water and BL PW from Suomi-NPP of approximately 15% and 40% (RMSE), respectively.