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Cu-Based Nanocomposite Produced by a Non-equilibrium Method
Kwon, Young-Soon,Kim, Ji-Soon,Choi, Pyuck-Pa,Song, Jun-Ho,Dudina, Dina 한국공업화학회 2005 Journal of Industrial and Engineering Chemistry Vol.11 No.1
A nanocomposite Cu-TiB₂ powder was synthesized in situ by means of self-propagating high-temperature synthesis (SHS) using high-energy ball-milled Ti-B-Cu elemental mixtures as powder precursors. The effect of the preliminary mechanical treatment on the SHS reaction was studied. The size of the TiB₂ particles produced by SHS decreased upon increasing the duration of the preliminary mechanical treatment. Subsequent mechanical treatment of the SHS products led to a reduction of the sizes of the TiB₂ particles down to 30~50 nm. The microstructural evolution of the synthesized powder compacts during sintering was investigated. During spark plasma sintering, a fine-grained skeleton of TiB₂ with well-connected particles was formed. This interpenetrating phase composite of Cu-TiB₂ is produced by the simultaneous action of pressure, temperature, and electrical current. The TiB₂ nanoparticles distributed in the copper matrix agglomerate to form a fine-grained skeleton. Upon conventional sintering, the nanoparticles show a surprising behavior: at low temperatures, fiber-like structures are formed while higher temperatures caused faceted crystals to be observed.
Kinetic and Thermodynamic Features of Combustion of Superfine Aluminum Powders in Air
Kwon, Young-Soon,Park, Pyuck-Pa,Kim, Ji-Soon,Gromov, Alexander,Rhee, Chang-Kyu The Korean Powder Metallurgy Institute 2004 한국분말재료학회지 (KPMI) Vol.11 No.4
An experimental study on the combustion of superfine aluminum powders (average particle diameter, a$_{s}$: ∼0.1 ${\mu}{\textrm}{m}$) in air is reported. The formation of aluminum nitride during the combustion of aluminum in air and the influence of the combustion scenario on the structures and compositions of the final products are in the focus of this study. The experiments were conducted in an air (pressure: 1 atm). Superfine aluminum powders were produced by the wire electrical explosion method. Such superfine aluminum powder is stable in air but once ignited it can burn in a self-sustaining way due to its low bulk: density (∼0.1 g/㎤) and a low thermal conductivity. During combustion, the temperature and radiation were measured and the actual burning process was recorded by a video camera. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and chemical analysis were performed on the both initial powders and final products. It was found that the powders, ignited by local heating, burned in a two-stage self-propagating regime. The products of the first stage consisted of unreacted aluminum (-70 mass %) and amorphous oxides with traces of AlN. After the second stage the AlN content exceeded 50 mass % and the residual Al content decreased to ∼10 mass %. A qualitative discussion is given on the kinetic limitation for AlN oxidation due to rapid condensation and encapsulation of gaseous AlN.N.
Mechanical, electrical and wear properties of Cu-TiB2 nanocomposites fabricated by MA-SHS and SPS
Ji-Soon Kim,Dae-Hwan Kwon,Thuy Dang Nguyen,Khoa Xuan Huynh,Pyuck-Pa Choi,Myung-Gyu Chang,Young-Jin Yum,Young-Soon Kwon 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.3
Cu-TiB2 nanocomposite powders were obtained by means of a combination of mechanical treatment and combustion reaction. Spark plasma sintering (SPS) was used to inhibit grain growth and thereby obtain fully dense Cu-TiB2 sintered bodies with a nanocomposite structure. The phases of the synthesized product were identified using X-ray diffraction and results showed only Cu and TiB2, with no other phases existing in the product. The particle size of self-propagating high-temperature synthesized powder was smaller than 250 nm. Mechanical and electrical properties were investigated after SPS at 650 oC for 30 minutes, the electrical conductivity decreased from 75 to 54% International Annealed Copper Standard (IACS) with the TiB2 content increased from 2.5 to 10 wt.%. while the hardness increased from 56 to 97 HRB. In addition, the tensile strength and wear resistance of the composites increased as the TiB2 content increased. Cu-TiB2 nanocomposite powders were obtained by means of a combination of mechanical treatment and combustion reaction. Spark plasma sintering (SPS) was used to inhibit grain growth and thereby obtain fully dense Cu-TiB2 sintered bodies with a nanocomposite structure. The phases of the synthesized product were identified using X-ray diffraction and results showed only Cu and TiB2, with no other phases existing in the product. The particle size of self-propagating high-temperature synthesized powder was smaller than 250 nm. Mechanical and electrical properties were investigated after SPS at 650 oC for 30 minutes, the electrical conductivity decreased from 75 to 54% International Annealed Copper Standard (IACS) with the TiB2 content increased from 2.5 to 10 wt.%. while the hardness increased from 56 to 97 HRB. In addition, the tensile strength and wear resistance of the composites increased as the TiB2 content increased.
Kwon Dae-Hwan,Nguyen Thuy Dang,Dudina Dina,Kum Jong-Won,Choi Pyuck-Pa,Kim Ji-Soon,Kwon Young-Soon 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Cu- nanocomposite powders were synthesized by combining high-energy ball-milling of Cu-Ti-B mixtures and subsequent self-propagating high temperature synthesis (SHS). Cu-40wt.% powders were produced by SHS reaction and ball-milled. The milled SHS powder was mixed with Cu powders by ball milling to produce Cu-2.5wt.% composites. particles less than 250nm were formed in the copper matrix after SHS-reaction. The releative density, electrical conductivity and hardness of specimens sintered at were nearly 98%, 83%IACS and 71HRB, respectively. After heat treatment at 850 to for 2 hours under Ar atmosphere, hardness was descedned by 15%. Our Cu- composite showed good thermal stability at eleveated temperature.
Production of Dispersion-strengthened Cu-TiB2 Alloys by Ball-milling and Spark-plasma Sintering
Kwon Dae-Hwan,Kum Jong-Won,Nguyen Thuy Dang,Dudinad Dina,Choi Pyuck-Pa,Kim Ji-Soon,Kwon Young-Soon 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Dispersion-strengthened copper with was produced by ball-milling and spark plasma sintering (SPS).Ball-milling was performed at a rotation speed of 300rpm for 30 and 60min in Ar atmosphere by using a planetary ball mill (AGO-2). Spark-plasma sintering was carried out at for 5min under vacuum after mechanical alloying. The hardness of the specimens sintered using powder ball milled for 60min at 300rpm increased from 16.0 to 61.8 HRB than that of specimen using powder mixed with a turbular mixer, while the electrical conductivity varied from 93.40% to 83.34%IACS. In the case of milled powder, hardness increased as milling time increased, while the electrical conductivity decreased. On the other hand, hardness decreased with increasing sintering temperature, but the electrical conductiviey increased slightly
( Hwan Lim ),( Jun Sang Ahn ),( Min Ji Kim ),( Gi Hwal Son ),( Joong Kook Park ),( Jae Yoon Shim ),( Il Young Kim ),( Ji Hyung Kim ),( Sung Myoun Cho ),( Eung Gi Kwon ),( Jong Suh Shin ),( Byung Ki Pa 한국축산학회(구 한국동물자원과학회) 2018 한국축산학회지 Vol.60 No.12
Background: Recently, as production costs have been increasing owing to rising feed prices worldwide, shortening the age of slaughter has been recognized as a way to increase farm income. In Korea, the raising period for Hanwoo steers is over 31 months with the delay of weaning and castration stated as one of the reasons for the increase in the raising period. Thus far, studies on age of weaning and castration have been conducted individually, and there have been no studies on the combined effects of weaning and castration ages on the growth performance and carcass characteristics in Hanwoo steers. Methods: Weaning ages were calculated at 80 or 130 days of age, and castration ages were calculated at 90 days and 180 days of age. Calves were allocated to one of the four treatment groups: W80C90 (weaning at 80 days of age and castration at 90 days of age), W80C180, W130C90, and W130C180. Results: For the entire experimental period, weaning and castration ages did not significantly affect growth performance of Hanwoo steers. In addition, weaning and castration ages did not affect the overall yield and quality traits of carcass in Hanwoo steers. Conclusion: Weaning and castration ages had small effects on growth performance and carcass characteristics in Hanwoo steers. Therefore, the early weaning and castration ages are recommended to reduce the slaughter age without any negative effects on meat quality grade.
( Yousang Ko ),( Hyung Woo Kim ),( Jinsoo Min ),( Jee Youn Oh ),( Ji Young Kang ),( Hyeon-kyoung Koo ),( Yunhyung Kwon ),( Jiyeon Yang ),( Jiyeon Han ),( You Jin Jang ),( Sung-soon Lee ),( Jae Seuk Pa 대한결핵 및 호흡기학회 2020 대한결핵 및 호흡기학회 추계학술대회 초록집 Vol.128 No.-
Background Early diagnosis and subsequent treatment for pulmonary tuberculosis (PTB) is essential for Tuberculosis prevention and control. Despite South Korea is an area of intermediate TB burden with a prevalence rate of 101/100,000 persons in 2014, there has been no investigation for determining factors associated with delays. It is necessary to guide public health action. Methods A nationwide, prospective, and observational cohort study for tuberculosis patients has been ongoing in Korea since September 2018. We described the distribution of delays from symptom onset to first visit of medical facility (patient-related delay) and from presentation to treatment (healthcare-related delay). Factors associated with patient-related delay and healthcare-related delay was identified using a multivariable analysis model. Results A total of 6,715 patients were diagnosed with PTB in 2019. For patient-related delay and healthcare-related delay were included as 3,783 and 5,660 cases, respectively. Mean patient-related delay was 49.4 (± 110.8). In multivariate regression analysis, Neuro-psychiatric disease was an independent risk factor for patient-related delay (HR 1.444; 95% confidence interval 1.191 to 1.750, p<0.001), malignancy (HR 1.313; 95% confidence interval 1.172 to 1.471, p<0.001), extra-PTB (HR 1.283; 95% confidence interval 1.150 to 1.431, p<0.001) and poor economic status (HR 1.090; 95% confidence interval 1.005 to 1.182, p=0.037). Mean healthcare-related delay was 13.3 (± 34.9). In multivariate regression analysis, Age over 65 years was an independent risk factor for healthcare-related delay (HR 1.120; 95% confidence interval 1.048 to 1.198, p=0.001) and early PTB defined as low microbiologic burden (HR 1.313; 95% confidence interval 1.206 to 1.429, p<0.001). Conclusions Our findings support continued initiatives to enable access to care for patients with neuro-psychiatric disease, malignancy, extra-PTB and poor economic status to reduce patient-related delayiagnosis of PTB. Moreover, clinician should pay attention in elderly and have awareness of TB clinical characteristics to find early PTB case.