우레아 첨가량 변화에 따라 수열합성법으로 제조 된 3mol%Y₂O₃-ZrO₂ 분말의 합성 및 기계적 특성 평가

이학주,고명원,김택남,Lee, Hak-Joo,Go, Myung-Won,Kim, Taik-Nam 한국재료학회 2011 한국재료학회지 Vol.21 No.8

The industrial manufacturing of YSZ products can be summarized as a three step process: a) hydrolysis of zirconyl chloride and mixing of other solutions, b) precipitation, and c) calcination. The addition of ammonia or OH- is essential in the precipitation process. However, a strong agglomeration was observed in the results of an ammonia or OH- addition. Thus, it is necessary to disperse the powders smoothly in order to improve the mechanical strength of YSZ. In this study, YSZ was synthesized using the urea stabilizer and hydrothermal method. YSZ powders were synthesized using a hydrothermal method with Teflon Vessels at $180^{\circ}C$ for 24 h. The mole ratio of urea to Zr was 0, 0.5, 1, and 2. The crystal phase, particle size, and morphologies were analyzed. Rectangular specimens ($33\;mm{\times}8\;mm{\times}1{\pm}0.5\;mm$) for three-point bend tests were used in the mechanical properties evaluation. The crystalline of YSZ powders observed a tetragonal phase in the sample with a ratio of Zr:urea = 1:2 addition and a hydrothermal reaction time of 24 h. The average primary particle size of YSZ was measured to be 9 nm to 11 nm. The agglomerated particle size was measured from 15 nm to 30 nm. The three-point bending strength of the YSZ samples was 142.47 MPa, which is the highest value obtained for the Zr:urea = 1:2 ratio addition YSZ sample.

심하게 흡수된 하악골에서 fixed detachable prosthesis를 이용한 임플란트 지지 보철 수복증례

이학주,임영준,권호범,김명주,Lee, Hak-Joo,Lim, Young-Jun,Kwon, Ho-Beom,Kim, Myung-Joo 대한치과보철학회 2017 대한치과보철학회지 Vol.55 No.2

완전 무치악 환자에서 임플란트를 이용한 치료 방법은 환자의 삶의 질 개선에 크게 기여하였으나, 잔존골 상태나 경제력 등에 의해 임플란트의 식립 개수에 제한을 받는 상황이 종종 나타난다. 이러한 경우 일반적으로 임플란트 피개의치나 임플란트 융합 국소의치 형태로 치료계획을 세울 수 있지만, 정확한 설계를 바탕으로 양측성 캔틸레버 형태의 고정성 보철물 역시 고려해 볼 수 있다. 본 증례에서는 심한 치조골 흡수를 보이는 완전 무치악 환자에서 상악 총의치 및 하악 임플란트 지지 고정성 캔틸레버 보철물 제작을 통해 기능적, 심미적으로 양호한 결과를 얻었기에 보고하고자 한다. Implant supported prostheses have improved the quality of lives of totally edentulous patients. However, there are some limitations on the number of implants related to the residual bone level or the economic concern and so on. In this situation, applying fixed detachable prosthesis with bilateral cantilevers can be considered. This clinical report describes implant supported prosthetic rehabilitation of a patient with severe bone resorption. The patient was satisfied and felt comfortable with upper complete denture and lower fixed detachable prosthesis.

Y₂O₃안정화제 첨가량에 따라 수열합성법으로 제조된 ZrO₂-Xmol% Y₂O₃분말의 합성 및 기계적 특성

이학주,김택남,배성철,고명원,류재경,Lee, Hak-Joo,Kim, Taik-Nam,Bea, Sung-Chul,Go, Myung-Won,Ryu, Jae-Kyung 한국재료학회 2010 한국재료학회지 Vol.20 No.10

In this study, partially stabilized zirconia was synthesized using a chemical $Y_2O_3$ stabilizer and hydrothermal method. First, $YCl_3-6H_2O$ and $ZrCl_2O-8H_2O$ was dissolved in distilled water. Y-TZP (a $Y_2O_3$-doped toughened zirconia polycrystalline precursor) was also prepared by conventional co-precipitates in the presence of an excess amount of $NH_4OH$ solution under a fixed pH of 12. The Y-TZP precursors were filtered and repeatedly washed with distilled water to remove $Cl^-$ ions. $ZrO_2$-Xmol%$Y_2O_3$ powder was synthesized by a hydrothermal method using Teflon Vessels at $180^{\circ}C$ for 6 h of optimized condition. The powder added with the Xmol%- $Y_2O_3$ (X = 0,1,3,5 mol%) stabilizer of the $ZrO_2$ was synthesized. The crystal phase, particle size, and morphologies were analyzed. Rectangular specimens of $33mm{\times}8mm{\times}3$ mm for three-point bend tests were used in the mechanical properties evaluation. A teragonal phase was observed in the samples, which contains more than 3 mol% $Y_2O_3$. The $3Y-ZrO_2$ agglomerated particle size was measured at $7.01{\mu}m$. The agglomerated particle was clearly observed in the sample of 5 mol % $Y_2O_3-ZrO_2$, and and the agglomerated particle size was measured at 16.4 um. However, a 20 nm particle was specifically observed by FE-SEM in the sample of 3 mol% $Y_2O_3-ZrO_2$. The highest bending fracture strength was measured as 321.3 MPa in sample of 3 mol% $Y_2O_3-ZrO_2$.

Inductively Coupled Plasma Etching of Chemical-vapor-deposited Amorphous Carbon in N₂/H₂/Ar Chemistries

이학주,권봉수,박영록,안정호,김진성,N.-E. Lee,J. W. Shon 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.5

In this study, we investigated the etching characteristics and the mechanism of an amorphous carbon (a-C) layer for a multi-level resist (MLR) structure. CVD (chemical-vapor-deposited) a-C layers with a SiO₂ hard-mask were etched in an ICP (inductively coupled plasma) etcher while varying the process parameters, such as the top electrode power, the bottom electrode power, and the gas flow ratio in the N₂/H₂/Ar plasma. The results indicated that the etch rate and the profile angle of the CVD a-C increased with increasing H₂ gas flow ratio in the N₂/H₂/Ar plasma. As the H₂ flow ratio increased, the etch rate and the profile angle increase, due to the increased formation of H radicals in the plasma, leading to enhanced chemical reactions with carbon atoms. Also, the etch rate of the CVD a-C increased with increasing top and bottom electrode powers.

공간적 채널 상관도에 따른 통계적인 채널 특성을 이용한 다중 안테나 선택 및 스위칭 시스템의 성능 분석

이학주,박승일,이충용,박현철,홍대식,Lee Hakju,Park Seungil,Lee Chungyong,Park Hyuncheol,Hong Daesik 대한전자공학회 2005 電子工學會論文誌-TC (Telecommunications) Vol.42 No.4

일반적으로 공간적 상관도가 존재하는 채널에서 다중 안테나 시스템은 그 성능이 열화되는 것으로 알려져 있다. 이를 극복하기 위한 방안으로 안테나 선택을 통해 공간적 상관도를 극복하고 다이버시티와 공간 다중화의 스위칭을 통해서 시스템의 에러 확률을 개선하는 안테나 선택 및 스위칭 시스템 방식을 들 수 있다. 그러나 이러한 시스템의 경우 채널의 공간적 상관도에 대한 모델링의 어려움으로 인해 이론적인 분석이 미비한 실정이다. 본 논문에서는 채널의 Frobenius norm과 최소 고유치들의 통계적인 특성을 이용하여 안테나 선택 및 스위칭 시스템의 성능을 이론적으로 분석하고, 모의 실험 결과와의 비교를 통해 유사한 성능을 보이고 있음을 확인한다. Multi-Input, Multi-Output system suffers for the spatial channel correlation due to lack of spatial diversity. To overcome this defect, the antenna selection and switching system is proposed which selects the adequate antenna subset with highest channel diversity gain and switches the trasmission techniques according to channel environments. However. its performance analysis is insufficient due to the difficulty of modeling the spatial channel correlation. In this paper, the theoretical upper bound of symbol error probability is derived by using the statistical properties of Frobenius norm and minimum eigen-value of channel matrix. By computer simulation, it is shown that the derived theoretical upper bound is similar to the simulation results.

Rheo-compocasting 및 열간압출에 의하여 제조한 Al-Si-Mg / SiC 입자강화 복합재료의 조직 및 기계적 특성

이학주,홍준표 ( Hag Ju Lee,Chun Pyo Hong ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.4

N/A Aluminum alloy matrix composites reinforced with various amounts of SiC particles have been produced by rheo-compocasting followed by hot extrusion. A relatively uniform distribution of SiC particles in the composites was obtained. The amounts of pore and SiC particles cluster were relatively small in the composites. Particle free zones were observed in the hot extruded composites when the amount of SiC particles was less than 20vol%. However, the width of particle free zone decreases with the increase of SiC particle content. Eutectic Si phase play an important role for improving bonding between SiC particle and matrix. Tensile and yield strength increased with the increase of SiC particle content. the strengthening effect of SiC particle addition was effective even at relatively high temperature of 573K.

Rheo-compocasting 및 열간압출에 의한 제조한 Al-Si-Mg / Al2O3 단섬유강화복합재료의 특성

이학주,홍준표 ( Ha Ju Lee,Chun Pyo Hong ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.4

N/A Aluminum alloy matrix composites reinforced with various amounts of Al₂O₃ short fibers have been produced by a combined technique of rheo-compocasting and hot extrusion. Distribution of fibers in the composites fabricated by rheo-compocasting was relatively uniform. A good degree of uniaxial fiber alignment has been achieved by hot extrusion, but a lot of fibers fractured during extrusion. The tendency of fiber fracturing increases as the aspect ratio and the amount of fibers increase. Relatively good bonding between fiber and matrix was obtained by the formation of MgAl₂O₄, and Mg(Al, Fe)₂O₄at the interface between fiber and matrix. In extruded composites, fiber strengthening effect was relatively small since a lot of fibers fractured during hot extrusion. On the other hand, dispersion strengthening effect may increase. In order to improve the fiber strengthening effect, it is important to optimize the extrusion condition with consideration of metal flow in extrusion die.

Rheo-compocasing 법에 의한 SiCp / Al 합금기 복합재료의 제조 및 마모특성

이학주,곽현만,홍준표 ( Hak Joo Lee,Hyun Man Kwak,Chun Pyo Hong ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.2

N/A Microstructure and wear characteristics of SiCp /Al - 6.5wt%Si - 1.7wt%Mg composite materials fabricated by rheo-compocast and hot press were investigated in this study. The results obtained are as follows : 1) It was possible to fabricate favorable composite materials containing SiCp which is up to 26 vol% by rheo-compocast and hot press. 2) Si and Al₂Si₄O_(10) were formed on the surface of SiC particles, and fairly good bonding condition was obtained on the interface between SiCp and matrix alloy. 3) Wear mechanism was transformed into adhesion, oxidation and fusion on the matrix alloy as wear rate increases, but in the composite material, the abrasive mechanism was shown not depending on the wear rate. 4) Wear resistance was improved as the amount of SiCp increases, however, no remarkable change in wear resistance was found above 8vol% of SiCp.

Ad-hoc 네트워크에서 다중경로를 지원하는 ATP 프로토콜에 대한 연구

이학주,장재신,이종협,Lee, Hak-Ju,Jang, Jae-Shin,Lee, Jong-Hyup 한국시뮬레이션학회 2009 한국시뮬레이션학회 논문지 Vol.18 No.3

Wireless networks have several unique features : node mobility, restricted bandwidth, time-variable bandwidth, large latency, and high bit error rates time due to channel fading. These features at wireless networks intend to decrease the performance TCP protocols are used in wireless networks. Lots of studies have been done for finding appropriate wireless transport protocols for current wireless communications. However, related studies have not provided good performance or some protocols have a good performance only in specific circumstances. Thus, these are not suitable for general wireless circumstance. Therefore, we propose a new wireless transport protocol which provides better performance than the previous ones. And we'd like to solve a problem that previous protocols cannot maintain their connections even though they have multiple paths until another path is successfully set up. To solve these problems, a new protocol ATP-M is proposed which is designed on already known TCP-M and ATP protocols. With NS-2 computer simulation, it is shown that this newly proposed protocol has better system throughput than TCP, TCP-M and ATP protocols.

가압연속주조법에 의한 SiCp / Al 합금기 복합재료의 조직 및 특성

이학주,홍준표 ( Hak Joo Lee,Chun Pyo Hong ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.1

N/A Microstructure and characteristics of the SiCp/Al-4.5wt%Cu-1wt%Mg composites fabricated by the combination of the compocasting and the pressurized continuous casting process, which is one of the processes to decrease the limitations of the size, and shops of the products, are investigated. The main results are as follows: 1) the SiCp /Al alloy matrix composites can be made continuously 2) as the amount of SiCp addition increases; (1) the degree of directional solidification of matrix structure decreases, and that of SiCp dispersion improves, (2) wear resistance improves, and especially these composites show the excellent wear resistance under the high sliding speed and high final load condition, (3) wear mechanism of these composites is changed from adhesive wear into abrasive wear, and the tendency of that becomes outstanding with increasing sliding speed.