AZ31-xCa 합금의 가공온도에 따른 열간 압연 특성

金完哲 弘益大學校 産業技術硏究所 2005 産業技術 Vol.15 No.-

In this study the microstructures, mechanical properties and hot rolling properties of the AZ31-xCa(x=0.5, 2.0wt%) magnesium alloy sheets were investigated by changing the amount of Ca, reduction ratio per pass, preheating temperature and heat treatment conditions. The reduction ratio per pass and preheating temperature were change in the ranges of 10~20% and 350~425℃, respectively. The sheets with best combination of external features and mechanical properties were fabricated under condition of reduction ratio per pass of 15% and preheating temperature of 400℃. It was considered that the inhomogeneity of as-cast AZ31-xCa alloys was reduced and the brittle Mg_(17)Al_(12) Phase was solved into matrix by homogenization treatment, which resulted in improvement of hot rolling properties and mechanical properties.

흙탕물 오염 시험법 개발 및 실차 시험 및 분석

김완철,임현택 한국신뢰성학회 2022 한국신뢰성학회 학술대회논문집 Vol.2022 No.11

급냉응고된 Mg-9Al-xCa 합금의 시효특성에 관한 연구

金完哲,朴祉河 홍익대학교 산업기술연구소 1999 産業技術 Vol.9 No.-

Mg-Al-Si-Ca alloys were fabricated into the ribbons by rapid solidification using a single-roll melt spinner. The time and temperature effect on age-hardening was investigated for the ribbons with varying Ca contents of 1, 3, 6 and 10 wt%. The behavior of precipitates, phase transitions, and mechanical properties were examined by measurements of micro-hardness, XRD analysis, and transmission electron microscopy. For the case of 1 hour's isochronal heat treatment, the temperature of 200℃ gave the most significant age hardening effect and the increase in Ca content caused enhanced hardening. In the aging treatment at 200℃, the hardness decreased with the increase in aging time from 1 up to 81 hour. The microstructural analysis for Ca-added sample showed uniformly distributed compounds of Al_4Ca and Al_2Ca, forming coherent precipitates with matrix. When the alloy contains more Ca than the solubility limit, the excess Ca precipitates as Mg_2Ca and an increased hardness is observed.

기계적 합금화에 의한 급속냉각된 Al 분말의 조직과 기계적성질의 개선

金完哲 홍익대학교 산업기술연구소 1996 産業技術 Vol.6 No.-

Severe working of splats produced a very fine grain size and substructural strengthening. The dispersed particles were spherical and much finer then those obtained by conventional SAP. MA-AI splats extruded bars had the recrystallized grains when isothermally aged for 100 hours at 450℃. At higher temperature, hower, only the Al_2O_3 patricles pinned the grain boundaries. Accordingly grain size become smaller and grain boundary sliding was retarded, providing a superior high temperature hardness as the amount of Al_2O_3 increased.

Ca 첨가한 AZ31합금의 열간압연 특성

金完哲 弘益大學校 産業技術硏究所 2004 産業技術 Vol.14 No.-

The effects of homogenization on hot rolling properties of gravity cast AZ31-xCa (x=0~2.0wt.%) alloys were evaluated by examination of surface and microstructures of sheets. The side cracking during hot rolling was decreased by homogenization by the elimination of local inhomogeneity and dissolution of brittle precipitate into matrix. The coarse grains in raw materials were changed to fine grains with the average particle size of 5~10μm by the dynamic recrystallization during repeated hot rolling . A deformation twinning was more favorably formed in the hot-rolled sheets after homogenization. It is considered that the grains grow and the precipitates are solved into the matrix during homogenization heat treatment, which results in increasing the possibility of formation of deformation twinning during hot rolling.

g-2Ca-0.3X계 합금의 첨가원소에 따른 용탕산화 거동

金完哲,김문회 홍익대학교 산업기술연구소 2001 産業技術 Vol.11 No.-

This study has examined the ignition characteristics and oxidation resistant of the non-combustible Mg- 2Ca-0.3 weight % X(Al, La, Nd, Y) alloys in an attempt to develop new alloy systems that can subject to melting in the atmosphere and also prevent natural ignition of chips produced in mechanical working. Both the ignition property and oxidation resistant were found to improve significantly in any case where one of the third elements was added to the binary MG-2Ca alloy. The new alloy systems also improved the solidification characteristics, and their ingots were found to be relatively free from impurities and thermal crack whose presence is hard to avoid in the production of pure Mg ingots. The oxidation experiments with molten metals at 700℃ and 750℃ for 1 and 5 hours showed that the addition of Al or Y causes fine and dense oxide layers to develop. The oxide layers appear to suppress the grower of MgO products and thereby enhance the resistance of the alloys to ignition and burning. In alloys with the Y addition, the thickness of oxide layers did not show any significant change with the increase in temperature and time, indicating that the Y is relatively stable compared with that of Mg-2Ca. The ignition temperature of Mg-2Ca alloys, which is 100℃ higher than of pure Mg, increased by 100℃ with the addition of 0.3 weight % Al. There was a substantial increase in the ignition temperature as much as 800℃ in Mg-2Ca alloys containing both Al and Y by 0.3 weight %.

프린지 필드에 의해 구동되는 하이브리드형 네마틱 액정 셀에서 러빙방향에 따른 전기광학 특성

김완철,안명환,이승희 한국전기전자재료학회 2004 전기전자재료학회논문지 Vol.17 No.1

We have studied the influence of rubbing directions on electro-optic characteristics of the fringe field driven hybrid aligned nematic liquid crystal (LC) cell by computer simulation. When a LC with positive dielectric anisotropy is used, the results show that the driving voltage and transmittance decreases as the rubbing direction with respect to horizontal electric field direction increases. The reason for decrease in light transmission is the increase of tilt angle on the center of common electrode. In this paper, we have studied how the rubbing angle effects on the transmittance of the cell by investigating a distribution of electric field and LC director.

안개 환경에서의 모빌리티용 라이다 성능 예측 기술 검토 및 분석

김완철,임현택 한국신뢰성학회 2022 한국신뢰성학회 학술대회논문집 Vol.2022 No.11

F-133 : 중환자실 입원 첫 24시간 소변량이 예후에 미치는 영향

김완철,김호철,서지영,나성원,고신옥,임채만,고윤석,최원일,이영주,이진석,김석찬,전규락,김제형,김재열,임재민,박성훈,이진화,이지현 대한결핵 및 호흡기학회 2013 대한결핵 및 호흡기학회 추계학술대회 초록집 Vol.116 No.0

서론: 소변량은 신손상의 정도와 혈역학적 안정성과 관련이 있기 때문에 중환자의 예후에 영향을 미칠 것으로 생각된다. 본 연구는 중환자실 환자에서 입원 첫 24시간 소변량이 예후와 관련이 있는지 알아보기 위한 것이다. 방법: 2010년 7월 1일부터 2011년 1월 31일까지 국내 15개 병원 22곳 중환자실에서 시행한 전향적 다기관 코호트 연구인 Validation of Simplified acute physiology score 3 in Korean ICUs (VSKI)자료를 토대로, 중환자실 입원 첫 24시간 소변량이 중환자실 사망률과 관련되어 있는지 분석하였다. 결과: 중환자실 사망 여부가 확인된 4035명의 환자를 대상으로 하였다. 평균나이는 59.2±16.7세였고, 64.3%가 남성이었다. 내원 첫 24시간 소변량이 500 cc 이하인 경우 중환자실 사망률은 48.7%로 500 cc 이상인 경우의 10.4%에 비해 유의하게 높았다(p<0.001). 입원 첫 24시간 소변량은 중환자실 사망과 유의한 상관관계가 있었으며, 500 cc 이하의 소변량은 독립적 사망인자였다(p<0.001). 혈청 크레아티닌이 1.3 mg/ml 이하인 환자에서 입원 첫 24시간 소변량이 500 cc 이하인 경우 중환자실 사망률은 12%로, 500 cc 이상인 경우 사망률 7.4%에 비해 유의하게 높았다(p=0.008). 혈청 크레아티닌이 1.3 mg/ml이상인 환자에서도 입원 첫 24시간 소변량이 500 cc 이하인 경우 중환자실 사망률은 61.8%로, 500 cc 이상인 경우의 사망률20.6%에 비해 유의하게 높았다(p<0.001). 다변량분석에서 혈청 크레아티닌이 1.3 mg/ml이 상인 경우에 입원 첫 500 cc 이하의 소변량은 중환자실사망과 관련된 독립적인 예후인자였다(p<0.001). 결론: 중환자실 환자에서 입원 첫 24시간 소변량은 예후와 관련이 있을 것으로 사료되며 적절한 소변량 유지를 위한 혈역학적 안정성 유지와 신손상의 최소화가 예후를 향상시킬 수 있을 것으로 생각된다.

Clinical Characteristics of the Development of Pneumothorax in Mechanically Ventilated Patients in Intensive Care Units

김완철,임수진,김경영,이승준,조유지,정이영,박미정,전경녀,이종덕,황영실,김호철 대한중환자의학회 2014 Acute and Critical Care Vol.29 No.1

Background: Pneumothorax (PTX) can occur as a complication of positive pressure ventilation in mechanically ventilated patients. Methods: We retrospectively reviewed the clinical characteristics of patients who developed PTX during mechanical ventilation (MV) in the intensive care unit (ICU). Results: Of the 326 patients admitted (208 men and 118 women; mean age, 65.3 ± 8.74 years), 15 (4.7%) developed PTX, which was MV-associated in 11 (3.3%) cases (6 men and 5 women; mean age, 68.3 ± 9.12 years) and procedure-associated in 4. Among the patients with MV-associated PTX, the underlying lung diseases were acute respiratory distress syndrome in 7 patients, interstitial lung disease in 2 patients, and chronic obstructive pulmonary disease in 2 patients. PTX diagnosis was achieved by chest radiography alone in 9 patients and chest computed tomography alone in 2 patients. Nine patients were using assist-control mode MV with the mean applied positive end-expiratory pressure, 9 ± 4.6 cmH2O and the mean tidal volume, 361 ± 63.7 ml at the diagnosis of PTX. Two patients died as a result of MV-associated PTX and their systolic pressure was below 80 mmHg and heart rates were less than 80/min. Ten patients were treated by chest tube insertion, and 1 patient was treated by percutaneous pigtail catheter insertion. Conclusions: PTX can develop in patients undergoing MV, and may cause death. Early recognition and treatment are necessary to prevent hemodynamic compromise in patients who develop PTX.