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.

집중조명 : 충남 연기군 ; 연기군의 지역 정체성과 새 천년의 비전

김완철 한국지방행정연구원 2000 지방포럼 Vol.5 No.-

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.

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 %.

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.

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.

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.

기계적 합금화한 Al-50Ni 합금의 조직에 관한 연구

金完哲,金容圭 홍익대학교 산업기술연구소 1993 産業技術 Vol.2 No.-

Particle properties such as size, distribution, shape, composition, and structure are greatly influencing on the mechanical properties of final P/M products. Therefore, it is necessary that powders should be uniformed and strengthened by mechanical alloying. Degree of mechanical alloying of Al-50Ni powders can be determined by observing the microstructural refinement, microhardness, and microstructure of composite metal powder during processing. The mechanical alloying Process could be divided in five stages : initial stage, welding predominance stage, spherical particle formation stage, random welding predominance stage and steady state. Mechanical alloying reached to a steady state after 600 min processing as the finer lamellar microstruture could to no longer resolved in the 10∼20㎛ and the powder particle size distribution remained constant with processing time and a saturation hardness of 450 Hv had been attained. The rate of structural refinement of Al-50 Ni Composite was roughly logarithmic with processing time : ε= 2.915 ln(1 + 0.014t).

F-23 : 개정된 GOLD 진료지침에 따른 만성폐쇄성폐질환 환자의 임상양상

김완철,이승준,조유지,정이영,김호철,이종덕,황영실 대한결핵 및 호흡기학회 2013 대한결핵 및 호흡기학회 추계학술대회 초록집 Vol.116 No.-

목적: 만성폐쇄성폐질환(COPD)의 진료지침은 2011년 새로 개정되었으며 과거 진료지침과는 달리 기도폐쇄의 정도 이외에 환자의 증상 및 급성악화의 위험성에 따라 환자군을 분류하고 있다. 개정된 진료지침에 따른 환자군간 임상양상의 차이에 대해서는 연구된 바가 많지않아 저자들은 이를 알아보고자 하였다. 방법: 2011년 10월부터 2013년 9월까지 경상대학교병원 호흡기 내과에서 COPD를 진단받은 166명의 환자를 대상으로 연구를 하였다. COPD의 진단은 GOLD 기준에 따라 FEV1/FVC 비가 0.7 미만인 경우로 정의하였다. 의무기록 검토를 통하여 대상환자들의 기저 특성, 폐기능 및 폐기능 변화, 폐확산능, mMRC 점수, 1년간 급성악화 빈도, 동반질환, BODE index를 조사하였고 A, B, C, D군에 따라 각각의 항목들을 비교하였다. 추가적으로 이전 GOLD 분류에 따른 각 병기(stage)의 임상양상과 개정된 GOLD 분류에 따른 각 군(group)의 임상양 상을 비교하였다. 성적: 총 대상자는 166명 이었고 남자가 143명(86.1%), 여자가 23명(13.9%)이었고 평균연령은 70.9±8.0세였다. A, B, C, D군의 FEV1, mMRC, 1년간 급성악화 빈도는 각각 1.88L, 1,64L, 1.11L, 1.01L (p<0.001), 0.88, 1.54, 1.14, 2.25 (p<0.001), 0.04회, 0.38회, 0.43회, 1.16회(p<0.001)이었다 A, B, C, D군의 BODE 지수와, 폐확산능은 각각 1.4, 2.4, 3.2, 5.3(p<0.001), 85.9, 74.8, 83.0, 59.4 (p<0.001) 이었다 각군간의 동반질환 유무는 유의한 차이가 없었으며 1년간의 폐기능 변화도 유의한 차의가 없었다. 결론: 개정된 COPD 진료지침에 따른 환자군의 임상양상은 유의한 차이가 있으며 향후 대규모 환자들을 대상으로 한 전향적 연구가 필요할 것으로 생각된다.

급냉 응고된 Mg-Al-Si 합금의 미세조직에 관한 연구

金完哲 홍익대학교 산업기술연구소 2002 産業技術 Vol.12 No.-

Effects of Si and Ca addition on the microstructural refinement of Mg based alloys were studied. The melt-spun ribbons were aged at the temperature between 100 and 400℃ for 1h. The effect of additional elements on microstructure and precipitation hardening after heat treatment was investigated using TEM, XRD and a Vickers microhardness tester. Age hardening occurred after aging at 200℃ in the Mg-Al-Si-Ca alloys mainly due to the formation of Al2Ca and Mg2Ca Phase, whereas in the Mg-Zn-Ca alloys mostly due to the distribution of Mg2Ca. TEM results revealed that spherical Al2Ca precipitate had the coherent interface with the matrix. Considering the total amount of additional elements, Mg-Zn-Ca alloy showed higher hardness and smaller size of precipitates than Mg-Al-Si-Ca alloys. Mg-6Zn-5Ca alloys showed the maximum value of age hardening peak after aging at 200℃for 1h.