Mg-Al 합금에서 등온 시효 중 경도 변화의 미세조직 의존성

한진구 ( Jin-gu Han ),전중환 ( Joong-hwan Jun ) 한국열처리공학회 2019 熱處理工學會誌 Vol.32 No.6

This study is intended to clarify the main microstructural factors that contribute to an increase of hardness during isothermal aging in Mg-Al alloy. For this work, Mg-9.3%Al alloy specimens were solution-treated at 688 K for 24 h followed by water quenching, and then aged at 473 K for up to 24 h. The aging at 473 K yielded nodular discontinuous precipitates (DPs) with (α+β) lamellar morphology at the grain boundaries, and the volume fraction of DPs increased from 0% to ~30% with increasing aging time up to 12 h. For the aging times longer than 12 h, further formation of DPs was substantially inhibited owing to the occurrence of significant continuous precipitation within the α-(Mg) matrix, and the density of continuous precipitates (CPs) becomes greater with increasing aging time. Hardness of the specimen was steadily increased with aging time up to 24 h. Microstructural examination on the aged specimens revealed that the increased overall hardness at the early stage of aging is associated with the increased volume fraction of DPs, but at the later stage of aging, where the amount of DPs was hardly changed, the increased hardness of the α-(Mg) matrix in response to the higher density of CPs within the matrix, plays a key role in increasing the overall hardness value. (Received October 14, 2019; Revised October 25, 2019; Accepted November 1, 2019)

주조 상태 및 용체화처리한 AZ91-4%RE 마그네슘 합금의 부식 거동

한진구 ( Jin-gu Han ),현승균 ( Soong-keun Hyun ),전중환 ( Joong-hwan Jun ) 한국열처리공학회 2018 熱處理工學會誌 Vol.31 No.5

The objective of this study is to investigate the effect of solution treatment on the microstructure and corrosion behavior of cast AZ91-4%RE magnesium alloy. In the as-cast state, microstructure of the AZ91-4%RE alloy was characterized by intermetallic β(Mg₁₇Al₁₂), Al₁₁RE₃ and Al2RE phase particles distributed in α-(Mg) matrix. After solution treatment, the β particles with low melting point dissolved into the matrix, but Al-RE phases still remained due to their high thermal stabilities. It was found from the immersion and potentiodynamic polarization tests that corrosion rate of the AZ91-4%RE alloy increased after the solution treatment. On the contrary, EIS tests and EDS compositional analyses on the surface corrosion products indicated that the stability of the corrosion product was improved after the solution treatment. Examinations on the corroded microstructures for the ascast and solution-treated samples revealed that dissolution of the β particles which play a beneficial role in suppressing corrosion propagation, would be responsible for the deterioration of corrosion resistance after the solution treatment. This result implies that the microstructural features such as amount, size and distribution of secondary phases that determine corrosion mechanism, are more influential on the corrosion rate in comparison with the stability of surface corrosion product. (Received August 7, 2018; Revised August 31, 2018; Accepted September 6, 2018)

Mg-4%Zn 주조 합금의 부식 거동에 미치는 Sn 첨가의 영향

한진구 ( Jin-gu Han ),전중환 ( Joong-hwan Jun ) 한국주조공학회 2017 한국주조공학회지 Vol.37 No.3

In the present study, effects of an addition of Sn on the microstructure and corrosion behavior were investigated in Mg-4%Zn-(0-3)%Sn casting alloys. With an increase in the Sn content, the α-(Mg) dendritic cell size was reduced, whereas the total amount of precipitates increased due to the formation of the Mg₂Sn phase. It was found in immersion and electrochemical corrosion tests that the addition of Sn has a detrimental effect on the corrosion resistance of the Mg-4%Zn alloy. Microstructural examinations of the corrosion product and the corroded surface indicated that an accelerated micro-galvanic effect by the Mg₂Sn-phase particles and a less protective corrosion product on the surface were responsible for the increased corrosion rate at a higher Sn content.

석면슬레이트 표면에서 시간에 따른 석면섬유 방출 연구

김현욱,박계영,강재옥,황범구,한진구,한영선,Kim, Hyeon-Wook,Park, Gye-Yeong,Gang, Jae-Ok,Hwang, Beom-Gu,Han, Jin-Gu,Han, Yeong-Seon 대한산업보건협회 2008 산업보건 Vol.243 No.-

슬레이트 지붕 노후화에 따른 석면 섬유 방출량

김현욱 ( Hyun Wook Kim ),박계영 ( Gye Young Park ),한진구 ( Jin Gu Han ),한영선 ( Young Sun Han ),황범구 ( Bum Gu Hwang ),이준혁 ( Jun Hyuk Lee ) 한국산업위생학회 2010 한국산업보건학회지 Vol.20 No.2

To confirm and quantify asbestos fibers released from the asbestos-cement slate roofs due to weathering, three houses, selected based on the year of built - 60`s, 70, and 80`s, were investigated. All of them were located in the downtown of Seoul. Rain or snow-melt water was collected from the roof in a 3.5 liter plastic bottle. A known amount of collected water was filtered on the 37 mm membrane filter, ashed in a muffle furnace, and subsequently treated with HCl to remove organic material. The treated remaining was refiltered on a 25mm membrane filter for PLM and PCM analyses. The NIOSH 7400 method was utilized for PCM counting. In addition, SEM/EDX was used to confirm the asbestos types. The results of this study showed that chrysotile fibers were confirmed by PLM in all samples analyzed. A significant amount of asbestos fibers were found in the water samples. The ranges of asbestos fibers counted from the samples collected in the 60`s, 70`s, and 80`s were; 10,406.3~55,575.6 f/L, 5,218.8~38,126.2 f/L, and 2,906.3~7,798.6 f/L, respectively. As anticipated, concentrations of asbestos fibers increased with time of installment of the roofing material. We conclude that weathering can be a significant factor on the release of asbestos fibers from the asbestos cement products. Since asbestos fibers released into environment can be a source of significant health hazard, countermeasures, such as replacement, removal, and encapsulation of weathered asbestos slate, should be initiated immediately.

마이크로파 전처리법을 이용한 요중연의 분석

노영만,한진구 가톨릭대학산업의학센타 산업의학연구소 1996 韓國의 産業醫學 Vol.35 No.4

요중연 농도는 혈중연에 비하여 10배 정도 낮아 이로 인해 요중연 분석시 어려움이 많고, 특히 요중에 함유되어 있는 방해물질의 영향이 크다. 또한 하루정도 시간이 경과한 뇨는 침전물이 생기게 되어 분석시의 어려운점이 많아 본 연구에서는 마이크로파 전처리법(MW)을 이용하여 기존방법(non-MW)과의 차이를 비교하고, 표준뇨(NIST, SRM 2670)를 사용하여 마이크로파 전처리법의 정확도를 산출하였고 표준뇨를 제조하여 분석의 정밀도 및 저장기간에 다른 시료의 재현성을 조사하여 우리나라의 생체시료 정도관리 및 연 특수검진시 분석의 정확도와 정밀도를 향상시킬 수 있는 분석방법을 제시하고자 하였다. 그 결과는 다음과 같다. 1. 표준뇨(SRM)을 MW로 처리한 뇨의 농도는 저농도가 23.1±1.6㎍/1 이고 고농도가 105.0±4.6㎍/1로 고농도 측정치가 기준값에 근접하는 수치를 보였고, 저농도와 고농도에서 모두 MW뇨와 non-MW뇨 사이에 통계적으로 유의한 차이가 있었다. 2. 표준뇨를 3가지 농도로 제작하여 전처리 방법에 따른 회수율의 차이를 보았는데 non-MW뇨의 회수율은 85.5%이었고 MW뇨의 경우는 101.56%이었으며 고농도 MW뇨의 경우 표준편차는 4.6㎍/1로 표준뇨(SRM)의 기준값고 근접하는 범위내에 들었다. 3. 제작한 표준뇨의 각농도에서 저장기간에 따른 요중연 농도변화를 보았는데 두 전처리 방법이 저장기간에 따른 변화양상이 동일하고 유의하게 감소하고 있었으며 또한 두 전처리 방법간에 있어 농도간의 차이가 있었다. 4. MW 방법으로 분석한 정상인의 요중연 농도는 남성이 33±7.8㎍/1이고 여성은 31.9±6.5㎍/1 이었다. 이상의 결과로 볼 때 마이크로파 전처리법을 이용한 요중연농도 분석법은 분석의 정확도와 정밀도가 우수하였고, 시료의 저장기간에 따른 농도의 변화도 적어 연노출근로자의 특수검진 및 생물학적 노출지표를 측정하기 위한 유용한 방법으로 이용될 수 있을 것이다. Two digestion methods of urine, the traditional (non-MW) and the microwave (MW) methods, were compared in order to improve the accuracy and precision of lead in urine analysis. The accuracy and precision of the MW method was determined with the standard reference material prepared by NIST and the urine samples prepared by our laboratory. The effect of storage condition on lead level in urine was determined by analyzing samples at three day interval for three weeks. 1. The mean leak concentrations of the NIST samples containing low level of lead treated with MW and with non-MW were 23.1?1.6 and 31.0?3.8?/1,respectively. A statistically significantly higher lead concentration was found in the non-MW method. For the NIST samples containing high level of urine, the mean lead conenbtration in urine treated with MW was 105.0?406 while that with noMW was 129.0?0.5?/1. The accuracy of the MW method which was compared with the NIST reference levels was better than that of the non-MW method. 2. The mean of recovery rate of MW in urine spiked lead at three levels were higher than that in non-MW. 3. The changes of concentrations in urine added known amounts at three levels reduced to show same tendency in MW and non-MW, but there was a significant difference between them. 4.The mean of lead level with MW in no previous occupational exposure in lead were 33?708?/1 for male and 31.9?6.5?/1 for female. The results obtained in this study shows that the MW digestion method is capable of improving the accuracy and precision of measuring lead levels in urine. Therefore, it is recommended to use the method when analyzing urine samples for lead determination.

주물사업장에서 발생하는 호흡성분진의 농도 및 석영함유량에 관한 연구

박용선,노영만,김현욱,한진구,안연순,강성규,김정만 한국산업위생학회 2003 한국산업보건학회지 Vol.13 No.1

This study was performed to measure and evaluate the concentration of respirable dust and quartz content at molding and shakeout process in the foundry. The 129 samples in 30 foundries were collected using 10mm Dorr-Oliver nylon cyclone and analysed for quartz concent by Fourier Transform Infrared Spectroscopy. The average quartz concentrations in the respirable dust was 0.0273mg/㎡ and ranged from 0.0007 to 0.3757mg/㎥. The average quartz concentrations of shakeout process wsa significantly higher than that of molding in the foundry. The average of respirable dust in foundry 102129mg/㎡ and ranged from 0.1524 to 7.0428mg/㎥. But there is no significant difference between molding and shakeout processes. The average contents of quartz for OEL-MOL was 2025% and ranged from 0.05 to 32.79% The non-compliance rates for quartz were 22.96% in Korea-OEL and 34.01% in ACGIH-TLV and NIOSH-REL, and 35.03% in OSHA-PEL. The airbome dust in the foundry was effectively controlled when local exhaust ventilation and/or wetting system were operated. The result of this study therefore showed that the engineering controls and periodic environmental suveillance in foundry will be very important for preventing the health effects of workers exposed to quartz.

일부 청소년들에서 흡연노출량에 따른 혈중 카드뮴 농도

장성실,권윤형,배진순,노영만,한진구 韓國學校保健學會 2001 韓國學校保健學會誌 Vol.14 No.2

Objectives: We surveyed the prevalence of smoking among the adolescent population and analysed the correlation of the two exposure biomarkers-concentration of blood cadmium and urinary cotinine-to the smoking status. Methods: Subjects were 193 middle and high school students in Chungnam province. Blood cadmium and urinary cotinine were compared by sex and smoking status. Smoking status were classified by either the concentration of urinary cotinine or subjective answering as a smoker in the questionnaire. Results: Smoking prevalence was 24.6%, 36.2% and 6.7% among all subjects, male and female subjects, respectively. Average smoking amount was 17.5 and 1.5 cigarettes per month among the male subjects and female subjects, respectively Mean concentration of urinary cotinine among the male subjects was 135.57 ㎍/ℓ, and that of female subjects was 116.59 ㎍/. Direct smokers showed higher concentration of urinary cotinine than those of indirect smokers, and subjects with higher urinary concentration showed higher prevalence of smoking, too. Mean concentration of blood cadmium was 0.0572 ㎍/㎗ among the male subjects, and 0.0693 ㎍/㎗ among the female subjects. Among the male subjects, both exposure biumarkers showed significant correlation to the smoking status, but among the female subjects urinary cotinine did not show significant correlation to the smoking status. Conclusion: Concentrations of these two biomarkers suggested that this population had significantly high evironmental tobacco smoking(ETS) and efficient stop-smoking programs to reduce ETS should be directed to this population. Key words : environmental tobacco smoking, urinary cotinine, blood cadmium

89하계지표조사보고 : 예천 호명면

박정숙,한진구,임정옥 안동대학 안동사연구회 1989 安東史硏究 Vol.3 No.1

작년 예천군 지보면 지역에 이어 올해는 예천군 호명면 지역을 조사하였다. 조금은 안동에서 먼 지역이고 해서 걱정이 되었지만 조사원 전체의 노력으로 큰 사고 없이 끝이 났다. 곳곳의 사정에 의해, 혹은 우천으로 인한 일정의 많은 변화를 겪었고, 미지의 지역인 탓에 여러가지 어려움도 겪었다. 산세를 모르고, 지역사정을 확실히 모르고 해서 부득이 하게 계획을 바꾸어야만 했다. 이제 3박4일간이 일정이 끝난 지금, 조사내용을 간략하게 소개하고자 한다. 지표조사는 6월 26일 활발하고 의지 있는 분위기 속에서 시작되었다.

敎育大學 藝體能 敎育課程 改善 方案의 硏究 : 國民學校 藝體能 敎科擔任敎師 養成을 中心으로 With Special Reference to the Training of the Teachers in Charge of Arts and Physical Education of the Elementary Schools

成義鏞,韓進九,朱完珣 春川敎育大學 1977 論文集 Vol.17 No.-