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고온 가공열처리가 AISI H13 열간공구강의 기계적 성질에 미치는 효과
김대훈,소명기,천성순 대한금속재료학회(대한금속학회) 1981 대한금속·재료학회지 Vol.19 No.1
An investigation has been performed on the effect of high temperature thermomechanical treatment (HTMT) on the mechanical properties, especially strength and toughness of AISI H13 hot work tool steel. The experimental results showed that HTMT increased the strength and toughness of hot work tool steel. 45% deformation at 980℃ increased the yield strength about 9.9% and the impact energy about 60% compared with conventional heat treatment. The improvement is due to the dispersion of fine carbides precipitates within the martensite lath and the refinement of martensite lath size.
Changes in the thermal conductivity of bentonite-based grouts with varying volumetric water content
김대훈,백환조,김경만,Seunghwan Park 한국자원공학회 2013 Geosystem engineering Vol.16 No.4
In this study, the thermal characteristics of pure bentonite and bentonite – sand grouts for backfilling geothermal heat exchangers were investigated. Mix proportions were 20% and 30% of the total weight of bentonite, to which 30% and 50% of the total weight of quartzite sand were added. Specimens were prepared in rectangular parallelepiped shapes, and the thermal conductivity of partially saturated specimens with varying volumetric water content was measured. As the saturated specimen slowly dried out at room temperature, the change in volumetric water content with the elapsed time showed a typical soil – water characteristics curve. Thermal conductivity of the specimens increased and, after reaching the peak value, decreased again. A parabolic trend curve could be drawn to deduce the relationship between the thermal conductivity and the volumetric water content for each specimen. Empirical equations representing the correlation between these two parameters were also suggested for predicting the thermal characteristics of bentonite-based grouts in geothermal heat pump applications.
불소 처리에 따른 ITO-ISFET pH 센서 특성 변화
김대훈,송광섭 대한전자공학회 2023 전자공학회논문지 Vol.60 No.5
In this study, a fluorine surface modification method was used to increase the reliability of an ion sensitive field-effect transistor (ISFET) pH sensor. An indium tin oxide (ITO) thin film was deposited by RF sputtering method. An ITO-ISFET with a channel length of 80 μm and a width of 2000 μm was fabricated through a photolithography process. The pH sensitivity of the ITO-ISFET was 60.2 mV/pH, the drift characteristic was 4.1 mV/h, and the hysteresis characteristic was 21.1 mV. The gate channel surface of the ITO-ISFET was functionalized to improve the drift and hysteresis characteristics. Functionalization was performed using a high-frequency plasma treatment method in a C3F8 gas environment, and the fluorine-treated ITO thin film was evaluated using X-ray photoelectron spectroscopy (XPS). The ITO-ISFET functionalized with fluorine by the plasma treatment exhibited the pH sensitivity of 58.7 mV/pH. The drift and hysteresis characteristics were 2.6 mV/h and 4.0 mV, respectively. The reliability of the ITO-ISFET was increased by fluorine functionalization. 본 연구는 이온 감응 전계효과 트랜지스터(ISFET) 방식의 pH 센서 신뢰성을 높이기 위해 불소 표면 개질 방법을 이용하였다. 인듐 주석 산화물(ITO) 박막을 RF 스퍼터링 방법으로 증착하였으며 포토리소그래피 공정을 통해 채널 길이 80 μm, 폭 2000 μm의 ITO-ISFET를 제작하였다. ITO-ISFET의 pH 센서 감도는 60.2 mV/pH 이었으며 드리프트 특성은 4.1 mV/h, 히스테리시스 특성은 21.1 mV 이었다. ITO-ISFET의 드리프트 및 히스테리시스 특성을 개선하기 위하여 게이트 채널 표면을 기능화 처리 하였다. 기능화는 C3F8 가스 분위기에서 고주파 플라즈마 처리 방법을 이용하였으며 불소 처리된 ITO 박막은 X-선 광전자 분광법(XPS)을 이용하여 평가하였다. 불소 원자는 플라즈마 처리에 의해 ITO 전극의 주석 또는 인듐 원자와 안정적인 이온 결합을 하였다. 플라즈마 처리에 의해 부분적으로 불소 개질된 ITO-ISFET의 pH 감도는 58.7 mV/pH이었다. 드리프트 특성은 2.6 mV/h, 히스테리시스 특성은 4.0 mV로 각각 감소되어 플라즈마 처리 전과 비교하여 ITO-ISFET의 신뢰성이 개선되었다.