• 한국재료학회지
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• 제30권9호
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• pp.465-473
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• 2020

For surface hardening of a continuous casting mold component, a fundamental metallurgical investigation on dissimilar laser clads (Cu-NiCrBSi) is performed. In particular, variation behavior of microstructures and mechanical properties (hardness and wear resistance) of dissimilar clads during long-term service is clarified by performing high-temperature post-clad heat treatment (temperature range: 500 ~ 1,000 ℃ and isothermal holding time: 20 ~ 500 min). The microstructures of clad metals (as-clads) consist of fine dendrite morphologies and severe microsegregations of the alloying elements (Cr and Si); substrate material (Cu) is clearly confirmed. During the post-clad heat treatment, the microsegregations are totally homogenized, and secondary phases (Cr-based borides and carbides) precipitated during the short-term heat treatment are also almost dissolved, especially at the heat treatment conditions of 950 ℃ for 500 min. Owing to these microstructural homogenization behaviors, an opposite tendency of the surface mechanical properties can be confirmed. In other words, the wear resistance (wear rate) improves from 4.1 × 10^-2 ㎣/Nm (as-clad condition) to 1.4 × 10^-2 ㎣/Nm (heat-treated at 950 ℃ for 500 min), whereas the hardness decreases from 453 HV (as-clad condition) to 142 HV (heat-treated at 950 ℃ for 500 min).

• 한국재료학회지
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• 제28권4호
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• pp.208-213
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• 2018

Epitaxial ($11{\bar{2}}0$) a-plane GaN films were grown on a ($1{\bar{1}}02$) R-plane sapphire substrate with photoresist (PR) masks using metal organic chemical vapor deposition (MOCVD). The PR mask with striped patterns was prepared using an ex-situ lithography process, whereas carbonization and heat treatment of the PR mask were carried out using an in-situ MOCVD. The heat treatment of the PR mask was continuously conducted in ambient $H_2/NH_3$ mixture gas at $1140^{\circ}C$ after carbonization by the pyrolysis in ambient $H_2$ at $1100^{\circ}C$. As the time of the heat treatment progressed, the striped patterns of the carbonized PR mask shrank. The heat treatment of the carbonized PR mask facilitated epitaxial lateral overgrowth (ELO) of a-plane GaN films without carbon contamination on the R-plane sapphire substrate. Thhe surface morphology of a-plane GaN films was investigated by scanning electron microscopy and atomic force microscopy. The structural characteristics of a-plane GaN films on an R-plane sapphire substrate were evaluated by ${\omega}-2{\theta}$ high-resolution X-ray diffraction. The a-plane GaN films were characterized by X-ray photoelectron spectroscopy (XPS) to determine carbon contamination from carbonized PR masks in the GaN film bulk. After $Ar^+$ ion etching, XPS spectra indicated that carbon contamination exists only in the surface region. Finally, the heat treatment of carbonized PR masks was used to grow high-quality a-plane GaN films without carbon contamination. This approach showed the promising potential of the ELO process by using a PR mask.

• 열처리공학회지
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• 제8권4호
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• pp.302-317
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• 1995

After initial structure of AISI 9260 steel is changed into pearlite and martensite, one is isothermally annealed at $700^{\circ}C$ below of $A_1$ transformation point and the other is isothermally annealed at the same condition after 3 cycles of heating and cooling between $680^{\circ}C$ and $780^{\circ}C$ of $A_1$ transformation point. Analyzing the changes of microstructure, mechanical properties and fractography of tension test, we obtained result as follows. The fastest spheroidization rate by changes of initial structure and heat treatment cycles is appeared at the heat treatment cycle which is isothermally annealed after 3 cycles of heating and cooling at below and above $A_1$ transformation point for martensite. At the above condition, the perfect spheroidization structure is appeared after 60hrs and after then, globular carbide is being coarsened. The mean diameter of globular carbide is $2.4{\times}10^{-3}mm$ after 90hrs. The changes of tension strength during spheroidization heat treatment follows Orwan function, ${\sigma}_o={\sigma}_i+Gb/l$, where l is interspacing of carbide particles and at the above condition, ${\sigma}_o=70.48+2.5{\times}10^{-3}/l(kg/mm^2)$. Fractography of fracture of spheroidization structure in tension test is appeared as dimple which is ductile rupture type by nucleation and growth of void, size of dimple is larger and deeper with increasing of heat treatment time.

• Journal of the Korean Wood Science and Technology
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• 제46권5호
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• pp.471-485
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• 2018

잣나무 열압밀화재의 완전한 치수안정화를 위해 열압밀화 후 열처리를 하였다. 열처리가 된 열압밀화재의 치수안정성 평가를 위해 흡수시험을 실시하였다. 0.43의 비중인 목재를 두께 압축률 50%로 열압밀화를 실시하여 0.79의 비중을 가진 고비중재를 얻었다. 열압밀화 후 열처리를 통하여 열처리 온도와 시간이 증가함에 따라 흡수성과 팽윤성이 감소하였다. 두께 회복률의 경우는 $120^{\circ}C$, $140^{\circ}C$, $160^{\circ}C$ 모두 24시간동안 열처리를 진행하였을 때, 1% 미만의 두께 회복도를 나타내었다. 따라서 열압밀화재의 치수안정화는 후 열처리 공정을 통하여 매우 효과적으로 시행할 수 있는 방법임을 확인할 수 있었다.

• 한국주조공학회지
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• 제36권5호
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• pp.167-173
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• 2016

The effect of various types of heat-treatment on the mechanical properties of cast Alloy 718 has been investigated. Cast Alloy 718 bars were subjected to 'standard heat-treatment'_(SHT), 'HIP (Hot Isostatic Pressing) heat-treatment'_(HHT), and 'HIP-simulated heat-treatment'_(HS). In the absence of long time high temperature heat-treatment, a small amount of Laves phase remained in the 'SHT' specimen, and needle shaped ${\delta}$ precipitated in the vicinity of the Laves phase. Due to the formation of the Laves and ${\delta}$ phases in the 'SHT' specimen, it exhibited lower tensile properties than those of the others_specimens. On the other hand, the Laves phase was completely dissolved into the matrix after 'HHT' and 'HS' treatments. It is known that isostatic pressure reduces the self-diffusion coefficient, because of the lower self-diffusivity under HIP conditions in the interdendritic region, Nb segregation and the high amount of ${\gamma}^{{\prime}{\prime}}$ precipitation that occurs. Due to the higher fraction of coarse ${\gamma}^{{\prime}{\prime}}$ phases, the 'HHT' treated Alloy 718 showed excellent tensile strength.

• 열처리공학회지
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• 제34권3호
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• pp.122-129
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• 2021

This study focuses on the microstructural development of 99% magnesium alloy sheet manufactured using twin roll casting (TRC) process. Herein, a plate with a thickness of 5 mm was manufactured using the TRC process, homogenization heat treatment was performed at 400℃ for 2-32 h, and finally, the change in microstructure was evaluated via optical microscopy and textural analysis. The results suggest that the plate manufactured using the TRC process was not destroyed and was successfully rolled into a plate. Microscopic observation suggested that the dendritic cast structure was arranged along the rolling direction. And the central layer of the rolled plate, where was present in a liquid state at the beginning of rolling, solidified later during the TRC process to form central segregation. The initial cast structure and inhomogeneous structure of the plate were recrystallized by homogenization heat treatment for only 2 h, and it was confirmed that the segregated part of the central layer became homogeneous and recrystallization occurred. Grain growth occurred as the heat treatment time increased, and secondary recrystallization occurred, wherein only some grains were grown. The textural analysis, which was conducted via X-ray diffraction, confirmed that the relatively weak basal plane texture developed using the TRC process was formed into a random texture after heat treatment.

• 한국식품영양학회지
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• 제36권6호
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• pp.489-495
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• 2023

This study evaluated the effects of heat treatment on gastrodin and gastrodigenin content, and antioxidant activities, in Gastrodia elata Blume. Gastrodin and gastrodigenin content was analyzed post-method validation, and antioxidant activity evaluation, including assessing total polyphenol content, DPPH, and ABTS radical scavenging activities, was done. The validation of the analysis method demonstrated excellent linearity. The limits of quantification of gastrodin and gastrodigenin were 2.89 and 3.47 ㎍/mL, respectively. Moreover, the results of intra- and inter-day precision analysis demonstrated relative standard deviation values, within 5%. The recovery rates for gastrodin and gastrodigenin were 97.22~98.85 and 97.99~99.91%, respectively, indicating good accuracy. Under different heat treatment conditions, gastrodin and gastrodigenin content significantly increased (p<0.05), ranging from 91.15 to 310.27 and 559.66 to 830.02 mg/100 g DW, respectively. Additionally, the total polyphenol content exhibited a significant (p<0.05) increasing trend, ranging from 1,444 to 1,798 mg/100 g DW, as the temperature and time of heat treatment increased. The DPPH and ABTS radical scavenging abilities demonstrated an increasing trend at 120℃ during heat treatment. These research findings are expected to enhance our understanding of the changes in gastrodin and gastrodigenin content, and antioxidant effects in Gastrodia elata Blume during heat treatment.

• 대한수의학회지
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• 제24권1호
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• pp.40-49
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• 1984

To investigate the factors influencing the artifical transformation in Escherichia coli, E. coli C600 was transformed by pBR322 DNA with tetracycline and ampicillin resistant gene purified by CsCl-Etbr equilibrium density gradient centrifugation from E.coli HB 101. The influencing factors in the transformation such as concentration of calcium chloride, time of ice incubation, temperature and time of heat shock, time of gene expression, effects of plasmid DNA concentration and adding time were examined in these experiments. The results obtained were as follows; 1. The highest transformation frequency was observed in the treatments of 100 mM $CaCl_2$ before heat shock and the treatment of $CaCl_2$ was essential step in the process of E. coli transformation. 2. The highest transformation frequency was observed in the treatment of heat shock at $42^{\circ}C$ for 4 min. or $37^{\circ}C$ for 6 min., but the prolonged heat shock resulted a decreased transformation frequency. 3. Treatments of ice incubation at $0^{\circ}C$ for 45 min. before heat stocks or at $0^{\circ}C$ for 30min. after heat shock resulted an increased transformation frequency. 4. There was a linear relationship between DNA concentration and transformation frequency at the concentration of $8{\times}10^3$ recipient cells. The highest transformation frequency reached in carte of 7 mcg of donor DNA, but above 1 mcg of DNA concentration, transformation frequency was not remarkably increased. Addition of donor DNA just after the treatment of $CaCl_2$ was the best. 5. The best condition of gene expression at $37^{\circ}C$ were 40min. for TC-resistant gene and 100min. for AP-resistant gene. TC-resistant gene was higher in the transformation frequency and faster in the gene expression time than AP-resistant gene. In these results, the best conditions for the transformation of E. coli C 600 with pBR322 DNA were: treatment with 100mM $CaCl_2$, ice incubation at $0^{\circ}C$ for 45 min, heat shock at $42^{\circ}C$ for 4 min., 30 min. of ice incubation and incubation at $37^{\circ}C$ for 100min. for gene expression in that order.

• Journal of the Korean Wood Science and Technology
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• 제40권6호
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• pp.370-377
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• 2012

잣나무(Pinus koraiensis S. et Z.)와 로지폴소나무(Pinus contorta Dougl)를 이용하여 열처리 목재를 제조한 후 처리조건에 따른 재색변화를 조사하였다. 반응표면분석법에 따라 설정된 9가지 처리조건(처리온도 : 170, 180, 200, 220, $230^{\circ}C$, 처리시간: 90, 120, 180, 240, 270 min.)에서 열처리 시편들을 제조하였으며, 색차계를 이용하여 재색을 측정한 후 흰개미 저항성을 평가하기 위하여 진주에 설치된 흰개미 시험장에서 6개월 동안 야외노출시험을 실시하였다. 처리온도와 처리시간이 증가함에 따라 명도가 감소하였으며 감소폭은 시간보다 온도에 의한 영향이 더 큰 것으로 나타났다. 미국국립표준국(National Bureau of Standards : NBS)에서 제시된 방식에 의해 평가된 색차를 처리온도와 처리시간의 함수로 표현한 반응표면분석모델은 잣나무의 경우 $R^2$의 값이 0.92, 로지폴파인의 경우 0.88로 열처리조건에 따른 색채의 예측가능성을 보여주었다. 6개월의 야외시험결과 열처리 조건에 상관없이 흰개미 가해가 심하게 발생된 것으로 나타났는데, 이는 제조된 열처리 목재의 흰개미 저항성이 야외에 사용하기에 적합하지 않다는 것을 보여준다.

• 한국표면공학회지
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• 제46권1호
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• pp.9-15
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• 2013

The effect of the additionally applied electrical current on the adhesion strength between electroless Cu and polyimide films was investigated. Peel tests were performed after applying electrical current within the range from 0.1 to 100 mA for the duration from 1 to 30 minutes. Sample with more than 1 mA of additional electrical current for 1 minute showed higher adhesion strength than that without additional electrical current. However, samples with 10 mA of additional electrical current for more than 10 miniutes showed the degradation of adhesion strength. Ra and RMS values of the peeled polyimide surface were proportional to the adhesion strength though there were no significant changes in the morphology of the peeled surfaces with varied amount and time-length of additional electrical current. Applying electrical current could increase the density of chemical bonding, which results in increase of the adhesion strength between copper and polyimide. However, in the case of applying additional electrical current for excessive amount or time, the degradation of the adhesion strength owing to the formation of copper oxide at the interface could occur.