• 한국분말재료학회지
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• 제29권3호
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• pp.226-232
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• 2022

In this study, a new manufacturing process for a multilayer-clad electrical contact material is suggested. A thin and dense BCuP-5 (Cu-15Ag-5P filler metal) coating layer is fabricated on a Ag plate using a high-velocity oxygen-fuel (HVOF) process. Subsequently, the microstructure and bonding properties of the HVOF BCuP-5 coating layer are evaluated. The thickness of the HVOF BCuP-5 coating layer is determined as 34.8 ㎛, and the surface fluctuation is measured as approximately 3.2 ㎛. The microstructure of the coating layer is composed of Cu, Ag, and Cu-Ag-Cu3P ternary eutectic phases, similar to the initial BCuP-5 powder feedstock. The average hardness of the coating layer is 154.6 HV, which is confirmed to be higher than that of the conventional BCuP-5 alloy. The pull-off strength of the Ag/BCup-5 layer is determined as 21.6 MPa. Thus, the possibility of manufacturing a multilayer-clad electrical contact material using the HVOF process is also discussed.

• 접착 및 계면
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• 제23권1호
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• pp.8-16
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• 2022

본 연구에서는 폴리올의 혼합으로 폴리우레탄의 물성 저하를 보완하고자 하였다. 신발 및 소재 코팅용으로서 자가치유 기능을 가지는 수분산 폴리우레탄 수지를 합성하기 위해 내구성 및 내열성이 우수한 polyether 폴리올과 기계적 물성이 뛰어난 polycarbonate 폴리올을 병용하여 합성하였으며, 자가치유 기능의 부여를 위해 disulfide기를 도입하였다. 합성된 자가치유 기능 수분산 폴리우레탄은 fourier transform-infrared spectroscopy (FT-IR)을 통해 확인되었으며, universial testing machine (UTM)과 scanning electron microscope (SEM) 측정을 통해 물리적 특성 및 자가치유 특성을 확인하였다. Polycarbonate 폴리올을 병용함으로써 인장강도 및 경도가 증가하였고, 신장율은 감소하였다. 또한 열적 특성의 비교 결과, polycarbonate 폴리올의 함량이 증가함에 따라 열 안정성이 증가하였다. 치료효율은 poly(tetramethylene ether)glycol : polycarbonate polyol = 0.75 : 0.25일 때 가장 높은 효율을 보여주었으며, 현미경 및 SEM을 이용한 표면 관찰을 통해 손상 부분이 치유된 것을 확인하였다.

• 대한본초학회지
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• 제34권3호
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• pp.19-30
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• 2019

Objectives : This study is to propose the identification keys based on stereoscopic examination of 8 seed herbs in 2 categories (Phyllolobobii Semen (PS) with 4 Astragali Semen (AS), and 2 Lepidii seu Descurainiae Semen (LDS) with 1 Drabae Semen (DS)) which have difficulties in discrimination with visual observation. Methods : We reviewed the description of original plants and their medicinal parts from the literature. The original plants were collected, identified, confirmed as specimens, and compared to the samples distributed in the market. The first identification was made by visual observation, and insufficient points were supplemented by stereoscopic observation. Identification criteria were set by considering morphological characteristics of authentic herbs, percentage of adulterants, and distinction between authentic herbs and adulterants. Results : The original plants of PS and AS could be distinguished by upright or lying form of stem, color of flowers, number of leaflets, and presence of hair of fruits. LDS and DS could be distinguished by leaf arrangement on stem: radical or cauline, whole plants size, leaf division, color of flowers, and shape of fruits. The herbal medicines of PS and AS could be distinguished by seed surface pattern, size, and hardness. LDS and DS could be distinguished by size, shape, viscosity when chewed, and degree of mucous layer formation when soaked in water. Conclusions : This study suggests the identification keys of original plants and herbal medicines. Especially, since fine seed herbs are difficult to distinguish by visual observation, the stereoscope should be applied to the discrimination.

• Corrosion Science and Technology
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• 제21권3호
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• pp.209-220
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• 2022

Erosion-corrosion behaviors of Hadfield steel under a neutral aqueous environment with fine SiO₂ particles were examined and compared with those of conventional carbon steel. A range of electrochemical experiments (potentiodynamic polarization, linear polarization, and impedance), immersion test, and slurry pot test (i.e., erosion-corrosion test) were performed. Results showed that the Hadfield steel composed of austenitic matrix with (Fe,Mn)-based carbide had lower corrosion potential and higher corrosion current density than carbon steel with a typical ferrite/pearlite structure. In addition, pipe forming increased total corrosion rates (i.e., pure corrosion and erosion-enhanced corrosion rates). Nevertheless, the erosion-corrosion rate of Hadfield steel was much smaller. Morphological observation showed that local damage in the form of a crater by erosion-corrosion was more noticeable in carbon steel. The higher resistance of Hadfield steel to erosion-corrosion was attributed to its lower total erosion rates (i.e., pure erosion and corrosion-enhanced erosion rates) highly depending on surface hardness. This study suggests that Hadfield steel with higher resistances to flowing erosion-corrosion in an aqueous environment can be applied widely to various industrial fields.

• 소성∙가공
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• 제31권2호
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• pp.51-56
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• 2022

In this study, finite element analyses were performed by applying a stress ring and split die design to relieve the tensile stress acting on the die due to high surface pressure during warm-closed forging. The applied material was a yield-ratio-control-steel (YRCS). It was used without quenching or tempering after forging. In the case of stress rings design, the number of stress rings and the tolerance for shrink fit were different. Vertical and horizontal splits were applied for insert die split design. Case 5 die with three stress rings, 0.2 % shrink fit tolerance, and vertical split was selected as an effective die design for tensile stress reduction. Based on die stress reduction analyses, Case 5 die for warm-closed forging was produced and smooth forgeability was secured, making it possible to manufacture forging product of yoke with the required geometry. In addition, controlled cooling using warm forging heat was applied to secure mechanical properties of yokes. When oil cooling was used for direct controlled cooling after warm-closed forging, a relatively uniform Rockwell hardness distribution and high mechanical properties could be obtained.

• 한국산업융합학회 논문집
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• 제25권4_2호
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• pp.699-706
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• 2022

In this study, Directed energy deposition (DED) among additive manufacturing is applied to repair damaged spindle key parts of planner miller. The material of the spindle key is SCM415, and the P21 Powder is used. In order to find the optimal deposition conditions for DED equipment, a single-line deposition experiment is conducted to analysis five parameters. The laser power affects the width, and the height is a parameter affected by coaxial gas and powder gas. In addition, laser power, powder feed rate, coaxial gas, and powder gas are parameters that affect dilution. Otimal deposition is that 400 W of laser power, 4.0 g/min of powder feed rate, 6.5 L/min of coaxial gas, 3.0 L/min of powder gas and 4.5 L/min of shield gas. By setting the optimum conditions, a uniform deposition cross section in the form of an ellipse can be obtained. Damage recovery process of spindle key consists of 3D shape design of the base and deposition parts, deposition path creation and deposition process, and post-processing. The hardness of deposited area with P21 powder on the SCM415 spindle key is 336 HV for the surface of the deposition, 260 HV for the boundary area, and 165 HV for the base material.

• 한국염색가공학회지
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• 제33권4호
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• pp.317-326
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• 2021

In this study, we investigated for Bio-EPDM foam with oyster shell surface modified earth coupling agent. Experiments were carried out to confirm the bio-EPDM/Oyster shell foam applying content of earth coupling agent. The cure characterization were evaluated by measuring the mooney viscosity and oscillating disc rheometer (ODR). Mechanical properties such as hardness, tensile strength, elogation at break and tear strength were measured, and changes of mechanical properties were also evaluated after immersion in NaCl solution. In addition degree of volume change was measured after immersing the Bio-EPDM foam in NaCl solution and the low-temperature permanent compression set was evaluated at 4℃. To evaluate the low-temperature characteristics of Bio-EPDM/Oyster shell, the glass transition temperature was measured using Differential Scanning Calorimeter (DSC). As a result as the content of the earth coupling agent increased up to 3phr, the crosslinking density and mooney viscosity increased, and the mechanical properties and low-temperature permanent compression set improved, but from 4phr, it was rather decreased. The change in the glass transition temperature was insignificant, and the foam cell appeared to be uniform when the earth coupling agent was applied.

• Tribology and Lubricants
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• 제38권1호
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• pp.8-14
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• 2022

Amorphous carbon (a-C) has excellent wear resistance and, therefore is used as a coating to protect numerous mechanical components to prolong their lifetimes. Among the a-C coatings, diamond-like carbon (DLC) and DLC-containing silicon (Si-DLC) receive extensive attention owing to their enhanced wear resistance and low frictional characteristics. In this study, the friction and wear characteristics of DLC and Si-DLC coatings are analyzed. For comparative analysis, DLC-coated and Si-DLC-coated vanes are utilized with the counterpart of a roller for the friction tests. Since the lubricated mechanical components are generally vulnerable to wear when a lubricant film does not form properly, friction tests are conducted under boundary lubrication conditions to promote wear. A cylinder-on-cylinder type tribometer is used to perform the friction tests with various normal load conditions. After the friction test, a 3D laser confocal microscope is used for quantifying the wear volume to calculate the wear rate of each specimen. Consequently, the DLC-coated specimen shows a lower coefficient of friction (COF) and wear rate than the specimen without the coating, while the Si-DLC coating shows a higher COF than the bare specimen. The results of this study are expected to contribute to improving the efficiency and reliability of compressors.

• 한국식품영양학회지
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• 제35권3호
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• pp.223-230
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• 2022

The purpose of this study was to examine the quality characteristics of cookies made with Angelica gigas Nakai fermented by Lactobacillus paracasei. As the content of Angelica gigas Nakai fermented by L. paracasei (AFL) powder increased, the pH of the cookies decreased from 6.3 to 5.2. There was no significant difference in the moisture content depending on AFL powder content. The content of reducing sugar also increased with increasing AFL powder content. Regarding the surface color of the cookies, the L- and b-values decreased with increasing AFL powder content, whereas the a-value increased. As the AFL powder content increased, the total polyphenol content and ABTS and DPPH radical scavenging activities significantly increased. Cookies with 8% AFL powder (AC8) had the highest levels of 107.16 mg%, 38.69%, and 65.56%, respectively. The texture, adhesiveness, and cohesiveness of the cookies with various AFL powder levels were not significantly different, and hardness, springiness, gumminess, and chewiness showed no tendencies toward changes. Taken together, these results showed that when AFL powder was added to cookies, bioactivities such as antioxidant activity increased, making AFL powder a good material with high potential for use in commercially baked products.

• 한국식생활문화학회지
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• 제21권3호
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• pp.325-329
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• 2006

This study was to investigate the effect of the addition of red ginseng powder in Dasik. The addition of red ginseng powder in Dasik that we used with was in the ratio of 0%, 2%, 4%, 6% and 8% of red ginseng powder to Dasik in weight. Also, we used two different kinds of Dasik. One was made of starch and the other was made of flour. The physic-chemical analysis and sensory test were performed on the Dasik. The red ginseng powder added flour and starch Dasik showed lower moisture content and higher ash content compared with the non-added control group. In color analysis, whereas L value lowed at the addition of red ginseng powder, a and b value increased at the addition of red ginseng powder. In mechanical texture test, addition of red ginseng powder starch Dasik showed high hardness, cohesiveness and brittleness. Addition of red ginseng powder flour Dasik showed high springiness and gumminess. In the sensory test, the addition of the red ginseng powder reduced the sweetness and increased the surface color and the flavor. There was no difference in preference between the Dasik with up to 4% of red ginseng powder added and the control group, but the Dasik with 6% or more red ginseng was found undesirable (p<0.05). In conclusion, the Dasik with up to 4% addition of red ginseng powder would be the useful method to fulfill the traditional quality of Dasik. It was also found that the flour Dasik was to be more preferable than the starch Dasik.