• Applied Microscopy
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• 제46권2호
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• pp.76-82
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• 2016

Aloe vera has been used in the pharmaceutical, food and cosmetic industry for its therapeutic properties. However, there are not many current studies on the microstructure of A. vera compared to studies on the chemical constituents and health efficacy of A. vera. Therefore, we compared the morphology of an A. vera leaf using an optical microscope, a conventional scanning electron microscope (SEM) and a cryo-SEM. Especially, this study focused on observing the gel in the inner leaf of A. vera, which is challenging using standard imaging techniques. We found that cryo-SEM is most suitable method for the observation of highly hydrated biomaterials such as A. vera without removing moisture in samples. In addition, we found the optimal analytical conditions of cryo-SEM. The sublimation conditions of $-100^{\circ}C$ and 10 minutes possibly enable the surface of the inner leaf of A. vera to be observed in their "near life-like" state with retaining moisture. The experiment was repeated with A. arborescens and A. saponaria to confirm the feasibility of the conditions. The results of this study can be applied towards the basic research of aloe and further extend previous knowledge about the surface structures of the various succulent plants.

• Applied Microscopy
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• 제48권3호
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• pp.62-72
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• 2018

This study investigated the anti-obesity effect of a pear (Fructus Pyri Pyrifoliae) extract fermented by lactic-acid bacteria on obesity induced by a high-fat diet in rats. Body-weight measurement, blood analysis, and light microscope observation of adipose tissue in liver and epididymis were conducted after 8 weeks. Gene expression of leptin, adiponectin, and tumor necrosis $factor-{\alpha}$ ($TNF-{\alpha}$) in liver cells were also investigated. Compared to CON, PFA and PFB showed 8% weight reduction along with weight reduction of adipose tissue in liver and epididymis. Observing the microstructure of liver cells showed that lipid droplets were smaller in PFA and PFB than in CON. We confirmed that Fructus Pyri Pyrifoliae extract fermented by lactic-acid bacteria can affect gene expression of leptin, adiponectin, and $TNF-{\alpha}$ in liver cells, showing an obesity treatment effect. From the results above, it was observed that weight gain from increased gene expression in adipose cells as well as from the increased proportion of adipose cells caused by a high-fat diet can be statistically significantly reduced by taking Fructus Pyri Pyrifoliae extract fermented by lactic-acid bacteria. Therefore, Fructus Pyri Pyrifoliae extract fermented by lactic-acid bacteria can be effective for preventing and treating obesity by reducing weight and adipose cells.

• 한국산업융합학회 논문집
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• 제23권4_1호
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• pp.531-539
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• 2020

When injection mold is repeatedly used for mass production, fatigue phenomenon due to cyclic stress may occur. The surface and interior of structure might be damaged due to cyclic stress or strain. The objective of this study was to analyze failure of SCM435 high-tension bolts connecting upper and lower parts of a three-stage injection molding machine. These bolts have to undergo an accurate heat treatment to prevent the formation of chromium carbide and the action of dynamic stresses. Bolts were fractured by cyclic bending stress in the observation of ratchet marks and beach marks. Damaged specimen showed an acicular microstructure. Impurity was observed. Chromium carbide was observed near the crack origin. Both shape parameters of the Vickers hardness were similar. However, the scale parameter of the damaged specimen was about 20% smaller than that of the as-received specimen. Much degradation occurred in the damaged specimen. Bolts should undergo an accurate heat treatment to prevent the formation of chromium carbide. They must prevent the action of dynamic stresses. Bolts need accurate tightening and accuracy of heat treatment and screws need compression residual stress due to peening.

• 한국주조공학회지
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• 제4권2호
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• pp.96-101
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• 1984

The morphologies of eutectic cell formed during solidification affect on the mechanical properties in high Cr cast iron. In order to investigate the influence of Si on the structure, five kinds of specimen containing 16.42% Cr with varying amount of Si (0.51%, 1.17%, 2.22%, 2.71%, 3.56%) were poured into shell mould preheated $330^{\circ}C$ at $1510^{\circ}C$. The effect of Si on matrix in hypo-eutctic Cr cast iron (2.48% C, 16.42%) were studied through its mechanical tests and observation of microstructure using of metallurgical microscope, EPMA, SEM and Image analyzer systematically. The results obtained from the above studies are as follows: 1. Because of ${\Delta}T$ decreasing with increasing Si content, the morpologies of colony change into uniform bar-type carbide from plate-type ones, moreover eutectic colony size (Ew) becomes narrow and spacing of carbide wider. 2. As Si content increases, the amount of carbides also increases and most of Cr were dissolved in carbides while Si in matrix. 3. The hardness, tensile strength and wear resistance were increasing while impact value decreased with increasing Si content. 4. In fracture section, small amount of dimple pattern was observed in less than 1.17% Si but more than 2.22% Si river pattern was presented.

• 한국주조공학회지
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• 제17권3호
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• pp.258-266
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• 1997

The purpose of this study is to improve hardness and wear resistance of high strength yellow brass by adding Fe, Cr, Mn, Si and Ni. Results showed that NiO, $FeCr_2O_4$ and intermetallic compound $Mn_5Si_3$ were produced when Ni, Fe-Cr and Mn-Si were added to the yellow brass. The hardness and wear tests showed the best results with the presence of the product precipitates and intermetallic compound. The calculation of relative wear resistance by volume fraction of each phases showed that the relative wear resistance of $Mn_5Si_3$ had the highest value, that of ${\beta}$ phase had the lowest. Observation of the worn surface showed that the main wear mechanism were found to be the abrasive wear, and also showed that the wear is caused by mechanical failure at the early stage.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 정기총회 및 창립40주년기념 학술대회 학회본부
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• pp.257-259
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• 1987

The photoelectronic properties of CdTe films sintered with various amounts of $CdCl_2$ and $CuCl_2$ have been investigated by measurements of dark electrical resistivity, photocurrent, thermoelectric power, optical transmission and by observation of microstructure. The grain size and optical transmission of sintered CdTe films increase with increasing amount of $CdCl_2$ indicating that $CdCl_2$ acts as a sintering aid. The photoconductivity gain(A-$cm^2/W$) increases and resistivity($\Omega$-cm) decreases with increasing amount of $CuCl_2$ up to 100ppm due to the occurance of Cu-doping during sintering. The dark resistivity could be reduced farther by post heat treatments. The dark resistivity was still high($10^3{\Omega}$-cm) so that the accurate determination of the hole concentration by Hall measurement or by thermoelectric power measurement was not possible. From the analysis of electrical activation energy, however it can be concluded that the hole concentration is less than $10^{14}/cm^3$ and all grains are depleted of carrier by the trapping centers at grain boundaries.

• Nuclear Engineering and Technology
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• 제46권6호
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• pp.857-862
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• 2014

Mechanical alloying under various gas atmospheres such as Ar, an Ar-$H_2$ mixture, and He gases were carried out, and its effects on the powder properties, microstructure and mechanical properties of ODS ferritic steels were investigated. Hot isostatic pressing and hot rolling processes were employed to consolidate the ODS steel plates. While the mechanical alloyed powder in He had a high oxygen concentration, a milling in Ar showed fine particle diameters with comparably low oxygen concentration. The microstructural observation revealed that low oxygen concentration contributed to the formation of fine grains and homogeneous oxide particle distribution by the Y-Ti-O complex oxides. A milling in Ar was sufficient to lower the oxygen concentration, and this led a high tensile strength and fracture elongation at a high temperature. It is concluded that the mechanical alloying atmosphere affects oxygen concentration as well as powder particle properties. This leads to a homogeneous grain and oxide particle distribution with excellent creep strength at high temperature.

• 한국재료학회지
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• 제16권8호
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• pp.511-515
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• 2006

The dispersion hardened $Cu-TiB_2$ composites are a promising candidate for applications as electrical contact materials. The $Cu-TiB_2$ composites for electrical contact materials can reduce material cost and resource consumption caused by wear, due to their good mechanical and electrical properties. In this study, we investigated the wear phenomenon for $Cu-TiB_2$ composites fabricated with hot extrusion, by varying particle sizes and volume fractions of $TiB_2$. The wear tests were performed under the dry sliding condition with a fixed total sliding distance of 40 m. The contact loads at a constant speed of 3.5 Hz were 20, 40, 60, and 80 N. The friction coefficients and wear losses were measured during wear tests. Worn surfaces and wear debris after wear tests were investigated using the scanning electron microscope and the optical microscope. The microstructures of interface between Cu matrix and $TiB_2$ particle before and after wear tests were studied by the transmission electron microscope.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.822-823
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• 2006

The compaction and sintering behavior of zirconium titanate $(ZrTiO_4)$ was investigated by means of the measurement of sintering density and shrinkage, and the observation of microstructure. With increasing the content of $Al_2O_3$ additive, $Al_2O_3$-modified zirconium titanate samples fired at $1300^{\circ}C$ showed the anisotropic shrinkage behavior that the upper region of sintered body has higher sintering shrinkage than the low region. This difference of sintering shrinkage decreased with increasing firing temperature from 1300 to $1400^{\circ}C$. The SEM micrographs of powder compation show that the anisotropic shrinkage behavior is related with non-uniform density in a uniaxial compaction.

• 한국세라믹학회지
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• 제43권12호
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• pp.775-780
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• 2006

Mechanical and electrical performance of anode-supported SOFC single cells were analyzed after thermal cyclic operation. The experiments of thermal cyclic cell-operation were carried out four times and performance of each cell was measured at different temperatures of 650, 700, and $750^{\circ}C$, respectively. As increasing the number of thermal cycle test, single cells showed poor I-V characteristics and lower 4-point bending strength. The anode polarization was also measured by AC-impedance analysis. The observation of the microstructure of the anodes in single cells proved that the average particle size of Ni decreased and the porosity of anode increased. It is thought that the thermal cycle caused the degradation of performance of single cells by reducing the density of three-phase boundary region.