• 한국정밀공학회지
• /
• 제18권1호
• /
• pp.89-97
• /
• 2001

A microgyroscope, which vibrates in two orthogonal axes on the substrate plane, is designed and fabricated. The shuttle mass of the vibrating gyroscope consists of two parts. The one is outer shuttle mass which vibrates in driving mode guided by four folded springs attached to anchors. And the other is inner shuttle mass which vibrates in driving mode as the outer frame does and also can vibrate in sensing mode guided by four folded springs attached to the outer shuttle mass. Due to the directions of vibrating mode, it is possible to fabricate the gyroscope with simplified process by using polysilicon on insulator structure. Fabrication processes of the microgyroscope are composed of anisotropic silicon etching by RIE, gas-phase etching (GPE) of the buried sacrificial oxide layer, metal electrode formation. An eletromechanical model of the vibrating microgyroscope was modeled and bandwidth characteristics of the gyroscope operates at DC 4V and AC 0.1V in a vacuum chamber of 100mtorr. The detection circuit consists of a discrete sense amplifier and a noise canceling circuit. Using the evaluated electromechanical model, an operating condition for high performance of the gyroscope is obtained.

• 한국분말재료학회지
• /
• 제26권4호
• /
• pp.305-310
• /
• 2019

In the present work, spheroidization of angular vanadium powders using a radio frequency (RF) thermal plasma process is investigated. Initially, angular vanadium powders are spheroidized successfully at an average particle size of $100{\mu}m$ using the RF-plasma process. It is difficult to avoid oxide layer formation on the surface of vanadium powder during the RF-plasma process. Titanium/vanadium/stainless steel functionally graded materials are manufactured with vanadium as the interlayer. Vanadium intermediate layers are deposited using both angular and spheroidized vanadium powders. Then, 17-4PH stainless steel is successfully deposited on the vanadium interlayer made from the angular powder. However, on the surface of the vanadium interlayer made from the spheroidized powder, delamination of 17-4PH occurs during deposition. The main cause of this phenomenon is presumed to be the high thickness of the vanadium interlayer and the relatively high level of surface oxidation of the interlayer.

• Corrosion Science and Technology
• /
• 제20권2호
• /
• pp.69-76
• /
• 2021

In this work, we have performed a corrosion failure analysis of a leaking tube connected to an upper header of a condensate pre-heater in a heat recovery steam generator. It was revealed that the leakage position in the tube was the location where the materials were easily vulnerable due to tensile residual stresses induced by the material manufacturing process and welding process. In addition to an imbalance in the module induced by temperature difference during operation of the pre-heater, the weight of the modules and thermal fatigue provoked a type of stress of tensile-tensile fatigue on the tube. Thus, the leakage position of the pre-heater was exposed to the tensile stress on the inner surface of the tube facing the gas, which rendered the unstable oxide layer susceptible to corrosion and the formation of pits on the water side. The cracks propagated along with the degraded microstructure in a transgranular cracking mode under fatigue loading and finally resulted in water leakage.

• Corrosion Science and Technology
• /
• 제22권4호
• /
• pp.221-231
• /
• 2023

Interest in aluminum alloys for the hydrogen valves of fuel cell electric vehicles (FCEVs) is growing due to the reduction in fuel efficiency by the high weight. However, when an aluminum alloy is used, deterioration in mechanical characteristics caused by hydrogen embrittlement and wear is regarded as a problem. In this investigation, the aluminum alloy used to prevent hydrogen embrittlement was subjected to surface treatments by performing hard anodizing and plasma ion nitriding processes. The hard anodized Al alloy exhibited brittleness in which the mechanical characteristics rapidly deteriorated due to porosity and defects of surface, resulting in a decrease in the ultimate tensile strength and modulus of toughness by 15.58 and 42.51%, respectively, as the hydrogen charging time increased from 0 to 96 hours. In contrast, no distinct nitriding layer in the plasma ion-nitrided Al alloy was observed due to oxide film formation and processing conditions. However, compared to 0 and 96 hours of hydrogen charging time, the ultimate tensile strength and modulus of toughness decreased by 7.54 and 13.32%, respectively, presenting excellent resistance to hydrogen embrittlement.

• E2M - 전기 전자와 첨단 소재
• /
• 제16권9호
• /
• pp.63.2-64
• /
• 2003

Epitaxial yttrium-stabilized HfO$_2$ thin films were deposited on p-type (100) Si substrates by pulsed laser deposition at a relatively lower substrate temperature of 550. Transmission electron microscopy observation revealed a fixed orientation relationship between the epitaxial film and Si; that is, (100)Si.(100)HfO$_2$ and [001]Si/[001]HfO$_2$. The film/Si interface is not atomically flat, suggesting possible interfacial reaction and diffusion, X-ray photoelectron spectrum analysis also revealed the interfacial reaction and diffusion evidenced by Hf silicate and Hf-Si bond formation at the interface. The epitaxial growth of the yttrium stabilized HfO$_2$ thin film on bare Si is via a direct growth mechanism without involoving the reaction between Hf atoms and SiO$_2$ layer. High-frequency capacitance-voltage measurement on an as-grown 40-A yttrium-stabilized HfO$_2$ epitaxial film yielded an dielectric constant of about 14 and equivalent oxide thickness to SiO$_2$ of 12 A. The leakage current density is 7.0${\times}$ 10e-2 A/$\textrm{cm}^2$ at 1V gate bias voltage.

• KSBB Journal
• /
• 제17권2호
• /
• pp.176-181
• /
• 2002

Astaxanthin (3,3＇-dihydroxy-${\beta}$, ${\beta}$-carotene-4-4＇-dione), a natural pigment of pink to red color, is widely distributed in nature particularly in the skin layer of salmonoids and the crust of shrimp, lobster, etc. Recently, it was produced from the yeast culture of Phaffia rhodozyma. Because of its high thermal stability and antioxidant functionality, its applications can be extended into food, cosmetics, and pharmaceutical ingredient beyond the traditional feed additive. Because of its very high lipophilicity, astaxanthin has been extracted traditionally by strong organic solvents such as chloroform, petroleum ether, acetone, etc. In this study, we developed a surfactant-based solubillization system for astaxanthin, and used it to extract astaxanthin from disrupted yeast cells. Among Tween 20, Triton X-100 and SDS, Tween 20 was identified as the most suitable surfactant in terms of extraction capacity and safety. The ethylene oxide group of Tween 20 was identified as the most significant factor to increase the HLB value that determined the extraction capacity. The effects of micelle formation condition, such as the molar ratio of astaxanthin and Tween 20, pH, and ionic strength were also investigated. pH and ionic strength showed no significant effects. The optimal molar ratio between astaxanthin and Tween 20 was 1 : 12. Antioxidant activity of astaxanthin was higher than ${\beta}$-carotene and ${\alpha}$-tocopherol. Astaxanthin in the crude extract from the yeast cell was more resistant to air and/or light degradation than pure astaxanthin, probably because of the presence of other carotenoids and lipids.

• 한국주조공학회지
• /
• 제34권6호
• /
• pp.194-199
• /
• 2014

The effect of $Al_2Ca$ on the oxidation resistance and tensile property of Al-5Mg alloys was investigated. According to the TGA (Thermogravimetric analysis) result at $550^{\circ}C$ after 24hrs, the Al-5Mg alloy showed parabolic behavior with weight gain. On the other hand, there was almost no difference in the weight changes of the $Al_2Ca$ added Al-5Mg alloys during the oxidation. It was thought that the improvement of oxidation resistance in $Al_2Ca$ added Al-5Mg alloys might be due to the formation of a protective oxide layer with CaO and MgO on the surface. The microstructures of the alloys showed grain refinement with an increasing $Al_2Ca$ content. From the tensile test, the yield strength of the alloys were improved with an increasing $Al_2Ca$ content. The 0.07 mass%$Al_2Ca$ added Al-5Mg alloy showed similar elongation and increased strength, simultaneously. It was considered that the addition of $Al_2Ca$, which was superior in the oxidation resistance of Al, reduced the formation of Mg oxides and inclusions during the alloying. This, partly led to the improvement of tensile properties.

• Restorative Dentistry and Endodontics
• /
• 제1권1호
• /
• pp.26-32
• /
• 1975

After a vital pulpotomy in dogs' teeth, the responses of the remaining pulp tissue under hydroxides (calcium hydroxide, magnesium hydroxide, aluminium hydroxide and zinc hydroxide) were studied histologically. The class V cavities were prepared on the teeth and the pulp was amputated. Each hydroxide was placed over the amputated tissue and the cavity was sealed with zinc oxide eugenol cement. Animals were sacrificed after 3 days, 1, 2, and 3 weeks following the operation. The teeth were decalcified, sectioned and stained with hematoxylin and eosin. Microscopic examination reveals as follows; 1. Calcium hydroxide: Inflammatory change was seen in the superficial portion of the remaining pulp tissue at the 3rd day and 1st week. The incompleted calicified material began to be deposited from the canal wall at the 2nd week, and the advanced calcified material was seen at the 3rd week. 2. Magnesium hydroxide: Severe inflammatory change was seen in the superficial portion of the remaining pulp from the 3rd day and the 1st week samples. Inflammatory change was decreased at the 2nd week and the slight calcified material was deposited from the root canal at the 3rd week. 3. Aluminium hydroxide: Severe inflammatory changes were seen in the remaining pulp tissue, the blood vessel was dilated, and the odontoblasts were destroyed at the 3rd day and 1st week. The fibrous degeneration spread to the apex at the 2nd week. There was no evidence of newly formed odontoblasts or deposition of calcified material underneath aluminium hydroxide. 4. Zinc hydroxide: The micrscopic picture was destructive. A thick necrotic layer was found under the amputated surface at the 3rd day and 1st week. Granulation tissue formation as well as chronic inflammatory changes extended to the apical area in the pulp tissue. Also there were no sign of odontoblastic formation or calcified material at the 2nd and 3rd week.

• 마이크로전자및패키징학회지
• /
• 제10권4호
• /
• pp.35-38
• /
• 2003

ITO/glass 기판 위에 발광물질로서 poly(2-methoxy-5-(2-ethylhexoxy)-1,4-phenylenevinylene (MEH-PPV)를 이용하여 스핀코팅법(spin coating)으로 Glass/ITOM/MEH-PPV/Al 구조를 가지는 고분자 유기 발광 다이오드를 제작하였다. MEH-PPV 박막형성시 열처리온도에 따른 다이오드의 전기적, 광학적 특성을 조사하였다. 열처리 온도를 $65^{\circ}C$에서 $170^{\circ}C$로 증가함에 따라 유기 발광다이오드의 발광휘도는 10V 인가전압에서 630 cd/$\m^2$에서 280 cd/$\m^2$로 크게 감소하였다. 또한 $65^{\circ}C$에서 열처리한 시료의 경우 약 2 lm/W의 최대 발광효율을 나타내었다. 이러한 결과는 높은 온도에서 열처리시 MEH-PPV 유기 형광층과 전극간의 상호반응에 의한 계면 거칠기의 증가와 새로운 절연층의 형성 등과 관련이 있는것으로 판단된다.

• 한국결정성장학회지
• /
• 제19권2호
• /
• pp.75-78
• /
• 2009

PBN 도가니를 이용하여 Si이 도핑된 GaAs 단결정을 수직경사 응고법으로 성장시켰다. PBN 도가니에 산화막인 $B_{2}O_{3}$의 양을 $0{\sim}0.2wt%$ 범위에서 변화시키면서, 성장 후 캐리어 농도를 측정하였다. $B_{2}O_{3}$ 첨가량이 증가함에 따라, 초기 0.1 정도의 Si 도판트의 편석계수는 0.01 부근까지 급격히 감소하고, 동시에 캐리어 농도도 감소하는 것을 알 수 있었다. 이는 성장도중 도판트인 Si이 $B_{2}O_{3}$과 반응하며 도너인 Si 양을 감소시키며, 동시에 억셉터인 B 양을 증가시키기 때문으로 보인다. 한편 PBN 도가니 내면에 얇은 유리질의 $B_{2}O_{3}$층 형성이 용이한 고온 산화막 처리가 결함감소에 효과적임을 확인하였다.