• Journal of the Korean Vacuum Society
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• v.8 no.1
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• pp.36-42
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• 1999

Field emission behaviors from diamond-like carbon films were investigated. The films were deposited on n-type Si wafer by ion beam sputtering method using 3 cm Kaufman type ion source. Regardless of the film thicknesses and atomic bond structure, the emission current was much enhanced by electrical breakdown between anode and the film surface. The effective work function was estimated to be about 0.1 eV. In order to identify the emission site, tungsten tip was scanned the damaged region damaged region but localized to a specific site. Analysis using Auger electron spectroscopy and SEM shows that SiC compound was not a sufficient condition for the electron emission. This result showed that the enhanced emission was mainly due to the changes in the chemical bond of the damaged region rather than the enhanced electric field caused by the morphological change.

• Journal of the Korean Magnetics Society
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• v.9 no.5
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• pp.234-238
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• 1999

Lithium ferrites are prominent in the element of microwave frequency communication core and high frequency memory core because of their low coercivity and the high squareness ratio. This paper reports primarily the development of lithium ferrites with the low coercivity and high squareness ratio. The materials with $Li_{0.48-0.5x}Bi_{0.02}Ni_{0.04}Zn_xFe_{2.46-0.5x}O_4$ (x = 0,0.01, 0.02, 0.03) have been prepared to investigate the physical properties. The addition of ZnO gave raised maximum induction $(B_m)$ and decreased coercive force $(H_c)$, but the squareness ratio $(R\;=\;B_m/B_r)$ was decreased. The specimen of squareness ratio R=0.82, coercive force $H_c=\;1.80\;Oe$ was obtained for $Li_{0.48-0.5x}Bi_{0.02}Ni_{0.04}Zn_xFe_{2.46-0.5x}O_4$ (X=0) sintered at 105$0^{\circ}C$. Also the sample of squareness ratio R = 0.75, coercive force $H_c=\;1.70\;Oe$ for $Li_{0.48-0.5x}Bi_{0.02}Ni_{0.04}Zn_xFe_{2.46-0.5x}O_4$ (X = 0) sintered at 110$0^{\circ}C$ was measured. The Tc was obtained 463$^{\circ}C$ and the Br of environmental temperature variation was stable.

• International Journal of Highway Engineering
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• v.11 no.4
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• pp.87-94
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• 2009

Volume of concrete slab changes by variations of temperature and moisture after its placement. Shrinkage due to evaporation causes tensile stress in the slab when contraction of the slab is restrained by its self weight, friction with subbase, and etc. Actual tensile stress caused by the shrinkage was less than theoretically predicted stress according to previous studies. It was the stress reduction due to visco-elastic property of the early-age concrete slab partially restrained. In this study, strains of restrained circumferential, unrestrained circumferential, and unrestrained square pillar concrete specimens were measured to investigate stress reduction of the specimens with age of concrete. Elastic modulus of the concrete was measured at the age of 1, 3, 7, 14, 28 days and penetration test was performed. The stress reduction was calculated by input the test results into theoretical equations suggested by previous researchers. The stress reduction of the restrained concrete specimens will be applied to design of concrete pavements based on results of the study.

• Clean Technology
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• v.15 no.1
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• pp.16-22
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• 2009

In this study, a fiber reinforced plastic (FRP) pipe with superior wear resistance was developed to replace the fly ash pipe of cast iron. Wear test was performed with various combinations of SiC filler and resin materials of unsaturated polyester, vinylester, epoxy, and phenol. Test results of ASTM D4060 showed the optimal combinations of resin, filler size, and resin/filler ratios. Test results of comparison between FRP and cast iron showed the possibility to replace cast iron pipe with the FRP pipe. Field test executed to compare the wear resistance between cast iron pipe and developed FRP pipe showed the superiority of the FRP pipe.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.356-364
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• 2020

An experimental study to investigate the effect of self-cleaning of mortar mixed with photocatalyst was performed out in this study. Test parameters included the photocatalyst content and surface roughness of the specimens. The experimental mortar specimens were manufactured by mixing a photocatalyst by cement weight of 2.5%, 5.0%, 7.5% and 10.0%. In addition, the surface roughness was categorized into three cases. They included flat surface condition, little surface roughness(medium roughness), and high surface roughness. After mortar specimens were cured for 28 days, they were illuminated by an ultraviolet lamp for 24 hours and immersed in a methylene blue conditioning solution for 12 hours. Thereafter, an ultraviolet(UV) lamp was illuminated on the specimens for 48 hours in an experimental chamber and then the color change of methylene blue solution was measured by using a spectrophotometer over illuminating time of UV lamp. The color change of methylene blue tended to increase as photocatalyst contents increased. Test results meant that photocatalyst was effective for self-cleaning in mortar. However, the color change of the methylene blue solution did not show a noticeable tendency at different surface roughness conditions. It might be due to the uneven photocatalyst distribution on the surface of mortar specimens.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.3
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• pp.303-314
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• 2009

Image analyses for sheared joint specimens are performed to study asperity degradation characteristics with respect to the roughness mobilization of rock joints. Four different types of joint specimens, which are made of high-strength gypsum materials, are prepared by replicating the three-dimensional roughness of rock joints. About twenty jointed rock shear tests are performed at various normal stress levels. The characteristic and scale of asperity degradation on the sheared joint specimens are analyzed using the digital image analysis technique. The results show that the asperity degradation characteristic mainly depends on the normal stress level and can be defined by asperity failure and wear. The asperity degradation develops significantly around the peak shear displacement and the average amount of degraded asperities remains constant with further displacement because of new degradation of small scale asperities. The shear strength results using high-strength gypsum materials can not fully represent physical properties of each mineral particles of asperities on the natural rock joint surface. However the results of this quantitative estimation for the relationship between the peak shear displacement and the asperity degradation suggest that the characterization of asperity degradation provides an important insight into mechanical characteristics and shear models of rock joints.

• Journal of the Korean Ceramic Society
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• v.35 no.7
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• pp.721-725
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• 1998

In this study solid-phase sintered silicon caribide samples composed of SiC powder having boron and car-bon black as additives were prepared by pressureless sintering at $1950^{\circ}C$. The bending strength the frac-ture toughness and the specific werar rate of the samples were examined and the micro structures of the broken and the worn surface were observed by SEM to understand the relationship between the tri-bological charcteristics and the micro structure. Additionally the relationship between the micro struc-tures and the tribological characteristics of the samples for the frictional opponents SiC and $Al_{2}O_{3}$ pins were investigated Conclusions are as follows ; 1. The specific were rate of the samples for the SiC pin was larger than that for the $Al_{2}O_{3}$ pin. HOwever the specific wear rate for the $Al_{2}O_{3}$ pin was increased about 6,45 times as that for the SiC pin under the load increasing. 2. The specific wear rate of the SiC pin was larger than that of the $Al_{2}O_{3}$ pin. owever the specific wear rate of the $Al_{2}O_{3}$ pin was increased about 4 times as that of the SiC pin under the load increasing 3. The micro stucture of the worn surface showed a flat face without cracks in the case that the frictional opponents has the low friction coefficient but in the case of without cracks in the case that the frictional opponents has the low friction coefficient but in the case of the high friction coefficient the micro structure of the worn surface showed an uneven face having spread-ed cracks. 4. The tribological characteristics of thesolid-phase sintered SiC samples was similar to that of li-quid-phase sintered ones when the pin having the high friction coefficient was used.

• Journal of dental hygiene science
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• v.17 no.4
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• pp.358-367
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• 2017

The purpose of this study was to evaluate the influence of water infiltration and flexural strength changes in dental porcelain with glazing treatment. The block specimens were prepared as experimental materials, using feldspar type commercial dental porcelain; then, these were fired at $940^{\circ}C$ for 1 minute. The fired specimens were polished with a dimension of $40{\times}5.5{\times}5mm$. The specimens were distributed to two experimental groups: with and without glazing treatment specimens (n=5), and they were immersed in a solution of pH 7 for 3, 7, and 20 days at $40^{\circ}C$ after fabrication. To evaluate the flexural strength changes with water infiltration treatment in specimens with and without glazing, the 3-point flexural test was performed, using a universal testing machine until failure occurred. Starting powder and fired specimens consisted of amorphous and leucite crystalline phase. The Vickers hardness of fired specimens was more than 1.6 times higher than that of the enamel of natural teeth. According to porosimeter results, the specimens without glazing treatment exhibited a porosity of about 14.7%, whereas the glazed specimens exhibited the lowest porosity at about 1.1%. The average flexural strength of glazed specimens was higher than the flexural strength of specimens without glazing treatment (p<0.05). The flexural strength of all specimens with and without glazing treatment deteriorated with accelerated aging in the solution. In addition, significant differences between these two treatment groups were observed in all of the specimens treated at various water infiltration periods (p<0.05). The exposure of internal pores and micro-cracks in the surface due to polishing of the fired specimens influenced mechanical behaviors. Especially, the flexural strength in specimens without glazing treatment has shown significant degradation with the infiltration of water. Therefore, this study suggests that glazing processes can improve mechanical properties of dental porcelain.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2006.10a
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• pp.1-4
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• 2006

공초점 자가 간섭 현미경은 측정 광학계에 복굴절 물질을 사용하여 반사된 빛에 대해 간섭 현상을 일으키는 것을 특징으로 한다. 이 간섭을 자가 간섭이라고 부르는데, 이는 시편의 한 점에서 반사되어 나온 빛이 간섭을 일으키기 때문에 붙여진 이름이다. 공초점 자가 간섭 현미경의 점 확산 함수는 종래의 공초점 현미경의 점 확산 함수와 자가 간섭의 곱으로 나타나며, 자가 간섭의 주기가 종래의 공초점 현미경의 점 확산 함수의 중심폭보다 작은 경우 점 확산 함수의 중심폭이 작아져서 수평 방향으로의 분해능이 향상되게 된다. 이러한 분해능 향상 정도를 측정하기 위하여 지름이 100nm 인 금으로 된 비드를 사용하였다. 측정된 결과는 전산모사한 결과와 잘 일치하며 공초점 자가 간섭 현미경에서 2배의 분해능 향상을 보여준다.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.153-158
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• 1997

Zr-2.5%Nb 합금에서 응력방향에 따른 DHC특성의 차이를 알아보고자 하였다. 판상의 CT시편을 이용하여 수소를 200 ppm 주입하고 응력을 압력관의 길이 방향으로 가하고 notch를 윈주방향으로 한 경우와 원주방향으로 응력을 가하고 notch를 길이 방향으로 한 경우의 균열전파속도를 측정하여 본 결과 길이 방향으로 응력을 가하였을 때 균열전파속도가 1/100 정도 감소하였으며, 균열발생을 위한 임계응력확대계수도 커짐을 알 수 있었다. 그리고 균열전파 방향도 원주방향으로 응력을 가하였을 때는 균열이 precrack을 따라 그대로 진행되었으나, 응력을 길이 방향으로 가하였을 때는 precrack을 따라 균열이 전파되지 못하고 균열분리 현상을 보였다 이것은 원래 모재가 보유하고 있는 집합조직과, 응력에의하여 수소화물이 재배열할 때 기존의 a상에서의 특정 방향 관계를 유지하여 석출함으로써 균열이 수소화물을 따라 전파됨이 원인인 것으로 생각된다. 응력을 원주방향으로 가하였을 때 균열주위에 수소화물이 길게 석출하지만, 응력을 길이 방향으로 기하였을 때는 수소화물이 20$\mu\textrm{m}$ 정도의 작은 크기로 분리된 균열과 같은 방향으로 분포하고 있음을 관찰하였다. 이로부터 집합조직을 개량함으로써 DHC저항성에 대한 효과를 얻을 수 있음을 확인 할 수 있었고 DHCV model에서 방향성을 수소화물의 재배열인자로부터 고려할 필요성이 있음을 알게 되었다.