• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.787-793
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• 2002

In this study, a bar impact test of low velocity was carried out to gain an insight into the damage mechanism and sequence induced in alumina plates(AD 85 and AD 90) under impact conditions. An experimental setup utilizing an instrumented long bar impact was devised, that can measure directly the impact force applied to the specimen and supply a compressive contact pressure to the specimen. During the bar impact testing, the influences of the contact pressure applied along the impact direction to the specimen on the fracture behavior were investigated. The measured impact force profiles explained well the damage behavior induced in alumina plates. The higher contact pressure to the specimen led to the less damage due to the suppression of radial cracks due to the increase in the apparent flexural stiffness of plate. It had produced the change of damage pattern developed in the specimen; from the radial cracks to the local contact stress dominant damage. It would contribute to the improvement of the ballistic property in ceramic plates. The observed results showed the following sequence in damage developed: The development of cone crack at impact region, the formation of radial cracks from the rear surface of plate depending on the plate thickness, the occurrence of crushing within the cone envelope and the fragmentation.

• Environmental Engineering Research
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• v.16 no.4
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• pp.231-236
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• 2011

Biological nitrogen removal, using a continuous flow packed-bed reactor (CPBR) in a consecutive nitrification and denitrification process, was evaluated. An apparent decline in the nitrification efficiency coincided with the steady increase in $NH_4{^+}$-N load. Sustained nitrification efficiency was found to be higher at longer empty bed contact times (EBCTs). The relationship between the rate of alkalinity consumption and $NH_4{^+}$-N utilization ratio followed zero-order reaction kinetics. The heterotrophic denitrification rate at a carbon-tonitrogen (C/N) ratio of >4 was found to be >74%. This rate was higher by a factor of 8.5 or 8.9 for $NO_3{^-}$-N/volatile solids (VS)/day or $NO_3{^-}-N/m^3$ ceramic media/day, respectively, relative to the rates measured at a C/N ratio of 1.1. Autotrophic denitrification efficiencies were 80-90%. It corresponds to an average denitrification rate of 0.96 kg $NO_3{^-}-N/m^3$ ceramic media/day and a relevant average denitrification rate of 0.28 g $NO_3{^-}$-N/g VS/day, were also obtained. Results presented here also constitute the usability of an innovative porous sulfur ceramic media. This enhanced the dissolution rate of elemental sulfur via a higher contact surface area.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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• pp.91-96
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• 1998

In recent years, the tribological behavior of coated ceramic material has been the topic of much interest. Particularly, the understanding of the tribological performance of thin film under light load is important for potential applications in MEMS. In this work under light load and low speed, the tribological behavior of coated silicon was investigated. The results show that both adhesive and abrasive wear occur depending on the sliding condition. Also the effect of humidity on friction was influenced by the apparent ares of contact between the two surfaces. Finally, undulations on the silicon wafer were found to be effective in trapping wear particles.

• Composites Research
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• v.20 no.2
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• pp.17-20
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• 2007

Superhydrophobic polytetrafluoroethylene ($Teflon^{(R)}$, Dupont) sub-micro and nanostructures were fabricated by the dipping method, based on anodization process in oxalic acid. The polymer sticking phenomenon during the replication creates the sub-microstructures on the negative polytetrafluoroethylene nanostructure replica. This process gives a hierarchical structure with nanostructures on sub-microstructures, which looks like the same structures as lotus leaf and enables commercialization. The diameter and the height of the replicated nano pillars were 40 nm and 40 um respectively. The aspect ratio is approximately 1000. The fabricated surface has a semi-permanent superhydrophobicity, the apparent contact angle of the polytetrafluoroethylene sub-micro and nanostructures is about $160^{\circ}$, and the sliding angle is less than $1^{\circ}$.

• Composites Research
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• v.25 no.3
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• pp.76-81
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• 2012

Atmospheric pressure plasma treatment on carbon nanotube (CNT) surfaces was performed to modify reinforcement effect and interfacial adhesion of carbon fiber reinforced CNT-phenolic composites. The surface changes occurring on CNT treated with plasma were analyzed by using Fourier transform infrared spectroscope (FT-IR). The significant improvement of wettability on CNT was confirmed by static contact angle test after plasma treatment. Such plasma treatment resulted in a decrease in the advancing contact angle from $118^{\circ}$ to $60^{\circ}$. The interfacial adhesion between carbon fiber and CNT-phenolic composites increased by plasma treatment based on apparent modulus test results during quasi-static tensile strength. Furthermore, the proposed database offers valuable knowledge for evaluating interfacial shear strength (IFSS).

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.42 no.1
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• pp.64-73
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• 2010

This study was conducted to modify the surface properties of papers by formation of hydrophobic self-assembled monolayer(SAM) on paper surface with silanes. A base paper I(0.5% AKD) and base paper II(1.0-1.5% AKD) were reacted with silanes(PFDTES, DMDCS, MODDCS) by immersion method and vapor deposition method. Hydrophobic SAMs(contact angle value>$120^{\circ}C$) were obtained on all papers after treatment with $10^{\mu}l$ PFDTES for 15min, with $50^{\mu}l$ DMDCS for 30min, with $50^{\mu}l$ MODDCS for 300min. When applying PFDTES to paper surface, lower silane concentration and shorter reaction time were required, whereas MODDCS with long alkyl chain required the longest reaction time of 300min. The st$\ddot{o}$ckight sizing degree of silane treated papers were increased between 105sec(base paper I) and 130sec(base paper II). The wet tensile strength of PFDTES-treated base papers(I, II) increased by 10-34% after SAM formation. However, the wet tensile strength of the DMDCS-treated base paper(I) was found to decrease from 0.067kN/m to 0.038kN/m; this may due to the cellulose degrading as a result of generated hydrogen chloride when hydroxyl group of cellulose were reacted with DMDCS. No apparent changes of PPS roughness on silane-treated papers are observed. The ATR-IR spectrum showed absorption peak located at 465 and 1200cm-1 which can be assigned to the Si-O-C asymmetric stretching and Si-O-C bonds, respectively.

• Journal of Conservation Science
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• v.36 no.1
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• pp.15-27
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• 2020

The Main Hall of the Fengguo monastery in Yixian county, Liaoning province, China, is the best preserved and largest wooden Buddhist structure, typical of the Liao dynasty style, in China. However, some degradation to the timber frame of the Main Hall has been noted, and this is causing concern in terms of the long-term preservation of the structure. In this study, wooden pillars showing the degradation phenomena of whitening, for areas in contact with the stone floor, and extensive surface damage at higher locations(mostly above 1 m) have been examined. Samples taken from wooden pillar surfaces were analyzed using X-ray powder diffraction, Fourier-transform infrared spectroscopy(FTIR), ion chromatography, and pH measurements. With respect to the whitening phenomenon, we found inorganic calcium precipitates and oxalate ions, along with higher pH values. These symptoms indicated that chemical changes were taking place in response to alkaline conditions, suggesting that alkaline mixtures with calcium content in the foundations may be responsible. Regarding the upper surface-damaged areas, no valid evidence for chemical degradation was found using FTIR analysis, while damaged areas exhibited the presence of more bat guano-related materials than which were apparent in undamaged areas. The occurrence of this surface-damaged phenomenon has therefore been attributed to physical damage caused by bat activity over long periods of time.

• Journal of the Korean institute of surface engineering
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• v.50 no.5
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• pp.352-359
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• 2017

The growth of nanocrystalline diamond films on a p-type poly silicon substrate was studied using microwave plasma chemical vapor deposition method. A 6 mm thick poly silicon plate was mirror polished and scratched in an ultrasonic bath containing slurries made of 30 cc ethanol and 1 gram of diamond powders having different sizes between 5 and 200 nm. Upon diamond deposition, the specimen scratched in a slurry with the smallest size of diamond powder exhibited the highest diamond particle density and, in turn, fastest diamond film growth rate. Diamond deposition was carried out applying different DC bias voltages (0, -50, -100, -150, -200 V) to the substrate. In the early stage of diamond deposition up to 2 h, the effect of voltage bias was not prominent probably because the diamond nucleation was retarded by ion bombardment onto the substrate. After 4 h of deposition, the film growth rate increased with the modest bias of -100 V and -150 V. With a bigger bias condition(-200 V), the growth rate decreased possibly due to the excessive ion bombardment on the substrate. The film grown under -150V bias exhibited the lowest contact angle and the highest surface roughness, which implied the most hydrophilic surface among the prepared samples. The film growth rate increased with the apparent activation energy of 21.04 kJ/mol as the deposition temperature increased in the range of $300{\sim}600^{\circ}C$.

• Economic and Environmental Geology
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• v.23 no.2
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• pp.215-219
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• 1990

Geological and electrical resistivity surveys along the survey line of about 3 km between Kyungsangbukdo Youngilgun Hodong and Gwangmyungdong using by dipole-dipole electrode array method were carried out to examine the boundary and structural relationship between Tertiary Pohang and Janggi basins. Electrical resistivity data were interpreted qualitatively and quantitatively by means of pseudosection of apparent electrical resitivity distribution and finite difference method for two dimensional geologic structure model. The nearly vertical fault zone with low electrical resistivity value of 1-5 Ohm-m and widths of about 200m at the surface and 400 m at depth exists around 1.2 km west of national road between Ocheoneup and Yangbukmyun. Mudrocks, sandstones and tuffaceous rocks are widely distributed with electrical resistivity values of 6-77 Ohm-m. Especially, tuffaceous rocks with relatively high electrical resistivity value are predominant at eastern side of fault zone. Consequently, it is known that Pohang and Janggi basins are in fault contact.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.423-430
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• 2002

A feasibility of a trial test method was evaluated analytically, in which the elastic modulus of a soil deposit was tried to estimate by analyzing dynamic signals measured during conducting the SPT. If there existed a reliable relationship between the impedance ratio of a rod to a soil and the amplitude ratio of a reflected to an incident wave signal at the tip of steel rod contacting the soil surface, it was expected that one could determine the impedance of soil, and then roughly estimate the elastic modulus from the impedance. For a simple rod-soil system, the existence of the relevant relationship was verified in this study by analyzing computed wave signals propagating up and down through the rod. On the basis of these results, thus, a potential of the test method to practical applications could be seen. However, apparent theoretical shortcomings possessed in this approach were also realized since the soil part had an unconfined contact area where contacted with the rod. Therefore, it was concluded that further studies needed to be conducted, in which the reliable theoretical relationship between the impedance and the amplitude ratio as well as the effective contacting soil area contributing to wave reflection should be justified.