• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.874-880
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• 2003

The effect of h-BN content on microstructure, mechanical properties, and machinability of AlN-BN based machinable ceramics were investigated. The relative density of sintered compact decreased with increasing h-BN content. The four-point flexural strength also decreased from 238 MPa of monolith up to 182 MPa by the addition of 30 vol％ h-BN. Both low Young's modulus and residual tensile stress, formed by the thermal expansion coefficient difference between AIN and h-BN, might cause the strength drop in AlN-BN composite. The crack deflection, and pull-out phenomena increased by the plate-like h-BN. However, the fracture toughness decreased with h-BN content. The second phases, consisted of YAG and ${\gamma}$-Al$_2$O$_3$, were formed by the reaction between Al$_2$O$_3$ and Y$_2$O$_3$. During end-milling process, feed and thrust forces measured for AlN-(10～30) vol％ BN composites decreased with increasing h-BN particles, showing excellent machinability. Also, irrespective of h-BN content, relatively good surfaces with roughness less than 0.5 m (Ra) could be achieved within short lapping time.

• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.1
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• pp.16-23
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• 2016

Purpose: The aim of this study was to evaluate whether fluorides at various pH cause changes in the surface roughness of titanium implants that alter the adherence of bacterial biofilms. Materials and Methods: The titanium disks were assigned randomly to the following seven groups according to the fluoride agents and application time (1 minute or 30 minute) used: control (no treatment); group 1 (1.23% acidulated phosphate fluoride [APF] at pH 3.5 for 1 minute); group 2 (1.23% APF at pH 3.5 for 30 minute); group 3 (1.23% APF at pH 4.0 for 1 minute); group 4 (1.23% APF at pH 4.0 for 30 minute); group 5 (2% NaF gel at pH 7.0 for 1 minute); group 6 (2% NaF gel at pH 7.0 for 30 minute). The surface roughness of the titanium disks and the amount of adherent bacteria were measured. Results: Group 2 showed a significantly greater surface roughness than the control group (P < 0.0001). No significant differences in the amount of surface bacteria were observed between the treated samples and the controls. In addition, there were no significant differences in bacterial adherence relative to the incubation period between the treated samples and the controls. Conclusion: The surface roughness of the titanium disks was significantly greater after treatment with APF at pH 3.5 for 30 min compared with that of the controls. In addition, we found that the amount of Porphyromonas gingivalis, Fusobacterium nucleatum, and Aggregatibactor actinomycetemcomitans was similar among all groups

• Journal of Periodontal and Implant Science
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• v.35 no.1
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• pp.153-161
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• 2005

파이브로넥틴은 세포외기질에 존재하는 당단백질로 세포의 부착, 이동, 성장 및 분화에 관여하며, 섬유아세포 성장인자는 세포의 증식 이동 및 분화에 영향을 주는 중요한 성장인자로 알려져 있다. 최근 연구에 의하면, 파이브로넥틴은 조골세포의 타이태늄 임플란트 표면으로 이주와 증식 및 골생성을 촉진하며, 섬유아세포 성장 인자는 파이브로넥틴에 상승작용을 한다고 보고된 바 있다. 이 실험의 목적은 파이브로넥틴 및 섬유아세포 성장인자의 복합 단백질을 이용하여 타이태늄 임플란트의 골 반응을 알아보는 것이다. 체중 2.5 kg 내외의 건강한 18 마리의 웅성가토를 준비하여 무균 사육하였고, 순수 타이태늄을 절삭가공하여 직경 3.5mm, 길이 6mm 의 machined surface를 지니는 screw type 의 임플란트를 준비하였다. 사람의 유전자를 기초로, 유전자 재조합법을 통해, 적절한 primer를 이용하여 얻은 섬유아세포 성장인자를 파이브로넥틴 III 형 분절의 9-10 번 도메인에 결합시켜 얻은 복합 단백질을 준비된 임플란트에 표면처리하여 실험군으로 하였고, 표면처리하지 않은 임플란트를 대조군으로 하여, 가토의 좌우 경골에 각각 2 개씩의 임플란트를 식립하였다. 4주 후, 가토를 희생시켜 각 경골 당 한 개의 임플란트에서 뒤틀림 제거력을 측정하였고 나머지 임플란트 식립 부위 에서는 경골을 포함하는 조직표본을 제작하였다. 조직표본상에서 골접촉이 가장 좋은 3 개의 나사산의 길이를 측정하고, 나사와 접촉하는 골의 길이를 측정하여 골-임플란트 접촉도를 구하고, 같은 부위에서 나사산 사이의 면적과 골이 차지하는 면적을 비교하여 골생성률을 얻었다. 실험군과 대조군의 결과는 Student t-test 를 이용하여 신뢰도 95% 수준에서 통계학적 유의성을 검정하였다. 파이브로넥틴과 섬유아세포 성장인자의 복합 단백질로 표면처리된 임플란트와 표면처리를 하지 않은 임플란트는 뒤틀림 제거력에서는 통계적 유의성이 나타나지 않았으나, 골-임플란트 접촉도와 골생성률에서 복합 단백질로 처리된 임플란트가 통계적으로 유의하게 높은 결과를 보였다. 이상의 연구결과로, 섬유아세포 성장인자와 파이브로넥틴 복합 단백질로 처리한 타이태늄 임플란트가 주변 골 형성을 촉진시켜, 골유합을 증진시킴을 알 수 있었다. 따라서, 복합 단백질이 타이태늄 임플란트의 성공률을 높이기 위한 표면개질 물질로 이용될 가능성을 확인할 수 있었다.

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.1
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• pp.41-56
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• 2008

The methods of surface modification of commercial implants were various according to the manufacturer. Surface modification of implant may produce diverse physical and chemical surface characteristics resulted from the treatment method and treatment condition. As a result, the bone response might be different. Even though surface modified implants have been used clinically, most researches are focusing on the bone response of surface modified implants comparing to machined implants rather than surface modified commercial implants. This study compare and analyze bone responses of 4 surface modified commercial implants with different shapes and surfaces. Eighty surface modified commercial implants with 4 different surface characteristics were installed in the tibia of white Newzealand rabbits. Biomechanical stability tests and histomorphometric evaluation were done. The results were as follows: 1. Surface modified commercial implants showed stable osseointegration at 6 weeks after installation. 2. Histomorphometric evaluation showed that there was no significant differences in bone to implant contact among 4 different commercial titanium implants. In comparing the implants with different shape the measurement of bone growth in subcortical area would be more reliable than entire bone to implant contact length. 3. Resonance Frequency Analysis showed that there was no significant differences among 4 types of implants, even though they were significantly different in installation. 4. There was significant differences in interfacial shear strength among 4 type of implants. 5. It is difficult to observe accurate bone to implant interface using Micro-CT. However, it is possible to measure the entire contact length of the implant to the bone.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.9
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• pp.107-115
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• 2020

The rotation accuracy of the main spindle that determines the accuracy of CNC machine tools is closely related to the quality of production because it directly affects the shape error and surface roughness of the workpiece. Therefore, the main spindle requires high rotation accuracy, rigidity, and rotation technology. This rotation accuracy is greatly affected by the bearing, center alignment between rotating parts, assembly tolerance, and unbalance of the rotation mass. In this study, the effects of the unbalance of the rotation mass of the main spindle on the rotation accuracy were investigated experimentally. In particular, we tried to study the technical reasons for improving the unbalance of the main spindle and maintaining the rotation accuracy as we verified the correlation between the vibration characteristics of CNC machine tools due to the specifically set unbalance amount and the surface roughness of the workpiece.

• Journal of Surface Science and Engineering
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• v.41 no.6
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• pp.335-340
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• 2008

Cutting performance and wear behavior were studied with the diamond micro-blade of Cu/Sn bond materials containing various amount of lubricant materials such as graphite and $MoS_2$. Measurement of instantaneous electric power consumption for cutting glass workpiece at the constant velocity was conducted and proposed as a method to assess cutting efficiency. The energy consumption of micro-blade for glass cutting decreased with the content of graphite and $MoS_2$ while wear amount of blade in volume increased with the amount of lubricant addition during the dicing test. It is because that hardness, flexural strength, and fracture toughness ($K_{IC}$) reduced with the amount of lubricant addition. Blades with $MoS_2$ additive showed higher mechanical properties than those with graphite additives when the same amount of the lubricant additive in wt.% was added. Due to the lower density of graphite than $MoS_2$, higher volume fraction of graphite could result in stronger effect on lowering electric power consumption by reducing the friction between blade and work piece however increasing wear rate due to the reduction in strength and fracture toughness. Adhesive wearing mode of micro blade could be remarkably improved by the addition of graphite as well as $MoS_2$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.3
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• pp.99-103
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• 1998

The curved surface machined by plate end mill causes a excess non-cutting volume, in these cases ball end mill is used for the curved surfaces. This study is aimed to obtain the optimum cutting conditions of various cutting speed, table speed, tool diameter, radius of curvature roughness on the conditions of various cutting speed, tool diameter, radius of curvature when machining the curved surface using the ball end mill. After designing curve rates, obtaining NC data by CAD/CAM system through CC-Cartesian method and transferred the data through DNC system, we machined the specimens by the CNC machining center, The surface roughness of specimens was measured by surface roughness tester and CNC 3D coordinate measuring machine. The cutting condition were the same as follow velocity; 15, 20, 25 30m/min, feed rate;40, 60, 80, 100m/min and radius of curvature; 30,40,50,60mm, tool diameters; ø8, ø12, ø16, ø 20mm. Analizing the working results, we can acquire the optimum cutting condition of curved specimen at the cutting velocity of 20~25m/min and the feed rate of 80mm/min. As the same cutting condition the best surface roughness was showed at ø16mm of the tool diameter. But the tool diameter was smaller than ø8mm. we could improve for the surface roughness by controlling the cusp.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.269-269
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• 2011

티타늄-알루미늄(Titanium-Aluminum) 질화물(Nitride)은 고경도 난삭재의 고능률 절삭 분야에 사용되는 공구의 수명 향상을 위한 표면처리 소재로 각광을 받고 있다. 건식고속가공을 효과적으로 수행하기 위해서는 코팅막 재료가 가공 중 발생하는 고온에서도 견디는 우수한 내산화성을 지니면서 내마모, 내충격 특성등의 기계적 성질이 우수한 코팅을 필요로 하며 이러한 분야에 TiAlN을 적용하기 위한 많은 연구가 진행되고 있다. 본 연구에서는 아크(Cathodic Arc) 코팅을 시스템을 이용하여 N2 유량변화에 따라 TiAlN 박막을 제조하고 그 특성을 평가하였다. 아크 소스에 장착된 타겟은 120 $mm{\Phi}$, Ti : Al=50 : 50 at% 의 TiAl 타겟을 사용 하였고, 시편과 타겟 간의 거리는 약 30 cm이며, 시편은 SUS를 사용하였다. 시편을 진공용기에 장착하고 ~10-6 Torr까지 진공배기를 실시하고, Ar 가스를 진공용기 내로 공급하여 ~10-4 Torr에서 시편에 bias (Pulse : 400V)를 인가한 후 아크를 발생시켜 약 5분간 청정을 실시하였다. 플라즈마 청정이 끝나면 시편에 인가된 bias를 차단하고 N2 유량을 변화시키며 코팅을 실시하였다. 질소 유량이 증가함에 따라 색상은 회색에서 어두운 보라색으로 변화하였고 SEM 사진을 통해 Micro paticle 이 감소하는 것을 확인 할 수 있었으며 이는 질소유량이 증가 할수록 표면조도 또한 감소하는 분석결과와도 일치하였다. XRD 분석을 통해 질소 유량이 160 sccm 이상에서 TiAlN이 합성되는 것을 볼 수 있었고 질소 유량이 240 sccm일 때 가장 높은 경도를 보였다. 따라서 본 연구에서 얻어진 결과를 바탕으로 더욱 다양한 조건에서 TiAlN 코팅에 응용한다면 다양한 색상 구현과 내마모성 등에서 많은 장점을 얻을 수 있을 것으로 예상된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1643-1648
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• 2010

It is very difficult to polish non-magnetic materials by the magnetic abrasive polishing (MAP) process because magnetic force is required for MAP, but the magnetic force for non.magnetic materials is low. In this study, we aimed to develop a magnetic array table and control the magnetic polarity such that the magnetic force can be increased for the MAP of non-magnetic materials. The newly designed magnetic array table has 32 electro magnets, and the magnetic polarity of each electro-magnet can be easily controlled by changing the electric polarity. It was analytically verified that the magnetic flux density of non-magnetic materials can be varied by varying the applied magnetic polarity.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.77.2-77.2
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• 2010

스크린 프린팅을 이용한 태양전지에서 전극소성 시 알루미늄 후면 전극이 실리콘으로 확산되어 후면전계(Back Surface Field)를 형성한다. 후면전계 형성시 알루미늄과 후면전계 사이에 알루미늄-실리콘 합금이 형성된다. 이 알루미늄-실리콘 합금은 알루미늄 후면전극의 전기전도도 및 휨현상, bead 형성 등에 영향을 끼친다. 본 논문은 알루미늄 페이스트에 첨가된 Glass frit이 알루미늄-실리콘 합금 형성에 끼치는 영향을 관찰하였다. 분산제, 유기바인더, 알루미늄을 섞어 1개의 페이스트를 만들었고, Glass frit을 1%, 2%, 3%, 4%, 5% 씩 첨가하여 총 6개의 알루미늄 페이스트를 만들었다. 절삭손상이 제거된 실리콘 기판의 후면에 알루미늄 페이스트를 스크린 프린팅하여 전극을 소성하였다. 주사전자 현미경(SEM)을 사용하여 시편의 단면사진으로부터 Glass frit 함량에 따른 알루미늄-실리콘 합금층의 변화를 관찰하였다. Glass frit이 첨가되지 않은 페이스트는 소성 후 알루미늄-실리콘 합금이 두껍게 형성되었으나, Glass frit이 첨가된 페이스트는 소성 후 알루미늄-실리콘 합금이 얇게 형성되는 결과를 얻었다. 또한 Glass frit을 첨가함에 따라 표면의 원형 모양의 무늬가 작아지면서 3%부터는 사라지는 것을 확인할 수 있었다.