• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.151-154
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• 2004

Despite of the excellent properties of carbon nanofiber, The properties of carbon nanofiber filled polymer composites were not increased largely. The reason is that it is still difficult to ensure the uniform dispersion of carbon nanofiber in a polymer matrix. In this study, For improvement properties of carbon nanofiber filled epoxy composites, the effect of dispersion was investigated. The compounds were prepared by two methods, solution blending and mechanical mixing. Mixing of solution blending method was used using ultrasonic. Dispersion of carbon nanofiber was observed by optical microscope and scanning electron microscope (SEM). UV adsorption and turbidity measured by UV spectrometer was used for the comparison of dispersion of carbon nanofiber.

• Computers and Concrete
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• 제16권3호
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• pp.487-502
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• 2015

This study investigated particle expansion in basic oxygen furnace slag (BOF) and desulfurization slag (DSS) after heat curing by using the volume method. Concrete hydration was accelerated by heat curing. The compressive strength, ultrasonic pulse velocity, and resistivity of the concrete were analyzed. Maximum expansion occurred in the BOF and DSS samples containing 0.30-0.60 mm and 0.60-1.18 mm particles, respectively. Deterioration was more severe in the BOF samples. In the slag aggregates for the complete replacement of fine aggregate, severe fractures occurred in both the BOF and DSS samples. Scanning electron microscopy revealed excess CH after curing, which caused peripheral hydration products to become extruded, resulting in fracture.

• 한국세라믹학회지
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• 제54권3호
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• pp.205-210
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• 2017

In this study, we examined the photo-degradation efficiency of $CoSe_2$-Graphene-$TiO_2$ ($CoSe_2-G-TiO_2$) nanocomposites under visible light irradiation using rhodamine B (RhB) as standard dye. $CoSe_2-G-TiO_2$ nanocomposites were synthesized by ultrasonication and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopic analysis and UV-Vis absorbance spectra analysis. Our results show that the $CoSe_2-G-TiO_2$ nanocomposite exhibited significant photo degradation efficiency compared to pure $TiO_2$ and $CoSe_2-G$, approximately 85.2% of the rhodamine (Rh B) degraded after 2.5 h. It is concluded that the $CoSe_2-G-TiO_2$ nanocomposite is a promising candidate for use in dye pollutants.

• Tribology and Lubricants
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• 제39권6호
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• pp.228-234
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• 2023

In this study, reciprocating wear tests are performed on AISI 52100 bearing steel to investigate its tribological behavior in a hexagonal boron nitride (h-BN) water solution. The h-BN-based aqueous lubricant is prepared using an atoxic procedure called ultrasonic sonication in pure water. Ball-on-flat reciprocating sliding experiments are conducted, where the ball is slewed on a fixed flat at 50-㎛ displacement. The lubricating behavior of h-BN is compared with that of deionized (DI) water. Results show that the friction coefficient is higher in h-BN testing than that in DI tests, but the results are equalized as the friction coefficient reaches a stable level. Scanning electron microscopic images reveal significant material loss in the center and mild abrasion on the edge of the wear scar in h-BN tests. However, these effects are minor in DI water situations. The results of energy-dispersive X-ray spectroscopy show that considerable oxidation occurs in the central zone of the wear scar in h-BN cases with strong adhesion and material removal. These findings reveal the importance of determining ideal circumstances that can tolerate material friction and wear.

• 한국구조물진단유지관리공학회 논문집
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• 제18권1호
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• pp.166-173
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• 2014

본 연구에서는 레이저 가진을 이용한 초음파 전파 영상 기반 배관 비파괴 검사에 관해 다룬다. 손상의 영상화를 위해 갈바노미터 기반 레이저 미러 스캐너와 Q-Switch Nd: YAG 레이저 시스템을 사용하였다. 레이저 시스템을 가진원으로 사용하면 빠른 속도로 비접촉 초음파 가진이 가능하며, 온도의 변화가 급격한 환경이나 유해 물질이 포함된 환경에서도 대상 구조물의 원거리 가진이 가능하다. 또한 공간 해상도가 높으며, 입사각이 넓어 표면 형상이 복잡한 대상 구조물도 가진이 가능하다. 본 연구에서는 이러한 레이저 시스템으로부터 생성된 유도 초음파를 단일 PZT 센서를 사용하여 계측하고, 계측된 신호는 레이저 가진점에 해당하는 좌표점에 나열함으로써 2차원 공간좌표 및 시간축을 더한 초음파 전파 영상 생성을 위한 3차원 데이터를 구성한다. 이 데이터를 시간 축에 따라 연속적으로 반복 재생하면 초음파 전파 영상을 구할 수 있다. 이 때 웨이블릿 변환을 이용하여 계측 신호의 특정 주파수 성분을 추출해냄으로써 관찰하고자 하는 특정 유도 초음파 모드를 추출할 수 있다. 이러한 일련의 과정으로부터 획득한 초음파 전파 영상 데이터를 시간-공간 영역에서 주파수-wavenumber 영역으로 변환시켜줌으로써 손상 특성을 추출할 수 있다. 본 연구에서는 손상의 진단 및 위치 추정을 위해 wavenumber 필터링 기술을 적용하였으며, 시스템 검증을 위해 다양한 배관구조물 Testbed를 대상으로 실험을 수행하였다.

• 대한치과보철학회지
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• 제40권3호
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• pp.275-286
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• 2002

Statement of problem. Surface alteration of the implant screws after function may be associated with mechanical failure. Theses metal fatigue appears to be the most common cause of structural failure. Purpose. The purpose of this study was to evaluate surface alteration of the implant screws after function through the examination of used and unused implant screws in SEM(scanning electron microscope). Materials and methods. In this study, abutment screws(Steri-oss, 3i), gold retaining screw(3i) and titanium retaining screw(3i) were retrieved from patients. New, unused abutment and retaining screws were prepared for control group. Each of the old, used screws was retrieved with a screwdriver. And retrieved implant complex of Steri-oss system was prepared for this study. Then, SEM investigation and EDS analysis of abutment and retaining screws were performed. And SEM investigation of cross-sectioned sample of retrieved implant complex was performed. Results. In the case of new, unused implant screws, as maunfactured circumferential grooves are regularly examined and screw thread are sharply remained. Before ultrasonic cleansing of old, used implant screw, a lot of accumulation and corrosion products were existed. After ultrasonic cleansing of old, used implant screws, circumferential grooves as examined before function were randomly deepened and scratches increased. Also, dull screw thread was examined. More surface alterations after function were examined in titanium screw than gold screw. And more surface alteration was examined when retrieved with driver than retrieved without driver. Conclusions. These surface alteration after function may result in the screw instability. Regularly cleansing and exchange of screws was recommended. We recommend the use of gold screw rather than titanium screw, and careful manipulation of the driver.

• Tribology and Lubricants
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• 제36권1호
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• pp.47-54
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• 2020

In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment at room and high temperatures (RT and HT of 400℃) on friction and wear behavior of Ti-6Al-4V alloy prepared by selective laser melting (SLM) were investigated. The objective of this study is to improve the mechanical properties and frictional behavior of Ti-6Al-4V alloy by UNSM treatment. Dry friction and wear tests were conducted using a ball-on-disk method at RT with a bearing steel as the counter ball. Due to the high HT and UNSM treatment, the surface hardness tended to increase and surface roughness tended to reduce. X-ray diffraction (XRD) analysis showed that nanocrystallization structure and compressive residual stress were formed at the surface layer after UNSM treatment at both RT and HT. After UNSM treatment, it was observed that the wear rate was reduced by about 6% for the specimen treated at RT and a 28% reduction for the specimen treated at HT in comparison with the untreated one. Based on scanning electron microscope (SEM) images showed that the damage caused by fatigue wear occurred in the wear track of the heat-treated specimen, and it is believed to be the cause of the highest wear rate. Mechanical properties and wear resistance of Ti-6Al-4V alloy were improved and prospect of industrial application was confirmed. Further research is still required to improve the characteristics of SLM Ti-6Al-4V alloy to the level of wrought Ti-6Al-4V alloy.

• The Journal of Advanced Prosthodontics
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• 제5권3호
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• pp.341-350
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• 2013

PURPOSE. To evaluate adherence of human gingival fibroblasts (HGFs) to transmucosal abutment of dental implant with different surface conditions with time and to investigate the roles of focal adhesion linker proteins (FALPs) involved in HGFs adhesion to abutment surfaces. MATERIALS AND METHODS. Morphologies of cultured HGFs on titanium and ceramic discs with different surface were observed by scanning electron microscopy. Biocompatibility and focal adhesion were evaluated by ultrasonic wave application and cell viability assay. FALPs expression levels were assessed by RT-PCR and western blot. RESULTS. There seemed to be little difference in biocompatibility and adhesion strength of HGFs depending on the surface conditions and materials. In all experimental groups, the number of cells remaining on the disc surface after ultrasonic wave application increased more than 2 times at 3 days after seeding compared to 1-day cultured cells and this continued until 7 days of culture. FALPs expression levels, especially of vinculin and paxillin, also increased in 5-day cultured cells compared to 1-day cultured fibroblasts on the disc surface. CONCLUSION. These results might suggest that the strength of adhesion of fibroblasts to transmucosal abutment surfaces increases with time and it seemed to be related to expressions of FALPs.

• 센서학회지
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• 제6권2호
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• pp.155-162
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• 1997

zinc acetate를 포함하는 용액으로부터 r-plane 사파이어 기판 위에 ZnO 막(膜)을 증착하였다. 초음파(超音波) 발생기(發生器)로 용액을 진동시켜 증기입자를 만든 후 이것을 고온 반응로(反應盧) 내에서 열분해(熱分解) 시켜 막(膜)을 증착하였다. 제조된 막(膜)의 결정성, 표면형태 및 조성을 XRD, SEM 및 AES로 각각 분석하였다. 기판온도가 막(膜)의 특성에 미치는 영향에 대해 조사하였다. 기판온도 $300^{\circ}C$에서 (110) 방향으로 강하게 성장된 막(膜)을 얻을 수 있었다. 구리의 첨가(添加)와 습식산화(濕式酸化)에 의해 막(膜)의 저항율을 $3{\times}10^{6}{\Omega}{\cdot}cm$이상으로 높일 수 있었다.

• 비파괴검사학회지
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• 제22권5호
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• pp.508-515
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• 2002

다층재료의 접합특성 평가는 오랫동안 많은 논의가 있어 왔는데, 본 연구에서는 후방복사 초음파 기술을 사용하여 여러 충이 있는 재료의 특성을 평가하기 위한 자동화된 시스템을 개발하고 스틸 판재와 고무가 접합된 스틸 판재의 후방복사 프로파일을 획득하였다. 후방복사의 rf 파형과 주파수 스펙트럼은 리키 램파 모드들의 특성을 나타내고 있다. 집합된 고무 두께의 증가에 따라 입사각이 $13.4^{\circ}$일 때의 후방복사 진폭이 지수적으로 감소함을 보이며 부분적으로 고무가 접합된 시편에서 선택되어진 입사각으로 입사위치를 바꾸어가며 스캐닝한 결과 정확하게 고무가 접합되어 있지 않은 지역을 결정할 수 있었다. 리키 램파에 의한 후방복사는 판재의 물성은 물론이고 다층 재료의 접합특성 평가에 활용할 수 있다.