• Progress in Superconductivity
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• 제7권2호
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• pp.130-134
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• 2006

Buffer layers such as $CeO_2\;and\;Yb_2O_3$ films for YBCO coated conductors were deposited on (100) $SrTiO_3$ single crystals and (100) textured Ni substrates by a metal organic chemical vapor deposition (MOCVD) system of the hot-wall type. The substrates were moved with the velocity of 40 cm/hr. Source flow rate, $Ar/O_2$ flow rate and deposition temperature were main processing variables. The degree of film epitaxy and surface morphology were investigated using XRD and SEM, respectively. On a STO substrate, the $CeO_2$ film was well grown epitaxially above the deposition temperature of $450^{\circ}C$. However, on a Ni substrate, the XRD showed NiO (111) and (200) peaks due to Ni oxidation as well as (111) and (200) film growth. For the films deposited with $O_2$ gas as oxygen source, it was found that the NiO film was formed at the interface between the buffer layer and the Ni substrate. The NiO layer interrupts the epitaxial growth of the buffer layer. It seems that the epitaxial growth of the buffer layer on Ni metal substrates using $O_2$ gas is difficult. We are considering a new method avoiding Ni oxidation with $H_2O$ vapor instead of $O_2$ gas.

• Applied Microscopy
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• 제29권3호
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• pp.281-289
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• 1999

교반관법으로 제조한 $AZ91HP/SiC_p$ Mg 복합재료를 틱소포팅하여 미세조직과 존재상들을 조사하였다. $AZ91HP/SiC_p$ Mg 복합재료를 반응고 가공시 액상율 50% 이상에서 완전 충전이 이루어겼으며 전형적인 반응고 조직을 보였다. 복합재료내의 강화상이 초정 $\alpha$상의 합체, 조대화를 억제하여 보다 용이하게 thixotropic 조직을 가질 수 있었다. TEM 관찰결과, 복합재료내의 계면반응 생성물은 MgO, $Mg_2Si$ 및 $Al_{12}Mg_{17}$등이며, 직접 가압시 정출상으로 나타나는 비평형상인 decagonal T상이 관찰되었으며, 이 상은 간접가압시 안정상인 $Al_6Mn$의 형태로 관찰되었다. 이는 간접가압시 승온시간이 직접가압보다 상대적으로 길어, 비평형의 decagonal T상이 안정한 $Al_6Mn$상으로 생성된 것으로 판단된다. 아직까지 생성과정이 명확하진 않으나 교반관법으로 제조 후, 2차가압 성형시 비평형상의 존재는 재료의 강화에 기여할 것으로 판단된다.

• 한국분말재료학회지
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• 제11권5호
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• pp.412-420
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• 2004

The purpose of the present study is to determine an optimum composition using cheaper powders keeping with high performance of hard rock cutting diamond saw blade. With 50Fe-20(Cu . Sn)-30Co specimen, a part of Co was replaced by Ni(5%, 10%, and 15%, respectively). These specimens were hot pressed and sintered for predetermined time at various temperature. Sintering is performed by two different methods of temperature controlled method and specimen dimension controlled method. In order to determine the property of the sintered diamond saw blade, 3 point bending tester, X-ray diffractometer, and SEM were used. As the Co in the bond alloy was replaced by Ni, the hardness of the specimen increased. Thus the 50Fe-20(CuㆍSn)-15Co-15Ni specimen showed the maximum hardness of 104(HRB). The results of 3 point bending test showed that flexure strength decreased along with increase in Ni content. This is attributed to the formation of intermetallic compound(Ni$_{x}$Sn) determined by X-ray diffraction. The fracture surface after 3 point bending test showed that diamond was fractured in the specimen containing 0%, 5%, and 10%Ni, and the fracture occurred at the interface between diamond and matrix in the specimen containing 15%Ni. The cutting ability test showed that the abrasive property was not changed in the specimen containing 0%, 5%, and 10%Ni. The optimum composition determined in this study is 50Fe-20(CuㆍSn)-20Co-10Ni.

• 대한치과보철학회지
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• 제43권2호
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• pp.149-157
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• 2005

Statement of problem. Dental ceramics exhibit excellent esthetic property, compressive strength, chemical durability biocompatibility and translucency. However, it suffers from inherent brittle fractures. Various techniques and materials for intraoral porcelain repair has been suggested. Purpose. This study is to compare the tensile bond strength of four commonly used porcelain repair systems (Vivadent, Bisco, Ulttadent, Voco) and to insure the best system for the clinical application to the fractured porcelain. Materials and methods. A total of fifty specimens were fabricated. Specimens were stored in $37^{\circ}C$ distilled water for 7 days and thermocycling was performed(1000 cycles), and subjected to a tensile force parallel to the repair resin and porcelain interface by use of an Universal Testing Machine. Result. 1. Voco showed the highest tensile bond strength. In decreasing order, the tensile bond strength of the other materials was as follows : Ultradent, Bisco, Vivadent. 2. There was a statistically significant difference between the porcelain repair systems(Voco, Ultradent > Bisco, Yivadent) (p<0.05). 3. SEM examination of prepared porcelain surfaces revealed that the surface treated with Voco showed brittle fracture. However, Ultradent, Bisco and Vivadent showed ductile fracture. 4. All specimens treated with four porcelain repair systems showed adhesive failure between porcelain and composite resin.

• 한국재료학회지
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• 제12권7호
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• pp.528-532
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• 2002

Anodic $TiO_2$film on Ti substrate was fabricated at 180V in sulfuric acid solutions containing phosphoric acid and hydrogen peroxide. Effects of the anodizing conditions on the morphology of the oxide layers, and chemical states of the component elements of the layers were studied primarily using SEM, XRD, AFM, and XPS. The pores in the oxide layer was not uniform in size, shape, and growth direction particularly near the interface between the substrate and the oxide layer, compared with those of the surface layer. The formation of irregular type of pores seemed to be attributed to spark discharge phenomena which heavily occurred during increasing the anodic voltage. The pore diameter and the cell size increased, and the number of cells per unit area decreased with the increasing time. From the XPS results, it was shown that component elements of the electrolytes, P and S, existed in the chemical states of $PO_4^{-3}$ , $P_2$$O_{5}$, $SO_4^{-2}$ , $SO_3^{-2}$ , P, S, etc., which were penetrated from the electrolytes into the oxide layer during anodization.

• Investigative Magnetic Resonance Imaging
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• 제23권3호
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• pp.228-240
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• 2019

Purpose: The aim of this study is to evaluate the T2 value of the articular cartilage of the glenohumeral joint in rotator cuff disease displayed on 3.0T MRI and to apply it in clinical practice. Materials and Methods: This study involved sixty-two patients who underwent shoulder MRI containing T2 mapping. The mean T2 value was measured by placing a free hand ROI over the glenoid or humeral cartilage from the bone-cartilage interface to the articular surface on three consecutive, oblique coronal images. The drawn ROI was subsequently divided into superior and inferior segments. The assessed mean T2 values of the articular cartilage of the glenohumeral joint were compared and evaluated based on the degree of rotator cuff tear, the degree of fatty atrophy of the rotator cuff, and the acromiohumeral distance. Results: ICC values between two readers indicated moderate or good reproducibility. The mean T2 value for the articular cartilage of the glenoid and humeral head cartilage failed to show any significant difference based on the degree of rotator cuff tear. However, the mean T2 values of articular cartilage, based on fatty atrophy, tended to be higher in fatty atrophy 3 or fatty atrophy 4 groups while some subregions displayed significantly higher mean T2 values. There was no correlation between the acromiohumeral distance and the mean T2 values of the articular cartilage of the glenoid and humeral head. Conclusion: T2 mapping of the glenohumeral joint failed to show any significant difference in quantitative analysis of the degenerative change of the articular cartilage based on the degree of rotator cuff tear. However, it also offers quantitative information on the degenerative change of cartilage of the glenohumeral joint in patients with rotator cuff tear and severe fatty atrophy of the rotator cuff.

• 마이크로전자및패키징학회지
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• 제28권2호
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• pp.95-103
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• 2021

대표적인 저온솔더인 Sn-58Bi에 Ru nanoparticles을 첨가하여 Sn-58Bi-xRu 복합솔더를 제작하고 Cu/OSP 및 ENIG 표면처리된 PCB 기판과 반응시켜 계면반응 및 솔더조인트 신뢰성을 분석하였다. Cu/OSP와의 반응에서 형성된 Cu₆Sn₅ IMC는 Ru 함량에 따른 두께 변화가 거의 없고 100hr aging 후에도 큰 변화없이 고속 전단시험시 솔더 내부로 연성파괴가 발생하였다. ENIG 와의 반응시에는 Ru 함량이 증가함에 따라서 Ni₃Sn₄ IMC 두께가 감소하는 경향을 보였으며 일부 시편에서 ENIG 특유의 취성파괴 현상이 발견되었다. Ru 원소는 계면 부근에서 발견되지 않아서 계면반응에 크게 관여하지 않는 것으로 판단되며 주로 Bi phase와 함께 존재하는 것으로 분석되고 있는데 어떠한 형태로 두 원소가 공존하고 있는지에 대해서는 추가적인 연구가 필요하다.

• 풍력에너지저널
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• 제14권3호
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• pp.83-90
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• 2023

The purpose of this study is to evaluate the inter-laminar fracture toughness characteristics of CFRP pultrusion spar cap materials reinforced with non-woven glass fabric. Test specimens were fabricated by the infusion technique. A non-woven glass fabric and artificial defects were embedded on the middle surface between two pultruded CFRP panels. Double cantilever beam (DCB) and End Notched Flexure (ENF) tests were performed according to ASTM standards. Fracture toughness and crack propagation characteristics were evaluated with load-displacement curves and delamination resistance curves (R-Curve). The fracture toughness results were calculated by compliance calibration (CC) method. The initiation and propagation values of Mode-I critical strain energy release rate value G_Ic were 1.357 kJ/m2 and 1.397 kJ/m2, respectively, and Mode-II critical strain energy release rate values G_IIc were 4.053 kJ/m2 for non-precracked test and 4.547 kJ/m2 for precracked test. It was found that the fracture toughness properties of the CFRP pultrusion spar-cap are influenced by the interface between the layers of CFRP and glass fiber non-woven.

• 한국결정학회지
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• 제3권2호
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• pp.98-110
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• 1992

Si(100) 기판위에 화학 기 장 증착법으로 상압에서 베타 탄화규소(β-SiC) 박막을 성장시키고 증착 조건이 박막의 물성 특히,기판 방향으로의 배향성과 결 정성에 미치는 영향에 대하여 고찰하여 보았다. 원료 가스로 SiH4와 CH4, 전달 가스로 H2를 사용하였다. 성장 온도, 원료 가스의 조성비,전달 가스에 대한 전 체 원료 가스의 비를 변화시키면서,이들 증착조건이 성장된 박막의 물성에 미치는 영향을 SEM, a-step, XRD, Raman Sepctroscopy, TEM 등을 이용하여 분석하였다. Chemical conversion과정을 통하여 SiC 버퍼층을 형성시킬 때 양질의 박막을 얻을 수 있었으며, CH4가SiH4에 대해 과량일때와 온도가 1150℃ 이상 일때 결정성이 좋아짐을 알 수 있었다. 또한, 결정성 이 좋아질수록 기판 방향으로의 배향성이 좋아짐도 관찰되었다. 결정성이 좋은 박막의 TEM분석 결과 성장 초기에 비해 표면으로 갈수록 결정이 커지는 것을 알 수 있었으며, 적층결함 및 쌍정 등의 분포정도는 원료 가스의 조성비와 무관하였다.

• Composites Research
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• 제17권1호
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• pp.29-37
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• 2004

하니컴 샌드위치 복합재료(HSC) 구조물은 높은 강성 및 경량화가 요구되는 항공ㆍ우주 및 군수 산업 등에 폭 넓게 이용되고 있으며 하니컴 샌드위치 복합재료의 정확한 강도 해석에 있어서 하니컴 코어의 기계적 물성 예측이 필요하다. 본 연구에서는 하니컴 코어 벽의 굽힘, 축 방향 및 전단 변형을 고려한 에너지 법을 사용하여 하니컴 코어 재료의 각 방향 탄성계수 및 포아송 비와 같은 기계적 물성 값을 구하기 위한 예측식을 유도하고, 이 이론 예측값이 유한요소 해석 프로그램인 ABAQUS 6.3을 이용하여 구한 결과와 거의 일치하고 있음을 알았다. 또한 하니컴 샌드위치 복합재료 평판의 인장 실험 및 유한요소 시뮬레이션을 수행하여 변형 거동 예측 및 층간 응력을 해석하였다. 하니컴 코어층과 표면층 사이의 전단 응력의 증가는 HSC 평판의 층간분리 현상의 주원인임을 알 수 있었다.