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- 저자 : Kohyama Akira (검색결과 6 건)
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Process development for porous Si-based ceramics by a decarburization method
박이현,Tatsuya Hinoki,Akira Kohyama 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.3
Recently, there has been an increasing interest in the applications of porous SiC ceramics as functional materials. A number of manufacturing approaches have been applied to fabricate porous SiC including polymer pyrolysis, oxidation bonding, and reaction bonding. However, these processes are complicated and conventional porous SiC shows insufficient physical and chemical stability under a high temperature environment. Therefore, from the view point of safety and stability, it is necessary to develop an uncomplicated manufacturing method for high performance porous SiC ceramics. In this study, SiC nano-powder and carbon particles have been used as starting material and pore former, respectively. Mixed powders were hot-pressed under a pressure of 20 MPa at 1900℃ for 1 h. Carbon powder which was added to the sintered body was burned out by a decarburization process in air at 700℃. The porosity was measured by the Archimedes method with an immersion medium of water and an image analysis method. The microstructure was examined by scanning electron microscopy. Mechanical properties were investigated using three-point bend test. It was established that the critical additive amount of carbon particles for porous SiC ceramics was about 20 vol.%, through the microstructure and thermogravimetric analysis during the decarburization process. The porosity of the porous SiC ceramics could be controlled with a high degree of accuracy, from the relationship between the added amount of carbon particles and porosity. The flexural strength of the porous SiC ceramics with 50% pores, where spherical pores were introduced, was about 170MPa. These porous SiC ceramics exhibited a substantially high strength in comparison with other conventionally processed porous SiC ceramics, due to their robust microstructures consisting of spherical pores.
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Tsutomu Ida,Hiroyuki Fujiwara,Takahiro Kiriu,Yoshimi Taniguchi,Akira Kohyama 대한부인종양학회 2019 Journal of Gynecologic Oncology Vol.30 No.6
Objective: To investigate the relationship between the precursors of high grade serousovarian cancer (HGSOC) and the characteristics of patients with a low HGSOC risk in termsof the effects of pregnancy. Methods: We prospectively examined consecutive cases in which the bilateral fallopian tubeswere removed during benign gynecological or obstetric surgery and assessed the relationshipbetween the patient characteristics, including parity and pregnancy, and the incidence ofHGSOC precursors. All the fallopian tubes were examined by applying the Sectioning andExtensively Examining the Fimbriated End (SEE-FIM) Protocol. Results: Of the 113 patients enrolled, 67 were gynecological and 46 were obstetric. The p53signature was identified in 21 patients. No other precursors were identified. In a comparisonof the p53 signature-positive and negative groups, parous women and pregnant womenwere significantly fewer in the p53 signature-positive group (53% vs. 86%, p=0.002, 10%vs. 47%, p=0.001, respectively). Current pregnancy was also associated with a significantlylower incidence of the p53 signature after multivariate adjustment (odds ratio [OR]=0.112;95% confidence interval [95% CI]=0.017–0.731; p=0.022). Among gynecological patients,parous women were fewer in the p53 signature-positive group on univariate (47% vs. 73%,p=0.047) and multivariate analysis (OR=0.252; 95% CI=0.069–0.911; p=0.036). No othercharacteristics were associated with p53 signature positivity. Conclusions: The incidence of the p53 signature was significantly lower in parous womenand pregnant women. This decreased incidence of early phase serous carcinogenesis may beone of the possible mechanisms underlying HGSOC risk reduction among parous women.
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SiC/SiC 복합재료 세라믹스 표면균열 탐지를 위한 초음파법 적용에 관한 기초연구
남기우(Ki Woo Nam),이건찬(Kun Chan Lee),香山晃(Akira Kohyama) 한국비파괴검사학회 2009 한국비파괴검사학회지 Vol.29 No.5
세라믹스의 비파괴평가 기술은 산업분야에 응용하기 위한 세라믹스 신뢰성 개발에 있어서 필수적인 기술이다. 본 연구는 초음파 C-Scan 방식을 이용하여 SiC 세라믹스의 표면균열을 탐상하기 위한 실험적 연구결과를 제시하고자 한다. 이를 위해 SDS-win과 μ-SDS 두 종류의 초음파 장치와 25, 50 및 125 ㎒의 초음파센서를 이용하여 세라믹스의 표면균열 탐상 가능성에 대해 실험적인 연구를 수행하였다. 본 연구 결과, 세라믹스의 표면미소균열은 결국 25 및 50 ㎒ 센스로 정밀하게 검출할 수 없었으나, 125 ㎒ 센서에 의한 집속법 탐상 결과 희미한 형상 정도를 검출할 수 있었으며, 비집속법의 경우는 비커스 압입자의 형상 검출이 가능함을 알 수 있었다. 따라서 본 연구를 통하여, 초음파 C-Scan 집속 및 비집속 방법은 미세균열의 탐상방식으로 어느 정도 접근 가능함을 실험적으로 확인하였다. Nondestructive evaluation(NDE) of ceramic matrix composites is essential for developing reliable ceramics for industrial applications. In the work, C-Scan image analysis has been used to characterize surface crack of SiC ceramics nondestructively. The possibility of detection of surface crack were carried out experimentally by two types of ultrasonic equipment of SDS-win and μ-SDS, and three types of transducer of 25, 50 and 125 ㎒. A surface micro-crack of ceramics was not detected by transducer of 25 ㎒ and 50 ㎒. Though the focus method was detected dimly the crack by transducer of 125 ㎒, the defocus method could detect the shape of diamond indenter. As a whole, the focus method and the defocus method came to the conclusion that micro crack have a good possibility for detection.
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차세대 원자력 시스템용 탄화규소계 세라믹스의 제조와 이온조사 특성 평가
김원주,강석민,박경환,류우석,박지연,Kim, Weon-Ju,Kang, Seok-Min,Park, Kyeong-Hwan,Kohyama Akira,Ryu, Woo-Seog,Park, Ji-Yeon 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.8
SiC-based ceramics are considered as candidate materials for the advanced nuclear energy systems such as the generation IV reactors and the fusion reactors due to their excellent high-temperature strength and irradiation resistance. The advanced nuclear energy systems and their main components adopting ceramic composites were briefly reviewed. A novel fabrication method of $SiC_f/SiC$ composites by introducing SiC whiskers was also described. In addition, the charged-particle irradiation ($Si^{2+}$ and $H^{+}$ ion) into CVD SiC was carried out to simulate the severe environments of the advanced nuclear reactors. SiC whiskers grown in the fiber preform increased the matrix infiltration rate by more than $60\%$ compared to the conventional CVI process. The highly crystalline and pure SiC showed little degradation in hardness and elastic modulus up to a damage level of 10 dpa at $1000^{\circ}C$.
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