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여러 가지 크기의 $SiC_{platelet}$ Seed를 함유한 SiC 세라믹스의 미세구조 및 기계적 특성
최명제,박찬,박동수,김해두,Choi, Myoung-Je,Park, Chan,Park, Dong-Soo,Kim, Hai-Doo 한국세라믹학회 1999 한국세라믹학회지 Vol.36 No.10
Liquid phase sintered silicon carbides were obtained by sintering of $\alpha$-SiC and $\beta$-SiC powders as starting materials at 2173K and 2273K respectively. The SiCplatelet seeds of different sizes were obtained by a repeated ball milling and sedimentation. Their mean size (d50) were 2.217 ${\mu}{\textrm}{m}$ 13.67 ${\mu}{\textrm}{m}$, 22.17${\mu}{\textrm}{m}$ respectively 6wt%Al2O3-4 wt% Y2O3 was used as the sintering additives for the liquid phase sintering. The two silicon carbides had a bimodal microstructure consisting of small matrix grains and large platelike grains when the SiCplatelet seeds were added. In the case of the $\beta$-SiC the appreciable phase transformation occurred as sintering temperature increased from 2173K to 2273K and resulted in matrix shape change from equiaxed into platelike grains. In contrast there was no shape change for the $\alpha$-SiC. The size of large grains in the $\alpha$-SiC of large grains in the $\alpha$-SiC was larger than that of the large grains in the $\beta$-SiC These results suggested that the growth of the $\alpha$-SiCplatelet in the $\alpha$-SiC matrix was more favored than that of the $\alpha$-SiCplatelet in the $\beta$-SiC matix. The three point flexural strength decreased as the added seed size increased. Fracture toughness values of samples sintered at 2273K were higher than those of samples sintered at 2173K.
최명제,김민숙 대한신경정신의학회 2015 신경정신의학 Vol.54 No.4
Objectives This study evaluated the structural characteristics of a scientific network of psychiatry and the effect of social networks on the performance of scholars. Methods The data were extracted from 261 articles published from 1996 to 2013 in the Journal of the Korean Neuropsychiatric Association, and were transformed into a co-author and their affiliation matrix. We used measures from network analysis (i.e., degree centrality, weighted degree centrality, eigenvector centrality, betweenness centrality) for evaluating the effect of co-authorship network on the performance of scholars (h-index). Netminer 4.1 was used for the network analysis. Results Both co-authorship and affiliation network demonstrated power law distribution. Coauthor’s centralities were correlated with research achievements. Results from poisson regression analysis showed that the eigenvector centrality has a significant positive influence on the hindex and the weighted degree centrality has a significant negative influence on the h-index. Conclusion This study shows that the small world phenomenon exists in the psychiatric coauthorship network, and finds collaboration patterns and effects on scientific performance. The results suggest that in order to achieve better research performance it would be helpful for scholars to work with other well-performing scholars and avoid other scholars who previously worked together.
최명제,노태욱,박찬,박동수,김해두,Choi, Myoung-Je,Roh, Tae-Wook,Park, Chan,Park, Dong-Soo,Kim, Hai-Doo 한국세라믹학회 2000 한국세라믹학회지 Vol.37 No.5
In this investigation, we fabricated RBSN (Reaction Bonded Silicon Nitride) using the static nitriding system which could be advantageous for commercialization. Firstly, Si compacts of different sizes were made, and then nitridation rates were investigated as a function of added static gas pressure. The reaction schedule was obtained by pre-experiments. In case of small samples, the variation of ${\alpha}$, ${\beta}$ phases between the inside and the outside region of the specimens was examined after the samples were nitrided under 1 bar and 1.5 bar reaction pressure. On the other hand, large samples of Si compact with the size of 36 mm for diameter and 23 mm for thickness were nitrided for 26 hours of the total nitridation time, which showed a complete and homogeneous nitriding reaction from the outside to the inside of the samples, although the time was considerably shorter than that needed for convertional nitridation. Nitridation rates obtained at the early stage of reaction were proportional to the reaction gas pressures. The sequences of the nitridation reaction with the thickness were as follows 1) the outside, 2) the inside and 3) the intermediate area of the specimen. These results wer eobtained from the coloration of cross sectioned specimens that had various nitridation rates. Total nitriding reaction kinetics was controlled by chemical reaction, not by diffusion of the nitrogen gas.