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목탄이 첨가된 $MgB_2$의 초전도 성질에 미치는 열처리 온도의 영향
김남규,탄카이신,전병혁,박해웅,주진호,김찬중,Kim, Nam-Kyu,Tana, Kai Sin,Jun, Byung-Hyuk,Park, Hai-Woong,Joo, Jin-Ho,Kim, Chan-Joong 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1
Charcoal was used as a carbon source for improving the critical current density of $MgB_2$ and the effect of annealing temperature on the $J_c$ of $MgB_2$ was investigated. The charcoal powder used in this study was $1{\sim}2$ microns in size and was prepared by wet attrition milling. $MgB_2$ bulk samples with a nominal composition of $Mg(B_{0.95}C_{0.05})_2$ were prepared by in situ process of Mg and B powders. The powder mixture was uniaxially compacted into pellets and heat treated at temperatures of $650^{\circ}C\;-\;1000^{\circ}C$ for 30 minutes in flowing Ar gas. It was found that superconducting transition temperature of $Mg(B_{0.95}C_{0.05})_2$ decreased by charcoal additions which indicates the carbon substitution for boron site. $J_c$ of $Mg(B_{0.95}C_{0.05})_2$ was lower than that of the undoped $MgB_2$ at the magnetic fields smaller than 4 Tesla, while it was higher than that of the undoped sample especially at the magnetic field higher than 4 T. High temperature annealing seems to be effective in increasing $J_c$ due to the enhanced carbon diffusion into boron sites.
마그네슘과 글리세린 처리한 붕소 분말로 합성한 Mg(B<sub>1-x</sub>C<sub>x</sub>)<sub>2</sub>의 초전도 특성
김이정,전병혁,박순동,탄카이신,김봉구,손재민,김찬중,Kim, Yi-Jeong,Jun, Byung-Hyuk,Park, Soon-Dong,Tan, Kai Sin,Kim, Bong-Goo,Sohn, Jae-Min,Kim, Chan-Joong 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.3
Carbon was known to be one of effective additives which can improve the flux pinning of $MgB_2$ at high magnetic fields. In this study, glycerin $(C_3H_8O_3)$ was selected as a chemical carbon source for the improvement of critical current density of $MgB_2$. In order to replace some of boron atoms by carbon atoms, the boron powder was heat-treated with liquid glycerin. The glycerin-treated boron powder was mixed with an appropriate amount of magnesium powder to $MgB_2$ composition and the powder pallets were heat treated at $650^{\circ}C\;and\;900^{\circ}C$ for 30 min in a flowing argon gas. It was found that the superconducting transition temperature $(T_c)$ of $Mg(B_{1-x}C_x)_2$ prepared using glycerin-treated boron powder was 36.6 K, which is slightly smaller than $T_c$(37.1 K) of undoped $MgB_2$. The critical current density $(J_c)$ of $Mg(B_{1-x}C_x)_2$ was higher than that of undoped $MgB_2$ and the $T_c$ improvement effect was more remarkable at higher magnetic fields. The $T_c$, decrease and $J_c$ increase associated with the glycerin treatment for boron powder was explained in terms of the carbon substitution to boron site.