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산화반응에 의한 이방성 메조페이스 탄소섬유의 구조 변화(I) - TEM 및 XRD를 이용한 분석
노재승,Roh, J.S. 한국재료학회 2003 한국재료학회지 Vol.13 No.12
Structural changes during oxidation of anisotopic mesophase carbon fiber(AMCFs) have been observed with TEM and XRD. It was shown that the AMCFs are three dimensionally stacked structure of turbostratic layers, and are non-homogeneous structure which consist of the highly ordered areas and the random areas. The $d_{ 002}$, Lc, and La of AMCFs which were measured by XRD were 3.44, 146, and $135\AA$, respectively. It was observed that the oxidation initiated at the random areas, because the $d_{002}$ / decreased to the value of 3.41 $\AA$ during initial oxidation stage. It was also observed that the La of the oxidized AMCFs increased up to 182 $\AA$ during the whole oxidation process, and the $d_{002}$ of that increases up to 9.44 $\AA$ when the burn-off is over the degree of 20%. Therefore, it was suggested that the micro-crystalline grew up by heat treatment effects during the fibers were oxidized, In addition, it was shown that there was difference in the measured value of La by XRD and TEM, in case of 39% oxidized fibers for example, the measured La was $ 165\AA$ by XRD and in the range of 180∼220 $\AA$ by TEM.
이산화탄소를 이용한 등방성 탄소섬유의 활성화과정 중 발생하는 구조변화(II)-TEM을 이용한 분석
노재승,Roh, J.S. 한국재료학회 2003 한국재료학회지 Vol.13 No.11
A development of micropores of $CO_2$activated isotropic carbon fibers from TEM was observed. It was observed that the micropores of activated carbon fibers(ACFs) were consisted of slit-shaped pores(SP) and cylinder-shaped pores(CP). The SPs were formed between two parallel-carbon layers, and the CPs were formed at a place which is connected polygonally by more than two carbon layers. It was shown that the CPs of the ACFs were developed at high degree of burn-offs and at high activation temperature. The pore size distribution of the best ACF, which was observed at a highest value of specific surface area(3,495 $\m^2$/g), showed a continuous distribution in the range of about $4∼l5\AA$, and the median pore size was 6.7$\AA$. The super-high specific surface area of ACFs was found to be due to that the SPs were connected with a maximum size of 7∼8$\AA$ continuously, It is possible that the SPs should be formed in the ACFs in order to show super-high SSA.
스파크 플라즈마 소결법으로 제조된 Sr - 페라이트의 특성
노재승(J. S. Roh),오명훈(M. H. Oh) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.1
Anisotropic Sr-ferrites were prepared by the spark plasma sintering process (SPS). The Ferrite particles were oriented and densified during sintering process, and the anisotropic ferrites were manufactured at low sintering temperature and a remarkable short time processing by SPS method. It was showed that the anisotropy of ferrite particles at the specimen outer side was more higher than that at the specimen center, and it seems possible that the orientation of ferrite particles was related to DC current. Magnetic and physical properties of sintered Sr-ferrites are Br = 3.15 kG, iHc = 2.67 kOe, and density = 5.033 g/㎤ when the samples were sintered for 8 minutes at 1060℃.