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강찬형 대한금속재료학회(대한금속학회) 1981 대한금속·재료학회지 Vol.19 No.7
The theoretical basis of Ostwald ripening has been reviewed with particular reference to the effect of medium grain fraction on the size distribution. And the procedure to obtain a reliable size distribution by linear intercept method has been specified in detail for cobalt grains in 50% Co-50% Cu alloy at 1,200℃. Systematic tests are performed to confirm the validity of the observed grain intercept distributions. The shortcomings of chi-square test are discussed. The grain intercept distribution approaches to a stabilized form when the number of intercepts reaches about 1,000 and that of photo-micrographs 5 to 6. This result does not vary with the grouping method of intercept size classes. During coarsening, the size distribution maintains a stationary form, which is consistent with the theoretical predictions for diffusion controlled growth when the grain volume fraction exceeds about 0.5.
전구체 공침 온도가 LiNi<sub>1/3</sub>Co<sub>1/3</sub>Mn<sub>1/3</sub>O<sub>2</sub> 분말의 특성에 미치는 영향
최웅희,강찬형,Choi, Woonghee,Kang, Chan Hyoung 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.4
$Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$ powders have been synthesized in a continuously stirred tank reactor via a co-precipitation reaction between aqueous metal sulfates and NaOH using $NH_4OH$ as a chelating agent. The co-precipitation temperature is varied in the range of $30-80^{\circ}C$. Calcination of the prepared precursors with $Li_2CO_3$ for 8 h at $1000^{\circ}C$ in air results in Li $Ni_{1/3}Co_{1/3}Mn_{1/3}O_2$ powders. Two kinds of obtained powders have been characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size analyzer, and tap density measurements. The co-precipitation temperature does not differentiate the XRD patterns of precursors as well as their final powders. Precursor powders are spherical and dense, consisting of numerous acicular or flaky primary particles. The precursors obtained at 70 and $80^{\circ}C$ possess bigger primary particles having more irregular shapes than those at lower temperatures. This is related to the lower tap density measured for the former. The final powders show a similar tendency in terms of primary particle shape and tap density. Electrochemical characterization shows that the initial charge/discharge capacities and cycle life of final powders from the precursors obtained at 70 and $80^{\circ}C$ are inferior to those at $50^{\circ}C$. It is concluded that the optimum co-precipitation temperature is around $50^{\circ}C$.