http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Rambabu Kuchi,Seunghyun Kim,Vitalii Galkin,Dongsoo Kim 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
NdFeB magnets are widely used in advanced electric vehicles, electric motors for power generators, wind turbine generators, energy conversion systems and many other novel applications. However, the high energy density (BHmax) magnets are needed to utilise them. For this purpose, the NdFeB magnetic particles should prepare with higher magnetic properties which could mainly depends on the Nd<sub>2</sub>Fe<sub>14</sub>B phase purity, crystallinity and microstructure. To wards this direction, we report the cost effective and a facile chemical synthesis including spray drying and reduction-diffusion (RD) process with some modifications [1, 2]. Since the RD process has considerably affected the structural and magnetic properties of Nd-Fe-B particles so the optimization of heat treatments for RD is in high demand. Different heating rates (5, 10, 20, and 30℃/min) to reach annealing temperature (1000℃) of RD and keeping times for the RD process were used to prepare Nd-Fe-B particles. Among them, the sample prepared at 20℃/min heating rate (HR) with a 5 h RD time exhibited superior magnetic properties including the remanence (M<sub>R</sub>) of 125 emu/g, saturation magnetization (M<sub>S</sub>) of 140 emu/g, and (BH)max of 10.66 MGOe. This was ascribed to the narrow particle size distribution, and phase purity with high crystallinity at optimized HR and RD time. Because the HR was controlling the particle nucleation and growth process and keeping time could ensure the completion of the RD process. This present modified RD process will also be useful to prepare other potential hard-magnetic particles.
Rambabu Kuchi,Viet Dongquoc,김도진,윤순길,박성용,정종률 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.2
In this work, we report on the large-scale room-temperature synthesis of Co superstructures using a facile liquidphase reduction method in an aqueous medium. This method yielded pure Co powders within a short periodof time without the use of any surfactants. The morphological changes in the Co superstructures could becontrolled simply by varying the amounts of reducing agent (hydrazine hydrate). The morphology of theCo powders systematically controlled from aggregated foliage to isolated microfoliage by increasing thehydrazine hydrate addition from 4 ml to 8 ml. The morphology-dependent electromagnetic properties, includingthe electric permittivity, and magnetic permeability, were investigated over the microwave frequencyrange, 2-18 GHz. Co isolated microfoliage showed a maximum reflection loss (RL) of -32 dB at 9 GHz with amatching thickness of 2.5 mm, whereas the aggregated foliage Co superstructures displayed a maximum RLof -17 dB at 11 GHz with a matching thickness of 2.5 mm. The stronger absorption for isolated microfoliagewas ascribed to a continuous micro networks and vibrating microcurrent dissipation arise from size and shapeof the isolated microfoliage. The calculated RL suggested that the as-prepared samples were potential microwaveabsorption candidates in the X-band region.
Viet Dongquoc,Rambabu Kuchi,Phuoc Cao Van,윤순길,정종율 한국물리학회 2018 Current Applied Physics Vol.18 No.2
This work investigated the effects of heating rate and annealing on the magneto-optical properties of bismuth-substituted yttrium iron garnet (Bi-YIG) thin films on glass and (111)-oriented single-crystalline gadolinium gallium garnet (GGG) substrates fabricated by metal-organic decomposition (MOD). We modified the MOD method by eliminating the pre-annealing process. We performed annealing at various temperatures to determine the optimal temperature for obtaining the Bi-YIG phase. We then annealed at the optimized temperature using various heating rates. The optimal conditions were annealing for 1 h at 750 °C at a heating rate of 30 °C/min on GGG to obtain highly crystallized fine grains. The Faraday rotation for this film was about −10.5°/μm. The optimized heating rate enhanced the magneto-optical properties due to improved crystallinity and saturated magnetization. The Bi-YIG thin films prepared by this prescribed MOD method exhibited excellent magneto-optical performance and are potential candidates for applications in optical devices.
Seunghyun Kim,Rambabu Kuchi,Vitalli Galkin,Dongsoo Kim 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
NdFeB based high energy density (BHmax) magnets are of enormous significance in various engineering applications include electric equipments, motors, generators, hard disc drives and electric vehicles. It has the high BHmax than other rare earth transition metal based magnets. The BHmax was strongly depends on the magnetic properties of NdFeB magnetic particles which are to be used to make the NdFeB magnets. The magnetic properties of NdFeB powder are determined from its phase purity, crystallinity and structure. These can be controlled in the powder synthesis process. In this work, we used spray drying and reduction diffusion methods for the production of Nd-Fe-B powders. In order to obtain excellent magnetic properties to the final powders, it is necessary to optimize the crystallinity and shape of the powder particles. Since the final NdFeB powders are obtained from their oxides so that the microstructure and phase purity of NdFeB oxides can effect them. The NdFeB oxides are formed from the heat treatment of spray dryed powders and their properties has been controlled using planetary ball milling (PBM). The PBM of oxides were performed with different time intervals (1, 2 and 4 hrs) at 200 rpm in dry condition. The 1 hr PBM powders resulted fine particles and uniform shape (spherical shape) compared to 2 and 4hrs. The final particles prepared using PBM (1 h) showed enhanced magnetic properties include the coercivity of 3900 Oe, and remaenant magnetization of 102 emu/g. It shows 21.9% higher coercivity compared to unmilled powder.