볼밀링법으로 제조된 강자성 Fe-MgO 분말의 벌크화 및 자기적 특성
Consolidation and magnetic properties of ferromagnetic Fe-MgO powders prepared by ball milling process
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헤마타이트와 순금속 Mg 분말에 대하여 볼밀링법을 이용하여 강자성 분말재료를 제조하였으며, 얻어진 분말시료를 800-1,000°C에서 방전플라즈마 소결법을 이용하여 벌크화를 실시하였다. 헤마타이트와 순금속 Mg의 혼합분말을 볼밀링 처리한 결과, 1시간 이전에 강자성 Fe-MgO 복합분말을 얻을 수 있었다. 얻어진 시료의 자화값 및 보자력은 볼밀링 처리 중 헤마타이트와 순금속 Mg의 고상반응에 의하여 변화하였는데, 포화자화 값은 볼밀링 시간에 따라 증가하여 5시간 후에 93.4 emu/g을 나타내었다. 볼밀링 5시간 시료는 방전플라즈마 소결 시 300°C 이상에서 급격히 수축이 발생한 후 800°C 까지 서서히 수축이 진행됨을 알 수 있었다. XRD 피크의 반가폭을 이용한 hall-plot으로부터 900°C에서 소결된 Fe-MgO 벌크체의 Fe 평균 결정립 크기는 50nm 이었다 . 또한 이 벌크시료의 보자력은 90Oe로 여전히 높은 값을 보였는데 이것은 강자성 Fe 상의 결정립 성장이 소결과정 중에 억제되었기 때문인 것으로 판단된다.
Abstract
Preparation of ferromagnetic powders for the mixture of hematite and pure Mg powders by ball milling has been investigated. Also, consolidation of the ball-milled powders was performed in a spark plasma sintering machine at 800-1,000°C. It is found that a ferromagnetic Fe-MgO composite powders are obtained by ball milling of hematite and pure Mg powders before 1 hour. The magnetization and coercivity of ball-milled samples change at the results of the solid state reaction of hematite by pure Mg during ball milling. The saturation magnetization of ball-milled samples increases with increasing ball milling time and reaches to a maximum value of 93.4 emu/g after 5 hours of ball milling. Shrinkage change after sintering of ball-milled sample for 5 hours was significant above 300°C and gradually increased with increasing temperature up to 800°C. X-ray diffraction result shows that the average grain size of Fe in Fe-MgO bulk sample sintered at 900°C is 50nm. It can be also seen that the coercivity of bulk sample sintered at 900°C is still high value of 90 Oe, indicating that the grain growth of magnetic Fe phase during sintering process tend to be suppressed.
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