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- 검색키워드
- 저자 : Mizutani Uichiro (검색결과 4 건)
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볼 밀중 solid-Gas Reaction 에 의해 제조된 비평형상 철질화물의 구조 및 자기특성
이충효,수곡우일랑,고곡야유 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.8
Pure iron powders are nitrified at room temperature by ball milling in NH₃ gas atmosphere. Super-saturated bcc iron-nitrides are obtained for the N concentration below 14.9 at.%N and the high temperature ε-phase with the hcp structure for more than 19.4 at.%N. The atomic volume of Fe in the metastable bcc phases is found to be smaller than that in the bct iron-nitrides reported in the literature. Saturation magnetization at room temperature gradually decreases with the nitrogen content, which is in sharp contrast to the enhancement in magnetization due to nitrification reported for the N-martensite. We have shown that mechanical alloying in the NH₃atmosphere can nitrify pure iron powders even at room temperature and gives rise to the super-saturated bcc iron-nitrides up to 14.9 at.% N. The high temperature ε-phase with the hcp structure is obtained for the iron-nitrides containing more than 19.4 at.%N. In the composition range between 14.9 at.%N and 19.4 at.%N, a mixture of the bcc and hcp phases is produced. The stomic volume of Fe in the bcc phase is found to be smaller than that in the N-martensite. We also reveal that the magnetization at room temperature gradually decreases with the N concentration. Here a lack of the tetragonal distortion has been proposed to be the tetragonal distortion has been proposed to be the likely cause for the low value of saturation magnetization compared to bct iron-nitrides.
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고에너지 볼밀법에 의해 제조된 비정질 Cu-Ta 합금의 원자구조관찰
이충효,복영준청,수곡우일랑 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.6
The mechanism for the amorphization induced by mechanical alloying has been studied in the immiscible Cu-Ta system characterized by a positive heat of mixing of 2kJ/㏖. Here a chemical driving force is no longer expected and instead an energetically up-hill process has been proposed for the formation of the amorphous phase. From the studies on the atomic-level structure through the neutron diffraction and extended X-ray absorption fine structure coupled with thermodynamical consideration, we provide various evidences for the amorphization due to mechanical alloying for a mixture of Cu and Ta powders, The coordination number around Cu and Ta atoms is deduced by assuming the first neighbors of the total pair distribution function g(r) to consist of the three partial ones. We conclude that the amorphization proceeds such that the smaller Cu atoms preferentially enter into the bcc Ta lattice and destroy the long range order edtructure of a crystalline phase.
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Mechanical Alloying (MA) 에 의한 비고용 Cu-Ta 계의 비정질화와 그 과정에 있어서의 분위기온도효과
이충효,복영준청,수용우일랑 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.2
The mechanism far the amorphization induced by mechanical alloying(MA) has been studied in the immiscible Cu-Ta system. A mixture of copper and tantalum powders at a composition ratio Ta : Cu=7 : 3 was used. The first 30h of milling essentially results in the reduction in Ta and Cu grain size down to about 100Å without measurable formation of an amorphous phase. The thermally assisted amorphization(TAA) becomes noticeable after 60h of milling. The higher the ambient temperature, the faster the amorphization proceeds. The TAA effect is also observed by annealing a partially amorphous MA powders. The microstructure after 30h of milling is such that fine Cu crystallites are embedded in the finely-grained Ta matrix. Here an interfacial energy contribution is large enough to raise the free energy to that of an amorphous phase. Now high temperature milling or annealing allows an energetically down-hill process to occur. This is most likely responsible for the observed TAA effect in the Cu-Ta system characterized by a positive heat of mixing. (Received August 10, 1992)
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기계적 합금화에 의한 비정질 Cu-Ta 분말의 제조 및 전자물성
Lee, Chung-Hyo,Asahina, Tadashi,Mizutani, Uichiro 한국재료학회 1994 한국재료학회지 Vol.4 No.6
자자들은 최근 비고용 Cu-Ta계의 기계적 합금화(Mechanical Alloying) 방법을 이용하여 이계에 있어서 비정질상의 형성에 대한 구조적 확인을 중성자 회절과 EXAFS(Extended X-ray Absorption Fine Structure)의 실험결과로 부터 얻었다. Cu-Ta계와 같이 혼합 엔탈피(Heat of Mixing: $\Delta$ Hmix)가 정인계에 있어서 비정질상 형성에 대한 연구는 구조적인 측면 뿐만 아니라. 시료의 전자물성에 대해서도 많은 연구가 되어야만 할 것으로 사료된다. 따라서 본 논문에서는 120시간 MA방법으로 제작한 시료에 대하여 초전도 천이온도 및 X선 광전자분광 실험에서 얻은 가전자대 구조의 전자물성을 측정하고, 그 결과로부터 이종원자 Cu와 Ta간의 결합은 화하결합에 의한 생성임을 확인하였는데, 이들 결과로부터 120시간 MA를 행하여 얻어진 시료는 확실하게 비정질 합금임을 알 수 있었다. We recently showed from the neutron diffraction and extended X-ray absorption fine structure studies the structural evidence for the formation of an amorphous phase in immiscible Cu-Ta system subjected to mechanical alloying. In a system with a positive heat of mixing like Cu-Ta, we consider it necessary to confirm the formation of an amorphous phase not only from the structural studies but also from a change in the electronic properties. We show the electronic evidence for the formation of the chemical bonding between the unlike atoms Cu and Ta for the 120 h-milling sample through changes in superconducting transition temperature and X-ray photoemission spectroscopy valence band structure.
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