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비정질 Tb-Fe 합금 박막의 자기적 상태에 대한 연구
이성래,정진덕,정희준,황상윤 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.11
Compositional dependence of the magnetic properties such as the saturation magnetization and the magnetic anisotropy energy were analysed using the three magnetic subnetwork mean field model and these results were compared to the radial distribution functions obtained from X-ray diffraction spectra and the hyperfine field distribution from Mossbauer spectroscopies. The ratio of the ferromagnetic Fe-subnetwork to the antiferromagnetic Fe-subnetwork and the spin value of Fe varied with the composition and all of Fe-subnetworks are coupled antiparallel to the Tb-subnetwork. Also, it was found that the hyperfine field at Fe nuclear is affected significantly by the conduction electron polarization due to the magnetic mean field near the center Fe atom as well as by the core electron polarization.
산소 및 수소 분위기하에서 철의 반복 산화 환원에 관한 속도론적 고찰
이성래,백영현 대한금속재료학회(대한금속학회) 1979 대한금속·재료학회지 Vol.17 No.5
철의 반복 산화-환원반응 속도는 산소 및 수소의 분압을 변화시켜가면서 thermogravimetric technique에 의하여 측정되었다. 이때 반응온도의 범위는 850℃∼1050℃였다. 제 1 단계와 제 2 단계 산화반응속도는 동일하게 산화철의 층을 통한 Fe^(++)ion의 확산과정으로 설명되며 t/Δw=Δw/k_p+1/k₁의 관계식을 따른다. 여기서 t; 반응시간, Δw; 중량변화 그리고 k_p와 k₁은 parabolic 및 linear rate constant를 각각 표시한다. 이에 따른 activation energy는 27㎉/㏖이다. 산화반응 속도는 단순한 반응계면으로 설명되나 후기에는 외층에 발달된 island의 반응에 의하여 특징 지워진다. 이와 같은 현상은 반복 산화-환원과정에 따라 현저하게 나타난다. 환원반응 속도는 900℃∼950℃ 사이에서 제일 크며 이를 전후한 온도 구역에서는 생성 pore의 조직이 치밀 또는 조대하여 반응속도는 느리며 속도는 수소분압에 크게 좌우된다. 산화반응의 경우와 같이 환원의 후기 반응은 역시 residual wustite의 환원에 의하여 특징 지워지며 이와 같은 현상은 높은 온도 및 수소 분압의 경우에 현저하다. Cyclic oxidation of iron sheet has been studied in the temperature range of 850℃∼1050℃ at various partial pressures of O₂ and H₂. Rates of the first and second stage oxidation could be described in terms of a solid state diffusion of iron ion through wustite layer, and expressed by the equation of t/Δw=Δw/k_p+1/k₁ where t, Δw, k_p and k₁ are reaction time, weight change, and parabolic and linear rate constant, respectively. The activation energy for oxidation was found to be about 27㎉/㏖. Results revealed that rate of oxidation follows simply the flat surface geometry, whereas at the later stage oxidation was characterized by the oxidation of residual iron island in product layer. Such an effect became more significant by repeated oxidation and reduction. Reduction rate of iron oxide was faster in temperature range of 900℃∼950℃ at which the product layer had proper pore structure. At the later stage of reduction the rate was also characterized by the reduction of residual wustite island in the outer product layer.
비정질 Gd-Fe 합금박막의 Auger electron Spectroscopy 및 X-ray Photoelectron Spectroscopy 분석에 관한 연구
이성래 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.5
Changes of the electronic structure as functions of oxygen content and composition of the co-evaporated amorphous Gd-Fe alloy films have been studied using an Auger electron spectroscopy and a x-ray photo-electron spectroscopy. A comparison of the spectra for oxidized species to trose of pure Gd element or alloy films showed characteristic differences in the low energy Auger transitions, usually incorporating the valence level and the L₁or L₂.₃ levels of oxygen. The disappearance of the N₂N_(4.5)O₂.₃transition at 122ev in an oxidized Gd was speculated to be due to a cross transition such as N₂N_(4.5)L₁(O). The charge transfer from a Cd atom to the 3d levee of Fe was less than leV per Gd atom, and binding energies of core levels were barely affected by the change of chemical composition of the alloy film, No, chemical effect was observed from the Auger spectra of the amorphous Gd-Fe films. SiO layers thicker than 200Å coated on both sides of the film were effective in preventing oxidation of the amorphous film.
이성래 建陽大學校 1993 建陽論叢 Vol.- No.2
In general, the P, PI and PID controllers are used to control the hydraulic systems. But the self-tuning control is better to improve the performance of the hydraulic system when its characteristics is time-varying. Since the accuracy of identification is the most important part of the self-tuning control, the identification characteristics of the hydraulic system is investigated. The degree of the identification model can be first-order if the frequency components of the process input signal is in the low frequency range or the system response speed is slow. When the internal or external leakage of the actuator, the supply pressure or the servovalve underlap is time-varying, the identification is performed successfully. Also, the existance of the bias input does not degrade the identification results of the hydraulic system. The goodness of the identification may verify the self-tuning control application to the hydraulic system.