• Title/Summary/Keyword: amorphous Fe

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Effect of bicarbonate concentration on iron biomineralization by psychrotolerant bacteria

  • Lee, Sang-Han;Yul-Roh;Lee, Insung
    • Proceedings of the KSEEG Conference
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    • 2003.04a
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    • pp.236-236
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    • 2003

  • Anaerobic Fe(III)-reducing bacteria are known to be able to reduce crystalline and amorphous Fe(III) oxides. Anaerobic Fe(III)-reducing bacterial reduction can induce several kinds of secondary minerals (Fe(II) containing minerals) such as magnetite, siderite, vivianite [($Fe_{3}(PO_{4}{\cdot}2H_{2}O$], and iron sulfide (FeS) according to variety of geochemical and biological conditions. (omitted)

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Magnetism of Amorphous Bulk $(Sm_{1-x}Pr_x)Fe_2$ Alloys in a Low Magnetic Field (저자장에서 비정질 후막$(Sm_{1-x}Pr_x)Fe_2$의 자성)

  • Kim, Jai-Young
    • Korean Journal of Materials Research
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    • v.5 no.8
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    • pp.913-920
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    • 1995

  • RFe$_2$(R=rare earth) Laves Phase intermetallic compounds are one of the promising materials for magnetostrictive applications, due to large magnetostriction coefficients in the order of 10$^{-3}$ . However, because RFe$_2$intermetallic compounds have large magnetostriction constants as well as large magnetocrystalline anisotropy constants, a large external magnetic field is necessary to reach saturation magnetostriction. Hence researches on giant magnetostriction have been concentrated on producing materials exhibiting a high value of magnetostriction in a low magentic field. The main research trend of the giant magnetostriction to obtain the large value in the low magnetic filed, fortunately as the signs of magnetocrystalline anisotropy constans in RFe$_2$intermetallic compounds alternate with the rare earth metals, has been to substitute the rare earth metal for others and hence to reduce the magnetocrystalline anisotropy energy. In addition, amorphous RFe$_2$alloys have been researched. In this research, both of the methods which are substitution of the rare earth metal and amorphization in RFe$_2$ intermetallic compounds are simultaneously conducted to obtain the large magnetostriction coefficient in the low external magnetic field. Among them, SmFe$_2$and PrFe$_2$are selected, and amorphized in substrate-free bulk state. Magnetism in amorphous bulk (Sm$_{1-x}$ Pr$_{x}$) Fe$_2$alloys is investigated in the low magnetic field.ld.

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Synthesis of amorphous Fe-Cr-N alloy powders by mechanical alloying (기계적 합금화에 의한 Fe-Cr-N 계 비정질 합금분말의 제조)

  • 이충효
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.9 no.1
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    • pp.132-136
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    • 1999

  • Mechanical alloying (MA) by ball mill of $Fe_{30}Cr_{70}$ elemental powders was carried out under the nitrogen gas atmosphere. Amorphization has been observed in this case, while MA under an inert argon gas atmosphere produces the bcc solid solution. The DSC spectrum for the mechanically alloyed $(Fe_{30}Cr_{70})_{0.85}N_{0.15)$powders exhibits a sharp exothermic peak due to crystallization at about $550^{\circ}C$. Structural transformation from the bcc crystalline to amorphous states was observed through X-ray and neutron diffractions. During amorphization process the octahedral unit, which is typical of a polyhedron formed in any crystal structures, was preferentially destroyed and transformed into the tetrahedral unit. Futhermore, neutron diffraction measurements revealed that a nitrogen atom is situated at a center of the tetrahedron formed by metal atoms.

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Effects of Heat Treatment on Choke Core Properties in $Fe_{78}Si_9B_{13}$ Amorphous Alloys ($Fe_{78}Si_9B_{13}$ 비정질 합금의 초크 코어 특성에 미치는 열처리 효과)

  • 노태환;장완희
    • Journal of the Korean Magnetics Society
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    • v.10 no.5
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    • pp.191-195
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    • 2000

  • With the object of developing a non-gap choke core, effects of annealing in oxygen atmosphere on magnetic properties for Fe$_{78}$Si$_{9}$B$_{13}$ amorphous alloy were investigated. After annealing for 2 hrs at 440 $^{\circ}C$, optimum magnetic properties for choke core were obtained, where the effective permeability was 180 and was almost constant up to several MHz, and the decrease in permeability upon large DC bias current of 12 A or DC bias magnetic field of 8,000 A/m was very little. Moreover the AC magnetic loss was very low as compared to the conventional choke cores. Upon the optimum annealing, the magnetic hysteresis loop was inclined accompanying the increase of coercive force and the appearance of fine crystallites of $\alpha$-Fe phase. The good choke core properties was considered to be due to the suppression of domain boundary motion and domain refinement by the crystallites.

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