• Bulletin of the Korean Chemical Society
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• 제33권10호
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• pp.3397-3406
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• 2012

Three types of spherulitic morphologies have been investigated in dual substrate mode of Belousov-Zhabotinsky (BZ) type reaction system. Prior to growth of spherulites, three distinct patterning behaviors have been observed sequentially during the reaction process. Initial and the early-phase of reaction showed the emergence of concentric ring-like wave patterns. A colloidal-state of reaction consists of numerous fine solid particles, which forms primarily some nucleation centers of dendritic characters. The nucleation centers were found to grow in sizes and shapes with the progress of reaction. It leads to growth of dendritic-like spherulitic crystal patterns. The resultant spherulites showed transitions in their morphologies, including sea-weeds and rhythmic spherulitic crystal patterns, by the effects substituted organic substrate and in the higher concentration of bromate-initiator respectively. The branching mechanism and crystal ordering of spherulitic textures were studied with help of optical microscope (OPM) and scanning electron microscope (SEM). Characteristics of crystal phases were also evaluated using X-ray diffraction (XRD) and differential thermal analysis (DTA). Results indicated that the compositions of reactants and crystal orderings were interrelated with morphological transitions of spherulites as illustrated and described.

• 대한금속재료학회지
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• 제50권10호
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• pp.703-710
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• 2012

The effects of the ordering reaction on high temperature mechanical behavior is investigated by tensile tests at $2{\times}10^{-2}/s-3.3{\times}10^{-5}/s$ up to $745^{\circ}C$. The tensile deformed region is examined by differential scanning calorimeter (DSC), TEM, and high resolution neutron diffraction (HRPD). The results showed that a plateau of tensile strength appeared at $150-500^{\circ}C$ whereas the elongation minimum occurred at about $600^{\circ}C$. This suggests that the occurrence of a plateau does not cause the elongation minimum. The temperature of the elongation minimum decreases with the strain rate. HRPD results show a lattice contraction in the tensile deformed specimen at the temperature of the plateau occurring region. The plateau of tensile strength, the lattice contraction, and the occurrence of serration appeared in the same temperature region.

• Journal of Magnetics
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• 제10권1호
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• pp.28-32
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• 2005

The magnetic properties and ordering behavior of Nb-doped FePt alloy films prepared by dc-magnetron sputtering were investigated. It was found that Nb addition retarded the ordering reaction from the disordered face-centered-cubic (fcc) Al phase to the ordered face-centered-tetragonal (fct) L1₀ phase. The tetragonality (c/a ratio) of the ordered fct L1₀ phase increased with the Nb concentration. Nb addition hampered c-axis contraction during ordering, probably because the larger Nb atoms occupy Pt sites. Consequently, the coercivity and magnetocrystalline anisotropic energy of Nb-doped FePt alloy films are lower than those of un-doped FePt film under equivalent annealing conditions.

• Journal of Magnetics
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• 제9권1호
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• pp.9-12
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• 2004

We have investigated sintering effects on Fe/Mo ordering and magnetoresistance (MR) in double perovskite-reflection lines due to $Sr_2FeMoO_6$ (SFMO). Polycrystalline samples have been prepared by the conventional solid-state reaction by sintering in a stream of 5% $H_2/Ar$ gas. All samples are single phase and exhibit a series of superstructurecation ordering at Fe and Mo sites. As sintering temperature increases from 900 to $1300^{\circ}C$, the degree of Fe/Mo ordering increases from 82 to 92%, magnetization (15 K, 7 kOe) increases from 1.6 to 2.7 ${\mu}_B/f.u.,$ and Curie temperature increases at a rate of 4.3 K/% with the increase of Fe/Mo ordering ratio. The magnitude of MR measured at 5 K is 19% for sample prepared at $1000^{\circ}C$ with magnetic fields of 7 kOe. The observed MR is proportional to the square of magnetization indicating that the MR feature in SFMO is explained by the spin-polarized tunneling at grain boundaries.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2005년도 춘계학술발표회
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• pp.529-530
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• 2005

• 대한금속재료학회지
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• 제49권6호
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• pp.462-467
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• 2011

In order to understand why annealing at $480^{\circ}C$ for several hour prevents the initiation of PWSCC, the residual stress variation with isothermal annealing at $480^{\circ}C$ and isochronal annealing between 480 and $800^{\circ}C$ in cold rolled Alloy 600 was investigated by the XRD method. The isothermal annealing decreased residual stress slightly in the rolling direction but not in the transverse direction, whereas the isochronal annealing for two hours increased residual stress. It seemed that the decrease in residual stress by isothermal annealing was due to lattice contraction by an ordering reaction because the isothermal annealing increased hardness. The effects of the isochronal annealing could be interpreted as the influence of thermal expansion and a disordering reaction.

• 자원환경지질
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• 제28권4호
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• pp.327-335
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• 1995

카나다 극지의 보포트-맥켄지 (Beaufort-Mackenzie) 분지에 분포하는 일라이트/스멕타이트 (illite/smectite)에 대한 광물학적 특성 연구가 육상 및 대륙붕의 석유시추공으로부터 215개 코아와 파쇄시료를 대상으로 수행되었다. 보포트-맥켄지 분지의 일라이트/스멕타이트는 구성층의 배열 양상에 따라 불규칙, R1-배열, R>1-배열, 불규칙과 R1-배열의 혼합으로 구분된다. 불규칙과 규칙적인 배열의 혼합 양상을 보이는 일라이트/스멕타이트는 불규칙으로부터 R1-배열로 변화하는 전이대에서 나타나는데 혼합층의 배열이 규칙화하는 과정에서 불안정하게 나타나는 준안정상으로 해석된다. 불규칙과 규칙 배열을 갖는 일라이트/스멕타이트가 함께 나타나는 현상은 느린 화학반응에서 흔히 관찰되는 반응물과 생성물이 공존하는 현상과 일맥 상통한다. K-포화 실험결과는 일라이트/스멕타이트 내의 스멕타이트층의 층전하가 다양함을 보여준다. 높은 층전하의 스멕타이트층은 K-포화시 준 일라이트층으로 변한다. K-포화는 일라이트/스멕타이트의 구성비와 배열을 변화시키는데 이는 자연에서의 일라이트화 현상도 기존 격자결합의 교란이 없이 일어날 수 있다는 것을 의미한다.

• 열처리공학회지
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• 제8권2호
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• pp.149-154
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• 1995

The alloying of 6.5wt % Silicon in iron decreases the magnetization and the anisotropy and minimizes the iron loss noticeably. But it is very difficult to make thin sheets because of its poor ductility which is due to an ordering reaction (body centered cubic to CsCI type crystal structure). However the ordering reaction can be suppressed by rapid solidification method. The cooling rate of rapidly solidified Fe-6.5wt % Si alloy is about $10^3K/s$ and rapidly solidified structure are fine structure, cellular structure, dendrite and equiaxed grain from surface. The precipitates of $DO_3$ Phase emerges on $B_2$ matrix and the coercive force was 0.51 Oe (50cycle, 15KGauss) in Fe-6.5wt% Si alloy which was processed by heat treatment of $1150^{\circ}C$ for 1hr in high vacuum.

• 한국국방경영분석학회지
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• 제23권2호
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• pp.72-84
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• 1997

In this paper, we consider an economic order quantity(EOQ) and an optimal discount pricing policy for the monopsony related to the weapon system acquisition. In the monopsony case, a buyer wishes to maximize the profit. However, a seller wants to minimize the total inventory related cost since a buyer can determine the purchase price for the product. We develop a generalized version of EOQ model for the monopsony, including one seller-one buyer model and two seller-one buyer model. A model of buyer reaction to any given pricing scheme is developed to show that there exits a unified pricing policy which motivates the buyer to increase its ordering quantity per order, thereby reducing the joint(buyer and seller) ordering and holding costs in the system.

• Applied Microscopy
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• 제27권4호
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• pp.473-481
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• 1997

Disorder-order transformation of nanocrystalline FeAl have been investigated by a combination of electron and X-ray diffraction analysis including high resolution electron microscopy and differential scanning calorimetry. Fe-50at.%Al powders mechanically alloyed for 90 hours consist of $5\sim10$ nm size grains haying either disordered b.c.c. structure or amorphous structure. X-ray and electron diffraction of mechanically alloyed FeAl powders show that disorder-order transformation occurs at the temperature range of $300^{\circ}C\sim320^{\circ}C$. Such a low-temperature ordering behavior exhibiting an exothermic reaction is attributable to the nm-scale grain structure with a large amount of defects accumulated during mechanical alloying process.