• 한국재료학회지
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• 제3권2호
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• pp.121-130
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• 1993

합성용질확산법으로 GaP 단결정을 성장시키고, 몇가지 성질을 조사하였다. 결정성장용 석영관을 전기로내에서 1.75mm/day의 속도로 하강시킴으로써 양질의 GaP 단결정을 성장하였다. 에치피트 밀도는 결정의 성장축 방향으로 3.8 ${\times}{10^4}$c$m^{-2}$부터 2.3 ${\times}{10^5}$c$m^2$이었다. 에너지갭의 온도의존성은 실험적으로 $E_g$(T)=[2.3383-(6.082${\times}{10^{-4}}$)$T^2$(373.096+T)eV로 구하여졌다. 저온에서의 광루미네센스 스펙트럼은 구속된 여기자의 복사재결합과 재결합 과정에 포논의 참여로 인하여 에너지갭 부근의 복잡한 선 스펙트럼이 나타났다. n형의 GaP내에서 Zn의 확산깊이는 확산시간의 제곱근에 비례하였으며, 확산계수의 온도의존성은 D(T)=3.2${\times}{10^3}$ exp(-3.486/KbTc$m^2$/sec이었다. p-nGaP 동종접합다이오드의 전기루미제센스 스펙트럼은 깊은 준위의 도너인 Zn-O 복합중심(complex center)과 Zn가 형성한 역셉터 준위사이의 도너-억셉터 쌍 재결합 천이에 의한 630nm의 발광과 에너지갭 부근의 케리어 재결합 처이에 의한 550nm의 발광으로 구성되었으며, 100mA보다 낮은 전류 영역에서 광자의 방출은 bane-filling 과정으로 이루어 진다.

• 한국세라믹학회지
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• 제29권4호
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• pp.265-272
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• 1992

Role of CaO in the sintering of 12Ce-TZP ceramics was studied. The addition of small amounts of CaO increase the densification rate of 12Ce-TZP by altering lattice defect structure and the diffusion coefficient of the rate controlling species, namely cerium and zirconium cations. CaO also inhibits grain growth during sintering and allows the sintering process to proceed to theoretical density by maintaining a high diffusion flux of vacancies from the pores to the grain boundaries. The inhibition of grain growth is accomplished by the segregation of solute at the grain boundaries, causing a decrease in the grain boundary mobility. The segregation of calcium was revealed by AES study.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.574-578
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• 2013

In this work, the friction and diffusion coefficients of a tracer in a mesoscopic solvent are evaluated as a function of the tracer size by a hybrid molecular dynamics simulation where solute molecules evolve by Newton's equations of motion but the solvent evolves through the multi-particle collision dynamics. The friction coefficient is shown to scale linearly with the tracer size for larger tracers in accord with predictions of hydrodynamic theories. The diffusion coefficient of tracer is found to be inversely proportional to tracer size. The behavior of Stokes-Einstein formula is validated as a function of tracer size.

• 한국재료학회지
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• 제28권6호
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• pp.317-323
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• 2018

Crystal structure of the $L1_2$ type $(Al,X)_3Ti$ alloy (X = Cr,Cu) is analyzed by X-ray diffractometry and the nonuniform strain behavior at high temperature is investigated. The lattice constants for the $L1_2$ type $(Al,X)_3Ti$ alloys decrease in the order of the atomic number of the substituted atom X, and the hardness tends to increase. In a compressive test at around 473K for $Al_{67.5}Ti_{25}Cr_{7.5}$, $Al_{65}Ti_{25}Cr_{10}$ and $Al_{62.5}Ti_{25}Cu_{12.5}$ alloys, it is found that the stress-strain curves showed serration, and deformation rate dependence appeared. It is assumed that the generation of serration is due to dynamic strain aging caused by the diffusion of solute atoms. As a result, activation energy of 60-95 kJ/mol is obtained. This process does not require direct involvement. In order to investigate the generation of serrations in detail, compression tests are carried out under various conditions. As a result, in the strain rate range of this experiment, serration is found to occur after 470K at a certain critical strain. The critical strain increases as the strain rate increases at constant temperature, and the critical strain tends to decrease as temperature rises under constant strain rate. This tendency is common to all alloys produced. In the case of this alloy system, the serration at around 473K corresponds to the case in which the dislocation velocity is faster than the diffusion rate of interstitial solute atoms at low temperature.

• 한국식품영양학회지
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• 제10권4호
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• pp.462-467
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• 1997

최근 건조 및 탈수공정으로 사용되고 있는 침지(soaking)에 의한 방법인 DIS 공정(dewatering and impregnation soaking process)은 상온에서 침지용액에 식품시료를 담금으로서 시료내의 수분이 탈수되는 현상을 이용한 공정으로서 이 때 용액 속의 용질들이 시료 속의 세포 내로 침투하는 확산현상도 동시에 발생한다. 따라서 영양분의 손실과 관능적 품질저하를 억제할 수 있으며, 건조시의 에너지를 절감하는 등의 특성을 갖는다. DIS 공정에서는 용질의 크기에 따라 원형질막 분리현상과 세포벽 붕괴현상이 발생하며, 시료의 조직상태와 운전조건에 의하여 그 탈수 정도는 차이가 나타난다. DIS 공정을 제어하기 위한 모형화는 주로 비정상상태에서의 Fick의 법칙과 물질수지를 기초로 한 여러 가지 모델들이 제안되어 등온상태에서 시간에 따른 탈수량과 용질 침투량을 정확히 예측하고자 하고 있다.

• 대한기계학회논문집B
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• 제24권3호
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• pp.426-434
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• 2000

This paper deals with a generalized similarity solution for the one-dimensional solidification of ternary or higher-order multicomponent alloys. The present approach not only retains the existing features of binary systems such as temperature- solute coupling, shrinkage-induced flow, solid-liquid property differences, and finite back diffusion, but also is capable of handling a multicomponent alloy without restrictions on the partition coefficient and microsegregation parameter. For an alloy of N-solute species, governing equations in the mushy region reduce to (N+2) nonlinear ordinary differential equations via similarity transformation, which are to be solved along with the closed-form solutions for the solid and liquid regions. A linearized correction scheme adopted in the solution procedure facilitates to determine the solidus and liquidus positions stably. The result for a sample ternary alloy agrees excellently with the numerical prediction as well as the reported similarity solution. Additional calculations are also presented to show the utility of this study. Finally, it is concluded that the present analysis includes the previous analytical approaches as subsets.

• Journal of applied mathematics & informatics
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• 제35권3_4호
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• pp.241-260
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• 2017

An analysis is made to study the solute transport in a Casson fluid flow through an annulus in presence of oscillatory flow field and determine how this flow influence the solute dispersion along the annular region. Axial dispersion coefficient and the mean concentration expressions are calculated using the generalized dispersion model. Dispersion coefficient in oscillatory flow is found to be a function of frequency parameter, Schmidt number, and the pressure fluctuation component besides its dependency on yield stress of the fluid, annular gap and time in the case of steady flow. Due to the oscillatory nature of the flow, the dispersion coefficient changes cyclically and the amplitude and magnitude of the dispersion increases initially with time and reaches a non - transient state after a certain critical time. This critical value varies with frequency parameter and independent of the other parameters. It is found that the presence of inner cylinder and increase in the size of the inner cylinder inhibits the dispersion process. This model may be used in understanding the dispersion phenomenon in cardiovascular flows and in particular in catheterized arteries.

• 한국결정성장학회지
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• 제9권3호
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• pp.286-288
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• 1999

When concentration of vacancies in a CZ silicon crystal is defined by molar fraction $X_{B}$, the degree for supersaturation $\sigma$ is given by $[X_{B}-X_{BS}]/X_{BS}=X_{B}/X_{BS}-1=ln(X_{B}/X_{BS})$ because $X_{B}/X_{BS}$ is nearly equal to unity. Here, $X_{BS}$ is the saturated concentration of vacancies in a silicon crystal and $X_{B}$ is a little larger than $X_{BS}$. According to Bragg-Williams approximation, the chemical potential of the vacancies in the crystal is given by ${\mu}_{B}={\mu}^{0}+RT$ ln $X_{B}+RT$ ln ${\gamma}$, where R is the gas constant, T is temperature, ${\mu}^{0}$ is an ideal chemical potential of the vacancies and ${\gamma}$ is and adjustable parameter similar to the activity of solute in a solute in a solution. Thus, ${\sigma}(T)$ is equal to $({\mu}_{B}-{\mu}_{BS})/RT$. Driving force of nucleation for the vacancy agglomeration will be proportional to the chemical potentialdifference $({\mu}_{B}-{\mu}_{BS})/RT$ or ${\sigma}(T)$, while growth of the vacancy agglomeration is proportaional to diffusion of the vacancies and grad ${\mu}_{B}$.

• Corrosion Science and Technology
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• 제23권2호
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• pp.93-103
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• 2024

In the present work, a phase-field model for dendritic solidification is applied to hot-dip ZnAlMg coatings to elucidate the morphology of zinc dendrites and the solute segregation leading to the formation of eutectics. These aspects define the microstructure that conditions the corrosion resistance and the mechanical behaviour of the coating. Along with modelling phase transformation and solute diffusion, the implemented model is partially coupled with the tracking of crystal orientation in solid grains, thus allowing the effects of surface tension anisotropy to be considered in multi-dendrite simulations. For this purpose, the composition of a hot-dip ZnAlMg coating is assimilated to a dilute pseudo-binary system. 1D and 2D simulations of isothermal solidification are performed in a finite element solver by introducing nuclei as initial conditions. The results are qualitatively consistent with existing analytical solutions for growth velocity and concentration profiles, but the spatial domain of the simulations is limited by the required mesh refinement.

• 한국물환경학회지
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• 제28권2호
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• pp.292-299
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• 2012

The objective of this study is to develop a novel method for evaluating forward osmosis (FO) membrane performances using a non-pressurized FO system. Basic membrane performance parameters including water (A) and solute (B) permeability coefficients and unique parameter for FO membrane such as the support layer structural parameter (S) were determined in two FO modes (i.e., active layer faces feed solution (AL-FS) and active layer faces draw solution (AL-DS)). Futhermore, these parameters were compared with those determined in a pressurized reverse osmosis (RO) system. Theoretical water flux was calculated by employing these parameters to a model that accounts for the effects of both internal and external concentration polarization. Water flux from FO experiment was compared to theoretical water fluxes for assessing the reliability of those parameters determined in three different operation modes (i.e., AL-FS FO, AL-DS FO, and RO modes). It is demonstrated that FO membrane performance parameters can be accurately measured in non-pressurized FO mode. Specifically, membrane performance parameters determined in AL-DS FO mode most accurately predict FO water flux. This implies that the evaluation of FO membrane performances should be performed in non-pressurized FO mode, which can prevent membrane compaction and/or defect and more precisely reflect FO operation conditions.