• 한국세라믹학회지
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• 제35권6호
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• pp.640-646
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• 1998

PbO-TiO2-B2O3-BaO계 유리에서 PbTiO3의 핵생성 및 결정화를 위한 최적조건의 확입을 위해 핵생성 속도 곡선을 도출하고자 열시차 분석법(DTA)을 응용하였다. PbTiO3의 함량비가 60mol%인 4성분계 유리 샘플은 용융액으로부터 자연 냉각시켜 제조되었으며, 핵생성을 위해 유리 샘플은 40$0^{\circ}C$와 50$0^{\circ}C$ 사이에서 열처리하였다. 이때 46$0^{\circ}C$에서 핵생성 속도가 최대값을 나타내었다. DTA의 결정화 피크 온도는 핵생성을 위한 열처리시간이 증가함에 따라 감소하였으며, DTA의 승온속도에 비례하여 증가하였다. 이러한 결과는 계에 생성된 핵의 밀도가 핵생성 처리온도와 시간의 증가에 따라 증가함을 보여주고 있다.

• 한국진공학회지
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• 제15권2호
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• pp.168-172
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• 2006

수소화물기상증착법을 이용하여 질화갈륨 핵화층을 성장시켰고, 성장 온도에 따라 상이한 구조적 특성을 갖는 핵화층이 질화갈륨 나노막대의 형성에 어떤 영향을 주는지 방사광 x-선 산란과 원자힘 현미경을 이용하여 연구하였다. 서로 다른 온도에서 성장시킨 질화갈륨 핵화층들의 (002) 브래그 봉우리에 대한 록킹 곡선(rocking curve)을 측정한 결과, 반폭치가 작은 주 봉우리와 반폭치가 넓은 작은 봉우리의 합으로 표현됨을 관측하였다. 이러한 현상은 핵화층의 표면 형상과 연관되어져서 설명될 수 있음을 정성적으로 보였고, AFM 결과와 비교해 볼 때 안정적인 나노막대 성장을 위해서는 핵화층이 저온에서 성장되어야 함을 확인하였다.

• 한국군사과학기술학회지
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• 제13권1호
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• pp.120-125
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• 2010

For application of transparent bulletproof materials, the SLS(soda-lime-silicate) glass was heated by 2-step crystallization. The DTA curve for SLS glass revealed the nucleation and crystal growth temperature at about $575^{\circ}C$ and $675^{\circ}C$, respectively. The crystallized glass was heated at various conditions(temperature, time). As a result, the maximum nucleation and crystal growth rates were $3.8\times10^5/mm^3{\cdot}hr$ at $575^{\circ}C$ and 20.58nm/min at $680^{\circ}C$, respectively. The bending strength, fracture toughness and vickers hardness were 451.7MPa, $0.9388MPa{\cdot}m^{1/2}$, and $693.9H_v$ which were 201%, 31%, and 22% higher than parent glass, respectively. Surface image and transmittance of crystallized SLS glass were analyzed by optical microscopy and UV/VIS/NIR spectrophotometer. Transmittance of crystallized SLS glass at visible-range(200~800nm) was not changed.

• 한국표면공학회지
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• 제21권2호
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• pp.76-82
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• 1988

The bright nickel electroplatings were carried out the Watt bath containg a solobel saccharin as class I brightner and para substituted benzaldehydes as class II one. Extended Huckel MO calculation was done and polarization was measured to examine between $\pi$-electron density and the brightness. The correlation is also investigated between $\pi$-electron density of oxygen atom of aldehyde group and slope of polarization curve. As a result of the analysis of rate equation of nucleation, the surface energy of the deposited particle was obtained from the slope of the plot of $\ell$nI against 1/η2, and also the reat equation of nucleation found to influnced on the leveling on the basis of adsorption theory. We have proposed the general electroplating mechanism that is applied other to all other electroplating but nickel one. The above elucidated mechanism can be extended can be extended to the all electroplating other than bright nickel electroplating.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 추계학술발표회논문집(1)
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• pp.230-235
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• 1996

The new concept of dry area formation based on Poisson distribution of active nucleation sites and the concept of the critical active site density is presented. A simple statistical model is developed to predict the change of slope of the boiling curve up to critical heat flux (CHF) quantitatively. The predictions by the present model are in good agreement with the experimental data. Also it turns out that the present model well explains the mechanism on how the surface wettability influences CHF.

• 한국세라믹학회지
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• 제22권3호
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• pp.53-59
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• 1985

Nucleation and crystallization of $\beta$-eucryptite in a glass of molecular percentage composition Li2O.Al2O3.2SiO2 are studied. The glasses are made by quenching of the melts from 143$0^{\circ}C$ to room temperature. Heat-treatment for nucleation and crystal growth are caried out at various temperature in the range between 50$0^{\circ}C$ and 80$0^{\circ}C$ with different duration of time. The amounts of crystallization are estimated by the method of x-ray powder diffraction. As the results a time-temperature-transformation relation for crystallization is derived. The maximum rate of crystallization is observed at about 75$0^{\circ}C$ from the T-T-T-curve while the crystallization temperature is detected at 67$0^{\circ}C$ by DTA measurement. The crystallization temperature moved to 62$0^{\circ}C$ by adding 5 weight percents of TiO2 and it moved to 78$0^{\circ}C$ by adding 2 weight percents of V2O5. The crystallization temperature moved to 62$0^{\circ}C$ by adding 5 weight percent of TiO2 it moved to 78$0^{\circ}C$ by adding 2 weight percents of V2O5 The activation energy for crystallization from the pure glass is calculated as 68 Kcal/mol and it varied to 53 Kcal/mol and 110Kcal/mol when 5 weight percents of TiO2 and weight percents of V2O5 are added respectively.

• 한국자동차공학회논문집
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• 제12권4호
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• pp.207-212
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• 2004

Full-beads of multi-layer steel engine head gaskets that are used to seal the combustion gas between the head and the block are subject to cyclic bending stresses due to the variation of the head/block gap during engine operation. The S-N curve for the fatigue durability assessment of the full-bead formed on NBR-coated SUS301 thin plate is deduced from the axial fatigue test results because of the difficulty in conducting the bending fatigue test of thin plate. The experimental verification of the deduced S-N curve is presented. It is shown that the NBR coating increases the endurance limit of the plate significantly. Mechanism of crack nucleation and propagation in the full-bead is discussed with photographs of the fatigue cracks.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.143-146
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• 2001

The evolution of dynamic recrystallization (DRX) was studied with torsion test for AISI 304 stainless steel in the temperature range of $900-1000^{\circ}C$ and strain rate range of 0.05-5/sec. The evolution of DRX was investigated with microstructural analysis and change of flow stress curve slope. The investigation of serrated grain boundaries using electron back scattered diffraction (EBSD) analysis indicated that the nucleated new DRX grain size was similar to the size of bulging part. Before the steady state, the dynamically recrystallizing grains do not remain a constant size and gradually grow to the size of fully DRX grain at steady state. The calculation of grain size was based on $X_{DRX}$ and the assumption, which the nucleated DRX grains are growing to the steady state, continuously. It was found that the calculated results agreed with the microstructure of the alloy.

• 한국광물학회지
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• 제11권1호
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• pp.32-44
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• 1998

The transformation sequence of kaolinite to mullite is examined with new electron diffraction data obtained mainly by an energy filtering transmission electron microscope. Kaolinite is transformed finally into mullite and cristobalite through several steps of continuous reactions by heating, which result in metakaolinite, microcrystalline spinel-type phase and amorphous silica. Metakaolinite maintains a short-range order in its structure ven at $920^{\circ}C$. Spinel phase results from a topotactictransformation of metakaolinite apart from the breakdown of metakaolinite structure. the first strong exothermic peak on DTA curve is mainly due to the extraction of amorphous silica from metakaolinite and the gradual nucleation of mullite. Metakaolinite decomposes around$ 940^{\circ}C$ to mullite that doesn't show a clear crystallographic relationship to the parent metakaolinite structure. However, spinel phase produced previously is maintained. The initially formed spinel and mullite phases are suggested to be Al-rich, but progressively gain Si in their structures at higher temperatures. Spinel phase decomposes completely through a second weak exothermic reaction promoting the growth of mullite, and crystallization of amorphous silica to cristobalite.

• 한국가스학회지
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• 제7권1호
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• pp.41-46
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• 2003

14atm, 233K의 아세틸렌 기체를 자유팽창 시켜서 생성한 아세틸렌 cluster의 상과 온도 변화를 실험적으로 측정하였으며, cluster를 여러 겹의 shell로 나누어 취급하고 각 shell 마다 증발과 열전도 현상에 근거한 온도계산을 하는 모델링을 적용하여 이론적인 온도를 구하고 실험값과 비교함으로써, 생성된 cluster의 크기를 4.88$\mu$으로 결정하였다.