• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.618-624
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• 1989

Ultrasonically induced bubble formation in thermoplastic matrix was investigated experimentally and theoretically. polystyrene was saturated with nitrogen under the pressure of 0.2 to 3.45 MPa in a pressure chamber, followed by pressure release and ultrasonic bubble nucleation. Zinc stearate was added to polystyrene as the nucleating agent to induce heterogeneous nucleation. Various mixture of low density polyethylene and polyethylene wax was also saturated with the gas. The foamed specimens with or without ultrasonically induced bubble nucleation was modeled by modifying the classical nucleation theory. The rate of ultrasonic nucleation was predicted for homogeneous and heterogeneous nucleation at a conical cavity. This study showed that the heterogeneous and heterogeneous nucleation at a conical cavity. This study showed that the heterogeneous nucleation must be employed for ultrasonic production of bubbles in a viscous fluid and the homogeneous nucleation for ultrasonic production of bubbles in a low viscosity fluid.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.11a
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• pp.28-30
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• 1992

Long incubation period of W nucleation on the TiN glue layer is a serious problem in blanket W process. In this study we investigated the dependence of W nucleation and growth rate on the preparation method of the TiN film, deposition temperature, chemistry, $SiH_4/WF_6$ ratio and sputter etching, ion implantation, and $SiH_4$ flushing pre-treatments. Incubation periods of W nucleation and deposition rates of W growth on three different TiNs are in the order of TiN>RTP-TiN> annealed TiN and TiN${\leq}$RTP-TiN${\leq}$ annealed TiN, respectively. $\beta$-W is not found on TiN substrate even for high $SiH_4/WF_6$ ratio. Sputter etching pre-treatment increases incubation period of W nucleation, while it decreases deposition rate. $SiH_4$ flushing pre-treatment decreases incubation period, but it slightly decreases deposition rate.

• Journal of the Korean Ceramic Society
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• v.18 no.3
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• pp.163-170
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• 1981

The crystallization of $Li_2O-SiO_2$ system glasses and the effect of phase separtion to crystal nucleation were studied. The crystallization temperatures of various glasses were determined by DTA and glasses were nucleation heat treated at the temperatures ranging from 45$0^{\circ}C$ to 5$25^{\circ}C$. These glasses were thengown at $700^{\circ}C$ to observable size in the optical microscope. Crystal nucleation rates of various glasses were obtained by estimating the number of crystals per unit volume. The main crystal phase of these glasses identified by X-ray diffraction was lithium disilicate ($Li_2O$.$2SiO_2$). It was found that the crystal nucleation rate of glass (19.5% $Li_2P$-80.5% $SiO_2$), the nearest composition to lithium disilicate, was higher than other glasses. The opalescence caused by phase separation was observed in the nucleation heat treated glass (16.3% $Li_2O$-83.7% $SiO_2$). The result from nucleation density measurement of this glass indicated that the nucleation was enhanced during early stage of phase separation. The molphologies of crystals in glasses and crystal growth rate at $600^{\circ}C$ were also discussed.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.169-182
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• 2014

이 연구에서는 Lennard-Jones (LJ) particle을 이용하여 상분리 현상을 이해하기 위한 컴퓨터 시뮬레이션 연구를 수행하였다. 초기에 균일하게 분포되어 있는 LJ 입자들을 시뮬레이션 하면 상대적으로 dense phase와 dilute phase로 상분리 현상이 일어나게 된다. 상분리 현상의 첫 번째 단계를 핵 생성 (nucleation) 이라고 한다. 본 연구에서는 Brownian Dynamics (BD) Simulation과 Molecular Dynamics (MD) Simulation을 이용하여 상평형 그림을 구하고 초기에 일어나는 LJ 입자들의 nucleation rates를 구하였다.

• Fibers and Polymers
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• v.4 no.3
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• pp.102-106
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• 2003

Crystallization behaviour of blends of different MFI isotactic polypropylenes (PP), and blends of PP with carbon nanofibre have been investigated by DSC and polarizing optical microscope. Both higher MFI PP component and the carbon nanofibre in the blend influence the nucleation activity of the melt during non-isothermal crystallization. In presence of carbon nanofibre, the sherulitic growth rate is highly disturbed. The calculation of nucleation activity indicates that carbon nanofibres act as active substrate for heterogeneous nucleation.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1885-1890
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• 2008

3-D heterogeneous nucleation was simulated by classical molecular dynamics (MD), where the Lennard-Jones (LJ) gas and solid cluster-seed molecules have argon and aluminum properties, respectively. There are three shapes of cluster-seeds, cube, rod, and sphere, and three classes of masses and the simulation took place under nine supersaturation ratios, making a total of 81 calculations. Results show that the dimension of the cluster-seed highly affects the rates of cluster development. In order to analyze heterogeneous nucleation above and below the critical supersaturation ratio, growth rate and liquefaction rate were separately defined to supplement the investigation. Design of experiments (DOE) was used for analysis which displayed that the shape and mass of the cluster-seed are prominent for the growth rate, while the supersaturation ratio is most significant followed by the mass for liquefaction rate. The significance of the supersaturation ratio for overall liquefaction suggests that thermal diffusion is more dominant than mass interactions for this system.

• Transactions of Materials Processing
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• v.22 no.8
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• pp.450-455
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• 2013

In the current study, a new dynamic recrystallization model for predicting high temperature flow stress is developed based on a physical model and the mean field theory. In the model, the grain aggregate is assumed as a representative volume element to describe dynamic recrystallization. The flow stress and microstructure during dynamic recrystallization were calculated using three sub-models for work hardening, for nucleation and for growth. In the case of work hardening, a single parameter dislocation density model was used to calculate change of dislocation density and stress in the grains. For modeling nucleation, the nucleation criterion developed was based on the grain boundary bulge mechanism and a constant nucleation rate was assumed. Conventional rate theory was used for describing growth. The flow stress behavior of pure copper was investigated using the model and compared with experimental findings. Simulated results by cellular automata were used for validating the model.

• Journal of Korean Vacuum Science & Technology
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• v.4 no.1
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• pp.18-22
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• 2000

For the enhancement of the nucleation density of the diamond film, we introduced the cyclic process. The cyclic process was carried out by the on/off control of CH$_4$ flow rate for a relatively short time (10 min), compared with the total reaction time (6 h). Prior to depositing the diamond film, we made the pretreated glass substrate via the unidirectional scratch using ∼l $\mu\textrm{m}$ size diamond powders. Diamond films were deposited on the pretreated glass substrate in a microwave plasma enhanced chemical vapor deposition (MPECVD) system. We observed the enhancement of the nucleation density of the diamond films caused by the cyclic process. Detailed surface morphologies of the substrate were investigated after the cyclic process. Based on these results, we discussed the cause for the enhancement of the nucleation density on the pretreated glass substrate by the cyclic process.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.8
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• pp.575-579
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• 2012

Heteroepitaxial InP films have been grown on GaAs substrates to study the effects of the nucleation layer's surface roughness on the epitaxial layer's quality. For this, InP nucleation layers were grown at $400^{\circ}C$ with various ethyldimethylindium (EDMIn) flow rates and durations of growth, annealed at $6200^{\circ}C$ for 10 minutes and then InP epitaxial layers were grown at $550^{\circ}C$. It has been found that the nucleation layer's surface roughness is a critical factor on the epitaxial layer's quality. When a nucleation layer is grown with an EDMIn flow rate of 2.3 ${\mu}mole/min$ for 12 minutes, the surface roughness of the nucleation layer is minimum and the successively grown epitaxial layer's qualities are comparable to those of the homoepitaxial InP layers reported. The minimum full width at half maximum of InP (200) x-ray diffraction peak and that of near-band-edge peak from a 4.4 K photoluminescence are 60 arcmin and 6.33 meV, respectively.

• Journal of the Korean Ceramic Society
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• v.35 no.6
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• pp.640-646
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• 1998

Nucleation and crystallzation of a quaternary glass system for lead titanate glass-ceramics were in-vestigated using DTA(differential thermal analysis ) with variation of nucleation temperature and crystal growth time. Glass samples containing 60mol% of PbO-{{{{ { TiO}_{2 } }} were prepared from melts by the conventional normal cooling method in a cylindrical brass mould. The glass sample was nucleated between 40$0^{\circ}C$ and 50$0^{\circ}C$ for a given time and showed the maximum nucleation rate at 46$0^{\circ}C$ The DTA crystallization peak temperature decreased with increasing nucleating time and decreasing heating rate during DTA runs which indicated an increase of the number of nuclei produced in the system.