• Title/Summary/Keyword: Nucleation

Search Result 1,107, Processing Time 0.026 seconds

Vapor Bubble Nucleation : A Microscopic Phenomenon

  • Kwak, Ho-Young
    • Journal of Mechanical Science and Technology
    • /
    • v.18 no.8
    • /
    • pp.1271-1287
    • /
    • 2004
  • In this article, vapor bubble nucleation in liquid and the evaporation process of a liquid droplet at its superheat limit were discussed from the viewpoint of molecular clustering (molecular cluster model for bubble nucleation). For the vapor bubble formation, the energy barrier against bubble nucleation was estimated by the molecular interaction due to the London dispersion force. Bubble nucleation by quantum tunneling in liquid helium under negative pressure near the absolute zero temperature and bubble nucleation on cavity free micro heaters were also presented as the homogenous nucleation processes.

Investigation on HT-AlN Nucleation Layers and AlGaN Epifilms Inserting LT-AlN Nucleation Layer on C-Plane Sapphire Substrate

  • Wang, Dang-Hui;Xu, Tian-Han
    • Journal of the Optical Society of Korea
    • /
    • v.20 no.1
    • /
    • pp.125-129
    • /
    • 2016
  • In this study, we have investigated a high-temperature AlN nucleation layer and AlGaN epilayers on c-plane sapphire substrate by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). High resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscope (SEM) and Raman scattering measurements have been exploited to study the crystal quality, surface morphology, and residual strain of the HT-AlN nucleation layer. These analyses reveal that the insertion of an LT-AlN nucleation layer can improve the crystal quality, smooth the surface morphology of the HT-AlN nucleation layer and further reduce the threading dislocation density of AlGaN epifilms. The mechanism of inserting an LT-AlN nucleation layer to enhance the optical properties of HT-AlN nucleation layer and AlGaN epifilm are discussed from the viewpoint of driving force of reaction in this paper.

Ultrasonic Processing of Polymer Foam (고분자 포움의 초음파 가공)

  • 변성광;윤재륜
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.13 no.4
    • /
    • pp.618-624
    • /
    • 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.

Nucleation of CVD Diamond on Various Substrate Materials

  • Fukunaga, O.;Qiao, Xin;Ma, Yuefei;Shinoda, N.;Yui, K.;Hirai, H.;Tsurumi, T.;Ohashi, N.
    • The Korean Journal of Ceramics
    • /
    • v.2 no.4
    • /
    • pp.184-187
    • /
    • 1996
  • Diamod nucleation by mw assisted CVD was examined various conditions namely, (1) diamond nucleation on variour substrate materials, such as Si, cubic BN, pyrolytic BN and AIN, (2) AST(Activated species transport) method which promote nucleation of diamond on single crystal and polycrystalline alumina substrate was developed. (3) Effect of bias enhancement of nucleation on single crystalline Si was examined, and finally (4) DST (Double step treatment) method was developed to enhance diamond nucleation on Ni. In this method, we separated carbon diffusing process into Ni, carbon precipitating process from the inside of Ni and diamond precipitation process.

  • PDF

Bubble Nucleation and Behavior on Square Micro Heaters (사각 마이크로 히터위에서의 기포의 형성 및 거동)

  • Jung, Jung-Yeul;Kwak, Ho-Young
    • Proceedings of the KSME Conference
    • /
    • 2004.04a
    • /
    • pp.1464-1469
    • /
    • 2004
  • In this study, micro square heaters having dimensions of $65{\times}65{\mu}m^2$and $100{\times}100{\mu}m^2$ were fabricated and bubble nucleation experiments on the heaters were performed. Bubble nucleation temperature was also measured using a bridge circuit and the photographs of bubble nucleation and subsequent growth were taken by a camera with a flash unit. Measured bubble nucleation temperatures were found to be closer to the superheat limit of working fluid (FC-72). Also quasi-1D analyses for the square heaters were performed. The quasi-1D analysis yielded proper temperature distribution of the square heater at steady state, however failed to predict the temperature rise up to the steady state. Similar time dependent temperature can be obtained with proper value of thermal diffusivity. For the $100{\times}100{\mu}m^2$ square heater, nucleation of several bubbles was observed while only one bubble was observed to be nucleated on $65{\times}65{\mu}m^2$ heater.

  • PDF

Nucleation Theory

  • 곽호영
    • Journal of the KSME
    • /
    • v.22 no.1
    • /
    • pp.34-39
    • /
    • 1982
  • 본 해설에서는 nucleation현상의 한 예로 과포화상태에 있는 증기 (vapor)의 응축과 정(condensation)을 중심으로 설명하고자 한다. 제 2절에서는 nucleation 현상의 예와 그 응용에 대해서 설명하기로 하고 제 3절에서는 열역학적인 면에서 제 4절은 운동론적인 면에서 제 5절은 nucleation theory의 문제점에 관해 고찰해 보려 한다.

  • PDF

Bubble Nucleation in Polymer Solutions (고분자 용액에서의 기포 형성)

  • 강성린;김기영;곽호영
    • Polymer(Korea)
    • /
    • v.28 no.1
    • /
    • pp.51-58
    • /
    • 2004
  • The molecular cluster model for the homogeneous bubble nucleation rather than the classical nucleation theory was extended to predict the bubble nucleation events in elastomers(cross-linked polymers), polymers and polymer which are dissolved in the organic solvent. The classical theory assumes the formation of the critical bubble while the molecular cluster model assumes the critical cluster as for the initiation of the bubble nucleation. For the bubble nucleation in elastomers and polymers, the strain energy overcome by a critical bubble was also considered. The calculation results for the number of bubbles nucleated in elastormers and polymer solutions, which are about 10$\^$8/∼10$\^$12/ bubbles/㎤ are in good agreement with observed ones.

Bubble Nucleation in Polymer Solutions (폴리머 용액에서의 기포 형성)

  • Kang, Sung-Lin;Kim, Ki-Young;Kwak, Ho-Young
    • Proceedings of the KSME Conference
    • /
    • 2003.11a
    • /
    • pp.1228-1233
    • /
    • 2003
  • The molecular cluster model for the homogeneous bubble nucleation was extended to predict the bubble nucleation events in elastomers, polymers and polymer solutions. For the bubble nucleation in elastomers and polymers, the strain energy overcome by a critical bubble was also considered. The calculation results for the number of bubbles nucleated are in good agreement with observed ones.

  • PDF

Effects of Nucleation Layer's Surface Roughness on the Quality of InP Epitaxial Layer Grown on GaAs Substrates (Nucleation Layer의 표면 거칠기가 GaAs 기판 위에 성장된 InP 에피층의 품질에 미치는 영향)

  • Yoo, Choong-Hyun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
    • /
    • v.25 no.8
    • /
    • pp.575-579
    • /
    • 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.

Immiscibility, nucleation and mechanical properties in the lithia-baria-silica system

  • Ertug, Burcu
    • Journal of Ceramic Processing Research
    • /
    • v.19 no.5
    • /
    • pp.394-400
    • /
    • 2018
  • The current work investigates the effects of nucleation heat treatments, on the microstructure and mechanical properties of a novel silicate glass in $Li_2O-BaO-SiO_2$ system with 1 mol% $P_2O_5$ as nucleating agent. As-cast glass was exposed to nucleation heat treatments at $490-550^{\circ}C$ for 1-3 h. The microstructural examination was performed by SEM/EDS. The highest Vickers microhardness was determined to be 650 Hv for the sample heat treated at $550^{\circ}C$ for 1 h. The increase in the nucleation time also affected Vickers microhardness and the highest one was determined to be 600 Hv after nucleation for 3 h. The fracture toughness, $K_{IC}$ reached $2.51MPa.m^{1/2}$ after nucleation at $550^{\circ}C$ for 1 h. The nucleation temperatures had a more pronounced effect on the fracture toughnesses in comparison to nucleation times. The indentation toughness data was used to determine Weibull parameters from Ln ln [1/(1-P)]-$lnK_{IC}$ plots. Weibull modulus, m of the samples nucleated at 500, 510, 530, $550^{\circ}C$ for 1h. and $540^{\circ}C$ for 2 h. were determined similarly to be 3.8, 3.5, 4.7 and 3.9, respectively. The rest of the samples indicated higher Weibull moduli, which may be attributed to the formations of microcracks due to the mismatch in between newly formed crystals and remaining glassy matrix.