• International Journal of Fluid Machinery and Systems
• /
• 제9권1호
• /
• pp.66-74
• /
• 2016

Concerning the numerical simulation of high-speed water jet with intensive cavitation this paper presents a practical compressible mixture flow method by coupling a simplified estimation of bubble cavitation and a compressible mixture flow computation. The mean flow of two-phase mixture is calculated by URANS for compressible fluid. The intensity of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the mean flow, and the effect of cavitation on the flow turbulence is considered by applying a density correction to the evaluation of eddy viscosity. High-speed submerged water jets issuing from a sheathed sharp-edge orifice nozzle are treated when the cavitation number, ${\sigma}=0.1$, and the computation result is compared with experimental data The result reveals that cavitation occurs initially at the entrance of orifice and bubble cloud develops gradually while flowing downstream along the shear layer. Developed bubble cloud breaks up and then sheds downstream periodically near the sheath exit. The pattern of cavitation cloud shedding evaluated by simulation agrees experimental one, and the possibility to capture the unsteadily shedding of cavitation clouds is demonstrated. The decay of core velocity in cavitating jet is delayed greatly compared to that in no-activation jet, and the effect of the nozzle sheath is demonstrated.

• Journal of Welding and Joining
• /
• 제15권4호
• /
• pp.126-135
• /
• 1997

$H_2/O_2$ 비에 따른 Hybrid HVOF 용사된 $Cr_3C_2$-7wt%(NiCr) 용사층의 특성 및 산화거동 This study was performed to investigate the influence of fuel/oxygen ratio (F/O=3.2, 3.0, 2.8) on the characteristics and the oxidation behavior of the hybrid-HVOF sprayed $Cr_3C_2$-7wt%NiCr coatings. Decomposition and the oxidation of the $Cr_3C_2$was occured during spraying. The degree of transformation from $Cr_3C_2$to $Cr_7C_3$ was increased with decreasing the F/O ratio. The microstructural differences of the as sprayed coating with F/O ratio can not be distinguished, However, large pores were diminished and then the coatings became dense by heat treatment. Microhardness of the as-sprayed specimen which sprayed with F/O=3.0 condition was hightest ($Hv_{300}$=1140) and the hardness was increased to 1500 after heat treatment at $600^{\circ}C$ for 50hrs in air. It was supposed that hardness was increased due to the formation of $Cr_2O_3$ within $Cr_3C_2$/$Cr_7C_3$matrix and the densification of coating layer during heat treatment. Apparent activation energy for oxidation was varied from 21.2 kcal$mol^{-1}K^{-1}$ to 23.8 kcal$mol^{-1}K^{-1}$ with respect to the F/O ratio. The surface morphology was changed to porous and oxide chusters were grown after oxidation $1000^{\circ}C$ for 50 hours by the aggressive evolution of gas phase ($CrO_3$ and$CO_2$). The oxide cluster was composed of Ni and Cr.

• 한국결정성장학회지
• /
• 제8권3호
• /
• pp.387-387
• /
• 1998

본 연구에서는 기상화학 증착법으로 성장되는 GaN 후막에 대한 열역학적 전사모사를 수행하고 이를 실험결과와 비교, 검토하였다. 열역학적계산은 화학양론적 연산방식을 이용하여 수치 해석하였으며, 모사의 변수로써 온도범위는 400∼1500K, 기상비율은 $(GaCl_3)/[GaCl_3+NH_3],(N_2)/(GaCl_3+NH_3)$를 취하였다. GaN의 성장온도 범위는 이론적인 계산이 실험결과보다 훨씬 낮은 450∼750K으로 예측되었다. 성장온도에서 모사결과와 실험결과와의 차이는 GaN의 기상 에픽텍시 성장이 박막성장의 높은 활성화 에너지 때문에 반응속도론적으로 국한된 영역 내에서 발생한다는 것을 나타낸다.

• 한국재료학회지
• /
• 제15권5호
• /
• pp.348-352
• /
• 2005

Gallium oxyhydroxide (GaOOH) powders were heat-treated in a flowing ammonia gas to form GaN, and the reaction kinetics of the oxide to nitride was quantitatively determined by X-ray diffraction analysis. GaOOH turned into intermediate mixed phases of $\alpha-\;and\;\beta-Ga_2O_3$, and then single phase of GaN. The reaction time for full conversion $(t_c)$ decreased as the temperature increased. There were two-types of rapid reaction processes with the reaction temperature in the initial stage of nitridation at below $t_c$, and a relatively slow processes followed over $t_c$ does not depends on temperatures. The nitridation process was found to be limited by the rate of an interfacial reaction with the reaction order n value of 1 at $800^{\circ}C$ and by the diffusion-limited reaction with the n of 2 at above $1000^{\circ}C$, respectively, at below $t_c$. The activation energy for the reaction was calculated to be 1.84 eV in the temperature of below $830^{\circ}C$, and decreased to 0.38 eV above $830^{\circ}C$. From the comparative analysis of data, it strongly suggest the rate-controlling step changed from chemical reaction to mass transport above $830^{\circ}C$.

• 열처리공학회지
• /
• 제6권4호
• /
• pp.204-212
• /
• 1993

The preparation of $TiO_2$ fine particles from $TiCl_4$ and oxygen by the vapor-phasereaction was investigated at $850^{\circ}C$ with an emphasis on the effect of its experimental conditions on the crystal type of the products. Anatase $TiO_2$ particles prepared by experiment were used to study anatase-rutile transition by calcination temperature, the additives and gas atmosphere. The results were as follows. The kinetics of anatase-rutile transition was well agreed with A vrami equation, and the activation energy of transition was 35kcal/mol. The addition of CuO in anatase $TiO_2$ particles accelerated the anatase-rutile transition, and its transition was retarded in vaccum.

• 대한화학회지
• /
• 제24권3호
• /
• pp.201-208
• /
• 1980

CNDO/2 MO 계산방법을 사용하여 양성자화된 아세트알데히드와 알코올 및 양성자화된 아세트산과 알코올간의 기체반응에 대한 전이상태구조를 최적화하였다. 계산으로 얻은 구조에 따르면 전자의 반응은 공격하는 알코올의 alkyl-O 절단으로 진행되고 후자의 반응은 acyl-O 절단으로 진행될 것임을 보여주어 실험결과와 일치하였다. 또 반응물질들의 eigenvector 성질들로 판단할 때 전자의 반응은 charge controlled인 반면 후자의 반응은 orbital controlled임을 예측케 해주었다. Caserio 등이 제안한 전이상태를 가정한 CNDO/2 활성화에너지 결과에 따르면 후자의 경우는 실험결과와 일치하는 알코올의 반응성 순위를 주지만 전자의 경우는 실험결과와 반대되는 순위를 주었다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
• /
• pp.47-47
• /
• 2008

P-type transparent semiconductor $SrCu_2O_2$ thin films have been prepared by RF sputtering using low-alkali glass for LCD and quartz as substrates. Single phase of $SrCu_2O_2$ powder was obtained by heating a stoichiometric mixture of CuO and $SrCO_3$ at 1223K for 96h under N2 gas flow, and target was fabricated at 1243K for 24h. Room temperature conductivity of the sintered body was about 0.02S/cm, and the activation energy in the temperature range of $-50^{\circ}C$~RT and RT~$150^{\circ}C$ were 0.18eV, 0.07eV, respectively. Effects of deposition pressure and post-annealing temperature on the electrical and optical properties of the obtained thin film have been investigated.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2009년도 제38회 동계학술대회 초록집
• /
• pp.195-195
• /
• 2010

$Ga_2O_3$ thin films have been grown on Si(001) substrates by metalorganic chemical vapor deposition (MOCVD) using dimethylgallium isopropoxide ($Me_2GaO^iPr$, DMGIP) with oxygen as the reactant gas. Suitability of the precursor for CVD was confirmed by thermogravimetric analysis (TGA) and vapor pressure measurement. Deposition was carried out in the substrate temperature range $450-650^{\circ}C$. Spectroscopic ellipsometry, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) and Rutherford back-scattering spectroscopy (RBS) were used to determine the thickness, crystallinity, and composition and stoichiometry of the films, respectively. From the slope of the Arrhenius plot in the temperature range $500-550^{\circ}C$, the activation energy of deposition was found to be $225.5\;kJ\;mol^{-1}$. As-deposited films were amorphous, but the monoclinic $\beta-Ga_2O_3$ phase was revealed after annealing the films in air at $1050^{\circ}C$. The XPS and RBS analyses indicate that the $Ga_2O_3$ films obtained by using DMGIP were found to be almost stoichiometric.

• 농약과학회지
• /
• 제17권4호
• /
• pp.388-393
• /
• 2013

Bacillus vallismortis strain EXTN-1은 근권세균으로써 생육촉진 효과와 함께 광범위한 식물 병 방제효과가 보고되어있다. 본 연구에서 EXTN-1으로부터 방출되는 휘발성 유기 화합물도 식물의 생육촉진과 방어시스템에 관여를 하는지 확인하기 위해 수행되었다. I-plate 시스템에서 각기 다른 배지(TSA, LBA, NA, KBA, PDA)에 EXTN-1을 배양하였을 때, KBA배지에서 가장 높은 생육촉진현상이 확인되었고 TSA, LBA, NA, PDA 배지에서도 생육촉진을 확인할 수 있었다. 생육촉진 현상에 $CO_2$가 관여 할 수 있지만 TSA, PDA, LBA의 배지에서는 $CO_2$와의 관계없음을 확인 할 수 있었다. SPME-GC/MS를 이용해 휘발성 유기화합물을 확인한 결과, 가장 많이 방출되는 휘발성 유기화합물은 3-Hydroxy-2- butanone으로 각 농도 (10 ppm~0.001 ppm)에서 생육차이와 발병도를 확인하였다. 1 ppm에서 생육은 무처리에 비해 2.6배 증가한 반면에 0.001 ppm에서 1.2배로 가장 적게 증가하였고 발병도는 10 ppm에서 46%, 0.001 ppm에서 65%로 가장 높게 발병되었지만 무처리(91%)에 비해 낮았다. 이러한 효과는 EXTN-1으로부터 방출되는 휘발성 유기 화합물이 식물의 생육촉진과 병에 대한 저항성 발현에 관여한다고 볼 수 있다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
• /
• pp.100-101
• /
• 2012

The plasma damage free and room temperature processedthin film deposition technology is essential for realization of various next generation organic microelectronic devices such as flexible AMOLED display, flexible OLED lighting, and organic photovoltaic cells because characteristics of fragile organic materials in the plasma process and low glass transition temperatures (Tg) of polymer substrate. In case of directly deposition of metal oxide thin films (including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS)) on the organic layers, plasma damages against to the organic materials is fatal. This damage is believed to be originated mainly from high energy energetic particles during the sputtering process such as negative oxygen ions, reflected neutrals by reflection of plasma background gas at the target surface, sputtered atoms, bulk plasma ions, and secondary electrons. To solve this problem, we developed the NBAS (Neutral Beam Assisted Sputtering) process as a plasma damage free and room temperature processed sputtering technology. As a result, electro-optical properties of NBAS processed ITO thin film showed resistivity of $4.0{\times}10^{-4}{\Omega}{\cdot}m$ and high transmittance (>90% at 550 nm) with nano- crystalline structure at room temperature process. Furthermore, in the experiment result of directly deposition of TCO top anode on the inverted structure OLED cell, it is verified that NBAS TCO deposition process does not damages to the underlying organic layers. In case of deposition of transparent conductive oxide (TCO) thin film on the plastic polymer substrate, the room temperature processed sputtering coating of high quality TCO thin film is required. During the sputtering process with higher density plasma, the energetic particles contribute self supplying of activation & crystallization energy without any additional heating and post-annealing and forminga high quality TCO thin film. However, negative oxygen ions which generated from sputteringtarget surface by electron attachment are accelerated to high energy by induced cathode self-bias. Thus the high energy negative oxygen ions can lead to critical physical bombardment damages to forming oxide thin film and this effect does not recover in room temperature process without post thermal annealing. To salve the inherent limitation of plasma sputtering, we have been developed the Magnetic Field Shielded Sputtering (MFSS) process as the high quality oxide thin film deposition process at room temperature. The MFSS process is effectively eliminate or suppress the negative oxygen ions bombardment damage by the plasma limiter which composed permanent magnet array. As a result, electro-optical properties of MFSS processed ITO thin film (resistivity $3.9{\times}10^{-4}{\Omega}{\cdot}cm$, transmittance 95% at 550 nm) have approachedthose of a high temperature DC magnetron sputtering (DMS) ITO thin film were. Also, AOS (a-IGZO) TFTs fabricated by MFSS process without higher temperature post annealing showed very comparable electrical performance with those by DMS process with $400^{\circ}C$ post annealing. They are important to note that the bombardment of a negative oxygen ion which is accelerated by dc self-bias during rf sputtering could degrade the electrical performance of ITO electrodes and a-IGZO TFTs. Finally, we found that reduction of damage from the high energy negative oxygen ions bombardment drives improvement of crystalline structure in the ITO thin film and suppression of the sub-gab states in a-IGZO semiconductor thin film. For realization of organic flexible electronic devices based on plastic substrates, gas barrier coatings are required to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency flexible AMOLEDs needs an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}gm^{-2}day^{-1}$. The key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (under ${\sim}10^{-6}gm^{-2}day^{-1}$) is the suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. For formation of high quality single inorganic gas barrier layer, we developed high density nano-structured Al2O3 single gas barrier layer usinga NBAS process. The NBAS process can continuously change crystalline structures from an amorphous phase to a nano- crystalline phase with various grain sizes in a single inorganic thin film. As a result, the water vapor transmission rates (WVTR) of the NBAS processed $Al_2O_3$ gas barrier film have improved order of magnitude compared with that of conventional $Al_2O_3$ layers made by the RF magnetron sputteringprocess under the same sputtering conditions; the WVTR of the NBAS processed $Al_2O_3$ gas barrier film was about $5{\times}10^{-6}g/m^2/day$ by just single layer.