• Title/Summary/Keyword: Micro-structure of Spray

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1-D Microstructure Evolution of Electrostatic Sprayed Thermosetting Phenol-formaldehyde Resin Coating (정전분무법으로 제작된 열경화성 Phenol-formaldehyde resin 코팅층의 1차원적 미세구조 형성 메카니즘)

  • Kim, Baek Hyun;Bae, Hyun Jeong;Goh, Yumin;Kwon, Do-Kyun
    • Korean Journal of Materials Research
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    • v.26 no.9
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    • pp.472-477
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    • 2016
  • Microstructure evolutions of thermosetting resin coating layers fabricated by electrostatic spray deposition (ESD) at various processing conditions were investigated. Two different typical polymer systems, a thermosetting phenol-formaldehyde resin and a thermoplastic polyvinylpyrrolidone (PVP), were employed for a comparative study. Precursor solutions of the phenol-formaldehyde resin and of the PVP were electro-sprayed on heated silicon substrates. Fundamental differences in the thermomechanical properties of the polymers resulted in distinct ways of microstructure evolution of the electro-sprayed polymer films. For the thermosetting polymer, phenol-formaldehyde resin, vertically aligned micro-rod structures developed when it was deposited by ESD under controlled processing conditions. Through extensive microstructure and thermal analyses, it was found that the vertically aligned micro-rod structures of phenol-formaldehyde resin were formed as a result of the rheological behavior of the thermosetting phenol-formaldehyde resin and the preferential landing phenomenon of the ESD method.

A Study on Nozzle Flow and Spray Characteristics of Piezo Injector for Next Generation High Response Injection (차세대 고응답 분사용 피에조 인젝터의 노즐유동 및 분무특성에 관한 연구)

  • Lee Jin-Wook;Min Kyoung-Doug
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.6 s.249
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    • pp.553-559
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    • 2006
  • Most diesel injector, which is currently used in high-pressure common rail fuel injection system of diesel engine, is driven by the solenoid coil energy for its needle movement. The main disadvantage of this solenoid-driven injector is a high power consumption, high power loss through solenoid coil and relatively fixed needle response's problem. In this study, a prototype piezo-driven injector, as a new injector mechanism driven by piezoelectric energy based on the concept of inverse piezo-electric effect, has been designed and fabricated to know the effect of piezo-driven injection processes on the diesel spray structure and internal nozzle flow. Firstly we investigated the spray characteristics in a constant volume chamber pressurized by nitrogen gas using the back diffusion light illumination method for high-speed temporal photography and also analyzed the inside nozzle flow by a fully transient simulation with cavitation model using VOF(volume of fraction) method. The numerical calculation has been performed to simulate the cavitating flow of 3-dimensional real size single hole nozzle along the injection duration. Results were compared between a conventional solenoid-driven injector and piezo-driven injector, both equipped with the same micro-sac multi-hole injection nozzle. The experimental results show that the piezo-driven injector has short injection delay and a faster spray development and produces higher injection velocity than the solenoid-driven injector. And the predicted simulation results with the degree of cavitation's generation inside nozzle for faster needle response In a piezo-driven injector were reflected to spray development in agreement with the experimental spray images.

HVOF Thermal Spray Coating of WC-Co for Durability Improvement of High Speed Spindle (초고속 스핀들의 내구성 향상을 위한 WC-Co 분말의 HVOF 용사 코팅)

  • Kim, K.S.;Baek, N.K.;Yoon, J.H.;Cho, T.Y.;Youn, S.J.;Oh, S.K.;Hwang, S.Y.;Chun, H.G.
    • Journal of the Korean institute of surface engineering
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    • v.39 no.4
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    • pp.179-189
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    • 2006
  • High velocity oxygen fuel(HVOF) thermal spray coating of WC-Co powder is one of the most promising candidate for the replacement of the traditional hard chrome plating and ceramics coating because of the environmental problem of the very toxic $Cr^{6+}$ known as carcinogen and the brittleness of ceramics coating. WC-Co micron and nano powder were coated by HVOF thermal spraying method for the study of durability improvement of the high speed spindle. Coatings were planned by Taguchi program for the four spray parameters of spray distance, flow rates of hydrogen, oxygen and powder feed rate. Optimal coating process was obtained by the studies of coating properties such as porosity, surface roughness, micro hardness, and micro structure. WC-Co micron and nano powder were coated on the Inconel 718 substrate by the optimal coating process obtained in this study. The wear behaviors were studied by the sliding wear tester at room temperature and at an elevated temperature of $500^{\circ}C$ for the application to high speed spindle. Sliding wear test was carried out for four most promising hard coatings of chrome coating, ceramics coatings such as $A1_2O_3,\;Cr_2O_3$ and HVOF Co-alloy T800 for the comparison of their wear behaviors. HVOF WC-Co coating was better than other coatings showing highest micro hardness of 1400 Hv and comparable friction coefficients with others. HVOF WC-Co coating is a strong candidate for the replacement of the traditional hard chrome plating for the high speed spindle.

Electrochemical Performance of Micro Sized Silicon/CNT/Carbon Composite as Anode Material for Lithium Ion Batteries (리튬이차전지용 음극활물질로서 Micro sized Silicon/CNT/Carbon 복합입자의 전기화학적 특성)

  • Shin, Min-Seon;Lee, Tae-Min;Lee, Sung-Man
    • Journal of the Korean Electrochemical Society
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    • v.22 no.3
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    • pp.112-121
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    • 2019
  • In this study, silicon / carbon nanotube / carbon composite particles with high capacity were fabricated by using micro-sized silicon particles and carbon nanotubes as an anode material for lithium ion batteries. The silicon / carbon nanotube / carbon composite particles were prepared by spray drying method to prepare spherical composite particles. The composite particles have the network structure of the carbon nanotubes around the silicon particles, in which the silicon particles and the carbon nanotubes are bonded by amorphous carbon. It appears that the volume expansion of silicon is effectively buffered and the electrical contact is maintained in the network structure of the composite particles during charge-discharge cycles.

Molecular Dynamics Study on Behaviors of Liquid Cluster with Shape and Temperature of Nano-Structure Substrate (나노구조기판의 형상 및 온도변화에 따른 액체 클러스터의 거동에 대한 분자동역학적 연구)

  • Ko, Sun-Mi;Jeong, Heung-Cheol;Shibahara, Masahiko;Choi, Gyung-Min;Kim, Duck-Jool
    • Journal of ILASS-Korea
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    • v.13 no.1
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    • pp.34-41
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    • 2008
  • Molecular dynamic simulations have been carried out to study the effect of the nano-structure substrate and its temperature on cluster laminating. The interaction between substrate molecules and liquid molecules was modeled in the molecular scale and simulated by the molecular dynamics method in order to understand behaviors of the liquid cluster on nano-structure substrate. In the present model, the Lennard-Jones potential is applied to mono-atomic molecules of argon as liquid and platinum as nano-structure substrate to perform simulations of molecular dynamics. The effect of wettability on a substrate was investigated for the various beta of Lennard-Jones potential. The behavior of the liquid cluster and nano-structure substrate depends on interface wettability and function of molecules force, such as attraction and repulsion, in the collision progress. Furthermore, nano-structure substrate temperature and beta of Lennard-Jones potential have effect on the accumulation ratio. These results of simulation will be the foundation of coating application technology for micro fabrication manufacturing.

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HVOF Spray Coating of Co-alloy(T800) for the Improvement of durability of High Speed Spindle (초고속 회전체의 내구성향상을 위한 Co-alloy(T800)의 초고속 용사코팅)

  • Cho, Tong-Yul;Yoon, Jae-Hong;Kim, Kil-Su;Youn, Suk-Jo;Back, Nam-Ki;Park, Byung-Chul;Chun, Hui-Gon
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.15 no.6
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    • pp.32-37
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    • 2006
  • Micron size Co-alloy(T800) powder was coated on Inconel 718 by HVOF thermal spraying for the studies of the improvement of durability of high speed spindle by using Taguchi program for the parameters of spray distance, flow rates of hydrogen and oxygen and powder feed rate. The optimal coating process was determined by the studies of coating properties such as micro-structure, porosity, surface roughness and micro hardness. Friction and wear behaviors of coatings were investigated by sliding wear test at room temperature and $1000^{\circ}F(538^{\circ}C)$. At both room temperature and $538^{\circ}C$ the sliding wear debris and friction coefficients of the coating were drastically reduced compared with the surface of non-coated parent material. This shows that Co-alloy powder coating is highly recommendable for the durability improvement surface coating of high speed air-bearing spindle. At high temperature wear traces and friction coefficients of both coating and non-coating were drastically reduced compared with those of room temperature since the brittle oxides were formed easily on the surface, and the brittle oxide phases were attrited by the reciprocating sliding wear according to the complicated mixed wear mechanisms These oxide particles, partially melts and the melts play role as lubricant and reduce the wear and friction coefficient. This also shows that Co-alloy powder coating is highly recommendable far the durability improvement surface coating on the surface vulnerable to frictional heat such as high speed spindles.

Synthesis of ceria by combination of spray pyrolysis, postheat, and ball-milling and its characterization (분무열분해, 후소성 및 볼밀링을 조합한 방법을 이용한 세리아의 합성 및 특성연구)

  • Kim, Hyun-Ik;Kim, Sang Pil;Song, Jae-Kyung;Kim, Sang Hern
    • Journal of the Korean Applied Science and Technology
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    • v.35 no.4
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    • pp.1057-1072
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    • 2018
  • In this study, micro-sized $CeO_2$ particles were synthesized by spray pyrolysis, and EG(ethylene glycol) and CA(citric acid) as organic additives were added to obtain hollow and porous particle during spray pyrolysis, and characteristics of obtained ceria were investigated according to the amount of added organic additives. Spray pyrolysis, postheat and ball-milling were combined to give 6 paths. $CeO_2$ nano-sized particle was obtained by the path which has sequence of Spray Pyrolysis with 0.5 M of EG and CA${\rightarrow}$Post-heat${\rightarrow}$Ball-milling${\rightarrow}$Post-heat among 6 paths. The average particle size(24 nm with standard deviation of 3.8 nm) of $CeO_2$ nano-sized particle by TEM analysis is close to the primary particle size(20 nm) which was calculated by Debye-Scherrer equation. To investigate the morphological characteristics and structure of the synthesized nanoparticle powders, SEM(Scanning Electron Microscopy), XRD(X-Ray Diffractometer) and TEM(Transmission Electron Microscopy) were used.

A Study on Characteristics of Gas/Liquid Coaxial Sprays Under Varying Flow Conditions (분사조건에 따른 기체/액체 동축형 인젝터의 분무특성에 관한 연구)

  • Jeong, W.H.;Kim, D.;Im, J.H.;Yun, Y.
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.1
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    • pp.54-61
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    • 2005
  • Characteristics of sprays injected by gas/liquid coaxial atomizers operated at atmospheric pressure are studied using shadowgraph, mechanical patternator and PDPA. The gas-to- liquid momentum flux ratio(M) and the liquid Reynolds number(Re) are selected as key parameters in characteristics of gas/liquid coaxial sprays from the dimensional analysis. The properties of shear coaxial sprays are compared with those of swirl coaxial sprays through the macroscopic and microscopic analysis. Macroscopic similarities between shear and swirl coaxial sprays are revealed under flow conditions of high momentum flux ratio. Also, empirical correlations between the mean drop diameters(D32) and operating conditions of coaxial sprays are proposed in this paper.

An Effect of the Micro Bubble Formation Depending on the Saturator and the Nozzle in the Dissolved Air Flotation System (DAF 공정에서 공기포화장치와 노즐 특성 별 미세기포 발생에 미치는 영향)

  • Park, S.C.;Oh, H.Y.;Chung, M.K.;Song, S.L.;Ahn, Y.H.
    • Journal of Korean Society of Environmental Engineers
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    • v.35 no.12
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    • pp.929-936
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    • 2013
  • The saturator and injection nozzle are important facilities on the dissolved air flotation process. To increase the formation of micro bubble, it is required to improve the air dissolving performance in the saturator and keep the pressure uniform from the saturator to the nozzle. This study aimed to evaluate the performance of the saturator and the hydraulic effect of the nozzle and the pipe structure. The air volume concentration, bubble size and bubble residual time were measured in the test. The saturator, which had mounted with the spray nozzle, showed a good performance for bubble formation. Also, the characteristics of micro bubble formation were influenced by pressure uniformity and flow velocity through the orifice in the nozzle.

Effect of the Coating Structure on the Corrosion Resistance of Al-Mg Coated Steel (Al-Mg 코팅층의 구조가 강판 내식성에 미치는 영향)

  • Jung, Jae-Hun;Yang, Ji-Hoon;Kim, Sung-Hwan;Byeon, In-Seop;Jeong, Jae-In;Lee, Myeong-Hoon
    • Journal of the Korean institute of surface engineering
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    • v.49 no.5
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    • pp.454-460
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    • 2016
  • Double-layered Al-Mg films have been deposited by using an e-beam deposition method on a cold-rolled steel sheet(CR), which the structure of the film was Al/Mg/CR. The micro-structure, alloy phase, and corrosion resistance of the Al-Mg coated CR were investigated before and after heat treatment at $400^{\circ}C$ for 2, 3, and 10 min in a nitrogen atmosphere. Total thickness of Al-Mg films was fixed at $3{\mu}m$ and the thickness ratio of Al and Mg layers(Al:Mg) has been changed from 5:1 to 1:5. The cross-sectional morphology of the films, which had the thickness ratio of 2:1(Al:Mg), 1:1, and 1:2, was changed after heat treatment from columnar to featureless structure. The x-ray diffraction data for as-deposited films showed only pure Al and Mg peaks. Al-Mg alloy peaks such as $Al_3Mg_2$ and $Al_{12}Mg_{17}$ phase appeared after the heat treatment. The Al-Mg coating with the thickness ratio of 1:1(Al:Mg) showed the best corrosion resistance of up to 500 hours by salt spray test.