• Title/Summary/Keyword: Gas porosity

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Thermal Spalling and Resistance to Slag Attack in Porous High Alumina Ceramic (According to Pore Size) (고Alumina질 다공성 세라믹스의 내열충격성 및 내Slag성 (기공크기에 따른))

  • 김병훈;나용한
    • Journal of the Korean Ceramic Society
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    • v.30 no.9
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    • pp.747-753
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    • 1993
  • The investigation was carried out to study the behaviors of the pore size and porosity, the mechanical strength, the resistance to thermal spallings and slag attacks according to particle sizes of starting raw materials in porous high Alumina ceramics. This porous ceramics have been used in processing of the clean steel by the blowing of the inert gas. The required properties in the practice are the suitable pores size, the sharp pores distribution for a uniform blowing of the gas, the strong corrosion resistance to slags and molten metals and the resistance to thermal spalling. The optimized properties in porous high alumina ceramics of the specimen No. 3 was found to be the very low slag intrusion and the superior resistance to thermal spalling because of the suitable pore size of 2.5${\mu}{\textrm}{m}$, the porosity of 30% and the high sinterability.

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A Study on the Performance Analysis of Mobile Fuel Cell (모바일용 연료전지의 성능해석에 관한 연구)

  • Kim, Kwang-Soo;Choi, Jong-Pil;Jeong, Chang-Ryeol;Jang, Jae-Hyeok;Jeon, Byeong-Hee;Kim, Byeong-Hee
    • Journal of the Korean Society for Precision Engineering
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    • v.25 no.1
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    • pp.115-121
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    • 2008
  • In this paper, a three-dimensional computational fluid dynamic model of a proton exchange membrane fuel cell(PEMFC) with serpentine flow channel is presented. A steady state, single phase and isothermal numerical model has been established to investigate the influence of the GDL (Gas Diffusion Layer) parameters. The GDL is made of a porous material such as carbon cloth, carbon paper or metal wire mesh. For the simplicity, the GDL is modeled as a block of material having numerous pathways through which gaseous reactants and liquid water can pass. The porosity, permeability and thickness of the GDL, which are employed in the model parameters significantly affect the PEMFC performance at the high current region.

Effect of Heat Treatment Environment on the Densification of Cold Sprayed Ti Coating Layer (저온 분사 공정으로 제조된 티타늄 코팅층의 치밀화에 미치는 열처리 분위기의 영향)

  • Yu, Ji-Sang;Kim, Hyung-Jun;Oh, Ik-Hyun;Lee, Kee-Ahn
    • Journal of Powder Materials
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    • v.19 no.2
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    • pp.110-116
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    • 2012
  • This study investigated the effects of annealing environment for the densification and purification properties of pure titanium coating layer manufactured by cold spraying. The annealing was conducted at $600^{\circ}C$/1 h and three kinds of environments of vacuum, Ar gas, and $5%H_2+Ar$ mixture gas were controlled. Cold sprayed Ti coating layer (as sprayed) represented 6.7% of porosity and 228 HV of hardness, showing elongated particle shapes (severe plastic deformation) perpendicular to injection direction. Regardless of gas environments, all thermally heat treated coating layers consisted of pure ${\alpha}$-Ti and minimal oxide. Vacuum environment during heat treatment represented superior densification properties (3.8% porosity, 156.7 HV) to those of Ar gas (5.3%, 144.5 HV) and $5%H_2+Ar$ mixture gas (5.5%, 153.1 HV). From the results of phase analysis (XRD, EPMA, SEM, EDS), it was found that the vacuum environment during heat treatment could be effective for reducing oxide contents (purification) in the Ti coating layer. The characteristic of microstructural evolution with heat treatment was found to be different at three different gas environments. The controlling method for improving densification and purification in the cold sprayed Ti coating material was also discussed.

Effects of Spraying Conditions on the Porosity and Hardness of Plasma Sprayed MgO Stabilized Zirconic Thermal Barrier Coatings (Plasma 용사된 MgO 안정화 지르코니아 단열피복의 기공도와 경도에 미치는 용사조건의 영향)

  • Park, Yeong-Gyu;Choe, Guk-Seon;Lee, Dong-Hui
    • Korean Journal of Materials Research
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    • v.2 no.2
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    • pp.85-94
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    • 1992
  • The size, morphology and distribution of pores which affect on the physical properties of thermal barrier coatings were investigated to find the relationship with spraying parameters. The plasma-sprayed zirconia coatings contained numerous micropores as well as macropores which were appeared as spherical and irregular pores, and cracks. The pore formation process and its characteristics were varied with spraying distance. Porosity itself was varied with spraying parameters such as spray gun current, gas flow rate and the gas used(Ar or $N_2). The Porosity of coatings was ranged from 10 to 18% with the variation of spraying conditions. The relative hardness measured by the scratch test, showed strong dependence on the porosity of coatings rather than spraying parameters.

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Adsorption characteristics of the sericite and diatomite for ammonia gas (견운모와 규조토에 대한 암모니아 기체의 흡착특성)

  • Lee, Suseung;Kim, Jinsoo;Yun, Chang Yeon;Yi, Jongheop
    • Clean Technology
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    • v.12 no.3
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    • pp.175-181
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    • 2006
  • The feasibility of the use of porous fossil diatoms for indoor air pollution control was investigated via the characterization of physical and chemical properties. The fossil diatoms were observed by SEM(Scanning Electron Microscope). Diatomite had well-distributed pores below 5 nm and relatively large surface area compare to sericite. However, no porosity in sericite was found. Results showed that diatomite had better performance than sericite in respect to porosity and large surface area. But diatomite which is thermally treated at $950^{\circ}C$ has no porosity and low surface area because of combustion of fossil diatoms or calcination of inorganic oxide at high temperature, and has poor adsorption capability of ammonia gas. In conclusion, porous diatomite has relatively high performance to adsorb noxious chemical compounds, such as ammonia gas and VOCs.

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Casting Simulation on the Integrated Twin-Scroll Turbine Housing with Exhaust Manifold

  • Kang, Ho-Jeong;Yun, Pil-Hwan;Cheon, Joo-Yong;Kim, Hyo-Jung;Kim, Chung-Min;Park, Jin-Young
    • Journal of Korea Foundry Society
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    • v.37 no.6
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    • pp.173-180
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    • 2017
  • In this paper, the casting design of the integrated twin-scroll turbine housing with exhaust manifold using stainless steel is investigated. Due to the complexity in its geometry and the poor castability of stainless steel, it is more crucial to set up the appropriate casting design to avoid casting defects. Gas porosity and shrinkage formation with the changes of gating systems (one-/two-side), riser conditions and pouring temperatures are examined via casting simulation and virtual castings. Simulation results show that two-side gating system produced better quality casting than that of one-side gating system, minimizing the gas content of the castings and it is also verified by X-ray analysis for the virtual castings. For the changes of riser conditions and pouring temperatures in the two-side gating system, it is found that the change of the height of two risers plays an important role in obtaining the best quality by reducing shrinkage defects.

Molecular Diffusion of Water in Paper(II)-Water-diffusion theory on pore structure of paper- (종이내 수분확산(제2보)-종이의 공극구조에 의한 수분확산 이론-)

  • Yoon, Sung-Hoon;Jeon, Yang
    • Journal of Korea Technical Association of The Pulp and Paper Industry
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    • v.30 no.3
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    • pp.46-56
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    • 1998
  • The objective of this study was to investigate the relationship between water vapor diffusion properties and the pore structure of paper. Gas-phase molecular diffusivity of water vapor through pores was determined based on the kinetic theory of gas. A mathematical model was derived to characterize the dimensional changes of the pore caused by the fiber-swelling mechanism. A modified-Fickean diffusion model was designed to simulate the water-vapor diffusion phenomena in porous paper web. Structural characterisocs of paper pores including the tortuosity and the shape factor was studied on a theoretical basis of Knudsen flow diffusion. Results are summarized as follows: 1. The theoretical water vapor diffusivity in gas-phase was 0.092$cm^2$ /min, 2. Porosity was inversely proportional to the degree of wet-swelling of paper, 3. Solid-phase water-diffusivity of fiber was 1.2 $ \times 10^{-5}cm^2/min$, 4. Modified diffusion model was fairly consistent to the experimental data (from part I), and 5. The Fickean pore tortuosity, ranging from 1,000 to 2,500, was in inverse proportion to the porosity of paper, and the Knudsen shape factor and length-angle factor for micro-pores in paper were 0.5~3.5 and about 340, respectively.

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Effects of the Pore Size of Graphite on the Mechanical Properties and Permeability of a Porous Nozzle for Continuous Casting Process

  • Cho, Yong-Ho;Kim, Juyoung;Yoon, Sanghyeon;Lee, Heesoo
    • Korean Journal of Metals and Materials
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    • v.49 no.7
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    • pp.530-534
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    • 2011
  • To analyze the effect of the pore size of graphite in a pore-forming agent, graphite was added to porous ceramics of $Al_2O_3-SiO_2-ZrO_2$ systems. The graphite had 45~75, 100~125, 150~180, and 75~180${\mu}m$ dimensions. The properties of the ceramics, such as apparent porosity, density, dynamic elastic modulus, mechanical strength, and permeability, were investigated. The average pore size increased from 15.35${\mu}m$ to 22.32${\mu}m$ with the increase of the graphite size. The sample with the largest average pore size showed the highest mechanical strength and gas permeability. This was due to the sample with the largest pore size at the same porosity having fewer pores and larger distance between the pores than the sample with the smallest pore size, making cracks less likely to propagate. In addition, the large pore size reduced the repulsive power originating from the drag force between the gas and internal pore walls.