• Korean Journal of Food Science and Technology
• /
• v.49 no.5
• /
• pp.507-512
• /
• 2017

The physicochemical properties of maize starch sonicated at various amplitudes (100, 200, and 300 W) and times (10, 30, and 50 min) were examined. The amount of enzyme-susceptible starch increased marginally after sonication. Sonication increased the amount of oil absorbed in the starch although the degree of oil absorption decreased with an extension of the sonication time, implied that different types and extent of damages occurred. Scanning electron microscopy revealed that ultrasound sonication did not form pores on the surfaces, but caused damages such as depression and erosion. Pasting viscosity of starch decreased with an increase in the severity of sonication conditions because of the weakened polymer network. X-ray diffraction suggested that the crystalline domains in starch were not susceptible to sonication and were more resistance to degradation. Sonicated starch formed more pin-holes on the surfaces in the initial glucoamylase reaction; subsequently, as the reaction proceeded, porous starch with enlarged pores was formed and finally, disrupted granular fragments were observed.

• Journal of the Korean Electrochemical Society
• /
• v.6 no.1
• /
• pp.53-58
• /
• 2003

It is well known that the anode substrate of anode-supported type SOFC should have high electrical conductivity and high gas permeability to minimize the polarization loss of the cell performance during operation. In this study, we made anode substrates of SOFC with two different methods, which gave different anode microstructures, especially different pore structures with each other. We performed electrical and microstructural characterization of Ni/YSZ cermet anode via extensive measurements of its electrical conductivity and gas permeability combined with adequate image analysis based on quantitative stereological theory

• Journal of the Korean Ceramic Society
• /
• v.39 no.1
• /
• pp.86-91
• /
• 2002

Solid Oxide Fuel Cells (SOFC) are of great interest of next generation energy conversion system due to their high energy efficiency and environmental friendliness. The basic SOFC unit consists of anode, cathode and solid electrolyte. Among these components, anode plays the most important role for the oxidation of fuel to generate electricity and also behaves as a substrate of the whole cell. It is normally requested that the anode materials should have the high electrical conductivity and gas permeability to reduce the polarization loss of the cell. In this study, the effect of pore former on the microstructure of anode substrate was investigated and thus on the electrical conductivity and the gas permeability. According to the results, microstructure and electrical conductivity of anode substrate were greatly influenced by the shape of pore former and especially by the anisotrpy of the pore former. The use of anisotropic pore former is supposed to deteriorate the cell performance by which the electrical conduction path is disconnected but also the effective gas diffusion path for the fuel is reduced.

• Korean Journal of Crystallography
• /
• v.9 no.1
• /
• pp.64-70
• /
• 1998

Porous body was prepared from coal fly ash 70 wt%0clay 30 wt% slip using DCC(Direct Coagulated Casting) method. Effect of the specific gravity of the slip on the pore size and distribution of the sintered body was examined by the SEM observation of microstructure and mercury porosimetry measurement of the pore size distribution. Average pore size of the porous sintered body was about 2.5μm for all slips with specific gravity of 1.55, 1.60 and 1.65g/cm3, respectively. Sintered body prepared from the slip of specific gravity of 1.60g/cm3 have the narrowest pore size distribution. slip of specific gravity of 1.55g/cm3 shows broader pore size distribution due to slow gellation process. Slip of specific gravity of 1.65g/cm3 required large amount of deflocculant and showed large variation of the viscosity with addition of coagulant which resulted in very unstable slip properties.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.8-8
• /
• 2009

알루미늄 합금 Al 6082-T6는 최근에 개발되어 북유럽 등의 선진국에서는 그 뛰어난 해양 내식성과 우수한 강도로 인하여 해양구조물의 헬리데크(Helideck), 타워 갱웨이(Tower gangway), 알루미늄 피팅류(Aluminium fitting)등의 해양구조물과 플랫폼(Flatform), 알루미늄 래더(Aluminium ladder)등의 선박부품, 차량, 기계부품 분야에서 전 세계적으로 널리 사용되기 시작하였다. 그러나 전통적으로 용접금속의 기공은 결함으로 분류 되고, Rakesh Kumar 등의 논문에 따르면 용접 시 용접금속 내에 발생되어진 미세기공이 기계적 성질에 악영향을 미치는 것으로 보고되어졌다. 따라서 용접금속내의 발생하는 기공을 방지하는 용접공정의 개발이 반드시 필요하다. 본 연구의 목적은 Al 6082-T6 고속 MIG용접에서 기공방지를 위한 용접공정을 개발하는 것이다. Al 6082-T6의 7t 플레이트에 Al 5356의 와이어를 사용하여 아크길이 변경 및 용접속도를 60cpm과 120cpm으로 변경하여 실험하였고, 용접속도 120cpm의 고속 MIG용접에서 토치 진행각을 변경하여 실험을 진행하였다. 용접공정 파라메터 변경에 따른 기공율 측정은 이미지 분석 소프트웨어를 사용하여 정량적으로 분석하였다.

• Journal of the Korean Magnetics Society
• /
• v.22 no.1
• /
• pp.6-10
• /
• 2012

We have observed the change in the film resistance of thin nickel film up to 13 nm, which is deposited on a porous anodic alumina substrate, prepared by two-step anodization technique under phosphoric acid. The resulting film grows as a porous film, following the pore structure on the surface of the alumina substrate, and the value of the resistance lies above $150k{\Omega}$ within the range of thickness studied here, decreasing very slowly with the film thickness. The observed resistance value is much higher than the reported value of a uniform film at the same thickness. Since the observed value of the surface coverage with the pores is smaller than the critical value, expected from the percolation theory, the pore structure limits the formation of conduction channel across the film. In addition, by comparing to the typical model of thickness-dependent resistivity, we expect that the scattering at the pore edge further increases the film resistance.

• Applied Chemistry for Engineering
• /
• v.22 no.3
• /
• pp.243-248
• /
• 2011

Pt deposited porous carbon nanofibers was prepared as a highly sensitive material of hydrogen gas sensor operating at room temperature. Nanofibers was obtained by electrospinning method using polyacrylonitrile as a carbon precursor and then thermally treated for carbon nanofibers. Chemical activation of carbon nanofibers was carried out to enlarge specific surface area up to $2093m^2/g$. Sputtered Pt layer was uniformly distributed keeping the original shape of carbon nanofibers. The hydrogen gas sensing time and sensitivity were improved based on effects of high specific surface area, micropore structure and deposited Pt catalyst.

• Analytical Science and Technology
• /
• v.5 no.2
• /
• pp.217-222
• /
• 1992

An attempt was made to analyze green microstructure of AIN samples prepared by slip casting and dry pressing through Hg-porosimetry. Slip cast samples with narrow pore size distribation and high packing density showed higher sinterability and homogeneous distribution of second phase(s). Hg-porosimetry is and effective way to determine pore structure if "ink bottle" phenomenon does not occur. A comparison study with porosity measurement by quantitative microscopy showed that the effectiveness of Hg-porosimetry measurement could be extended to higher sintered density as long as pores remained open.

• Journal of the Korean Ceramic Society
• /
• v.36 no.1
• /
• pp.97-105
• /
• 1999

In the binary system of SiC and carbon, porosity and pore size distribution of green body was controlled by varying pH, by the addition of polyelectrolyte dispersants, and by using different particle size of starting powders. The preforms having different green microstructure were fabricated by slip casting from suspensions having different dispersion condition. The reaction bonding process was carried out for these preforms. The condition of reaction bonding was 1600$^{\circ}C$ and 20 min. under vacuum atmosphere. The analyses of optical and SEM were studied to investigate the effect of green microstructure on that of reaction bonded silicon carbide and subsequently the mechanical properties of sintered body was investigated. Different green microstructures were obtained from suspensions having different dispersion condition. It was found that the pore size could be remarkably reduced for a fine SiC(0.5$\mu\textrm{m}$). The bimodal microstructure was not found in the present study, which is frequently observed in the typical reaction bonded silicon carbide. It is considered that the ratio between SiC and C was responsible for the formation of bimodal microstructure. For the preform fabricated from the well dispersed suspension, the 3-point bending strength of reaction-bonded silicon carbide was 310${\pm}$40 MPa compared to the specimen fabricated from relatively agglomerated particles having lower value 260${\pm}$MPa.

• Applied Chemistry for Engineering
• /
• v.34 no.2
• /
• pp.170-174
• /
• 2023

CO₂ is known as one of the causes of global warming, and various studies are being conducted to capture it. In this study, a tetrafluoromethane (CF₄) plasma reaction was performed to improve the CO₂ adsorption of activated carbons (ACs) through changes in surface characteristics, and the adsorption characteristics according to the reaction time were considered. After the reaction, the micropore volume increased up to 1.03 cm³/g. In addition, as the reaction time increased, the fluorine content on the surface increased to 0.88%. It was possible to simultaneously control the pore properties and surface functional groups of the ACs through this experiment. Also, the CO₂ uptake of surface-treated ACs improved up to 7.44% compared to untreated ACs, showing the best performance at 3.90 mmol/g when the reaction time was 60 s. This is due to the synergy effect of the fluorine functional groups introduced on the surface of the ACs and the increased micropore volume caused by the etching effect. It was found that the micropore volume had a greater effect on CO₂ adsorption in the region where the CO₂ uptake was less than 3.67 mmol/g, while the added fluorine content had a greater effect in the region above that.