• Korean Journal of Materials Research
• /
• v.25 no.1
• /
• pp.27-31
• /
• 2015

This paper proposes a novel way of fabricating aligned porous Sn by freeze-drying of camphene slurry with stannic oxide ($SnO_2$) coated Sn powders. The $SnO_2$ coated Sn powders were prepared by surface oxidation of the initial and ball-milled Sn powders, as well as heat treatment of tin chloride coated Cu powders. Camphene slurries with 10 vol% solid powders were prepared by mixing at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$. Improved dispersion stability of camphene slurry and the homogeneous frozen body was achieved using the oxidized Sn powder at $670^{\circ}C$ in air after ball milling. The porous Sn specimen, prepared by freeze-drying of the camphene slurry with oxidized Sn powder from the heat-treated Sn/tin chloride mixture and sintering at $1100^{\circ}C$ for 1 h in a hydrogen atmosphere, showed large pores of about $200{\mu}m$, which were aligned parallel to the camphene growth direction, and small pores in their internal walls. However, $100{\mu}m$ spherical particles were observed in the bottom part of the specimen due to the melting of the Sn powder during sintering of the green compact.

• Journal of Powder Materials
• /
• v.22 no.2
• /
• pp.129-133
• /
• 2015

Porous W with controlled pore structure was fabricated by thermal decomposition and hydrogen reduction process of PMMA beads and $WO_3$ powder compacts. The PMMA sizes of 8 and $50{\mu}m$ were used as pore forming agent for fabricating the porous W. The $WO_3$ powder compacts with 20 and 70 vol% PMMA were prepared by uniaxial pressing and sintered for 2 h at $1200^{\circ}C$ in hydrogen atmosphere. TGA analysis revealed that the PMMA was decomposed at about $400^{\circ}C$ and $WO_3$ was reduced to metallic W at $800^{\circ}C$. Large pores in the sintered specimens were formed by thermal decomposition of spherical PMMA, and their size was increased with increase in PMMA size and the amount of PMMA addition. Also the pore shape was changed from spherical to irregular form with increasing PMMA contents due to the agglomeration of PMMA in the powder mixing process.

• Journal of the Korean institute of surface engineering
• /
• v.34 no.6
• /
• pp.575-584
• /
• 2001

Erosion due to abrasive particles contained in gas streams from boilers has been emerged as a significant problem in the coal fired power plants. Particle erosion accounted for approximately 50% of boiler failures and especially flyash erosion was responsible for 20~30% of emergency boiler shutdowns. Particularly, because of the high ash loading and high velocity, most erosion occurs in the boiler tubes and economiser tube bank where the direction of the gas stream changes to $180^{\circ}$ .In this study, a high temperature particle erosion tester was used to evaluate erosion rate in a simulated environment. The erosion parameters such as erosion temperature, particle impact angle, particle velocity and various particle size were changed. Flyash is the combustion product of the pulverized coal, where size is ranging from 1 to $200\mu\textrm{m}$. Flyash composed of mainly SiO$_2$, $A1_2$$_O3$, and $Fe_2$$O_3$has dense spherical particles and irregular particles containing numerous pores and cavities. From the erosion tests at various conditions, the maximum erosion was experienced at impact angles of $30^{\circ}$ to $60^{\circ}$ In addition, erosion rate increased in proportional to velocity and temperature. And from the observation of the eroded surfaces, it was also concluded that 304 stainless steel was mainly eroded by extrusion-forging at high impact angle ($90^{\circ}$) and by microcutting mechanism at low impact angles ($30^{\circ}$ and $45^{\circ}$).

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.56 no.4
• /
• pp.293-298
• /
• 2011

Physical and structural characteristics of four local barnyardgrass flour and starch were investigated. Amylose content ranged from 6.9 to 12.5%. The BP 3563 and BP 3606 were low amylose lines, and the BP 3592 and BP 3610 showed very low amylose lines. Peak viscosities of four barnyardgrass collections BP-3563, BP-3592, BP-3606, and BP-3610 ranged 264 to 2397. All barnyard grass lines displayed an A-type X-ray diffraction pattern showing the strong diffraction peak at around $2{\theta}$ values $15^{\circ}$, $17^{\circ}$, $18^{\circ}$ and $23^{\circ}$, and a small peak at $20^{\circ}$ $2{\theta}$. Scanning electron microscopy revealed that the starch granule sizes ranged $5.5-12.5{\mu}m$ in diameter showing polygonal and rarely spherical in shape with round edges and some pores at the surface. Starch crystallinity of BP 3563, BP 3592, BP 3606, and BP 3610 was 23.9, 25.0, 24.7, and 25.5%, respectively.

• Animal Systematics, Evolution and Diversity
• /
• v.32 no.1
• /
• pp.1-8
• /
• 2016

Vermamoeba vermiformis is a very important free-living amoeba for human health in association with Legionnaires' disease and keratitis. This interesting amoeba was firstly isolated from a freshwater of Dokdo (island), which was historically used for drinking water. Trophozoites and cyst forms of V. vermiformis strain MG1 are very similar to previous reported species. Trophozoites of V. vermiformis strain MG1 showed cylindrical shape with prominent anterior hyaline region. The average ratio of length and width was about 6.5. Typically, cysts of the strain MG1 showed a spherical or slightly ovoidal shape with smooth wall, and lacked cyst pores. Some cysts had crenulate-walled ectocyst, which was separated from endocyst wall. Further, 18S rRNA gene sequence of V. vermiformis strain MG1 showed very high similarity to other V. vermiformis species (99.4%-99.9% identity). Molecular phylogenetic analysis based on 18S rRNA gene sequences clearly confirmed that the isolate was one strain of V. vermiformis with maximum bootstrap value (maximum likelihood: 100%) and Bayesian posterior probability of 1. Thus, the freshwater of Dokdo in Korea could harbor potentially pathogenic amoeba that may cause diseases in humans.

• Journal of the Mineralogical Society of Korea
• /
• v.9 no.1
• /
• pp.17-25
• /
• 1996

Usual experimental adsorption isotherms as a function of relative humidity were constructed from adsorbed water contents in soils, which were kept more than 2 days in vacuum desiccators with constant humidities controlled by sulfuric acids of various concentrations. From the experimental data, the adsorption surface areas were calculated on the basis of the existing adsorption theory, such as Langmuir, BET, and Aranovich. Based on the Gibbs function describing chemical potential of perfect gas, the relative humidities in the desiccators were transformed into their chemical potentials, which were assumed to be the same as the potentials of equilibratedly adsorbed water in soils. Moreover, the water potentials were again transformed into the equivalent capillary pressures, heads of capillary rise, and equivalent radius of capillary pores, on the basis of Laplace equation for surface tension pressure of spherical bubbles in water. Adsorption quantity distributions were calculated on the profile of chemical potentials of the adsorbed water, equivalent adsorption and/or capillary pressures, and equivalent capillary radius. The suggested theories were proved through its application for the prediction of temperature rise of sulfuric acid due to hydration heat. Adsorption heat calculated on the basis of the potential difference was dependant on various factors, such as surface area, equilibrium constants in Langumuir, BET, etc.

• KSBB Journal
• /
• v.26 no.1
• /
• pp.69-77
• /
• 2011

In this study, poly (L-lactic acid) (PLLA) microparticles containing gemcitabine hydrochloride were prepared by a supercritical fluid process, called aerosol solvent extraction system (ASES), utilizing supercritical carbon dioxide as antisolvent. The influence of process parameters such as temperature, pressure, $CO_2$ and solution flow rate, solution concentration, and feed ratio of drug to polymer on the morphology and characteristics of the microparticles was studied in detail. The gemcitabine-loaded microparticles exhibited a spherical shape with a smooth surface. The entrapment efficiency of gemcitabine increased with increasing temperature, solution concentration and $CO_2$ flow rate and with decreasing drug/polymer feed ratio. The maximum drug loading obtained from the ASES process was found to be about 11%. The ASES-processed PLLA microparticles containing gemcitabine showed a relatively high initial burst due to the presence of surface pores on the microparticles and the poor affinity between drug and polymer.

• Journal of the Korean Ceramic Society
• /
• v.44 no.10
• /
• pp.574-579
• /
• 2007

Porous $Al_2O_3$ ceramics were prepared by the gelcasting foams method (a slurry foaming process) with acrylamide monomer. The foaming and gelation behavior was investigated with the parameters such as the type and concentration of surfactant, solid loading of slurry, and the concentrations of initiator and catalyst. Density, porosity, microstructure, and strength of the green and sintered samples were characterized. Of the four kinds of surfactants tested, Triton X-114 showed the highest foaming ability for the solid loading of 55-30 vol%. The gelation condition giving the idle time off min was found to set the foamed structure without significant bubble enlargement and liquid lamella thinning. The green samples were fairly strong and machinable and showed maximum strength of 2.4 MPa in diametral compression. The sintered samples showed densities of 10-36% theoretical (i.e. porosity 90-64%) with a highly interconnected network of spherical pores with sizes ranging from 30 to $600{\mu}m$. The pore size and connectivity increased but the cell strut thickness decreased with decreasing the solid loading. Flexural strength of 37.8-1.7 MPa was obtained for the sintered samples.

• Journal of the Korean Ceramic Society
• /
• v.45 no.10
• /
• pp.584-588
• /
• 2008

Porous hydroxyapatite(HA) and HA-coated porous $Al_2O_3$ possessing pore characteristics required for bone substitutes were prepared by a slurry foaming method combined with gelcasting. The HA coating was deposited by heating porous $Al_2O_3$ substrates in an aqueous solution containing $Ca^{2+}$ and ${PO_4}^{3-}$ ions at $65{\sim}95^{\circ}C$ under ambient pressure. The pore characteristic, microstructure, and compressive strength were investigated and compared for the two kinds of samples. The porosity of the samples was about 81% and 80% for HA and $Al_2O_3$, respectively with a highly interconnected network of spherical pores with size ranging from 50 to $250{\mu}m$. The porous $Al_2O_3$ sample showed much higher compressive strength(25 MPa) than the porous HA sample(10 MPa). Fairly dense and uniform HA coating(about $2{\mu}m$ thick) was deposited on the porous $Al_2O_3$ sample. Since the compressive strength of cancellous bone is $2{\sim}12$ MPa, both the porous HA and HA-coated porous $Al_2O_3$ samples could be successfully utilized as scaffolds for bone repair. Especially the latter is expected suitable for load bearing bone substitutes due to its excellent strength.

• Journal of Korean Society of Water and Wastewater
• /
• v.19 no.6
• /
• pp.713-719
• /
• 2005

SPME (Soild phase microextraction) has been used in the analysis of many volatile organic compounds, such as geosmin and 2-methylisoborneol (2-MIB), trihalomethanes (THMs) in drinking water. SPME fiber is characterized by high adsorption capacity (DVB/CAR/PDMS, DVB/PDMS etc.). Although the highly active adsorption capacities of the SPME fiber are often to the chemical functional group, surface properties play a significant role in determining the surface adsorption capacities. The objectives of this study were to evaluate effect of residual chlorine on analysis of geosmin and 2-MIB. Image taken by SEM before preloaded with chlorine, the surface and porous media was almost perfect spherical shape and no clogging of pores. However, after preloaded with chlorine the surface was aggregated and pore was blocked. The recovery rate of geosmin and 2-MIB coexisting with chlorine was reduced by 35 to 62%. The recovery rate with preloaded with chlorine was reduced by 25 to 43%. The lower concentration of geosmin and 2-MIB and the higher concentration of chlorine existed in water, the lower the recovery rate was.