• Journal of the Korean Ceramic Society
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• v.49 no.5
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• pp.427-431
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• 2012

The $TiO_2$ foam synthesized using freeze-casting is a promising photocatalyst and photovoltaic electrode for a variety of energy applications, because the freeze-casting technique is easy to use, cheap, and suitable for mass-production. Despite its several advantages, little scientific information is available on the processing and morphology of the $TiO_2$ foams processed by freeze-casting. In particular, no systematic study has been performed on the microstructural evolution and morphological change of the rutile-phase $TiO_2$ foams during sintering. Therefore, in the present study, several $TiO_2$ foam samples were produced using the freeze-casting technique, which were then sintered at a relatively high temperature of $1200^{\circ}C$ for 1, 2, and 4 h to compare the morphological changes in the microstructure and to understand the effects of processing parameters of the rutile-phase $TiO_2$ foams. The foam ligament size increased near linearly with increasing sintering time whereas the average pore size decreased only slightly with increasing sintering time, with changes in particle morphology from sphere to rod and complete phase transformation from anatase to rutile.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.6
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• pp.594-598
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• 2015

The effects of Ni on the mechanical properties of WC-Xwt.%Ni-1.5wt.%Si-1.1wt.%$B_4C$ composite (X = 21.6, 23.6, 25.6 and 27.6 wt.%) were investigated in order to replace Co with Ni as the binder metal for hard materials based on WC-Co system. Using X-ray diffraction, optical microscopy, field-emission scanning electron microscopy results, the microstructure, pore distribution and grain size of the composites sintered at $1,150^{\circ}C$ were examined with different fraction (X = 21.6, 23.6, 25.6 and 27.6 wt.%) of binder metal Ni. The average WC grain size of the $WC-Ni-Si-B_4C$ composites was about $1{\mu}m$. The Rockwell hardness : A (HRA) and transverse rupture strength were about 88HRA and $110kgf/mm^2$, respectively. The obtained sample was bonded with SM45C at a temperature of $1,050^{\circ}C$. The thickness and mechanical properties of the bonded area were investigated with different dwell time at a bonding temperature of $1,050^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.25 no.6
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• pp.631-638
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• 1988

Effect of Ca/P mole ratio on the precipitates and powder properties of hydroxyapatite was investigated. Powder and precipitates of hydroxyapatite were synthesized by the reaction of Ca(NO3)2.4H2O and (NH4)2 HPO4 solutions at room temperature. The pH value and compositions (Ca/P mole ratio) in starting solutions were 11 and 1.64-1.79(or 1.85), respectively. Rodlike hydroxyapatite precipitates were agglomerated together. The average agglomerated particle size was ranged from 2-8${\mu}{\textrm}{m}$. Among compositions, the minimum agglomerated particle size was shown at the Ca/P mole ratio 1.75. CO2 was contained in hydroxyapatite powders and these ultrafine powders had poor crystallinity. The specific surface area and specific total pore volume of hydroxyapatite powders were 104-137$m^2$/g and 0.396-0.467cc/g, respectively. When the Ca/P mole ratio was 1.75, these values were the maximum. And water content increased with the Ca/P mole ratio(Ca/P mole ratio>1.67). In most cases, hydroxyapaite was stable to 130$0^{\circ}C$. However, in the case of Ca/P mole ratio 1.64, hydroxyapatite was changed to $\alpha$-whitlockite at 120$0^{\circ}C$.

• Membrane Journal
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• v.15 no.4
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• pp.338-348
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• 2005

The permeate flux decline on microfiltration capillary membrane operation was investigated with inorganic colloidal solutions. The permeate flux of the alumina solution is two times higher in average than that of the bentonite solution. The flux decline with increase in operation time was less in the alumina solution than in the bentonite solution. The rate of initial flux decline until 10 min was higher on the bentonite solution over the alumina solution. The decline in permeate flux was due to both the cake formation and the pore blocking. The latter effect was higher in the operation of the bentonite solution. In comparing the ratio of each fouling component to the total fouling fur the $1.0\;kg_f/cm^2$ TMP condition, complete blocking was $9.35\%$, standard blocking was about $6.82\%$ and cake filtration was $83.83\%$, respectively. With the increase in cross flow velocity, the permeate flux increased by $6.0\%$ for the alumina solution and by 14.0 for the bentonite solution. With the increase in average pore size fromm $0.24\;{\mu}m\;to\;0.34\;{\mu}m$, the permeate flux increases 1.61 times for the alumina solution and 1.76 times far the bentonite solution.

• Journal of Biomedical Engineering Research
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• v.20 no.2
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• pp.221-230
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• 1999

A new technique for the preparation of porous polyurethane vascular prostheses was investigated. Synthetic vascular grafts with porous wall have been widely proposed, claiming that strength, suture retention, kink resistance, and other handling properties are improved over those with nonporous solid wall. Related to these facts, the control of pores and compliance match have been very important and interesting issues. Two kinds of polymer sheets were compared. One was the porous PU-sheet made at room temerature by the solvent/non-solvent exchange. And the other was the porous PU-sheet fabricated by thermal phase transition and solvent/non-solvent exchange in the thermal controlled bath. According to the result of the above experiments, polyurethane solution was injected into a mold designed for U-type graft. After freezing at low temperature, solvent was dissolved out with alcohol at < $0^{\circ}C$ and water at room temperature to form porous vessels. The average pore size and pore occupation were easily changed by changing polyurethane concentration and freezing rate. This technique can give a proper pore size for tissue ingrowth, and suitable compliances for matching with arteries and veins. In addition, the fabrication of more complicated shaped vessels such as the U-type vascular grafts is easily controlled by using a mold. This method might give a desired compliact graft for artificial implantaion with the commercially available medical polymers.

• Polymer(Korea)
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• v.32 no.6
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• pp.509-515
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• 2008

The aminated polypropylene melt blown ion exchange fibers were synthesized with acrylic acid monomer onto polypropylene melt blown fibers by radiation-induced polymerization and subsequent amination. Degree of grafting was increased with increasing the acrylic acid monomer concentration and total dose. The highest degree of grafting was obtained 140% at a monomer concentration of 20 v/v% acrylic acid and total dose of 4 kGy. Optimum condition of Mohr's salt was 5.0 $\times10^{-3}$ M. Degree of amination was increased with increasing degree of grafting. Water content was about 1.5 times higher than that of trunk polymer. The maximum ion-exchange capacity was 7.3 meq/g which was 2$\sim$3 times higher than a commercial ion exchange fiber. The average pore size was decreased and BET surface area was increased in order of PPmb, PPmb- g- AAc and APPmb- g- AAc. The average pore size and BET surface area of synthesised fibers were $366.1\;{\AA},\;3.71m^2/g,\;143.3\;{\AA},\;4.94m^2/g,\;40.97\;{\AA},\;8.98m^2/g$, respectively.

• Journal of Environmental Health Sciences
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• v.45 no.2
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• pp.126-133
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• 2019

Objectives: In this study, a nine-stage cascade impactor was used to collect dust, and the concentration of $PM_{2.1}$ & $PM_{10}$ and alveolar deposition ratio were investigated. Methods: This study was conducted at Kunsan National University from May to June 2016. A nine-stage Cascade Impactor was used to analyze the concentrations of fine and ultrafine dust and to estimate the alveolar deposition rate by particle size of atmospheric dust particles. The pore size of each stage of the collector used in this study gradually increased from F to 0, with the F-stage as the last stage. Results: The mass fraction of PM showed a bimodal distribution divided into $PM_{2.1}$ & $PM_{10}$ based on $2.1-3.1{\mu}m$. The average mass fraction of particulate matter in the range of $2.1-3.1{\mu}m$ was 44%, and the area occupied by $PM_{2.1}$ was similar. Therefore, the Gunsan area is considered to be a region where there are similar effects from anthropogenic and natural sources. Conclusion: Dust collecting efficiency increased with the stage of collecting fine dust, and the efficiency of collection was very low at the stage of collecting ultra-fine dust. The seasonal overall efficiency of the Cascade Impactor was 44% in spring and 37.4% in summer, and the average overall efficiency was 40.7%. The alveolar deposition rate of $PM_{2.1}/PM_{10}$ during the sampling period was estimated to be about 75% deposited in the alveoli.

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.604-608
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• 2012

Recently, inorganic-organic hybrid materials have attracted much attention not only for their excellent thermal conductivity but also for their flame retardant properties. In this study, the properties of organic-inorganic hybrid insulating materials using inorganic fillers and polyurethane foam with different foaming conditions have been investigated. The addition of 1.5 wt% water to polyurethane as foaming agent shows the best foaming properties. The pore size was decreased in the foaming body with increasing of the $CaCO_3$ addition. The apparent density and thermal conductivity were increased by increasing the $CaCO_3$ addition. With an increasing amount of $CaCO_3$ powder, the flame retardant property is improved, but the properties of thermal conductivity and apparent density tend to decrease. When the addition of fine particles of $CaCO_3$, the apparent density and thermal conductivity were increased and, also, with the addition of coarse particles over $45{\mu}m$ in size, the apparent density and thermal conductivity were increased as well. In this study, the adding of $CaCO_3$ with average particle size of $27{\mu}m$ led to the lowest thermal conductivity and apparent density. After evaluation with different inorganic fillers, $Mg(OH)_2$ showed the highest thermal conductivity; on the other hand, $CaCO_3$ showed the lowest thermal conductivity.

• Journal of Powder Materials
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• v.25 no.1
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• pp.25-29
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• 2018

Porous Cu with a dispersion of nanoscale $Al_2O_3$ particles is fabricated by freeze-drying $CuO-Al_2O_3$/camphene slurry and sintering. Camphene slurries with $CuO-Al_2O_3$ contents of 5 and 10 vol% are unidirectionally frozen at $-30^{\circ}C$, and pores are generated in the frozen specimens by camphene sublimation during air drying. The green bodies are sintered for 1 h at $700^{\circ}C$ and $800^{\circ}C$ in $H_2$ atmosphere. The sintered samples show large pores of $100{\mu}m$ in average size aligned parallel to the camphene growth direction. The internal walls of the large pores feature relatively small pores of ${\sim}10{\mu}m$ in size. The size of the large pores decreases with increasing $CuO-Al_2O_3$ content by the changing degree of powder rearrangement in the slurry. The size of the small pores decreases with increasing sintering temperature. Microstructural analysis reveals that 100-nm $Al_2O_3$ particles are homogeneously dispersed in the Cu matrix. These results suggest that a porous composite body with aligned large pores could be fabricated by a freeze-drying and $H_2$ reducing process.

• Parasites, Hosts and Diseases
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• v.21 no.2
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• pp.150-156
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• 1983

Five cases of Diphyllobothrium latum infection were proved by collection of worms after treatment with bithionol, niclosamide or praziquantel, during 1975~1983. The patients were 4 males and one female aged 10~64 years residing in Seoul or Wando-gun, Chollanam-do, Korea. All of them remembered the history of eating several kinds of raw marine fish and 2 persons said they ate the raw mesh of perch, Lateolabrax japcnicus. Three amcnE them experienced abdominal pain, 2 natural discharge of a chain of segments, but none revealed any sign of anemia. The average egg size in stool varied $59~67{\times}41~48{\mu\textrm{m}}$ according to cases. The eggs were characterised by ovoid to elliptical shape, terminal operculum, and distinct abopercular protuberance. One naturally discharged segment (30cm) and 4 complete strobilae (320~680cm) with scolices obtained after treatments were examined. The morphological characters of proglottids such as rosette-form uterus with 3~6 loops, vaginal pore included in the cirrus sac, separated seminal vesicle from cirrus sac, etc. were all compatible with D. latum. These are the 7th~11th cases of D. latum infection proved by worms in Korea.