• Journal of the Korean Ceramic Society
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• v.32 no.4
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• pp.507-515
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• 1995

The monolithic dry gels of the Li2O-Al2O3-TiO2-SiO2 system were prepared by the sol-gel technique using metal alkoxides as starting materials to obtain monolithic glass-ceramics at low temperature without melting. Activation energy for the crystal growth of the gel with 6.05% TiO2, nucleating ageng, for the preparation of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was 101.14kcal/mol. As a result of the analysis of DTA & XRD, it was confirmed that the crytallization of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was the most efficient when 6.05% TiO2, nucleating agent, was added. $\beta$-eucryptite solid solution crystals and $\beta$-spodumene solid solution crystals were detected in the sample heat treated above 85$0^{\circ}C$. The sintered gel heat treated at 85$0^{\circ}C$ had the specific surface area of 185$m^2$/g, the pore volume of 0.19cc/g and the average pore radius of 20.8$\AA$. This shows that the sintered gel is also comparatively porous material. In temperature range of 25~85$0^{\circ}C$ thermal expansion coefficient of the specimen which was crystallized for 10hrs at 85$0^{\circ}C$ was 6.7$\times$10-7/$^{\circ}C$, which indicated that the crystallized specimen was turned out to be the glass-ceramic with low thermal expansion.

• Electrical & Electronic Materials
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• v.9 no.2
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• pp.146-151
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• 1996

PZT powders were prepared by the molten salt synthesis method. The porous PZT ceramics were made from a mixture of PZT and polyvinylalcohol(PVA) by BURPS(Bumout Plastic Sphere) technique. The 3-3 type composites were fabricated by impregnating an sintered porous PZT ceramics with various polymer matrices. The relative permittivity of 3-3 type composite specimens was shown 860-1,100 smaller than that of solid PZT ceramics(2,100), and the dissipation factors of composite specimens were about 0.02 to 0.03. The piezoelectric coefficient d$_{33}$ of composite specimens(285-328*10$^{12}$ C/N) was comparable with that of single phase PZT specimens(364*10$^{-12}$ C/N). The thickness mode coupling factor k$_{t}$(O.5-0.6) of composite specimens was comparable with that of single phase PZT specimens(k$_{t}$-0.7), and the mechanical quality factor of composite specimens was smaller than 10, and thus these 3-3 type composite specimens would be believed as a good candidates for broad band transducer applications.ons.

• Journal of Aerospace System Engineering
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• v.8 no.3
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• pp.1-5
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• 2014

An inner flow of a porous cylinder with partial slots was visualized to study fluidic phenomena in a solid rocket motor. A high-pressure chamber and an air supply system for high flow rate were used. In order to visualize the inner flow, the smoke generator with a cam-driven pump and heaters and high speed camera were adopted. The results of the cylinder type and the partial slot type were compared. As a result, the injected smoke flow in the partial slot type had circumferential fluctuations unlike the cylinder type. It was found that the circumferential flow induced from the partial slots could be the cause of combustion instability and roll torque.

• Journal of the Korean Ceramic Society
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• v.40 no.3
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• pp.273-278
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• 2003

The effects of content and particle size of sewage sludge slag on the sound absorption was investigated and the physical$.$mechanical properties of porous ceramics for sound absorbent material was studied. The physical$.$mechanical properties of specimens have depended on sintering temperature and slag content without particle size effect of slag. As water glass content increase and particle size of slag decrease at the same slag content, physical$.$mechanical properties of them have been improved. The bulk density and compressive strength of specimens with the batch composition of 77∼89 wt% of slag content and particles with 1∼3 mm, and sintered at 1,050$^{\circ}C$ for 2 h were 1.48∼1.71 and 86∼163 kgf/$\textrm{cm}^2$, respectively. The specimens with 1∼3 mm and <1 mm of particles size showed good sound absorption property at low frequency and high frequency region. With increasing thickness of specimens, sound absorption properties at low frequency region were increased.

• Journal of Powder Materials
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• v.20 no.4
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• pp.253-257
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• 2013

Freeze drying for porous Mo was accomplished by using $MoO_3$ powder as the source and camphor-naphthalene eutectic system as the sublimable material. Eutectic composition of camphor-naphthalene slurries with the initial $MoO_3$ content of 5 vol%, prepared by milling at $55^{\circ}C$ with a small amount of oligomeric dispersant, was frozen at $-25^{\circ}C$. The addition of dispersant showed improvement of dispersion stability in slurries. Pores were generated subsequently by sublimation of the camphor-naphthalene during drying in air for 48 h. To convert the $MoO_3$ to metallic Mo, the green body was hydrogen-reduced at $750^{\circ}C$, and sintered at $1100^{\circ}C$ for 2 h. The sintered samples, frozen by heated Teflon cylinder, showed large pores with the size of about 40 ${\mu}m$ which were aligned parallel to the sublimable vehicles growth direction. The formation of unidirectionally aligned pores is explained by the rejection and accumulation of solid particles in the serrated solid-liquid interface.

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.690-695
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• 2007

Scandia stabilized zirconia (ScSZ) is adapted for electrolyte material of solid oxide fuel cell (SOFC) because of its high ionic conductivity and chemical stability. ScMnSZ1 powder having a composition of $((ZrO_2)_{0.89}(Sc_2O_3)_{0.1}(MnO_2)_{0.01})$ is synthesized by ultrasonic spray pyrolysis (USP) method. Porous ScMnSZ1 powder is obtained by using a pore forming agent. Microstructure and morphology, particle size distribution of porous powder synthesized with 3wt% pore forming agent are investigated. Sintered ScMnSZ1 sample with ground fine powder are also investigated their microstructure and electrical conductivity. The electrical conductivity of sintered ScMnSZ1 samples with ground fine powder was 0.082 S/cm, 0.127 S/cm and 0.249 S/cm at $750^{\circ}C$, $800^{\circ}C$ and $900^{\circ}C$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.6
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• pp.289-294
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• 2010

Ni-YSZ (Yttria Stabilized Zirconia) composite powders for SOFC were fabricated by glycine nitrate process. $ZrO(NO_3)_2{\cdot}2H_2O$, $Y(NO_3)_3{\cdot}6H_2O$, $Ni(NO_3)_2{\cdot}6H_2O$ and glycine were chosen as the starting materials. The structural properties of the sintered Ni-YSZ cermets have been investigated with respect to the volume contents of Ni. A porous microstructure consisting of homogeneously distributed Ni and YSZ phases together with well-connected grains was observed. The sintered Ni-YSZ cermets showed a porous microstructure consists of homogeneously distributed Ni and YSZ phases and the grains were well-connected. It was found that the open porosity is sensitive to the volume content of Ni. The Ni-YSZ cermet containing 35 vol% Ni seems to be suitable for the electrode material of SOFC since it provides sufficient open porosity higher than 30%.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.533-536
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• 2006

A light-weight aggregate with a surface layer was fabricated using glass abrasive sludge and expanding agents. The glass abrasive sludges were mixed with expanding agents ($Fe_2O_3,\;graphite,\;CaCO_3$) and formed into precursors. These precursors were sintered in the range of $700-900^{\circ}C$ for 20min. The sintered light-weight aggregate had a surface layer with smaller pores and an inner region with larger pores. The surface layer and pores controlled the water absorption ratio and physical properties. As the expanding agent fraction and the sintering temperature increased, the porosity and pore size increased. The light-weight aggregate with $Fe_2O_3$ and graphite as the expanding agents had a low water absorption ratio while the porous material with $CaCO_3$ as the expanding agent had a higher water absorption ratio and more open pores.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.5
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• pp.617-627
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• 2006

Statement of problem: HA has been used as a coating material on Ti implants to improve osteoconductivity. However. it is difficult to form uniform HA coatings on implants with complex surface geometries using a plasma spraying technique. Purpose : To determine if Ti6Al4V sintered porous-surfaced implants coated with HA sol-gel coated and hydrothermal treated would accelerate osseointegration. Materials and Methods : Porous implants which were made by electric discharge were used in this study. Implants were anodized and hydrothermal treatment or HA sol-gel coating was performed. Hydrothermal treatment was conducted by high pressure steam at $300^{\circ}C$ for 2 hours using a autoclave. To make a HA sol, triethyl phosphite and calcium nitrate were diluted and dissolved in anhydrous ethanol and mixed. Then anodized implant were spin-coated with the prepared HA sols and heat treated. Samples were soaked in the Hanks solution with pH 7.4 at $37^{\circ}C$ for 6 weeks. The microstructure of the specimens was observed with a scanning electron microscope (SEM), and the composition of the surface layer was analyzed with an energy dispersive spectroscope (EDS). Results : The scanning electron micrographs of HA sol-gel coated and hydrothermal treated surface did not show any significant change in the size or shape of the pores. After immersion in Hanks' solution the precipitated HA crystals covered macro- and micro-pores The precipitated Ca and P increased in Hanks' solution that surface treatment caused increased activity. Conclusion : This study shows that sol-gel coated HA and hydrothermal treatment significantly enhance the rate of HA formation due to the altered surface chemistry.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.4
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• pp.343-353
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• 2017

Processing and equipment were tailored for engineering scale fabrication of $UO_2$ porous pellets, a feed material for the electrolytic reduction process in the PRIDE (PyRoprocessing Integrated DEmonstration) facility at KAERI (Korea Atomic Energy Research Institute). The starting materials, $UO_2$ powder and pre-milled surrogate oxide powders, were proportioned to simulate the chemical composition of spent fuel (so-called Simfuel). The Simfuel powders were homogenized by mixing, compacted into a pellet shape, and finally heat treated using a tumbling mixer, rotary press, and sintering furnace. After sintering at $1450^{\circ}C$ for 24 h in $4%\;H_2-Ar$, the average bulk density of the $UO_2$ Simfuel pellets was $6.89g{\cdot}cm^{-3}$, which meets the standard of the following electrolytic reduction process. In addition, the results of a microstructural analysis demonstrated that the sintered Simfuel $UO_2$ porous pellets accurately simulate the properties of spent fuel in terms of the formation of second phases. These results provide essential information for the massive fabrication of $UO_2$ porous pellets for engineering scale pyroprocessing research.