• 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.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.5
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• pp.89-95
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• 1999

In this study, the corrosion resistance of the aluminum casting commercial materials used in the automotive engine parts with respect to the anti-freeze coolant environment has been tested by the potentio dynamic method. especially, the effect of borax additive in engine coolant on the corrosion resistance of the aluminum casting materials has been evaluated. It was found that the borax in commercial engine coolant, used to prevent the corrosion in cast iron engine, causes a pit corrosion of aluminum casting materials at high temperature. During the engine endurance test with the coolant containing borax, the aluminum cylinder head was failed by the pitting corrosion near the exhaust port. Conclusively, it was suggested that the use of borax in the anti-freeze coolant be restricted for the automotive with aluminum cylinder head.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.84.2-84
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• 2003

• Journal of Powder Materials
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• v.22 no.6
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• pp.438-442
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• 2015

Porous thick film of alumina which is fabricated by freeze tape casting using a camphene-camphor-acrylate vehicle. Alumina slurry is mixed above the melting point of the camphene-camphor solvent. Upon cooling, the camphene-camphor crystallizes from the solution as particle-free dendrites, with the $Al_2O_3$ powder and acrylate liquid in the interdendritic spaces. Subsequently, the acrylate liquid is solidified by photopolymerization to offer mechanical properties for handling. The microstructure of the porous alumina film is characterized for systems with different cooling rate around the melting temperature of camphor-camphene. The structure of the dendritic porosity is compared as a function of ratio of camphene-camphor solvent and acrylate content, and $Al_2O_3$ powder volume fraction in acrylate in terms of the dendrite arm width.

• Journal of Pharmaceutical Investigation
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• v.30 no.2
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• pp.93-98
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• 2000

In order to evaluate the effect of fabrication methods on the controlled release of an antibiotic from a polymeric device, two types of polyurethane-cefadroxil matrix were prepared by the solvent casting method or the freeze drying method, using bovine serum albumin as a pore former. The amount of cefadroxil released from various formulations at $37^{\circ}C$ was measured by HPLC. The duration of antimicrobial activity of matrices against S. aureus was evaluated by measuring the diameters of the inhibition zone. The morphology of the matrices was investigated by scanning electron microscopy (SEM). Changing the fabrication method could alter the release rate of cefadroxil from the matrix. The matrix fabricated by the freeze drying method had more porous inner structure and showed higher release rate than that prepared by the solvent casting method. However, the duration of antimicrobial activity was shorter when the matrix was fabricated by the freeze drying method.

• Korean Journal of Materials Research
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• v.26 no.2
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• pp.61-66
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• 2016

In order to fabricate porous mullite ceramics with controlled pore structure and improved mechanical strength, a freeze casting route has been processed using camphene mixed with tertiary-butyl alcohol (TBA) and coal fly ash/alumina as the solvent and the ceramic material, respectively. After sintering, the solidification characteristics of camphene and TBA solvent were evident in the pore morphology, i.e., dendritic and straight pore channels formed along the solidification directions of camphene and TBA ice, respectively, after sublimation. Also, the presence of microcracks was observed in the bodies sintered at $1500^{\circ}C$, mainly due to the difference in solidification volume change between camphene and TBA. The compressive strength of the sintered bodies was found generally to be dependent, in an inverse manner, on the porosity, which was mainly determined by the processing conditions. After sintering at $1300{\sim}1500^{\circ}C$ with 30~50 wt% solid loading, the resulting mullite ceramics showed porosity and compressive strength values in ranges of 83.8~43.1% and 3.7~206.8 MPa, respectively.

• Journal of the Korean Ceramic Society
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• v.45 no.2
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• pp.105-111
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• 2008

Symmetric three layer composites have been prepared by freeze casting and then pressureless sintered at $l700-1800^{\circ}C$ in $N_2$ gas atmosphere. The relative sintered density of multilayer composites having microstructural characteristics of later intermediate-stage densification increased with sintering temperature and reached about 95% theoretical value at $1800^{\circ}C$. Although the indentation strength of the multilayer composites was generally reduced with increasing Vickers indentation load up to 294N, the damage resistance of multilayer composites was superior compared to monolithic layer 95AL/5SN material. The three-point bend strength of the layered materials remained at the values 266-298 MPa after indentation with a load of 49N, while that of the monolithic 95AL/5SN material was 219 MPa. The fracture toughness of the multilayer material was $5.4-6.6\;MPa\;m^{1/2}$.

• Journal of Powder Materials
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• v.29 no.2
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• pp.118-122
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• 2022

The synthesis of porous W by freeze-casting and vacuum drying is investigated. Ball-milled WO₃ powders and tert-butyl alcohol were used as the starting materials. The tert-butyl alcohol slurry is frozen at -25℃ and dried under vacuum at -25 and -10℃. The dried bodies are hydrogen-reduced at 800℃ and sintered at 1000℃. The XRD analysis shows that WO₃ is completely reduced to W without any reaction phases. SEM observations reveal that the struts and pores aligned in the tert-butyl alcohol growth direction, and the change in the powder content and drying temperature affects the pore structure. Furthermore, the struts of the porous body fabricated under vacuum are thinner than those fabricated under atmospheric pressure. This behavior is explained by the growth mechanism of tert-butyl alcohol and rearrangement of the powders during solidification. These results suggest that the pore structure of a porous body can be controlled by the powder content, drying temperature, and pressure.

• Journal of Pharmaceutical Investigation
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• v.30 no.4
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• pp.295-297
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• 2000

A new method to evaluate erosion of biodegradable polymer, polyanhydrides, was developed. The polymer devices were prepared with the melt-casting method and weight loss was accurately measured after agitating the devices in buffers (pH 1-9), and removing the device at selected time intervals and freeze-drying the device. The erosion rate was estimated from the plot of the weight loss(%) of device as a function of time. The freeze-drying technique used in this study is particularly useful for estimating the erosion rate of biodegradable polymer.

• Journal of the Korean Ceramic Society
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• v.43 no.3 s.286
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• pp.193-197
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• 2006

Symmetric three-layer $Al_2O_3/ZrO_2$ composite has been prepared by freeze casting and pressureless sintering at $1400-1600^{\circ}C$ in air. The layered material sintered at $1600^{\circ}C$ showed the maximum fracture strength (410 MPa), measured by a four-point bending test. Contact damage strength was superior in three-layer composite compared with corresponding mono-layered material, possibly due to the development of relatively large compressive stress. The grain growth of $ZrO_2$ particles was mainly governed by coalescence mechanism.