• Korean Journal of Materials Research
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• v.21 no.9
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• pp.520-524
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• 2011

Porous W with controlled pore characteristics was fabricated by a freeze-drying process. $WO_3$ powder and camphene were used as the source materials of W and sublimable vehicles, respectively. Camphene slurries with $WO_3$ contents of 10 and 15 vol% were prepared by milling at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing of a slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$ while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at $800^{\circ}C$ for 30 min and sintered in a furnace at $900^{\circ}C$ for 1 h under a hydrogen atmosphere. Microstructural observation revealed that all of the sintered samples were composed of only W phase and showed large pores which were aligned parallel to the camphene growth direction. The porosity and pore size increased with increasing camphene content. The difference in the pore characteristics depending on the slurry concentration may be explained by the degree of powder rearrangement in the slurry. The results strongly suggest that a porous metal with the required pore characteristics can be successfully fabricated by a freeze-drying process using metal oxide powders.

• Korean Journal of Materials Research
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• v.23 no.6
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• pp.339-343
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• 2013

Porous Ti-systems with unidirectionally aligned channels were synthesized by freeze-drying and a heat treatment process. $TiH_2$ powder and camphene were used as the source materials of Ti and sublimable vehicles, respectively. Camphene slurries with $TiH_2$ content of 10 and 15 vol% were prepared by milling at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing of the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$ while unidirectionally controlling the growth direction of the camphene. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was heat-treated at $1100^{\circ}C$ for 1 h in a nitrogen and air atmosphere. XRD analysis revealed that the samples composed of TiN and $TiO_2$ phase were dependent on the heat-treatment atmosphere. The sintered samples showed large pores of about 120 mm which were aligned parallel to the camphene growth direction. The internal wall of the large pores had relatively small pores with a dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry. These results suggest that a porous body with an appropriate microstructure can be successfully fabricated by freeze-drying and a controlled sintering process of a camphene/$TiH_2$ slurry.

• Journal of Powder Materials
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• v.24 no.6
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• pp.472-476
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• 2017

Porous W-10 wt% Ti alloys are prepared by freeze-drying a $WO_3-TiH_2$/camphene slurry, using a sintering process. X-ray diffraction analysis of the heat-treated powder in an argon atmosphere shows the $WO_3$ peak of the starting powder and reaction-phase peaks such as $WO_{2.9}$, $WO_2$, and $TiO_2$ peaks. In contrast, a powder mixture heated in a hydrogen atmosphere is composed of the W and TiW phases. The formation of reaction phases that are dependent on the atmosphere is explained by a thermodynamic consideration of the reduction behavior of $WO_3$ and the dehydrogenation reaction of $TiH_2$. To fabricate a porous W-Ti alloy, the camphene slurry is frozen at $-30^{\circ}C$, and pores are generated in the frozen specimens by the sublimation of camphene while drying in air. The green body is hydrogen-reduced and sintered at $1000^{\circ}C$ for 1 h. The sintered sample prepared by freeze-drying the camphene slurry shows large and aligned parallel pores in the camphene growth direction, and small pores in the internal walls of the large pores. The strut between large pores consists of very fine particles with partial necking between them.

• Korean Journal of Materials Research
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• v.23 no.12
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• pp.722-726
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• 2013

Freeze drying of a porous Cu-Sn alloy with unidirectionally aligned pore channels was accomplished by using a composite powder of CuO-$SnO_2$ and camphene. Camphene slurries with CuO-$SnO_2$ content of 3, 5 and 10 vol% were prepared by mixing with a small amount of dispersant at $50^{\circ}C$. Freezing of a slurry was done at $-25^{\circ}C$ while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green bodies were hydrogen-reduced at $650^{\circ}C$ and then were sintered at $650^{\circ}C$ and $750^{\circ}C$ for 1 h. XRD analysis revealed that the CuO-$SnO_2$ powder was completely converted to Cu-Sn alloy without any reaction phases. The sintered samples showed large pores with an average size of above $100{\mu}m$ which were aligned parallel to the camphene growth direction. Also, the internal walls of the large pores had relatively small pores. The size of the large pores decreased with increasing CuO-$SnO_2$ content due to the change of the degree of powder rearrangement in the slurry. The size of the small pores decreased with increase of the sintering temperature from $650^{\circ}C$ to $750^{\circ}C$, while that of the large pores was unchanged. These results suggest that a porous alloy body with aligned large pores can be fabricated by a freeze-drying and hydrogen reduction process using oxide powders.

• Conservation Science in Museum
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• v.7
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• pp.43-51
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• 2006

From the low swamp remains in Sinchang-dong, Gwangju, a number of wooden lacquerware along with various wooden artifacts were excavated. These excavated lacquerware have deteriorated and weak wooden parts and the lacquer layer come off from the wooden parts; they are very likely to peel off and crack. Therefore, we impregnated the lacquerware in PEG#4000 40% solution that was effective for vacuum freeze drying and finished freeze-drying below 0°…. We compared the weight of wood and lacquerware right after the freeze-drying with the weight after leaving them in a airtight space with 60% RH (relative humidity). The comparison results showed no change in weight; thereby we confirmed controlling the finishing temperature during freeze-drying could control the moisture in wood after drying and it could stabilize wood against the change in moisture in the atmosphere. according to the analysis of the lacquer fragment, the base layer was pasted on the wooden surface with mixed black pigment and the upper layer was pasted three or four times with the mixture of lacquer and black pigment; or it was pasted without the black base coating.

• 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.

• Korean Journal of Food Science and Technology
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• v.30 no.5
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• pp.1107-1113
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• 1998

This work was to study the potential use of germinated and microwave-vacuum-dried brown rite as a raw material for enzyme food. Brown rice was soaked in water at $15^{\circ}C$ for 2 days and then germinated at $25^{\circ}C$ for 4 days. The germin ated brown rice was then dried by different drying methods: microwave vacuum drying 1(drying only), microwave vacuum drying 2 $(drying{\rightarrow}crushing{\rightarrow}drying)$, hot air drying, vacuum drying and freeze drying. Each drier except freeze drier was set to maintain the sample temperature to be $60^{\circ}C$. During microwave vacuum drying 1 and 2 the sample reached $60^{\circ}C$ much faster (5 min) and was dried much faster (2 to 3 hrs for microwave vacuum drying 1 and 2 than the other drying methods. The initial drying rate of microwave vacuum drying was ten times faster than that of hot air drying. The microwave vacuum drying produced a dry sample of the highly retained enzymic activity, followed by freeze drying, vacuum drying and hot air drying.

• Food Science and Preservation
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• v.11 no.4
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• pp.516-521
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• 2004

The study was intended to develop a yam snack to increase the consumption and the added value of the yam which has many kinds of medicinal effects and functions. Moisture content of a freeze-drying yam snack was higher than those of hot wind drying and vacuum drying yam snack. However, carbohydrate content was opposed to it. The content of soluble proteins in freeze drying yam snack was 6.43 mg/100g, and lower than that those in hot wind drying and vacuum drying yam snack. The contents of total sugar and reducing sugar were not noticeably different by processing methods. The major organic acids of yam snack were malic, acetic, acids, and acetic acid. Citric acid were rich contented in hot wind and vacuum dried yam snack, but the content of malic acid in freeze dried yam snack was higher than those in hot wind and vacuum dried yam snack. The contents of the amino acids and total amino acids showed the highest contents in vacuum dried snack and the next came in hot wind dried snack and freeze dried snack order. The content of free amino acids were not different by processing methods. Total content of vitamin C were not different by processing methods, but a ascorbic acid was higher in freeze dried yam snack than those in other. The dehydroascorbic acid contents of the hot-air and vacuum dried snack was higher than those of the freeze dried snack, Potassium, sodium and magnesium were the main minerals of the yam snacks.

• Korean Journal of Plant Resources
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• v.12 no.1
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• pp.20-26
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• 1999

To investigate phytotoxic substances in Equisetum arvense, the aqueous extracts(25 and 8$0^{\circ}C$) or the freeze-drying matter from aqueous extracts($25^{\circ}C$) of E. arvense were tested at different concentrations for biological activities on callus induction and growth, seed germination, seedling growth and antibacterial function. Callus induction and growth of Oryza sativa and Brassica campestris ssp. pekinensis were inhibited by the aqueous extracts at 8$0^{\circ}C$ than at $25^{\circ}C$ and the higher concentrations. Callus growth of four receptor species was inhibited in order of Platycodon grandiflorum, Sesamum indicum, Brassica campestris ssp. pekinensis and Oryza sativa. Seed germination of Ο. sativa, S. indicum, and B. campestris ssp. pekinensis was not affected at low concentration, but it was proportionally inhibited by the higher concentrations. The greatest inhibition of seed germination was 28.3% compared to control, when 2,000$\mu\textrm{g}$/ml of freeze-drying matter was applied to B. campestris ssp. pekinensis. Shoot growth was stimulated by 500$\mu\textrm{g}$/ml of freeze-drying matter, but it was inhibited by the higher concentrations. Root growth was significantly inhibited compare to control at all concentrations. Antibacterial activity of freeze-drying matter didn't showed against Xantomonas oryzae and Eschrichia coli, but a small clear zone was formed by 500$\mu\textrm{g}$ of freeze-drying matter against Erwinia carotovora ssp. carotovora.

• Journal of Powder Materials
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• v.21 no.1
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• pp.34-38
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• 2014

Cu-Ni alloys with unidirectionally aligned pores were prepared by freeze-drying process of CuO-NiO/camphene slurry. Camphene slurries with dispersion stability by the addition of oligomeric polyester were frozen at $-25^{\circ}C$, and pores in the frozen specimens were generated by sublimation of the camphene during drying in air. The green bodies were hydrogen-reduced at $300^{\circ}C$ and sintered at $850^{\circ}C$ for 1 h. X-ray diffraction analysis revealed that CuO-NiO composite powders were completely converted to Cu-Ni alloy without any reaction phases by hydrogen reduction. The sintered samples showed large and aligned parallel pores to the camphene growth direction, and small pores in the internal wall of large pores. The pore size and porosity decreased with increase in CuO-NiO content from 5 to 10 vol%. The change of pore characteristics was explained by the degree of powder rearrangement in slurry and the accumulation behavior of powders in the interdendritic spaces of solidified camphene.