• 한국재료학회지
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• 제21권9호
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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.

• 한국재료학회지
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• 제23권6호
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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.

• 한국분말재료학회지
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• 제24권6호
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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.

• 한국재료학회지
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• 제23권12호
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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.

• 박물관보존과학
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• 제7권
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• pp.43-51
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• 2006

광주 신창동 저습지유적에서 다양한 목재유물과 더불어 목재표면에 옻칠이 된 칠기들이 다량으로 출토되었다. 칠기들은 목질부가 열화 되어 취약하며 칠층이 들떠있어 박락과 갈라짐의 발생우려가 높다. 따라서 진공 동결건조에 효과적인 PEG#4000 40%로 함침처리 하였고 동결건조의 종료온도를 0℃이하로 하였다. 동결건조 직후 목제와 칠기의 중량과 상대습도 60% 의 밀폐공간에서 방치 후 중량을 비교하였다. 그 결과 중량변화가 없었으므로 동결건조 중 종료 온도 조절로써 건조 후 목재함유수분조절과 대기 중 습도변화에 안정성을 확인하였다. 칠도막 분석결과 밑층에 흑색안료를 혼합하여 목재표면에 밑칠을 하고 칠층의 상부에 옻칠과 흑색안료를 혼합하여 3~4회 칠한 것과 검은 밑칠을 하지 않고 칠층에 옻칠과 흑색 안료를 혼합하여 3~4회 칠한 것으로 확인되었다.

• 한국분말재료학회지
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• 제25권1호
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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.

• 한국식품과학회지
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• 제30권5호
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• pp.1107-1113
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• 1998

품질이 우수한 효소식품으로의 활용가능성 검토를 위해 현미를 발아시킨 후 마이크로파 진공건조로 건조하고 그 건조특성과 품질특성을 열풍건조, 진공건조, 그리고 동결건조의 경우와 비교해 보았다. 마이크로파 진공건조 1 및 2의 경우 열전달속도가 빨라 건조 개시후 5분 경과후 $60^{\circ}C$에 도달하였고 건조시간 내내 $60{\pm}2^{\circ}C$를 유지하였으나 열풍건조의 경우는 건조개시 60분 경과 후, 진공건조의 경우는 2시간 경과 후에야 $60^{\circ}C$에 도달하였다. 마이크로파 진공건조 1의 경우 건조 3시간 후 수분함량 0.08 kg water/kg solid까지 감소하였으나, 마이크로파 진공건조 2의 경우 총건조시간 2시간만에 수분함량 0.O6 kg water/kg solid까지 감소하였다. 열풍건조의 경우 건조시간 4시간만에 수분함량 0.14 kg water/kg solid까지 감소하였으나 최소한 2시간은 더 건조시켜야 할 것으로 예상되었다. 마이크로파 진공건조 1 및 2의 초기 건조속도는 0.05 kg water/kg solid/min이었으며 처음부터 건조속도가 계속 감소하는 감률건조를 보였다. 열풍건조의 경우는 초기 건조속도가 0.0057 kg water/kg solid/min으로서 마이크로파 진공건조 1 및 2의 1/10 수준이었으며 건조개시 30분까지 항률건조를 보이다가 임계수분함량 0.81 kg water/kg solid 부근부터 감률건조가 시작되었다. 건조시료의 ${\alpha}-amylase$ 활성 및 protease 활성은 마이크로파 진공건조, 동결건조, 진공건조 및 열풍건조의 순서를 보였고, diastatic activity의 경우 동결건조와 마이크로파 진공전조가 거의 대등한 품질보존효과를 보여 주었다. 이로부터 마이크로파 진공건조를 이용하여 건조할 경우 최소한 동결건조와 대등한 품질의 건조제품을 제조할 수 있으리라 예상되었다.

• 한국식품저장유통학회지
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• 제11권4호
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• pp.516-521
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• 2004

본 연구는 각종 약리 및 기능성을 함유한 마의 소비증대와 부가가치 증대를 위하여 새로운 마의 가공식품인 마 스낵을 개발하고자 당절임 최적조건에서 당절임한 마스낵의 제조방법에 따라 성분변화를 조사하였다. 수분함량은 열풍, 진공 건조한 것에 비해 동결건조한 것이 높았고, 탄수화물 함량은 반대되는 경향이었다. 수용성 단백질 함량은 동결건조한 것에서 6.43 mg/100 g으로서 열풍 및 진공 건조한 것에 비해 낮았으나, 총당과 환원당의 함량은 건조방법에 따라 뚜렷한 차이가 없었다. 주요 유기산은 malic, acetic, citric acid이었고, acetic acid와 citric acid의 함량은 동결 건조한 것에 비해 열풍, 진공 건조한 것에 많았고, malic acid는 열풍 및 진공 건조한 것에 비해 월등히 높았다. 구성아미노산 중대부분의 아미노산과 총 유리아미노산의 함량은 진공 건조한 것에 가장 많았고, 다음으로 열풍, 동결 건조한 순이었으며, 유리아미노산의 함량은 큰 차이가 없었다. 총 비타민 C의 함량은 건조방법에 따라 차이가 없었으나, 환원형 비타민 C는 열풍, 진공 건조한 것에 비해 동결 건조한 것에서 많았고, 산화형 비타민 C는 동결건조한 것에서 가장 낮았다. 무기질의 함량은 칼륨, 나트륨, 마그네슘의 함량이 높았다.

• 한국자원식물학회지
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• 제12권1호
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• pp.20-26
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• 1999

쇠뜨기에 다른식물의 생장을 저해하는 물질이 생성되는지를 알아보기 위하여, 수용추출액으로 몇가지 식물의 캘러스 생장, 종자발아, 유묘생장 및 항균활성에 미치는 영향을 조사하였다. 수용 추출액의 첨가농도가 높은 배지에서 벼와 배추의 캘러스 유기 및 발달을 억제하였으며, 8$0^{\circ}C$ 추출액이 $25^{\circ}C$ 추출액보다 유의하게 캘러스 유기 및 생장을 억제하였다. 20%추출액 첨가배지에서 공시식물의 캘러스 생장은 추출온도에 관계없이 도라지, 참깨, 배추, 벼 순으로 억제되었다. 냉동건조한 수용추출액 고형물은 저농도에서는 영향이 적었으나, 처리농도에 비례하여 벼, 참깨, 배추의 종자발아를 억제하였고, 특히 배추는 2,000$\mu\textrm{g}$/mι농도에서 대조구의 28.3%로 급격한 발아억제를 보였다. 유식물 생장은 500$\mu\textrm{g}$/mι의 저농도에서는 대조구보다 초장이 약간 촉진되는 경향을 보였으나, 처리농도가 증가함에 따라 심하게 억제되었으며, 특히 근장이 유의하게 억제되었다. 추출액 고형물의 항균활성은 500$\mu\textrm{g}$에서 E. carotovora에서만 약간의 억제대를 형성하였으며, X. oryzae pv. oryzae와 E. coli에 대해서 는 항균활성을 보이지 않았다.

• 한국분말재료학회지
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• 제21권1호
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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.