Camphene Slurries Research Articles

Synthesis of Porous Cu-Co using Freeze Drying Process of Camphene Slurry with Oxide Composite Powders

Synthesis of Porous Cu-Co using Freeze Drying Process of Camphene Slurry with Oxide Composite Powders

Porous W-Ni Alloys Synthesized from Camphene/WO3-NiO Slurry by Freeze Drying and Heat Treatment in Hydrogen Atmosphere

The present study demonstrates the effect of raw powder on the pore structure of porous W-Ni prepared by freeze drying of camphene-based slurries and sintering process. The reduction behavior of WO3 and WO3-NiO powders is analyzed by a temperature programmed reduction method in Ar-10% H2 atmosphere. After heat treatment in hydrogen atmosphere, WO3-NiO powder mixture is completely converted to metallic W without any reaction phases. Camphene slurries with oxide powders are frozen at −30 oC, and pores in the frozen specimens are generated by sublimation of the camphene during drying in air. The green bodies are hydrogen-reduced at 800 °C and sintered at 1000 °C for 1 h. The sintered samples show large and aligned parallel pores to the camphene growth direction, and small pores in the internal wall of large pores. The strut between large pores, prepared from pure WO3 powder, consists of very fine particles with partially necking between the particles. In contrast, the strut densification is clearly observed in the Ni-added W sample due to the enhanced mass transport in activation sintering.

In situ growth of one-dimensional nanowires on porous PDC-SiC/Si3N4 ceramics with excellent microwave absorption properties

Abstract Enhanced microwave absorption properties of porous PDC-SiC/Si 3 N 4 ceramics were successfully prepared through in situ growth of Si 3 N 4 nanowires (NWs) by the unidirectional freeze casting of Si 3 N 4 /camphene slurries with various polycarbosilane (PCS) contents at 1400 °C in N 2 . Si 3 N 4 NWs were in situ formed in the pore channels via a vapor-solid (VS) mechanism, the content of Si 3 N 4 NWs increased with increasing of PCS content, which tailored the microstructure and mechanical property of porous PDC-SiC/Si 3 N 4 ceramics. With the increase of PCS content, the minimum reflection coefficient (RC) of porous PDC-SiC/Si 3 N 4 ceramic decreased from −20.2 dB to −56.2 dB, and the effective absorption bandwidth (EAB) increased from 5.3 to 7 GHz, demonstrating that the porous PDC-SiC/Si 3 N 4 ceramics decorated with Si 3 N 4 NWs had a superior microwave-absorbing ability, which could be ascribed to the electronic dipole polarization and interfacial scattering enhanced by the various interfaces among Si 3 N 4 , in-situ formed PDC-SiC nanograins, nanosized carbon and Si 3 N 4 NWs phases. These findings provide significance guidance in the development of new broadband EM absorbing materials.

Effect of Freezing and Sintering Condition of CuO-SnO2/Camphene Slurries on the Pore Structure of Porous Cu-Sn

The present study demonstrates the effect of freezing conditions on the pore structure of porous Cu-10 wt.% Sn prepared by freeze drying of /camphene slurry. Mixtures of CuO and powders are prepared by ball milling for 10 h. Camphene slurries with 10 vol.% of are unidirectionally frozen in a mold maintained at a temperature of for 1 and 24 h, respectively. Pores are generated by the sublimation of camphene at room temperature. After hydrogen reduction and sintering at for 2 h, the green body of the is completely converted into porous Cu-Sn alloy. Microstructural observation reveals that the sintered samples have large pores which are aligned parallel to the camphene growth direction. The size of the large pores increases from 150 to with an increase in the holding time. Also, the internal walls of the large pores contain relatively small pores whose size increases with the holding time. The change in pore structure is explained by the growth behavior of the camphene crystals and rearrangement of the solid particles during the freezing process.

Fabrication of Porous W by Freeze-Drying Process of Camphene Slurries with Spherical PMMA and WO3 Powders

Porous W with spherical and directionally aligned pores was fabricated by the combination of sacrificial fugitives and a freeze-drying process. Camphene slurries with powder mixtures of WO3 and spherical PMMA of 20 vol% were frozen at −25 oC and dried for the sublimation of the camphene. The green bodies were heat-treated at 400 oC for 2 h to decompose the PMMA; then, sintering was carried out at 1200 oC in a hydrogen atmosphere for 2 h. TGA and XRD analysis showed that the PMMA decomposed at about 400 oC, and WO3 was reduced to metallic W at 800 oC without any reaction phases. The sintered bodies with WO3-PMMA contents of 15 and 20 vol% showed large pores with aligned direction and small pores in the internal walls of the large pores. The pore formation was discussed in terms of the solidication behavior of liquid camphene with solid particles. Spherical pores, formed by decomposition of PMMA, were observed in the sintered specimens. Also, microstructural observation revealed that struts between the small pores consisted of very fine particles with size of about 300 nm.

CuO가 코팅된 Cu 분말을 혼합한 Camphene 슬러리의 동결건조에 의한 Cu 다공체 제조

This study reports a simple way of fabricating the porous Cu with unidirectional pore channels by freeze drying camphene slurry with Cu oxide coated Cu powders. The coated powders were prepared by calcination of ball-milled powder mixture of Cu and Cu-nitrate. Improved dispersion stability of camphene slurry could be achieved using the Cu oxide coated Cu powders instead of pure Cu powders. Pores in the frozen specimen at <TEX>$-25^{\circ}C$</TEX> were generated by sublimation of the camphene during drying in air, and the green bodies were sintered at <TEX>$750^{\circ}C$</TEX> for 1 h in <TEX>$H_2$</TEX> atmosphere. XRD analysis revealed that the coated layer of Cu oxide was completely converted to Cu phase without any reaction phases by hydrogen heat treatment. The porous Cu specimen prepared from pure Cu powders showed partly large pores with unidirectional pore channels, but most of pores were randomly distributed. In contrast, large and aligned parallel pores to the camphene growth direction were clearly observed in the sample using Cu oxide coated Cu powders. Pore formation behavior depending on the initial powders was discussed based on the degree of powder rearrangement and dispersion stability in slurry.

WO3/Camphene 슬러리의 동결건조 공정에서 동결제의 응고거동이 기공구조에 미치는 영향

This paper describes the effect of the solidification behavior of camphene on the pore structure of porous W fabricated via a freeze-drying process. Camphene slurries with 10 and 15 vol% WO3 were prepared by milling at 50 °C with a small amount of dispersant. Porous W with unidirectionally aligned pore channels was prepared by freeze-drying of slurry and heat treatment in a hydrogen atmosphere. The sintered specimen with 10 vol% WO3 showed large pores with a size of about 100 μm which were aligned parallel to the growth direction of camphene. The internal wall of large pores had relatively small pores. In the slurry with 15 vol% WO3, large pores were not observed in the sintered body, and only small pores existed. The difference in the pore size in the two specimens is explained on the basis of the growth characteristics of the camphene dendrite depending on the amount of particles in the slurry. †(Received June 27, 2013)

Cu 입자가 분산된 Al2O3다공체의 제조 및 항균특성

In order to fabricate the porous <TEX>$Al_2O_3$</TEX> with dispersion of nano-sized Cu particles, freeze-drying of camphene/<TEX>$Al_2O_3$</TEX> slurry and solution chemistry process using Cu-nitrate are introduced. Camphene slurries with 10 vol% <TEX>$Al_2O_3$</TEX> was frozen at <TEX>$-25^{\circ}C$</TEX>. Pores were generated by sublimation of the camphene during drying in air. The sintered samples at 1400 and <TEX>$1500^{\circ}C$</TEX> showed the same size of large pores which were aligned parallel to the sublimable vehicles growth direction. However, the size of fine pores in the internal walls of large pores decreased with increase in sintering temperature. It was shown that Cu particles with the size of 100 nm were homogeneously dispersed on the surfaces of the large pores. Antibacterial test using fungus revealed that the porous <TEX>$Al_2O_3$</TEX>/1 vol% Cu composite showed antifungal property due to the dispersion of Cu particles. The results are suggested that the porous composites with required pore characteristics and functional property can be fabricated by freeze-drying process and addition of functional nano particles by chemical method.

CuO-NiO 혼합분말의 동결건조 및 수소환원에 의한 Cu-Ni 다공체 제조

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 <TEX>$-25^{\circ}C$</TEX>, and pores in the frozen specimens were generated by sublimation of the camphene during drying in air. The green bodies were hydrogen-reduced at <TEX>$300^{\circ}C$</TEX> and sintered at <TEX>$850^{\circ}C$</TEX> 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.

금속산화물 복합분말의 동결건조 및 수소분위기 환원처리에 의한 Cu-Sn 다공체 제조

Freeze drying of a porous Cu-Sn alloy with unidirectionally aligned pore channels was accomplished by using a composite powder of CuO-<TEX>$SnO_2$</TEX> and camphene. Camphene slurries with CuO-<TEX>$SnO_2$</TEX> content of 3, 5 and 10 vol% were prepared by mixing with a small amount of dispersant at <TEX>$50^{\circ}C$</TEX>. Freezing of a slurry was done at <TEX>$-25^{\circ}C$</TEX> 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 <TEX>$650^{\circ}C$</TEX> and then were sintered at <TEX>$650^{\circ}C$</TEX> and <TEX>$750^{\circ}C$</TEX> for 1 h. XRD analysis revealed that the CuO-<TEX>$SnO_2$</TEX> powder was completely converted to Cu-Sn alloy without any reaction phases. The sintered samples showed large pores with an average size of above <TEX>$100{\mu}m$</TEX> 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-<TEX>$SnO_2$</TEX> 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 <TEX>$650^{\circ}C$</TEX> to <TEX>$750^{\circ}C$</TEX>, 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.

Fabrication of Porous Ti by Freeze-Drying and Heat Treatment of TiH2/Camphene Slurries

Porous Ti-systems with unidirectionally aligned channels were synthesized by freeze-drying and a heat treatment process. powder and camphene were used as the source materials of Ti and sublimable vehicles, respectively. Camphene slurries with content of 10 and 15 vol% were prepared by milling at 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 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 for 1 h in a nitrogen and air atmosphere. XRD analysis revealed that the samples composed of TiN and 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/ slurry.

Synthesis and Microstructure of Porous Al2O3 with Nano-Sized Cu Dispersions

Porous <TEX>$Al_2O_3$</TEX> dispersed with nano-sized Cu was fabricated by freeze-drying process and solution chemistry method using Cu-nitrate. To prepare porous <TEX>$Al_2O_3$</TEX>, camphene was used as the sublimable vehicle. Camphene slurries with <TEX>$Al_2O_3$</TEX> content of 10 vol% were prepared by milling at <TEX>$50^{\circ}C$</TEX> 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 to <TEX>$-25^{\circ}C$</TEX> while unidirectionally controlling the growth direction of the camphene. Pores were subsequently generated by sublimation of the camphene during drying in air for 48 h. The green body was sintered in a furnace at <TEX>$1400^{\circ}C$</TEX> for 1 h. Cu particles were dispersed in porous <TEX>$Al_2O_3$</TEX> by calcination and hydrogen reduction of Cu-nitrate. The sintered samples showed large pores with sizes of about <TEX>$150{\mu}m$</TEX>; these pores were aligned parallel to the camphene growth direction. Also, the internal walls of the large pores had relatively small pores due to the traces of camphene left between the concentrated <TEX>$Al_2O_3$</TEX> particles on the internal wall. EDS analysis revealed that the Cu particles were mainly dispersed on the surfaces of the large pores. These results strongly suggest that porous <TEX>$Al_2O_3$</TEX> with Cu dispersion can be successfully fabricated by freeze-drying and solution chemistry routes.

텅스텐 다공체의 기공특성에 미치는 분말특성 및 동결조건의 영향

Dependence of the freeze-drying process condition on microstructure of porous W and pore formation mechanism were studied. Camphene slurries with contents of 10 vol% were prepared by milling at with a small amount of dispersant. Freezing of a slurry was done in Teflon cylinder attached to a copper bottom plate cooled at . Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at for 30 min, and sintered in the furnace at for 1 h. After heat treatment in hydrogen atmosphere, powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores with dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry.

Fabrication and Properties of Porous Tungsten by Freeze-Drying Process

Porous W with controlled pore characteristics was fabricated by a freeze-drying process. <TEX>$WO_3$</TEX> powder and camphene were used as the source materials of W and sublimable vehicles, respectively. Camphene slurries with <TEX>$WO_3$</TEX> contents of 10 and 15 vol% were prepared by milling at <TEX>$50^{\circ}C$</TEX> 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 <TEX>$-25^{\circ}C$</TEX> 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 <TEX>$800^{\circ}C$</TEX> for 30 min and sintered in a furnace at <TEX>$900^{\circ}C$</TEX> 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.

Fabrication of porous titanium scaffolds with high compressive strength using camphene-based freeze casting

We herein report the fabrication of highly porous titanium (Ti) scaffolds with unusually high compressive strength by freezing a titanium hydride (TiH 2)/camphene slurries at 42 °C. As the freezing time was increased from 1 to 7 days, the pore size obtained was increased significantly from 143 to 271 μm due to the continual overgrowth of camphene dendrites. However, interestingly, the formation of the micro-pores inside the Ti walls was suppressed at longer freezing time. This resulted in a significant increase in compressive strength up to 110 ± 17 MPa with a porosity of 64%. It is believed that this unusually high compressive strength with large interconnected pores makes this material suitable for applications as load-bearing parts.

Improvement of compressive strength of porous hydroxyapatite scaffolds by adding polystyrene to camphene-based slurries

The compressive strength of porous hydroxyapatite (HA) scaffolds was enhanced by adding polystyrene (PS) polymer as a binder to hydroxyapatite (HA)/camphene slurries. As the PS content was increased from 0 to 20 vol.% in relation to the HA content, the compressive strength was significantly increased from 1.1 ± 0.2 to 2.3 ± 0.5 MPa, while the pore size was decreased from 277 ± 47 to 170 ± 29 µm. The improvement in the compressive strength was mainly attributed to both the suppression of the cracking of the green sample during freeze drying and the mitigation of the formation of micro-pores in the HA walls.

Porous titanium (Ti) scaffolds by freezing TiH 2/camphene slurries

Porous titanium (Ti) scaffolds with interconnected pores were fabricated by freezing titanium hydride (TiH 2)/camphene slurries at 33 °C for 24 h, followed by freeze-drying and subsequent heat-treatment at 1300 °C for 2 h in vacuum. All of the fabricated samples revealed highly porous structures having large pores up to 100 μm in size surrounded by Ti metal walls without any secondary phases. When the initial TiH 2 content was increased from 15 to 25 vol.%, the porosity was decreased from 63 to 49%, while the compressive strength was significantly improved from 81 to 253 MPa.

In-situ fabrication of porous hydroxyapatite (HA) scaffolds with dense shells by freezing HA/camphene slurry

We fabricated a novel type of porous HA scaffold with a dense shell/porous core structure by freezing a hydroxyapatite (HA)/camphene slurry in-situ. During freezing, the camphene dendrites from the mold wall grew 2-dimensionally by pushing the HA particles into the remaining slurry, which resulted in the formation of a camphene layer/concentrated HA particles layer as the surrounding skin of the sample. After removing the frozen camphene and sintering the HA walls at 1250 °C for 3 h, a dense shell integrated with a porous core was formed in-situ. We prepared two types of porous HA scaffold, a porous HA cylinder with a dense shell and a 3-D HA scaffold, consisting of periodic HA networks with a dense shell/porous core structure. These novel scaffolds would be expected to have improved mechanical integrity due to the use of a dense shell, as well as efficient bone ingrowth inside pores formed in a porous core.

Fabrication of Al2O3 Dispersed Porous Cu by Freeze Drying of CuO-Al2O3/Camphene Slurry

&lt;p&gt;Porous Cu with a dispersion of nanoscale Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; particles is fabricated by freeze-drying CuO-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/camphene slurry and sintering. Camphene slurries with CuO-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; contents of 5 and 10 vol% are unidirectionally frozen at -30°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°C and 800°C in H&lt;sub&gt;2&lt;/sub&gt; atmosphere. The sintered samples show large pores of 100 μm in average size aligned parallel to the camphene growth direction. The internal walls of the large pores feature relatively small pores of ~10 μm in size. The size of the large pores decreases with increasing CuO-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt; reducing process.&lt;/p&gt;