• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.625-630
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• 2012

Highly porous silicon carbide (SiC) ceramics were fabricated from polysiloxane, SiC and carbon black fillers, AlN-$Y_2O_3$ additives, and poly (ether-co-octene) (PEOc) and expandable microsphere templates. Powder mixtures with a fixed PEOc content (30 wt%) and varying SiC filler contents from 0-21 wt% were compression-molded. During the pyrolysis process, the polysiloxane was converted to SiOC, the PEOc generated a considerable degree of interconnected porosity, and the expandable microspheres generated fine cells. The polysiloxane-derived SiOC and carbon black reacted and synthesized nano-sized SiC with a carbothermal reduction during a heat-treatment. Subsequent sintering of the compacts in a nitrogen atmosphere produced highly porous SiC ceramics with porosities ranging from 78 % to 82 % and a flexura lstrength of up to ~7 MPa.

• Bulletin of the Korean Chemical Society
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• v.35 no.4
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• pp.1110-1116
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• 2014

The cuprous oxide cubes with the special porous surface constructed by nano-prisms have been successfully fabricated by a solvothermal method. The template-free method is simple and facile without any surfactant. The X-ray powder diffraction (XRD) pattern suggests that the as-prepared product is the pure primitive cubic $Cu_2O$. The effects of the experimental parameters, such as the reaction temperature, reaction time and the concentration of sodium acetate anhydrous, on the morphologies of the products were investigated in detail by the scanning electron microscopy (SEM). Based on the time-dependent experiments, the possible formation mechanism was proposed. Using photocatalytic degrading reactive dyes as the model reaction and xenon lamp to simulate sunlight, the $Cu_2O$ cubes with the porous surface might possess higher photocatalytic activity than those of the commercial $Cu_2O$ powder in the visible-light region, indicating the excellent photocatalytic performance.

• Journal of Powder Materials
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• v.11 no.6 s.47
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• pp.528-534
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• 2004

Using the nano Fe powders having 50 nm in diameter, Fe compact bodies were fabricated by injec-tion molding process. The relationship between microstructure and material properties depending on the volume ratio of powder/binder and sintering temperature were characterized by SEM, TEM techniques. In the compact body with the volume percentage ratio of 45(Fe powder) : 55(binder), which was sintered at $700^{\circ}C,$ the relative density was about $97{\%},$ and the values of volume shrinkage and hardness were about $66.3{\%}$ and 242.0 Hv, respec-tively. Using the composition of 50(Fe powder) : 50(binder) and sintered at $700^{\circ}C,$ the values of relative density, volume shrinkage and hardness of Fe sintered bodies were $73.3{\%},\;47.6{\%}$ and 152.8 Hv, respectively. They showed brittle fracture mode due to the porous and fine microstructure.

• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.479-485
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• 2008

Porous $TiO_2$ nanostructured particles containing both mesopores and macropores were fabricated by utilizing an aerosol templating method from two kinds of starting materials (colloidal mixture of $TiO_2$ nanoparticles and PS particles, and that of TTIP solution and PS particles). The effects of mixing ratio of PS to $TiO_2$ and reactor temperature on the particle properties were investigated. When $TiO_2$ nanoparticles were used as starting materials, the increase of macropores number was observed by SEM and the specific surface area and total pore volume were increased from $31.6m^2/g$ to $39.1m^2/g$ and $0.068cm^3/g$ to $0.089cm^3/g$, respectively, by increasing the weight mixing ratio of $PS/TiO_2$ from 0.79 to 1.31. When TTIP was used as precursor, the specific surface area and mesopore volume of particles prepared at same condition decreased by 67% and 75%, respectively.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.7-7
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• 2011

Quantum beam technology has been expected to develop breakthroughs for nanotechnology during the third basic plan of science and technology (2006~2010). Recently, Green- or Life Innovations has taken over the national interests in the fourth basic science and technology plan (2011~2015). The NIMS (National Institute for Materials Science) has been conducting the corresponding mid-term research plans, as well as other national projects, such as nano-Green project (Global Research for Environment and Energy based on Nanomaterials science). In this lecture, the research trends in Japan and NIMS are firstly reviewed, and the typical achievements are highlighted over key nanotechnology fields. As one of the key nanotechnologies, the quantum beam research in NIMS focused on synchrotron radiation, neutron beams and ion/atom beams, having complementary attributes. The facilities used are SPring-8, nuclear reactor JRR-3, pulsed neutron source J-PARC and ion-laser-combined beams as well as excited atomic beams. Materials studied are typically fuel cell materials, superconducting/magnetic/multi-ferroic materials, quasicrystals, thermoelectric materials, precipitation-hardened steels, nanoparticle-dispersed materials. Here, we introduce a few topics of neutron scattering and ion beam nanofabrication. For neutron powder diffraction, the NIMS has developed multi-purpose pattern fitting software, post RIETAN2000. An ionic conductor, doped Pr2NiO4, which is a candidate for fuel-cell material, was analyzed by neutron powder diffraction with the software developed. The nuclear-density distribution derived revealed the two-dimensional network of the diffusion paths of oxygen ions at high temperatures. Using the high sensitivity of neutron beams for light elements, hydrogen states in a precipitation-strengthened steel were successfully evaluated. The small-angle neutron scattering (SANS) demonstrated the sensitive detection of hydrogen atoms trapped at the interfaces of nano-sized NbC. This result provides evidence for hydrogen embrittlement due to trapped hydrogen at precipitates. The ion beam technology can give novel functionality on a nano-scale and is targeting applications in plasmonics, ultra-fast optical communications, high-density recording and bio-patterning. The technologies developed are an ion-and-laser combined irradiation method for spatial control of nanoparticles, and a nano-masked ion irradiation method for patterning. Furthermore, we succeeded in implanting a wide-area nanopattern using nano-masks of anodic porous alumina. The patterning of ion implantation will be further applied for controlling protein adhesivity of biopolymers. It has thus been demonstrated that the quantum beam-based nanotechnology will lead the innovations both for nano-characterization and nano-fabrication.

• Korean Journal of Materials Research
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• v.20 no.8
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• pp.418-422
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• 2010

As a starting material, BCP (biphasic calcium phosphate) nano powder was synthesized by a hydrothermal microwave-assisted process. A highly porous BCP scaffold was fabricated by the sponge replica method using 60 ppi (pore per inch) of polyurethane sponge. The BCP scaffold had interconnected pores ranging from $100\;{\mu}m$ to $1000\;{\mu}m$, which were similar to natural cancellous bone. To realize the antibacterial property, a microwave-assisted nano Ag spot coating process was used. The morphology and distribution of nano Ag particles were different depending on the coating conditions, such as concentration of the $AgNO_3$ solution, microwave irradiation times, etc. With an increased microwave irradiation time, the amount of coated nano Ag particles increased. The surface of the BCP scaffold was totally covered with nano Ag particles homogeneously at 20 seconds of microwave irradiation time when 0.6 g of $AgNO_3$ was used. With an increased amount of $AgNO_3$ and irradiation time, the size of the coated particles increased. Antibacterial activities of the solution extracted from the Ag-coated BCP scaffold were examined against gram-negative (Escherichia coli) and gram-positive bacteria (Staphylococcus aureus). When 0.6 g of $AgNO_3$ was used for coating the Ag-coated scaffold, it showed higher antibacterial activities than that of the Ag-coated scaffold using 0.8 g of $AgNO_3$.

• Korean Journal of Materials Research
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• v.21 no.6
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• pp.314-319
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• 2011

Melt foaming method is one of cost-effective methods to make metal foam and it has been successfully applied to fabricate Mg foams. In this research, AZ31 Mg alloy ingot was used as a metal matrix, using AlCa granular as thickening agent and $CaCO_3$ powder as foaming agent, AZ31 Mg alloy foams were fabricated by melt-foaming method at different foaming temperatures. The porosity was above 41.2%~73.3%, pore size was between 0.38~1.52 mm, and homogenous pore structures were obtained. Microstructure and mechanical properties of the AZ31 Mg alloy foams were investigated by optical microscopy, SEM and UTM. The results showed that pore structure and pore distribution were much better than those fabricated at lower temperatures. The compression behavior of the AZ31 Mg alloy foam behaved as typical porous materials. As the foaming temperature increased from $660^{\circ}C$ to $750^{\circ}C$, the compressed strength also increased. The AZ31 Mg alloy foam with a foaming temperature of $720^{\circ}C$ had the best energy absorption. The energy absorption value of Mg foam was 15.52 $MJ/m^3$ at a densification strain of 52%. Furthermore, the high energy absorption efficiencies of the AZ31 Mg alloy foam kept at about 0.85 in the plastic plateau region, which indicates that composite foam possess a high energy absorption characteristic, and the Vickers hardness of AZ31 Mg alloy foam decreased as the foaming temperature increased.

• Korean Journal of Materials Research
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• v.20 no.3
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• pp.142-147
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• 2010

Nano-sized $BaNd_2Ti_5O_{14}$ powders were prepared by the spray pyrolysis process. Sucrose used as the organic additive enabled the formation of nano-sized $BaNd_2Ti_5O_{14}$ powders. The powders prepared from the spray solution without sucrose had a spherical shape, dense structure and micron size before and after calcination. However, the precursor powders prepared from the spray solution with sucrose had a large size, and hollow and porous morphology. The precursor powders had an amorphous crystal structure because of the short residence time of the powders inside the hot wall reactor. The complete decomposition of sucrose did not occur inside the hot wall reactor. Therefore, the precursor powders obtained from the spray solution with sucrose of 0.5M had a carbon content of 39.2wt.%. The powders obtained from the spray solution with sucrose of 0.5M had a slightly aggregated structure of nano-sized primary powders of $BaNd_2Ti_5O_{14}$ crystalline phase after calcination at $1000^{\circ}C$. The calcined powders turned into nano-sized $BaNd_2Ti_5O_{14}$ powders after milling. The mean size of the $BaNd_2Ti_5O_{14}$ powders was 125 nm.

• Journal of the Korean Ceramic Society
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• v.46 no.6
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• pp.662-667
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• 2009

Porous SiC candle filter preforms were fabricated by extrusion and ramming process. To fabricate SiC candle filter preform, commercially available 85 ${\mu}m\;{\alpha}-$-SiC powder and 44 ${\mu}m$ mullite, CaC$O_3$ powder were used as the starting materials. The candle type preforms were fabricated by vacuum extrusion and ramming process, and sintered at $1400{^{\circ}C}$ 2 h in air atmosphere. The effect of forming method on porosity, density, strength (flexural and compressive strength) and microstructure was investigated. Also, corrosion test of the sintered candle filter specimens as forming method was performed at $600{^{\circ}C}$ in IGCC syngas atmosphere. The sintered SiC filter which was formed by ramming process has more higher density and exhibit higher strength than extruded filter. Its maximum density and 3-point bending strength were 2.00 g/$cm^3$ and 45 MPa, respectively.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2000.04a
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• pp.11-11
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• 2000

Large-size ceramic/metal bulk FGMs have been fabricated on a recently developed and the world's largest Spark Plasma Sintering(SPS) systems, As a part of the development program for practical production processes and machines for FGMs by SPS, the processes, mechanical properties, dimensional size and shape effects, and production machine systems were investigated. In the past, $ZrO_{2}$/TiAI, $ZrO_{2}$/Ni, $Al_{2}O_{3}$/Ti, WC/Co, WC/Co/Steel, A1/P, Polymide, Cu/Polymide, nano-composites, porous and other combinations of bulk FGMs have already been processed using SPS. However, most of the specimen sizes were small, in a range of 20 to 30mm in diameter. Recently disk-shape sintered compacts with diameters of 100 and 150 mm, and thickness of approximately 15 and 17 mm, $ZrO_{2}$(3Y)/ stainless steel FGMs were homogenous consolidated in a shorter sintering time, while maintaining high quality and repeatability by utilizing a temperature gradient sintering method. The SPS heating up and holding time totaled less than one hour. Therefore, the SPS process in expected to find increased use in the fabrication of large-size FGMs as a new industrial processing technology. This paper introduces SPS systems, the processing principles, features and the characteristies of ceramic/metal bulk FGM.