• Journal of Powder Materials
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• v.16 no.6
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• pp.403-409
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• 2009

Plasma spray forming is recently explored as a near-net-shape fabrication route for ultra-high temperature metals and ceramics. In this study, monolithic tungsten has been produced using an atmospheric plasma spray forming and subsequent high temperature sintering. The spray-formed tungsten preform from different processing parameters has been evaluated in terms of metallurgical aspects, such as density, oxygen content and hardness. A well-defined lamellae structure was formed in the as-sprayed deposit by spreading of completely molten droplets, with incorporating small amounts of unmelted/partially-melted particles. Plasma sprayed tungsten deposit had 84-87% theoretical density and 0.2-0.3 wt.% oxygen content. Subsequent sintering at 2500$^{\circ}C$ promoted the formation of equiaxed grain structure and the production of dense preform up to 98% theoretical density.

• Journal of the Korean Ceramic Society
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• v.39 no.4
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• pp.336-340
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• 2002

Pure and nano-sized $TiO_2$ and $CaTiO_3$ powders were fabricated by a polymeric steric entrapment route and planetary milling process. An ethylene glycol was used as a polymeric carrier for the preparation of organic-inorganic precursors. Titanium isopropoxide and calcium nitrate were dissolved in liquid-type ethylene glycol without any precipitation. At the optimum amount of the polymer, the metal cations were dispersed in solution and a homogeneous polymeric network was formed. The dried precursor ceramic gels were turned to porous powders through calcination process. The porous powders were crystallized at low temperatures and the crystalline powders were planetary milled to nano size.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.440-441
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• 2006

Several titanate powders ($Al_2TiO_5,\;SrTiO_3$, etc.) were synthesized by an ethylene glycol solution route. Titanium isopropoxide and nitrate salts were dissolved in stoichiometric proportions in liquid-type ethylene glycol without any precipitation. The parent precursor sols were dried to porous gels, and then the gels were calcined and crystallized. All synthesized titanate powders had stable crystallization behavior at low temperature and high specific surface area after a simple ball-milling process. A three-component PZT $(Pb(Zr_{0.52}{\cdot}Ti_{0.48})O_3)$ powder was also synthesized successfully by the ethylene glycol method. In this study, the characteristics of the multi-component titanate powders by the ethylene glycol method are examined.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.8.1-8.1
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• 2009

The self-assembly of peptide-based building blocks into nanostructures is an attractive route for fabricating novel materials because of their capacity for molecular recognition and functional flexibility as well as the mild conditions required in the fabrication process. Among various peptide-based building blocks forming nanostructures, the simplest building blocks are aromatic dipeptides like diphenylalanine, which can readily self-assemble into nanotubes in aqueous solutions at ambient conditions. Recently, we have developed a high-temperature solid-phase self-assembly process for diphenylalanine. Through this novel process, we succeeded in the growth of vertically well-aligned, uniform nanowires from amorphous peptide thin film. To demonstrate the versatility of our approach, we also fabricated a micropattern of peptide nanowires by combining our solid-phase growth method and simple soft lithographic techniques. We believe that our studies on peptide self-assembly will provide a new horizon for peptide-based nanofabrication.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.92.1-92.1
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• 2013

Molecular electronics has been the subject of intese research for many years because of the fundamental interest in molecular charge transport and potential applications, such as (bio)nanosensors and molecular memory devices. Molecular electronics requires a method for making reliable eletrical contacts to singlemolecules. To date, several approaches have been reported: scanning-probe microscopy, mechanical break junctions, nano patterning, and direct deposition of electrode on a self-assembled monolayers. However, most methods are laborious and difficult for large-scale application and more importantly, cannot control the number of moleucles in the junction. Recently, DNA has been used as a template for metallic nanostructures (e.g., Ag, Pd, and Au nanowires) through DNA metallization process. Furthermore, oligodeoxynucleotides have been tethered to organic molecules by using conventional organic reactions. Collectively, these techniques should provide an efficient route toward reliable and reproducible molecular electronic devices with large-scale fabrication. Therefore, I will present a paradigm for the fabrication of moleuclar electronic devices by using micrometer-sized DNA-singe organic molecule and DNA triblock structures.

• Journal of Powder Materials
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• v.8 no.3
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• pp.192-196
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• 2001

Ag doped Hydroxyapatite powder in nano-scale was successfully synthesized either by co-precipitation or by ion exchange route. The fabricated powder was successfully dispersed through freeze drying due to the prevention of secondary particles. The antimicrobial effects of nano-HAp against E.coli was superior to micron ones not only in its strength but also in duration.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.117-123
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• 2018

Recently, aqueous method has attracted lots of attention because it enables the solution-processed metal oxide thin film with high electrical properties in low temperature fabrication condition to various flexible devices. Focusing the development of aqueous route, many researchers are only focused on metal oxide materials. However, for expansive application of the aqueous-based metal oxide films, the systematic study of performance change with process variables for the development of aqueous-based metal oxide insulator film is urgently required. Here, we propose importance of process variables to achieve high electrical-performance metal oxide insulator based on the aqueous method. We found that the significant process variables including precursor solution temperature and humidity during the spincoating process strongly affect chemical, physical, and electrical properties of $AlO_x$ insulators. Through the optimization of significant variables in process, an $AlO_x$ insulator with a leakage current value approximately $10^5$ times smaller and a breakdown voltage value approximately 2-3 times greater than un-optimized $AlO_x$ was realized. Finally, by introducing the optimized $AlO_x$ insulators to solutionprocessed $InO_x$ TFTs, we successfully achieved $InO_x/AlO_x$ TFTs with remarkably high average field-effect mobility of ${\sim}52cm^2V^{-1}\;s^{-1}$ and on/off current ratio of 106 at fabrication temperature of $250^{\circ}C$.

• Korean Journal of Materials Research
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• v.12 no.8
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• pp.595-599
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• 2002

A homogeneous and stable, amorphous-type, anorthite (CaO $Al_2$$O_3$ $2SiO_2$)powder was synthesized by an organic-inorganic steric entrapment route. Polyvinyl alcohol ( PVA) was used as an organic carrier for the precursor ceramic gel. The PVA content, its degree of polymerization and type of silica sol had a significant influence on the calcination and crystallization behavior of the precursors. For densifiction and crystallization at low temperature, porous and soft, amorphous-type anorthite powder was planetary milled for 20h. The milled powder crystallized to stable anorthite phase and densified to a relative density of 94% below $1000^{\circ}C$. In the development of crystalline phases of the planetary milled powder, omisteinbergite phase was unusually observed at $900^{\circ}C$, and then anorthite was observed at $950^{\circ}C$. The sintered anorthite had a thermal expansion coefficient of $4.6$\times$10^{-6}$ /$^{\circ}C$ and a dielectric constant of 7.5 at 1 MHz. Finally, the anorthite synthesized by the new process is expected to be an useful material for low-firing ceramic substrate.

• Journal of the Korean Ceramic Society
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• v.28 no.11
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• pp.865-872
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• 1991

LAS (lithium aluminosilicate) sol was synthesized using the hydrolysis-condensation reaction of TEOS, chelated Al(OBus)3 and LiNO3 with H2O in alcohol (ethanol+2-propanol) medium. Lowering Li content by a factor of 1/2 significantly enhanced densification and retarded the crystallization of LAS gel by ~30$0^{\circ}C$. Dense LAS specimen with essentially pore-free microstructure was obtained by sintering the sol-gel derived gel at 80$0^{\circ}C$ for 4 h and annealing at 120$0^{\circ}C$ for 2 h. Similary, a mixed colloidal processing was attempted as a convenient, alternative route for the fabrication of dense LAS sintered body. The $\beta$-spodumene seeding (~0.8 ${\mu}{\textrm}{m}$) in the sol-gel derived LAS modified the sequence of phase transformations and lowered the temperature of crystallization by ~12$0^{\circ}C$. Combining the epitaxial seeding with the sol-gel process, we could lower the crystallization temperature to the sintering temperature range (~80$0^{\circ}C$) and, demonstrate a possibility of making the viscous sintering/crystallization as a continuous as a continuous unit process.

• Journal of Powder Materials
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• v.6 no.4
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• pp.301-306
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• 1999

Mechanical properties of oxide based materials could be improved by nanocomposite processing. To investigate optimum route for fabrication of nanocomposite enabling mass production, high energy ball milling and Pulse Electric Current Sintering (PECS) were adopted. By high energy ball milling, the $Al_2O_3$-based composite powder with dispersed Cu grains below 20 nm in diameter was successfully synthesized. The PECS method as a new process for powder densification has merits of improved sinterability and short sintering time at lower temperature than conventional sintering process. The relative densities of the $Al_2O_3$-5vol%Cu composites sintered at $1250^{\circ}C$ and $1300^{\circ}C$ with holding temperature of $900^{\circ}C$ were 95.4% and 95.7% respectively. Microstructures revealed that the composite consisted of the homogeneous and very fine grains of $Al_2O_3$ and Cu with diameters less than 40 nm and 20 nm respectively The composite exhibited enhanced toughness compared with monolithic $Al_2O_3$. The influence of the Cu content upon fracture toughness was discussed in terms of microstructural characteristics.