• Journal of Sensor Science and Technology
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• v.20 no.6
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• pp.406-411
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• 2011

$Co_3O_4$ thick film gas sensor using the powder prepared by hydrothermal reaction method(HRM) was fabricated. For comparison study, we also prepared the sensor using commercial $Co_3O_4$ powder under the same fabrication conditions. Sensitivity, time response, and selectivity of them to variable gases such as iso-$C_4H_{10}$, CO, $NH_3$, and $CH_4$ were investigated. The sensor from the powder prepared by HRM showed higher sensitivity to every gas than those from commercial powder. For iso-$C_4H_{10}$ gas, the sensitivities of both sensor to 100 ppm are 160 % and 40 %, respectively. Time response and selectivity of the sensor using the powder prepared by HRM were better than those of the sensor using commercial powder.

• Journal of Powder Materials
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• v.12 no.1
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• pp.56-63
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• 2005

Ag powder was prepared from $AgNO_3$ by wet chemical reduction method using various reduction agent system involving $AgNO_3$, $AgNO_2$(AgCl) and Ag complex ion aqueous solution. The pure Ag powder could be prepared regardless of reaction system but the particle shape and distribution were affected very much according to the kind of reduction agents and reaction systems. The optimum reaction system for the preparation of the silver powder having the uniform particle shape and size distribution was Ag complex ion aqueous solution-reduction agent system and in particular, $H_2O_2$ and $C_6H_8O_6$as a reduction agent leaded the more uniform particle shape and size distribution.

• Journal of Powder Materials
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• v.6 no.1
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• pp.88-95
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• 1999

The purpose of this study is to investigate the manufacturing feasibility of WC-Co milling inserts via Powder Injection Molding (PIM) process. WC-Co is used in a wide variety of cutting tools due to its high hardness, stiffness, compressive strength and wear resistance properties. WC-Co parts for a high stress application were conventionally produced by the press and sinter method, which were Iimited to 2 dimensional shapes. Manufacturing WC-Co parts for a high stress application by PIM implies that tool efficiency can be highly improved due to increased freedom is design. P30 grade WC powder (WC-Co-TiC-TaC system) was mixed with RIST-5B133 binder and injection molded into milling inserts (Taegu Tech. Model WCMX 06T 308). The mean grain size of the powder was about 0.8$\mu$m. Injection molded specimens were debound by solvent extraction and thermal degradation method at various conditions. The specimens were sintered at 140$0^{\circ}C$ for 1 hr in vacuum. Carbon content, weight loss, dimensional change, and macro defects of the specimen were carefully monitored at each stage of the PIM process. PIMed WC-Co milling inserts reached 100% full density after sinteing. Its mechanical properties and micro-structures were comparable with the press and sintered milling insert. Carbon content of the sintered WC-Co insert was mainly determained by the atmosphere of thermal debinding. By controlling powder loading and injection molding condition, dimensional accuracy could be obtained within 0.4%. We confirm that PIM can not only be an alternative manufacturing method for WC-Co parts economically but also provide a design freedom for more effieient cutting tools.

• Proceedings of the Korean Nutrition Society Conference
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• 1999.05b
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• pp.60-61
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• 1999

The present study examined optimal level of mulberry leave powder, and the method of bread-making were proposed to utilize mulbery leave powder by investigating rhelogical properties of dough and sensory evaluation of bread. The difference of amino acids compositions in flour brew were also investigated by fermentation of S. cerevisiae or bifidobacteria. As the % of mulberry leave powder increases absorption rate of dough was steadily increased, but stability and R!E ratio if dough were dramatically decreased more than 1% leave respectively. R!E ratio value, which indicates gas retnetion property of dough, was not obtained at the level 5%. Gelatinization temperature and maximum viscosity temperature showed a tentency of decrease, resulting in easier cooking of dough. The delay of temperature cauesd by addition of mulberry leave powder was overcome by two step bread making, that is, modified straight dough method adding flour brew fermented 16hrs by bifidobacteria. The firmness of bread was progressively dreased as the amount of mulbery leave powder increased. The addition of 2% level of mulberry powder to bread showed no significant difference comparing with control in sensery evaluation. Amino acids compositions of Flour brew fermented by bifidobacteria was superior th that by S. cerevisae nutritionally.onally.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.311-314
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• 2003

Superconduction materials possess electrical/electronic and magnetic properties. Because superconduction materials is a ceramic powder, that can not be produced singlehandedly. So Ag sheathed Bi-2223 wire was produced by drawing process using powder-in-tube(PIT) method This superconductor has many difficulties to produce. The main difficulty is that the mechanical properties of the ceramic powder are very different from those of the Ag sheath. Actually, the fabrication of Ag sheathed Bi-2223 superconductor by PIT tends to lead to non-uniformity in the core thickness during drawing process. That is so called “Sausaging”. This study analyzed a sausaging using the finite-element method. Also, Effects of drawing process parameters on a sausaging has been carried out using finite element method. Finally, A way to prevent a sausaging has been discussed.

• Applied Science and Convergence Technology
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• v.27 no.1
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• pp.14-18
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• 2018

In order to understand the mechanism of the synthesis of particles using a plasma torch, it is necessary to understand the reaction mechanisms using a computer simulation. In this study, we have developed a simulation method to combine the Lagrangian scheme to follow microparticles and a nodal method to treat nanoparticles categorized with different particle sizes. The Lagrangian scheme includes the Coulomb force which affects the dynamics of larger particles. In contrast, the nodal method is adequate for the nanoparticles because the charge effect is negligible for nanoparticles but the number of nanoparticles is much larger than that of microparticles. This method is helpful to understand the dynamics and growth mechanism of micro- and nano-powder mixture observed in the experiment.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.1
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• pp.16-20
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• 2002

In conventional metallothermic reduction(MR) for obtaining tantalum powder in batch-type operation, it is difficult to control morphology and location of deposits because the reaction occurs by direct physical contact between reductants and feed materials. On the other hand, a electronically mediated reaction(EMR) is capable to overcome these difficulties through the reaction by electron transfer and have a merit of continuous process. In this study an MR and EMR method has been applied to the production of a tantalum powder by sodium reduction of $K_2TaF_7$. As the reduction temperature increases, the particle size and yield of tantalum powder obtained by MR and EMR method is increased.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.101-104
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• 2002

The influences of the powder packing density on the Bi-2223/Ag tape have been investigated. For packing powder, both method of uniaxial press and packed rod form made by cold isostatic press(CIP) have been applied. As the pressure of cold isostatic press(CIP) is increased, fill factor and critical current (Ic) of Bi-2223/Ag tape is increased. At a pressure of 2000kgf/cm$^2$, fill factor reach ∼3l% and this sample has the engineering current density(Je) value of ∼8.5kA/cm$^2$(Ic ∼77A, Jc ∼ 30kA/cm$^2$). The tape sample packed by uniaxial press method shows more sawsaging effect than the sample processed by cold isostatic press(CIP), resulting from inhomogity of powder distribution produced by the process of uniaxial press.

• Food Science and Preservation
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• v.6 no.1
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• pp.87-91
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• 1999

In an attempt to test experimental condition of preparing grape powder, grapes having less commercial value was used and tried. With drying method, spray and freeze drying were satisfactory to produce power. Moisture content and odor retention were better by the latter method. Three grape strains stored for 40 days contained more odors than those stored for 5 days. Maltose 90% plus dextrin 10% was suitable for drying support. To increase odror sense, citric acid and vitamin C can be added up to 0.1 and 0.2%, respectively. Considering these conditions, grape complex powder prapared from grape powder 20% comprising drying support, glucose 79.7%, citric acid 0.1%, vitamin C 0.2% with freeze drying was the best by overall evaluation including sensory test. When campbell and neomuscut were mixed by 15:5 or 10:10, sensory evaluation was also ameliorated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.119-122
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• 2006

In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve full density of 1 vol.% carbon nanotube (CNT)-metal matrix composites with superior mechanical properties by improved particle bonding and least grain growth, which were considered as a bottle neck of the bottom-up method using the conventional powder metallurgy of compaction and sintering. ECAP (equal channel angular pressing), the most promising method in SPD, was used for the CNT-Cu powder consolidation. The powder ECAP processing with 1, 2, 4 and 8 route C passes was conducted at room temperature. It was found by mechanical testing of the consolidated 1 vol.% CNT-Cu that high mechanical strength could be achieved effectively as a result of the Cu matrix strengthening and improved particle bonding during ECAP. The ECAP processing of powders is a viable method to achieve fully density CNT-Cu nanocomposites.