• 한국분말재료학회지
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• 제27권3호
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• pp.203-209
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• 2020

The automotive industry has focused on the development of metallic materials with high specific strength, which can meet both fuel economy and safety goals. Here, a new class of ultrafine-grained high-Mn steels containing nano-scale oxides is developed using powder metallurgy. First, high-energy mechanical milling is performed to dissolve alloying elements in Fe and reduce the grain size to the nanometer regime. Second, the ball-milled powder is consolidated using spark plasma sintering. During spark plasma sintering, nanoscale manganese oxides are generated in Fe-15Mn steels, while other nanoscale oxides (e.g., aluminum, silicon, titanium) are produced in Fe-15Mn-3Al-3Si and Fe-15Mn-3Ti steels. Finally, the phases and resulting hardness of a variety of high-Mn steels are compared. As a result, the sintered pallets exhibit superior hardness when elements with higher oxygen affinity are added; these elements attract oxygen from Mn and form nanoscale oxides that can greatly improve the strength of high-Mn steels.

• 한국분말재료학회지
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• 제5권3호
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• pp.178-183
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• 1998

Ultrafine WC-10wt.%Co cemented carbides powders were synthesized by direct carburization. W-Co composite powders and carbon black powders were mixed by wet ball milling and dried. The mixed powders were heated to 800 $^{\circ}C$ with heating rate of 8.2$^{\circ}C$/min and held for various times in flowing $H_2$. For carbon addition of 140%, the carburization was completed by heating at 80$0^{\circ}C$ for 4 hours. The carburization time decreased with increasing amount of carbon and carburization was completed by heating at 800 $^{\circ}C$ for 2 hours with carbon addition of 150%. WC-10 wt%Co cemented carbides powders fabricated by direct carburization have nanoscale WC($\/leqq$100 nm) size.

• 한국분말재료학회지
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• 제9권4호
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• pp.273-279
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• 2002

In this study, the WC-10 wt.%Co nanopowders doped by grain growth inhibiter were produced by three different methods based on the spray conversion process. Agglomerated powders with homeogenous distribution of alloying elements and with internal particles of about 100-200 nm in diameter were synthesized. The microstructural changes and sintering behavior of hardmetal compacts were compared with doping method and sintering conditions. The microstructure of hardmetals was very sensitive to doping methods of inhibitor. Nanostructured WC-Co hardmetal powder compacts containing TaC/VC doped by chemical method instead of ball-milling shown superior sintering densification, and the microstructure maintained ultrafine scale with rounded WC particles.

• 한국분말재료학회지
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• 제22권3호
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• pp.208-215
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• 2015

Fe-TiC composite powders were fabricated by planetary ball mill processing. Two kinds of powder mixtures were prepared from the starting materials of (a) (Fe, TiC) powders and (b) (Fe, $TiH_2$, Carbon) powders, respectively. Milling speed (300, 500 and 700 rpm) and time (1, 2, and 3 h) were varied. For (Fe, $TiH_2$, Carbon) powders, an in situ reaction synthesis of TiC after the planetary ball mill processing was added to obtain a homogeneous distribution of ultrafine TiC particulates in Fe matrix. Powder characteristics such as particle size, size distribution, shape, and mixing homogeneity were investigated.

• Food Science and Biotechnology
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• 제18권6호
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• pp.1439-1446
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• 2009

The surfaces of different-sized endosperm, bran, and husk rice powders were modified using carboxymethylation. Carboxymethylation was carried out using aqueous alkalization and neutralization. After the carboxymethylation process, the centrifuged products were milled and classified by size: particles passed through sieves of 45, 106, and $300-{\mu}m$ width. The effect of carboxymethylation on physical properties such as solubility and dispersibility of endosperm, bran, and husk particles were studied. Overall, carboxymethylation increased solubility of the particles, while size reduction increased dispersibility. In particular, carboxymethylation created good aqueous suspensions by minimizing interparticle agglomeration. Our results show that the combination of size reduction and carboxymethylation improves solubility and dispersibility, resulting in better stability of the suspension. This study may be helpful for expanding the use of rice and its byproducts as ingredients in a variety of food and beverage applications.

• 한국식품과학회지
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• 제38권4호
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• pp.495-500
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• 2006

본 연구에서는 제분기, 건조방법별 등 다양한 조건별로 현미쌀가루 제조하여 각 쌀가루별 품질특성을 조사하였다. 건조조건에 따른 roll mill 제분한 현미쌀가루의 수분함량은 열풍건조 10.7% 마이크로파건조 13.7%로 측정되었다. 대조구인 백미쌀가루의 수분함량은 10.0%였다. Zet mill 분쇄 후 쌀가루의 수분함량은 8.0-8.6%로 측정되었다. WAI는 전분손상도가 높을수록 흡수되는 수분의 양이 증가하여 전분손상도가 가장 높은 Zet mill로 분쇄한 현미쌀가루가 0.58-0.79g/g으로 높았고, 전분손상도가 낮은 roll mill 분쇄한 대조구와 BrWRH 쌀가루가 각각 0.45, 0.40g/g으로 낮은 값을 나타내었다. WSI 역시 WAI와 같이 전분손상도가 증가할수록 증가하는 경향을 나타내었고 입자크기가 감소함에 따라 증가하였다. 대조구 백미 쌀가루 L, a, b는 97.1, -0.4, 4.2로 측정되었고, 현미쌀가루는 분쇄과정에서 생성된 미강층 때문에 L값은 대조구보다 낮고 반면에 b값은 높은 결과를 나타내었다. 제분방법에 따른 L값, b값은 roll mill로 분쇄한 현미쌀가루의 L, b값은 각각 91.3-91.9, 9.2-10.1이었고, zet mill로 제분한 현미쌀가루의 L, b값은 각각 94.1-96.8, 5.8-6.8로 측정되어 입자크기가 작을수록 L값은 증가하였고, b값은 감소하였다. 전분손상도는 대조구가 8.2%로 가장 낮았고, 마이크로파 건조 시 열품건조보다 4-10%정도 높은 전분손상도 값을 보였다. 제분기 종류에 따른 전분손상도는 roll mill 15.5%, zet mill 28.2% 그리고 micro mill 51.9%로 입자크기가 작을수록 전분손상도는 증가하였다. RVA 측정결과 대조구 호화개시온도는 $65.4^{\circ}C$로 가장 낮은 값을 나타내었다. 제분방법에 따른 대조구, BrWRH, BrWZH, HBrZMU 쌀가루의 호화특성 측정결과 최고점도(peak), 최저점도(trough)는 각각 321, 255, 221, 162 RVU와 217, 185, 175, 113 RVU로 측정되어 입자크기가 작아질수록 감소하였다 또한 호화액의 안전성을 나타내는 breakdown 값은 대조구가 105 RVU, 현미 쌀가루가 37-96 RVU로 측정되어다 DSC 분석결과 호화엔탈피$({\Delta}H)$는 대조구가 10.4 J/g으로 가장 높은 값이었고, 가장 작은 입도분포를 나타낸 HBrZMU가 6.1 J/g으로 가장 낮은 값을 보였다. 본 연구결과 가공제품으로 현미쌀가루 이용 시 침지, 건조방법 보다는 제분방법 즉 입도분포가 현미쌀가루의 품질특성에 않은 영향을 미치는 것을 알 수 있었다.