• 한국분말재료학회지
• /
• 제8권1호
• /
• pp.49-54
• /
• 2001

The synthesis and characteristics of W-Ni-Fe nanocomposite powder by hydrogen reduction of ball milled W-Ni-Fe oxide mixture were investigated. The ball milled oxide mixture was prepared by high energy attrition milling of W blue powder, NiO and $Fe_2O_3$ for 1 h. The structure of the oxide mixture was characteristic of nano porous agglomerate composite powder consisting of nanoscale particles and pores which act as effective removal path of water vapor during hydrogen reduction process. The reduction experiment showed that the reduction reaction starts from NiO, followed by $Fe_2O_3$ and finally W oxide. It was also found that during the reduction process rapid alloying of Ni-Fe yielded the formation of $\gamma$-Ni-Fe. After reduction at 80$0^{\circ}C$ for 1 h, the nano-composite powder of W-4.57Ni-2.34Fe comprising W and $\gamma$-Ni-Fe phases was produced, of which grain size was35nm for W and 87 nm for $\gamma$-Ni-Fe, respectively. Sinterability of the W heavy alloy nanopowder showing full density and sound microstructure under the condition of 147$0^{\circ}C$/20 min is thought to be suitable for raw material for powder injection molding of tungsten heavy alloy.

• 한국분말재료학회지
• /
• 제12권3호
• /
• pp.186-191
• /
• 2005

A formation of aluminum hydroxide by hydrolysis of nano and micro aluminum powder has been studied. The nano aluminum powder of 80 to 100 nm in diameter was fabricated by a pulsed wire evaporation (PWE) method. The micro powder was commercial product with more than $10\;{\mu}m$ in diameter. The hydroxide type and morphology depending on size of the aluminum powder were examined by several analyses such as XRD, TEM, and BET. The hydrolysis procedure of micro aluminum powder was different from that of nano aluminum powder. The nano aluminum powder after immersing in the water was transformed rapidly to a nano fibrous boehmite, accompanying with a remarkable temperature increase, and then further transformed slowly to a stable bayerite. However, the micro powder was changed to the stable bayerite slowly and directly. The formation of fibrous aluminum hydroxide from nano aluminum powder might be due to the fine cracks which were formed by hydrogen gas pressure on the surface hydroxide layer during hydrolysis. The nano powder with large specific surface area and small size reacted more actively and faster than the micro powder, and transformed to meta-stable hydroxide in relatively short reaction time. Therefore, the formation of fibrous boehmite is special characteristic of hydrolysis of nano aluminum powder.

• 한국조리학회지
• /
• 제15권2호
• /
• pp.309-321
• /
• 2009

연구는 당귀분말을 첨가한 쿠키의 품질특성과 관능특성을 평가한 것으로써, 당귀분말 첨가 쿠키 반죽의 pH는 6.13~6.26의 범위였으며, 반죽의 밀도는 0.99~1.15의 범위였다. 당귀분말 첨가의 증가에 따라 쿠키의 퍼짐성은 작아졌으며, 명도와 황색도의 감소, 적색도의 증가로 인해 전반적으로 쿠키가 어두워지고 진해지는 경향을 나타내었다. 기계적 조직감의 특성은 강도와 경도가 당귀분말의 첨가비율에 따라 높아지는 경향을 나타내어 쿠키 제조에 있어 당귀분말의 첨가는 쿠키를 단단하게 하는 역할을 하였다. 관능 선호도에서는 색, 냄새, 조직감, 맛, 전반적인 선호도의 항목에서 당귀분말 무첨가 쿠키보다 일정 범위의 당귀분말을 첨가한 쿠키의 선호도가 높아졌으며, 그 중에서도 쿠키의 전체 재료 배합량 대비 1.5%의 당귀분말을 첨가하는 것이 가장 이상적인 것으로 평가되었다.

• 한국분말재료학회지
• /
• 제16권2호
• /
• pp.104-109
• /
• 2009

Niobium powder was made from potassium heptafluoroniobite ($K_2NbF_7$) as the raw material using sodium (Na) as a reducing agent based on the hunter process. The apparatus for the experiment was designed and built specifically for the present study. The niobium particle size greatly increased as the reduction temperature increased from $710^{\circ}C$ to $800^{\circ}C$. The particle size was fairly uniform, varying from $0.09{\mu}m$ to $0.4{\mu}m$ depending on the reduction temperatures. The niobium powder morphology and particle size are very sensitive to a reaction temperature in the metallothermic reduction process. The yield of niobium powder increased from 55% to 80% with a increasing a reaction temperature.

• 한국분말재료학회지
• /
• 제19권4호
• /
• pp.310-316
• /
• 2012

Nanocrystalline $BaTiO_3$ powder could be synthesized by solid-state reaction using the mixture which was prepared by a high energy milling process in a bead mill for $BaCO_3$ and nanocrystalline $TiO_2$ powders mixture. Effect of the milling time on the powder characteristic of the synthesized $BaTiO_3$ powder was investigated. Nanocrystalline $BaTiO_3$ with a particle size of 50 nm was obtained at $800^{\circ}C$. High tetragonal $BaTiO_3$ powder with a tetragonality(=c/a) of 1.009 and a specific surface area of $7.6m^2/g$ was acquired after heat-treatment at $950^{\circ}C$ for 2 h. High energy ball milling was effective in decreasing the reaction temperature and increasing the tetragonality.

• 한국초전도ㆍ저온공학회논문지
• /
• 제12권3호
• /
• pp.49-54
• /
• 2010

This paper presents apparent thermal conductivity of various powder at different vacuum levels for cryogenic insulation. Four kinds of powder insulator are examined by using boil-off calorimetry at pressure range from 50 Torr to 3 mTorr. The first material is perlite which is widely used in cryogenic application. Microsphere is the second one that is recently proposed as a replacement powder for liquid hydrogen storage tanks. It is a hollow sphere made of silica with the diameter in the order of 10 to $100{\mu}m$. Popped rice and polystyrene beads are also selected as candidates for powder insulation even though they are polymers. With their porous elliptic and spherical configuration and light density, they demonstrate fairly good thermal insulation performance at pressure range from 50 Torr to 3 mTorr. According to the experimental investigation in this paper, microsphere and polystyrene beads possess promising insulation characteristic as powder insulators and further study is desired.

• 한국초전도ㆍ저온공학회논문지
• /
• 제25권3호
• /
• pp.28-33
• /
• 2023

Magnetic relaxation properties of pure MgB₂ powder samples and diluted water-treated MgB₂ powder samples were investigated. The magnetic field H-dependence, m(H), and the time t-dependence, m(t), of the magnetic moment m were measured and analyzed using the PPMS-VSM magnetometer equipment, respectively. The m(t) reduction rates of pure MgB₂ powder samples and diluted water-treated MgB₂ powder samples decreased to about 0.7 ~ 1.8% and 0.6 ~ 1.0% for about 7200 s, respectively, at temperature T = 15 K. The magnetic relaxation properties of the two types of MgB₂ powders were analyzed by calculating the magnetic relaxation rate S = -dln(M_irr)/dln(t) values according to Anderson-Kim theory. The magnetic relaxation ratio S values of the two types of MgB₂ powder samples were almost similar. As a result of the quantum creep effect, the constant magnetic relaxation rate S characteristic was confirmed at a temperature range of T = 10 K or less.

• 한국식생활문화학회지
• /
• 제22권1호
• /
• pp.77-82
• /
• 2007

The general composition like moisture content, and the physical and sensory characteristics of the steamed rice cake added with powder of roots of balloonflowers were as follows. The moisture content in the roots was 4.13${\pm}$0.01%, crude protein 9.24${\pm}$0.11%, crude fat 3.07${\pm}$0.04%, crude fiber 33.82${\pm}$0.01%, and crude ash 8.16${\pm}$0.02%. The moisture content of the cake was decreased with increase of the root’s powder added. In physical characteristic, the hardness of the cake was increased with increase of the powder. The control cake was the highest in the cohesiveness. The springiness tended to be increased with increase of the powder. The gumminess was higher with increase of the powder, being 530.33% in the control and 284.44% in the sample with 12.0% powder added. The adhesiveness was decreased with increase of the powder. The color change was significantly decreased with increase of the powder. With increase of the powder, the value a was decreased, while the value b showed to be increased. In a sensory test, the favorite degree to color, flavor, bitter taste, moistness, soft-ness and overall acceptability was measured to get the follow result. To color, the lot with 6% of the balloonflower powder added showed the highest accept-ability with the same highest result also to flavor and bitter taste. The moistness and the softness were revealed as the highest at the control, and the chewiness was also highest at the lot with 3% of the powder added. The overall acceptability was highest as 5.75 at the lot with 6% of the powder added, coming out to be higher in order of the 3% added-lot, the control, the 9%-lot and the 12%-lot.

• 한국세라믹학회지
• /
• 제29권4호
• /
• pp.253-258
• /
• 1992

ZnO varistors were prepared by the organochemical method which used citric acid and ethylene glycol as gelling agents. The microstructure of the sintered specimens exhibited small grains, uniform grain size distribution, and few intragranular pores. Thermal decomposition of the organic resin formed during the powder preparation process was completed around 450$^{\circ}C$. No significant changes were observed in microstructure and current voltage characteristic with respect to calcination temperatures. A major advantage of the organochemical method used in this experiment is a possible uniform mixing of trace amounts of dopants. Therefore, this powder preparation method seems promising in investigating the effect of Li or In ion, which is added in ppm level to ZnO varistors, on the pulse respose characteristic.

• 한국분말재료학회지
• /
• 제9권3호
• /
• pp.148-152
• /
• 2002

The microstructures and indentation fracture of pressureless-sintered $DyNbO_4$ crystalline were investigated as a basic study for the application of weak phase of fibrous monolithic composites. They were comprised with many lamella twins as well as micro-cracks at the grain boundaries. The hardness at room temperature was remarkably low value(575 Hv) due to the low relative density and existence of microcracks at grain boundaries. The main fracture mode was a typical intergranular fracture, and showed remarkable micro-cracking effect. The heavy plastic deformation was observed around the site of indentation. In addition, the $DyNbO_4$ was expected to apply as a weak phase in the fibrous monolithic composites because of the low hardness and easily plastic deformation that could be led the preferable pulled-out and microcracking toughening under the failure.