• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.682-690
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• 1989

Fine mullite powder was prepared by colloidal sol-gel route. Boehmite as a starting material of Al2O3 and silica sol or fumed silica as a starting material of SiO2 were used. $\alpha$-Al2O3, TiO2 and ZrO2 were used as seeding materials. The combination of boehmite and silica was found to be the stoichiometric mullite powder. Techniques for drying used were spray drying, freeze drying, reduced pressure evaporation and drying in a oven. The gelled powder was heated at 130$0^{\circ}C$ for 100min and was attrition-milled for 1~3hrs. The mullite powder obtained was composed of submicrometer, uniform and spherical particles with a narrow size distribution. The mullite powder was characterized by BET, SEM, XRD and IR spectroscopy.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1401-1407
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• 1995

Zirconia powder coated with alumina was prepared by hydrolysis of alumina butoxide. The coated powder was obtained by a hydrolysis reaction between the adsorbed water on the surface of zirconia particles and aluminum sec-butoxide. Amorphous aluminum hydroxide was uniformly coated on the surface of zirconia particles with the thickness of about 30 nm. The shape and distribution of aluminum hydroxide was varied with an existence of surfactant. The coated layer of aluminum hydroxide consists of the fine particle size, and the zirconia powder coated by alumina hydroxide have the large specific surface area of 120 $m^2$/g, compared with that of starting zirconia powder.

• Journal of Powder Materials
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• v.8 no.3
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• pp.157-162
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• 2001

An optimum route to fabricate the ferrous alloy dispersed $Al_2O_3$ nanocomposites such as $Al_2O_3$/Fe-Ni and $Al_2O_3$/Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of $Al_2O_3$ and nano-sized ferrous alloy, in which the alloy was prepared by solution-chemistry routes using metal nitrates powders and a subsequent hydorgen reduction process. Microstructural observation of reduced powder mixture revealed that the Fe-Ni or Fe-Co alloy particles of about 20 nm in size homogeneously surrounded $Al_2O_3$, forming nanocomposite powder. The sintered $Al_2O_3$/Fe-Ni composite showed the formation of Fe$Al_2O_4$ phase, while the reaction phases were not observed in $Al_2O_3$/Fe-Co composite. Hot-pressed $Al_2O_3$/Fe-Ni composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of alloy particles.

• Korean Journal of Materials Research
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• v.14 no.5
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• pp.338-342
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• 2004

Ni-Zn ferrite powder was obtained by wet method that was to be coprecipitated the metal nitrates, Fe($NO_3$)$_3$ㆍ$9H_2$O, Ni($NO_3$)$_2$ㆍ$6H_2$O, Zn($NO_3$)$_2$ㆍ$6H_2$O to make a high permeability material. The composition of the ferrite powder was $Fe_2$$O_3$ 52 mol%, NiO 14.4 mol%, ZnO 33.6 mol%. Ni-Zn ferrite powder was compounded by precipitating metal nitrates with NaOH in vessel at the synthetic temperature of $90^{\circ}C$ for 8 hours. Calcination temperature and sintering temperature were $700^{\circ}C$ and $1150^{\circ}C$～$1250^{\circ}C$, respectively, for 2 hours. And the other ferrite powder was also prepared by the wet ball milling that was to be mixed the metal oxides as same as the above chemical composition. We studied the properties of the powder and the electromagnetic characteristics of the sintered cores obtained from there two different processes. Wet direct process produced smaller particle size with narrower distribution of the size and more purified ferrite whose sintered cores had high permeability and high magnetization.

• Journal of the Korean Ceramic Society
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• v.43 no.10 s.293
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• pp.666-672
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• 2006

GDC20($Ce_{0.8}Gd_{0.2}O_{1.9}$) powder was synthesized by oxalate co-precipitation and milling and its thermal decomposition, phase formation, and sinterability were investigated. As-prepared precipitates were non-crystalline due to the milling process and completely decomposed at 400$^{\circ}C$ The powder calcined at 800$^{\circ}C$ for 2 h contained fine p]sty particles with an average size of 0.69 $\mu$m. Attrition milling of the calcined powder for 2 h had a little milling effect, resulting in a slight decrease in the particle size to 0.45 $\mu$m. The milled powder consisted of small spherical primary particles and some large particles, which had been agglomerated during calcination. Due to the excellent sinterability of the powder, sintering of the powder compacts for 4 h showed relative densities of 78.7% at 1000$^{\circ}C$ and 97.8% at 1300$^{\circ}C$, respectively. Densification was found to almost complete at temperature above 1200$^{\circ}C$ and a dense and homogeneous microstructure was obtained. A rapid grain growth occurred between 1200$^{\circ}C$ and 1300$^{\circ}C$. Grains in 0.1$\sim$0.5 $\mu$m sizes at 1200$^{\circ}C$ grew to 0.2$\sim$2 $\mu$m and their size distribution became broader at 1300$^{\circ}C$.

• Journal of Powder Materials
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• v.26 no.3
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• pp.201-207
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• 2019

Tungsten heavy alloys (W-Ni-Fe) play an important role in various industries because of their excellent mechanical properties, such as the excellent hardness of tungsten, low thermal expansion, corrosion resistance of nickel, and ductility of iron. In tungsten heavy alloys, tungsten nanoparticles allow the relatively low-temperature molding of high-melting-point tungsten and can improve densification. In this study, to improve the densification of tungsten heavy alloy, nanoparticles are manufactured by ultrasonic milling of metal oxide. The physical properties of the metal oxide and the solvent viscosity are selected as the main parameters. When the density is low and the Mohs hardness is high, the particle size distribution is relatively high. When the density is high and the Mohs hardness is low, the particle size distribution is relatively low. Additionally, the average particle size tends to decrease with increasing viscosity. Metal oxides prepared by ultrasonic milling in high-viscosity solvent show an average particle size of less than 300 nm based on the dynamic light scattering and scanning electron microscopy analysis. The effects of the physical properties of the metal oxide and the solvent viscosity on the pulverization are analyzed experimentally.

• Resources Recycling
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• v.15 no.4 s.72
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• pp.19-26
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• 2006

The preparation of Ag nano-powder from aqueous silver nitrate solution, which would be available for the recycling of silver bearing wastes, was investigated by a reductive precipitation reaction using hydrazine hydrate as a reducing agent. Silver solution was prepared by dissolving silver nitrate with distilled water, and then the dispersant, Tamol NN8906 or Tween 20, was also mixed to avoid the agglomeration of particles during the reductive reaction followed by the addition of hydrazine hydrate to prepare Ag nano-particles. Ag particles obtained from the reduction reaction from silver solution were characterized using the particle size analyzer and TEM to determine the particle size distribution and morphology. It was found that about 100% excess of hydrazine hydrate was required to reduce completely silver ions in the solution. Ag powders with very narrow distribution could be obtained when Tamol NN8906 was used as the dispersant. In case of Tween 20, the particle size distribution showed typically the bimodal or multimodal distribution and the morphology of Ag particles was found to be irregular shape in both cases.

• Applied Chemistry for Engineering
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• v.10 no.4
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• pp.509-514
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• 1999

In Preparing $BaTiO_3$ powder under hydrothermal conditions, effects of reaction period feedstock concentration and mixing rate on crystallinity, mean size and size distribution of particles were studied. Experimental results showed that the particle size became smaller with its narrow distribution as the reaction period and mixing rate increased, but feedstock concentration decreased in contrast with the results based on the classical nucleation-growth model. From these results, $BaTiO_3$ particles seem to be prepared hydrothermally through a multiple reaction procedure that includes dissolution, precipitation, hydrolysis-condensation, aggregation, diffusion and transformation.

• Journal of Powder Materials
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• v.14 no.1 s.60
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• pp.19-25
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• 2007

This study was focused on the optimization of low-pressure ultrasonic spraying process for synthesis of pure ${\gamma}-Fe_2O_3$ nanoparticles. As process variables, pressure in the reactor, precursor concentration, and reaction temperature were changed in order to control the chemical and microstructural properties of iron oxide nanoparticles including crystal phase, mean particle size and particle size distribution. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies revealed that pure ${\gamma}-Fe_2O_3$ nanoparticles with narrow particle size distribution of 5-15 nm were successfully synthesized from iron pentacarbonyl ($Fe(CO)_{5}$) in hexane under 30 mbar with precursor concentrations of 0.1M and 0.2M, at temperatures over $800^{\circ}C$. Also magnetic properties, coercivity ($H_c$) and saturation magnetization ($M_s$) were reported in terms of the microstructure of particles based on the results from vibration sampling magnetometer (VSM).

• Journal of Sensor Science and Technology
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• v.17 no.6
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• pp.418-424
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• 2008

The PZT based piezoelectric thick films prepared by screen printing method have been mainly used as a functional material for MEMS applications due to their compatibility of MEMS process. However the screen printed thick films generally reveal poor electrical and mechanical properties because of their porous microstructure. To improve microstructure we mixed attrition milled powder with ball milled powder of 0.01Pb$(Mg_{1/2}W_{1/2})O_3$-0.41Pb$(Ni_{1/3}Nb_{2/3})O_3$-$0.35PbTiO_3$-$0.23PbZrO_3$+0.1 wt% ${Y_2}{O_3}$+1.5 wt% ZnO composition. By mixing 25 % of attrition milled powder and 75 % of ball milled powder, the broadest particle size distribution was obtained, leading to a dense thick film with crack-free microstructure and improved dielectric properties. The X-ray diffraction analysis revealed that the film was in wellcrystallized perovskite phase. The remanent polarization was increased from $13.7{\mu}C/cm^2$ to $23.3{\mu}C/cm^2$ at the addition of 25 % attrition milled powder.