• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.2
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• pp.73-79
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• 2002

The polyol process which applies to cobalt, nickel. copper and precious metals is a interesting and unexpected example of such a method for preparing uniform metal powders. The reaction proceeds via dissolution, and the polyol acts simultaneously as a solvent, a reducing agent, and to some extent a protective agent. Submicrometer uniform cobalt particles can be obtained by seeding the reactive medium ($AgNO_3$) to achieve a complete substitution of homogeneous by heterogeneous nucleation. By varying the number of nuclei it is possible to control to some extent the average particle size in the submicrometer (0.5$\mu$m) range.

• Korean Journal of Crystallography
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• v.3 no.1
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• pp.1-8
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• 1992

The morphology of lead titanate powders prepared by sol-gel and coprecipitation techniques was investigated as a function of firing temperature and soaking time. PbTiO3 precursor powders were derived from a mixed solution of lead nitrate and titanium tetrachloride at 40℃ to 43℃ and pH of 9.0 to 9.7, and fired at temperatures 350-1000℃ for 1-10h in air. An increase of particle size and agglomeration with increasing calcination temperature and duration could be observed. By annealing sol-gel derived powder at 700℃, the tially-formed acicular(and/or prismatic) primary particles transformed to polyhedral shape with soaking time, and further soaking caused coarsening the polyhedral particles with rounded edges. However, the morphology of the coprecipitated powders was not varied during crystallization.

• Transactions on Electrical and Electronic Materials
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• v.14 no.4
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• pp.165-171
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• 2013

Nanostructured pure a-C and nitrogen doped a-C: N thin films with small particle size of, ~50 nm were obtained by Aerosol-assisted CVD method from the natural precursor camphor oil. Five samples were prepared for the a-C and a-C: N respectively, with the deposition temperatures ranging from $400^{\circ}C$ to $600^{\circ}C$. At high temperature, the AFM clarifies an even smoother image, due to the increase of the energetic carbon ion bombardment at the surface of the thin film. An ohmic contact was acquired from the current-voltage solar simulator characterization. The higher conductivity of a-C: N, of ${\sim}{\times}10^{-2}Scm^{-1}$ is due to the decrease in defects since the spin density gap decrease with the nitrogen addition. Pure a-C exhibit absorption coefficient, ${\alpha}$ of $10^4cm^{-1}$, whereas for a-C:N, ${\alpha}$ is of $10^5cm^{-1}$. The high ${\sigma}$ value of a-C:N is due to the presence of more graphitic component ($sp^2$ carbon bonding) in the carbon films.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.8
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• pp.626-631
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• 2012

$SnO_2$ nanoparticles were synthesized by flame spray pyrolysis, which were directly deposited on Pt interdigitated substrates. Gas sensing performance was evaluated for various gases such as $H_2$, CO, $H_2S$, and $NH_3$, and it was compared with that of commercial $SnO_2$ nanopowder. The synthesis of $SnO_2$ nanoparticles was also conducted in various solvents. As a result, the primary particle size was changed with the solvent of precursor solution, and their $H_2$ sensing properties were significantly affected.

• Journal of Powder Materials
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• v.21 no.2
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• pp.131-136
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• 2014

Cathode materials and their precursors are prepared with transition metal solutions recycled from the the waste lithium-ion batteries containing NCM (nickel-cobalt-manganese) cathodes by a $H_2$ and C-reduction process. The recycled transition metal sulfate solutions are used in a co-precipitation process in a CSTR reactor to obtain the transition metal hydroxide. The NCM cathode materials (Ni:Mn:Co=5:3:2) are prepared from the transition metal hydroxide by calcining with lithium carbonate. X-ray diffraction and scanning electron microscopy analyses show that the cathode material has a layered structure and particle size of about 10 ${\mu}m$. The cathode materials also exhibited a capacity of about 160 mAh/g with a retention rate of 93~96% after 100 cycles.

• Bulletin of the Korean Chemical Society
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• v.26 no.4
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• pp.563-568
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• 2005

The Pt/C and Pd/C catalysts were prepared from conventional chloride precursors by adsorption or precipitation-deposition methods. Their activities for hydrogenation reactions of cyclohexene and acetophenone were compared with those of commercial catalysts. The Pt/C and Pd/C catalysts obtained from the adsorption procedure reveal higher hydrogenation activity than commercial catalysts and the catalysts prepared by the precipitation-deposition method. Their improved performances are attributed to the decreased metal crystallite sizes of Pt or Pd formed on the active carbon support upon the adsorption of the precursors probably due to the same negative charges of the chloride precursor and the carbon support. Under the preparation conditions studied, the reduction of the supported catalysts using borohydrides in liquid phase is superior to a gas phase reduction by using hydrogen in the viewpoint of particle size, hydrogenation activity and convenience.

• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2279-2282
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• 2007

Highly crystalline, uniform Fe nanoparticles were successfully synthesized and encapsulated in zirconia shell using sol-gel process. Two different approaches have been employed for the coating of Fe nanoparticle with zirconia. The thickness of zirconia shell can be readily controlled by altering molar ratio of Fe nanoparticle core to zirconia precursor in the first case where as reaction time was found to be most effective parameter to controlled the shell thickness in the second method. The structure and magnetic properties of the ZrO2-coated Fe nanoparticles were studied. TEM and HRTEM images show a typical core/shell structure in which spherical α-iron crystal sized of ~25 nm is surrounded by amorphous ZrO2 coating layer. TGA study showed an evidence of weight loss of less than 2% over the temperature range of 50-500 °C. The nanoparticles are basically in ferromagnetic state and their magnetic properties depend strongly on annealing temperature. The thermal treatment carried out in as-prepared sample resulted in reduction of coercivity and an increase in saturation magnetization. X-ray diffraction experiments on the samples after annealing at 400-600 °C indicate that the size of the Fe@ZrO2 particles is increased slightly with increasing annealing temperature, indicating the ZrO2 coating layer is effective to interrupt growing of iron particle according to heat treatment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.12
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• pp.812-816
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• 2017

$Fe_3O_4$ was prepared on the $TiO_2-coated$ natural mica substrate. The natural mica has an average particle size of $22{\mu}m$. The substrate was coated on $TiO_2$ thin films using hydrothermal synthesis at pH 1.5-2.5 at $75^{\circ}C$. The Fe precursor solution was prepared by mixing $FeSO_4$ (for $Fe^{2+}$ ion) and $FeCl_3$ (for $Fe^{3+}$ ions) with different molar ratios such as 1/2, 1/1, 2/1, 3/0, and $Fe_3O_4$ only. X-ray diffraction analysis shows that the crystal structure depends on the $FeCl_3-to-FeSO_4$ molar ratio. $Fe_3O_4$ crystal phase could be obtained at higher $FeSO_4$ contents.

• Journal of the Korean Ceramic Society
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• v.45 no.7
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• pp.380-386
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• 2008

Optimized volume production of nanoscale phosphor powders synthesized by radio frequency (RF) plasma process was developed for the application to plasma display panels. The nano powders were synthesized by feeding the both solid and liquid type precursors, and nanoparticle phosphors were characterized in terms of particle size, shape, and photoluminescence (PL) intensities. Computer simulation was performed in advance to determine the process parameters, and nano phosphors were evaluated by comparing with current commercial micron-sized phosphor powders. Practical feeding of both solid and liquid type precursor was proved to be effective for volume production.The developed process showed a potential as a production method for red, blue and green phosphor although the PL intensity still needs further improvement.

• Journal of Electrochemical Science and Technology
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• v.5 no.3
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• pp.87-93
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• 2014

The fluorine-substituted $0.3Li_2MnO_3{\cdot}0.7Li[Mn_{0.60}Ni_{0.25}Co_{0.15}]O_{2-x}F_x$ cathode materials were synthesized by using the transition metal precursor, $LiOH{\cdot}H_2O$ and LiF. This was to facilitate the movement of lithium ions by forming more compact SEI layer and to reduce the dissolution of transition metals. The $0.3Li_2MnO_3{\cdot}0.7Li[Mn_{0.60}Ni_{0.25}Co_{0.15}]O_{2-x}F_x$ cathode material was sphere-shaped and each secondary particle had $10{\sim}15{\mu}m$ in size. The fluorine-substituted cathodes initially delivered low discharge capacity, but it gradually increased until 50th charge-discharge cycles. These results indicated that fluorine substitution gave positive effects on the structural stabilization and resistance reduction in materials.