• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.10a
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• pp.239-239
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• 2009

We prepared Au nanoparticles by seed-mediated method and investigated the effects of process variables on the seed-mediated growth of Au nanoparticles. The monodispersed Au seed nanoparticles in the size range from 14.3 nm to 20.3 nm were prepared by the reduction reaction between $HAuCl_4$ and citrate. We added the $HAuCl_4$ precursors with citrates into the Au seed solution and prepared the Au nanoparticles in the size range from 16.8 and 37.8 nm with monodisperse distribution and could control the size of Au nanoparticles by changing the amount of $HAuCl_4$ precursor.

• Bulletin of the Korean Chemical Society
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• v.20 no.8
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• pp.893-896
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• 1999

Novel citric acid based Ti, Nb and Ta precursors that are highly stable in the presence of water were developed. No alkoxides of Ti, Nb and Ta were utilized in the preparation, instead much less moisture-sensitive metallic Ti, NbCl5 and TaCl5 were chosen as starting chemicals for Ti, Nb and Ta, respectively. The feasibility of these chemicals as precursors is demonstrated in the powder synthesis of BaTi4O9, Y3NbO7 and LiTaO3. The water-resistant Ti precursor was employed as a new source of water-soluble Ti in the amorphous citrate method, and phase pure BaTi4O9 in powdered form was successfully synthesized at 800 ？. The Pechini-type polymerizable complex method using the water-resistant Nb and Ta precursors was applied to the synthesis of Y3NbO7 and LiTaO3, and both the powder materials in their pure form were successfully synthesized at reduced tempera-tures, viz. 500-700 ？. The remarkable retardation of hydrolysis of these water-resistant precursors is explained in terms of the partial charge model theory.

• Korean Chemical Engineering Research
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• v.47 no.3
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• pp.310-315
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• 2009

Perovskite-type ceramic powder, $La_{0.7}Sr_{0.3}Co_{0.3}Fe_{0.7}O_{3-{\delta}}$, have been synthesized successfully by the citrate method. As a result of TGA for precursor, metal-citrate complex in precursor was decomposed in the temperature range of $150{\sim}650^{\circ}C$. XRD analysis showed the single perovskite structure was observed over $1,000^{\circ}C$ without impurities. Typical dense membrane with 1.6 mm thickness has been prepared using as-prepared powder by pressing unilaterally and sintering at $1,300^{\circ}C$. The electrical conductivity of $La_{0.7}Sr_{0.3}Co_{0.3}Fe_{0.7}O_{3-{\delta}}$ membrane increased with increasing temperature at atmosphere of air and then decreased over $600^{\circ}C$ due to oxygen loss from the crystal lattice. The oxygen flux of $La_{0.7}Sr_{0.3}Co_{0.3}Fe_{0.7}O_{3-{\delta}}$ membrane in the range of 700 to $950^{\circ}C$ increased with the increasing temperature from 0.045 to $0.415ml/cm^2{\cdot}min$. The activation energy for oxygen permeation was calculated to be 89.17 kJ/mol.

• Korean Journal of Materials Research
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• v.14 no.8
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• pp.587-594
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• 2004

Three-dimensionally ordered macroporous (3DOM) structures of the $LiCoO_2$ electrode materials for Li secondary batteries were fabricated by using the close-packed arrays of PMMA spheres served as templates. In order to successfully fabricate the cathode materials with highly ordered array form, the metal citrates were applied to new precursors. The precursor/template composites were prepared by the infiltration with metal citrate precursors into the voids of template. By removing the PMMA templates, then, the inverse opal structures with the uniform pores of narrow size distribution were resulted. It was confirmed that the 3DOM $LiCoO_2$ material is to take a single phase of rocksalt (R3m) structure. In addition, 3DOM $LiNiO_2$ and $LiMn_{2}O_4$ cathode materials were fabricated using an identical preparation procedure. Also, the morphology of the 3DOM cathode materials calcined at $500^{\circ}C\;to\;700^{\circ}C$ was observed by scanning electron microscope.

• Advances in nano research
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• v.2 no.2
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• pp.111-119
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• 2014

The chemical synthesis of anisotropic defective polyaniline/Ag composite (PANI/Ag) is explored using silver nitrate ($AgNO_3$) as the precursor material. This study provides a simple method for the formation of PANI/Ag nanocomposites at two different aniline concentrations $5{\mu}l$ (PANC5) and $10{\mu}l$ (PANC10). The composite PANC5 exhibits UV-Visible absorption peaks at 436 nm and 670 nm whereas, PANC10 exhibits absorption peaks at 446 nm and 697 nm. This shift is caused by the strong interaction between polyaniline and silver. The characterized FTIR peaks observed at around $3410cm^{-1}$ (PANC5) and $3420cm^{-1}$ (PANC10) was due to the N-H stretching vibrations. The appearance of a broad band instead of a sharp peak can be attributed due to the presence of a high concentration of N-H groups in the nanocomposite. The TEM images show that the sample contains defective spherical, truncated triangular and rod shaped particles. The results showed that the PANI/Ag nanocomposites are composed of nano-sized particles of 43-53 nm that contain Ag domains of 33-37 nm with polymer thickness 5.7-11.2 nm at two different aniline concentrations.

• Particle and aerosol research
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• v.6 no.1
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• pp.21-27
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• 2010

New process consisting of electrospray and epitaxial crystal growth processes was applied to the preparation of c-plane oriented barium ferrite ($BaFe_{12}O_{19}$) thin film for high density magnetic recording media. Sodium citrate aided process was proper to preparation of amorphous $BaFe_{12}O_{19}$ nanoparticles with geometric mean diameter of 3 nm and geometric standard deviation of 1.1. The electrospray was applicable to the prepare of amorphous $BaFe_{12}O_{19}$ thin film on a substrate, and the film thickness could be controlled by adjusting the electrospray deposition time. The c-plane oriented $BaFe_{12}O_{19}$ thin film was successfully prepared by 3 step annealing process of the $BaFe_{12}O_{19}$ amorphous film on a sapphire($Al_2O_3$) substrate; annealing at $350^{\circ}C$ for 30 min, annealing at $500^{\circ}C$ for 30 min, and annealing at $700^{\circ}C$ for 60 min.

• Advances in nano research
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• v.12 no.4
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• pp.415-426
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• 2022

Nickel substituted cobalt-zinc ferrite nanoparticles with composition Co_0.5Zn_0.5Ni_xFe_2-xO₄ (x = 0.25, 0.5, 0.75, 1.0) were synthesized using a wet chemical method named citrate precursor method. Various characterizations of the prepared nanoferrites were done using X-ray powder diffractometry (XRD), Scanning electron microscopy (SEM), UV visible spectroscopy and Fourier transform spectroscopy technique (FT-IR). XRD confirmed the formation of cubic spinel structure of the samples with single phase having one characteristic peak at (311). The value of optical band gap (E_g) was found to decrease with Ni substitution and have values in the range 2.30eV to 1.69eV. A Fenton-type system was created by photocatalytic activity using source of visible light for removal of methylene blue dye. Observations revealed increase in the degradation of methylene blue dye with increasing nickel content in the samples. The degradation percentage was increased from 77.32% for x = 0.25 to 90.16% for x = 1.0 in one hour under the irradiation of visible light. Also, the degradation process was found to have pseudo first order kinetics model. Hence, it can be observed that synthesized nickel doped cobalt-zinc ferrites have good capability for water purification and its degradation efficiency enhanced with increase in nickel concentration.

• Applied Chemistry for Engineering
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• v.19 no.5
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• pp.477-483
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• 2008

$La_{0.7}Sr_{0.3}Co_{0.2}Fe_{0.8}O_{3-{\delta}$ oxide was synthesized by a citrate method and a typical dense membrane of perovskite oxide has been prepared using as-prepared powder by pressing and sintering at $1300^{\circ}C$. Precursor of $La_{0.7}Sr_{0.3}Co_{0.2}Fe_{0.8}O_{3-{\delta}$ prepared by citrate method was investigated by TGA and XRD. Metal-citrate complex in precursor was decomposed into perovskite oxide in the temperature range of $260{\sim}410^{\circ}C$ but XRD results showed $SrCO_3$ existed as impurity at less than $900^{\circ}C$. Electrical conductivity of membrane increased with increasing temperature but then decreased over $700^{\circ}C$ in air atmosphere ($Po_2=0.2atm$) and $600^{\circ}C$ in He atmosphere ($Po_2=0.01atm$) respectively due to oxygen loss from the crystal lattice. The oxygen permeation flux increased with increasing temperature and maximum oxygen permeation flux of $La_{0.7}Sr_{0.3}Co_{0.2}Fe_{0.8}O_{3-{\delta}$ membrane with 1.6 mm thickness was about $0.31cm^3/cm^2{\cdot}min$ at $950^{\circ}C$. The activation energy for oxygen permeation was 88.4 kJ/mol in the temperature range of $750{\sim}950^{\circ}C$. Perovskite structure of membrane was not changed after permeation test of 40 h and the membrane was stable without secondary phase change with 0.3 mol Sr addition.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.3
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• pp.45-50
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• 2015

The goal of this research is the create novel magnets with no rare-earth contents, with larger energy product by comparison with currently used ferrites. For this purpose we developed nano-sized hard-type/soft-type composite ferrite in which high remanent magnetization (Mr) and high coercivity (Hc). Nano-sized Ba-ferrite, Ni-Zn ferrite and $BaFe_{12}O_{19}/Ni_{0.5}Zn_{0.5}Fe_2O_4$ composite ferrites were prepared by sol-gel combustion method by use of glicine-nitrate and citric acid. Nanocomposite ferrites were calcined at temperature range $700-900^{\circ}C$ for 1h. According to the X-ray diffraction patterns and FT-IR spectra, single phase of NiZn-ferrite and Ba-ferrite were detected and hard/soft nanocomposite ferrite was indicated to the coexistence of the magnetoplumbite-structural $BaFe_{12}O_{19}$ and spinel-structural $Ni_{0.5}Zn_{0.5}Fe_2O_4$ that agreed with the standard JCPDS 10-0325 data. The particle size of nanocomposite turn out to be less than 120 nm. The nanocomposite ferrite shows a single-phase magnetization behavior, implying that the hard magnetic phase and soft magnetic phase were well exchange-coupled. The specific saturation magnetization ($M_s$) of the nanocomposite ferrite is located between hard ($BaFe_{12}O_{19}$) and soft ferrite($Ni_{0.5}Zn_{0.5}Fe_2O_4$). The remanence (Mr) of nanocomposite ferrite is much higher than that of the individual $BaFe_{12}O_{19}$ and $Ni_{0.5}Zn_{0.5}Fe_2O_4$ ferrite, and $(BH)_{max}$ is increased slightly.

• Korean Chemical Engineering Research
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• v.54 no.3
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• pp.404-409
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• 2016

Thermal Characteristics and kinetic parameters of $LaMnO_3$ synthesis reaction were investigated by means of TGA (Thermogravimetric analysis) at non-isothermal heating conditions (5.0, 10.0, 15.0 and 20.0 K/min). The reaction was occurred rapidly at 450~600K (X=0.4~0.7) depending on the heating rate. Activation energy for the synthesis of $LaMnO_3$ from the precursor, which was determined by different method such as Friedman, Ozawa-Flynn-Wall and Vyazovkin methods, was in the range of 23~243 kJ/g-mol depending on the fractional conversion level and estimation method. The reaction order decreased with increasing heating rate and fractional conversional level. The average reaction order was 4.50 in case of X=0.1~0.3, while it was 1.87 in case of X=0.7~0.9, respectively. The value of frequency factor of reaction rate increased with inceasing heating rate and fractional conversion level. The aveage value of frequency factor was 205.6 ($min^{-1}$) when X=0.1~0.3, while it was 475.2 ($min^{-1}$) when X=0.7~0.9, respectively.