• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.245-246
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• 2006

A propyl alcohol based sol-gel method was used as to replace the 2-methoxyethanol with 1,1,1 tris (hydroxymethyl) ethane for preparation of pzt piezoelectric ceramic. The powder obtained by this sol-gel process were calcined at $900^{\circ}C$ and followed by the sintering at $1100^{\circ}C$ for ca2 hrs as to reach a pyrochlore-free crystal phase. The characterization of synthesized material was carried out by the XRD analysis and the surface morphology were determined by high resolution scanning electronmicroscopy. Further, the prepared small sized pzt thin powders are likely to be used m various applications.

• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.177-182
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• 2010

To synthesize $Gd_2O_3:Eu^{3+}$ phosphor, gadolinium-europium oxalate precursors were prepared from oxalic acid, NaOH or aqueous ammonia via coprecipitation method. The obtained precursors were heat-treated and then characterized by XRD, SEM and PL. The kinds and amounts of coprecipitant (NaOH or aqueous ammonia) were found to affect the powder morphology and properties of gadolinium-europium oxalate precursors. Two crystalline precursors and one amorphous precursor were synthesized. The nanometer-sized amorphous gadolinium-europium oxalate precursor was first prepared using the oxalate coprecipitation technique. The calcined powders obtained from the amorphous precursor were nearly spherical in shape, and a narrow size distribution was obtained. The NaOH coprecipitant was more effective in the preparation of nanometer-sized spherical powders. A thermal decomposition process was conducted for the three kinds of precursors. The photoluminescence property was also measured as a function of europium content, and concentration quenching occurred for samples with europium concentrations of over 10 mol%.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.254-262
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• 1996

$Pb(Zr_{0.52}Ti_{0.48})O_{3}$ (PZT) ceramics were prepared with uniform particle size of $1~3\;\mu\textrm{m}$ by hydrothermal synthesis at various conditions, such as hydrothermal reaction temperature, concentration of mineralizer and reaction time. PZT ceramics were formed above $180^{\circ}C$ for 2 hrs reaction using 10 M KOH solution as a mineralizer, but reaction condition was slightly different by starting materials. Morphology and characterization of PZT powders were investigated by XRD and SEM. By increasing the reaction temperature, KOH concentration and reaction time, the composition of the PZT phase tended to be homogeneous phase.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.3-6
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• 2003

In this work, poly(ethylene oxide) nanofibers were fabricated by electrospinning to prepare nanofibers-reinforced composites. And the PEO powders-impregnated composites were also prepared to compare with physicochemical properties of nanofibers-reinforced composites. Morphology and fiber diameter of PEO nanofibers were determined by SEM observation. Mechanical interfacial properties of the composites were investigated in fracture toughness tests and interlaminar shear strength (ILSS) test. As a result, the fiber diameter decreased in increasing applied voltage. However the optimum condition for the fiber formation was 15 ㎸, resulting from increasing of jet instability at high voltage and the prepared PEO nanofibers were useful in fiber reinforced composites. The PEO-based nanofibers-reinforced composites showed an improvement of fracture toughness factors ($K_{IC} and G_{ IC}$) and ILSS, compared to the composites impregnated with PEO powders. These results were noted that the nanofibers had higher specific surface area and larger aspect ratio than those of the powder, which played an important role in improving the mechanical interfacial properties of the composites.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.168-170
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• 2005

Nickel base brazes containing boron and silicon as melting point depressants are used extensively in the joining and repair of hot-section components in next generation nuclear reactor and aero-engine. Therefore, the present study has investigated the preliminary applicability of nickel based alloying nano powders. Nano Ni-based alloying powders synthesized by Pulsed Wire Evaporation (PWE) method. It's powder morphology and phase transformation temperature were analyzed by scanning electron microscopy, transmission electron microscopy, and differential scanning calorimeter(DSC). The powder particle size was approximately 10${\sim}$100nm and exhibits a quite even equiaxed shape. The results of DSC measurement show that both the nano Inconel 625 nano powder and Inconel 718 nano powder presents similar liquidus temperatures approximately $1373^{\circ}C$ and $1380^{\circ}C$ respectively.

• Journal of Powder Materials
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• v.10 no.3
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• pp.186-189
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• 2003

A chemical vapor condensation (CVC) process using the pyrolysis of metal-organic precursors was applied to produce the nanosized $WO_3$ powders. Morphology and phase changes of the synthesized $WO_3$ powder as a function of CVC parameters were investigated by XRD, BET and TEM. The agglomerated nanosized monoclinic $WO_3$ powders with nearly spherical shape and 10-38 nm in mean diameter could be obtained. Conditions to produce the $WO_3$ nanopowders are presented in this paper.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.201-209
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• 1989

Fine Si-Al-OH coprecipitate powders were prepared from Si- and Al-alkoxides by the hydrolysis method. $\beta$-Sialon powder was obtained from prepared Si-Al-OH coprecipitate by the simultaneous reduction and nitridation method. The syntehsized Sialon powder was pressureless sintered at 175$0^{\circ}C$ for 90 min in N2 atmosphere. The characterization of the Sialon powder was performed with XRD, BET, SEM, TEM and particle size analysis. The sinterability and mechanical properties of sintered bodies were investigated in terms of relative density, M.O.R., fracture toughness, hardness and the morphology of microstructure. The highest values of their mechanical properties were obtained for the $\beta$-Sialon ceramics at Z=1 and those values are as follows : M.O.R., KIC and HV of $\beta$-Sialon ceramics(Z=1) are 499.1 MPa, 5.9MN/m3/2 and 18.7GPa, respectively.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.503-504
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• 2006

The MIM technology is an alternative process for fabricating near net shape components that usually uses gas atomised powders with small size $(<\;20\;{\mu}m)$ and spherical shape. In this work, the possibility of changing partially or totally spherical powder by an irregular and/or coarse one that is cheaper than the former was investigated. In this way, different bronze 90/10 components were fabricated by mixing three different types of powder, gas and water atomised with different particle sizes, in order to evaluate how the particle shape and size affect the MIM process.

• Proceedings of the KWS Conference
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• 2001.10a
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• pp.220-222
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• 2001

The average grain size, the grain-size distribution, the morphology and the microstructure are fundamental characteristics of a spraying powder. Now that the significance of the grain size for the pattern of properties of the powder has been recognised, greater consideration is also being given to it in standards and regulations. However, unfortunately, the processes according to which the grain size and the grain-size distribution must be determined are specified in the rarest of cases. The contribution therefore dealt with the comparison of different particle-size measuring techniques, such as diffraction spectroscopy, sedimentation, sieving and microscopic measurement. The comparability of the measured results was investigated on twelve plasma spraying powders with different compositions, nominal sizes and morphologies.

• Korean Journal of Metals and Materials
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• v.47 no.1
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• pp.21-25
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• 2009

The reduction of $Ni(OH)_2$ by hydrazine-sodium phosphinate in water and water-diethylene glycol solutions for the preparation of spherical nickel particles has been studied at room temperature. The effect of reaction conditions on the size and morphology of Ni powder was revealed using SEM and XRD analysis technique. It was shown that in the presence of sodium phosphinate the reduction process become activated and a formation of Ni particles was completed within several minutes at room temperature. As a desired result spherical Ni powders with particles size from 0.07 to 2.0 mm were obtained.