• Korean Journal of Materials Research
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• v.30 no.10
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• pp.533-541
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• 2020

UO₂ kernels, a key component of fuel elements for high temperature gas cooled reactors, have usually been prepared by sol-gel methods. Sol-gel processes have a number of advantages, such as simple processes and facilities, and higher sphericity and density. In this study, to produce 900 ㎛-sized UO₂ particles using an external gelation process, contact length extension of the NH₃ gas of the broth droplets pass and the improvement of the gelation device capable of spraying 14 M-NH₄OH solution are used to form 3,000 ㎛-sized liquid droplets. To produce high-sphericity and high-density UO₂ particles, HMTA, which promotes the gelation reaction in the uranium broth solution, is added to diffuse ammonium ions from the outside of the gelation solution during the aging process and generate ammonium ions from the inside of the ADU gel particles. Sufficient gelation inside of ADU gel particles is achieved, and the density of the UO₂ spheres that undergo the subsequent treatment is 10.78 g/㎤; the sphericity is analyzed and found to be 0.948, indicating good experimental results.

• Journal of the Korean Ceramic Society
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• v.24 no.1
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• pp.70-76
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• 1987

The effect of C12A7 and OH group on the synthesis of C3A by the sol-gel process using aluminum-sec-butoxide and calcium nitrate was studied. C3A by sol-gel method was compared with C3A obtained by the conventional method with respect to their reactivity of formation and crystal size. The sol-gel process for initial formation of C12A7 and C3A at lower temperature (1100, 1200$^{\circ}C$) was superior, but that for complete crystallization of C3A at higher temperature (1300, 1400$^{\circ}C$) was inferior to oxide mixture process. When heat treated under the atmosphere oxygen-free dried nitrogen eliminate the influence of OH group in C12A7, the reactivity of C3A from sol-gel sample incorporated OH group were poor, whereas that from oxide mixture sample showed remarkable effect. The poor crystallization of C3A at higher temperature is presumed to be due to the fact that incorporated OH group in C12A7 formed at lowr temperature might interrupt the diffusion of CaO to C12A7 to from C3A. The crystal size and the hydration characteristics of both C3A obtained by different processes exhibited almost the same results.

• Journal of the Korean Ceramic Society
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• v.40 no.3
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• pp.279-285
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• 2003

Ferroelectric S $r_{0.9}$B $i_{2.1}$T $a_{1.8}$N $b_{0.2}$ thin films with 200 nm thicknesses were deposited on Pt/Ti $O_2$/ $SiO_2$/Si Substrates by a sol-gel method. In these experiments, Sr(O $C_2$ $H_{5}$)$_2$, Bi(TMHD)$_3$, Ta(O $C_2$ $H_{5}$)$_{5}$ and Nb(O $C_2$ $H_{5}$)$_{5}$ were used as precursors, which were dissolved in 2-methoxyethanol. After UV-irradiation and RTA processes, the remanent polarization value (2 $P_{r}$) of SBTN thin films with annealed at $650^{\circ}C$ was 8.49 and 11.94 $\mu$C/$\textrm{cm}^2$ at 3 V and 5 V, respectively.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.257-262
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• 2019

The control of microstructure is critical for the porous fuel particles used for infiltrating actinide nuclides. This study concerns the effect of heating processes on properties and microstructure of the fuel particles. The uniform gel precursor beads were synthesized by a microfluidic sol-gel process and then the porous $CeO_2$ microspheres, as a surrogate for the ceramic nuclear fuel particles, were obtained by heating treatment of the gel precursors. The fabricated $CeO_2$ microspheres have a narrow size distribution and good sphericity due to the feature of microfluidics. The effects of heating processes parameters, such as heating mode and peak temperatures on the properties of microspheres were studied in detail. An optimized heating mode and the peak temperature of $650^{\circ}C$ were selected to produce porous $CeO_2$ microspheres. The optimized heating mode can avoid the appearance of broken or crack microspheres in the heating process, and as-prepared porous microspheres were of suitable pore size distribution and pore volume for loading minor actinide (MA) solution by an infiltration method that is used for fabrication of MA-bearing nuclear fuel beads. After the infiltration process, $1000^{\circ}C$ was selected as the final temperature to improve the compressive strength of microspheres.

• Journal of the Korean Ceramic Society
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• v.55 no.6
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• pp.581-589
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• 2018

This work concentrated on the effect of different laser beams on the microstructure and dielectric properties of $BaTiO_3$ nanoparticles at different calcinations times during the gelling preparation step. The nanoparticles were prepared by the sol-gel method. A green (1000 mW, 532 nm) and red laser beam (500 mW, 808 nm), were applied vertically at the center of stirring raw materials. The samples were sintered at $1000^{\circ}C$ for 2, 4, and 6 h. X-ray diffraction (XRD) analysis showed that samples prepared under the green laser have the highest purity. The FT-IR spectra showed that the stretching and bending vibrations of TiO bond without any other bonds, which are compatible to the X-ray diffraction (XRD) results. Samples were characterized by transmission electron microscopy (TEM), Scan electron microscopy (SEM), and UV-Visible spectrophotometer. Characterization showed the samples prepared under the green laser to have the highest particle size (~ 50 nm) and transparency for all sintering durations. Laser beam effects on electrical characterization were studied. BT nanoparticles prepared under the green laser show the higher dielectric constant, which was found to increase with sintering temperature.

• Journal of the Korean Ceramic Society
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• v.42 no.5 s.276
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• pp.333-337
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• 2005

In order to improve the performance of green emitting phosphors for plasma display panel, the $Zn_2SiO_4:Mn,Al$ phosphors were synthesized using sol-gel technique and studied using SEM and VUV photoluminescence spectrometer. pH values of the starting solutions (pH = 0.5$\~$2.34) were controled by HCl as the catalysis of hydrolysis and wet gels were dried at $80^{\circ}C$ and $120^{\circ}C$, respectively. We investigated the effects of pH and drying temperatures during sol-gel processes. The results indicated that the phosphor prepared at pH = 1 showed the maximum emission intensity in both drying conditions and the effect of pH of the starting solution on morphology were increased with particle size as HCl and phosphor dried at high temperature showed more spherical and smaller particles than at low.

• Applied Microscopy
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• v.42 no.4
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• pp.207-211
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• 2012

We examined the electrical properties and microstructure of NiO produced using a sol-gel method and Ni nitrate hexahydrate ($Ni[NO_3]_2{\cdot}6H_2O$) to investigate if this NiO thin film can be used as an insulator layer for resistance random access memory (ReRAM) devices. It was found that as-prepared NiO film was polycrystalline and presented as the nonstoichiometric compound $Ni_{1+x}O$ with Ni interstitials (oxygen vacancies). Resistances-witching behavior was observed in the range of 0~2 V, and the low-resistance state and high-resistance state were clearly distinguishable (${\sim}10^3$ orders). It was also demonstrated that NiO could be patterned directly by KrF eximer laser irradiation using a shadow mask. NiO thin film fabricated by the sol-gel method does not require any photoresist or vacuum processes, and therefore has potential for application as an insulating layer in low-cost ReRAM devices.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.428-432
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• 2012

Polyamidimide (PAI)-colloidal silica (CS) nanohybrid films were synthesized by an advanced sol-gel process. The synthesized PAI-CS hybrid films have a uniform and stable chemical bonding and there is no interfacial defects observed by TEM. The thermal degradation ratio of PAI-CS (10 wt%) hybrid films is delayed by 100 ℃ compared with pure PAI sample determined by on set temperature range in TGA. The dielectric constant of PAI-CS (10 wt%) hybrid films decreases with increasing CS content up to about 5 wt% but increases at higher CS content, which is not explained simply by effective medium therories (EMT). The duration time of PAI-CS (10 wt%) hybrid coil is 38 sec, which is very longer than that of pure PAI coil sample. The PAI-CS (10 wt%) hybrid film has a higher breakdown voltage resistance than the pure PAI film at surge environment and exhibits superior heat resistance. The PAI-CS (10 wt%) sample shows the advanced and stable thermal emission properties in transformer module compared with the pure PAI sample. This result illustrates that the advanced thermal conductivity and expansion properties of PAI-CS sample in the case of appropriate sol-gel processes brings the stable thermal emission in transformer system. Therefore, new PAI-CS hybrid samples with such stable thermal emission properties are expected to be used as a high functional coating application in ET, IT and electric power products.

• Bulletin of the Korean Chemical Society
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• v.18 no.6
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• pp.588-594
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• 1997

Gelation time, gel structure and volatility of by-products during gelation of PZT sol-gel processing were investigated by FT-IR spectroscopy. FT-IR spectroscopic study was performed on PZT gels with the various H₂O contents (1, 2 and 3 mol) and the several types (HNO₃, NH₄OH) and amounts (0.1, 0.2 mol) of catalysts, monitoring temporal (0, 1, 3, 10 weeks, 3 months and 3 years) and thermal (100-700 ℃) changes of FT-IR spectra. The interpretation of temporal change of the spectra revealed two trends. One is under the condition of 1 mol H₂O, 1 mol H₂O+0.1 mol HNO₃, 3 mol H₂O and the other is for 1 mol H₂O+0.1 mol NH₄OH, 2 mol H₂O, 1 mol H₂O+0.2 mol HNO₃. The gel structures and the gelation times for these conditions were discussed in comparison with the reported results of SiO₂, and we suggested the reaction mechanisms for these structural characteristics. Thermal variation of FT-IR spectra was interpreted as the evolution processes of gel by investigating the evaporation of solvent and the decomposition of organic residues.

• Journal of the Korean Ceramic Society
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• v.33 no.8
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• pp.915-920
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• 1996

Fine mullite precursor was prepared by colloidal sol-gel processes. Aluminum isopropoxide $[Al(i-OC_3H_7)_3]$ as a starting material of $Al_2O_3$ and silicic acid extracted by THF from sodium silicate as a starting material of $SiO_2$ were used. Sodium silicate was first acidified by dilute sulfuric acid to form silicic acid. ; followed by extraction using THF, Mullite precursor was synthesized by sol-gel processes from aluminum isopropoxide and sillicic acid considering the degree of extraction of Si and the removal efficiency of Na. The impurity content of silicic acid extracted by THF was below 0.04% Synthetic mullite precursor consisted of $3Al_2O_3{\cdot}2SiO_2$ and showd spherical particles of $0.05{\mu}m$ diameter and below 0.462% of impurites. The mullite precursor was characterized by EDS, XRD, TG/DSC SEM, FT-IR spectroscopy ICP and TEM.