• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.60-66
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• 1991

The polymeric alumina sol was prepared by partial hydrolysis of aluminum sec-butoxide reacted with acetylacetone and its characteristics was investigated. The effects of alcohol solvent, acetylacetone, and acid concentration to the sol were investigated. FT-IR and Al27-MASNMR were used to study hydrolysis and polymerization reaction of aluminum complex. Synthesized sol showed the characteristics of polymeric alumina sol. To make a clear polymeric alumina sol, the optimum contents of acetylacetone, H2O and alcohol solvent were 0.4-0.6 mole, 0.25-1.25 mole, 3-5 mole per one mole alkoxide respectively. As a result of the Al27-MASNMR analysis, it was noted that hexa-penta-coordinated Al were main structure.

• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.4 s.23
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• pp.85-90
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• 2005

We report the phase transition temperatures of the $PbZrO_3$ perovskite nanotubes made by sol-gel template synthesis. The lead zirconate($PbZrO{_3}$) nanotubes were prepared with a chelate sol-gel of zirconium tetrabutoxide($Zr(OBu){_4}$) and leadacetate($Pb(OAc){_2}-3H_2O$). $Whatman^(r)$ anodisc membranes, with a 200nm pore size, served as the template. After removing the template in the 6M-NaOH solution, the $PbZrO{_3}$ nanotubes so far have shown an anomalous transition temperature, $123.6^{\circ}C$ as measured by DSC with a small particle size, 15.4nm determined by X-ray analysis with the aid of Scherrer's equation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.557-560
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• 2003

The submicron $YBa_2Cu_3O_x$ powder was prepared by the sol-gel method. The particle size is distributed from 0.2 to $1.0\;{\mu}m$, which benefits to eliminate the micro-cracks formed in the $YBa_2Cu_3O_x$ films deposited by electrophoresis. The powder was single phase of $YBa_2Cu_3O_x$ examined by X-ray diffraction. In the sol-gel process the citrate gel was formed from citric acid and nitrate solution of $Y_2O_3$, $Ba(NO_3)O_2$ and CuO. When pH values were adjusted to $6.4{\sim}6.7,\;Ba(NO_3)O_2$ could be dissolved in the citrate solution completely. Appropriate evaporative temperature of the sol-gel formation is discussed. After the heat treatment the transition temperature($T_c$) and critical current density($J_c$) of the $YBa_2Cu_3O_x$ samples made of the submicron powder were measured.

• Journal of the Korean Ceramic Society
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• v.29 no.5
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• pp.335-340
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• 1992

Undoped PbTiO3 ceramics was successfully prepared by using sol-gel process, which had not been fabricated due to its microcracks created by anisotropic stress during phase transition from cubic to tetragonal phase. Fabrication of undoped PbTiO3 ceramics via sol-gel processing was very much affected by the PbO content of the samples as well as PbO vapor from sintering atmosphere. Excess PbO was found to promote rapid grain growth in PbTiO3 ceramics. After sintering at 1100$^{\circ}C$ average grain size of PbTiO3 ceramics with excess PbO was about 8 times greater than that of stoichiometric composition, which may be due to PbO liquid phase from excess PbO.

• Journal of Surface Science and Engineering
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• v.30 no.3
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• pp.183-190
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• 1997

Fabrication and crystallization characteristics of yttria($T_2O_3$) stabilized zirconia(YSZ) thin film by sol-gel process were studied. YSZ sol was synthesized with zirconium n-propoxide($Zr(OC_3H_7)_4)$) and yttrium nitrate pentahydrate ($Y(NO_3)_3.5H_2O$). YSZ film was prepared by depositing the polymeric sol on porous $Al_2O_3$ substrate by spin-coating, and the film characteristics were investigated by FRIR, TG-DTA, XRD, DSC, optical microscopy and SEM. The film topology was uniform and cracks were not found. It was found that the annealing temperature and the concentration of stabilizer affect the crystallization of YSZ film. The YSZ film began to crystallize from amorphous to tetragonal phase at 40$0^{\circ}C$, and it was not converted to cubic structure until $1100^{\circ}C$. It seemed that the grains were formed over $700^{\circ}C$and the average grain size was obtained about 0.2$\mu\textrm{m}$.

• Journal of the Korean Ceramic Society
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• v.33 no.12
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• pp.1301-1310
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• 1996

Generally it requires high sintering temperatures more than 135$0^{\circ}C$ to make semiconductive BaTiO3 ceramics. Also it is very difficult to achieve a homogeneous mixing in solid-state reaction method. Therefore the liquid phase distributed to non-uniform dilute the characteristics of PTCR. In order to improve the uniformity this study is used the sol-gel coating method. Using this method we studied the new manufacturing process that had a high reproducibility and mass production capability. Tetraethyl orthosilicate (TEOS) was used as a source of Si. The semiconductive BaTiO3 ceramics which was produced by sol-gel method for the SiO2 addition and sintered between 124$0^{\circ}C$ and 130$0^{\circ}C$ showed almost same resistivity at room temperature among 125$0^{\circ}C$ and 130$0^{\circ}C$. As the results We could be sintered the semiconducting BaTiO3 ceramics at lower temperature even at 125$0^{\circ}C$ maintaining the same specific resistivity ratio ($\rho$max/$\rho$min) at 130$0^{\circ}C$. The specific resistivity both below and above the Curie temperature were increased by slow cooling and the steepness of the plots in the reasion of transition from low to high resistance increased as the cooling rate decreased.

• Journal of the Korean Ceramic Society
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• v.40 no.4
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• pp.380-384
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• 2003

The effects of the mole concentrations of precursor solution on the microstructure and dielectric properties of sol-gel deposited $Ba_{0.85}$S $r_{0.15}$Ti $O_3$(BST) thin films have been investigated. The films were of single perovskite phase with strong (100) preferred orientation when grown on LaNi0$_3$ buffered Pt/Ti/ $SiO_2$Si substrates using a diluted precursor solution. Variation of the precursor solution concentration resulted in a different microstructure and, in turn, affected the tunability of the sol-gel deposited films. It was observed that leakage currents increased asymmetrically for the negative and positive bias voltage with decreasing thickness. Overall results suggest that those BST films have acceptable properties f3r applications as room-temperature tunable elements.

• Journal of the Korean Ceramic Society
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• v.24 no.5
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• pp.423-430
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• 1987

Characteristics of Al2O3-ZrO2 powders prepared by sol-gel process and their sintering behavior were investigated as a function of calcination temperature. The sol-gel processed powders were calcined at 800, 900, 1000, 1100, 1200$^{\circ}C$, and analyzed by X-ray diffraction technique. Pore size and distribution of green compact of the calcined powders were measured by mercury porosimeter. It is suggested that the optimal temperature of calcination for the sintering of Al2O3-ZrO2 powder prepared by sol-gel process is 1100$^{\circ}C$. In the Al2O3-17vol.% ZrO2 sintered specimen, which was sintered at 1600$^{\circ}C$ for 2hrs in air, 69vol.% tetragonal phse existed.

• Journal of the Korean Ceramic Society
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• v.31 no.6
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• pp.671-677
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• 1994

To improve the low resistance of ceramics to tensile stress, many techniques, for introducing and retaining surface compressive stress have been suggested. In present work, in order to introduce the compressive stress on the surface of TZP ceramics TZP-Al2O3 composites were made with infiltration technique. Highly porous 3Y-TZP pre-sintered specimens were submerged in AlOOH(boehmite) sol and the sol penetrated into them through open pore channels with moderate depth after that specimens were sintered. It was known that controlling the number of infiltration time can vary the amount of Al2O3 phase and the fraction of alumina at surface reached up to 18%. The depth of composite surface layer were 100~200 ${\mu}{\textrm}{m}$, and these were acceptable in surface strengthening which were proved by Vickers hardness indentation method.

• Journal of Biomedical Engineering Research
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• v.18 no.3
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• pp.217-222
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• 1997

Hydroxyapatite(HA)-coated metal composites were made by the dipping method. The specimen substrates were Ti plates with a thickness of 2 mm. The HA coating was carried out in HA-sol for 1 min by the dipping method. The concentration of HA-sol for the coating ranged from 3.28 to 9.99 wt%. Excellent coating was observed on Ti substrate dipped once in 9.99 wt% sol. Preparation of Ti plates by sandblasting provided the better environment for coating HA on Ti surface than non-treated surface. As the concentration of sol increased, the weight change and the coating thickness increased. Above 7 wt% sol, they increased sharply.