• 한국세라믹학회지
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• 제28권9호
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• pp.705-711
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• 1991

Alumina precursor sol was obtained by the reaction of Al(OC4H9)3 and acetylacetone in the solvent followed by the partial hydrolysis. This sol was measured by viscosity and the effect of pH. The powders obtained from this sol were calcined at the various temperatures. The transition of crystals and crystal state were investigated at the various temperatures. The powders dried at 90$^{\circ}C$ showed amorphous and ${\gamma}$-Al2O3 at 900$^{\circ}C$, ${\alpha}$-Al2O3 mono-phase at 1050$^{\circ}C$ respectively. As a result of Al27-MASNMR analysis, amorphous and ${\alpha}$-Al2O3 powders showed 6-coordinated Al, ${\gamma}$-Al2O3 4-coordinated Al respectively.

• 한국세라믹학회지
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• 제28권2호
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• pp.146-152
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• 1991

Ultra fine and homogeneous (Ni0.4Zn0.6)Fe2O4 ferrite powders were prepared by direct-wet, Hydrothermal and coprecipitation methods. In case that specific surface areas of Ni-Zn ferrite powders were over 220㎡/g, 100㎡/g, 30㎡/g individually direct-wet, hydrothermal and coprecipitation methods. The Ni-Zn ferrite magnetic fluids of which Solvents were benzene or kerosene was prepared by making cation surfactant adsorbed on the surface of the (Ni0.4Zn0.6)Fe2O4. The results that measured dispersion and viscosity by making cation surfactant adsorbed were as follows. 1. The adsorption amount of Oleric acid be proportioned the specific surface area of powders. 2. The maximum amount of Oleric acid was 36wt% of dried powders which has 220㎡/g of specific surface area. 3. The stability of fluid by direct-wet synthesis emthod in benzene or kerosene solvent excellent.

• 한국세라믹학회지
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• 제37권2호
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• pp.181-185
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• 2000

A new technique capable of accelerating the crystallization of ferrite powder at low temperature is developed. Effects of the ultrasonic waves on the crystallization were studied for ferrite powders prepared using the co-precipitation method. The crystallization of the ferrite powders exposed to the ultrasonic waves were characterized by the XRD. The amorphous ferrite powders prepared using the co-precipitation method were crystallized as a result of the exposure to the ultrasonic waves for 5h and the crystallization of the ferrite powders became more enhanced in proportion to the time exposed. The ferrite powder exposed to the ultrasonic waves for 25h had higher crystallinity a larger specific surface area than the ferrite powder calcined at 500$^{\circ}C$ for 2h.

• 한국세라믹학회지
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• 제34권10호
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• pp.1009-1014
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• 1997

Ammonia gas was blown into the solution of zirconium ion to induce precipitation of supersaturated zirconium ion at gas-liquid interface with increase in pH. The influence of pH on the phase and particle size of precipitate and calcined powders has been investigated. At pH 4.5 of zirconium solution, maximum yield of 98.7% was obtained. Above pH 4.5, there was no more increase of yield. Above pH 5.5, large aggregates consisting of primary particles were observed in precipitate and calcined powders. At pH 4.5, almost aggregate-free fine spherical zirconia powders were obtained.

• 한국세라믹학회지
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• 제31권3호
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• pp.291-297
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• 1994

Cordierite powders were prepared by controlled hydrolysis of metal alkoxides with catalysts in water medium without using organic solvents. Water was adjusted to a certain pH by HC1 and NH4OH. $\alpha$-Cordierite powder was prepared from aluminum isopropoxide, tetraethyl orthosilicate and magnesium ethoxide mixed with water adjusted to pH of 3. At water pH of 11, $\alpha$-cordierite, mullite and $\beta$-quartz phases were coexisted. The powders were freeze dried, calcined and then fired at different temperatures. The characteristics of powders were examined by means of DTA, X-ray diffraction, FT-IR, and electron microscopy. It was found that $\alpha$-cordierite could be synthesized at temperature of 120$0^{\circ}C$ from the powders prepared by alkoxides with water medium without organic solvents.

• 한국세라믹학회지
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• 제31권1호
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• pp.1-10
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• 1994

Monodispersed alumina and Mg-doped alumina fine particles were prepared by controlled hydrolysis of alkoxides. Aluminium alkoxide and magnesium alkoxide were dissolved into complex solvent which was composed of hydrophobic n-octanol and hydrophilic acetonitrile. Hydroxypropyl cellulose(HPC) was used as a dispersant for the alumina particles. The size of these prepared powders was approximately 0.3 ${\mu}{\textrm}{m}$. In the case of sintering above 100$0^{\circ}C$, most of these prepared powders were transformed to $\alpha$-alumina. The relative density of the sintered body of these prepared powders at 1$600^{\circ}C$ was 98%. The sintered body of the Mg-doped alumina powder had more uniform grain size than that of the undoped alumina podwer.

• 한국세라믹학회지
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• 제28권1호
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• pp.74-78
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• 1991

Willemite powders which have been prepared by solid state reaction were easy to intermixed impurities, and particle surfaces were demaged in the progress of crushing. The above defacts were easy to accompany non-crystallization for mechanochemical effects and luminescence efficiency was deteriorated. The goal of this study improve each of defacts, and synthesize high purity and fine Mn doped willemite powders by wet and hydrothermal methods without crushing progress. It has been experimentally verified that the single phase Zn1.98Mn0.02SiO4 willemite powders which prepared by hydrothermal synthes is at 220$^{\circ}C$ for 10 hours in 2N KOH solution. The products are like needle and composition is the same with starting composition.

• 한국세라믹학회지
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• 제28권3호
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• pp.225-233
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• 1991

In this study, we tried to find out the appropriate synthetic condition and magnetic properties of Ni-Zn ferrite {(NixZn1-x)Fe2O4} powders (where X=0, 0.1, 0.2, 0.3, ……0.9, 1). Ferrite powders were prepared by wet-direct method at 86℃ for 6hrs from FeCl36H2O, NiCl26H2O, and ZnCl2. The powders of (NixZn1-x)Fe2O4 (where X=0.4, 0.5, 0.6) have a good crystallinity, but the other ferrite powders consist of crystal and precursor ferrite. The ferrite powder's lattice constant is increased when ratio of ZnO contant is increased in the ferrite composition. And initial permeability was measured after sintering, result indicated regular pattern except (Ni0.4Zn0.6)Fe2O4 when the frequency were changed 10KHz to 10MHz.

• 한국세라믹학회지
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• 제40권11호
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• pp.1058-1061
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• 2003

Gallium Nitride (GaN) powders were synthesized by calcining a gallium(III) sulfate salt in flowing ammonia in the temperature range 500-1100$^{\circ}C$. The process of conversion of the salt to GaN was monitored by X-Ray Diffraction (XRD). The salt decomposed to ${\gamma}$-Ga$_2$O$_3$ and then converted to GaN without ${\gamma}$-${\beta}$Ga$_2$O$_3$ phase transition. Variations in XRD patterns and weight loss of samples with temperature indicate that the conversion of ${\gamma}$-Ga$_2$O$_3$ to GaN does not proceed through Ga$_2$O but stepwise via amorphous gallium oxynitride (GaO$\_$x/N$\_$y/) as intermediates. Room-temperature photoluminescence spectra of GaN powders obtained showed the emission peak at 363 nm and no yellow band.

• 한국세라믹학회지
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• 제26권3호
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• pp.361-370
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• 1989

Mullite powders were synthesized from the common solution of aluminum sulfate and sodium silicate solutions by the emulsion-hot kerosene technique. The reaction temperature and mechanism for mullitization and the characteristics of synthesized mullite powders were investigated. The effect of Na components introduced from sodium silicate solution on the physical property and microstructure of sintered mullite was also examined. It was proved that mullites were formed at 75$0^{\circ}C$ through the reaction mechanism of Na2O.2.2SiO2＋3.3Al2(SO4)3longrightarrow1.1(3Al2O3.2SiO2)＋Na2SO4＋8.9SO3. Synthetic mullite powders consisted of the compositiion of 3Al2O3.2SiO2 and showed highly agglomeration of hollow spherical particles of 1${\mu}{\textrm}{m}$ diameter. The density and fracture toughness of sintered mullites were somewhat reduced because of the effect of a very small amount of residual Na components.