• Journal of the Korean Ceramic Society
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• v.27 no.3
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• pp.361-368
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• 1990

The properties of the powder of ZrO2＋3m/o Y2O3 system prepared by co-precipitation method at the pH values of 7, 9, 10 and 11 were investigated. ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Zirconium hydroxide near by Zr(OH)4 structure showed more excellent crystallinity and lower formation temperature of tetragonal ZrO2. In the range of this study, cubic ZrO2 was not formed and stability of tetragonal ZrO2 prepared in the conditiion of pH 7 was most excellent. Average particle sizes and specific surface areas of tetragonal ZrO2 powders, prepared as calcining amorphous zirconium hydroxides at $600^{\circ}C$ for 1h, were 0.6-0.8${\mu}{\textrm}{m}$ and 45-70$m^2$/g, respectively.

• Journal of the Korean Ceramic Society
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• v.16 no.2
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• pp.89-98
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• 1979

In order to prepare ferroxplana ZnY $(Ba_2Zn_2Fe_{12}O_{22})$, which would be useful for GHz-band communication, the optimum coprecipitation condition of 1 $BaCl_{2-1} Zn(NO_3)_2-6FeCl_3$ in $NaOH-Na_2CO_3$ solution was investigated by use of a new apparatus invented in our laboratory. By freeze-drying and calcining the coprecitated hydroxide-carbonate, the very reactive powder was obtained, from which the synthesis process of ZnY and the other related crystals were investigated by means of X-ray diffraction. In results, it was found that the reactive powder containing ZnY as the major component can be prepared by this method, which may be used in manufacturing the various magnetic cores for the microwave communication.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.11a
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• pp.39-40
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• 2011

This study is to analyse possibility cementitious powder from waste concrete as row material of recycled cement. From the results, we ascertained possibility as recycled cement through XRF & XRD of cementitious powder & recycled cement. As a result of the experiment, cementitious powder from waste concrete, which appeared to recovery hydration chemically at the calcining temperature of 700, suggested highly possibility as recycled cement.

• Journal of the Korean Ceramic Society
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• v.40 no.2
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• pp.113-117
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• 2003

To reduce the doming of the shadow mask due to thermal expansion and to prevent the color discrepancy, the electron reflecting layer with lead tungsten oxides on the electron gun side of shadow mask was formed by screen printing method and doming property was evaluated in CRT. First, the lead tungsten oxides were prepared by calcining the mixture of lead oxide and tungsten oxide above 600$^{\circ}C$. Second, the paste which has the anti-doming composition including the lead tungsten oxides was coated by screen-printing method. As a result, the doming of the shadow mask was reduced about from 30 to 45%.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.11-16
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• 1995

High reaction heat evolved from the oxidation of Al was used to synthesize SiC, which might be difficult to be formed by SHS. Al2O3-SiC composite powder was easily manufactured using KNO3 as an ignition and reaction catalyst. Unreacted Si and C were observed after reaction dependent upon the composition of starting powders, reaction atmosphere and relative densities of compacted bodies. The unreacted carbon could be removed by calcining at $600^{\circ}C$ and the remaining Si could be removed by dissolving in NaOH solution. The final powder particles were smaller than 1${\mu}{\textrm}{m}$ in size.

• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.495-506
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• 1996

Monodispersed colloidaly yttria(Y2O3) can be used in a variety of applications such as phosphors. IR transparent materials and fine ceramics. For preparing monodispersed yttria homogeneous precipitation has been regarded as a fovorable method that is monodispersed yttria can be obtained through calcining monodispersed colloidal compound of yttrium (eg:Y(OH)CO3.nH2O)which can be prepared by homogeneous precipitation with urea. It is however still required to find out the quantitative effects of important variables of precipitation such as concentration of yttrium and urea reaction temperature and initial pH of reactant even though homogeneous precipitation of Y3+ with urea has been studied extensively. Among the effects of these variables we investiga-ted 1) the effect of yttrium concentration on the shape and size of precipitate and the reation rate 2) range of yttrium concentration required to make monodispersed colloidal particles 3) the reason for limited concentra-tion range of yttrium and 4) the effect of ultrasonic radiation on the limited concentration.

• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.563-571
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• 1996

In order to fabricate solid electrolyte CaO-stabilized ZrO2 of high density sintered body economically 13 mol% CaO-stabilized ZrO2 powders were synthesized by the coprecipitation method. The characteristics and sintering behavior of fine powder were investigated. The precipitates has the specific surface area of 193 m2/g and apperaed to be fine and spherical primary particles with a size of approximately 5nm. The crystalliza-tion temperture of CaO-stabilized ZrO2 was 462$^{\circ}C$. The tetragonal phase was stable in the low calcining tempe-rature regions and the cubic zirconia solid solution was formed from above 120$0^{\circ}C$ through an intermediate stage of formation of CaZrO3 By introducing fine powders washed with alcohol and ball-milling process after calcination the sintered body was possible to attain the value of above 92% of the theoretical density at low temperature of 120$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.23 no.6
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• pp.52-58
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• 1986

$Pb(Zr_{0.525} Ti_{0.475})O_3$ piezoelectric ceramics both unmodified and doped with NiO were prepared by the conventional oxide techniques using sintering temperature from 900 to to 125$0^{\circ}C$. The difference in densification process between unmodified and NiO doped PZT ceramics was studied by shrinkage vs. firing temperatures and it was caused by increasing defect concentration in calcining process of NiO doped PZT ceramics. And nickel oxide solubility limit for $Pb(Zr_{0.525} Ti_{0.475})O_3$ ceramics is shown to be at the range from 0.2wt% to 0.5wt% from this defect model micro-structures dielectric and piezolectric properties of Nio doped PZT ceramics.

• Journal of the Korean Ceramic Society
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• v.22 no.5
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• pp.29-34
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• 1985

The PTCR characteristics of the $BaTiO_3$ as a function of the molten KCl and dopant $Sb_2O_3$ were investitated. When the weight ratio of KCl to raw materials was above 0.1, $BaTiO_3$ was synthesized by calcining at 80$0^{\circ}C$ for 6 hrs. As the amount of the KCl increased the resistivity of the $BaTiO_3$ at room temperature incr-eased. This can be explained by charge compensation effect between electrons and holes and with microstruc-tures change of the specimens. The resistivity of the $BaTiO_3$ decreased with increasing amount of $Sb_2O_3$. In the time-current characteristics initial current decreased with increasing the ratio of KCl to raw materials but initial current increased and then decreased with the increase of the dopant $Sb_2O_3$. These results of the time-current characteristics can be explained by the resistivity-temperature characteristics.

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.211-218
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• 1990

CA2-based clinker with highly activated surface and hydraulic properties was synthesized at a comparatively lowr temperature than that of conventional synthesis by "hydration-burning method". This consists of calcining the mixture of CaCO3 and Al2O3 to obtain a primary clinker, hydrating the primary clinker and reburning the hydrates to obtain final clinker. Burning of primary clinker above 1200℃ was necessary to eliminate free CaO in it and to obtain it's solid hydrate. However, rising the burning temperature above 1300℃ is ineffective due to the decrease in hydraulic properties of the primary clinker with the temperature. Hydration of primary clinker at the elevated temperature(>35℃) was required to obtain the hydrate with more porous structure and final clinker with more active surface. CA2 was formed and increased with temperature at above 1150℃, finally became a primary phase of the final clinker. However, burning at the temperature above 1300℃ resulted in reverse effect on the hydraulic properties of the final clinker due to rapid decrease in it's surface area with the temperature.