• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.145-156
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• 1997

ZrO2 phase transformations depending on the type and amount of dopants and the sintering temperatures were studied for the 2 components (CaO-, Y2O3-, MgO-ZrO2) and the 3 components(MgO-ZrO2-Al2O3)ZrO2 powder by X-ray diffraction and Raman spectroscopy. In the CaO- and Y2O3-ZrO2 systems, as the CaO and Y2O3 contents increased to 6~15mol% and 3~15mol% respectively, we were not able to identify between tetragonal and cubic in the X-ray diffraction patterns. On the other hand, all Raman modes shifted to lower wavenumbers, decreasing in intensity and the number of bands, markedly. These phenomena were caused by tetragonallongrightarrowcubic phase transformation and interpreted by the breakdown of the wave vector selection rule(k=0) and the structural disorder associated with the formation of oxygen sublattice which was caused by the substitution between Zr4+ ion and Ca2+ or Y3+ ion in ZrO2 matrix. The monoclinic to cubic phase transformation occurred in 10mol% MgO-ZrO2 system. As the Al2O3 content increased from 0 to 20mol% in the MgO-ZrO2-Al2O3 systems, cubic phase transformed to monoclinic phase, this is because the MgO didn't play a role in a stabilizer because of the formation of the spinel(MgAl2O4) by the reaction between MgO and Al2O3, Also, the ZrO2 phase transformation was explained by the change of it's lattice parameters depending on the type and amount of dopants. Namely, as the amount of dopant increased to 10~13mol%, the axial ra-tio c/a came close to unity with increasing the lattice parameter a and decreasing the lattice parameter c. At that time, the tetragonallongrightarrowcubic phase transformation occurred.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.12
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• pp.1017-1024
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• 2000

Effect of the microwave dielectric properties and the microstructure on a mole fraction(x=0.1~0.9) of (1-x)Mg$_2$SiO$_4$-xZnAl$_2$O$_4$ ceramics was investigated. When (1-x)Mg$_2$SiO$_4$-xZnAl$_2$O$_4$(x=0.1~0.9) ceramics were sintered at 130$0^{\circ}C$, 135$0^{\circ}C$ and 140$0^{\circ}C$ for 2hr, the microwave dielectric properties were obtained $\varepsilon$r=6.8~8.3, Q.f$_{0}$=36000~77600. On the other hand, the temperature coefficients of resonant frequency($\tau$$_{f}$) were obtained in the properties of -62ppm/$^{\circ}C$ to -49ppm/$^{\circ}C$. In order to adjust the temperature coefficient of resonant frequency($\tau$$_{f}$), CaTiO$_3$was added in (1-x)Mg$_2$SiO$_4$-xZnAl$_2$O$_4$ceramics. 0.7Mg$_2$SiO$_4$-0.2ZnAl$_2$O$_4$-0.1CaTiO$_3$ceramics sintered at 135$0^{\circ}C$ for 2hr showed the excellent microwave dielectric properties of $\varepsilon$r=7.7, Q.f$_{0}$=32000, and $\tau$$_{f}$=-7.9 ppm/$^{\circ}C$.EX>.>.EX>.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.4
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• pp.479-488
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• 2011

Nanofiltration was performed with polyaluminium chloride solutions at different pH conditions to understand effects of inorganic compounds on aluminum hydrolysis products, i.e., three distinctive groups of aluminum species: polymeric Al at low pH; $Al(OH)_3$ at neutral pH; and ${Al(OH)_4}^-$ at high pH. The PACl solution was prepared to be approximately 4.0mM and adjusted to the designated pH. The influence of inorganic compounds on Al species fouling was investigated with 4.9mM $CaCl_2$ and 3.5mM $MgSO_4$ because $Ca^{2+}$, $Mg^{2+}$, $Cl^-$, ${SO_4}^{2-}$ are the most common inorganics in the drinking water. NF membrane fouling was measured by flux decline rate. The impact of $CaCl_2$ was not significant on the individual Al hydrolysis products fouling. However, the flux decline rate was drastically changed in the presence of $MgSO_4$. The concentration of particulate matters was considerably increased possibly due to interaction between Al species and ${SO_4}^{2-}$ where $MgSO_4$ was introduced. The particulates were accumulated on the membrane and enhanced the hydraulic resistance of the cake layer. In addition, conductivity removal of the membrane was decreased when Al-hydroxide was dominant due to reduction of membrane surface charge. The rejection of $Ca^{2+}$and $Mg^{2+}$ were considerably different, which implys that composition of inorganics paly a role on conductivity removal.

• Journal of the Korean Ceramic Society
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• v.39 no.6
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• pp.528-534
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• 2002

CaO ceramics were prepared by conventional sintering process and their hydration behaviors were evaluated by measuring weight increment on saturated water vapor pressure at ambient temperature. CaCO$_3$ and limestone were used as CaO source materials and $Al_2$O$_3$, MgO and SiO$_2$ were added as sintering agents. $Al_2$O$_3$ was a liquid phase sintering agent to increase densification and grain growth rates, whereas MgO and SiO$_2$, densification and grain growth inhibitors. Regardless of composition, all of the prepared CaO ceramics showed the improved hydration resistance as bulk density increased. Especially, when bulk density was more than 3.0 g/㎤, there was no weight increment after 120 h of hydration. Therefore, to decrease contact area between CaO and water vapor by increasing bulk density with the $Al_2$O$_3$ sintering additive was effective for the improvement of CaO hydration resistance.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.3
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• pp.127-131
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• 2001

The effect of grain shape on the grain growth behavior of oxide system was investigated as afunction of liquid content during liquid phase sintering. As a model system, the solid grains of $Al_{2}O_{3}$ and MgO were selected during liquid phase sintering, i.e. faceted shape of $Al_{2}O_{3}$ in $CaAl_{2}Si_{2}O_{8}$ liquid phase and spherical shape of MgO in $CaMgSiO_{4}$ liquid phase. The average grain size of MgO with spherical shape was decreased with increasing the liquid phase content, whereas that of $Al_{2}O_{3}$ with faceted shape was independent of liquid phase content. In the case of $Al_{2}O_{3}$ grains with faceted shape, which interfaces are expected to be atomically flat, are likely to grow by the interfacial reaction controled process. Whereas, in the case of MgO grains with spherical shape, which interface are expected to be atomically rough, are likely to grow by the diffusion controlled process.

• Journal of the Korean Ceramic Society
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• v.20 no.1
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• pp.25-30
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• 1983

This experiment was studied in the system of (1-x) CaO MgO $2SiO-Al_2O_3$ to investigate forming of solid solution. The technique empolyed was the well known water-quenching method. Differential thermal analysis of the each glass water quenched indicated that under 30 mole% $Al_2O_3$ was lowered with increasing of the amount of $Al_2O_3$ It was supposed by X-ray diffraction patterns of each specimen sintered at various temperature that only solid solution was formed under the 30mole % $Al_2O_3$ compositions solid solution and anorthite were formed at the 20mole% $Al_2O_3$ composition anorthite solid solution and spinel$(MgAl_2O_4)$ were formed over the 40mole% $Al_2O_3$ compositions. The maximum density and thermal expanison coefficient was 2.89g/cm 7.74x106./C$^{\circ}$ respectively in the composi-tion of 10 mole% $Al_2O_3$ . All the specimens showed linear thermal expansion behavior. Microhardness was as high as 850kg/nm2 in the composition of 5, 10, 20 mole % $Al_2O_3$ and dielectric constant was 7.3-6.9.

• Journal of the Korean Ceramic Society
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• v.15 no.1
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• pp.3-8
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• 1978

Effects on the sintering of zircon by minor additives such as $Al_2O_3$, MgO and CaO were studied at $1450^{\circ}C$~$1550^{\circ}C$ for 30 minutes. Shrinkage, compressive strength, bulk density and apparent porosity of sintered specimens were measured in relation to content of minor additives and temperature. Mineral constitutions of the sintered specimens were idenified with X-ray diffractometer. And microstructures of the sintered specimens were observed by scanning electron microscope. The results obtained were as follow. 1) Effect ofthe minor additives such as Al2O3, MgO and CaO on the sintering of zircon was related to reaction between added oxide and silica by dissociation of zircon. 2) Zircon did not dissociate at $1550^{\circ}C$, but it did slightly on the specimen added by Al2O3 5 wt% at $1550^{\circ}C$. 3) Sintering of zircon was promoted by the addition of MgO, $(Al_2O_3＋CaO)$ and (MgO＋CaO), then, this phenomenon was due to the formation of liquid phase.

• Journal of the Korean institute of surface engineering
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• v.50 no.1
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• pp.42-45
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• 2017

The magnesium-base AZ61 alloy was cast while adding 1% CaO powder into the melt. It was hot extruded, and oxidized at $550-650^{\circ}C$ in air in order to study its microstructure and oxidation behavior. Initially added CaO powder reacted with Al in the melt to $Al_2Ca$ particles that aligned along the extrusion direction. The formed $Al_2Ca$ particles increased the oxidation resistance through forming the superficial CaO scale at the upper part of the thin MgO oxide scale.

• Journal of the Korean Ceramic Society
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• v.17 no.1
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• pp.20-26
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• 1980

The crystallization behaviors of slag-based glass in $CaO-MgO-Al_2O_3-SiO_2(-Na_2O)$ system have been studied. The mother glass containing 16.50 CaO, 7.50MgO, 19.70Al2O3, 50.80SiO3 and 2.09wt% $Na_2O$ was prepared by using Korean domestic raw materials such as granulated slag, serpentine, sea sand and etc. The glass-ceramics composed of major crystalline phase diopside was produced by the heat treatment in a temperature range from 850$^{\circ}$ to 9$25^{\circ}C$ for 0-6hr. The composition and morphology of diopside phase formed in the system were examined by X-ray diffraction analysis and electron microscopy. The kinetic measurements such as J.M. A plot and Arrhenius plot indicated that the process of nucleation of the initially formed diopside phase could be described from the view point of instantaneous nucleation. It was also demonstrated that the linear crystal growth of diopside phase was proceeded by short range diffusion of $Mg^{2+}$ and $Ca^{2+}$ ion. The microstructures of the resulting glass-ceramics were consisted of leafroidal shaped crystalline aggregations.

• Journal of Life Science
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• v.11 no.2
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• pp.153-158
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• 2001

To investigate the effects of soil acidification on growth of Impatiens balsamina L. plants were transplanted to acidified soils with H$_2$SO$_4$ solution. The concentrations of soluble Ca, Mg, K, Al and Mn in the acidified soils increased with increment of H$^{+}$ addition to the soil. In both species, the plant height and root length were inhibited by soil acidification, showing much severer inhibition in Impatiens balsamina L. than in Tagetes patula L., As the soil pH decreases, the growth of underground parts decreased greatly than that of above ground parts in both species. Total dry weight decreased with increased Al concentration as well as lowered soil pH in both plants. There was a strong positive correlation between relative total dry weight and molar (Ca+Mg+K) / Al ratio of the soil. The results suggest that molar(Ca+Mg+K)/ Al ratio of the soil may be useful indicator for assessing the critical load of acid deposition in herb species.s.