• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.3
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• pp.291-298
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• 1995

Abstract The growth and dissolution behaviour of reaction phase was studied during dissolution reaction between sintered alumina and $CaMgSiO_4$ at $1600^{\circ}C$ for various times. The formation of $CaO{\cdot}6Al_2O_3$ an intermediate reaction phase, and $CaMgSiO_4$ spinel, the final reaction product were observed during dissolution reaction of alumina into $CaMgSiO_4$ liquid phase. The growth and dissolution shape of $CaO{\cdot}6Al_2O_3$, an intermediate phase, was quite different.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.799-807
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• 1990

In this study, effects of oxide additives on mechanical properties and microstructure of A1N and A1N polytype ceramics were investigated. Fine A1N powder was synthesized by nitriding alumiuim hydroxide prepared from Al-isopropoxide, at 1350$^{\circ}C$ for 10h in N2 atmosphere. By adding 3w/o Y2O3, 0.56w/o CaO, and 10w/o SiO2 to AlN powder, AlN and AlN polytype ceramics were prepared by hot-pressing under the pressure of 30 MPa at 1800$^{\circ}C$ for 1h. AlN ceramics with no additives formed considerable amount of AlON phase, while AlN ceramics doped with Y2O3 or CaO decreased AlON phase and formed Y-Al or Ca-Al oxide compound. AlN＋10w/o SiO2(＋3w/o Y2O3) composition produced AlON and AlN polytype compound having 21R as a major phase. Room temperature flexural strength of AlN ceramics with no additive was 246MPa, and room temperature flexural strength and critical temperature difference by thermal shock(ΔTc) of AlN ceramics dooped with Y2O3 or CaO were 532MPa/340$^{\circ}C$ and 423MPa/300$^{\circ}C$, respectively. Y2O3 and CaO used as sintering agent played roles of densification and oxygen removal of AlN ceramics, and affected grain growth/grain morphologies of AlN ceramics.

• Journal of the Korean Ceramic Society
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• v.19 no.1
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• pp.13-18
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• 1982

The crystallization of metastable "orthorhombic" phase from the glass in the system of Na $AlSi_3O_8-CaAl_2Si_2O_8$ is studied. These crystals are crystallized in the range of composition from $Ab_80An_20$ to An100. The symmetry of these crystals show orthorhombic as a possible space group P22121. Two probable twin models are proposed. proposed.

• Journal of the Korean Ceramic Society
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• v.44 no.9
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• pp.471-476
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• 2007

The hydration mechanism of the $3CaO{\cdot}Al_2O_3-CaSO_4{\cdot}2H_2O$ system in the presence of alkali sulfates has been investigated. The early hydration rate of $3CaO{\cdot}Al_2O_3$ was accelerated by the addition of $Na_2SO_4$ and $K_2SO_4$. This is closely related to the formation of syngenite $(CaSO_4{\cdot}K_2SO_4{\cdot}H_2O)$, and the U-phase added $K_2SO_4$ and $Na_SO_4$ in the $3CaO{\cdot}Al_2O_3-CaSO_4{\cdot}2H_2O$ system, respectively. The formation of the rigid syngenite and U-phase structure led to rapid setting and decreases the sulfate content in the liquid phase of the hydrating cement to the extent that it cannot adequately retard the hydration of $3CaO{\cdot}Al_2O_3$. In case of the alkali sulfate not added to the $3CaO{\cdot}Al_2O_3-CaSO_4{\cdot}2H_2O$ system, the ettringite was transformed to monosulfoaluminate immediately after the consumption of gypsum. However, when the alkali sulfates were added to this system, the ettringite did not transform to monosulfoaluminate immediately even though the gypsum was completely consumed. There was a stagnation period to transform to the monosufoaluminate after the consumption of gypsum because the syngenite and U-phase remained as the sulfate source.

• Korean Journal of Materials Research
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• v.16 no.2
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• pp.92-98
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• 2006

Molecular dynamics simulations were performed to study interface structures between an $Al_2O_3$ crystalline phase and a interface phase of $CaAl_2Si_2O_8$. We calculated atomic structures and excess interface energies in systems with different thicknesses of the interface film. It was found that excess interface energies at first readily decreased with increasing film thickness, but increased for larger thicknesses of more than 2 nm. The excess energies of $Al_2O_3/CaAl_2Si_2O_8$ interfaces exhibit a minimum at a thickness around 1 nm. In this range of film thicknesses, the atoms in the interface film show a short-range ordered structure and slow diffusion rather than the random structure and rapid diffusion expected to an observation of an equilibrium thickness for interface films in ceramics.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.2
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• pp.53-59
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• 2021

Due to high specific strength and low density, AZ series magnesium alloys have been receiving high interest as a lightweight material. However, their industrial application is limited due to the phenomenon that the strength decreases at elevated temperature by the occurrence of softening effect because of the Mg17Al12 phase decomposition. To solve this problem, many research were conducted to increase the high-temperature strength by forming a thermal stable second-phase component by adding new elements to the AZ magnesium. Especially, adding Ca to AZ magnesium has been reported that Ca forms the new second-phase. However, studies about the analysis of decomposition or precipitation temperature, formation composition, and components to understand the formation behavior of these precipitated phases are still insufficient. Therefore, the effect of Ca addition to AZ61 on the phase change and microstructure of the alloy during annealing was investigated. As a result of analysis of the initial and heat-treated specimen, AZ61 formed α-Mg matrix and precipitated phase of Mg17Al12, and AZX611 formed one more type of precipitated phase, Al2Ca. Also, Al2Ca was thermal stable at high temperatures. And after annealing, the laves phase was decomposed to under 10 ㎛ size and distributed in matrix.

• Journal of the Korean Ceramic Society
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• v.36 no.4
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• pp.410-416
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• 1999

The reactivity of three kinds of spinels which CaO-Al2O3-SiO2 slag was investigated in terms of mineral phases and microstructures. New crystal products were not formed by reaction of 12CaO.7Al2O3 in the slag with spinels and free MgO components was preferenctially dissolved into slag for MgO-rich spinel and stoichiometric spinel. Meanwhile mineral phase was changed from 12CaO.7Al2O3 to CaO.Al2O3 to CaO.2Al2O3 finally to CaO.6Al2O3 having high melting point for Al2O3 -rich spinel. The Fe-oxide component of the slag was taken up by only stoichiometric spinel grains within the spinel clinker and the trapped amount of Fe-oxide was independent of MgO content of MgO in spinel clinker the more th resistance to slag corrosion but the less resistance to slag penetration.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.5
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• pp.397-404
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• 2009

Effects of ceramic filler types and dose on the low temperature sintering and dielectric properties of ceramic/$CaO-Al_2O_3-SiO_2$ (CAS) glass composites were investigated. All of the specimens were sintered at $850{\sim}900^{\circ}C$ for 2 h, which conditions are required by the low-temperature co-firing ceramic (LTCC) technology. Ceramic fillers of $CaCO_3$, $Al_2O_3$, $CaCO_3-Al_2O_3$ mixture, and $CaCO_3-Al_2O_3$ compound ($CaAl_2O_4$), respectively, were used. The addition of $Al_2O_3$ yielded the crystalline phase of alumina, which was associated with the inhibition of sintering, while, $CaCO_3$ resulted in no apparent crystalline phase but the swelling was significant. The additions of $CaCO_3-Al_2O_3$ mixture and $CaAl_2O_4$, respectively, yielded the crystalline phases of alumina and anorthite, and the sintering properties of both composites increased with the increase of filler addition and the sintering temperature. In addition, the $CaAl_2O_4$/CAS glass composite, sintered at $900^{\circ}C$, demonstrated good microwave dielectric properties. In overall, all the investigated fillers of 10 wt% addition, except $CaCO_3$, yielded reasonable sintering (relative density, over 93 %) and low dielectric constant (less than 5.5), demonstrating the feasibility of the investigated composites for the application of the LTCC substrate materials.

• Journal of Korea Foundry Society
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• v.34 no.6
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• pp.187-193
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• 2014

In the present work, the effect of adding Ce on the corrosion behavior of Mg-4Al-2Sn-1Ca alloy was investigated. The studied alloys were fabricated by gravity casting method and a potentiodynamic polarization, A.C. impedance and hydrogen evolution tests were carried out in a 3.5% NaCl solution with pH 7.2 at room temperature to measure the corrosion properties of Mg-4Al-2Sn-1Ca-xCe alloys. The microstructure of the Mg-4Al-2Sn-1Ca alloy was composed of ${\alpha}$-Mg, Mg17Al12, Mg2Sn and CaMgSn phase. Also, a $Al_{11}Ce_3$ phase was newly formed by the addition of Ce. With an increase of the Ce contents, the microstructure became refined and the corrosion resistance improved.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.1-4
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• 2008

The phase transformations and luminescent properties of Eu-doped $Ca_{1-x}Sr_xAl_2O_4$ phosphors were investigated. $Ca_{1-x}Sr_xAl_2O_4:Eu^{2+}$ phosphors were synthesized by a solid-state reaction with a flux, $H_3BO_3$. A phase transformation from monoclinic $CaAl_2O_4$ to monoclinic $SrAl_2O_4$ was observed as the x values increased. A high-temperature hexagonal phase of $SrAl_2O_4$ was formed during this transformation as an intermediate phase under an $H_2$ atmosphere due to oxygen vacancies; this did not occur in an air atmosphere. Accordingly, the emission spectra shifted from a blue region to a green region as x increased.