• 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.

• Resources Recycling
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• v.30 no.4
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• pp.27-34
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• 2021

In this study, the leaching behavior of vanadium (V) was investigated through CaO roasting and sulfuric acid leaching from domestic V-bearing titanomagnetite (VTM). Changes in the phase according to the amount of CaO added and roasting temperature were analyzed. Regardless of the roasting conditions, perovskite (CaTiO₃) was preferred to form. When the CaO content was increased, the calcium ferrite (CaFeO_x) phase was formed; otherwise, ferrite (Fe₂O₃) was preferred. After CaO was roasted, leaching was performed for 6 h with 1M sulfuric acid at 50℃ and a 10% solid-liquid ratio. Results of leaching revealed that when the roasted product was sintered, V was not sufficiently oxidized, and the leaching efficiency decreased. In addition, when the roasting temperature was low, the leaching efficiency of V decreased due to the influence of unreacted excess CaO. To lower the leaching efficiency of iron and titanium in VTM concentrates, suppressing the formation of CaTiO₃ and CaFeO_x was necessary by minimizing the amount of CaO added. Consequently, a leaching efficiency of 86% V, 4.3% Fe, and 6.5% Ti was obtained when the roasted product of 1150℃ and 10 wt% CaO was leached.

• Korean Journal of Materials Research
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• v.25 no.6
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• pp.269-273
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• 2015

The effect of adding Ca on the microstructural and mechanical properties of as-cast Mg-11Li-3Zn-1Sn(wt%) alloys were investigated. Mg-11Li-3Zn-1Sn-0.4Mn with different Ca additions (0.4, 0.8, 1.2 wt%) were cast under an $SF_6$ and $Co_2$ atmosphere at $720^{\circ}C$. The cast billets were homogenized at $400^{\circ}C$ for 12h and extruded at $200^{\circ}C$. The microstructural and mechanical properties were analyzed by OM, XRD, SEM, and tensile tests. The addition of Ca to the Mg-11Li-3Zn-1Sn-0.4Mn alloy resulted in the formation of $Ca_2Mg_6Zn_3$, MgSnCa intermetallic compound. By increasing Ca addition, the volume fraction and size of $Ca_2Mg_6Zn_3$ with needle shape were increased. This $Ca_2Mg_6Zn_3$ intermetallic compound was elongated to the extrusion direction and refined to fine particles due to severe deformation during hot extrusion. The elongation of the 0.8 wt% Ca containing alloy improved remarkably without reduction strength due to the formation of fine grain and $Ca_2Mg_6Zn_3$ intermetallic compounds by Ca addition. It is probable that fine and homogeneous $Ca_2Mg_6Zn_3$ intermetallic compounds played a significant role in the increase of mechanical properties.

• 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.

• BMB Reports
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• v.32 no.6
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• pp.561-566
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• 1999

CA(1-8)-ME(1-12) [CA-ME], composed of cecropin A(1-8) and melittin(1-12), is a synthetic antimicrobial peptide having potent antibacterial and antitumor activities with minimal hemolytic activity. In order to investigate the effects of the flexible hinge sequence, Gly-Ile-Gly, of CA-ME on antibiotic activity, CA-ME and three analogues, CA-ME1, CA-ME2, and CA-ME3, were synthesized. The Gly-Ile-Gly sequence of Ca-ME was deleted in CA-ME1 and replaced with Pro and Gly-Pro-Gly in CA-ME2 and CA-ME3, respectively. CA-ME1 and CA-ME3 showed a significant decrease in antitumor activity and phospholipid vesicle-disrupting ability. However, CA-ME2 showed similar antitumor and vesicle-disrupting activities, as compared with CA-ME. These results suggest that the flexibility or ${\beta}$-turn induced by Gly-Ile-Gly or Pro in the central part of CA-ME may be important in the electrostatic interaction of the N-terminus cationic ${\alpha}$-helical region with the cell membrane surface and the hydrophobic interaction of the C-terminus amphipathic ${\alpha}$-helical region with the hydrophobic acyl chains in the cell membrane. CA-ME3 exhibited lower antitumor and vesicle-disrupting activities than CA-ME and CA-ME2. This result suggests that the excessive ${\beta}$-turn structure caused by the Gly-Pro-Gly sequence in CA-ME3 seems to interrupt ion channel/pore formation in the lipid bilayer. We concluded that the appropriate flexibility or bilayer. We concluded that the appropriate flexibility or ${\beta}$-turn structure provided by the central hinge is responsible for the effective antibiotic activity of the antimicrobial peptides with the helix-hinge-helix structure.

• Korean Journal of Materials Research
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• v.2 no.3
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• pp.207-212
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• 1992

The defect structure of calcium titanates with CaO excess or $TiO_2$ excess was studied by measuring electrical conductivities as a funcition of oxygen partial pressure at $85O^{\circ}C$ to $1050^{\circ}C$. Execess CaO may divide itself equally between A and B sites, resulting in $Ca_{Ti}$" and Vo", while excess $TiO_2$ form $V_{Ca}$" and Vo". The equilibrium electrical conductivity data indicate that the solubilities of CaO and $TiO_2$ in $CaTiO_3$ are 5000ppm and 2000ppm, respectively. Oxygen vacancies contributed to the ionic conduction which flatten the conductivity minima and did not make any defect association with oppositely charged defects.ely charged defects.

• Journal of Nutrition and Health
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• v.44 no.6
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• pp.474-480
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• 2011

Calcium (Ca) is an essential element to maintain body homeostasis. However, many factors disturb calcium absorption. Aspartic acid chelated calcium (AAC) was synthesized by new methods using calcium carbonate and aspartic acid. This study was carried out to investigate the bioavailability of AAC in Ca-deficient rats. The experimental groups were as follows: NC; normal diet control group, CD-C; untreated control group of Ca-deficient (CD) rats, CD-$CaCO_3$; $CaCO_3$ treated group of CD rats, CD-AAC; AAC treated group of CD rats, and CD-SWC; and seaweed-derived Ca treated group of CD rats. The Ca content of various types of Ca was held constant at 32 mg/day, and the four CD groups were fed for 7 days after randomized grouping. Ca content in serum, urine, and feces within feeding periods were analyzed to confirm Ca absorption. Serum Ca content was significantly higher in the CD-AAC (11.24 mg/dL) and CD-SWC (10.12 mg/dL) groups than that in the CD-C (8.6 mg/dL) group 2 hours following the first administration. The Ca content in feces was significantly lower in the CD-AAC (35.4 mg/3 days) and CD-SWC (71.1 mg/3 day) groups than that in the CD-$CaCO_3$ (98.7 mg/3 days) group (p > 0.05). AAC had a 2.3-fold higher absorption rate of Ca than that of SWC. No differences in fibula length were observed in the NC and CD groups. The fibula weights of the CD-AAC (0.33 g) and CD-SWC (0.33 g) groups increased compared to those in the CD-C (0.27 g) group; however, no significant difference was observed between the CD groups. We conclude that bioavailability of AAC is higher than that of seaweed-derived Ca or inorganic Ca. Thus, these findings suggest the AAC has potential as a functional food material related to Ca metabolism.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.399-402
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• 2000

For improvement of B constant in $CaMnO_3$-$CaTiO_3$ perovskite type thermistors, effect of $Cr_2$$O_3$ addition ranged from 0.0wt% to 5.0wt% on electrical properties were investigated with contents and sintering temperatures in the view of crystal and microstructures. The solubility limit of Cr$_2$O$_3$was up to 0.5wt% judging from the result of lattice parameter. The grain size was decreased and the resistance at room temperature and B constant were increased with the addition of $Cr_2$$O_3$.On particular, B constant of$CaMnO_{3-x}$$Cr_2$$O_3$ system was increased greatly from 1574k to 2598k at 0.5wt% $Cr_2$$O_3$addition. Further addition of $Cr_2$$O_3$, however, resulted in the decrease of the resistance and B constant due to the $Cr_2$$O_3$ precipitation on the grain boundary. As the$CaTiO_3$contents increased in the $CaMnO_3$-$CaTiO_3$ system, the resistance at room temperature and B constant were highly changed.

• Resources Recycling
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• v.15 no.5 s.73
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• pp.47-51
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• 2006

The total amount of ash generated from the municipal solid waste incineration(MSWI) in Korea was approximately 420,000 tons in 2005 including 68,000 tons of fly ash. Fly ash from MSWI generally contains high amount of CaO (upto ${\sim}50%$) due to the treatment of flue gas by spraying CaO-base materials. Currently, most of fly ash generated is finally ended up with specially designed landfill sites and only less then 20% of fly ash is recycled. In the present work, preparation of $CaCO_3$ from the MSWI ny ash was studied to promote the fly ash recycling. Fly ash obtained from the dust collector in stoker-type MSWI is used to selectively dissolve CaO by using the sugar solution. Then, $CO_2$ gas was passed through the dissolved solution to pro- duce $CaCO_3$ powder. The optimum conditions for CaO dissolution were solid content 10%, reaction time 15 minutes, sugar concentration $10{\sim}15%\;and\;pH\;10.5{\sim}11.0$. The high grade $CaCO_3$ powder was obtained and the experimental conditions are also discussed.

• Journal of the Korean Ceramic Society
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• v.30 no.8
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• pp.635-642
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• 1993

To obtain a higher dielectric constant material, we investigated Ca substitution for Pb in PbZrO3. In this study, the four mixtures of (Pb0.68Ca0.32)ZrO3, (Pb0.65Ca0.37)ZrO3, (Pb0.63Ca0.37)ZrO3, and (Pb0.60Ca0.40)ZrO3 were prepared by coprecipitation reaction of Pb(NO3)2, ZrOCl2, and CaCl2 with (NH4)2CO3 and NH4OH in aqueous solution. The (Pb1-xCax)ZrO3 with different x mole fractions (x=0.35, 0.37) showed not only high dielectric constant, but also high Q values and low temperature coefficient of the capacitance.