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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korean Ceramic Society
Journal Basic Information
Journal DOI :
The Korean Ceramic Society
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Volume & Issues
Volume 27, Issue 8 - Aug 1990
Volume 27, Issue 7 - Jul 1990
Volume 27, Issue 6 - Jun 1990
Volume 27, Issue 5 - May 1990
Volume 27, Issue 4 - Apr 1990
Volume 27, Issue 3 - Mar 1990
Volume 27, Issue 2 - Feb 1990
Volume 27, Issue 1 - Jan 1990
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Composite Powders by the Use of Emulsions(IV) : Emulsion-Spray Pyrolysis Method
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 955~964
A new process of emulsiion-spray pyrolysis for synthesizing ceramic powders was developed and the characteristics of Al2O3-20w/o ZrO2 composite powders prepared by this method were investigated. The composite powders synthesized in this study were spherical dense particles with 0.1~0.4
of diameter. As found in powders derived by the emulsion-hot kerosene drying method, all zirconia in Al2O3-20w/o ZrO2 powders heat-treated at 120
was in the tetragonal form at room temperature. The relative density and the fracture toughness of composites sintered at 1
for 4hrs were 95% and 5.2MPa.m1/2, respectively.
Nitrogenation of Coal Ash in the Presence of Carbon and Product Distributions of AlN, SiC and Si₃N₄
양현수 ; 홍원표 ; 노재성 ; 서동수 ; 손응권 ;
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 956~956
A nitrogenation of coal ash in the presence of carbon was carried out to examine the effects of reaction temperature, reaction time and carbon composition on the formation of AlN, SiC and Si3N4. Decreasing the particle size increased the formation of AlN and its maximum composition in the product was obtaiend under 1450∼1500℃, 2 hours of reaction time and about 30% of carbon addition(on the basis of sample weight). Compositions of SiC and Si3N4 were distributed to the opposite so that SiC showed a higher composition compared with Si3N4 at a lower temperature, a shorter reaction time and a greater carbon addition.
Nitrogenation of Coal Ash in the Presence of Carbon and Product Distributions of AlN, SiC and
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 965~970
A nitrogenation of coal ash in the presence of carbon was carried out to examine the effects of reaction temperature, reaction time and carbon composition on the formation of AlN, SiC and Si3N4. Decreasing the particle size increased the formation of AlN and its maximum composition in the product was obtaiend under 1450~150
, 2 hours of reaction time and about 30% of carbon addition(on the basis of sample weight). Compositions of SiC and Si3N4 were distributed to the opposite so that SiC showed a higher composition compared with Si3N4 at a lower temperature, a shorter reaction time and a greater carbon addition.
The Isothermal Phase Transformation by Low Temperature Aging in Y-TZP Powders
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 971~978
The ifluence of transformability and stabilized effects in tetragonal phase on the isothermal phase transformation of Y-TZP at low temperature were investigated. The transformability of Y-TZP powders were gradually increased with calcination temeprature and reached maximum at critical temperature, but when the Y-TZP powders were calcined above critical temperature, transformability of Y-TZP were gradually decreased with increasing calcination temperature. It was concluded that maximum transformability was appeared because particle size effects decreased and constrain effects increased with calcined temperature. The isothermal phase transformation during aging at 25
only observed in Y-TZP stabilized by constrain effects and the amounts of transformation during aging at 25
only observed in Y-TZP stabilized by constrain effects and the amount of transformed monoclinic phase during aging decreased with increasing constrain effects. From these results, the mechanism of isothermal phase transformation and degradation behaviors at low temperature in Y-TZP was concluded that occurred by decreasing of constrain effects due to stress relaxation at grian boundary.
Effect of Substitution of MgO for CaO on the Bioglass Structure, Properties and Hydroxyapatite Formation
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 979~990
The possible use of bioglass as implant materials is due to its biocompatibility to human body. Even if many animal studies for the bioglasses have been performed, their structures and physical properties are not fully understood. In the present work, several investigations such as Raman spectroscopic analysis, density, thermal expansion coefficient, softening temperature, and refractive index measurement were carried out to find the structures and physical properties of bioglasses, where MgO is substituted for CaO in bioglass composition (46.1%SiO2, 24.4%Na2O, 26.9%CaO, 2.6%P2O5 ; mole%). Hydroxyapatite formation on the glass surface reacted in Tris-buffer solution was also examined. When CaO was replaced by MgO, nonbridging oxygen in glass structuer was diminished but the degree of disorder increased. Thermal expansion and softening properties showed the mixed oxide effect. Hydroxyapatite were formed on the surface of 0~11mole% of MgO containing bioglasses, and the thickness of SiO2-rich layer as well as hydroxyapatite layer were unchanged with MgO content. However, the hydroxyapatite was not formed on the surface of the bioglasses containing over 11 mole percent MgO, even if the glasses were reacted for long period.
Microstructures and Mechanical Properties of
Ceramics Prepared by a Precipitation Method
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 991~1003
A precipitation method, one of the most effective liquid phase reaction methods, was adopted in order to prepare high-tech Al2O3/ZrO2 composite ceramics. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent, various types of metal hydroxides were obtained by single precipitation(series A) and co-precipitation(series B) method at the pH condition between 7 and 11. Fine Al2O3-ZrO2 powders were prepared at optimum calcination condition and the effects of ZrO2 on microstructures and mechanical properties of Al2O3 were investigated. The composition of Al2O3/ZrO2 composites wax fixed as Al2O3-15 v/o ZrO2(＋3m/o Y2O3). ZrO2 limited the grain growth of Al2O3 and increased grain size homogeneity of Al2O3 more effectively than MgO.Flexural strength values in Al2O3 and Al2O3/ZrO2 composites were 340-430 MPa and 540-820 MPa, respectively, and the effect of strength improvement showed 20-50% by adding ZrO2 to Al2O3. Fracture toughness of Al2O3/ZrO2 composites was improved by stress-induced phase transformation of tetragonal ZrO2 and toughening effect by microcrack was not observed. Also, ZrO2 particles located at Al2O3 grain junction contributed to toughening, while spherical ZrO2 particles located within Al2O3 grain did not contribute to toughening. Weibull moduli of Al2O3 ceramics and Al2O3/ZrO2 composites of series A and series B were 4.34, 5.17 and 9.06, respectively. Above 0.5 of failure probability, strength values in Al2O3 ceramics and Al2O3/ZrO3 composites of series A and series B were above 400 MPa, 700 MPa and 650 MPa, respectively.
Dependency of SnO2 System Carbon Monoxide Gas Sensor on the Atmospheric Temperature & Humidity
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 1004~1010
SnO2-ThO2-PdCl2-In2O3 gas sensing ceramic systems were studied in order to lowr the operating temperatures and reduce the dependence of ambient temperatures and humidities. Sensing materials were coated by brush on the alumina tube followed by the impregnation of solidfier(ethylsilicate). Coated species were dried and sintered at 75
for 30min. carbon monoxide gas detecting sensitiviteis were measured in various ambinet temperatures and humidities. In the composition of 94SnO2-5ThO2-PdCl2 system carbon monoxide gas detecting sensors showed the highest detecting sensitivities and the lowest operating temperature(15
). As the ambient temperatures and humidities were increased, sensitivities were decreased. Because the oscillation effects were observed at high humidities, it was suggested that the sensitivities of sensors depend greatly on the humidities.
A Study on the Preparation of Alumina Powders from Bauxite by Wet Acid Process and Their Utilization (II) : Mullitization of Pyrophyllite-Aluminum Hydrate Gel Mixture
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 1011~1019
Pyrophyllite, which has low impurities, was used in the synthesis of mullite to decrease the glass phase, which can be formed from impurities such as alkali and alkali earth elemetns present in raw materials. But, as pyrophyllite has less alumina content than other aluminosilicate materials such as kaolin, more alumina sources were needed in the synthesis of mullite. In other to investigate the effect of particle size of alumina sources on the mullitization of pyrophyllite, aluminum hydrate gel and activated alumina were used. When activated alumina, which has large particle size, was added to pyrophyllite, mullitization was not fully accomplished regardless of temprature. In the case of aluminum hydrate gel, which has small particle size, the maximum yield of mullite was about 90.3% at 1700
, and grain size of mullite was larter than the case of activated alumina was added.
Effect of heating Rate on the Microstructural Evolution during Sintering of PZT Ceramics
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 1020~1026
The effect of heating rate on the microstructural evolution during sintering of PZT ceramics has been investigated. In case of PZT powder compacts containing excess of PbO, fast heating caused incomplete rearrangement of solid grains in a liquid, resulting in lower density and inhomogeneous pore shape ; on contrary, slow heating resulted in better densification. In contrast, in case of compacts without excess PbO, the densification was enhanced by fast heating due to suppression of the grain growth.
Effects of Chemical Inhomogeneity on Phase Coexistence in Pb(Zr, Ti))
Ceramics at Morphotropic Tetragonal and Rhombohedral Phase Boundary
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 1027~1033
In order to identify the origin of phase coexistence at morphotropic tetragonal and rhombohedral boundary in PZT ceramics, the effect of chemical inhomogeneity on phase coexistence region was investigated. Two kinds of PZT ceramics with different chemical homogeneity were prepared by conventional solid state reaction and co-precipitation method. There was coexistence of tetragonal and rhombohedral phase over a wide composition range in PZT ceramics calcined by solid state reaction, and there was also phase coexistence of which region was reduced considerably in sintered samples. And phase coexistence region was not observed in co-precipitated PZT ceramics(within 1 mole%). Therefore compositional fluctuation is considered to be major origin of the phase coexistence at morphotropic phae boundary in PZT ceramics.
Effect of Microstructure on the Prooperties of High Strength Hardened Cement Paste (II)
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 1034~1042
Investigation for the preparation of high strength hardened cement paste using ordinary portland cement, hydroxypropyl methyl cellulose(HPMC) with various admixtures was carried out. The cement paste was mixed with 0.1 of water cement ratio by twin roll mill and cured 60 days in humidity chamber. When the quartz powder or white cement was added to the paste, the flexural strength was 900∼1000kg/㎠ and the Young's modulus was 8∼9×105kg/㎠. When the silicafume was added, the flexural strength was 800kg/㎠ and the Young's modulus was 6×105kg/㎠.
Application of Weifull강s Theory to Evaluation of Strength for Ceramic Fibers
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 1043~1049
In this work, strength of ceramic fibers and monofilament composites were evaluated on the basis of Weibull's theory. The fibers used were β-SiC and γ-Al2O3 monofilament composites was fabricated by coating Al on the fiber surface by the use of vacuum evaporation method. Average tensile strength of ceramic fibers showed the tendency to linearly decrease with increasing gauge length. Also, Weibull moduli of ceramic fibers were decreased with increasing gauge length, Weibull modulus of β-SiC was 3.5 for 6-50mm, 2.8 for 100-200mm. Weibull modulus of γ-Al2O3 was 6.5 for 20-50mm, 6 for 100mm. Fibers in monofilament retained their original as-produced strength to exposure temperature of 400℃. However, tensile strength of both monofilament composites approved to remarkably degrade due to interfacial reaction-induced flaws on the fiber surface after thermal exposure of 600℃. In this case, Weibull modulus of monofilament composites was 2.7 for β-SiC and 5.2 for γ-Al2O3 respectively.
Growth of Rutile Single Crystal by Floating Zone Method
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 1050~1054
Rutile(TiO2) single crystals were grown by FZ method. Feed rod was sintered in the longitudinal tube-shaped furnace at 135
and optimum growth condition was growth rate 5-8mm/hr, rotation rate 30-40rpm. When crystal was growing, atomosphere was oxidized condition, and grown single crystal was annealed at 110
. The rutile single crystals were oriented to  direction and color change of single crystals were related to atmosphere, and difference of electric conductivity and resistance was due to the fact above.
The Early Hydration Characteristics of the System
(I) : Effect of Clinker Composition Variations
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 1055~1063
The early hydration characteristics of the system C3S-C3A-C4AF according to the clinker composition variations, in order to establish the mutual interactionof clinker minerals during the portland cement hydration, have been studied. The early hydration rate of C3S was greatly effected by the change of C3S/C3A ratio. The lower the C3S/C3A ratio was, the faster the apex reaching time and the rate of heat liberation of the 2nd exothermic peak originating from the formation of Ca(OH)2 were. The effect of C3S/C3A ration on the amounts of Ca(OH)2 formation was decreased, in process of hydration time, but the effect of C3S content was increased.
Preparation of Spherical Monodispersed
Fine Powders by Metal Alkoxide Method
Journal of the Korean Ceramic Society, volume 27, issue 8, 1990, Pages 1064~1070
ZrO2 fine powders were prepared by hydrolysis, adding 0.1, 0.2, 0.3, 0.4, 0.5, 0.6mol/1H2O/ethanol to 0.1 mol/l Zr(OC3H7)4/ethanol. When hydrolized by adding 0.1mol/l Zr(OC3H7)4/ethanol to 0.1, 0.2mol/l H2O/ethanol., spherical monodispersed ZrO2 fine powders were obtained. And in this condition average sizes were about 0.5, 0.3
, respectively. The more H2O/ethanol concentration increased, the more the particle size decreased and the particles were agglomerated strongly. Prepared powders were amorphous and hydrates. The calcined powders with 43
were showed tetragonal and monoclinic phase, respectively.