• 한국세라믹학회지
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• 제30권5호
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• pp.347-356
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• 1993

In joining alumina ceramics to metal by using Mo-Mn metallizing process the effects of metallizing thickness, temperature, and the composition of paste on the bond strength and the microstructure of joining interface were investigated. The bond strength variation in the range of metallizing temperature, 1350~155$0^{\circ}C$ was more than 150MPa above 145$0^{\circ}C$ and the optimum metallizing thickness was 30${\mu}{\textrm}{m}$. The optimum contents of Mn in Mo-Mn paste was 5% due to the bond strength decrease with the increase of addition. The effect of SiO2 addition in paste on bond strength was saturated around 200MPa. It was also observed that as the particle size of Mo decreased, the joinning with higher bond strength was shown in spite of low metallizing temperature.

• 한국세라믹학회지
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• 제35권3호
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• pp.264-272
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• 1998

The effect of catalytic condition on the properties of SiO2 aerogels has been investigated and then the dri-ed aerogels were partially densified to induce mechanical strength by heat treatment in order to prepare Type-VI silica by Sol-Gel method. Aerogel made by 1-step base process had the highest skeletal density lowest shrinkage and the smallest particle size. But in case of using acid catalyst in both 1st and 2nd step had the lowest skeletal density highest shrinkage and the largest particle size The aerogel synthesized by 1-step base process was most transparent because of its homogeneous microstructure. During heat treatments cracks occurred below 200$^{\circ}C$ for aerogel with the skeletal density lower than 1.9 g/cm3 but the with the higher skeletal density did not cracked up to 800$^{\circ}C$ shrinkage and skeletal density increased as heating temperature increased due to condensation and viscous sintering mechanism.

• 한국세라믹학회지
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• 제31권2호
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• pp.117-128
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• 1994

Hematite particles were obtained by hydrothermal reaction of ferric hydroxide in the presence of small amount of citric acid which is acted as crystal growth controller. The effects of hydrothermal reaction condition son the morphology and crystal structure of powder were investigated using X-ray, TEM and FT-IR. Ellipsoidal or rectangular hematite particles were formed in the range of pH 10.75~11.75 as initial basicity of reactants and 3$\times$10-5 ~9$\times$10-5 mol as citric acid content. Crystallization of hematite was inhibited in the range of pH9. 0~10.5 and above citric acid content of $1.5\times$10-4 mol. Hematite particle length and aspect ratio were decreased gradually with increasing of citric acid content. Hematite particles formed at 14$0^{\circ}C$ exhibited particle properties with the length of 0.7 ${\mu}{\textrm}{m}$ and aspect ratio of 8. Hematite particles having a good acicular-type were not obtained above 22$0^{\circ}C$.

• 한국세라믹학회지
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• 제23권2호
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• pp.31-37
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• 1986

The effect of dehydration temperature on the reduction process of silica-coated hematite was invest-igated The particle shape and magnetic properties of the products reduced from hematite at various conditions and the oxidation resistance of silica-coated iron powder were examined. It was revealed that single phase iron powder obtained over 45$0^{\circ}C$ had good magnetic properties. The iron powder manufactured between 45$0^{\circ}C$ and 50$0^{\circ}C$ displayed the maximum coercive force as a result of maintaining its acicular shaped. However the coercive force of iron powder reduced over 50$0^{\circ}C$ was decreased. The oxidation resistance of silica-coated iron powder in air was very good up to 11$0^{\circ}C$ and for 12 days.

• 한국세라믹학회지
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• 제16권2호
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• pp.99-105
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• 1979

Themogravimetric analysis was used to investigate the kinetics of the $Si_3N_4$ formation from Korean rice hulls in the temperature range from $1990^{\circ}C$ to $1370^{\circ}C$. The experimental results indicated that the reaction rate controlling step in the overall process is the diffusion of CO gas from the surface of carbon particle to main body of $N_2$ gas fluid through the stagnant gas film around the carbon particle. The kinetics followed a nearly linear rate law at the initil reaction stage. The activiation energy for the formation of $Si_3N_4$ from Korean rice hulls was 43.5Kcal/mole.

• 한국세라믹학회지
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• 제31권11호
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• pp.1378-1386
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• 1994

The characteristic of calcined BaTiO3 powder and sintered PTC ceramics was investigated varing with calcination temperature and time of BaTiO(C2O4)2.4H2O synthesized from BaCl2.2H2O, TiCl4, oxalic acid and ethanol by oxalic acid method. When the particle size was less than 0.1 ${\mu}{\textrm}{m}$ by controlling calcination temperature and time, the resistance at room temperature was measured very high (above M{{{{ OMEGA }}). However, when the calcined particle sizes ranged from 0.2 to 0.3 ${\mu}{\textrm}{m}$, the resistance was 100 {{{{ OMEGA }} (After sintering, the grain size was 10~30 ${\mu}{\textrm}{m}$ homogeneously with the addition of dopant in sintering, the resistivity, resistance, $\alpha$ value and jumped to were 110{{{{ OMEGA }}.cm, 24$^{\circ}C$/% and 106{{{{ OMEGA }}, respectively.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.814-817
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• 2003

The sintering behavior of $BaO-B_{2}O_{3}-ZnO$, which is Pb-free glass-ceramic system, was examined as functions of the composition and the amount and particle size of $Al_{2}O_{3}$ filler. Different kinds of modifiers were added and $Al_{2}O_{3}$ fillers with different particle sizes ($1.5{\mu}m$ and $4.5{\mu}m$) were added. The glass frit-filler composites were sintered in the temperature range $520{\sim}580^{\circ}C$. X-ray diffraction results revealed that some of the composites crystallized during sintering. Dielectric constant and thermal expansion coefficient the glass-ceramics were analyzed.

• 한국세라믹학회지
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• 제32권1호
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• pp.37-44
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• 1995

TiO2 fine powders were synthesized using oxygenolysis and hydrolysis reaction of TiCl4 vapor in gas phase. The TiO2 powder synthesized showed morphological differences depending on reaction system as follows: TiCl4-O2 reaction system produced the monosized particles having polyhedral shape with well-defined crystal planes and the particles did not agglomerate into secondary particles. TiCl4-H2O reaction system, whereas, produced the spherical secondary particles which consisted of fine primary particles. Other powder characteristics such as particle size, impurity content and rutile content are also reported in this study.

• 한국세라믹학회지
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• 제32권1호
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• pp.17-24
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• 1995

The TEA complex polymeric sol was prepared by the alkoxide sol-gel method. The purpsoe of this experiment was to vefity the particle shape in the sol from the investigation of the rheological properties. TEA retarded hydrolysis rate by the reaction with alkoxide enough to make a stable transparent sol in the wide range of composition. From the results of the viscosity change with time, the optimum mole ratio for spinning was selected as 0.5 mole of TEA, 3 mole of H2O and the optimum viscosity was 104 cPs. The rheological behavior of the sol showed that the particle shape in the sol was linear, which was adequate for fiber drawing.

• 한국세라믹학회지
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• 제27권2호
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• pp.265-273
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• 1990

Fine Si-Al-OH-C coprecipitate powders were prepared from Si(OC2H5)4, Al(i-OC3H7)3, and carbon black by a hydrolysis method before fabrication of Sialon-SiC composite powder by carbothermal reduction at 1350$^{\circ}C$ for 10h under N2/H2 mixed atmosphere. The characterization of the synthesized Sialon-SiC composite powders was performed using XRD, BET, SEM, TEM and particle size analysis methods. The average particle size and specific surface area of the synthesized Sialon-SiC composite powder were 0.13$\mu\textrm{m}$ and 20.1㎡/g, respectively when Z=1 and N2 : H2=50 : 50.