• Transactions on Electrical and Electronic Materials
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• 제7권6호
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• pp.279-282
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• 2006

[ $Pb(Zr_{0.4}Ti_{0.6}O_{3}\;and\;Pb(Zr_{0.6}Ti_{0.4})O_{3}$ ] paste were made and alternately screen-printed on the $Al_{2}O_{3}$ substrates. We have introduced a press-treatment to obtain a good densification of screen printed films. The porosity of the thick films was decreased with increasing the applied pressure and the thick films pressed at 60 MPa showed the dense microstructure and thickness of about $76\;{\mu}m$. The remanent polarization and coercive field increased with increasing applied pressure and the values for the PZT thick films pressed at 60 MPa were $17.04{\mu}C/cm^{2}$ and 78.09 kV/cm, respectively.

• 한국세라믹학회지
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• 제34권9호
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• pp.915-920
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• 1997

Tetragonal ZrO2 polycrystal (TZP), consisted of 90.24 mol% ZrO2-5.31 mol% Y2O3-4.45 mol% Nb2O5, were prepared using hot-press and mechanical properties and high-temperature degradation were investigated. The specimen, hot-pressed for 1 h at 140$0^{\circ}C$ in Ar atmosphere, exhibited flexural strength of 1010 MPa and fracture toughness of 7.5 MPam1/2 and experienced no low-temperature degradation below 40$0^{\circ}C$. However, as aged for 100h at temperatures higher than 40$0^{\circ}C$, TZP was suffered by high-temperature degradation due to an extensive cavitation caused by the oxidation of carbon. XPS observation revealed that the carbon incorporated in TZPs during hot-pressing exists as either an ether-type CO or a carbonyl-type C=O. Despite of the high-temperature degradation of t-ZrO2 co-doped with Y2O3 and Nb2O5, its flexural strength and fracture toughness were superior to those of the commercial 3 mol% Y2O3-TZP hot-pressed under the identical condition as determined before and after the aging treatments.

• 한국세라믹학회지
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• 제29권5호
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• pp.410-418
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• 1992

Si3N4, AlN and Y2O3 powder mixtures of the Y0.1(Si, Al)12(N, O)16 composition were hot-pressed at 1900℃ for 0 to 60 min under 30 MPa in order to fabricate the partially-stabilized α-Sialon ceramics (X=0.1). Room and high temperature flexural strengths of the specimens were compared with those of Si3N4-5 wt%Y2O3, Si3N4-5 wt%Y2O3-2 wt%Al2O3, and β-Sialon (Z=0.5) ceramics. The flexural strength of the α-Sialon ceramics which was hot-pressed for 15 min showed the highest value of 820 MPa at 1400℃ that is relatively higher temperature. It is guessed that a little amount of glassy phase existed in grain boundary because Y2O3 and AlN components were incoperated in Si3N4 grains, or transient liquid phase sintering, and microstructure with the smaller grain size and the interlocked grains of α'-and β-Si3N4 was obtained by the hot-pressing at high temperature of 1900℃ for the short time (15 min).

• 한국세라믹학회지
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• 제31권12호
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• pp.1513-1520
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• 1994

Mechanical properties of hot-pressed SiC whisker/Al2O3 composites were strongly dependent on the granular characteristics of mixed powder, which were controlled by co-dispersion condition, the existence of steric barrier on whisker surface, and granulating method, etc. Heat-treatment of SiC whiskers at $700^{\circ}C$ for 1 hr in air was very effective both for achieving dispersion stability of whiskers with PVA adsorption and for obtaining excellent mechanical properties of resulting composites. It is believed from the fractography of composites prepared with various whisker dispersion conditions that the most common fracture origin of Al2O3 agglomerate could be attributed to whisker clusters arising due to flocculation. Further improvement of mechanical properties of composites were achieved by hot pressing green tapes prepared by Doctor-blade process, which promoted two-dimensional random alignment of whiskers.

• 한국세라믹학회지
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• 제27권3호
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• pp.394-400
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• 1990

Mullite and cordierite were prepared by the sol-gel route. Boehmite, fumed silica and Mg(NO3)2$.$6H2O were their starting materials. Mullite and cordierite powder were mixed by various weight percent. These mixed sols were ball-milled for 48hrs, dried at 100$^{\circ}C$, pressed, cold isostatic pressed and sintered at 1490$^{\circ}C$ for 2hrs. Mullite-cordierite composites sintered at 1490$^{\circ}C$ for 2hrs had>98% of theoretical density. Bending strength of the sintered bodies were 329-249MPa, dielectric constant 7.1-6.7 at 1MHz and thermal expansion coefficient at 800$^{\circ}C$ was matched with Si in the range of 30-35wt% cordierite.

• 한국세라믹학회지
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• 제32권8호
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• pp.865-872
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• 1995

Ultra-fine $\beta$-SiC powders were fabricated by self-propagating high temperature synthesis process (SHS) using microwave oven. The flexural strength, fracture toughness, and hardness of hot pressed sample at 200$0^{\circ}C$ for 60 min using synthesized SiC powders, which had 2 wt% of Al2O3 and 2.5 wt% of B4C content, showed 438 MPa, 4.15MPa.m1/2 and 28 GPa, respectively. The highest strength, fracture toughness, and hardness of composites containing 4wt% of Al2O3, which had highest relative density of 99.9%, showed 458 MPa, 4.6MPa.m1/2 and 36.2 GPa, respectively.

• 한국세라믹학회지
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• 제37권2호
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• pp.158-163
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• 2000

Six different SiC ceramics with SiO2-Re2O3 (Re=Yb, Er, Y, Dy, Gd, Sm) as sintering additives have been fabricated by hot-pressing the SiC-Re2Si2O7 compositions at 1850$^{\circ}C$ for 2 hr under a pressure of 25 MPa. The room temperature strneth and the fracture toughness of the hot-pressed ceramics were characterized and compared with those of the ceramics sintered with YAG (Y3Al5O12). Five SiC ceramics (Re=Yb, Er, Y, Dy, Gd) investigated herein showed sintered densities higher than 94% of theoretical. Tthe SiC-Re2Si2O7 compositions showed lower strength and comparable toughness to those from SiC-YAG composition, owing to the chemical reaction between SiO2 and SiC during sintering. SiC ceramics fabricated from a SiC-Y2Si2O7 composition showed the best mechanical properties of 490 MPa and 4.8 MPa$.$m1/2 among the compositions investigated herein.

• 한국세라믹학회지
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• 제33권2호
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• pp.135-142
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• 1996

Fly Ashes which are produced from coal-fired powder plants and classified as general waste can be used as raw materials for bricks and tiles because of their compositional similarity with clays. There was a limit of substituting fly ash for clay because plasticity decreased with increasing fly ash additions. Accordingly this study tried to suggest a feastibility of enhancing the substitution ratio by controlling the interfacial properties of fly ash. The slip with 1:1 volume ratio showed that best dispersive characteristics under the condition of pH 2 Filter pressed cakes made of pH 2 slips also showed better plastickity than those of untreated ones. of pH 2 Filter pressed cakes made of pH 2 also shwoed better plasticity than those of untreated ones.

• 한국세라믹학회지
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• 제24권2호
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• pp.139-146
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• 1987

${\beta}$-SiC powders were prepared by the simultaneous reduction and carbiding of Jecheon quartzite at 1400$^{\circ}C$ for 7 hours in hydrogen atmosphere, using graphite or carbon black as the reducing and carbiding reagent. The prepared SiC powder was acid-treated with the mixture of fluoric acid and hydrochloric acid at room temperature and also by heating on an alcohol lamp for one hour, respectively. The impurities were mostly eliminated and the purity of SiC became 98.5% after hot acid treatment. The specific surface area of SiC powder was also increased up to 115㎡/g by hot acid treatment. This pure and fine SiC powder was hot-pressed at 1900$^{\circ}C$ for 30min, using 5wt% Al2O3 as a sintering aid. The density, M.O.R., KIC and hardness of the hot-pressed SiC ceramics were 3.195g/㎤, 48.7Kgf/$\textrm{mm}^2$, 5.4MN/㎥/2 and 2,182Kgf/$\textrm{mm}^2$, respectively.

• 한국세라믹학회지
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• 제31권4호
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• pp.407-414
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• 1994

Compacts were prepared using the SHS(Self-propagating High-temperature Synthesis) method and nitrided at temperatures range from 145$0^{\circ}C$ to 175$0^{\circ}C$, and pressed at 180$0^{\circ}C$ under N2 atmosphere. The samples were characterized for bulk density, porosity, pore size and distribution, phase composition, microstructure and fracture toughness. Compacts were composed of whiskers, which showed a good candidate for the composite materials. The major phases of the compacts nitrided at 175$0^{\circ}C$ and pressed at 180$0^{\circ}C$ were 15R-sialon with a large aspect ratio.