• 한국세라믹학회지
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• 제45권5호
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• pp.290-296
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• 2008

$AB'_{0.5}B"_{0.5}O_3$ type complex perovskite structures which have been reported as proton conductors over $600^{\circ}C$ were studied. The $AB'_{0.5}B"_{0.5}O_3$ type complex perovskite structure is known to be more easily synthesized and has better stability than normal $ABO_3$ perovskite structure. And it is stable at about $800^{\circ}C$ in the $CO_2$ atmosphere, whereas the $BaCeO_3$ perovskite is easily decomposed into carbonate. In addition, this $AB'_{0.5}B"_{0.5}O_3$ type complex perovskite structure could simply produce oxygen vacancies within their structure not by introducing additional doping oxides but by just controling the molar ratio of $B'^{+3}$ and $B"^{+5}$ metal ions in the B site. Hence it is easy to design the structure which shows highly sensitive electrical conductivity to humidity. In this study, the single phase boundary of $BaR_{0.5+x}Ta_{0.5-x}O_{3-{\delta}}$(R = rare earth) complex perovskite structures and it's phase stability were investigated with changes in composition, x. And the humidity dependance of electrical conductivity at different $P_{H2O}$ conditions was investigated.

• 한국분말재료학회지
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• 제24권6호
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• pp.431-436
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• 2017

SiAlON-based ceramics are some of the most typical oxynitride ceramic materials, which can be used as cutting tools for heat-resistant super-alloys (HRSA). SiAlON can be fabricated by using gas-pressure reactive sintering from the raw materials, nitrides and oxides such as $Si_3N_4$, AlN, $Al_2O_3$, and $Yb_2O_3$. In this study, we fabricate $Yb_{m/3}Si_{12-(m+n)}Al_{m+n}O_nN_{16-n}$ (m=0.3, n=1.9, 2.3, 2.7) ceramics by using gas-pressure sintering at different sintering temperatures. Then, the densification behavior, phase formation, microstructure, and hardness of the sintered specimens are characterized. We obtain a fully densified specimen with ${\beta}$-SiAlON after gas-pressure sintering at $1820^{\circ}C$ for 90 min. under 10 atm $N_2$ pressure. These SiAlON ceramic materials exhibited hardness values of ~92.9 HRA. The potential of these SiAlON ceramics for cutting tool application is also discussed.

• 한국세라믹학회지
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• 제51권4호
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• pp.231-242
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• 2014

An interconnect in solid oxide fuel cells (SOFCs) electrically connects unit cells and separates fuel from oxidant in the adjoining cells. The interconnects can be divided broadly into two categories - ceramic and metallic interconnects. A thin and gastight ceramic layer is deposited onto a porous support, and metallic interconnects are coated with conductive ceramics to improve their surface stability. This paper provides a short review on ceramic materials for SOFC interconnects. After a brief discussion of the key requirements for interconnects, the article describes basic aspects of chromites and titanates with a perovskite structure for ceramic interconnects, followed by the introduction of dual-layer interconnects. Then, the paper presents protective coatings based on spinel-or perovskite-type oxides on metallic interconnects, which are capable of mitigating oxide scale growth and inhibiting Cr evaporation.

• 한국세라믹학회지
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• 제53권6호
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• pp.652-658
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• 2016

Gadolinium zirconate, $Gd_2Zr_2O_7$, is one of the most versatile oxides among the new thermal-barrier-coating (TBC) materials for replacing conventional yttira-stabilized zirconia (YSZ). $Gd_2Zr_2O_7$ exhibits excellent properties, such as low thermal conductivity, high thermal expansion coefficient comparable with that of YSZ, and chemical stability at high temperature. In this study, bulk and coating specimens with $Gd_{2-x}Zr_{2+x}O_{7+0.5x}$ (x = 0.0, 0.5, 1.0) compositions were fabricated in order to examine the characteristics of this gadolinium zirconate system with different Gd content for TBC applications. Especially, coatings with $Gd_{2-x}Zr_{2+x}O_{7+0.5x}$ (x = 0.0, 0.5, 1.0) compositions were produced by suspension plasma spray (SPS) with suspension of raw powder mixtures prepared by planetary milling followed by ball milling. Phase formation, microstructure, and thermal diffusivity were characterized for both sintered and coated specimens. Single phase materials with pyrochlore or fluorite were fabricated by normal sintering as well as SPS coating. In particular, coated specimens showed vertically-separated columnar microstructures with thickness of $400{\sim}600{\mu}m$.

• 한국세라믹학회지
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• 제46권3호
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• pp.336-343
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• 2009

Nickel oxide thin films exhibit the resistive switching as a function of applied voltages. The switching phenomena involve low and high resistance states after electroforming. The electrical features are believed to be associated with the formation and rupture of filaments. The set and reset behaviors are controlled by the oxidation and reduction of filaments. The indirect evidence of filaments is corroborated by the presence of nanocrystalline nickel oxides found in high-resolution transmission electron microscopy. The insertion of insulating layers seems to control the current-voltage characteristics by preventing the continuous formation of conductive filaments, potentially leading to artificial control of resistive behaviors in NiO-based systems.

• 한국세라믹학회지
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• 제15권2호
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• pp.66-71
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• 1978

The cobalt blue spinel stains (main composition; CoO:$Al_2O_3$=1 : 1) in CoO-NiO-$Al_2O_$3 and $CoO-Al_2O_3-Cr_2O_3$ system were prepared by the calcination of each component oxides to be adequate for the factory. The color development, the change of the lattice constnat of the spinel and its application to colored glazes were studied. The results were summarized as follows. 1) In CoO-Al_2O_3$ spinel, the excess addition of each component hardly made any variation in lattice constantand alumina-rich spinel specimens caused the brilliant blue color fade. 2) An increase of $Ni^{2+}$ in $CoO-NiO-Al_2O_3$ system, made the lattice constnat of the $CoO-Al_2O_3$ spinel smaller, and an increase of $Cr^{3+}$ in $CoO-Al_2O_3-Cr_2O_3$, larger. 3) Glazed stains under lead glaze were colored nearly same dark blue color fade.

• 한국세라믹학회지
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• 제13권3호
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• pp.3-12
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• 1976

The corelation between surface tensions and surface appearances of SK O5a opaque glazes for earthen wares were investigated. The surface tension values were theoretically calculated by using Dietzel's factors of constituent oxides of glaze. The surface appearances of glazes, especially the pinhole phenomena were strongly effected by the surface tension values showing the following general tendencies: (1) In the range of 305±3 dynes/cm of surface tensions, glazes showed almost no pjnholes. (2) In the range of surface tensions less than 300 dynes/cm, the large numbers of small pinholes or eggshell textures were observed. (3) In the range of surface tensions higher than 310 dynes/cm, large and deep pinholes were observed. (4) The contact angles of glazes on the wall tile body substrate are in the good proportional agreement with the surface tension values calculated by Dietzel's factors.

• 한국세라믹학회지
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• 제27권1호
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• pp.127-135
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• 1990

Characteristics of the sol-gel derived (Ba1-xPbx)TiO3 powders are compared with those of powders prepared by the calcining ofmixed oxides method (CMO) and molten salt synthesis method(MSS). The sol-gel derived powder has a higher surface area (50$m^2$/g) than those of CMO(3.8$m^2$/g) and MSS(11.5$m^2$/g) derived powders. In the sol-gel method, the (Ba1-xPbx)TiO3 was synthesized at $600^{\circ}C$ for 1hr, indicating that this method has a crystalline temperature 20$0^{\circ}C$-30$0^{\circ}C$ lowr than those of the CMO and MSS methods.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2013년도 춘계학술대회 논문집
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• pp.85-85
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• 2013

A ceramic coating material with nano-sized silicon oxide on AISI 4340 steel for a thermal conductor at a high temperature was analyzed to find an optimum coating process. Average surface roughness of the coating layers prepared by dipping process was about $5.26{\mu}m$. Potassium silicate addition as a binder of the coating material tended to improve its hardness. A pencil scratch hardness testing showed that a loading more than 800 g made fragments of the coating layer.

• 한국세라믹학회지
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• 제43권1호
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• pp.28-32
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• 2006

Diarylethene in photochromic materials was doped in organic-inorganic hybrid low-melting glasses were synthesized through a nonaqueous acid-base reaction process, which consists of network units including a small number of bridging oxides. The organic phase is a dichlorodimethylsilane while the inorganic phase is a tin(II) chloride. Diarylethene was incorporated into the glasses without any degradation of its functionality. The open form of diarylenthene, which is converted from the opening one upon UV-irradiation, is change to the closed form visible light-irradiation. The rate constant of the photochemical reaction is $31.78\times10^{-3}s^{-1}$ with 400 W UV lamp irradiation.