• Korean Journal of Materials Research
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• v.2 no.5
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• pp.330-336
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• 1992

Four distinctive hot pressed and heat treated S${i_3}{N_4}$ceramics, S${i_3}{N_4}$-8%${Y_2}{O_3}$, S${i_3}{N_4}$-6% ${Y_2}{O_3}$-2% $A{l_2}{O_3}$, S${i_3}{N_4}$-4% ${Y_2}{O_3}$-3% $A{l_2}{O_3}$, 그리고 S${i_3}{N_4}$-1% MgO-1% Si$O_2$(in wt%), were prepared and characterized by X-ray diffraction, scanning electron microscopy, image analysis and mechanical tests. The fracture toughness of S${i_3}{N_4}$-8% ${Y_2}{O_3}$specimens containing large elongated grains showed the highest value of about 9.8MPa$m^{1/2}$. Two out of four S${i_3}{N_4}$, ceramics(S${i_3}{N_4}$-6% ${Y_2}{O_3}$-2% $A{l_2}{O_3}$and S${i_3}{N_4}$-4% ${Y_2}{O_3}$-3% $A{l_2}{O_3}$) heat treated at 200 $0^{\circ}C$retained the fracture strength of over 900MPa and fracture toughness of over 8.0MPa$m^{1/2}$. Large ${\beta}$-S${i_3}{N_4}$grains having a diameter larger than 1${\mu}$m appeared to contribute to increase in fracture toughness.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.11-18
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• 1991

A precipitation method, one of the most effective liquid phase reaction methods, was adopted in order to prepare high-tech Al2O3/ZrO2 composite ceramics, and the effects of stress-induced phase transformation of ZrO2 on thermal shock behavior of Al2O3-ZrO2 ceramics were investigated. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Metal hydroxides were obtained by single precipitation(process A) and co-precipitation(process B) method at the condition of pH=7, and the composition of Al2O3-ZrO2 composites was fixed as Al2O3-15v/o ZrO2(+3m/o Y2O3). Critical temperature difference showing rapid strength degradation by thermal shock showed higher value in Al2O3/ZrO2 composites(process A : 20$0^{\circ}C$, process B : 215$^{\circ}C$) than in Al2O3(175$^{\circ}C$). The improvement of thermal shock property for Al2O3/ZrO2 composites was mainly due to the increase of strength at room temperature by adding ZrO2. The strength degradation was more severe for the sample with higher strength at room temperature. Crack initiation energies by thermal shock showed higher values in Al2O3/ZrO2 composites than in Al2O3 ceramics due to increase of fracture toughness by ZrO2.

• Korean Journal of Materials Research
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• v.11 no.12
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• pp.1080-1085
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• 2001

Dielectric properties and leakage current characteristics of 100 nm-thick $Ta_2O_5/Al_2O_3$multilayer thin films, which were fabricated by reactive sputtering of$Al_2O_3$and$Ta_2O_5$ successively on top of each other for total 9 layers, have been investigated with variation of the$Al_2O_3$content$(i.e,\;Ta_2O_5/Al_2O_3 \;thickness\;ratio)$.$Ta_2O_5/Al_2O_3$films were amorphous regardless of the$Al_2O_3$content. With increasing the$Al_2O_3$content from 0% to 100%, refractive index of the $Ta_2O_5/Al_2O_3$films decreased linearly from 2.03 to 1.56 and dielectric constant was lowered from 23.9 to 7.7 Variation of the dielectric constant with the$Al_2O_3$content was in good agreement with the behavior that was obtained by assuming parallel capacitors of$Al_2O_3$and Ta_2O_5$. Leakage current characteristics of $Ta_2O_5/Al_2O_3$ multilayer films were superior to those of $Ta_2O_5$ and$Al_2O_3$films. $Ta_2O_5/Al_2O_3$ films of 5% and 10%$Al_2O_3$content exhibited excellent leakage current densities which were lower than $10^{-7} A/cm^2$ at 1MV/cm.

• Journal of the Korean Ceramic Society
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• v.29 no.3
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• pp.223-231
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• 1992

CaO and ZnO were added to Al2O3-SiO2 binary system respectively as flux, then ZrO2 and TiO2 were applied as nucleating agent to these CaO-Al2O3-SiO2 and ZnO-Al2O3-SiO2 ternary system glass. The transparency could not be kept in CaO-Al2O3-SiO2 system glass, whereas the transparent glass-ceramics were prepared in ZnO-Al2O3-SiO2 system glass containing ZrO2 as the nucleating agent. At this time the optimum heating temperatures for the nucleation and the crystal growth were 78$0^{\circ}C$ and 97$0^{\circ}C$. The sizes of the precipitated crystals in the transparent glass-ceramics were below 0.1 ${\mu}{\textrm}{m}$, and their light transmissibilities were more than 80%.

• Journal of the Korean Ceramic Society
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• v.36 no.3
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• pp.301-306
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• 1999

CO2 감지용 La2O3-SnO2 계 후막형 소자를 제조하여 CO2가스에 대한 기초 감지 특성을 조사하였고, 감지 분말의 입자크기와 제조방법에 따른 감도 변화를 고찰하였다. 후막 소자는 40$0^{\circ}C$의 작동온도와 4wt.%의 La2O3가 첨가되 srjt에서 가장 좋은 감도를 나타내었고, 낮은 습도영역에서 우수한 감지 특성을 보였다. 분말 혼합법에 의해 제조된 소자에 있어서 La2O3와SnO2 분말의 입자가 미세할수록 우수한 감도를 나타내었고, La2O3의 입도가 SnO2의 입도 보다 감도에 더 큰 영향을 주었다. SnO2 후막 표면에 La 용액을 코팅하여 제조된 센서는 가장 우수한 CO2 감도특성을 보였다.

• Journal of the Korean Ceramic Society
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• v.23 no.2
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• pp.38-42
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• 1986

The adsorption behavior of 3CaO.$Al_2O_3$-sodium gluconate-$H_2O$ system by measuring adsorp-tion isotherm DTA and IR sepctra. The adsorbed amount of sodium gluconate on 3CaO.$Al_2O_3$ is exceedingly larger than 3CaO.$SiO_2$ and portland cement. From the DAT experiment the formation of complex is observed by the characteristic exothermic peak of the complex at 45$0^{\circ}C$ It is now strong deduced that the chemical bonding between gluconate anion and 3CaO.$Al_2O_3$ should be coordinative due to the complex formation on the surface 3CaO.$Al_2O_3$ from the IR spectra of sod-ium gluconate only and 3CaO.$Al_2O_3$ -sodium gluconate-$H_2O$.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.412-417
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• 2001

본 연구는 습식법으로 수산화 알루미늄과 티타니아를 출발물질로 하여 $Al_2$O$_3$-TiO$_2$복합분체를 제조하였으며, 2 mol의 Al(OH)$_3$분말에 대하여 TiO$_2$분말량을 1, 3, 5, 7, 9, 11 wt%로 첨가하여 $Al_2$O$_3$-TiO$_2$복합분체의 특성을 조사하였다. 제조된 $Al_2$O$_3$-TiO$_2$계 복합분체는 $700^{\circ}C$~140$0^{\circ}C$까지 하소하여 XRD 분석을 한 결과 100$0^{\circ}C$까지는 TiO$_2$(rutile)상과 η-Al$_2$O$_3$상이 공존하다가 110$0^{\circ}C$부터 130$0^{\circ}C$까지는 η-Al$_2$O$_3$에서 $\alpha$-Al$_2$O$_3$로의 상전이가 일어나서 $\alpha$-Al$_2$O$_3$상과 TiO$_2$(rutile)상이 나타났으며 하소온도 140$0^{\circ}C$, TiO$_2$첨가량이 5 wt%일 때부터 $Al_2$TiO$_{5}$가 생성되기 시작하였다. TiO$_2$첨가량에 따른 비표면적값은 첨가량이 7 wt%까지는 감소하였으나 그 이상 첨가시 증가하였다. 입도분석 결과 평균입경은 15.74~23.21$mu extrm{m}$로서 TiO$_2$첨가량이 3 wt%일 때 가장 작은 값을 가졌으며 TiO$_2$첨가량은 5 wt% 이상부터 점차 감소하였다.

• Korean Chemical Engineering Research
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• v.57 no.5
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• pp.714-722
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• 2019

Catalysts were prepared by using incipient wetness impregnation method with 17 wt% Ni on a support ($SiO_2-Y_2O_3$, $Al_2O_3$, $SiO_2-ZrO_2$, $SiO_2$, $TiO_2$, MgO) and the catalytic activity in the reductive amination of ethanol with ammonia in the presence of hydrogen was compared and evaluated. The catalysts used before and after the reaction were characterized using X-ray diffraction, nitrogen adsorption, ethanol-temperature programmed desorption (EtOH-TPD), isopropanol-temperature programmed desorption (IPA-TPD), and hydrogen chemisorption etc. In the case of preparing $ZrO_2$ and $Y_2O_3$ supports, the small amount of Si dissolution from the Pyrex reactor surface provoked the formation of mixed oxides $SiO_2-ZrO_2$ and $SiO_2-Y_2O_3$. Among the catalysts used, $Ni/SiO_2-Y_2O_3$ catalyst showed the best activity, and this good activity was closely related to the highest nickel dispersion, and low desorption temperature in EtOH-TPD and IPA-TPD. The low catalytic activity on Ni/MgO catalysts showed low activity due to the formation of NiO-MgO solid-solutions. In the case of $Ni/TiO_2$, the reactivity was low due to the low nickel metal phase due to strong metal-support interaction. In the case of using a support as $SiO_2-Y_2O_3$, $Al_2O_3$, $SiO_2-ZrO_2$, and $SiO_2$, the selectivities of ethylamines and acetonitrile were not significantly different at similar ethanol conversion.

• Journal of the Korean Ceramic Society
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• v.30 no.5
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• pp.397-403
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• 1993

Widely used dielectrics, barium titanate was promising material for ceramic capacitor. It was produced by specific formulation with various dopants-La2O3, ZrO2, SnO2, CaZrO3, CaTiO3, CaSnO3, Bi2O3, and etc.-according to demanded properties of capacitor. In this study, we would examinate the study of dielectric properties and temperatuer characteristics (T.C.) with the amount of Bi2O3. The sample was prepared with [BaTiO3]10＋[BaZrO3, SnO2, La2O3, ZrO2]10 and Bi2O3 varied from 1.0, 1.5, 2.0, 2.5 to 3.0wt%. After milling and mixing for 15hrs, each sample was dried and then pressed at 700kg/$\textrm{cm}^2$ into pellets. Pellets were fired at 131$0^{\circ}C$, for 3hrs in air. As the result of measurements, dielectric constant, break down voltage, and insulation resistance were increased with the amount of Bi2O3, and the resonant frequency was shifted from high frequency to low frequency range. In the case of temperature characteristics, capacitance change rate was symmetrically changed at -$25^{\circ}C$ and ＋85$^{\circ}C$ respectively. Therefore, it is recognized that the temperature characteristics can be moderated with doping Bi2O3 in our study.

• Journal of the Korean Ceramic Society
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• v.28 no.4
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• pp.305-314
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• 1991

This study was conducted to research the formation and the color development of NiO-ZnO-Fe2O3-TiO2-SnO2 system for the purpose of synthesizing the spinel pigments which are stable at high temperature. After preparing ZnO-Fe2O3 as a basic composition, {{{{ chi }}NiO.(l-{{{{ chi }})ZnO.Fe2O3 system, {{{{ chi }}NiO.(l-{{{{ chi }})ZnO.TiO2 system, and {{{{ chi }}NiO.(l-{{{{ chi }})ZnO.SnO2 system were prepared with {{{{ chi }}=0, 0.2, 0.5, 0.7, 1 mole ratio respectively. The manufacturing was carried out at 128$0^{\circ}C$ for 30 minutes. The reflectance measurement and the X-ray analysis of these specimens were carried out and the results were summarized as follows. 1. In the specimens which included NiO, it was difficult for the spinel structure to be formed. 2. As increasing the contents of NiO and Fe2O3, all the groups which were yellow or green colored changed to brown. 3. NiO-ZnO-Fe2O3 system and NiO-ZnO-TiO2 system formed the spinel structure and the illmenite structure appeared in NiO-TiO2 system.