• Applied Chemistry for Engineering
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• v.28 no.1
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• pp.87-94
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• 2017

In this study, a catalyst based on $Pt/Al_2O_3$ supported on Mg was prepared by a wet impregnation method to investigate the $CH_4-SCR$ reaction characteristics of various alumina supports. Alumina supported on $Pt/Al_2O_3$ catalyst was converted to an $Al_2O_3$ composite, and when Mg was added, oxygen species of the active metal Pt were controlled due to electrophobic characteristics. Oxygen-controlled Pt used as a reducing agent inhibited the oxidation of $CH_4$ to $CO_2$. The addition of Mg also promoted the adsorption of NO species and the conversion of NO to $NO_2$ due to the NOx storage property on the catalyst surface.

• Journal of the Korean Ceramic Society
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• v.17 no.2
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• pp.96-100
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• 1980

The castable refractory, CaO.$2Al_2O_3$ is a useful alumina cement for iron, steel and cement for iron, steel and cement industries, however it is difficult to produce CaO.$2Al_2O_3$because of its high melting point(180$0^{\circ}C$) and narrow firing range. In this study, the coprecipitation method was used to produce CaO.$2Al_2O_3$ for lower temperature firing . This method involved the titration of mixed solution of calicum and aluminate which extracted from domestic kaolin with $NH4_OH$ solution under blowing $CO_2$ gas into the solution. The coprecipitate and its clacined products were analyzed by X-ray diffraction and DTA. The calcined products fired between 400 and 90$0^{\circ}C$ were amorphous, but at 100$0^{\circ}C$ the coprecipitate was converted into one compound, CaO$2Al_2O_3$. From those experimental results, it was found that we could synthesizze CaO.$2Al_2O_3$ at about 100$0^{\circ}C$ which is lower than conventional firing temperature by around 80$0^{\circ}C$. The refractoriness of this alumina cement was SK 34 and the compressive strength ( 1 day) was about 250kg/$\textrm{cm}^2$.

• Journal of the Korean Ceramic Society
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• v.33 no.2
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• pp.235-241
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• 1996

Self-Propagating high temperature synthesis(SHS) technique was used to synthesize the spinel phase of MgAl2O from MgO and Al powder. Processing factors such as mixing time preheating temperature and ignition catalyst were varied to determine the optimum condition to form MgAl2O4 phase. The reaction products were heat treated at the temperature range of 120$0^{\circ}C$ and 150$0^{\circ}C$. to observe phase transformation of unreacted materials. Processing factors such as 48 hrs-mixing 80$0^{\circ}C$-preheating and 20wt% KNO3-ignition catalyst were effective of the formation of MgAl2O spinel. An activation energy 49.7kcal/mol. was calculated to form a MaAl2O4 spinel from unreacted materials.

• Journal of the Korean Ceramic Society
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• v.28 no.8
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• pp.625-625
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• 1991

The specimens for the corrosion test were made by hot-pressing of SiC power with 2 wt% Nl2O3 and 10wt% Al2O3 additions at 2000℃ and 2050℃. The specimens were corroded in 37 mole% NaCl and 63 mole% Na2SO4 salt mixture at 1000℃ up to 60 min. SiO2 layer was formed on SiC and then this oxide layer was dissolved by Na2O ion in the salt mixture. The rate of corrosion of the specimen containing 10 wt% Al2O3 was slower than that of the specimen containing 2 wt% Al2O3. This is due to the presence of continuous grain boundary phase in the specimen containing 10 wt% Al2O3. The oxidation of SiC produced gas bubbles at the SiC-SiO2 interface. The rate of corrosion follows a linear rate law up to 50 min. and then was accelerated. This acceleration is due to the disruption oxide layer by the gas evolution at SiC-SiO2 interface. Pitting corrosion has found at open pores and grain boundaries.

• The Korean Journal of Ceramics
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• v.2 no.3
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• pp.142-146
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• 1996

The molten carbonate fuel cell matrices, which are usually made of high surface, fine particle size ${\gamma}-LiAlO_2$ are reinforced with coarse particles of the same material and alumina fibers. An the effects of reinforcing materials on pore characteristics, sintering properties and mechanical properties of the matrices are examined.Among the matrices examined, the highest mechanical reinforcement has been achieved in the one containing 10 wt.% coarse particles and 20 wt.% alumina fibers.

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1266-1273
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• 1998

Al2O3/(5~20vol%)LaAl11O18 composites in which the second phase was dispersed with a elongated grain shape were fabricated using Al2O3 and La2O3 composition by hot-pressing. In order investigate the in-fluence of LaAl11O18 on the toughening of LaAl11O18 on the toughening of Al2O3 matrix composites AE(acoustic emission) analysis was con-ducted together with an evaluation of fracture toughness using of SEPB technique. The degree of AE events occurred in composites were more than those in monolithic alumina. The occurrences of AE event increased with increasing the amount of LaAl11O18 phase in the Al2O3/LaAl11O18 composite is two times higher compared to monolithic alu-mina. The main toughening mechanism was attributed to the bridging of LaAl11O18 grains at tip of pro-pagating crack.

• Journal of the Microelectronics and Packaging Society
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• v.3 no.2
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• pp.39-50
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• 1996

본 연구에선 주어진 조성의 알루미나 green sheet에 대하여 텅스텐의 입경 및 산화 물의 조성을 변화시키므로써 수축률을 제어하여 camber를최소화하여 결합강도를 최대로 하 는 텅스텐 페스트조성을 찾아내는 것을 목적으로 하였다. 본 실험에서 사용한 텅스텐 분말 의 입경은 0.35$\mu$m, 0.6$\mu$m, 0.72$\mu$m, $1.5\mu$m, 1.9$\mu$m, 3.2$\mu$m이며 frit는 Al2O3, MgO, SiO2 와 Al2O3, CaO, SiO2를 사용하여 각각의 조성에 따라 함량을 변화시키며 실험하였다. 소성 은 154$0^{\circ}C$로 습윤 수소분위기에서 시행하였으며 사용된 알루미나 green sheet의 알루미나 중심 입경은 2.8$\mu$m이었다. 분석은 주사전자 현미경으로 미세구조를 관찰하였고 EPMA Line Profile로 원소 분석을 하였으며 잔류응력을 측정하기 위하여 XRD분석을 하였다. Frit 을 함유하지 않은 경우 텅스텐 분말의 입경이 1.9$\mu$mdlfEo 최대 접합 강도를 나타내었다. Frit을 함유한 경우 Mgo계 frit조성에서는 MgO/Al2O3/SiO3=1/1/1일 때 CaO계 frot 조성에 서는 CaO/Al2O3/SiO2=1/2/1일 때 최대 접합 강도를 나타내었다. Frit 함량을 변화시킨 경우 MgO계는 10wt%함유하였을 때 CaO 계는 5wt%함유하였을 때 최대 접합강도를 나타내었 다. Frit 함량을 변화시킨 경우 MgO계는 10wt%함유하였을 때, CaOr계는 5wt%함유하였을 때 최대 접합강도를 나타내었다.

• Journal of environmental and Sanitary engineering
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• v.15 no.1
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• pp.62-68
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• 2000

This study was investigated to the recovery of alumina from the first calcined waste pottery using alkaline sintering. This study was based on calcination result of a commercial ${\alpha}-Al2_O_3$ with NaOH powder. $NaAlO_2$ was formed by calcination of ${\alpha}-Al_2O_3$ with NaOH and conversion of $NaAlO_2$ from ${\alpha}-Al_2O_3$ was 91.4% at calcination condition ; weight ritio of $NaOH/{\alpha}-Al2_O_3$ 1.5, $800^{\circ}C$, and 90min. The first calcined waste porrery from the manufacturing Procedure of H Ltd. was grinded to 170/270mesh by a ball mill and calcined over $500^{\circ}C$ with NaOH powder. The calcined sample was dissolved in $25^{\circ}C$ water and sodiumaluminosilicate solid was formed. After filtration, the contained aluminum was leached out by dissolving sodiumaluminosilicate solid in 1N HCl. We estimated the efficiency of Al extraction from waste pottery by ICP analysis and NaOH was added to the filtrate and then aluminum compound was precipitated with $Al(OH)_3$ and recovered. The investigation was carried out with the variables ; the calcination temperature($500-900^{\circ}C$), the calcination time(30~90min), and the weight ratio of NaOH/waste pottery(0.5~1.5). The treatment efficiency of the waste pottery and the recovery of Al as 97.9%, 91.9% were obtained under the optimum conditions as followed ; the weight ratio of NaOH/waste pottery was 1.5 and the calcination conditions were $900^{\circ}C$ and 60min.

• Journal of the Korean Ceramic Society
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• v.34 no.8
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• pp.908-913
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• 1997

Multilayer NbCxC1-x/Y2O3/Ti were sputter-coated on the alumina substrate, starting with a 0.7 ㎛ thick NbCxC1-x layer grown on substrate, followed by 0.7 ㎛ thick Y2O3 layer and 1 ㎛ thick Ti layer. To find out the optimum conditions for thickness uniformity and adhesion, sputtering works have been done with the variation of sputtering power and Ar pressure. After vacuum annealing at 950℃ and 1000℃, the thermal stability of the NbCxC1-x/Y2O3/Ti coated alumina substrates has been investigated by peel off test. The coating scheme didn't cause any debonded layer after an annealing at 950℃ for 3hrs. However, it was peeled off after annealing at 1000℃ for 3hr. It was found that the thermal stability of Al2O3/NbCxC1-x/Y2O3/Ti coating scheme changed with the NbCxC1-x composition.

• Journal of the Korean Ceramic Society
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• v.29 no.5
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• pp.347-356
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• 1992

Various kaolin samples with different alumina content were prepared from calcined admixture of kaolin and ammonium sulfate by varying the treatment time in sulfuric acid. Samples were nitridated under N2 or N2-H2 atmosphere with changing the amount of added carbon, the reaction time and temperature. As the alumina content lowered, the size of kaolin particles decreased and the specific surface area increased. XRD analysis indicated that ${\alpha}$-quartz remained by decomposition of halloysite and meta-halloysite. Experimental results of nitridation behavior are summerized as follows; 1) Nitridation under N2 atmosphere. With the increase of C/SiO2 ratio and with the decrease of Al2O3 content, disappearance of XRD pattern peaks of mullite, ${\alpha}$-quartz and ${\alpha}$-Al2O3 were accelerated at 1300$^{\circ}C$. SiC was the main phase in the reaction product of acid-treated kaolin samples nitridated at 1300$^{\circ}C$ for 10 hours regardless of C/SiO2 ratio. But the XRD peak intensities of ${\beta}$-Si3N4, ${\beta}$-sialon and SiC did not show much difference when untreated raw kaolin was fired at the same condition. When the ratio of C/SiO2 was 3.5, ${\beta}$-sialon and ${\beta}$-Si3N4 existed in the reaction product of about 22% alumina containing kaolin sample fired at 1350$^{\circ}C$ for 7 hours. Only ${\beta}$-sialon existed in the same sample fired at 1400$^{\circ}C$ for 10 hours. ${\beta}$-sialon was obtained from all of the acid-treated kaolin samples fired at 1400$^{\circ}C$ for 40 hours, but AlN and SiC remained in the untreated kaolin sample. Z value of the ${\beta}$-sialon obtained from the 22% alumina containing kaolin sample fired at 1400$^{\circ}C$ for 40 hours was about 1.3(XRD) and 1.5(EDS). 2) Nitridation under 80N2+2OH2 mixed gas atmosphere with the C/SiO2 ratio of 1 Mullite was not found, but ${\alpha}$-Si3N4, and ${\beta}$-sialon were present in the reaction product of about 22% alumina containing kaolin sample fired at 1300$^{\circ}C$ for 10 hours. When untreated kaolin sample was nitridated at the same condition, mullite remained. AlN and SiC were not found in the reaction product of about 22% alumina containing kaolin sample fired at 1350$^{\circ}C$ for 5 hours. On the other hand, AlN and SiC remained in the product of untreated kaolin fired at the same condition.