• Korean Chemical Engineering Research
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• v.45 no.3
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• pp.209-214
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• 2007

Sr hexaaluminate($Sr_{1-x}La_xMnAl_{11}O_{19-\alpha}$) were prepared by sol-gel method of metal alkoxide with 1-butanol or ethylene glycol as a solvent. The physical properties of prepared hexaaluminates were examined by TG/DTA, XRD and $N_2$ adsorption. When ethylene glycol was used as a solvent, the decomposition reaction and dehydroxylation reaction was observed above $400^{\circ}C$ and the temperature of the formation of a crystal structure of hexaaluminate was also increased resulting in small specific surface area and low catalytic activity of methane compared to Sr-hexaaluminate with 1-butanol.

• Clean Technology
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• v.26 no.3
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• pp.196-203
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• 2020

In this study, a Cu/hexaaluminate catalyst was prepared by a co-precipitation method, and then a binder was added to form a pellet. A catalyst in which Ni and Ru promoters were added to a Cu/hexaaluminate pellet catalyst was prepared. This study focused on examining the effect of the addition of Ni and Ru promoters on the properties of Cu/hexaaluminate catalysts and the decomposition reaction of ADN-based liquid monopropellants. Cu/hexaaluminate catalysts had few micropores and well-developed mesopores. When Ru was added as a promoter to the Cu/hexaaluminate pellet catalyst, the pore volume and pore size increased significantly. In the thermal decomposition reaction of ADN-based liquid monopropellant, the decomposition onset temperature was 170.2 ℃. Meanwhile, the decomposition onset temperature was significantly reduced to 93.5 ℃ when the Cu/hexaaluminate pellet catalyst was employed. When 1% or 3% of Ru were added as a promoter, the decomposition onset temperatures of ADN-based liquid monopropellant were lowered to 91.0 ℃ and 83.3 ℃, respectively. This means that the Ru promoter is effective in lowering the decomposition onset temperature of the ADN-based liquid monopropellant because the Ru metal has excellent activity in the decomposition reaction of ADN-based liquid monopropellant, simultaneously contributing to the increase of the pore volume and pore size. After the thermal treatment at 1,200 ℃ and decomposition of ADN-based liquid monopropellant were repeatedly performed, it was confirmed that the addition of Ru could enhance the heat resistance of the Cu/hexaaluminate pellet catalyst.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.2
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• pp.142-151
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• 1995

Complex alkoxides were synthesized using metal alkoxide method and were then hydrolyzed to prepare the precursors using sol - gel method. Then, the precursors were calcined in order to make barium hexaaluminate. Factors affecting the material properties of the barium hexaaluminate precursors were studied and they are the kinds and amount of alcohols, and reaction time. In addition, in the course of hydrolysis, the effects of the amount of water, reaction temperature and aging time were also studied in terms of the specific surface area and average particle size of the barium hexaaluminates.

• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.134-139
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• 2000

The main objective of the present investigation is to show the feasibility of combinatorial chemistry by applying this method to phosphor syntehses. In this respect barium hexaaluminate phosphor was prepared by the split-pool combinatorial method, which enabled much more rapid search of optimum compositions of target phosphors than conventional synthetic methods. Barium hexaaluminate phosphors doped with Eu2+ exhibit blue emission while those co-doped with Mn2+ and Eu2+ exhibit green emission. Basically, the phosphor doped with 1.3 mole of Ba and 0.06~0.15 mole of Eu2+ exhibit the maximum value of emission intensity at 435${\mu}{\textrm}{m}$. Under the UV and VUV extitations, the barium hexaaluminate phosphor co-doped with Mn2+ and Eu2+ shows strong green emission.

• Clean Technology
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• v.24 no.4
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• pp.371-379
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• 2018

The objective of this study is to develop a platinum/hexaaluminate pellet catalyst for the decomposition of eco-friendly liquid propellant. Pellet catalysts using hexaaluminate prepared by ultrasonic spray pyrolysis as a support and platinum as an active metal were prepared by two methods. In the case of the pellet catalyst formed by loading the platinum precursor onto the hexaaluminate powder and then adding the binder (M1 method catalyst), the mesopores were well developed in the catalyst after calcination at $550^{\circ}C$. However, when this catalyst was calcined at $1,200^{\circ}C$, the mesopores almost collapsed and only a few macropores existed. On the other hand, in the case of a catalyst in which platinum was supported on pellets after the pellet was produced by extrusion of hexaaluminate (M2 method catalyst), the surface area and the mesopores were well maintained even after calcination at $1,200^{\circ}C$. Also, the catalyst prepared by the M2 method showed better heat resistance in terms of platinum dispersion. The effects of preparation method and calcination temperature of Pt/hexaaluminate pellet catalysts on the decomposition of liquid propellant composed mainly of ammonium dinitramide (ADN) or hydroxyl ammonium nitrate (HAN) were investigated. It was confirmed that the decomposition onset temperature during the decomposition of ADN- or HAN- based liquid propellant could be reduced significantly by using Pt/hexaaluminate pellet catalysts. Especially, in the case of the catalyst prepared by the M2 method, the decomposition onset temperature did not show a large change even when the calcination temperature was raised at $1,200^{\circ}C$. Therefore, it was confirmed that Pt/ hexaaluminate pellet catalyst prepared by M2 method has heat resistance and potential as a catalyst for the decomposition of the eco-friendly liquid propellants.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.511-512
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• 2008

For the $CO_2$ reforming of $CH_4$, Ni catalyst was supported on La-hexaaluminate or on $\gamma$-$Al_2O_3$. The catalytic activities of Ni/La-hexaaluminate catalysts were measured at $700^{\circ}C$ using gas chromatography (GC) for 72 h, and the reaction was maintained up to 72 hfor the investigation of catalyst deactivation. The surface of each catalyst after 72 h reaction was investigated using SEM and TEM, and the composition of the carbon deposits was investigated by using EA, TPO and TGA. Ni/La-hexaaluminate shows higher resistance to coke deposition than conventional Ni/$Al_2O_3$ which seems to be due to strong interaction between Ni and the support material. As a result of the reforming reaction, various types of carbon deposits were created on catalyst surface and the amounts of them were much smaller in the case of La-hexaaluminate than on $Al_2O_3$.

• Korean Journal of Crystallography
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• v.11 no.3
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• pp.176-181
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• 2000

Computer-based atomistic simulation methods are applied to address quantitatively the crystal defect chemistry of strontium hexaaluminate, SrAl/sub 12/O/sub 19/. Our calculations show that oxygen Frenkel disorder is the dominant intrinsic defect mode to be expected in the multi-component oxide, though Schottky disorder may also exist. When La and Mg enter into SrAl/sub 12/O/sub 19/. Mg prefers to occupy Al(3)4f tetrahedral sites in the magnetoplumbite structure. Our calculations also indicate that O/sub Sr/ defect is improbable in the structure.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.435-442
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• 2021

Mn-added Barium hexaaluminates were manufactured by homogeneous precipitation method using Urea. The effects of water wash and dry temperature were analyzed by thermal weight analysis, X-ray diffraction analysis, and scanning electron microscopy. Catalysts that went through the filtration step only produced pure hexaaluminate images compared to those that went through the water wash step. During the drying process, it seems that the remaining urea helps dehydration of the precursor and affects the phase shift of gibbsite to boehmite, which is easy to convert to pure hexaaluminate. The catalyst WO200 gave the best performance in the methane combustion reaction, and NOx was not emitted in the reaction for all catalysts. Hexaaluminates were found to affect reducing the highest CO emissions.

• Clean Technology
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• v.25 no.4
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• pp.331-335
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• 2019

Interest in environmental pollution is increasing all over the world, and technology development to solve it is actively carried out. In areas where heat is used, especially, combustion is causing countless pollutants in the air environment. Combustion catalyst is a technology that reduces NOx and CO by lowering combustion temperature and enabling complete combustion. Traditional combustion catalysts are expensive and complex in the synthesis process using precious metal catalyst. In this study, hexaaluminate, a high-temperature combustion catalyst, was manufactured using urea, and the properties were investigated according to the synthesis time. The combustion performance and characteristics were evaluated using this catalyst. As the temperature increased, the changing methane conversion rate was shown in two patterns. The conversion rates for 1 hour, 9 hours, and 12 hours were similar, while the conversion rates for 3 hours and 6 hours showed similar patterns. Methane combustion performance increased rapidly as the synthesis time increased from 6 hours to 9 hours, whereas the temperature at T50 was approximately 745 ℃. The performance of the synthesized combustion catalyst for 9 hours was optimum as the NOx emission of this combustion catalyst was not present and the maximum emission of CO was 72 ppm.

• Korean Chemical Engineering Research
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• v.43 no.5
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• pp.616-620
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• 2005

The morphology and photoluminescence characteristics of green light emitting hexaaluminate phosphor particles prepared by high temperature spray pyrolysis from spray solution with and without ammonium dihydrogen phosphate flux were investigated. The particles prepared from spray solution without flux material had hollow morphology at preparation temperatures between $900^{\circ}C$ and $1,650^{\circ}C$. Ammonium dihydrogen phosphate flux added into spray solution enabled the formation of particles with spherical shape and filled morphology at preparation temperatures between $900^{\circ}C$ and $1,650^{\circ}C$. The hexaaluminate phosphor particles with magnetoplumbite structure were directly prepared by spray pyrolysis from spray solution with ammonium dihydrogen phosphate flux above $1,600^{\circ}C$. Ammonium dihydrogen phosphate flux was effective in improving the photoluminescence intensity of the phosphor particles at low preparation temperatures. The phosphor particles prepared from spray solution with and without flux material by spray pyrolysis under reducing atmosphere at $1,650^{\circ}C$ had comparable photoluminescence intensities with that of the phosphor particles optimized by post-treatment.