• Journal of the Korean Applied Science and Technology
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• v.16 no.2
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• pp.163-170
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• 1999

Spherical alumina powders were prepared by the controlled hydrolysis of aluminum iso-propoxide in a solution consisting of n-octyl alcohol and acetonitrile. As aluminum alkoxide's concentration increased, the particle size was increased and size distribution was more broad. As-prepared particle morphology was not spherical when acetonitrile volume fraction was increased over than 60%. As-prepared amorphous powders crystallized to ${\gamma}$-alumina at $1000^{\circ}C$ and converted to ${\alpha}$-alumina at $1150^{\circ}C$. The particle morphology was retain after crystallization ${\alpha}$-alumina. When aluminum iso-propoxide was used as aluminum source, the optimum preparation condition of spherical alumina was 0.1M AIP, 0.2M H2O, $0.1g/{\ell}$ HPC with a volume fraction (1/1) of the n-octyl alcohol/acetonitrile, 10min of reaction time and 30min of aging time.

• Journal of Korea Foundry Society
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• v.31 no.5
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• pp.267-273
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• 2011

Erosion and thermal shock resistance of several refractory materials have been investigated, which are expected to be used as nozzles in a planar flow casting equipment for amorphous alloys. The test was conducted on five materials; graphite, boron nitride, fused silica, alumina and zirconia. Test specimens were preheated and dipped into the melt of carbon steel and amorphous alloys. Some test specimens were rotated to develop high erosion and to shorten the test periods. Fused silica and boron nitride specimens showed the excellent erosion and thermal shock resistance irrespective of the kind of melt and melting atmosphere.

• Analytical Science and Technology
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• v.24 no.2
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• pp.61-68
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• 2011

Ni-coated alumina was prepared by sonochemical method. To increase an efficiency of Ni coating on alumina, amorphous alumina was prepared by sol-gel method and Ni was coated to fine particles of alumina. Ni-coated alumina was prepared from various calcination temperatures ($500^{\circ}C$, $1,000^{\circ}C$), concentrations of Ni solution (0.01 M~0.2 M) and sonochemical reaction times (30 min, 2h). The prepared fine particles were characterized by X-Ray Diffractometer (XRD), Scanning Electron Microscope (SEM), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), and Particle Size Analyzer (PSA). The coating amount of Ni increased, as Ni concentration and ultrasonication time increased. The maximum amount of Ni was coated to fine particles of alumina, when Ni-coated alumina was prepared with 0.1 M concentration of Ni solution for 2 h of sonication time at $1000^{\circ}C$ of calcination temperature. The average particle size was in the range of 835.9 to 986.7 nm.

• Journal of the Korean Ceramic Society
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• v.23 no.6
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• pp.71-75
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• 1986

The forming reaction processes of magnesium aluminate spinel by a thermal decomposition of sulfate hydrate were studied with DTA, TG. SEM and X-ray powder diffraction methods. The hydrous salt composed of the mixture of the two compounds of $MgSO_4$ $6H_2O$ and ${AL_2}({SO_4})_17H_2O_3$ in which both sulfates were crystalline. On heating the hydrous slat the crystalline magnesium and aluminum sulfate anhydride to amorphous alumina magnesium sulfate anhydride decomposed to amorphous magnesia and these amorphous oxides reacted completely each other to form a spinel at $1000^{\circ}C$ The apparent activation energy of forming reaction of spinel was 36.5 kcal/mole($900^{\circ}C$~$1000^{\circ}C$) The crystallite size of spinel obtained at $1000^{\circ}C$ after 1 h was 380$\AA$.

• Journal of the Korean institute of surface engineering
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• v.23 no.2
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• pp.30-38
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• 1990

For the purpose of suggesting the thermal resistant catalyst for automobile emission control, various catalysts, Pd-WO3 and PD-La2O3 systems, were charactrized before and after thermal aging. It was found that La2O3 formed amorphous surface compound on the support by strong metal-support interaction(SMSI). And by Temperature Programmed Desorption (TPD) expeiment, it was found that the distribution of acid site which is strong acid sites by adding the promoters. After thermal aging, it was observed that the acidity of Pd-WO3 system was decreased largely because of losing acid site by metal vaporization. On the other hand, there was pretty small change in the properties of matter of Pd-La2O3 system. Therefore, it could be considered that La2O3 formed heat resisting amorphous surface compound on the support by SMSI.

• Applied Chemistry for Engineering
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• v.5 no.4
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• pp.597-608
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• 1994

A new process for the production of high purity ${\alpha}-Al_2O_3$ from ammonium aluminium sulfate solution abtained through the sulfation of low grade bauxite ore with $(NH_4)_2SO_4$, and leaching of the sulfated product was investigated. This process is consisted of solvent extraction for Fe component removal from ammonium aluminum sulfate solution and homogeneous precipitation of Al containing precipitate from the refined ammonium aluminium sulfate solution by using urea as precipitator. The optimum conditions of solvent extraction with Alamine 336 as extractant were shaking time of 4min, organic phase ratio to aqueous phase of 0.25. The types of precipitation products from this precipitation were amorphous alumina gel, pseudo-boehmite and crystalline boehmite in the lower temperature of $100^{\circ}C$, in the range from $125^{\circ}C$ to $150^{\circ}C$, and above $150^{\circ}C$, respectively. And also amorphous alumina gel hydrate in $1000^{\circ}C$ and crystalline boehmite in $1250^{\circ}C$ were tranfered to ${\alpha}-Al_2O_3$, respectively. This alumina was identified as ${\alpha}-Al_2O_3$ of purity 99.7%.

• Journal of the Korean Ceramic Society
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• v.31 no.1
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• pp.79-87
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• 1994

Aluminum nitride was hydrolyzed in contact with water, evolving the reaction heat of 172 cal/g within 12 hours to form alumina trihydrates. At 4$0^{\circ}C$ >, amorphous alumina hydrate was easily produced by the spontaneous breaks of AlN particle at the beginning of the hydrolysis process, while bayerite was formed by the dissolution-recrystallization processes of amorphous alumina hydrate at the temperature between 4$0^{\circ}C$ and 6$0^{\circ}C$, and pseudo-boehmite was generated on the surface of AlN particle by the condensation process of the corresponding phase at 6$0^{\circ}C$ <. The longer the hydrolysis timje or the higher the value of pH in solution, the more the bayerite phase was produced. However, pseudo-boehmite was easily generated under the following favorable conditions; when the hydrolysis reaction occured rapidly at the beginning and when the absorption of OH radical on the surface of AlN particle was disturbed by ethyl alcohol in a solution. However, aluminum nitride was hardly hydrolyzed in a solution of pH 2.0.

• Analytical Science and Technology
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• v.13 no.4
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• pp.433-439
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• 2000

Adsorption behaviors of Ni(II) ions were investigated using amorphous alumina as adsorbent. In the adsorption kinetic study, it was observed that Ni(II) ions were bound to the alumina surface in two adsorption stages, the rapid and slow adsorption stages. The rapid adsorption proceeded within 1 hr, thereafter the slow adsorption occurred. The results of adsorption isotherm experiments showed that the Ni(II) adsorption obeyed the Langmuir-Freundlich isotherm, and that the adsorption enhanced with increasing pH. The change in ionic strength did not exhibit a conspicuous trend in Ni(II) adsorption, thereby suggesting that the adsorption occurs through surface complexation rather than electrostatic interactions. The amounts of adsorption were measured with varying pH at three different Ni(II) concentrations under the condition of constant ionic strength, showing that with increasing Ni(II) concentration, the percentage of adsorption decreased and the adsorption edge was shifted to a higher pH value.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.6
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• pp.292-298
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• 2002

Densified cordierite matrixes added alumina platelets were studied as a ceramic substrate material having a low thermal expansion coefficient, low dielectric constant and proper strength. Amorphous-type cordierite powders were filled with four kinds of alumina platelet powders in various compositions. All samples were sintered at $1300^{\circ}C$ for 2 h in an air atmosphere. Improved flexural strength of about 80 MPa, low dielectric constant of 5.0 at 1 MHz and low thermal expansion coefficient of $3.5 \times 10^{-6}/^{\circ}C$ were obtained by the control of the microstructure. Isolated micropores were formed in the matrix and the porosity was dependent on the platelet content and size. In the 10 vol% of alumina platelet content, the isolated micropores were 3~8 $\mu \textrm{m}$ in size, and an increase in dielectric constant by adding alumina platelet filler was inhibited by the micropores.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.2
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• pp.122-128
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• 1995

Sintered bodies were prepared from ${\alpha} - Al_2O_3/SiO_2$ composite powders which each alumina particles were surrounded by silica particles and investigated the mullitization behavior on the process of reaction - sintering. Mullitized reaction was started by formation of amorphous aluminosilicate inter - layer and proceeded by diffusion of alumina through this inter-layer. The growth of mullite was happened along the surface of alumina and controlled by the rate of diffusion.