• Journal of the Korean Ceramic Society
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• v.13 no.4
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• pp.25-35
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• 1976

Mullite was synthesized by using kaolin and $\alpha$-alumina, and halloysite and aluminum hydroxide as raw materials at the various temperature in the range of 1200$^{\circ}$-1750$^{\circ}$C. The degree of mullitization was measured respectively by a quantitative X-ray diffraction method and a chemical analysis method. The rate and the maximum degree of mullitization were found to increase with temperature . The reaction completed at 1600$^{\circ}$Cfor less than 30 minutes, and yielded 98% mulllite inpurity in the case of kaolin-Al(OH)3. TiO$_2$ up to 3% was added to the batches of kaolin-Al(OH)$_3$. the effect of addition on the mullitization was investigated and found to decrease the sintering temperature for the mullitization. The mechanism of TiO$_2$ addition on the formation of mullite was also discussed.

• Elastomers and Composites
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• v.55 no.1
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• pp.40-45
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• 2020

In this study, the mechanical and flame-retardant properties of ethylene-propylene-diene-termonomer (EPDM) based rubber compounds and various other environmentally friendly inorganic flame retardants were investigated. Alumina trihydrate (ATH) and magnesium hydroxide (MDH) were used as inorganic flame retardants. The mechanical properties after thermal oxidation aging and the flame-retardant properties of the EPDM compounds were measured using a moving die rheometer, a universal testing machine, a compression set, and a UL 94 V flammability test. We focused on how the properties were affected by the type and amount of flame retardants. The results demonstrated that the optimal mechanical and flame-retardant V-0 grade properties were obtained at an ATH content of 200 phr.

• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.561-566
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• 2005

For the homogeneous dispersion of $ZrO_2$ particles in $Al_2O_3/ZrO_2$ceramics, Zr-precusors were mixed with oxide $Al_2O_3$powders by chemical routes such as partial precipitation or partial polymerization of Zr-nitrate solutions. In case of the mechanical mixing of ultrafine $Al_2O_3$ and $ZrO_2$ oxide powders, relatively homogeneous dispersion was difficult to achieve so that the particle size and distributions of $ZrO_2$ were relatively inhomogeneous after sintering at high temperature. But when the Zr-Y-hydroxide were co-precipitated to ultrafine $Al_2O_3$ oxide powders followed by calcinations, homogeneous dispersion of nano-sized $ZrO_2$ particles in $Al_2O_3/ZrO_2$ composite ceramics were obtained. But because of the coalescence of dispersed $ZrO_2$ particles, dispersed $ZrO_2$ was grown up to more than 0.2${mu}m$ (200 nm) when sintered at the temperature of higher than $1500^{\circ}C$ But when the sintering temperature was kept to lower than $1400^{\circ}C$ by using nano-sized $\alpha-alumina$, the particle size of dispersed $ZrO_2$ could be sustained below 0.1 ${\mu}m$. But the coalescence of dispersed $ZrO_2$ between $Al_2O_3$ particles could not be avoided so that the mechanical properties were not enhanced contrary to the expectations. So Zr-polyester precursors were precipitated and coated to the surface of ultrafine $\alpha-alumina$ powders by the polymerization of Ethylene Glycol with Citric Acid and Zirconium Nitrate. By this dispersion much more uniform dispersion of $ZrO_2$ was achieved at $1450\~1600^{\circ}C$ of sintering temperature ranges. And due to especially discrete dispersion of $ZrO_2$ between $Al_2O_3$ particles, their mechanical strength was more enhanced than mechanical mixing or hydroxide precipitation methods.

• Journal of the Korean Chemical Society
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• v.35 no.3
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• pp.275-279
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• 1991

Ultra-fine alumina, ${\alpha}-Al_2O_3$, with ${\phi}$ = 0.1∼0.5 ${\mu}$m was obtained from pure ammonium aluminum sulfate(alum) as the thermal decomposition product. Pure alum(> 99.7%) could be prepared by the precepitation and the successive recrystallization in an acidic aqueous solution at pH = 1.5∼2.5, which was theoretically predicted by only considering the concentrations of hydroxide and carbonate for aluminum and sodium in the solution, and also experimentally confirmed as the optimum precepitation condition for alum without forming any impurities like aluminum hydroxide or sodium one.

• Journal of the Korean Ceramic Society
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• v.47 no.5
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• pp.401-406
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• 2010

For the lower-temperature preparation of calcium monoaluminate(CA, C:CaO, A:$Al_2O_3$) clinker which is hard to synthesize purely within its melting point, an equimolar hydrate was obtained and then used as a starting raw material of clinker burning. The hydrate was prepared from a mixture of waste oyster shell and industrial aluminium hydroxide by heating to $1200^{\circ}C$, grinding and mixing with water. The hydrate was composed of amorphous aluminium hydroxide and $C_3AH_6$(H:$H_2O$) formed by resolution-precipitation mechanism of the system C-A-H. By heating the hydrate, nearly pure and porous calcium monoaluminate clinker was formed at $1400^{\circ}C$ which is fairly lower temperature than that of its melting point. The formation of calcium monoaluminate was performed mainly by the reaction between amorphous alumina and $C_{12}A_7$ caused by the decomposition of $C_3AH_6$. The immediate and earlier formation of $C_{12}A_7$ seemed to be accelerated by not only high surface area and instability of the thermally decomposed hydrate but also the catalytic effect of water decomposed from the hydrate. The final calcium monoaluminate clinker was very porous because of the influence of highly porous shape of the thermally decomposed hydrate.

• Journal of the Korean Ceramic Society
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• v.28 no.4
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• pp.338-346
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• 1991

The alumina-titania composite powders coated with Al2O3 were prepared by the method of hydrolysis-deposition of mixed aluminium salt solution of Al2(SO)4-Al(NO3)3-Urea. The effects of coating-process parameters on the characteristics of coated composite powders were also investigated. As the content of TiO2 dispersed in deionized water increased, the coated composite powders were found to be more uniform in size and unagglomerated. When TiO2 powders were coated for 30 min, the optimum TiO2 content in the coating process was 400 mg/ι. The size of TiO2 particle was increased approximately from 0.7${\mu}{\textrm}{m}$ to 1.0${\mu}{\textrm}{m}$ through coating of Al2O3. The IEP of coated composite powders was pH=8.3 identical to the value of aluminium hydroxides and the zeta-potential showed nearly similar values each other. When heat treating coated composite powders at 130$0^{\circ}C$, only two phases of TiO2(rutile) and Al2TiO5 were observed. These results showed that the suface of TiO2 could be uniformly coated with the aluminium hydroxide.

• Resources Recycling
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• v.15 no.5 s.73
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• pp.52-56
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• 2006

Waste aluminum dross was leached with hydrochloric acid to prepare PAC, poly aluminium chloride, used as water treatment chemicals. Metallic aluminum remained in the waste aluminum dross was dissolved into the hydrochloric acid solution. The solution could be used as PAC after adjusting the required alumina concentration and the basicity. Comparing to the conventional method far preparation of PAC using aluminum hydroxide, material cost could be saved in this method. Also, there is an additional merit in view of recycling of the waste aluminum dross by reducing the amount of waste dross to be landfilled.

• Resources Recycling
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• v.16 no.5
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• pp.3-7
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• 2007

Waste aluminum dross was processed to prepare alum with sulfuric acid, and poly aluminum chloride(PAC) with hydrochloric acid. Metallic aluminum remained in the waste dross was dissolved into the sulfuric acid solution, and the solution could be used as alum for water treatment chemicals after adjusting the required alumina concentration and pH of the solution. Also, it was dissolved into the hydrochloric acid solution and processed to make PAC solution. Compared with the conventional method for preparation of alum and PAC using aluminum hydroxide, material cost could be saved in this method. Also, there is an additional merit in view of recycling of the waste aluminum dross by reducing the amount of waste disposed to landfill.

• Resources Recycling
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• v.15 no.4 s.72
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• pp.60-63
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• 2006

Waste aluminum dross was leached with sulfuric acid to prepare alum used for water treatment product. The remained metallic aluminum in the waste aluminum dross was extracted into the solution to make aluminum sulfate solution. The solution could be used as alum for water treatment product after adjusting the required alumina concentration and the basicity. Comparing to the conventional method for alum using aluminum hydroxide, material cost could be saved in this method. Also, there is an additional merit in view of recycling of the waste aluminum dross by reducing the amount of waste dross to be landfilled.

• Journal of the Korean Ceramic Society
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• v.39 no.7
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• pp.704-709
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• 2002

To improve the mechanical properties of $Al_2$O$_3$/ZrO$_2$composites, the homogeneous dispersion of ultra low size ZrO$_2$ particles in $Al_2$O$_3$ceramics have been controlled by coprecipitation method. In case of mechanical mixing of ZrO$_2$ powders with $Al_2$O$_3$, homogeneous dispersion and controlling the ZrO$_2$ size were relatively difficult due to high sintering temperature. So nanosized Zr hydroxide was coprecipitated from ZrOCl$_2$/Y(NO$_3$)$_3$ solution with commercial sub-micron sized $\alpha$-alumina (Sumitomo : AES-11(0.4 ${\mu}{\textrm}{m}$)) and high purity ultra low sized $\alpha$-alumina (Taimei Chemical (0.22 ${\mu}{\textrm}{m}$)) for low temperature sintering. By this partial coprecipitation method, relatively low sized ZrO$_2$ dispersion in $Al_2$O$_3$/ZrO$_2$ composites was achieved at 150$0^{\circ}C$-1$600^{\circ}C$ of sintering temperature range and their mechanical properties were measured.