• Resources Recycling
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• v.28 no.1
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• pp.15-22
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• 2019

There are three hydrometallurgical methods by which pure alumina can be prepared, such as hydrolysis of aluminum alkoxides, thermal decomposition of ammonium alum and thermal cracking of ammonium aluminum carbonate (AACH). The effect of solution pH and temperature and the nature of the impurities on the phase transition and the purity of the alumina thus produced was investigated. Hydrolysis of aluminum alkoxides and thermal decomposition of ammonium alum produce ${\alpha}$ and ${\gamma}$ alumina, while only ${\alpha}$ alumina can be produced by thermal cracking of AACH.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.242-246
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• 2006

[ ${\alpha}-Al_2O_3$ ] nanopowders were fabricated by the thermal decomposition and synthetic of Ammonium Aluminum Carbonate Hydroxide (AACH). Crystallite size of 5 to 8 nm were fabricated when reaction temperature of AACH was low, $8^{\circ}C$, and the highest $[NH_4{^+}][AlO(OH)_n{(SO_4){^-}}_{3-n/2}][HCO_3]$ ionic concentration to pH of the Ammonium Hydrogen Carbonate (AHC) aqueous solution was 10. The phase transformation fem $NH_4Al(SO_4)_2$, rhombohedral $(Al_2(SO_4)_3)$, amorphous-, ${\theta}-,\;{\alpha}-Al_2O_3$ was examined at each temperature according to the AACH. A Time-Temperature-Transformation (TTT) diagram for thermal decomposition in air was determined. Homogeneous, spherical nanopowders with a particle size of 70 nm were obtained by firing the 5 to 8 m crystallites, which had been synthesized from AACH at pH 10 and $8^{\circ}C,\;at\;1150^{\circ}C$ for 3 h in air.