The activation mechanism of oxalic acid on γ-alumina and the formation of α-alumina

• Published in: Ceramics international Vol. 47; no. 19; pp. 26869 - 26876
• Main Authors: Lin, Shao-Min, Yu, Ya-Ling, Zhong, Ming-Feng, Yang, Huan, Zhang, Chen-Yang, Zhang, Zhi-Jie, Xu, Wei, Xie, Jiong-Yan, Qiu, Yu-Chun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2021
• Subjects: Activation; Oxalic acid; Phase transformation; α - Al2O3; γ - Al2O3; Phase transformation; Activation; Oxalic acid; α - Al2O3; γ - Al2O3
• ISSN: 0272-8842; 1873-3956
• DOI: 10.1016/j.ceramint.2021.06.096

Converting the γ phase into the α phase completely is necessary in the presintering stage of industrial alumina (Al2O3), which requires high temperature and energy consumption. To reduce the presintering temperature, γ-Al2O3 was activated by oxalic acid. XRD, 27Al-MAS-NMR and TG-DSC were used to characterize the γ - alumina before and after activation, and the phase transformation was studied. The formation temperature of α-Al2O3 decreased to 1029 °C for oxalic acid activated γ-Al2O3, and the α-fraction was 100% for activated γ-Al2O3 at 1300 °C. After oxalic acid activation, the diffraction peak intensity of γ-Al2O3 decreased significantly; the results of 27Al-MAS-NMR suggested that octahedral [AlO6] in γ-Al2O3 was easier than tetrahedral [AlO4] to be attacked by oxalic acid, and the formation of pentavalent [AlO5] with higher reaction activity, which was in favour of the lowering formation temperature of α-Al2O3. The dissolution concentration of Al increased after oxalic acid activation, and the dissolution process was controlled by surface reactions. Oxalic acid mainly attacked the octahedral aluminium in γ-Al2O3 and extracted Al as three complexes of [Al(C2O4)]+, [Al(C2O4)2]- and [Al(C2O4)3]3-. Oxalic acid activated γ - Al2O3 with a lower phase transformation temperature has broad application prospects in the alumina industry.