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

作者：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

来源：Ceramics International, 2021, 47(19): 26869-26876.

DOI：10.1016/j.ceramint.2021.06.096

• Oxalic acid
• Activation
• gamma - Al2O3
• Phase transformation
• alpha - Al2O3

Converting the gamma phase into the alpha phase completely is necessary in the presintering stage of industrial alumina (Al2O3), which requires high temperature and energy consumption. To reduce the presintering temperature, gamma-Al2O3 was activated by oxalic acid. XRD, Al-27-MAS-NMR and TG-DSC were used to characterize the gamma -alumina before and after activation, and the phase transformation was studied. The formation temperature of alpha-Al2O3 decreased to 1029 degrees C for oxalic acid activated gamma-Al2O3, and the alpha-fraction was 100% for activated gamma-Al2O3 at 1300 degrees C. After oxalic acid activation, the diffraction peak intensity of gamma-Al2O3 decreased significantly; the results of Al-27-MAS-NMR suggested that octahedral [AlO6] in gamma-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 alpha-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 gamma-Al2O3 and extracted Al as three complexes of [Al(C2O4)](+), [Al(C2O4)(2)](-) and [Al(C2O4)(3)](3-). Oxalic acid activated gamma - Al2O3 with a lower phase transformation temperature has broad application prospects in the alumina industry.

• 单位
  韩山师范学院