Mechanism of catalyst on morphological evolution of Al(OH)3 during Al-H2O reaction
(1. State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;
2. School of Mechanical Engineering, Shanghai Dianji University, Shanghai 201306, China;
3. Collaborative Innovation Center for Advanced Ship and Deep-sea Exploration, Shanghai Jiao Tong University, Shanghai 200240, China)
2. School of Mechanical Engineering, Shanghai Dianji University, Shanghai 201306, China;
3. Collaborative Innovation Center for Advanced Ship and Deep-sea Exploration, Shanghai Jiao Tong University, Shanghai 200240, China)
Abstract: The morphologies of Al(OH)3 crystals prepared via the Al-H2O reactions with various catalysts and the growth mechanisms of these crystals were investigated. The reaction was carried out with NaOH, KOH, tetramethylguanidine (TMG), and tetramethylammonium hydroxide (TMAH) as catalysts. The evolution of the obtained product was observed in situ, and the products obtained after 120 min of reaction have the shapes of the hexagonal prism, long-hexagonal prism, long rod, and irregular rod, respectively. In the NaOH and KOH systems, the products are gibbsite, and the gibbsite crystals grow along the (110), (001), and (100) faces in the NaOH system, and the (100), (102), and (110) faces in the KOH system. However, in the TMG and TMAH systems, the products are bayerite, and the bayerite crystals grow along the (110), (111), and (001) faces. It is worth mentioning that gibbsite has more Al—O bonds than bayerite, giving rise to the formation of columnar crystals.
Key words: crystal growth; aluminum hydroxide; preferential orientation coefficient; aluminum-water reaction; in situ observation