Cracking Behavior and Mechanism of Gibbsite Crystallites during Calcination

Abstract

Cracking is one of the major contributors to the breakage of gibbsite particles during calcination, which generates superfine particles causing detrimental effects to the quality of product in the downstream smelter grade alumina production. Therefore, understanding the cracking behavior and mechanism can provide a solution to avoid the generation of superfine particles. In this study, for the first time, the phase transformation and structural evolutions from gibbsite to boehmite then to amorphous alumina during calcination via using focus ion beam–scanning electronic microscopy and in situ transmission electron microscopy are investigated. After detailed and real-time observations, it is illustrated that the crack formation on gibbsite particles during calcination can be attributed to the stress introduced by crystal shrinkage inside the crystallites during the phase transformation. Moreover, cracks in calcined gibbsite crystallites are found to initiate as pores inside the crystallites, which grow toward the surface and then form open cracks. Studies will open the possibility to tune the breakage of gibbsite particles.