Investigating the crystallite morphologies and aggregation in boehmite powders: a combined analysis of two- and three-dimensional electron microscopy with x-ray diffraction

Abstract

Boehmite (AlOOH) is considered as an important precursor to γ-Al2O3 which when calcinated undergoes topotactic transformation to form the latter. Alumina has extensive applications in fields such as catalysis, abrasives, cosmetics among others. Boehmite falls under the category of hierarchical structures whose structural and textural properties are a result of its compositional and porous hierarchy. Although research has been carried out exquisitely to understand the complete representation of its structure, a true morphological model is an important key to understand and fully explain its transport properties during catalytic processes. 3D electron microscopy helps us to dive deeper into the different hierarchical entities of boehmite, bridging the gaps between the models and assumptions made using some more traditional characterization techniques. We present here deeper insight into the structural and morphological parameters of different commercial boehmites using 3D-TEM. Through the extraction of quantitative descriptors pertaining to hierarchical entities and subsequent comparison with bulk analyses, precise and comprehensive information regarding these microstructures can be obtained. The results of our study indicate that boehmite grades, which appear to be identical in terms of their grades, display discrepancies in the uniformity of particle sizes. Moreover, diverse platelet interactions result in varying types of pores in these grades. Furthermore, it has been observed that the interfacial interactions among various crystallographic planes exhibit variations across different specimens, thereby contributing to the distinctive compositions within the aggregates. The variation in aggregates of different boehmite grades is also reflected in the combination of four distinct quantified morphologies.