There are many methods for preparing nano alumina, which can be divided into three categories according to different reaction modes: solid-phase method, gas-phase method, and liquid-phase method^[3]In order to verify whether the prepared nano alumina powder results meet expectations, it is necessary to characterize the alumina structure under each process, and the most intuitive characterization method among many is microscopic observation.

As a conventional microscopic characterization device, scanning electron microscopy has the advantages of high magnification, high resolution, large depth of field, clear imaging, and strong stereoscopic effect, making it a preferred equipment for characterizing nano alumina structures.

The following figure shows aluminum oxide powders prepared under different processes observed using the national instrument quantum field emission scanning electron microscope SEM5000. The powders contain cubic, sheet-like, and rod-shaped nano aluminum oxide powders with particle sizes ranging from tens of nanometers to hundreds of nanometers.