## 3 Results and Discussion
### Influence of Precipitant Type on the Morphology of the Aluminum Oxide  
To further investigate the influence of the precursors on the microstructure of the aluminum oxide, SEM analysis was conducted on the products obtained after calcination of the precursors prepared with different precipitants. The test results are shown in Figure 4.  
Figure 4: SEM images of alumina prepared with different precipitants. (**a**) Sodium bicarbonate; (**b**) ammonium bicarbonate; (**c**) potassium bicarbonate. Figure 3: The TG-DTG curves of alumina precursors prepared from different precipitants. (**a**) Sodium bicarbonate; (**b**) ammonium bicarbonate; (**c**) potassium bicarbonate. Figure 4 shows that, when sodium bicarbonate was used as the precipitant, the precursor sodium basic aluminum carbonate underwent high-temperature calcination, resulting in the formation of fused aluminum oxide with an average particle size of 80 nm. The aluminum oxide particles were interconnected and exhibited poor dispersion. This is attributed to the thermal decomposition of sodium basic aluminum carbonate during high-temperature calcination, which generates a significant amount of sodium oxide [22]. Sodium oxide acts as a fluxing agent, causing the rod-shaped precursor to melt and ultimately form a fused state with mutual adhesion, as indicated by the chemical reaction in Equation (6). The experimentally prepared fused alumina and rod-shaped alumina, due to their abundant porosity, excellent hardness, and wear resistance, along with their stable chemical properties, can disperse active substances on their surface and within their pores. They are suitable for applications in petroleum processing, catalytic cracking, and other fields. When ammonium bicarbonate was used as the precipitant, the precursor, sodium basic aluminum ammonium carbonate, contained a large amount of ammonium ions, carbonate ions, and hydroxyl groups. During the formation of aluminum oxide through high-temperature calcination, these ions not only had spatial filling effects but also contributed to the formation of aluminum oxide with a greater pore volume and larger pore size due to the gas-expanding pore-forming effect. The rod-shaped precursor structure was disrupted, and the microstructure of the aluminum oxide appeared as irregular short rods, as indicated by the chemical reaction in Equation (7). When potassium bicarbonate was used as the precipitant, the precursor boehmite underwent thermal decomposition. Due to the limited gas generation, the hexagonal precursor structure remained intact, and the microstructure of the aluminum oxide still predominantly consisted of hexagonal plates, as indicated by the chemical reaction in Equation (8). The experimentally prepared platelet alumina can serve as a filler, playing a crucial role in ceramics, plastics, and rubber products. It enhances hardness and adjusts the coefficient of thermal expansion, while its corundum structure improves heat resistance. Platelet alumina also possesses good dispersibility and parallel alignment, making it suitable for polishing powders. It enables the surface to be nearly parallel to the material being polished, minimizing surface damage, and maintaining a smooth, mirror-like finish after polishing. \[2 NaAl(OH)_{2}CO_{3}=Al_{2}O_{3}+2 CO_{2}\uparrow+2H_{2}O+Na_{2}O \tag{6}\]  
\[2 NH_{4}Al(OH)_{2}CO_{3}=Al_{2}O_{3}+2 CO_{2}\uparrow+3H_{2}O+2 NH_{3}\uparrow \tag{7}\]  
\[2\gamma-AlOOH=Al_{2}O_{3}+H_{2}O \tag{8}\]  
The N\({}_{2}\) adsorption-desorption results are shown in Figure 5. The curves in the N\({}_{2}\) adsorption-desorption isotherm plot exhibit a type IV adsorption branch with an H3 hysteresis loop. According to the BJH calculation, as shown in the pore size distribution curve, these shapes indicate the presence of a significant amount of mesopores. The specific surface area of alumina prepared with ammonium bicarbonate (68.54 m\({}^{2}\)/g) is higher than that prepared with potassium bicarbonate (27.07 m\({}^{2}\)/g) and sodium bicarbonate (6.34 m\({}^{2}\)/g).