## 3 Results and Discussion  
### Influence of Preparation Process on Flaky Al\({}_{2}\)O\({}_{3}\) Particles  
The methods for preparing large-sized flaky alumina primarily involve molten salt synthesis, the hydrothermal method, solid-state calcination, and the sol-gel process. A specific proportion of AlCl\({}_{3}\):6H\({}_{2}\)O, urea, and pure water is mixed and dissolved. Ammonia solution is gradually added while stirring. The mixture undergoes hydrothermal treatment at 220 \({}^{\circ}\)C for 24 h, followed by washing, drying, and calcination at 1000 \({}^{\circ}\)C for 4 h to obtain the desired product. Molten salt method: A specific ratio of aluminum sulfate, sodium sulfate, potassium sulfate, sodium phosphate, and titanium oxysulfate is combined with deionized water. The mixture is stirred and dissolved at 65 \({}^{\circ}\)C. Sodium hydroxide is subsequently added slowly and uniformly to adjust the pH values to neutrality. The resulting solution is then transferred to an oven and dried at 120 \({}^{\circ}\)C. Finally, the dried material is calcined at 1200 \({}^{\circ}\)C for 4 h to yield the final product. Solid phase method: large-sized sheet-like boehmite is mixed with 5-15% AlF\({}_{3}\) and subjected to calcination at 1200 \({}^{\circ}\)C for a duration of 2 h to achieve the desired outcome. Sol-gel method: A specific ratio of aluminum sulfate decahydrate is mixed with deionized water and stirred uniformly at 65 \({}^{\circ}\)C until completely dissolved. A predetermined amount of sodium hydroxide solution is slowly added while the PH is continuously tuned to neutrality. The resulting sol is then transferred to an oven and dried at 120 \({}^{\circ}\)C. Following this, the dried material is sintered in a high-temperature furnace at 1200 \({}^{\circ}\)C for 4 h. After cooling, the product is washed and dried again to yield flake alumina.  
We compared the flaky alumina samples prepared by these processes. From Figure 1, it is evident that the flaky alumina produced via the hydrothermal and sol-gel methods exhibited a small particle size, aligning with the literature's description. This suggests that these two methods are not suitable for developing large flaky alumina crystals but can yield a high diameter-to-thickness ratio. In contrast, the molten salt method, which leverages the Ostwald ripening effect, can produce large-sized, ultra-thin flaky alumina in inorganic molten salt environments. These flakes have a particle size greater than 20 \(\upmu\)m and a diameter-to-thickness ratio exceeding 100. The conventional solid-state sintering method employs a high-temperature calcination process of the boehmite/hydrogen aluminum precursor and fluoride ions to obtain large-sized flaky alumina. However, the resulting product is layered, with inconsistent thickness and significant interlayer interlocking [12]. The experimental results demonstrated that the molten salt method is an important meansof preparing large, flaky alumina with a high diameter-to-thickness ratio. However, the complex preparation process, severe environmental pressure, and poor stability of molten salts must be taken into account. Therefore, we innovatively combined the molten salt method with the solid-state sintering process, incorporating inorganic molten salts with fluoride ions. This approach utilized a large-sized boehmite precursor to obtain flaky alumina with a large size and a high diameter-to-thickness ratio, fully exploiting the synergistic effects of Ostwald ripening and Al-O-F traction from fluoride ion activation.