Methods Spherical zirconia particles with a diameter of 500 μm were used to simulate uranium dioxide particles. Irregular tungsten carbide (WC) particles， sized between 50-100 μm, were utilized as the core to simulate irregular U₃Si₂ cores. The Al coating was prepared using an FB-CVD device with a conical fluidization tube, ensuring uniform coating by moving the particles like a fountain. In the experimental setup, triisobutylaluminum (TIBA) served as the precursor, placed in an evaporation tank outside the equipment. The TIBA vapor was transported to the fluidized bed by carrier gas, and the Al coating was deposited on particles through the high-temperature decomposition of TIBA. During the experiment, particle fluidization and the precursor deposition rate were regulated by adjusting the deposition temperature and carrier gas flow rate, while the precursor transport rate was controlled by modifying its evaporation temperature and carrier gas rate. The effects of various process parameters on the growth of Al coating were studied.

Results and Discussion A uniform and durable aluminum coating was achieved by optimizing the precursor carrier gas velocity, reaction temperature, and precursor evaporation temperature. The coated particles showed a metallic luster, with no adhesion between them, indicating good fluidity during the coating process without stagnation in any specific region. A uniform and intact Al coating free from cracking, protrusions, or delamination was formed, and it was well-bonded with the matrix particles. Energy dispersive spectroscopy (EDS) analysis revealed that Al was the main component of the coating, with a growth rate of approximately 2. 6 μm/h. Additionally, by co-fluidizing zirconia particles with irregular WC particles, a uniform Al coating on the surface of the irregular particles was realized as the irregular WC particles were driven to form a uniform flow pattern.

Conclusion A uniform and dense Al coating was successfully deposited on the surfaces of the spherical zirconia particles and irregular WC particles using TIBA as the precursor via the FB-CVD method. The conclusions are: 1) An Al coating preparation system was designed, and stable transport of the TIBA precursor was successfully realized. A stable and durable Al coating was achieved through process parameter optimization. 2) The relationship between the growth rate of Al coating and process parameters was verified. The deposition rate of the Al coating increased with higher reaction temperatures and precursor transport volumes, but excessive increases led to undesirable deposition in other areas of the equipment. 3) The growth rate of the Al coating was about 2. 6 μm/h， and the prepared Al coating exhibited uniform thickness with interior pores. Also, the coating was tightly bonded to the core without gaps or delamination. 4) A uniform Al coating on the surface of irregular particles was achieved through the co-fluidization process.

Keywords：coated particle; advanced nuclear fuel; aluminum coating; fluidized bed; chemical vapor deposition