Formation and characterization of hollow spherical Al₂O₃ granules synthesized by plasma-assisted spray pyrolysis

Plasma spray pyrolysis is an advanced technique for the synthesis of ceramic and metallic particles through the interaction of powder precursors with a high-temperature gas flow. In this research, the process was implemented using an experimental plasma-chemical reactor operated with a direct-current (DC) plasma torch to generate an atmospheric-pressure air plasma jet. Aluminum hydroxide (Al(OH)₃) was used as a precursor material. Under plasma heating, Al(OH)₃ decomposes into Al₂O₃ after the melting, drying, and crystallization processes within the reactor, resulting in the production of aluminum oxide particles.
Experiments were carried out with plasma torch powers ranging from 30 to 35 kW, when the gas temperature was sufficient to induce Al₂O₃ melting. The formed particles were analyzed using scanning electron microscopy (SEM) to determine their morphology and X-ray diffraction (XRD) to identify their crystalline phases and structural composition. The obtained Al₂O₃ particles exhibited a narrow size distribution (50–150 µm), spherical shape, and predominantly hollow internal structure with smooth hexagonal surfaces. Plasma spray technology enables the controlled formation of uniform, spherical granules: the morphology and size of the produced Al2O3 particles can be controlled by adjusting flow parameters, residence time, and injection geometry. Al2O3 particles prepared by this method exhibit excellent characteristics, including a fine size, narrow size distribution, pure phase, and hollow spherical morphology. The morphological analysis demonstrates the ability to manufacture powders with controlled characteristics for specific applications. The produced hollow spherical Al₂O₃ granules are promising as lightweight ceramic fillers, high-temperature insulators, catalyst supports, and feedstock materials for plasma spraying or thermal barrier coatings, where controlled particle morphology and narrow size distribution are essential.