Enhanced flowability of fine cohesive Y2O3 powders in an enlarged atmospheric-pressure microwave plasma

The poor flowability of fine yttrium oxide (Y 2 O 3 ) powders poses a critical bottleneck in semiconductor and advanced ceramic applications, where consistent handling, coating, or compaction is essential. This study aims to address this challenge by implementing a scalable, solvent-free modification method based on atmospheric-pressure microwave plasma (APMP) treatment to improve both physical and electrostatic powder flow characteristics. Using an enlarged TE 20 -mode microwave torch, cohesive Y 2 O 3 powders were exposed to varying plasma powers (3–8 kW) to induce surface and morphological transformations. Post-treatment analyses revealed progressive partial spheroidization and smoothing of particle surfaces, as confirmed by SEM and surface fractal dimension measurements. Flowability improvements were quantitatively validated through multiple complementary metrics: the Hausner ratio and Carr index decreased from 1.47 to 31.9 % to 1.21 and 13.2 %, respectively, while the angle of repose declined from 56° to 28°. Rheological properties such as avalanche energy and static friction coefficient also dropped significantly, and electrostatic charging was neutralized (average potential shifting from −78.8 V to +0.4 V). Furthermore, dynamic flow tests indicated up to a 10-fold increase in fluidized volume, and mass flow rate exceeded 65 g/s through a standard 11 mm aperture at 8 kW plasma power. These results demonstrate that APMP treatment, particularly under stable high-power TE 20 -mode discharge, provides a robust mechanism for tailoring the flow performance of fine oxide powders. The findings offer practical implications for improving powder processability in next-generation manufacturing environments, including dry coating, additive manufacturing, and fluidized bed reactors.