Multiscale particle grading of monodisperse spherical Al₂O₃ ceramics: Sintering activation energy and densification mechanisms

To address the limitations of existing research on ceramic particle grading regarding powder agglomeration and mechanistic depth, this study employed four types of uniform, monodisperse spherical α-Al₂O₃ powders. A series of grading systems, ranging from binary to quaternary, were constructed to systematically investigate the influence of multiscale particle grading on the microstructure, sintering kinetics, and mechanical properties of the ceramics. Through multiscale characterization spanning from nano- to microscale and from two to three dimensions, it was confirmed that the quaternary grading system (PG5) exhibited the fastest densification rate, the lowest porosity, and superior mechanical properties. Based on thermomechanical analysis (TMA) combined with Arrhenius equation calculations, the PG5 sample possessed the lowest sintering activation energy (129.95 kJ/mol). The results of the Rietveld refinement also showed the same trend. This revealed the essence of its rapid densification from the perspectives of geometric packing, atomic-level sintering shrinkage, and sintering kinetics. Specifically, multiscale grading not only optimized the particle contact network and mass transport pathways but, more crucially, significantly reduced the energy barrier for atomic migration, thereby fundamentally accelerating and completing the densification process. This study provides a clear mechanistic understanding and experimental basis for tailoring ceramic microstructures and sintering kinetics through rational powder structural design.