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 multi-scale particle grading on the microstructure, sintering kinetics, and mechanical properties of the ceramics. Through multi-scale characterization spanning from nano- to micron-scales 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 was found to possess 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, the atomic level sintering shrinkage and sintering kinetics. Specifically, multi-scale 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.

Three-dimensional (3D) printing technology is becoming a promising method for fabricating highly complex ceramics owing to the arbitrary design and the infinite combination of materials. Insufficient density is one of the main problems with 3D printed ceramics, but concentrated descriptions of making dense ceramics are scarce. This review specifically introduces the principles of the four 3D printing technologies and focuses on the parameters of each technology that affect the densification of 3D printed ceramics, such as the performance of raw materials and the interaction between energy and materials. The technical challenges and suggestions about how to achieve higher ceramic density are presented subsequently. The goal of the presented work is to comprehend the roles of critical parameters in the subsequent 3D printing process to prepare dense ceramics that can meet the practical applications.