Kinetics and properties of porous alumina with a dense surface layer prepared via bimodal powder sintering

Porous alumina with a dense surface layer was prepared via pressureless sintering of bimodal powders followed by vacuum impregnation using a nano-alumina sol. Optimal properties (>25 % porosity, >500 MPa compressive strength) were achieved at 1200 °C using 6 wt% 600 nm alumina mixed with 200 nm alumina. Sintering kinetics analysis revealed that the incorporation of larger alumina powder increased the sintering activation energy by approximately 22 % at 8 wt%, with surface diffusion being the dominant mechanism during the initial sintering stage. The nano-alumina sol successfully sealed the surface pores, creating a uniform and dense surface layer that significantly improved the hydrophobicity of the material.