Electrostatic integrated granulation of polymethyl methacrylate (PMMA)–Al2O3 composite granules for graded porous alumina fabrication

Electrostatic integrated granulation (EIG) enables the formation of spherical composite granules by tuning the surface charge of suspended particles. In this work, polymethyl methacrylate (PMMA, with an average diameter of 800 nm) was electrostatically integrated with Al 2 O 3 particles with an average diameter of 140 nm to prepare PMMA–Al 2 O 3 composite granules containing 0–50 vol% PMMA as a sacrificial pore former. Granules were uniaxially pressed and converted into porous Al 2 O 3 bodies via thermal decomposition at 255 °C followed by sintering at 1350–1450 °C for 1 h. SEM observations confirmed homogeneous PMMA dispersion within the granules and progressive pore generation after PMMA removal. Low PMMA contents (10–20 vol%) produced near-dense microstructures with very low water-accessible open porosity, whereas higher PMMA contents yielded increasingly open pore networks. The effective thermal conductivity decreased with increasing porosity, from 23 to 27 W m −1 K −1 for dense Al 2 O 3 to approximately 10 W m −1 K −1 for bodies fabricated from 50 vol% PMMA granules. Finally, graded porous Al 2 O 3 was demonstrated by stacking granules with stepwise PMMA contents (0–50 vol%), giving an intermediate bulk density (approximately 3.0–3.2 g cm −3 ) and thermal conductivity comparable to that of the sample containing 30 vol% PMMA. These results demonstrate that EIG-derived pore-former composite granules offer a practical and potentially scalable route for fabricating porous and graded-porosity ceramics.