3D Printing Transparent γ-Alumina Porous Structures Based on Photopolymerizable Sol–Gel Inks

A novel method for fabricating transparent porous γ-alumina 3D structures by printing at high resolution is presented. The process is based on combining digital light processing 3D printing (DLP) and sol–gel reactions, all performed in transparent solutions, resulting in ceramic monolithic porous structures. The aqueous printing solution contains mainly aluminum chloride, propylene oxide (PO), ethanol, and acrylic acid (AA). The printed polymerized structures are aged, followed by supercritical drying (SCD), and sintered at high temperatures. During aging and sintering, the printed objects shrink, thus enabling a final printing resolution far beyond the nominal value of the used printer. The resulting structures are crystalline γ-Al₂O₃, with a very high surface area, above 1800 m² g⁻¹, and optical transmission above 80% at 600 nm. In addition, SCD enables precise control of pores’ dimensions and total surface area, which are essential for applications including thermal insulation and catalyst support and for obtaining heat-resistant transparent optical devices.