Fabrication of Porous 3D Glass‐Ceramics by Direct Ink Writing of Alkali‐Activated Waste Fiberglass

This study demonstrates a strategy to overcome excessive foaming and geometric loss during thermal treatment of alkali‐activated waste fiberglass fabricated via direct ink writing (DIW). Waste Al 2 O 3 –ZrO 2 –SiO 2 (AZS) refractory and glass microspheres (GMs) were incorporated into the ink formulation. The GMs improved the rheological properties required for printing and subsequently acted as pore‐forming agents during firing at 800°C. Firing at 800°C generated hierarchical porosity through the incorporation of GMs and the decomposition of hydrated products. The thermally stable phases in the AZS controlled viscous flow and excessive foaming during firing, enabling retention of the printed geometry. The resulting structure exhibited a total porosity of 78.2%, a bulk density of 0.46 g/cm 3 , and a compressive strength of 5.8 MPa. This inorganic waste‐derived approach enables the fabrication of shape‐retaining porous glass‐ceramics with potential for lightweight insulation and filtration applications.