Tunable properties of extrusion-based 3D-printed metakaolin ceramics achieved by adjusting CaCO3 content and sintering temperature

• DIW-fabricated metakaolin ceramics exhibit tunable properties. • CO2 release from CaCO3 creates pores and reduces shrinkage during sintering. • CaO forms anorthite, reinforcing pores and improving flexural strength. • CaO reduces densification temperature via liquid-phase sintering mechanism • Porous (1200 °C) and dense (1250 °C) ceramics are achieved using the same slurry. Ceramic components with tunable pore structures and properties are important for multifunctional ceramic materials. In this study, metakaolin ceramics with tunable properties were fabricated using extrusion-based additive manufacturing, including porous ceramics with suitable strength, high porosity, and low shrinkage rates, and dense ceramics with high strength, low porosity, and high shrinkage rates. The effects of CaCO 3 content and sintering temperature on the microstructure and properties of the metakaolin ceramics were systematically investigated and discussed. Rheological testing, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM) were used to analyze the phase composition and microstructural evolution during the sintering process. The results showed that slurries containing CaCO 3 exhibited apparent shear-thinning and thixotropic behavior, thus improving the forming quality and reducing the surface roughness of the green bodies. During sintering, CaCO 3 served as both a pore-forming agent and sintering aid. The release of CO 2 gas facilitated pore generation, and the resulting CaO promoted liquid-phase formation and reacted with Al 2 O 3 and SiO 2 to form anorthite, improving densification and flexural strength. When the CaCO 3 content increased to 16 wt%, the porous ceramics sintered at 1200 °C exhibited flexural strength of 14.34 MPa, porosity of 42.84%, and low shrinkage rates (<2.68%) in the X, Y , and Z directions. Meanwhile, the dense ceramics sintered at 1250 °C possessed flexural strength of 37.68 MPa, porosity of only 2.54%, and relatively high shrinkage rates (>14.09%). Therefore, metakaolin ceramics with tunable properties were successfully fabricated by adjusting the CaCO 3 content and sintering temperature to satisfy the diverse application requirements.