A novel composite binder design for direct ink writing alumina-based ceramics with enhanced strength at low sintering temperature

Direct ink writing (DIW), an extrusion-based additive manufacturing method, has been proposed as a versatile process for preparing ceramics for structural and functional applications. However, controlling the strength of ceramics during processing remains a challenge. In this study, a novel composite binder system consisting of aqueous polyvinylpyrrolidone solution and Al(H₂PO₄)₃ gel was adopted for the DIW of alumina ceramics. Throughout the process, the mechanical performance, dimensional shrinkage, phase compositions and microstructure of samples were evaluated. The results indicate that the composite binder improves green strength by generating hydrogen bonding, which considerably enhances the strength of alumina ceramics under low-temperature sintering due to the reaction between Al(H₂PO₄)₃ gel and nanosized clay particles. This also promotes the high-temperature sintering performance of Al₂O₃-based ceramics. Overall, the current composite binder is anticipated to be promising for DIW of alumina ceramics, providing sufficient strength for post-processing and greatly improving strength after low-temperature sintering.