The effects of cold sintering parameters on the densification of Na₂WO₄ ceramics using Na₂WO₄·2H₂O dry powders

Cold sintering process (CSP) combines transient liquid phase and/or external pressure to assist the densification of ceramics, the sintering mechanism of which is typically dominated by the “dissolution–precipitation” process. In this work, Na₂WO₄·2H₂O dry powders without liquid water have been used as the “liquid phase” to realize the densification of Na₂WO₄ ceramics. The effects of sintering parameters on the CSP of Na₂WO₄ ceramics using Na₂WO₄·2H₂O dry powders are systematically studied, including sintering temperature, external pressure, sintering process time and the amount of Na₂WO₄·2H₂O phase. It is found that the “liquid phase,” that is, Na₂WO₄·2H₂O is the key factor for controlling the CSP of Na₂WO₄ ceramics, and Na₂WO₄·2H₂O hydrate shows an advantage of homogeneous dispersion of liquid water. The sintering temperature affects the densification mechanism involved with plastic deformation and the “dissolution–precipitation,” external pressure accelerates the densification process, and enough sintering process time ensures the completion of CSP. Finally, the optimum cold sintering parameters of Na₂WO₄ ceramics by Na₂WO₄·2H₂O powders are obtained at 150°C and 240 MPa for 60 min with a pretreatment at 150°C for 30 min.