Densification and mechanical properties of photopolymerized Si3N4 ceramics via oxygen reduction and phosphate adhesion

Vat photopolymerization 3D printing of Si 3 N 4 ceramics enables complex geometries, but oxygen inhibition during photocuring induces incomplete resin polymerization. Additionally, although larger Si 3 N 4 particles improve curing depth, their sparse packing after debinding compromises sintering densification. In the present work, the oxygen reduction effect of potassium iodide was utilized to mitigate the influence of surface oxygen on resin curing. As a result, the curing depth was enhanced to 132 µm, surpassing the previously reported values of less than 90 µm. This advancement enabled the successful fabrication of complex Si 3 N 4 ceramic components with a single-layer thickness of 50 µm. Furthermore, Al(H 2 PO 4 ) 3 was incorporated as a binder, which decomposes during the debinding process to form A-type phosphate salts on the surface of the large-size (2.66 µm) Si 3 N 4 powders. These salts establish physical bonds among the powders, effectively reducing interparticle spacing and promoting densification. The present work synthesized Si 3 N 4 ceramics with a flexural strength of 304 MPa at a relatively low sintering temperature of 1700°C.