Effect of Inorganic Salt Coating on Light Scattering and Photocuring Behavior of Si3N4 Suspensions for DLP Printing

In this study, a novel inorganic surface modification strategy was proposed by coating silicon nitride (Si 3 N 4 ) powders with potassium chloride (KCl) to enhance their optical and rheological behavior for high-precision digital light processing (DLP) additive manufacturing. The influence of KCl coating content (0–8 wt%) on the photopolymerization, rheological properties, densification behavior, microstructure, and mechanical performance of Si 3 N 4 ceramics was systematically investigated. The results revealed that molten KCl at 900 °C effectively wet and redistributed on the Si 3 N 4 surface, forming a uniform KCl/SiO 2 composite coating. This coating reduced the refractive index mismatch at the particle–resin interface, suppressed Mie scattering, and significantly increased the curing depth while minimizing lateral over-curing. The optimal coating condition (3 wt% KCl, 900 °C, 5 h) achieved enhanced curing depth, improved slurry flowability, and stable dispersion without excessive agglomeration. However, excessive coating (≥ 5 wt%) intensified surface oxidation and led to Si 2 N 2 O formation, resulting in porous microstructures and severely reduced mechanical strength. The bending strength declined from 697 MPa (0 wt%) to 97 MPa (8 wt%). By contrast, the 3 wt% KCl-coated powder yielded Si 3 N 4 components with relatively high density, smooth surfaces, and excellent dimensional fidelity after sintering. These findings demonstrate that ionic-salt coatings offer a controllable and scalable approach to tuning light–matter interactions and interfacial behavior in ceramic slurries, paving the way for the additive manufacturing of complex Si 3 N 4 structures with superior precision.