Investigations on the Rheology and Deagglomeration of Digital Light Processing Based Vat Polymerisation of Si3N4-Slurries Containing Different Dispersing Additives

Abstract

Silicon nitride (Si3N4) is a non-oxide ceramic with excellent material properties such as high toughness and strength, high temperature stability, and good wear and chemical resistance. Due to its good osseointegration and stimulated cell differentiation, as well as its osteoblastic activity and anti-infective behaviour, it can also be used as a medical implant. Its excellent biocompatibility and simultaneous mechanical strength are superior to calcium phosphates and make silicon nitride very attractive as scaffolds for bone regeneration in biomedical engineering. [1] Digital light processing based vat polymerization (DLP) is a 3D additive manufacturing technology and provides the possibility to produce complex-shaped, dense ceramic structures with high resolution. The ceramic component is mixed with a photosensitive formula to form a ceramic filled resin (slurry) that is cured layer-by-layer with layer thicknesses between 10 and 100 µm. The structured body, the so-called green body, must then be further processed to remove the organic components by evaporation or decomposition during debinding and densification by fusing the ceramic particles during sintering. In contrast to oxide ceramics, Si3N4 as a non-oxide ceramic is more challenging to process as it absorbs and scatters light due to its dark colour and high refractive index. Therefore, properties such as curing and penetration depth, as well as critical energy of Si3N4 slurries must be examined and tuned. Further requirements for good processability of a slurry are deagglomeration and stability, as well as suitable rheological properties. The agglomerates must not be larger than the layer thickness. Both, the agglomerates and the rheological properties, can be influenced by dispersants. For this reason, we have investigated the effect of different polymeric dispersants in a 39 vol% Si3N4 slurry.

[1] A. A. Altun, T. Prochaska, T. Konegger, und M. Schwentenwein, „Dense, Strong, and Precise Silicon Nitride-Based Ceramic Parts by Lithography-Based Ceramic Manufacturing“, Appl. Sci., Bd. 10, Nr. 3, S. 996, Feb. 2020, doi: 10.3390/app10030996.