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A. Kutsch, C. Hofstetter, S. Baudis, M. Schwentenwein, J. Stampfl:
"Investigations on the rheology and deagglomeration of digital light processing based vat polymerisation of Si3N4 slurries containing different dispersing additives";
Talk: ESIAM, Online; 09-08-2021 - 09-10-2021.

There is a huge variety of patients suffering from health issues, which require bone
implants. One approach to treat patients needing bone implants is to use personalized bone
implants fulfilling specified needs of the patient. A promising approach to provide these
patient-specific implants is by additive manufacturing as complex geometries can be
produced using a CAD-CAM file. One material, which is very attractive for implants is Si3N4
as research has shown that medical grade Si3N4 is biocompatible, stable in vivo, and it can
be seen on radiographic images. Si3N4 has superior properties like its mechanical strength
in combination with wear resistance, hardness, and high temperature stability.[1] In contrast
to oxide ceramics, non-oxide ceramics as Si3N4 are more challenging to process as they
absorb and scatter light due to their dark colour and high refractive indices, respectively.
Producing dense ceramic bodies by digital light processing based vat polymerization (DLP)
is a two step process. First, a green body is generated via layer by layer polymerization of a
ceramic filled resin. Second, the green body is thermally treated to obtain a dense ceramic
object. We focused on the first process step as it is challenging to process Si3N4 using DLP
due to the scattering and absorption of light leading to a low penetration depth. Hence, we
examined the curing depth, penetration depth and critical energy of Si3N4 slurries.
One requirement to process Si3N4 slurries by DLP is a deagglomerated stable slurry
whereby agglomerates must be smaller than the layer heights. Moreover, the rheologic
properties are important for processability. Both, agglomerates and rheologic properties
can be influenced by dispersants. Thus, the effect of different polymeric dispersants was
analysed in a 39 vol% Si3N4 slurry.