Development of ceramic slurries for Digital Light Processing (DLP) technique

Nowadays, additive manufacturing (AM) techniques are increasingly diffusing due to the use of materials without waste, with a view to sustainability and better use of resources. AM allows to minimise both the amount of material used for forming complex-shaped component layer by layer and post-process processing. Therefore, AM also minimises costs, energy consumption and process time, making the entire production process highly sustainable.

AM technologies are widely known and developed for metallic and polymeric materials, for which they are created. Recently the great interest in ceramic materials is leading to the application of AM technology for this class of materials. The use of 3D-printing for technical ceramics represents a sustainable solution, thanks to overcoming the limitations with conventional production process (e.g., onerous post-forming processing); at the same time, it is innovative because there are currently few commercially available feedstocks for AM.

This study describes the development of ceramic slurries for AM; specifically, slurries were developed for DLP technology. DLP is a new forming technique for advanced ceramics: a photosensitive liquid resin is filled with ceramic powder and selectively polymerized layer-by-layer by means of the light of a projector.

The slurry developed in this work, based on silicon nitride (Si₃N₄) powders, has optimized characteristics for DLP, such as low viscosity and high solid content. This process involved several steps:

- rheological characterization of the slurry, to identify the constituent percentages: functionalised monomers, dispersants, photoinitiators, and ceramic powders

- fine-tuning of the 3D-printer parameters

- verification of the slurry printability, with standard geometries

Therefore, the obtained slurries were developed both for the specific DLP technique and for obtaining ceramic materials and components for high-performance applications, i.e., applications that require a combination of high thermomechanical properties, thus taking full advantage of the characteristics of advanced ceramics.