Additive manufacturing of porous ceramic structures from preceramic polymers

Abstract

This doctoral thesis describes the additive manufacturing of porous structures starting from preceramic mixtures. Preceramic polymers are a class of inorganic polymers which can be converted to a ceramic with high yield. The use of a preceramic polymer has been explored in this work with the double aim of providing the desired ceramic phases and of facilitating the shaping processes. The work is divided in three parts. In a first project, the powder-based three-dimensional printing technology has been applied to a preceramic polymer powder. Complex porous structures with Kagome and octahedral geometries have been replicated. The preceramic polymer was successively converted to a unique SiOC phase upon heat treatment in inert atmosphere. This approach, in contrast to the use of a ceramic powder, allows an easier shaping and the achievement of relatively higher green densities, due to the dissolution and re-solidification of the polymer in the process. The shaping of fine porous structures is particularly suited to this material because problems related to gas release during the polymer-to-ceramic transformation are limited. In a second project, the same powder-based technology was applied to mixtures of a preceramic polymer and ceramic fillers. In this case, the preceramic polymer acts as a binder for the fillers during the printing process. Upon heat treatment in air, the polymer is converted to silica, which then can be reacted with the fillers in the mixture in order to form silicate ceramic phases. This approach is very versatile and has been used to form apatite-wollastonite bioceramic composites, which have been shaped into porous scaffolds with designed porosity and cylindrical or cubic geometries. Finally, a different technology, which is an extrusion-based printing, has been applied. In this technique, as opposite to powder-based technologies, the part is not supported during its build-up, therefore a careful tailoring of the ink rheology is necessary in order to create spanning features. In this context, mixtures of a preceramic polymer and fillers were formulated which had a suitable shear-thinning behaviour, with the help of additives. A hardystonite ceramic, which is a bio-silicate phase, was formed upon heat treatment in air. Hardystonite scaffolds with orthogonal pores were successfully shaped by the deposition of fine (< 0.5 mm) filaments.%%%%Diese Dissertation beschreibt die Additive Fertigung von porosen Strukturen aus prakeramischen Mischungen. Prakeramische Polymere sind eine Gruppe von anorganischen Polymere die, nach Pyrolyse, zu keramischen Materialien mit einer hohen Ausbeute verwandelt werden konnen. Die Verwendung von prakeramischen Polymeren wurde in dieser Arbeit mit zwei Zielsetzungen erforscht: die gewunschte keramische Phasen zu generieren und die Formgebung zu erleichtern. Diese Arbeit ist in drei Abschnitte eingeteilt: In einem ersten Projekt, wurde das Pulver-Bett 3D Druck Verfahren auf ein prakeramisches Pulver angewendet. Komplizierte porose Strukturen wurden mit Kagome und…