Polymer-derived ceramics with hierarchical porosity by phase separation

Abstract

Porous ceramics are desired materials in gas storage, separation and catalysis applicationsas they are thermally and chemically stable in harsh environments and may provide highspecific surface areas. However, the fabrication of components with complex geometriesand the introduction of and control over porosity is a task difficult to achieve through theconventional ceramic production process.Polymer-derived ceramics open up a plethora of manufacturing routes, additive manufacturing(AM) among many, during which pores can be integrated as a functional structurethrough sacrificial templating techniques. This diploma thesis investigates a promisingapproach for the fabrication of ceramic components via stereolithographic digital lightprocessing (DLP) 3D printing and the simultaneous introduction of porosity via phaseseparation. A phase-separating resin system, essentially consisting of silicon-based preceramicpolymer (PCP) and photo-curable monomer, was developed through cloud-pointtitration. The resin allowed for the printing of green bodies that subsequently underwentpyrolysis during which the PCP phase is thermally converted to SiOC and the monomerphase removed, leaving the space occupied behind as pores. The obtained porous ceramicparts were characterized by scanning electron microscopy, N2 physisorption and mercuryintrusion porosimetry. Additionally, NIR-Photorheology, thermogravimetric and differentialthermal analysis, combustion analysis and ATR-IR measurements were conducted.A resin system that enables the fabrication of intricate green bodies, consisting of Silres-MK as the preceramic polymer phase, and acrylate monomer (TMPTMA) as the sacrificialfiller phase, was successfully developed. Silicon oxycarbide ceramic components with specificsurface areas of up to 335m2/g and accessible porosity on multiple scales of lengthwere obtained after thermal post-curing and pyrolysis. The formation of macropores witha monomodal size distribution was achieved through the formation of a bicontinuousnetwork during DLP printing, resulting in samples with average macropore widths of0.226μm. Furthermore, an average mesopore width of 6.8 nm and micropores <2nmwere generated. Fine-tuning of the micro- and mesoporosity was achieved by varying theresin composition and the pyrolysis temperature, which highlights the potential for implementationas functional structure with adjustable porosity in green energy technology.