Development of Stochastic and Anisotropic Multiscale Ceramics Using High Aspect Ratio Sacrificial Fillers

Abstract

This thesis aims to establish a straightforward and cost-effective way to form porous ceramics. There is a specific emphasis on creating anisotropic structures via a directional ice-templating technique and hard-templating using the sacrificial filler method. Cellulose nanocrystals (CNCs) aerogels have been created via a ceramic suspension of 100g/mL of CNC powder and deionized water. Samples were then frozen, in cylindrical stainless-steel molds, using a directional ice-templating method, followed by a freeze-drying process to sublimate out solvent and create a mesoporous aerogel. The porous aerogels formed were of white color and extremely lightweight, and showed various microstructural morphologies including lamellar sheeting, channels, and honeycomb structures. These samples were used as a hard-template for a chosen ceramic precursor. The precursor of choice was titanium isopropoxide (TTIP), which is a well-known titania precursor that has been reported in literature. TTIP infiltrated the aerogel structures via a one-step "wicking" procedure that induced a hydrolysis reaction between the TTIP and the hydroxyl groups within the already-formed CNC aerogel. Infiltrated aerogels were then heat-treated to 1000 °C to burnout the CNC sacrificial filler material, and densify the final porous ceramic structure. Throughout each stage of the creation of these structures, various characterization techniques were utilized to further understand morphology and chemical structure. Specific techniques include scanning electron microscopy (SEM), x-ray diffraction (XRD), thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) analysis.