Exploring new solvent mixtures for near-net shaping of Ultra-High Temperature Ceramics via colloidal processing

Abstract

Suspensions of Ultra-High Temperature Ceramic (UHTC) powder with various organic solvents and co-solvent mixtures were prepared with the intention of verifying and understanding the relationship between interparticle interactions, flow behavior, and resulting particle packing. These relationships can be used to predict optimal solvent choices in colloidal processing of UHTCs to guarantee suspension stability through an adequate balance of the interparticle forces in suspension. Four organic solvents were selected: cyclohexane (CYC), tetrahydrofuran (THF), acetone (ACE) and N,N-dimethylformamide (DMF). The theoretical performance of each suspension, based on interparticle interaction energies, was compared to the empirical results. Detailed flow behavior was studied through rheological measurements and particle packing was measured by Archimedes’ method. The relationship between interparticle forces, viscosity and particle packing is discussed. Other contributing factors such as the performance of the dispersing agent were also considered and surface characteristics were reported using X-ray Photoelectron Spectroscopy (XPS), providing a modification to the adsorption parameter in the repulsive model. Low viscosity slurries were obtained at approximately 40% solid loading. CYC and THF demonstrated the ability to be effective co-solvents and produce the highest suspension stability with 100% CYC. These findings will help to produce UHTC complex shape component with minimal flaws during processing that can withstand extreme, high temperature oxidizing environments after densification.