Ink design, rheology and printability of silicon carbide colloidal paste

The design and formulation of colloidal inks for robocasting present significant challenges, particularly when printing high-solids inks through fine nozzles. While low-solids inks are easier to print, they compromise dimensional accuracy due to excessive shrinkage post-sintering. To mitigate shrinkage and maintain dimensional accuracy, high-solids inks are preferred. However, the high concentration of solids required for these inks makes them difficult to print. This study investigates the influence of attrition milling on silicon carbide (SiC) particle size and morphology and its subsequent effect on the printability of SiC colloidal inks. Attrition milling was carried out on SiC powders for durations of 15, 30, 60, 120, 180, 300, and 600 minutes. The milled powders were characterized using scanning electron microscopy (SEM) and acoustic spectroscopy to assess changes in particle size and morphology. Based on the milled and as-received powders, eight (8) different inks were formulated to investigate the effect of particle size on the printability of the colloidal paste. In a subsequent experiment, a systematic ink formulation process was employed to optimize dispersant and flocculant concentrations, aiming to increase the solids content from 44 vol% to 50 vol%. The results demonstrated that attrition milling effectively reduces particle size and improves morphology, with a milling duration of 180 minutes identified as the most efficient for producing printable pastes while minimizing energy consumption. Rheological modeling and characterization revealed that a dispersant-to-flocculant ratio of approximately 12:1 was optimal for 50 vol% inks, achieving higher yield stress and elastic modulus compared to the 3:1 ratio used for 44 vol% inks. The fabricated 3D SiC lattice structures demonstrate the potential of this approach to produce geometrically complex, high-performance ceramic components. This work advances additive manufacturing techniques for ceramics by providing critical insights into ink design, particle size optimization, and controlled bridging flocculation, enabling the development of robust ceramic pastes for robocasting.