Robocasting of advanced ceramics: ink optimization and protocol to predict the printing parameters - A review

Direct-Ink-Writing (or robocasting) is a subset of extrusion-based additive manufacturing techniques that has grown significantly in recent years to design simple to complex ceramic structures. Robocasting, relies on the use of high-concentration powder pastes, also known as inks. A successful optimization of ink rheology and formulation constitutes the major key factor to ensure printability for the fabrication of self-supporting ceramic structures with a very precise dimensional resolution. However, to date achieving a real balance between a comprehensive optimization of ink rheology and the determination of a relevant protocol to predict the printing parameters for a given ink is still relatively scarce and has been not yet standardized in the literature. The current review reports, in its first part, a detailed survey of recent studies on how ink constituents and composition affect the direct-ink-writing of ceramic parts, taking into account innovative ceramic-based-inks formulations and processing techniques. Precisely, the review elaborates the major factors influencing on ink rheology and printability, specifically binder type, particle physical features (size, morphology and density) and ceramic feedstock content. In the second part, this review suggests a standardized guideline to effectively adapt a suitable setting of the printing parameters, such as printing speed and pressure, printing substrate, strut spacing, layer height, nozzle diameter in function of ink intrinsic rheology

Printability of carboxymethyl cellulose/glass-containing inks for robocasting deposition in reversible solid oxide cell applications

Water-based inks containing carboxymethyl cellulose (CMC) and glass particles were investigated in terms of rheological properties and printability for solid oxide cell joining application using robocasting for the first time. The ink formulation containing 36 vol% of glass showed the highest yield stress (9.6 × 102 Pa) and viscosity (4 × 104 Pa.s). CMC-based paste with 37 vol% of glass was selected for printing on Crofer22APU steel substrate due to its relatively low viscosity (2.6 × 104 Pa.s) and high storage modulus (1.4 × 105 Pa), thus ensuring an easier extrusion and shape retention upon printing. The high solid loading of 37 vol% along with optimised debinding and sintering stages enabled achieving high-quality Crofer22APU/glass sealant joining with a reproducible thickness and low porosity