Direct-Write Electrospinning of Highly-Loaded Ceramic Slurries for Additive Manufacture
Ceramics are desirable materials for a range of mechanical, electrical and biomedical applications, but they can be difficult to form and process. Additive manufacture is increasingly being explored for producing ceramic parts without moulds. In this work, a method for controllably patterning filaments containing high volume fractions of ceramic particles was explored, using electrospinning as the deposition method. Inks containing 50 vol% alumina powder in mineral oil or wax were deposited from a 200 μm inner diameter blunt, grounded needle at distances from 0.5 to 5.0 mm from a conductive plate with positive voltages of up to 10 kV applied to it. For the oil-based ink, jets with widths down to 25 μm were produced and an empirical relationship between the minimum jet width, nozzle height, flow rate and voltage was established. An average electric field of 2.0-2.5 kV/mm was found to give the most stable jets. The substrate speed was found to have a major effect on the jet width and entirely determine the deposit diameter due to the ink still being molten upon impact, as predicted by thermal modelling. Patternable features were explored with the wax-based ink. It was found that filaments deposited within 0.5 mm of each other would be attracted together and that the ability to bridge gaps was limited. Sharp corners were rounded to a radius of 0.4 mm, with deviations up to 2 mm from the corner. Investigation was constrained by the speeds achievable with the motion platform used, resulting in filament diameters around 100 μm. Several lattices produced by this process were successfully sintered to pure alumina, although little consolidation was achieved and the filaments were very porous. These samples had approximately 15 % of the strength expected if they were made of solid alumina.