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Direct aqueous ink writing of piezoelectric BCZT ceramics
Keywords: 3D printing, Piezoelectric ceramic, Rheology
Additive manufacturing techniques have been rapidly developed over the last thirty years and are applied in many different fields such as fused deposition modelling (FDM) in plastics and polymer based materials, and direct metal laser sintering (DMLS) in metal based materials [1-2]. Such technological approaches have gained gradual maturity and diversified the fields of application, being nowadays successfully applied not only to the fabrication of medical scaffolds, aerospace components and tooling, but also extending to daily life activities such as the food industry and construction [3-5]. The well-known traditional lead-based piezoelectric ceramics and the related composites have been designed since 1980s and fabricated by different techniques including extruding, tape- casting, dice and fill, gel-casting and additive manufacturing [6-7]. With the increasing awareness of environmental protection, lead-free piezoelectric ceramics and their doped counterparts have been investigated aiming at searching for potential substitute materials alternative to traditional lead-based ceramics [8]. Among the many compositions studied, barium titanate (BaTiO3) and its doped compositions such as (Ba,Ca)TiO3- x(Ba,Zr)TiO3 have been investigated and emerged to be a potential candidate with promising properties. However, most of the work carried out so far has been focused on improving its functional properties in the form of ceramic pellets prepared by dry pressing. Few reports concerning the fabrication of more complex shapes by other consolidation techniques, in order to expand the potential applications of functional materials. For example, BaTiO3 has been recently printed together with ABS polymer by FDM, where the feedstock derived from both thermoplastic polymer and ceramic powder is preheated and extruded. This is a traditional way of 3D-printing lead-free ceramics but the cost of the feedstock preparation is still high and the whole process is time- consuming [9]. Compared with the FDM, direct ink writing (DIW) is another way of 3D filament printing. Instead of hot extruding thermoplastic filaments and solidifying, DIW requires only shear- thinning viscoelastic fluids under ambient conditions, which makes the ink a key factor for the whole processing. Composed of ceramic powder with well distributed particle size, appropriate dispersing mediums and concentrated polymer, the fluid flows through the nozzle under the applied stress and build the objects in designed shapes. For BaTiO3 and its related powder, the biggest challenge lies in its inevitable hydrolysis during the preparation of ink. What hydrolysis brings also may change the stoichiometric composition of a doped powder and undermine the functional properties. Based on our previous works, hydrolysis reactions and non- stoichiometric dissolution could be effectively prevented by surface treating the powders of functional ceramics [10-11]. This paper reports on the preparation of stable aqueous suspensions from a surface treated (against hydrolysis) lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) powder synthesized by solid state reaction and the analysis of the possible detects which may happen during DIW. Inspired by the preparation of biological scaffolds, the required amounts of additives namely dispersant, thickener and flocculant were selected based on zeta potential and rheological measurements. Changing the rheology of the fluid suspensions by adding suitable thickening and flocculating agents enabled obtaining suitable inks for printing crack-free BCZT components.
Bo Nan,
Central European Institute of Technology
Brno, South Moravia
Czech Republic

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