Formulation of sodium borosilicate glass inks from ceramic precursors for Direct Ink Writing

Abstract

Additive manufacturing (AM) refers to a series of techniques in which, in contrast to traditional manufacturing techniques, the final pieces are achieved by adding material instead of subtracting it. These technologies have been developing for more than 25 years and they are also referred to as Rapid Prototyping, Freeform Fabrication, Layered Manufacturing, 3D Printing and others, being all synonyms. By using these techniques, complex shapes can be produced with practically any material, allowing virtually infinite applications for AM techniques. The way the material is added depends on the specific technique used. Each one has its own characteristics, advantages and limitations. Extrusion processes are the most common ones among AM. To form final pieces with these processes, the material is forced through a nozzle and deposited creating a three dimensional matrix. The need of a post treatment also depends on the technique. Nevertheless, all AM processes produce final or near-final pieces. This work aims to study the possibility of formulating sodium borosilicate glass (NBS) inks for Direct Ink Writing (DIW), an extrusion based AM technique. DIW ceramic inks are highly viscous solutions with specific rheological properties that let them retain its shape after being extruded. These inks are commonly a mixture of ceramic powders and a rheological agent, however, it is also possible to mix ceramic precursors with rheological agents to formulate them. Specifically in the synthesis of silica and silica derivate glasses, the ceramic powder method is the most utilized. In contrast, little information can be found for the ceramic precursors approach. Therefore, a first approach to produce NBS glass from precursors has been studied. Sol-gel method was used as the route to produce NBS glass from precursors. Addition of a poloxamer (Pluronic-F127) was explored to achieve the rheological behaviour desired and different inks where formulated. The rheological properties of the inks formulated were characterized, being the most suitable ones printed and sintered to verify the feasibility of the process developed. Finally, a series of characterization techniques where proposed to fully determine the properties of the material synthesized. Sol-gel method is suitable to form NBS glass from precursors and the optimizations explored gave positive results. Pluronic-F127 as rheological agent in combination with the NBS glass solution behaves as a pseudoplastic non-Newtonian fluid. The highest loaded printable ink is the formulation with a content of 75% PLU-F127 33% (w/w) + 25% NBS-12 by volume. Higher concentrations of NBS-12 cannot retain the given shape after printing. Altogether, is possible to produce printable NBS glass inks as a proof of concept. The sintered samples are unable to retain their given shape and the final appearance is not the expected one, however, the process developed does yield a final NBS glass piece