Freeform 3D-Printing of Pure Ceramics

Achieving a viable process for 3-dimensional printing of ceramics is a sought after goal in a wide range of fields including electronics and sensors for harsh environments, microelectromechanical devices, energy storage materials, and structural materials, among others. Low laser absorption of ceramic powders renders available additive manufacturing (AM) technologies for metals not suitable for ceramics. Polymer solutions that can be converted to ceramics (preceramic polymers) offer a unique opportunity to 3D-print ceramics; however, due to the low viscosity of these polymers, so far their 3D printing has only been possible by combining them with specialized light-sensitive agents and subsequently cross-linking them layer by layer by rastering an optical beam. The slow rate, lack of scalability to large specimens, and specialized chemistry requirement of this optical process are fundamental limitations. Here, we demonstrate 3D-printing of ceramics enabled by dispensing the preceramic polymer from the tip of a moving nozzle into a gel that can reversibly switch between fluid and solid states, and subsequently thermally cross-linking the entire printed part “at-once” while still inside the same gel. The solid gel, which is composed of mineral oil and silica nanoparticles, converts to fluid at in the vicinity of the nozzle as it moves, allows the polymer solution to be dispensed in the wake formed behind the nozzle path, and quickly returns to a solid state to maintain the geometry of the printed polymer both during printing and the subsequent high temperature (160 °C) cross-linking. We retrieve the cross-linked part from the gel and convert it to ceramic by high temperature pyrolysis. The specially designed gel was three orders of magnitude more viscous than the preceramic polymer at no shear, which provided a stable medium during the whole process for maintaining the shape of the printed material and prevented possible instabilities. The SEM images showed that the printed material was dense and without any apparent porosity or cracks. Three point bending tests were performed since both tension and compression are exerted to the specimens to obtain the mechanical performance of the material. Statistical analysis on the mechanical properties of the printed preceramic polymer and casted specimens revealed that the printed specimens had better characteristic strength (~260 Mpa) compared to the casted specimens (80 MPa). This scalable process opens up new opportunities for low-cost and high-speed production of complex 3-dimensional ceramic parts, and will be widely used for high temperature and corrosive environment applications, including electronics and sensors, microelectromechanical systems, energy and structural applications.