3D Printing of Inorganic Materials for Industrial Applications

3D printing of inorganic particles was first introduced in the 1990s, and since, multiple technologies have been developed for the purpose of printing inorganic structures. This thesis focuses on the possibilities and limitations of 3D printing of inorganic structures for industrial applications using the direct ink writing technology. The objective of this study was to prepare a shear-thinning and rapidly recovering printable paste with as high concentrations of inorganic particles as possible. Experimental methods involved preparation of different inorganic pastes, rheological evaluations of the different paste’s behavior, 3D printing and post-processing of different structures, and evaluation of post-processed structures by visual and mechanical analyses. Two different series of experiments were conducted in this thesis. In the first part a replication of a printable salt paste, as described in the article “3D Printing of Salt as a Template for Magnesium with Structured Porosity” by Kleger et al. (2019), was prepared, optimized, and printed to evaluate printability of a solids loaded paste. In the second part, the salt was replaced by a mixture of inorganic materials, and paste properties, printability, and quality of post-processed structures were evaluated. Another type of binder was also used in the inorganic pastes. After exploring different components and approaches, a suitable inorganic paste which met the required rheological requirements was obtained. This paste allowed 3D printing of each collection of particle size available for this work. The initial pastes consisted of one collection of particles and two binders. As the particle size increased, issues regarding the printing process occurred as inconsistent extrusion. To overcome this issue, particles of different sizes were incorporated in the paste, resulting in an even extrusion and improved flowability of pastes with larger particles present. The most promising structures contained approximately 75 wt-% of solids. The printed structures were post-processed at elevated temperatures. For this process, graphite powder was used to allow free contraction of the structures as they shrunk, and to prevent the structures from sticking to the platform. Apart from a few unsuccessfully post-processed structures, most structures showed no signs of failure. The post-processed structures were evaluated by different analyses, depending on components in the paste and structure design. DSC-TGA, SEM-EDS, and 4-point bending tests were performed on selected samples. Based on performance during processing and the results from post-processed structures evaluation, it can be concluded that a promising paste has successfully been developed for 3D printing of inorganic structures for industrial applications