3D Printing of Carbides Using Renewable Resources
Authors: Sullivan Morgan Claire , Islam Monsur , Martinez-Duarte Rodrigo 
Published: February 2020

Here we present preliminary results on fabrication of 3D complex shapes of porous carbide material by additive manufacturing. Porous carbides feature unique properties such as high melting point, high chemical stability, low thermal expansion coefficient, low density, high surface area and high specific strength [1]. The current state of the art for fabrication of carbide parts includes incomplete sintering and templating method. However, these methods use non-renewable carbon precursors, which is a matter of concern for the sustainability of the Earth. Furthermore, the shape of the carbide parts strongly depends on the use of mold and making of a 3D complex shape is challenging in these methods. Here we postulate the fabrication of 3D complex shapes of porous carbide material by 3D printing of a biopolymer composite followed by carbothermal reduction reaction. Recently we reported an environment friendly and sustainable approach for synthesis of tungsten carbide using a renewable biopolymer composite [2], which resembles a gel material. The renewable biopolymers eliminate the use of non-renewable carbon precursors and the Bingham plastic nature of the composite allows for layer-by-layer fabrication. The additive manufacturing will eliminate the dependence of mold and it can be possible to fabricate 3D intricate shapes, which are challenging in current methods. The potential application of such 3D printed carbide shapes includes lightweight structural material, catalysts supports, high temperature filters and insulations.
The biopolymer composite we used here was composed of iota-carrageenan (IC) and chitin. The IC powder was mixed to chitin in a 1:4 weight ratio. As our initial target was to fabricate 3D printed shapes of tungsten carbide (WC), we mixed tungsten trioxide (WO3) nanoparticles with the biopolymer powders such that a molar ratio of WO3:C equal to 1:6 was achieved. Ultrapure water was added to the biopolymer-WO3 nanoparticle mixture and stirred with a homogenizer to obtain the gel-like composite. The gel composite was loaded into a syringe and extruded into 3D shapes using a paste extruder (Discov3ry) coupled with a 3D printer (LulzBot TAZ 5). Figure 1a shows such a 3D printed shape of the polymer composite. Once the printing was done, the 3D printed composite was dried overnight to obtain a 3D shape of xerogel (Figure 1b). The 3D shape of the xerogel was heat treated at 1300 °C for 3 hours in nitrogen atmosphere to obtain 3D shapes of WC (Figure 1c). The composition of the heat-treated sample was confirmed by the x-ray diffraction (XRD) spectroscopy, as only peaks of WC were observed in the XRD pattern.
Ongoing work is 1) characterizing of the shrinkage of the 3D printed parts during drying and heat treatment; 2) implementing a design of experiments to obtain different dimensions of cellular architectures and understanding the effect of printing on those cellular architectures; 3) characterizing the mechanical properties of the 3D printed cellular architectures of WC.
References:
[1] Presser, V.; Heon, M.; Gogotsi, Y. Advanced Functional Materials., 21, 810-833 (2011).
[2] Islam, M., Martinez-Duarte, R., 2017, “A sustainable approach for tungsten carbide synthesis using renewable biopolymers,” Ceram. Int., 43(13), pp. 10546-10553.

Figure 1