| Summary: | Porous metal oxides are an important class of engineering materials with unique combinations of lightweight, mechanical, photovoltaic, catalytic and thermal properties. The structural stability and load-bearing capabilities of porous metal oxides can be improved if stretch/compression-dominated lattice designs are used instead of bending-dominated foam structures. Here, we introduce a simple, scalable technique that involves the dip-coating of 3D printed polymeric lattices, of simple cubic design, in a metal particle (Fe and Cu) suspension. Subsequent heat treatment in a furnace removed the polymeric core and binder, leaving behind a hollow-truss lattice structure composed of sintered and oxidized metal particles. Examination of its microstructure reveals that the hollow-truss lattices have three levels of hierarchy, namely, the length/ width of the lattice strut (∼1 mm), the thickness of the coating (∼0.1 mm) and the size of the pores/ particles (∼0.01 mm). This hierarchical arrangement of material enabled the hollow-truss metal oxide lattices to achieve ∼1% relative density, which is lower than that achievable with ceramic foams. Under quasi-static compression, the hollow-truss lattices experienced multiple steps of fractures and exhibited highly serrated stress–strain curves. The relative modulus and relative strength of hollow-truss lattices were found to be related to the relative density by a power law relationship, with an exponent of 1.2 and ∼1.3, respectively. A detailed analysis showed that the slight deviation of the mechanical properties from an ideal stretch-dominated design was primarily due to the presence of small amounts of porosity in the metal oxide coating. Nevertheless, the load-bearing efficiency exhibited by the hollow-truss metal oxide lattices was found to be comparable or superior to that of hollow-truss alumina micro- and nano-lattices, as well as ceramic foams.
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