3D printing of dense and porous alkali-activated refractory wastes via Direct Ink Writing (DIW)

Alkali-activated pastes prepared starting from refractory wastes were successfully 3D-printed via Direct Ink Writing. In particular, as raw powders, two different aluminosilicates were used: chamotte (CH, mainly composed of corundum, mullite and andalusite) and alumina-zirconia-silica (AZS, mainly baddeleyite, corundum and amorphous silica). First, pastes rheological parameters were optimized in terms of liquid-to-solid ratio and polyethylene glycol content. Then, both dense prismatic samples and lattice structures were successfully 3D-printed. Additionally, PMMA beads of 20 and 60 μm diameter were used to generate an additional porosity in both dense and lattice structures, leading to hierarchically porous materials. Indeed, samples were partially sintered up to 800 °C, to decompose PMMA beads, when present, and provide very high mechanical properties: a flexural strength of approx. 45 MPa was obtained for both AZS and CH dense samples. Moreover, the addition of 30 vol% of PMMA beads leads to macroporous samples without affecting mechanical properties.