Silica‐assisted cold sintering of diopside for sustainable cementitious composites

Abstract This study explores cold sintering of naturally occurring minerals as supplementary cementitious materials (SCM) or cement analogs, which have the potential to transform the traditional high‐energy, high‐emission cement manufacturing pathways. Diopside (MgCaSi 2 O 6 ), a natural inosilicate, is used as the model system. As diopside is hard for cold sintering directly (by itself), this study demonstrates that the addition of amorphous silica nanoparticles can enable cold sintering of diopside. The cold‐sintered diopside–silica composites are characterized by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The effect of the relative weight percentage of silica added is examined. The relative density of the cold‐sintered composite reaches nearly 90% at 400 MPa and 200°C in 60 min. For specimens with the addition of 30 wt% or more of amorphous SiO 2 , cold sintering also induces partial crystallization, converting a fraction of amorphous silica to quartz. The crystallization kinetics exhibits a stochastic nature. The Vickers hardness of the cold‐sintered diopside–silica composite increases with increasing amount of silica, whichpromotes cold sintering, reaching ∼3 GPa with 20 wt% or more silica. The diopside–silica composites studied here serve as a model system for metal‐leached silicate mine tailings, which are expected to have nanoporous amorphous silica shells on silicate particles to enable the silica‐assisted cold sintering mechanism discovered in this study.