Search for: All records

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 (MgCaSi₂O₆), 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 SiO₂, 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. 

A series of perovskite oxides (Ln = La, Pr, Nd, Gd; A = Ba, Sr) was investigated to understand the effects of A-site cation size on oxygen vacancy formation. Quasirandom mixed structures were generated using Alloy Theoretic Automated Toolkit (ATAT), followed by density functional theory (DFT) calculations. While mixing the orthorhombic structures with the hexagonal AMnO3 structures leads to lattices and global symmetries closer to cubic, the average volume generally increases with the average ionic size, and the local bond and angles exhibit more variations due to A-site mixing. DFT calculations and a statistical model were combined to predict oxygen reduction abilities. Thermogravimetric analysis (TGA) provided experimental validation of these predictions by measuring changes in oxygen non-stoichiometry under controlled conditions. Both indicated that larger A-site ionic size differences lead to greater, consistent with the larger variation in local structures, and enhanced redox capabilities. This combined computational-experimental approach highlights the importance of local structure variation, instead of average properties, in A-site cation engineering to optimize perovskite oxides for different devices relying on oxygen vacancy redox activity.