Towards understanding the surface interaction mechanism of the Cold Sintering Process: A combined computational and experimental study

The Cold Sintering Process is an innovative protocol to obtain high density ceramic solids at extraordinary low temperatures ( [ view full abstract ]

The Cold Sintering Process is an innovative protocol to obtain high density ceramic solids at extraordinary low temperatures (<300 °C), with short processing times. This protocol has been used to successfully densify a wide variety of materials, including many electroceramics. The Cold Sintering Process benefits aqueous solutions to aid the densification of material through dissolution and precipitation/recrystallization processes. Differently from other sintering techniques in the literature, in the Cold Sintering Process, the free energy is lowered at the interfaces through hydrothermal reactions. This study combined computational and experimental work to investigate the interfacial reaction kinetics during the precipitation/recrystallization in the Cold Sintering Process. The computational studies were performed using molecular dynamics simulations with ReaxFF, a reactive force field which is capable of modeling large atomistic systems with reactive events for long simulation times. The acetic acid/water/zinc oxide (ZnO) interfaces were investigated for a variety of pH values (i.e. acetic acid concentrations). The simulation results show that the pH of the solution used during the dissolution in the Cold Sintering Process affects the precipitation. This observation, along with the outcomes of the experiments conducted in this study, suggests that the acetic acid concentrations result in a change in the amounts of defects in the final high-density solids. Furthermore, depending on its concentration, the presence of the acid might be augmenting the precipitation process, as it enables clustering of the ions in the solution. The water molecules have been observed not only to facilitate atomic diffusion through dissolution, but also might be assisting the reorientation of the precipitated compounds. The ReaxFF simulation results are in great agreement with the experimental findings. The investigations have also been extended to an important Li-electrolyte lithium aluminum titanium phosphate (LATP) ceramics to provide insight into the application of the Cold Sintering Process considering incongruent dissolution kinetics.