Anisothermal sintering of ZnO. The

Anisothermal sintering of ZnO. The relative density evolution33 and specific surface area reduction28 during the anisothermal ZnO cold sintering resembles the basic shape form of the higher temperature solid state sintering process (Fig. 1a). By assuming no powder extrusion and no radial pellet shrinkage taking place during the cold sintering, the relative density can be directly projected from the linear shrinkage and initial/final relative densities. As ZnO cold sintering employs acetic acid solution as a transient phase in an open system, allowing it to mostly evaporate during the heating ramp, the rapid linear shrinkage between 3 and 6 minutes may be recognized as combined effects of powder densification and liquid evaporation. However, as thermal gravimetric analysis (TGA) of the wet green body showed that the weight loss was only 3% of the total weight up to 120◦C (Fig. S4), despite the initial 15 wt.% of the added transient phase. Hence, the TGA result indicates that following points; 1) excessive transient liquid can be extruded from the wet green body during the 5-minute pressure stabilization prior to the cold sintering (Fig. S5) and 2) liquid evaporation can be considered as only a minor effect for the linear shrinkage, as the remining liquid will be likely located in the pore spaces between particles.