Cold Sintering: Progress, Challenges, and Future Opportunities

Abstract

Cold sintering is an unusually low-temperature process that uses a transient transport phase, which is most often liquid, and an applied uniaxial force to assist in densification of a powder compact. By using this approach, many ceramic powders can be transformed to high-density monoliths at temperatures far below the melting point. In this article, we present a summary of cold sintering accomplishments and the current working models that describe the operative mechanisms in the context of other strategies for low-temperature ceramic densification. Current observations in several systems suggest a multiple-stage densification process that bears similarity to models that describe liquid phase sintering. We find that grain growth trends are consistent with classical behavior, but with activation energy values that are lower than observed for thermally driven processes. Densification behavior in these low-temperature systems is rich, and there is much to be investigated regarding mass transport within and across the liquid-solid interfaces that populate these ceramics during densification. Irrespective of mechanisms, these low temperatures create a new opportunity spectrum to design grain boundaries and create new types of nanocomposites among material combinations that previously had incompatible processing windows. Future directions are discussed in terms of both the fundamental science and engineering of cold sintering.

Mechanism studies of hydrothermal cold sintering of zinc oxide at near room temperature

“…One means of achieving this is with a low pH, whereas another is dissolving Zn(OAc) 2 . The transport mechanism for densification appears to be the exchange of Zn 2+ from one grain surface to a second grain surface into and out of the acetate solution facilitated by the uniaxial pressure applied …”

Materials research & measurement needs for ceramics additive manufacturing

“…Developed largely in academia, cold sintering is realized by adding a small quantity of water (or other solvent) to ceramic powder, so that densification occurs through the partial dissolution of solid particles in transient aqueous phase, followed by re-precipitation. [57][58][59][60] See Figure 9. The process requires some pressure (typically less than 200 MPa) and heating, typically to less than 300°C-much lower than used in conventional sintering.…”

Single‐step densification of nanocrystalline CeO2 by the cold sintering process

“…Given the recent success in cold sintering ceramics, the present work aims to extend cold sintering to the CeO 2 system. A first attempt was made by Charoonsuk et al using water as a transient solvent for cold sintering at 180°C, 500 MPa and up to 60 hours, followed by an annealing step at 1100°C to obtain 96% dense CeO 2 samples …”