Roadmap for densification in cold sintering: Chemical pathways

The cold sintering process (CSP) is a technique that enables densification of ceramics and composites at extremely low temperatures (T ​< ​400 ​°C) with the application of a uniaxial pressure and a transient solvent. At the laboratory scale, comparing direct sintering methods relative to CSP evidences that the latter could enable a sustainable eco-manufacturing path with considerable energy and emission savings, as well as fast processing times. Thus far, cold sintering has been applied to different materials, compounds, solid solutions, and functional composites, pointing to multiple future opportunities. This paper summarizes some of the transient phase selections, different chemical approaches and subtle chemical reactions with the powders which can be used to drive the cold sintering processes in many important ceramics and composites. In doing so, this paper highlights some of the reasons why the fundamental understanding of CSP mechanisms remains challenging, but classification of the pathways as outlined here should aid progress towards a more comprehensive understanding.