A Single Particle Nanomechanical Model for Cold Sintering

Ceramic materials are often manufactured by sintering at high temperatures, an energy intensive process that can introduce defects during cooling from processing temperatures. Recently a low temperature “cold sintering” process has been developed that uses high pressures to provide a driving force and a transient liquid phase as a rapid transport route to densify ceramic powders with significantly lower energy costs (Guo et al. J. Amer. Ceram. Soc. 2017; 100: 669).

Although the general mechanisms of the cold sintering process are understood, there has been little quantitative study of the process and no modelling carried out. The project will build on recent work in the Derby group where we have studied the enhanced dissolution of NaCl underneath a nanoindenter immersed in a saturated solution of the salt. Here creep indentation is driven by the extremely high contact pressure beneath the diamond indenter that drives diffusion transport of material to recrystallize on the crystal surface. This “pressure solution” mechanism for cold sintering is also believed to control the deformation of some minerals in the Earth’s crust. This experimental model will be extended by replacing the diamond tip of the indenter with a micromachined ceramic tip with a controlled spherical radius in the range 200 nm – 5 m. Using a Nanoindenter to apply precise loads in the N – mN range, and monitoring displacements at a resolution of 1 nm, the indentation of the spherical radius into a flat surface of the same material immersed in an appropriate saturated solution will be used as a model for the cold sintering process. This data will be used to develop a model for the approach of particles during cold sintering and finally a full predictive model of the process.