Heterogeneous nucleation of thermal storage material LiNO3·3H2O from stable lattice-matched nucleation catalysts

Abstract

Promoting heterogeneous nucleation in liquid to solid phase transformations decreases undercooling (ΔT) and can dramatically alter the microstructure of a material. However, the design of material-specific nucleation catalysts remains non-trivial, especially for phases with complex structures. Here, we investigate heterogeneous nucleation in the technologically important thermal energy storage material LiNO3·3H2O (LNH), and demonstrate a close correlation of ΔT with lattice mismatch between planes of closely packed coordination polyhedra in a number of potential nucleation catalysts. This result supports extending the planar matching model for nucleation catalyst design to more complex structures by focusing on lattice matching of planes containing closely packed coordination polyhedra. In particular, Cu3(OH)5(NO3)·2(H2O) (CHNH) has a lattice mismatch of δa=−0.03, δc=−0.01 for the orientation (010)LNH||(100)CHNH and [100]LNH||[010]CHNH, and decreases ΔT by up to 66% over previously known catalyst phases. CHNH has a layered structure which delaminates along (100)CHNH, maximizing the number of potential nucleation sites for LNH along this lattice-matched plane and potentially contributing to the nucleation catalyst activity of this phase. Mixtures of LNH/CHNH are quite stable despite large numbers of cycles (N>900 cycles), and aging at elevated temperature for extended periods of time (t>250days).