Heterogeneous nucleation of thermal storage material LiNO33H2O from stable lattice-matched nucleation catalysts
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2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Promoting heterogeneous nucleation in liquid to solid phase transformations decreases undercooling (T) 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 LiNO33H2O (LNH), and demonstrate a close correlation of T 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 a = -0.03, c = -0.01 for the orientation (010)LNH||(100)CHNH and [100]LNH||[010]CHNH, and decreases T 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 > 250 days).
