New Polymorphs of the Phase-Change Material Sodium Acetate

Birger Dittrich,Peter Roloff,Justin Bergmann,Guido Reiss

doi:10.3390/cryst8050213

Abstract

Two new polymorphs of the phase-change material sodium acetate were characterized by single-crystal X-ray diffraction. A tetragonal form was found first. It converted to a orthorhombic form after measurement of a single crystal of the tetragonal form at 100 K and subsequent warming to ambient temperature. Hirshfeld surface fingerprint plots show the different packing environments of the two new compared to the two known orthorhombic polymorphs Forms I and II. The accuracy and precision of the structures were improved compared to conventional independent atom model refinement through the use of aspherical scattering factors of the invariom database. We think that the layered nature of all sodium acetate forms, and the thereby limited (“quantized”) availability of vibrational modes, is related to the phenomenon of supersaturation, which is connected to its phase-change properties.

Highlights

The use of fossil fuels is in most cases unsustainable
A phase change can be induced when the heat is required again. This way, energy can be stored and released in a controlled manner in space and time; or further converted if so desired or required, which cannot be achieved using water. Another major advantage of Phase-change materials (PCMs) over using water for storing heat is the significant reduction in storage volume
We want to speculate on the link between molecular vibration, lattice vibration, crystallization and supersaturation. The latter is of fundamental importance for the technical suitability of phase-change materials

Summary

Introduction

The use of fossil fuels is in most cases unsustainable. A necessary approach to cope with the limited availability of such fuels is to improve energy efficiency and to change to renewable sources of energy. Phase-change materials (PCMs) [1,2,3] can absorb and release excess heat through reversible changes in their solid state structures For such processes, the term latent heat thermal energy storage was coined. A phase change can be induced when the heat is required again This way, energy can be stored and released in a controlled manner in space and time; or further converted if so desired or required, which cannot be achieved using water. Another major advantage of PCMs over using water for storing heat is the significant reduction in storage volume.

Methods

Results

Discussion

Conclusion