Crossed analysis by T-history and optical light scattering method for the performance evaluation of Glauber's salt-based phase change materials

Glauber's salt (sodium sulfate decahydrate) is a phase change material (PCM) with promising thermal and physical properties. Moreover, it is very interesting from an economic point of view because it is possible to recover it as a waste product after the disposal of lead batteries. Nevertheless, it is restricted in its applications because of supercooling and phase segregation which require suitable additives that decrease the melting temperature and latent heat of fusion. The obtained mixtures are dispersions of powders in liquids, complex energy storage systems with properties depending not only on composition but also on preparation method. This last aspect is poorly addressed in literature for PCMs. Moreover, these systems are thermodynamically unstable, therefore information about the destabilization kinetic is necessary. The thermal analysis was based on the T-history method, considered by many authors as a more suitable method than Differential Scanning Calorimeter (DSC) for heterogeneous materials, since it requires larger-size samples. Nevertheless, long-term destabilization phenomena were not sufficiently investigated in literature, but they are very relevant because they influence the dispersion stability, homogeneity and energy performances. For this same reason, an optical light scattering method, based on the use of an innovative instrument, the Turbiscan(R), was proposed in this work to study the stability of such heterogeneous PCMs. Two different compositions of Glauber's salt/borax/bentonite were prepared under controlled sonication conditions and analyzed, as a case study. Transmission and backscattering profiles were studied, explained and correlated with thermal properties and sample compositions and preparation.