An important feature when using low-melting mixtures of halides of s-elements as a refiner of electrolytes for chemical power sources and thermal storage materials in thermal batteries is the amount of volume increase in the melting process which can be calculated by the formula [1]:
?V = ((Vк – Vж) / Vк)·100% = (?V/Vк)·100%,(1)
where Vк – the volume of a solid substance (or mixture) at the melting temperature; Vж – the volume of liquid at the melting temperature (substance or mixture); ?V – volume difference in the liquid and solid states of the substance.
Identification of ?V is necessary because all the halides increase their volume, therefore melting increases the mixture of halides volume. So, when filling chemical power sources and storage heaters by mixtures it is necessary to keep a share of the free volume not only for expansion of the mixture in the solid (including the transition from one crystal structure to another) and liquid state, but also for increasing of the melting compounds volume. But, in the literature [2,3] provides data on the increase volume in the melting is not for everyone halides s-elements (table 1).