Thermokinetic characteristics of lithium chloride

Abstract

The characterisation of the ionic compound of lithium chloride, LiCl, through XRD, SEM, DSC, TG, DTG and TG-MS analysis is reported. The results show that nominally anhydrous LiCl particles can readily absorb water from the ambient atmosphere to form a surface layer of lithium chloride mono-hydrate, LiCl·H₂O. Solid surface-hydrated LiCl is de-dehydrated via a two-stage mechanism at low heating rates and via a single-stage mechanism at high heating rates. Molten LiCl exhibits substantial evaporation at temperatures below its nominal boiling point, with the rate of evaporation increasing significantly before complete evaporation occurs. The melting process of de-hydrated LiCl is marginally affected by the heating rate; whilst the evaporation process is strongly affected by the heating rate and also dependent on the quantity of material used and the flow rate of the gas passed over it. Heating of surface-hydrated LiCl up to the point of evaporation under a flow of argon and under a flow of ambient air gives identical results, proposing the possibility of performing LiCl-based processes in an air environment. The enthalpies and activation energies for the processes of surface de-hydration, melting, and high-temperature evaporation are determined. The results are consistent with the following thermal phase evolution:

$$ [{\text{LiCl + LiCl}} \cdot {\text{H}}_{{\text{2}}} {\text{O}}]_{{{\text{solid}}}} \to [{\text{LiCl}}]_{{{\text{solid}}}} \to [{\text{LiCl}}]_{{{\text{liquid}}}} \mathop\rightarrow\limits^{{{{\text{H}}_{{\text{2}}} {\text{O}} \downarrow {\text{ HCl}} \uparrow}}}[{\text{LiCl-LiOH}}]_{{{\text{liquid}}}} \mathop\rightarrow\limits^{{{{\text{H}}_{{\text{2}}} {\text{O}} \uparrow}}}[{\text{LiCl-Li}}_{{\text{2}}} {\text{O}}]_{{{\text{liquid}}}} \to {\text{Gas}} $$