Competitive interactions and glassy state extension in lithium salt solutions

We report measurements of high- and low-temperature limits of the liquid states of aqueous solutions for two common aqueous salt solutions. The liquid range extends from the glass transition temperature to the boiling point, and is maximized when the anion basicity is minimized. These limits and other characteristic temperatures have been determined by DTA and DSC studies of solution samples which are used to generate the most complete phase diagram yet available for the LiBr + H₂O system. The glass-formation region has been extended by developing an emulsification technique suitable for use with concentrated aqueous salt solutions. Comparison of boiling points, liquidus temperatures, and glass transition temperatures shows that the reduction of the water content below 3H₂O per Li⁺ is accompanied by important energetic effects. These are not present in the corresponding lithium acetate solutions, which exhibit relatively much lower boiling points. This is attributed to the stronger water - anion interaction in the lithium acetate system which is proportional to the anion basicity. Water activity increases and boiling points are lowered when the anions are more basic, but total cohesion, manifested by the glass transition temperature, increases. By contrast, addition of anion complexing salts such as ZnBr₂ and ZnCl₂ to LiBr-H₂O solutions to reduce the anion basicity results in increased boiling points to over 200 °C as well as decreased crystallization temperatures.