Glass forming ability and phases of (Li,Na)acetate salt mixtures

Anhydrous mixtures of lithium acetate and sodium acetate were investigated by differential scanning calorimetry and X-ray powder diffraction. A tentative phase diagram is derived from these data. The Li _{1- x}Na _xCH ₃ COO system has a eutectic for the NaCH ₃COO molar fraction of x ≈ 0.55 . The relatively low eutectic melting point at 448 K (175 ∘ C) may make this composition an interesting molten salt solvent. Peritectic reactions correspond to phases with compositions near Li ₄Na(CH ₃COO) ₅ and LiNa ₃(CH ₃COO) ₄. On the Li-rich side of the eutectic, the system, prepared as a glass, can crystallized deliberately. This allows checking the data validity with the first law of thermodynamics. The stability range of the supercooled liquid increases with x up to Li _0.55Na _0.45CH ₃COO. For higher sodium concentrations, the samples remain mixtures of glass and crystalline phases, with the amount of the vitreous component decreasing linearly from x = 0.45 to x = 1. The fragility of the liquid state, highest for pure LiCH ₃COO, decreases by a factor of two over the range 0 < x < 0.2 , and remains constant for higher x.