Structural Analysis of Molten LiCl-CaCl_2 System by X-ray Diffraction(Materials, Metallurgy & Weldability)

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The structures of molten system (LiCl)_x-(CaCl_2)_<1-x>, with x=1, 2/3, 1/2 and 0, are investigated by X-ray diffraction analysis. The obtained nearest neighbour coordination number n_<Li/Cl> in molten LiCl is explained well with the volume expansion ΔV_∫/V_S (=26.2%) on melting. In molten CaCl_2, the obtained distances and coordition numbers are close to those found in the crystalline form, which are consistent with the extraordinary small ΔV_∫/V_S (=0.9%). n_<Li/Cl> and n_<Ca/Cl> in molten LiCaCl_3 or Li_2CaCl_4 are similar to those found in molten LiCl and CaCl_2, respectively. In addition, over the whole range of concentration in this system, the nearest neighbour distance r_<Cl-Cl> appeares to show the linear dependence on the molar fraction. These behaviors in this system are analized to be a result of the strong Coulombic attraction between Li^+ or Ca^<2+> and Cl^-, which implies the formation of LiCl_4 and CaCl_6 ionic groups. Our results by X-ray analysis do not give the evidence of the existence of some ionic complexes proposed previously being based on results of thermodynamical measurements.
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