Synergistic use of Knudsen effusion quadrupole mass spectrometry, solid-state galvanic cell and differential scanning calorimetry for thermodynamic studies on lithium aluminates

Abstract

Three ternary oxides LiAl 5O 8(s), LiAlO 2(s) and Li 5AlO 4(s) in the system Li–Al–O were prepared by solid-state reaction route and characterized by X-ray powder diffraction method. Equilibrium partial pressure of CO 2(g) over the three-phase mixtures {LiAl 5O 8(s)+Li 2CO 3(s)+5Al 2O 3(s)}, {LiAl 5O 8(s)+5LiAlO 2(s)+2Li 2CO 3(s)} and {LiAlO 2(s)+Li 5AlO 4(s)+2Li 2CO 3(s)} were measured using Knudsen effusion quadrupole mass spectrometry (KEQMS). Solid-state galvanic cell technique based on calcium fluoride electrolyte was used to determine the standard molar Gibbs energies of formations of these aluminates. The standard molar Gibbs energies of formation of these three aluminates calculated from KEQMS and galvanic cell measurements were in good agreement. Heat capacities of individual ternary oxides were measured from 127 to 868 K using differential scanning calorimetry. Thermodynamic tables representing the values of Δ f H 0(298.15 K), S 0(298.15 K) S 0( T), C p 0( T), H 0( T), { H 0( T)– H 0(298.15 K)}, G 0( T), Δ f H 0( T), Δ fG 0( T) and free energy function (fef) were constructed using second law analysis and FACTSAGE thermo-chemical database software.