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

Three ternary oxides LiAl5O8(s), LiAlO2(s) and Li5AlO4(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 CO2(g) over the three-phase mixtures {LiAl5O8(s)+Li2CO3(s)+5Al2O3(s)}, {LiAl5O8(s)+5LiAlO2(s)+2Li2CO3(s)} and {LiAlO2(s)+Li5AlO4(s)+2Li2CO3(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 ΔfH0(298.15 K), S0(298.15 K) S0(T), Cp0(T), H0(T), {H0(T)–H0(298.15 K)}, G0(T), ΔfH0(T), ΔfG0(T) and free energy function (fef) were constructed using second law analysis and FACTSAGE thermo-chemical database software.

Comparison of ΔfGm0 of ternary oxides determined from KEQMS and solid-state galvanic cell techniques. (O) KEQMS, (■) solid-state galvanic cell and solid line: combined fit of both the experimental data.Figure optionsDownload as PowerPoint slide