Determination of Thermodynamic Properties of Si-B Alloys

This study establishes the thermodynamic properties of the Si-B binary alloy system. The electromotive force (emf) as a function of temperature (823 K to 923 K) was measured using solid-state electrochemical cells, represented as $$(-)\,{\text{Pt}},{\text{Ar}}/\{\text{Si}\|{\text{CaF}}_{2}\|\;\{{\text{Si}} - {\text{B}}({\text{alloy}})\}/{\text{Ar}},{\text{Pt}}( + )$$ Using the experimental emf data obtained from the solid-state heterogeneous phase equilibrium, the activities of Si and B in Si-B alloys were calculated. The integral Gibbs energy of mixing \( (\Delta G^{\text{M}} ) \) of alloys were calculated from the activity of Si and B. A large negative deviation from ideality was found for the integral Gibbs energy of mixing \( (\Delta G^{\text{M}} ) \) of the binary Si-B system. From the activities of Si and B, the Gibbs energies of formation \( \left( {\Delta G_f^{0 } } \right) \) of phases present were calculated. The \( \Delta G_{f}^{ 0 } \) of SiB3, the most thermodynamically stable phase, was calculated as − 13.13 ± 0.19 kJ/mole-atoms at 923 K. The heterogeneous phases and microstructure after the equilibrium study of the electrode were characterized using XRD, SEM, and EDS analyses.