Thermodynamic and Mass Transport Properties of “ LiAl ”

Abstract

The compositional variations of the thermodynamic and mass transport properties of the β phase in the lithium‐aluminum system have been investigated over the temperature range from 415° to 600°C. At 415°C, the emf of the single phase lies between 300 and 70 mV relative to pure Li and this corresponds to a Li activity increasing from 0.0063 to 0.31 over the phase stability range from 46.8 to 55.0 atomic percent Li. At the ideal stoichiometry, the standard Gibbs free energy of formation of is −29.2 kJ/mole at 415°C and the corresponding enthalpy and entropy are −43.3 kJ/mole and −20.6 J/mole °K, respectively. Two different electrochemical transient techniques have been used to measure the chemical diffusion coefficient in as a function of the stoichiometry; the experimental results obtained are in good agreement. On the lithium deficit side of the ideal stoichiometry, the chemical diffusion coefficient increases with decreasing Li concentration, becoming about 10 −4 cm 2 /sec near the phase boundary. On the other hand, it is composition independent on the Li excess side of varying with temperature from at 415°C to at 600°C.