Sodium-sulfur system. I. Differential thermal analysis

Abstract

Attempts to gain a better understanding of the reactive species in the sodium-sulfur battery system developed at Ford Motor Co. have led us to reexamine the sodium-sulfur phase diagram published by Pearson and Robinson in 1930. A modified phase diagram was constructed based on dta studies. In addition, dta revealed that when a mixture of Ña2S and NajSj or Ña2S4 and S8 is heated, a reaction takes place around the melting point of sulfur, with the formation of the pentasulfide, Na2Ss, as the initial step. Unless the sulfur:sodium ratio in the mixture is 5:2 or higher, further interaction between the sulfides can be observed by dta, until at equilibrium only those species are observed corresponding to the given stoichiometric Na:S ratio. The highest sulfide is Na2Ss, whereas the trisulfide, Na2S3, does not exist at the melting point, and the mixture with the same stoichiometry was found to be a 1:1 Na2S2-Na2S4 eutectic.

Volcanogenic Sulfur on Earth and Io: Composition and Spectroscopy

“…This finding is consistent with the immiscibility of sodium sulfides in molten sulfur at temperatures near sulfur's melting point (Rosén and Tegman 1972, Oei 1973, Tegman 1976). …”

The Effects of Current Density, Temperature, and Discharge Beyond Na2 S 3 on Sodium‐Sulfur Cell Performance and Life

“…Oei (2,3) and Janz et al (4) have shown that, at temperatures greater than -100~ Na2S~ is a eutectic mixture of Na2S2 and Na2S~. Capacities were determined by dividing the ampere-hours removed during discharge by the theoretical capacity.…”

Thermodynamic evaluation and optimization of the (Na + K + S) system

“…The phase equilibrium and the thermodynamic properties of the phases in system (Na + S) have been widely investigated [16,[31][32][33][34][35][36]. Due to experimental difficulties, a notable scatter exists for different experimental investigations.…”

“…The phase diagram has been investigated by visual-polythermal methods [34], thermal analysis [31][32][33][34], differential thermal analysis [16,34,36], quenching techniques [34] and EMF-studies [35,37]. The experimental data points are shown in figure 1.…”