Thermodynamic properties of calcium-bismuth alloys determined by emf measurements
The thermodynamic properties of Ca-Bi alloys were determined by electromotive force (emf) measurements to assess the suitability of Ca-Bi electrodes for electrochemical energy storage applications. Emf was measured at ambient pressure as a function of temperature between 723 K and 1173 K using a Ca(s)vertical bar CaF2(s)vertical bar Ca(in Bi) cell for twenty different Ca-Bi alloys spanning the entire range of composition from chi(Ca) = 0 to 1. Reported are the temperature-independent partial molar entropy and enthalpy of calcium for each Ca-Bi alloy. Also given are the measured activities of calcium, the excess partial molar Gibbs energy of bismuth estimated from the Gibbs-Duhem equation, and the integral change in Gibbs energy for each Ca-Bi alloy at 873 K, 973 K, and 1073 K. Calcium activities at 973 K were found to be nearly constant at a value a(Ca) = 1 x 10(-8) over the composition range chi(Ca) = 0.32-0.56, yielding an emf of similar to 0.77 V. Above chi(Ca) = 0.62 and coincident with Ca5Bi3 formation, the calcium activity approached unity. The Ca-Bi system was also characterized by differential scanning calorimetry over the entire range of composition. Based upon these data along with the emf measurements, a revised Ca-Bi binary phase diagram is proposed. (C) 2011 Elsevier Ltd. All rights reserved.
- Sponsoring Organization:
- USDOE Advanced Research Projects Agency - Energy (ARPA-E)
- DOE Contract Number:
- DE-AR0000047
- OSTI ID:
- 1211033
- Journal Information:
- Electrochimica Acta, Vol. 60; ISSN 0013-4686
- Country of Publication:
- United States
- Language:
- English
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