An electrochemical investigation of the thermodynamic properties of the NaCl-AlCl3 system at subliquidus temperatures

Autor: T. O. M. Mathews, N. Sanil, P. Rodriguez, K. S. Mohandas
Rok vydání: 2001
Předmět:
Zdroj: Metallurgical and Materials Transactions B. 32:669-677
ISSN: 1543-1916
1073-5615
DOI: 10.1007/s11663-001-0121-8
Popis: The phase relations in the NaCl-AlCl3 system ( $$0.3 \leqslant N_{AlCl_3 } \leqslant 0.65$$ ) have been determined in the temperature range from 373 to 623 K by isothermal equilibration, electrical conductivity, and electromotive force measurements. Only one ternary compound, NaAlCl4, was found to be stable, with a melting point of 426 K. The standard Gibbs energy of formation of NaCl and NaAlCl4 has been measured in the temperature range from 423 to 623 K by a novel galvanic cell technique involving in-situ electrogenerated chlorine electrode in the Na/β″-alumina/NaCl, NaAlCl4/Cl2,C and Al/NaCl, NaAlCl4/Cl2,C cells along with the Na/β″-alumina/NaCl,NaAlCl4/Al cell. The Δ f G NaCl( )/o and $$\Delta _f G_{NaAlCl_4 (l)}^ \circ $$ values have been calculated as −412.4+0.095 T (±1) kJ mol−1 and −1117.5+0.2460 T (±2) kJ mol−1, respectively. The standard entropy of NaAlCl4 (s) at 298 K, computed from the results of the study and the auxiliary information from the literature (184 J K−1 mol−1), show good agreement with the estimated JANAF value (188.28 J K−1 mol−1). The enthalpy of formation of NaAlCl4 (l) from NaCl (s) and AlCl3 (s) at 550 K obtained in the present study (−1850 J mol−1) is in agreement with that computed from the heat-capacity measurements (−1910 J mol−1). The present measurements are unique, as a new electrochemical technique is employed in a cell with low-melting sodium chloroaluminate electrolyte to obtain the thermodynamic properties of NaCl and NaAlCl4 at significantly low temperatures. The Gibbs energy of formation of NaCl (s) is, thus, measured at temperatures as low as 423 K by an electrochemical technique for the first time, in this work.
Databáze: OpenAIRE
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