Phase equilibria and thermodynamics of the system Dy-Mg-Cl at 1073 K

The phase relations in the system Dy-Mg-Cl at 1073 K have been established by isothermal equilibration and chemical analysis of quenched samples. Liqu id Mg-rich alloy was found to be in equilibrium with molten DyCl2. Therefor e, DyCl2 can be synthesized by reduction of MgCl2 with excess of metallic D y at 1073 K. The Gibbs energy of formation of DyCl2 at 1073 K was evaluated by two different methods. From voltammetric determination of decomposition voltage, the upper limit for the standard Gibbs energy of formation of DyC l2 was estimated to be -505(+/-20) kJ mol(-1). A value of -543(+/-10) kJ mo l(-1) was deduced from phase relations using Gibbs-Duhem integration. The v alue for the standard Gibbs energy of DyCl2, indicates that the Dy2+ ion ha s a potential capability for reducing TiCl4 to metal titanium. At the same time, Mg is a reductant for Dy3+ produced during the reduction of TiCl4. Th us, it is thermodynamically confirmed that reduction of TiCl4 by magnesium using a reaction mediator in the salt phase is feasible. (C) 1999 Elsevier Science S.A. All rights reserved.