KINETIC AND THERMODYNAMIC STUDIES ON THE SOLID-STATE REACTION BETWEEN AGCL AND YCL3

The kinetics of the solid state reaction 3 AgCl + YCl3 = Ag3YCl6 has been investigated in the temperature range between 310 and 365-degrees-C. The formation of the ternary compound is governed by the cation counter-diffusion mechanism while the reaction rate is determined by the transport of the yttrium-ions through the product layer. From the experimentally obtained reaction rate constants diffusion-coefficients of Y3+ have been calculated. Thermodynamic investigations in the system AgCl/YCl3 have been performed in the temperature range between 150 and 370-degrees-C by electromotive force measurements on solid state galvanic cells. The compound Ag3YCl6 is metastable at room temperature. A loss in lattice enthalpy during formation of Ag3YCl6 from the binary chlorides is compensated by a gain in entropy. Above 186-degrees-C the ternary compound is stable with regard to the decomposition to AgCl and YCl3.