Calorimetric measurements on GdAl₃ intermetallic compound

Abstract

The paper deals with the high-temperature calorimetric measurements on GdAl₃(s), an intermetallic compound in the Gd–Al (GdAl₃, GdAl₂, GdAl, Gd₃Al₂ and Gd₂Al) system. The intermetallic compound was prepared by arc melting method. The sample was annealed at 800 K for 700 h and the X-ray diffraction pattern and energy dispersive X-ray spectroscopy of the annealed sample verified the presence of single phase alloy. High-temperature heat flux differential calorimetry was used to measure the enthalpy increments of GdAl₃. The experimental data cover the temperature range 800–1300 K by employing the method of inverse drop calorimetry. The other thermodynamic functions like heat capacity, entropy and Gibbs energy function of GdAl₃ were derived as a function of temperature using measured enthalpy increment data. Heat capacity of GdAl₃ was carried out the temperature between 320 and 700 K using a heat flux type differential scanning calorimeter for the first time. Enthalpy increments, entropies and Gibbs energy functions were derived using measured heat capacity data. The Gibbs energy of formation of GdAl₃ has been derived using change in Gibbs energy function estimated from the present data and $\Delta H_{298}^{o}$ from the literature data. The results of these measurements are presented and discussed in this paper.