Physico-chemical properties of therbium, magnesium and gallium alloys
The physicochemical properties of terbium alloys with magnesium and gallium have been studied by X-ray diffraction (XRD), thermal analysis, and solution calorimetry. Terbium concentration in alloys varied in the range of 0-25 at. %. Alloys were obtained by direct alloying of components at 800-850 °C and annealing at 400 °C for 350 h. The phase composition of alloys was established by XRD. It was found that the ternary compound TbMgGa (structure type of ZrNiAl, P62m) is in equilibrium with the binary compounds of TbGa <sub>6</sub>, GaMg <sub>2</sub>, TbMg, TbGa <sub>2</sub>. Enthalpy of formation of alloys under standard conditions was determined using the experimental values of the enthalpies of dissolution of alloys and pure metals in hydrochloric acid at 25 °C. Enthalpy of formation of ternary alloys is changed from -308 to -161 kJ/(mol <sup>.</sup>at) depending on the metal content. Thermal stability of the alloys was investigated by DTA in air in the range of 20-1000 °C. A noticeable oxidation alloys begins at 390-430 °C indicating a high resistance to oxidation of alloys. Transformation effects both in the alloys and in the protective oxide film have influence on oxidation process of alloys. According to the results of DTA, the apparent activation energy and reaction rate constants of oxidation of alloys were calculated.