Conferences

Thermodynamic Properties and High-Temperature Behavior of Lanthanum Selenides La3Se4–La2Se3

V.Litvinenko,
  

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2008, #07/08
http://www.materials.kiev.ua/article/1355

Abstract

The enthalpy of the La3Se4 and La2Se3 bounding compositions of the La3–хSe4 phase (0 ≤ х ≤ 1/3) at temperatures from 370 to 2260 K is studied calorimetrically. The values obtained are used and the equilibria of the La–Se system are analyzed to establish, for the first time, the temperature–concentration relationships for the thermodynamic properties of La3–хSe4 selenides in the homogeneity region at 298 ≤ Т ≤ 2123 K. The enthalpy function (J/mole) of La3–хSe4 is given by H(Т) – (298 K) = (3837 · 103Т-1 – 85852 + 266,925 · Т – 8,7503 · 10-2T2 + 3,437 · 10-5T3) · е–0,2869х. The formation and melting enthalpies of La3Se4 are determined: (∆f H°(298 K) = –1340 ± 28 (kJ/mole), (∆mH = 147.5 ± 9.6 (kJ/mole).It is shown that the high-temperature stability of different La3–хSe4 compositions is strongly dependent on pressure: as the pressure decreases and the temperature increases, the selenium content is reduced and the composition tends to La3Se4.


ENTHALPY, ENTROPY, FORMATION ENTHALPY, GIBBS FREE ENERGY, HEAT CAPACITY, HOMOGENEITY REGION, LANTHANUM SELENIDES, THERMODYNAMIC PROPERTIES