STANDARD ENTHALPIES OF FORMATION OF SOME CARBIDES, SILICIDES AND GERMANIDES OF CERIUM AND PRASEODYMIUM

The standard enthalpies of formation of some congruent-melting compounds in the binary systems Re-X, where Re=Ce, Pr or La and X=C, Si or Ge have been determined by direct-synthesis calorimetry at 1473+/-2 K. The following values of Delta H-f degrees are reported: CeC2, -25.4+/-1.4 kJ (mol atom)(-1); CeSi2, -60.5+/-2.0 kJ (mol atom)(-1); CeSi, -71.1+/-3.3 kJ (mol atom)(-1); Ce5Ge3, -73.4+/-2.3 kJ (mol atom)(-1); CeGe1.6, -75.6+/-1.9 kJ (mol atom)(-1); PrC2, -29.4+/-1.6 kJ (mol atom)(-1); PrSi2, -61.5+/-1.7 kJ (mol atom)(-1); PrSi, -78.1+/-1.9 kJ (mol atom)(-1); Pr5Ge3, -70.4+/-2.3 kJ (mol atom)(-1); PrGe1.6, -81.7+/-1.7 kJ (mol atom)(-1); LaSi2, -56.8+/-2.5 kJ (mol atom)(-1). The results are compared with earlier experimental data, with predicted values from Miedema's semiempirical model, and with available data obtained for Sn and Pb compounds by Borzone et al., by Palenzona and by Palenzona and Cirafici.