Vaporization and thermodynamic properties of samarium dicarbide ans substoichiometric disamarium tricarbide

The vaporization reactions of SmC2(s) and Pu2C3-type SmC/sub y/(s) have been characterized and equilibrium pressures have been measured using a target-collection effusion technique. The carbides vaporize incongruently as follows: SmC2(s) → 2C(s) + Sm(g), and 2/(2-y) SmCy(s) → y/(2-y) SmC2(s) + Sm(g). The complex reaction for SmC/sub y/ occurs because the composition of the carbon-rich boundary of the phase decreases as temperature increases. For the first reaction, the equilibrium pressure is described by log P(Sm, g, atm, 1548 K < T < 2049 K) = (3.60 +- 0.01) - (14309 +- 21)T-1. The non-linear pressure equation for the second reaction is log P(Sm, g, atm, 1.42 < y < 1.44, 1372 K < T < 1636 K) = [(12.009 - 28449 T-1 + 7018500 T-2) +- 0.038]. Thermodynamic values for the vaporization and formation reactions of SmC2(s) and SmC/sub y/(s) at 2980K have been calculated; ΔH/sub f/0 (SmC2,s, 2980K) = -(96.2 +- 7.5) kJ mol-1 and ΔH/sub f/0 (SmC143,s, 2980K) = -(89.0 +- 8.0) kJ mol-1. The thermodynamic results are discussed and compared with values reported for other lanthanide carbides