1980 Volume 66 Issue 14 Pages 2032-2039
The ratio of the vapor pressures of P(g) and P2(g) above Fe-P alloys were determined by a combination of a mass spectrometer and a Knudsen cell. The effused vapors from Knudsen cell were collected onto target plates and the amounts of phosphorus in the deposits on the target plates were determined by a secondary ion mass spectrometer. The vapor pressures of P(g) and P2(g) were calculated from these results, and the following values for the standard free energy changes were obtained.
P(g) = P (%) ΔG°= - 95.3 + 1.55 × 10-2 T (±2.2) kcal/mol
1/2 P2 (g) = P (%) ΔG°= - 37.7 + 0.13 × 10-2 T (±1.1) kcal/mol
P(g) = 1/2 P2(g) ΔG°= - 57.6 + 1.42 × 10-2 T (±1.1) kcal/mol
(1-3 wt% P, 1 590-1 650°C)