Determination of Gibbs free energy of formation of Cr 3P by double Knudsen cell mass spectrometry

Abstract

The vapor pressure of phosphorus in equilibrium with a mixture of elemental Cr and Cr 3P at (1523 to 1623) K was estimated by double Knudsen cell mass spectrometry with a Cu–P alloy as a reference substance. The Gibbs free energy of formation of Cr 3P was calculated from the vapor pressure as follows: 3Cr(s) + 1/2P 2(g) = Cr 3P(s) Δ f G ∘ = - 261 , 000 + 83.0 ( T / K ) ± 6800 J · mol - 1 ( 1523 < T / K < 1623 )