Pressure—Temperature Phase Diagram of Iron to 200 kbar, 900°C

The resistance changes in iron during the transitions between the α(bcc), γ(fcc), and ε(hcp) phases have been studied quantitatively in the high-compression belt apparatus. The samples were monitored by thermocouples and voltage probes. The P,T locations of the (α,γ) (α,ε), and (ε,γ) phase lines, and the (α,γ,ε) triple point were determined. The latter is placed at 110 ±3 kbar and 490 ±10°C. The changes of molar volume at the triple point are deduced to be −0.275, +0.135, and +0.140 cc/mole for the (α,ε), (ε,γ), and (γ,α) transitions, respectively. The resistivity of the α phase follows a quadratic relationship with temperature, whereas the γ and ε forms vary linearly with temperature.