The &egr;-&ggr; transition and the melting curve of pure iron have been measured in an internally heated diamond cell to 430 kbar. The sample, an iron wire with 0.02-mm diameter, was resistively heated in a sandwiched gasket arrangement, using alumina as the pressure medium. The phase transitions were determined by discontinuities in the resistance-temperature curves of the heated wire. Temperatures were measured with an optical multi-channel analyzer (OMA) by fitting a black-body radiation function to the emission spectrum of the hot wire. Pressures were measured at room temperature using the ruby scale. New data on the &agr;-&egr; transition by Huang et al. (1986) and the present result on the &egr;-&ggr; transition yield a &agr;-&egr;-&ggr; triple point of 116 kbar and 810 K. The slope of the &egr;-&ggr; transition is 2.9 K/kbar. At 500 kbar the present melting temperatures of iron are about 1000 K lower than those calculated by Anderson (1986). From this data, one would expect a &egr;-&ggr;-l triple point at 750 kbar and 2500 K. The solid-solid transition found in shock wave experiments at 2 Mbar could therefore be the appearance of a new iron phase, which would be the phase of the inner core of the Earth. |