The melting of iron up to 200 kbar

Abstract

The effect of pressure on the melting temperature of iron has been measured by passing current through a very fine wire of pure iron held under pressure in a diamond anvil pressure cell. The temperature was measured by optical pyrometry, and the pressure was calculated from the lattice parameters of iron at room temperature after being heat-treated. On the basis of recent work by Strong et al. on measuring the δ-γ-liquid triple point and the initial slope between γ and liquid iron, we have calculated the melting temperature for γ iron to about 200 kbar. A third-order polynomial equation fitted to our data yields the following equation: Tm = 1718 + 3.85(P − 52) − 1.95×10−2(P − 52)2 + 6.24×10−5(P − 52)3, where Tm is the melting temperature in degrees Celsius and P is the pressure in kilobars. When the linear relationship of Tm-ΔV/V0 proposed by Kraut and Kennedy (1966) was used, the extrapolation of the present data to the inner core-outer core boundary, 3.3 Mbar, yields temperatures between 3460° and 3870°C if the inner core consists of pure iron with the γ phase.