Melting of tantalum at high pressure determined by angle dispersive x-ray diffraction in a double-sided laser-heated diamond-anvil cell

Abstract

The high pressure and high temperature phase diagram of Ta has been studied in a laser-heated diamond-anvil cell (DAC) using x -ray diffraction measurements up to 52 GPa and 3800 K. The melting was observed at nine different pressures, being the melting temperature in good agreement with previous laser-heated DAC experiments, but in contradiction with several theoretical calculations and previous pistoncylinder apparatus experiments. A small slope for the melting curve of Ta is estimated ( dT m /dP ˜ 24 K/GPa at 1 bar) and a possible explanation for this behaviour is given. Finally, a P -V-T equation of states is obtained, being the temperature dependence of the thermal expansion coefficient and the bulk modulus estimated.

Microscopic evidence of a flat melting curve of tantalum

“…As described above, this conclusion is supported by SEM measurements. Figure 3 summarizes the present and previous data (Errandonea et al, 2001;Errandonea et al, 2003;Fatteva et al, 1971, Moriarty et al, 2002Taioli et al, 2007).…”

“…The solid squares show the lowest temperatures were evidence of melting has (Errandonea et al, 2003) or the speckle method (Errandonea et al, 2001), the present data show a larger data scatter. In addition, they show a tendency to slightly higher melting temperatures.…”

“…Melting temperatures were measured by heating every sample at a constant load, by increasing the temperature in steps of about 100 K starting at temperatures 500 K lower than the melting temperature reported in previous DAC experiments (Errandonea et al, 2001;Errandonea et al, 2003). After each heating cycle, lasting no more than 10 seconds, the sample surface was examined and photographed, while samples were still under pressure, using a microscope with a 20x objective.…”

“…The melting curves determined from diamond-anvil cell (DAC) experiments performed up to 120 GPa (Errandonea et al, 2001;Errandonea et al, 2003;Foata-Prestavoine et al, 2007;Santamaría-Pérez et al, 2009) are much flatter than those obtained from shockwave experiments carried out at higher pressures (Hixon et al, 1989;Dai et al, 2009;Zhang et al, 2009). Substantial variations are also found among calculations (Moriarty et al, 2002;Cazorla et al, 2008), but the majority of them disagree with the DAC results.…”

“…In particular, the melting of the late transition metal iron at high pressures has wide scientific implications, including geophysical and geochemical modeling of the Earth's interior. This fact has triggered a substantial effort to determine the melting curve of Fe (for a review see: Boehler, R. et al, 2007) and other transition metals including Mo, Ta, and W (Belonoshko et al, 2008;Cazorla et al, 2008;Dai et al, 2009;Errandonea et al, 2001;Errandonea et al, 2003;Foata-Prestavoine et al, 2007;Hixon et al, 1989;Liu et al, 2008;Moriarty et al, 2002;Santamaría-Pérez et al, 2009;Taioli et al, 2007;Zhang et al, 2009). However, despite important advances in experimental and theoretical methods, considerable controversy exists about the pressure dependence of the melting temperatures ( M T ) of Mo, Ta, and W.…”