Short communicationMicroscopic evidence of a flat melting curve of tantalum
Introduction
A longstanding problem in the study of materials at high pressure is the determination of their melting curves and phase diagrams. 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 and Ross, 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, Hixson et al., 1989, Liu et al., 2008, Moriarty et al., 2002, Santamaria-Pérez et al., 2009, Taioli et al., 2007, Zhang et al., 2008). However, despite important advances in experimental and theoretical methods, considerable controversy exists about the pressure dependence of the melting temperatures (TM) of Mo, Ta, and W. 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, Santamaria-Pérez et al., 2009) are much flatter than those obtained from shock-wave experiments carried out at higher pressures (Hixson et al., 1989, Dai et al., 2009, Zhang et al., 2008). 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. Therefore, it is clear that further studies are needed to accurately determine the melting temperatures of transition metals. In this letter, we report new experimental data on the melting curve of Ta up to 48 GPa. Melting was determined by observing changes in the Ta surface as the temperature increases. Additional evidence of melting is provided by scanning electron microscopy measurements. The new melting temperatures confirm previous DAC experiments.
Section snippets
Experimental details
Measurements were carried out in a Boehler-Almax DAC (Boehler and De Hantsetters, 2004, Boehler, 2006) with 360-μm diameter culets. The gasket was made from a 250 μm thick rhenium disk, pre-indented to a 40 μm thickness and laser-drilled to a diameter of 130 μm. Samples were prepared by extracting small pieces from freshly polished tantalum (Goodfellow, 99.9% purity) and squeezing them between two diamond flats to a thickness of 9–12 μm and about 60 μm in diameter, resulting in mirror-like surfaces
Results and discussion
Five different experiments were made from 13 to 48 GPa in order to cover the pressure range where experimental DAC values and theoretical calculations start to disagree. Fig. 1 shows three images of one of the Ta samples compressed at 13 GPa. The first one was taken after compression at 13 GPa before laser-heating (left), the second one after heating up to 3300 ± 100 K (center, the location of the hot spot is shown), and the third one after heating to 3600 ± 100 K (right, the location of the hot spot is
Concluding remarks
In summary, we provide extra experimental evidence for a flat melting curve of Ta from optical and scanning electron microscopic analysis of the quenched samples. The reported melting temperatures are in agreement with earlier DAC studies (Errandonea et al., 2001, Errandonea et al., 2003). They support the conclusion that near 100 GPa Ta has a flat melting curve.
Acknowledgements
D.E. and J.R.-F. thank the support of Spanish MEC (MAT2007-65990-C03-01 and CSD-2007-00045) and the MPI für Chemie at Mainz for its hospitality. We thank J. Huth for assistance in SEM measurements.
References (30)
- et al.
Improving the understanding of the melting behaviour of Mo, Ta, and W at extreme pressures
Physica B
(2005)Phase behavior of metals at very high P–T conditions: a review of recent experimental studies
J. Phys. Chem. Solids
(2006)- et al.
Dendritic crystal growth in pure materials
J. Cryst. Growth
(2004) - et al.
SEM structure and properties of ASP2060 steel after laser melting
Surf. Coat. Technol.
(2004) - et al.
Molybdenum at high pressure and temperature: melting from another solid phase
Phys. Rev. Lett.
(2008) - et al.
Melting, thermal-expansion, and phase-transitions of iron at high-pressures
J. Geophys. Res.
(1990) - et al.
High-pressure melting curves of argon, krypton, and xenon: deviation from corresponding states theory
Phys. Rev. Lett.
(2001) - et al.
New anvil designs in diamond-cells
High Pressure Res.
(2004) New diamond cell for single-crystal X-ray diffraction
Rev. Sci. Inst.
(2006)
Comment on “Molybdenum at high pressure and temperature: melting from another solid phase”
Phys. Rev. Lett.
Hugoniot temperatures and melting of tantalum under shock compression determined by optical pyrometry
J. Appl. Phys.
Systematics of transition-metal melting
Phys. Rev. B
Melting of tantalum at high pressure determined by angle dispersive X-ray diffraction in a double-sided laser-heated diamond-anvil cell
J. Phys.: Condens. Mat.
Transition metals: can metals be a liquid glass?
Nat. Mater.
Cited by (24)
The melting curve of cobalt under high pressure
2020, Solid State CommunicationsCitation Excerpt :A longstanding problem in the study of materials is the determination of their melting curves and phase diagrams. The melting of transition metal at high pressures has wide scientific implications, particularly for earth and planetary sciences [2–12]. Cobalt, as one of the typical representatives of transition metal, which is adjacent to iron and nickel in the periodic table, is potentially necessary for understanding the properties of the Earth's core, which is believed to be composed of iron dominated alloys, with possibly Co or Ni as minor components.
In situ synchrotron X-ray diffraction in the laser-heated diamond anvil cell: Melting phenomena and synthesis of new materials
2014, Coordination Chemistry ReviewsCitation Excerpt :To reach such conditions experimentally at present, one turns to static DAC or dynamic ramp/shock compression techniques. There are several techniques that are used in DAC experiments to probe the onset of melting: (1) observation of visual changes at the sample surface using the laser speckle technique [92]; (2) sharp jumps in the resistivity of the sample, as measured in situ during heating [93]; (3) abrupt changes in the absorption of the laser radiation in the sample as a function of temperature [71]; (4) laser-heating to specific temperatures and looking for visual signs of melting post experiment [94]; (5) in situ XRD measurements to look for the first sign of diffuse scattering from the liquid phase [95]. There are advantages to all of these techniques, with methods (1–4) being possible to perform without a synchrotron X-ray source.
Molecular dynamics study of melting curve, entropy of fusion and solid-liquid interfacial energy of cobalt under pressure
2014, Physica B: Condensed MatterCitation Excerpt :However, accurate determination for the equilibrium melting points of the transition metals is still a challenge to both experimental and theoretical researches. Hence, there exist large discrepancies in the melting curves of transition metals among laser-heated diamond-anvil cell (DAC) measurements [3,30–37], shock wave experiments [35–37] and theoretical simulations [13,20,38,39]. And such discrepancies and therein causes are still under further investigations.
On the volume-dependence of the Grüneisen parameter and the Lindemann law of melting
2013, Journal of Physics and Chemistry of SolidsImproving the understanding of the melting curve of tantalum at extreme pressures through the pressure dependence of fusion volume and entropy
2012, Physica B: Condensed MatterCitation Excerpt :They claimed that the flat curve observed previously could be induced by chemical reactions of metals with carbon and/or pressure transmitting media, and by the pyrometer technique. But we also notice that in one DAC measurement Errandonea et al. [14] have excluded the possibility of chemical reactions and pyrometer problems, and used different measurement techniques to confirm their early observations [15]. Furthermore, more than one theory has predicted that bcc-Ta will transform into other structures under high pressure and high temperature prior to melting which might play an important role in solving the discrepancy in the high-pressure melting curves obtained from SW and DAC experiments.