Temperature measurement and melting determination in the laser-heated diamond-anvil cell

Jephcoat, A. P.; Besedin, S. P.

doi:10.1098/rsta.1996.0051

Cited by 82 publications

(18 citation statements)

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“…Both cases may be used in the same experiment. For example, if iron is embedded in an argon pressure medium, both melting temperatures can be observed in one temperature cycle, even though the signal from argon is significantly weaker than that from the metal [Jephcoat and Besedin, 1996].…”

Section: Diamond Cell Melting Experimentsmentioning

confidence: 99%

High‐pressure experiments and the phase diagram of lower mantle and core materials

Boehler

2000

Reviews of Geophysics

386

256

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Abstract. The interpretation of seismic data and computer modeling requires increased accuracy in relevant material properties in order to improve our knowledge of the structure and dynamics of the Earth's deep interior. To obtain such properties, a complementary method to classic shock compression experiments and theoretical calculations is the use of laser-heated diamond cells, which are now producing accurate data on phase diagrams, equations of state, and melting. Data on one of the most important measurements, the melting temperatures of iron at very high pressure, are now converging. Two other issues linking core properties to those of iron are investigated in the diamond cell: One is the melting point depression of iron in the presence of light elements, and the other is the structure of iron at the conditions of the inner core. First measurements on eutectic systems indicate a significant decrease in the melting point depression with increasing pressure, which is in contrast to previous predictions. X-ray diffraction measurements at simultaneously high pressure and high temperature have improved significantly with the installation of high-pressure "beam lines" at synchrotron facilities, and structural measurements on iron are in progress. Considerable efforts have been made to develop new techniques to heat minerals at the conditions of the deep mantle in the diamond cell and to measure their phase relations reliably. Even measurements of the melting behavior of realistic rock compositions at high pressure, previously considered to be impossible in the diamond cell, have been reported. The extrapolated solidus of the lower mantle intersects the geotherm at the core-mantle boundary, which may explain the seismically observed ultra low velocity zone. The diamond cell has great potential for future development and broad application, as new measurements on high-pressure geochemistry at deep mantle and core conditions have opened a new field of research. There are, however, strict experimental requirements for obtaining reliable data, which are summarized in the present paper. Results from recent measurements of melting temperatures and phase diagrams of lower mantle and core materials at very high pressure are reviewed. INTRODUCTIONThe interpretation of seismic data that have gained significantly in resolution and amount in the last few years poses a challenge in the fields of computer modeling, geochemistry, and experimental high-pressure research. A picture has evolved in which the Earth is much more heterogeneous in its internal structure than previously thought [Kellogg et al., 1999], and the causes for these heterogeneities are only poorly understood. The observed lateral and depth variations in seismic velocities may have thermal, structural, dynamical, and/or chemical causes. A key element in the understanding of this complexity is the study of physical and chemical properties of the relevant Earth materials. However, at the very high pressure and temperature conditions of the Earth's deep interior th...

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Section: Diamond Cell Melting Experimentsmentioning

confidence: 99%

High‐pressure experiments and the phase diagram of lower mantle and core materials

Boehler

2000

Reviews of Geophysics

386

256

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“…In particular, numerous attempts have been made to obtain its high pressure melting properties [4,5,6,7,8,9,10,11,12]. Experimentally, Earth's core conditions can only be reproduced by shock wave (SW) experiments, in which a high speed projectile is fired at an iron sample, and upon impact high pressure and high temperature conditions are produced.…”

Section: Pacs Numbersmentioning

confidence: 99%

“…I also report on the same figure the DAC experiments of Refs. [4,5,6,7,9], the SW experiments of Refs. [10,11,12] and the calculations of Refs.…”

Section: Fig 4: As Inmentioning

confidence: 99%

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Temperature of the inner-core boundary of the Earth: Melting of iron at high pressure from first-principles coexistence simulations

Alfè

2009

Phys. Rev. B

151

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The Earth's core consists of a solid ball with a radius of 1221 Km, surrounded by a liquid shell which extends up to 3480 Km from the centre of the planet, roughly half way towards the surface (the mean radius of the Earth is 6373 km). The main constituent of the core is iron, and therefore the melting temperature of iron at the pressure encountered at the boundary between the solid and the liquid (the ICB) provides an estimate of the temperature of the core. Here I report the melting temperature of Fe at pressures near that of the ICB, obtained with first principles techniques based on density functional theory. The calculations have been performed by directly simulating solid and liquid iron in coexistence, and show that and at a pressure of ∼ 328 GPa iron melts at ∼ 6370 ± 100 K. These findings are in good agreement with earlier simulations, which used exactly the same quantum mechanics techniques, but obtained melting properties from the calculation of the free energies of solid and liquid Fe [1,2,3]. PACS numbers:The study of iron under extreme conditions has a long hystory. In particular, numerous attempts have been made to obtain its high pressure melting properties [4,5,6,7,8,9,10,11,12]. Experimentally, Earth's core conditions can only be reproduced by shock wave (SW) experiments, in which a high speed projectile is fired at an iron sample, and upon impact high pressure and high temperature conditions are produced. By varying the speed of the projectile it is possible to investigate a characteristic pressure-volume relation known as the Hugoniot [13], and even infer temperatures, although a word of caution here is in order, as temperature estimates are often based on the knowledge of quantities like the constant volume specific heat and the Grüneisen parameter, which are only approximately known at the relevant conditions [10]. If the speed of the projectile is high enough, the conditions of pressure and temperature are such that the sample melts, and it is therefore possible to obtain points on the melting curve, of course with the caveat mentioned above about temperature measurements. An alternative route to high pressure high temperature properties is the use of diamond anvil cells (DAC), in which the sample is surrounded by a pressure medium and statically compressed between two diamond anvils. In DAC experiments pressure and temperatures can be directly measured, and therefore these techniques should in principle be more reliable to investigate melting proeprties. Unfortunately, in the case of iron is it not so, and there is a fairly large range of results obtained by different groups [4,5,6,7,8,9].An alternative approach used for the past ten years or so has been to employ theory -and in particular quantum mechanics techniques based on density functional theory-to calculate the high pressure melting curve of iron. A number of groups have used different approaches to the problem. Our own strategy has been to calculate the Gibbs free energy of solid and liquid iron, and then obtain the melting curve...

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“…The most reliable static data (open symbols: squares [17], diamond [18] and triangle [19]) with consistent shock wave data (filled symbols: square [20], diamond [21], triangles [22] and inverted triangles [23]) are used to find the theoretical curve for TM (solid line) and thus the coordinates of the tricritical point (Ptc,Ttc) (cross). Other data (see discussion in [12]) are also shown: short dashed [24] and dashed [25] lines and open inverted triangle [26] are for static data, filled symbols are for shock data (lower right corner triangles [27], lower left corner triangle [28]), but the long dashed line [29] represents static data extrapolated to high pressures using shock data. The vertical lines show the pressures at the Earth's core mantle boundary (CMB) and inner core boundary (ICB).…”

Section: Landau Theorymentioning

confidence: 99%

Tricritical Points and Liquid-Solid Critical Lines

Aitta¹

2009

European Women in Mathematics

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Tricritical points separate continuous and discontinuous symmetry breaking transitions. They occur in a variety of physical systems and their mathematical models. A tricritical point is used to determine a liquid-solid phase transition line in the pressure-temperature plane [Aitta, J. Stat. Mech., 2006]. Excellent experimental agreement has been obtained for iron, the material having the most high pressure data. This allows extrapolation to much higher pressures and temperatures than available experimentally. One can predict the temperature at the liquid-solid boundary in the Earth's core where the pressure is 329 GPa. Light matter, present as impurities in the core fluid, is found to generate about a 600 K reduction of this temperature.Keywords: Tricritical point, phase transitions, critical phenomena, iron melting curve, temperature in the Earth's core Melting or solidification is a first order phase transition since the order changes discontinuously from liquid to solid. Landau (1937) gave a theoretical description for first order phase transitions and the point where they change to second order phase transitions (with a continuous change of order) [1]. Such a point was later named a tricritical point by Griffiths (1970) [2]. Tricritical points occur in a variety of physical systems. Examples of tricritical points are presented in Table 1 with the corresponding adjustable variables. Experimentally they were first found in fluid mixtures, compressed single crystals and magnetic and ferroelectric systems (see old reviews in [3] and [4]). Paper [11] is an example of two-dimensional melting.The rest of this paper provides bifurcation theoretical analysis for the solidification/melting problem for iron [12], following the earlier work in Paper [13] which presents the symmetry breaking analysis in the first experimentally studied nonequilibrium tricritical point.

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Temperature measurement and melting determination in the laser-heated diamond-anvil cell

Cited by 82 publications

References 84 publications

High‐pressure experiments and the phase diagram of lower mantle and core materials

High‐pressure experiments and the phase diagram of lower mantle and core materials

Temperature of the inner-core boundary of the Earth: Melting of iron at high pressure from first-principles coexistence simulations

Tricritical Points and Liquid-Solid Critical Lines

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