Diamond: Molten under pressure (original) (raw)
Related papers
Melting temperature of diamond at ultrahigh pressure
Nature Physics, 2009
Since Ross proposed that there might be 'diamonds in the sky' in 1981 (ref. 1), the idea of significant quantities of pure carbon existing in giant planets such as Uranus and Neptune has gained both experimental 2 and theoretical 3 support. It is now accepted that the high-pressure, high-temperature behaviour of carbon is essential to predicting the evolution and structure of such planets 4 . Still, one of the most defining of thermal properties for diamond, the melting temperature, has never been directly measured. This is perhaps understandable, given that diamond is thermodynamically unstable, converting to graphite before melting at ambient pressure, and tightly bonded, being the strongest bulk material known 5,6 . Shockcompression experiments on diamond reported here reveal the melting temperature of carbon at pressures of 0.6-1.1 TPa (6-11 Mbar), and show that crystalline diamond can be stable deep inside giant planets such as Uranus and Neptune 1-4,7 . The data indicate that diamond melts to a denser, metallic fluid-with the melting curve showing a negative Clapeyron slope-between 0.60 and 1.05 TPa, in good agreement with predictions of first-principles calculations 8 . Temperature data at still higher pressures suggest diamond melts to a complex fluid state, which dissociates at shock pressures between 1.1 and 2.5 TPa (11-25 Mbar) as the temperatures increase above 50,000 K.
Doklady Earth Sciences, 2020
Data on the interaction of the Fe-Ni melt with CaCO 3 and graphite at 5 GPa and 1400°С under the thermogradient conditions used in experiments on the growth of diamond on the BARS high-pressure apparatus are presented. The phase composition and component composition of the fluid captured by diamonds in the form of inclusions were studied by gas chromatography-mass spectrometry (GC-MS). Diamonds were synthesized from graphite. During the interaction of the Fe-Ni melt with CaCO 3 , CaFe oxides and (Fe, Ni) 3 C carbide were formed. The stability of heavy hydrocarbons under the experimental conditions was confirmed. It was established that the composition of the fluid in synthesized diamonds is close to the composition of the fluid from inclusions in some natural diamonds. Nevertheless, it was concluded that crystallization of large diamonds under natural conditions is hardly possible due to the filling of the main crystallization volume with refractory oxide phases.
Growth of diamond in liquid metal at 1 atmosphere pressure
Natural diamonds were (and are) formed (some, billions of years ago) in the Earth’s upper mantle in metallic melts in a temperature range of 900–1400°C and at pressures of 5–6 GPa1,2; indeed, diamond is thermodynamically stable under high pressure and high temperature (HPHT) conditions as per the phase diagram of carbon3. Scientists at General Electric invented and used a HPHT apparatus in 1955 to synthesize diamonds from melted iron sulfide at about 7 GPa and 1600°C4–6. There is an existing paradigm that diamond can be grown using liquid metals only at both high pressure (typically 5–6 GPa) and high temperature (typically 1300–1600°C) where it is the stable form of carbon7. Here, we describe the growth of diamond crystals and polycrystalline diamond films with no seed particles using liquid metal but at 1 atmosphere pressure, and at 1025°C, breaking this paradigm. Diamond grew at the interface of liquid metal composed of gallium, iron, nickel, and silicon and a graphite crucible, b...
European Journal of Mineralogy
The origin and evolution of metal melts in the Earth's mantle and their role in the formation of diamond are the subject of active discussion. It is widely accepted that portions of metal melts in the form of pockets can be a suitable medium for diamond growth. This raises questions about the role of silicate minerals that form the walls of these pockets and are present in the volume of the metal melt during the growth of diamonds. The aim of the present work was to study the crystallization of diamond in a complex heterogeneous system: metal-melt-basalt-carbon. The experiments were performed using a multianvil high-pressure apparatus of split-sphere type (BARS) at a pressure of 5.5 GPa and a temperature of 1500 • C. The results demonstrated crystallization of diamond in metal melt together with garnet and clinopyroxene, whose chemical compositions are similar to those of eclogitic inclusions in natural diamond. We show that the presence of silicates in the crystallization medium does not reduce the chemical ability of metal melts to catalyze the conversion of graphite into diamond, and, morphologically, diamond crystallizes mainly in the form of a cuboctahedron. When the content of the silicate material in the system exceeds 5 wt %, diamond forms parallel-growth aggregates, but 15 wt % of silicate phases block the crystallization chamber, preventing the penetration of metallic melt into them, thus interrupting the growth of diamond. We infer that the studied mechanism of diamond crystallization can occur at lower-mantle conditions but could also have taken place in the ancient continental mantle of the Earth, under reducing conditions that allowed the stability of Fe-Ni melts.
Crystals
The accurate determination of melting curves for transition metals is an intense topic within high pressure research, both because of the technical challenges included as well as the controversial data obtained from various experiments. This review presents the main static techniques that are used for melting studies, with a strong focus on the diamond anvil cell; it also explores the state of the art of melting detection methods and analyzes the major reasons for discrepancies in the determination of the melting curves of transition metals. The physics of the melting transition is also discussed.
Image analysis as an improved melting criterion in laser-heated diamond anvil cell
2015
The precision of melting curve measurements using laser-heated diamond anvil cell (LHDAC) is largely limited by the correct and reliable determination of the onset of melting. We present a novel image analysis of speckle interference patterns in the LHDAC as a way to define quantitative measures which enable an objective determination of the melting transition. Combined with our low-temperature customized IR pyrometer, designed for measurements down to 500K, our setup allows studying the melting curve of materials with low melting temperatures, with relatively high precision. As an application, the melting curve of Te was measured up to 35 GPa. The results are found to be in good agreement with previous data obtained at pressures up to 10 GPa.
A simple method for detection of melting event in laser-heated diamond anvil cells (DACs) is introduced. The melting is registered optically by the formation of spherical drops of the investigated material as heated in an inert pressure transmitting medium. Feasibility of the method is demonstrated on the examples of metal (iron and gold) and iron oxide (Fe 2 O 3 ), materials molten at pressures over 40 GPa employing a portable laser heating system.
Indian Journal of Physics, 2018
Laser-heated diamond anvil cell (LHDAC) technique is a unique and powerful experimental tool for studying the phase behaviour of materials at thermodynamic conditions comparable to the Earth's deep interior. Fine tuning of the two thermodynamic variables viz., pressure and temperature enables one to manipulate matter on an atomic scale leading to the synthesis of novel compounds or transformation of the properties of existing materials. In this article the details of an ytterbium doped fibre laser based LHDAC facility are presented. The advantages and excellent performance of the off-axis angular heating geometry is demonstrated through results of high pressure melting experiments on KBr up to 24 GPa and high temperature high pressure synthesis of c-Mo 2 N carried out by laser heating molybdenum metal and molecular nitrogen at 7 GPa and 2000 K in a Mao-Bell type diamond anvil cell.
American Mineralogist
The volume bulk modulus, together with its temperature dependence, and the thermal expansion of 13 diamond at various pressures, were calculated from first principles in the [0, 30GPa] and [0, 3000K] 14 pressure and temperature ranges. The hybrid HF/DFT functional employed (WC1LYP) proved to be 15 particularly effective in providing a very close agreement between the calculated and the available 16 experimental data. In particular, the bulk modulus at 300K was estimated to be 444.6 GPa (K' = 3.60); 17 at the same temperature, the (volume) thermal expansion coefficient was 3.19·10 -6 K -1 . To the 18 authors' knowledge, among the theoretical papers devoted to the subject, the present one provides 19 the most accurate thermo-elastic data in high pressure and temperature ranges. Such data can 20 confidently be used in the determination of the pressure of formation using the "elastic method" for 21 minerals found as inclusions in diamonds, thus shading light upon the genesis of diamonds in the 22 Earth's upper mantle. 23 keywords: diamond, thermo-elastic properties, thermal expansion, ab initio calculations. 24 25 35 Earth's mantle) at which the inclusions were formed (Nestola et al. 2011; Izraeli et al. 1999) using the 36 so called "elastic method" (see Shirey et al. 2013 for a review). However, to this end, very accurate 37 data concerning the pressure-volume equation of state, the thermal expansion and the bulk modulus 38 temperature dependence of both diamond and its inclusions are absolutely crucial in order to obtain 39 low error in the pressure of formation. 40 As concerns diamond, previous experimental and theoretical determinations of the elastic parameters 41 and thermal expansion existed. In particular, from the experimental side, the elastic constants 42 measurements from Brillouin scattering, at room or higher temperatures, allowed the estimation of 43