Detection of melting by in-situ observation of spherical-drop formation in laser-heated diamond-anvil cells

Source: arXiv


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 (Fe2O3), materials molten at
pressures over 40 GPa employing a portable laser heating system.

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    ABSTRACT: A novel diamond-anvil cell (DAC) design has been constructed and tested for in situ applications at high-pressure (HP) operations and has proved to be suitable even for HP sample environments at non-ambient temperature conditions. The innovative high-precision guiding mechanism, comparable to a dog clutch, consists of perpendicular planar sliding-plane elements and is integrated directly into the base body of the cylindrically shaped DAC. The combination of two force-generating devices, i.e., mechanical screws and an inflatable gas membrane, allows the user to choose independently between, and to apply individually, two different forcing mechanisms for pressure generation. Both mechanisms are basically independent of each other, but can also be operated simultaneously. The modularity of the DAC design allows for an easy exchange of functional core-element groups optimized not only for various analytical in situ methods but also for HP operation with or without high-temperature (HT) application. For HP-HT experiments a liquid cooling circuit inside the specific inner modular groups has been implemented to obtain a controlled and limited heat distribution within the outer DAC body.
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    ABSTRACT: Magnesium carbonate MgCO3 (magnesite) was experimentally studied at pressures of 12–84 GPa and tem- peratures between 1,600 and 3,300 K. We applied the high- pressure technique using a multianvil press and a diamond anvil cell with laser heating. The phase relations and melting of magnesite were investigated by means of raman and time- resolved multi-wavelength spectroscopy. Magnesite is found to melt congruently within the entire studied pressure range at temperatures of 2,100–2,650 K. at temperatures above 2,700 K, we observed decomposition of magnesite with for- mation of MgO and a carbon phase (diamond). Our results demonstrate that at high pressures, the magnesium carbonate melt can exist at a wide range of thermodynamic conditions.
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