NEWDIA4Planet · Development of the new internally-heated diamond-anvil cell for planetary mineral physics: Application to high-pressure melting of H2O ice

Development of the new internally-heated diamond-anvil cell for planetary mineral physics: Application to high-pressure melting of H2O ice

The front-line discoveries on high pressure mineralogy of planetary materials coincide with development of high pressure (P) and temperature (T) technology. Diamond anvil cell (DAC) experiment is a major approach to generate static P-T conditions up to that of Earth’s inner core. In particular, laser-heated DAC technique has been used to make the important mineralogical discoveries of planetary interiors including the Earth’s. However, there is a critical drawback of the laser heated DAC, involving a large temperature uncertainty due to laser fluctuation and large temperature gradients in the sample (ca.±10%). Precise experimental temperature determination is crucial to implications for planetary interior models; e.g. the location of the phase transition is a key to understand the origin of the seismic discontinuity; high-pressure melting temperatures of planetary materials place important constraints on the temperature of deep planetary interiors. Therefore, the Fellow aimed to provide a new heating system for the DAC, which offers stable and homogeneous heating to a variety of samples under wide pressure and temperature conditions. The basic design of the new heating system was adopted from a so-called internally heated DAC (IHDAC). The IHDAC is the most advanced high P-T generating system, in which a metallic foil inside a sample chamber is heated through supplied electricity. The internal heating benefits from steady and uniform heating due to resistive heating, resulting in smaller temperature uncertainty than laser heating (ca.±5%). The Fellow improved the IHDAC by developing a micron-sized heater made of chemically inert metals that heat up an adjacent sample. This was significant improvement to make the new IHDAC highly versatile i.e. applicable to diverse samples, because the conventional IHDAC can heat only metals. This was due to the fact that the sample also served as a heater in the conventional system to allow passage of enough electricity necessary for resistive heating. Another important aspect of the new IHDAC is its applicability to H2O. H2O is a major constituent of planetary bodies in the outer solar system, such as Uranus and Neptune. However, the high-pressure melting temperatures of H2O differs significantly between previous studies (±300 degC at P = 40 GPa), hence there is no clear-cut answer to a basic question whether H2O is in liquid or solid state in these planets. Therefore, as the second part of this project, the Fellow re-examined the high-pressure melting curve of H2O using the newly developed IHDAC. H2O, or water, is particularly challenging material for the DAC experiments because of its liquid state and high chemical activity at the ambient condition. In addition to the inert metal heater, the Fellow employed a unique sample-loading method for water using liquid nitrogen. This further delivered variations to the sample heatable in the IHDAC. By using the newly developed IHDAC system, the high-pressure melting temperature of H2O was measured up to P = 44 GPa in this project.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз