MAPPING TEMPERATURES DURING FLASH HEATING IN A DIAMOND-ANVIL CELL: MELTING IRON AT HIGH PRESSURES

With the invention of the laser-heated diamond-anvil cell (DAC), simultaneous high pressures and high temperatures can be achieved while visually observing and probing the sample. This technique has facilitated large advances in nearly all branches of science and engineering, in particular Earth science. Investigation of material behavior at extreme thermodynamic conditions requires accurate characterization of the high pressures and high temperatures. As such, there have been many studies designed to quantify the high-temperature and high-pressure conditions within the laser-heated DAC. One of the most significant challenges stems from the nature of diamonds themselves: diamond is an excellent thermal conductor and encourages steep thermal gradients (up to ~10² K/μm). In general, as pressure and temperature increase, the gradients in these quantities also increase. Even so, the DAC has become the tool of choice for obtaining high pressures under static conditions due to its simple and flexible design, and the optical access afforded by the diamond anvils over a wide range of the electromagnetic spectrum. Consequently, the need to accurately characterize gradients in pressure and temperature within the laser-heated DAC remains.

Among the most fundamental problems undertaken in high-pressure science is the determination and measurement of melting temperatures. Coupling two-dimensional, 4-color multi-wavelength imaging radiometry with laser flash heating we determine the temperature profiles and melting temperatures under high pressures in a DAC. This technique combines the attributes of flash heating (e.g., minimal chemical reactions, thermal runaway, and sample instability), with those of multi-wavelength imaging radiometry (e.g., 2D temperature mapping and reduction of chromatic aberrations). Using this new technique in conjunction with electron microscopy makes a powerful tool to determine melting temperatures at high pressures generated by a diamond-anvil cell. Here we will present the melting curve of iron at high pressures as measured with this new technique. Additionally, longer-duration laser heating shows movement within the molten region suggesting low viscosity of the molten metal if Brownian motion is assumed.