An international team of scientists from DESY Photon Science, Lawrence Livermore National Laboratory (U.S.), the University of Edinburgh (UK), and Karlsruhe Institute for Technology (Germany) has developed a novel approach to accurately determine the melting temperature of opaque materials using X-ray phase contrast imaging and X-ray diffraction in the laser-heated diamond anvil cell at up to pressures of 500 000 bar and 4000 Kelvin. The team lead by Emma Ehrenreich-Petersen from DESY and Earl Francis O’Bannon from Lawrence Livermore National Laboratory developed the technique at beamline P02.2 at DESY´s high-energy photon source PETRA III and published their results in the journal Results in Physics.
For decades, determining the high pressure melting of opaque materials has been a significant challenge. Many approaches have been developed over the last decades since the introduction of laser heated diamond anvil cell. This fist-large high-pressure device consists of two opposed modified diamonds which compress the sample in between them. It can generate pressures that are higher than the pressure found at the center of the Earth. The sample – in this case a metal foil – can be heated through the transparent diamonds with very powerful infrared lasers that illuminate the sample from both sides of the diamonds. “It is extremely difficult to detect the first appearance of very small amounts of melt by means of optical imaging or X-ray diffraction of the sample. This led to discrepancies in melt temperature determination in earlier studies,” explains lead author Emma Ehrenreich-Petersen from DESY. “In our study we combine the otherwise well-established technique of X-ray phase contrast imaging with diffraction and apply it to the laser heated diamond anvil cell, to detect the smallest amount of phase contrast between the solid and the liquid sample”
“This approach has the advantage that one does not need to melt the entire sample, since this setup can resolve features as small as about one micron” states project leader Earl Francis O’Bannon from Lawrence Livermore National Laboratory. “We benchmarked this novel approach at the PETRA III Extreme Conditions Beamline P02.2 by determining the melting line of platinum up to pressures of 500 000 atmospheres and temperatures up to 4000 Kelvin. We demonstrated that the technique is much more sensitive in determining the onset of melting than any other previous technique.”
Read more on PETRAIII website
Image: The technique developed at PETRA III allows the incipient melting process in platinum (centre) to be tracked precisely.
Credit: DESY, Hanns-Peter Liermann