In-situ Phase Transformation and Deformation of Iron at High Pressure andTemperature Page: 2 of 33
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intensity changes along Debye rings (texture) and variations in d-spacings relative to the
compression direction (lattice strain).
While previous work using the rDAC has provided important information on in-
situ rheological behavior through interpretation of texture patterns, these studies were
limited to ambient temperature. As a result little is known about the behavior of
materials at high-temperature and ultra-high pressures. This is of particular importance
to the field of Earth and planetary sciences as it is questionable whether room
temperature studies are appropriate for extrapolation to behavior in planetary interiors
where materials are deforming both at high-pressure and temperature. In order to expand
rDAC experiments to the high-temperature regime, an in-situ laser-heating system for
radial diffraction geometry has been developed at the Advanced Light Source (ALS) of
the Lawrence Berkeley Laboratory (LBL).5 Previously, pressure/stress increase in
rDACs has been controlled through load screws pushing the piston of the rDAC into its
cylinder. This requires manual intervention and is incompatible with in-situ observations
of the effects of pressure and stress increase at high-temperature. Furthermore, manual
pressure change requires re-aligning the sample on the x-ray beam, which is time
intensive and thus limits the resolution in pressure steps for radial diffraction
experiments, even at ambient temperatures. A remote controlled pressure changing
mechanism is thus required. A membrane driven DAC for axial diffraction has been
developed, but the closed design in the radial direction does not allow its application to
radial diffraction.6 Alternately a motor driven mechanism can be used to remotely
change pressure on a screw-driven Mao-Bell DAC from outside a synchrotron
experimental hutch.' While the solution of a remotely controlled mechanical cell is
advantageous in terms of long-term pressure stability, it bears some drawbacks in terms
of weight and flexibility, especially in view of the need to combine it with in-situ laser
heating. Here we present an approach based on gas-membrane technology. Instead of
designing a new rDAC, we aimed to construct a frame applicable to various designs of
rDACs. In our design, we paid special attention to flexibility (easy to accommodate
several types of rDAC designs), weight (it should not exceed the load limitations of the
high-precision stages on the end-station) and open access (for combination with in-situ2
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Miyagi, Lowell; Kunz, Martin; Knight, Jason; Nasiatka, James; Voltolini, Marco & Wenk, Hans-Rudolf. In-situ Phase Transformation and Deformation of Iron at High Pressure andTemperature, article, July 1, 2008; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc930239/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.