Transcript No Slide Title

mXRF and mXAFS with the GSECARS X-ray Microprobe
Matthew Newville, Steve Sutton, Mark Rivers, Peter Eng, Tom Trainor
Consortium for Advanced Radiation Sources (CARS)
University of Chicago, Chicago, IL
Cu in Quartz Fluid Inclusions at Hydrothermal Conditions
John Mavrogenes, Andrew Berry
Australian National University, Canberra, ACT
High-Pressure C K-Edge X-ray Raman Spectroscopy
H. K. (Dave) Mao, Carnegie Institute of Washington, HP-CAT
Yue Meng, Carnegie Institute of Washington, HP-CAT
Chi-Chang Kao, Brookhaven National Lab
Wendy Mao, University of Chicago
20-Jun-2003
Advanced Photon Source Undulator A
Period length
Number of periods
Length
Minimum gap
Power (closed gap)
Kmax (closed gap)
3.30 cm
72
2.47 m
10.5 mm
6 kW
2.78
Source Size and Divergence:
Vert: s = 16mm, s’ = 4mrad
Horiz: s = 240mm, s’ = 14mrad
Energy Tuning Range:
2.9 - 13.0 keV (1st harmonic)
2.9 - 45.0 keV (3rd and 5th harmonic)
On-axis peak brilliance (at 6.5 keV):
9.6x1018 ph/s/mrad2 /mm2 /0.1%bw
On-axis power density (closed gap):
167 kW/mrad2
20-Jun-2003
GSECARS Beamline Layout and Optics
GeoSoilEnviroCARS: Sector 13, APS, Argonne National Lab
Undulator Beamline: High collimation allows efficient focusing, for x-ray microprobe,
and x -ray diffraction (small crystals, high pressure).
High Pressure Station:
Diamond-Anvil-Cell
Large Volume Press
X-ray Microprobe:
XAFS, XRF,
fluorescence tomography
Diffractometer:
surface diffraction
inelastic scattering
Monochromator:
LN2-cooled Si (111)
Energy range: 4.5 – 40keV
Large Focusing Mirrors:
1m KB pair
Storage Ring,
undulator
BM Station: tomography, diffraction, DAC,
Large Volume Press, bulk XAFS
Bending Magnet Beamline: 2nd-generation source, with high energy x-rays (up to 100KeV)
20-Jun-2003
GSECARS XRF/XAFS Microprobe Station
Focusing: Kirkpatrick-Baez mirrors: Rh-coated Si, typically using
3x3mm spot sizes, at 50mm from end of mirrors.
Incident Beam:
LN2 cooled Si (111)
Sample Stage:
x-y-z stage,
1mm resolution
Slits: typically
200 to 300 mm,
accepting ~20% of
undulator beam at
50m from source.
Data Collection:
Flexible, custom
software for
X-Y XRF mapping,
and XAFS, based
on EPICS.
Optical Microscope:
5x to 50x objective
to external video
system / webcam.
Fluorescence detector: 16-element Ge detector / DXP electronics,
Lytle Detector, or Wavelength Dispersive Spectrometer
20-Jun-2003
Kirkpatrick-Baez Focusing Mirrors
The table-top Kirkpatrick-Baez mirrors use four-point
benders and flat, trapezoidal mirrors to dynamically
form an ellipsis. They can focus a 300x300mm beam to
1x1mm - a flux density gain of 105.
With a typical working distance of 100mm, and an
energy-independent focal distance and spot size, they
are ideal for micro-XRF and micro-EXAFS.
We use Rh-coated silicon for horizontal and vertical
mirrors to routinely produce 2x3mm beams for XRF,
XANES, and EXAFS.
20-Jun-2003
X-ray Fluorescence Detectors
16 element Ge Detector: energy resolution ~250 eV,
which separates most fluorescence lines, and allow a
full XRF spectrum (or the windowed signal from several
lines) to be collected in seconds.
Limited in total count rate (to ~250KHz), so multiple
elements (10 to 30) are used in parallel. Detection limits
are at the ppm level for XRF. XANES and EXAFS
measurements of dilute species (~10ppm) in
heterogeneous environments can be measured.
Wavelength Dispersive Spectrometer has much better
resolution (~20eV), and much smaller solid angle, but
can be used for XAS,
is able to separate
fluorescence
lines
that overlap with a
Ge detector.
20-Jun-2003
Metal Speciation in Hydrothermal Fluid Inclusions
John Mavrogenes, Andrew Berry (Australian National University)
Hydrothermal ore deposits are important
sources of Cu, Au, Ag, Pb, Zn, and U.
Metal complexes in high-temperature, highpressure solutions are transported until
cooling, decompression, or chemical reaction
cause precipitation and concentration in
deposits.
To further understand the formation of these
deposits, the nature of the starting metal
complexes need to be determined.
XRF and XAFS are important spectroscopic
tools for studying the chemical speciation and
form of these metal complexes in solution.
This is challenging to do at and above the
critical point of water (22MPa, 375oC).
Fluid inclusions from hydrothermal deposits
can be re-heated and used as sample cells for
high temperature spectroscopies.
Natural Cu and Fe-rich brine / fluid inclusions in
quartz from Cu ore deposits from New South Wales,
Australia were examined at room temperature and
elevated temperatures by XRF mapping and XAFS.
20-Jun-2003
Hydrothermal Fluid Inclusion Measurements
Linkham TS1500 Heating Stage.
Normally, this can easily heat to
1200C for optical microscopy. We
had to take off most of the protective
front plates to cut down on
background Cu and Fe fluorescence.
In the end, we ran the quartz
inclusion samples in air, with water
flowing, but no heat shielding.
20-Jun-2003
Cu speciation in Hydrothermal Fluid Inclusions
XRF Mapping
Cu 25oC
Fe 25oC
Cu 495oC
Fe 495oC
Understanding the metal complexes
trapped in hydrothermal solutions in
minerals is key to understanding the
formation of ore deposits.
Natural Cu and Fe-rich brine and vaporphase fluid inclusions in quartz from Cu
ore deposits were examined at room
temperature and elevated temperatures
by XRF mapping and EXAFS.
Initial Expectation: chalcopyrite (CuFeS2)
would be precipitated out of solution at
low temperature, and would dissolve into
solution at high temperature. We would
study
the
dissolved
solution
at
temperature.
XRF mapping (2mm pixel size) showed that for large vapor-phase inclusions, a
uniform distribution of Cu in solution at room temperature was becoming less
uniform at temperature. This was reversible, and seen for multiple inclusions.
20-Jun-2003
Cu XANES: Speciation in Fluid Inclusions
XAFS measurements at low and high
temperature for the
vapor-phase
inclusiong were also very different, with
a very noticeable differences in the
XANES:
Low temp: Cu2+ , aqueous solution
High temp: Cu1+ , Cl or S ligand.
These results are consistent with Fulton et al [Chem Phys Lett. 330, p300 (2000)]
study of Cu solutions near critical conditions: Cu2+ solution at low temperature,
and Cu1+ associated with Cl at high temperatures.
20-Jun-2003
Cu XAFS in Fluid Inclusions
EXAFS from the high temperature phase.
Fit to high-temperature (450C) Cu solution in fluid
(vapor phase) inclusion: can get good fits with 1
Cl at ~2.09Å and 1 O at ~2.00Å, or 2 Cl at
~2.08Å.
This is also consistent with the
model of for aqueous Cu1+ of Fulton et al,
O
2.35Å
Cu2+
O
Cl
2.09Å
Cu1+
1.96Å
J. A. Mavrogenes, A. J. Berry, M. Newville, S. R. Sutton,
Am. Mineralogist 87, p1360 (2002)
Low temp
High temp
20-Jun-2003
Inelastic X-ray Scattering: X-ray Raman
- 6-element Si (440) Crystal Analyzer
- Kappa Diffractometer
- Large Beamline KB mirrors, giving ~1013ph/s
10keV in a 20x80mm spot.
at
Ideal for inelastic x-ray scattering in a Diamond Anvil
Cell, including XANES-like information from X-ray
Raman measurements.
DAC sample, lead-covered detector
Analyzer Crystals: Si (440) 870mm Rowland circle
20-Jun-2003
X-ray Raman: high pressure carbon
There is very little spectroscopic study of the phase transitions from
graphite -> hcp C -> fcc C (diamond).
Here is preliminary X-ray Raman measurements on graphite in a
Diamond Anvil Cell (yes, background diamond is a possibility!)
20-Jun-2003