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20-Jun-2003
XRF and XAFS 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
H. K. (Dave) Mao, Carnegie Institute of Washington, HP-CATYue Meng, Carnegie Institute of Washington, HP-CATChi-Chang Kao, Brookhaven National LabWendy Mao, University of Chicago
John Mavrogenes, Andrew BerryAustralian National University, Canberra, ACT
Cu in Quartz Fluid Inclusions at Hydrothermal Conditions
High-Pressure C K-Edge X-ray Raman Spectroscopy
20-Jun-2003
Advanced Photon Source Undulator APeriod length 3.30 cmNumber of periods 72Length 2.47 m Minimum gap 10.5 mmPower (closed gap) 6 kW Kmax (closed gap) 2.78
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
Source Size and Divergence:Vert: = 16m, ’ = 4radHoriz: = 240m, ’ = 14rad
20-Jun-2003
GSECARS Beamline Layout and Optics
Undulator Beamline: High collimation allows efficient focusing, for x-ray microprobe,
and x -ray diffraction (small crystals, high pressure).
Bending Magnet Beamline: 2nd-generation source, with high energy x-rays (up to 100KeV)
Storage Ring, undulator
High Pressure Station: Diamond-Anvil-Cell Large Volume Press
Monochromator: LN2-cooled Si (111) Energy range: 4.5 –
40keV
Large Focusing Mirrors: 1m KB pair
X-ray Microprobe: XAFS, XRF, fluorescence tomography
BM Station: tomography, diffraction, DAC, Large Volume Press, bulk XAFS
Diffractometer: surface diffraction inelastic scattering
GeoSoilEnviroCARS: Sector 13, APS, Argonne National Lab
20-Jun-2003
Focusing: Kirkpatrick-Baez mirrors: Rh-coated Si, typically using 3x3m spot sizes, at 50mm from end of mirrors.
Incident Beam:LN2 cooled Si (111)
Sample Stage: x-y-z stage, 1m resolution
Fluorescence detector: 16-element Ge detector / DXP electronics, Lytle Detector, or Wavelength Dispersive Spectrometer
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.
GSECARS XRF/XAFS Microprobe Station
Slits: typically 200 to 300 m, accepting ~20% of undulator beam at50m from source.
20-Jun-2003
The table-top Kirkpatrick-Baez mirrors use four-point benders and flat, trapezoidal mirrors to dynamically form an ellipsis. They can focus a 300x300m beam to 1x1m - 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 2x3m beams for XRF, XANES, and EXAFS.
Kirkpatrick-Baez Focusing Mirrors
20-Jun-2003
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.
X-ray Fluorescence Detectors
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
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, high-pressure 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 andXAFS 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.
Metal Speciation in Hydrothermal Fluid Inclusions
100m
20-Jun-2003
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.
Hydrothermal Fluid Inclusion Measurements
20-Jun-2003
Understanding the metal complexes trapped in hydrothermal solutions in minerals is key to understanding the formation of ore deposits.
Cu 25oC
Cu 495oC
Fe 25oC
Fe 495oC
65m
Natural Cu and Fe-rich brine and vapor-phase 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.
Cu speciation in Hydrothermal Fluid Inclusions
XRF mapping (2m 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.
XRF Mapping
20-Jun-2003
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.
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.
20-Jun-2003
Cu XAFS in Fluid Inclusions
Cu2+
O
O
2.35Å
1.96Å
Cl
2.09Å
Cu1+
Low temp High temp
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,
J. A. Mavrogenes, A. J. Berry, M. Newville, S. R. Sutton, Am. Mineralogist 87, p1360 (2002)
20-Jun-2003
- 6-element Si (440) Crystal Analyzer- Kappa Diffractometer- Large Beamline KB mirrors, giving ~1013ph/s at 10keV in a 20x80m spot.
Ideal for inelastic x-ray scattering in a Diamond Anvil Cell, including XANES-like information from X-ray Raman measurements.
Inelastic X-ray Scattering: X-ray Raman
DAC sample, lead-covered detector
Analyzer Crystals: Si (440) 870mm Rowland circle