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Specific heat
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO
Thermal expansion
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO
Once have F(V.T) -- can get everything
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO
M-G EOS Parameters -- from Stixrude et al, 2005 with modifications
High pressure experiments
2) Anvil Devices: 2 broad types
Static Measurements:
i) Large volume multi-anvil press
(MAP)
ii) Symmetric opposed anvil design (many different designs e.g. DAC)
Types of Large Volume Presses
• Piston-Cylinder- 4-6 Gpa
• Multi-Anvil- 25GPa
• Paris-Edinburgh- 12GPa
A large-volume high-pressure and high-temperature apparatus
for in situ X-ray observation, ‘SPEED-Mk.II’By Katsura et al
SPEED-Mk.II’ is a multi-anvil KAWAI-type press
Large volume multi anvil cells:
Large volume: House probes, synthesize larger specimens, some experiments require large V (e.g. ultrasonic interferometry)
Hydrostatic Pressure: Closer, since squeezing from 8 directions, But, not easily used with gas pressure medium
Pressures: Top of lower mantle at best with sintered diamonds and synchrotron radiation
3 orders of magnitude higher than DACs!
P/T Measurement
• Pressure can be measured by calibrating the machine to a sample with well known diffraction patterns, such as NaCl.
• Since this is a large volume press, temperature can be measured directly with thermocouples.
Diamond Anvil Cells:
Why Diamonds?
Can use: Steel, tungsten carbide, boron carbide, sapphire, cubic zirconia, sintered diamond,
or single-crystal diamond
Single crystal diamond:
1) Strongest material known 2) Transparent (IR, optical, UV, and X-ray)
3) Non-magnetic insulator: ,
Creating Temperature:
3 ways:
1) External heating
2) Internal heating
3) IR Laser Heating
unheated ruby chips
Sample size
Optics to enlarged image
Pressure medium
P-T gradient
Laser heating - use black body radiation
T: temperatureI: intensity: wavelengthCs: constants: emissivity
Perfect black body: = 1Grey body: < 1
is wavelength dependent
But dependence not known for many materials! (known for Fe)
Advances in laser heating…
- Double sided laser heating
- split beam and heat from both ends
- Or mix 2 lasers at different modes - flat T distribution
- Can now get temps ~3000K (+/- 10K) at high P
- Bottom line: use caution when trusting results from laser heating experiments prior to 1996-98
Pressure media
• low shear strength • Chemical inertness• Low thermal conductivity• Low emissivity• Low absorption of laser light• Ar 8GPa, Ne 20GPa, He >100GPa• Draw back: high fluorescence, high
compressibility
Pressure gradients
Synchrotron Radiation
• Bi-product of particle accelerators
• Transverse emission of EM radiation tangential to ring
• Advantages: 1) Focussing (on small samples)2) Bandwidth3) Strength to penetrate high pressure
vessels4) Polarized - elasticity, structure,
density of states
Now: ‘3rd generation’ synchrotron radiation
• Provides Crystal Structure, Density and melting points
• Synchrotron Radiation provides highly collimated x-ray source • Braggs Law: 2q = angle of diffraction
d = spacing of crystal planes = wavelength of X-ray
In-Situ X-Ray DiffractionMeasuring Material Parameters…
€
=2d sin(q)
X-Ray Spectrography
• Use polychromatic X-rays and Be gaskets
• Observe absorption freq.
• Absorption changes with phase
• Observe:– Atomic Coordination– Structures– Electronic/Magnetic Properties
Measuring Material Parameters…
X-ray detected lattice parameters during a phase transformation
For X-ray studies:• Know temp gradients
• Suitable pressure mediums
• Angular Diffraction method• Monochromatic X-rays used• Best for quantitative intensity• Precision Lattice Parameter measurement
• Energy Diffraction method• Fastest method
• Gasket Selection• Be allows trans-gasket measurements at 4 keV+
• Diamonds allow hard X-rays. 12 keV+
Measurement of Pressure
• Ruby Chips Fluorescence Method– Freq. shift of ruby with increasing pressure
– Linear to 30 GPa
– Calibrated to 100 GPa by Raman Spec.
– Calibrated to >200 GPa by Gold
– Accurate to 15-20% at 200 GPa
– Diffuses with temperature (>700K)
– Ruby and Diamond Fluorescence overlap between 120-180 GPa
– KEY: Allows sampling at multiple points in pressure medium
Measuring Material Parameters…
Need higher pressure
Optical Probes
• Optical Absorption– High pressure melting, crystallization, phase transitions
• Infrared Spectroscopy– Detailed bonding properties
• Raman Spectroscopy (10-1000cm-1)– Most definitive diagnostic tool for the identification of specific molecules– Diagnostic evidence for phase transition in simple molecular compounds
• Brillouin Spectroscopy (<1cm-1)– Wave velocities and elasticity tensor– New primary pressure standard
• Fluorescence Spectroscopy– Electronic states
Raman Spectroscopy• Raman Techniques
– Measures scattering of monochromatic light due to atomic vibrations.
• Provides vibration frequencies in a solid
– Temperature = noise : most samples temperature quenched.
– Synchrotron radiation: a powerful, narrow beam of highly collimated light source.
• Parameters Measured– Entropies– Specific Heats– Grüneisen Parameters– Phase Boundaries
Measuring Material Parameters…
Elastic Moduli:
, , Vp, Vs
3 ways to get these:
1) Static compression (no info on shear properties)2) Shock compression3) Acoustic vibration (frequencies 10^13 Hz) (applicability?)
Extending elastic observations to higher P-T:
Brillouin Spectroscopy -
• Optical beam scattered by an acoustic wave
• Compression and dilatation by acoustic wave results in change in refractive index of material
• Look at Doppler shift of laser frequency - get wave velocity of the acoustic wave
• can get up to ~60GPa• at ~2500K in DAC with laser• (mid lower mantle)
Some conclusions
• Early DAC measurements suspect because non-hydrostatic
• Still very hard to do simultaneous high T and P – very few elasticity measurements at high T
• Pressure calibrations improving and becoming more consistent – but take care when using older measurements!
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO
Raman Spectroscopy