1 / 53

Specific heat

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.

hall
Download Presentation

Specific heat

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Specific heat

  2. Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO

  3. Thermal expansion

  4. Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO

  5. Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO

  6. Once have F(V.T) -- can get everything

  7. Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO

  8. Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO

  9. M-G EOS Parameters -- from Stixrude et al, 2005 with modifications

  10. High pressure experiments

  11. Static Measurements: 2) Anvil Devices: 2 broad types • Large volume multi-anvil press (MAP) • ii) Symmetric opposed anvil design (many different designs e.g. DAC)

  12. Types of Large Volume Presses • Piston-Cylinder- 4-6 Gpa • Multi-Anvil- 25GPa • Paris-Edinburgh- 12GPa

  13. 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

  14. Large volume multi anvil cells: 3 orders of magnitude higher than DACs! 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

  15. 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.

  16. 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: , 

  17. Creating Temperature: 3 ways: 1) External heating 2) Internal heating 3) IR Laser Heating

  18. unheated ruby chips Sample size Optics to enlarged image Pressure medium P-T gradient

  19. Laser heating - use black body radiation T: temperature I: intensity : wavelength Cs: constants : emissivity • is wavelength dependent But dependence not known for many materials! (known for Fe) • Perfect black body:  = 1 Grey body:  < 1

  20. 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

  21. 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

  22. Pressure gradients

  23. Synchrotron Radiation • Bi-product of particle accelerators • Transverse emission of EM radiation tangential to ring • Advantages: • Focussing (on small samples) • Bandwidth • Strength to penetrate high pressure vessels • Polarized - elasticity, structure, density of states • Now: ‘3rd generation’ synchrotron radiation

  24. Measuring Material Parameters… In-Situ X-Ray Diffraction • 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

  25. Measuring Material Parameters… X-Ray Spectrography • Use polychromatic X-rays and Be gaskets • Observe absorption freq. • Absorption changes with phase • Observe: • Atomic Coordination • Structures • Electronic/Magnetic Properties

  26. 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+ X-ray detected lattice parameters during a phase transformation

  27. Measuring Material Parameters… 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

  28. Need higher pressure

  29. 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

  30. Measuring Material Parameters… 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

  31. Elastic Moduli: , , Vp, Vs 3 ways to get these: Static compression (no info on shear properties) Shock compression Acoustic vibration (frequencies 10^13 Hz) (applicability?)

  32. 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)

  33. 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!

More Related