1 / 30

Quantrainx50 Module 7.2Peltier

place photo here. Quantrainx50 Module 7.2Peltier. Feb 2011. Cold Stage Use. Keep wet samples wet Increase contrast in non-conductive, hydro-phillic samples Perform dynamic experimentation. 15. Liquid phase. Solid phase. 10. Pressure - Torr. Gaseous phase. 5. 0. -10. 0. 10. 20.

bat
Télécharger la présentation

Quantrainx50 Module 7.2Peltier

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. place photo here Quantrainx50Module 7.2Peltier Feb 2011 Confidential

  2. Cold Stage Use • Keep wet samples wet • Increase contrast in non-conductive, hydro-phillic samples • Perform dynamic experimentation

  3. 15 Liquid phase Solid phase 10 Pressure - Torr Gaseous phase 5 0 -10 0 10 20 30 Temperature - Celsius Pressure/temp Phase Diagram for H2O

  4. Connector flange Specimen holder Stage platform Peltier - cooled stage Temperature range: • -5° - +60 °C Relative humidity: • 0-100% achievable Copper braid (no water cooling) Water cooling

  5. ESEM- Applications 5 P (Torr) l s 5 g 4 3 4 5 2 1 Suberabsorbents T 0 -10 0 10 20 3 2 1

  6. Cold Stage use • Keep wet samples wet • Increase contrast in non-conductive, hydro-phillic samples • Perform dynamic experimentation

  7. 1800 Liquid phase Solid phase 1200 ESEM Gaseous phase 600 LOW VAC 0 -10° 0° 10° 20° 30° Temperature - °Celsius Pressure / Temp phase diagram for H2O Pressure - Pa

  8. Keep samples WET during pump down cycle • Desired final environment: 5ºC, 850 Pa (6.5 torr) • Use cyclic pumping and flooding: Cycle between 850 - 1300 Pa • Put some extra water droplets inside chamber

  9. Live animals

  10. Water in an SEM…

  11. Maintaining WET Samples During Pumpdown Cycle • Desired final environment: 3 ºC, 5.5 Torr • Use cyclic pumping and flooding Initial pump  5.5 Torr First flood  9.6 Torr Second pump  5.5 Torr (perform 8x) Final flood  9.8 Torr Final pump  5.5 Torr

  12. Dry to Wet to Dry Experimentation

  13. Keeping Wet Samples Wet Can Preserve Natural Structures

  14. Basics of Chemistry and Physics • Water in a pure state behaves differently than when it has a soluble substance in it • Solutes generally change the vapor dynamics of a material • Any system will have a unique vapor identity which will determine the ease of driving off water or keeping it around • Water activity is a measure of the total water attraction of a substance

  15. Water Activity • Definition from book with reference

  16. Imaging Hydrated Specimens • Fact: • wet, soft & squishy specimens look ‘better’ & remain stable at pressures lower than prescribed by the SVP curve for water • Why is this? • We need to consider the thermodynamic equilibria and kinetics of the specimen!

  17. Condensing Stable Evaporating Vapour: a dynamic phase

  18. Specimen equilibria • Vapour pressure is proportional to mole fraction of solute (Raoult’s law) • Consequence: • Vapour pressure of aqueous phase is less than that of pure water

  19. Osmotic pressure • Thermodynamics, Van’t Hoff:

  20. ‘ESEM phase diagram’ ESEM mode Condensing Evaporating Low vacuum mode

  21. Vapour: a dynamic phase Condensing Stable Evaporating Warmer Colder

  22. Water loss rate is greater the greater the temp 1.6 ) -1 1.4 -sec 1.2 -2 0 ºC 1 5 ºC 0.8 0.6 10 ºC 0.4 20 ºC Mass Loss (mg-mm 0.2 30 ºC 0 -0.2 -0.4 0 2 4 6 8 10 Vapour Pressure (torr)

  23. Thermodynamics & kinetics ESEM mode Condensing Slow water loss Evaporating Low vacuum mode

  24. Thermal Gradients • Samples have differing thermal properties in addition to their hydrophilic properties which must be considered • Conductive samples will have a thermal gradient from the side temperature is applied to (samples will be more different on the side farthest from the source) • Samples which are not thermally conductive will have a larger temperature gradient than thermally conductive samples • Mounting can play an important part in minimizing this difference and making an experiment successful

  25. Dealing with thermal gradients • In an SEM the surface to be imaged is the most important and needs to be at the proper condition • It may be necessary to over apply temperature in order to achieve a desired surface condition • It may be necessary to wrap thermally-conductive materials around non-thermally-conductive samples • It may be necessary to innovate with mounting schemes to place a sample in a colder space • Vacuum is a great insulator and will provide a vapor gradient around a sample (where it is coldest it will have a higher vapor pressure and when warmest the pressure will be lower)

  26. Mounting suggestions for thermal stability Placing a sample in a tight thermally-conductive space will help keep it uniformly cold as the conduction area is in more contact with the sample surface. Placing samples in a well or covering with a washer can often be beneficial to keeping a sample at a desired condition. The tighter the contact the better the conduction.

  27. X-ray can be done in ESEM mode Oil Brine

  28. Contrast Enhancement can sometimes be achieved on hydrophilic samples 25C (~25% RH) 5C (~95%RH)

  29. STEM-2 :High-resolution EDS

  30. End of Quantrain 7.2 Peltier.ppt

More Related