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What kinds of specimens?

What kinds of specimens?. Examples from literature Catalysts - mask large pores by filling w/ medium of same electron density as catalyst support (ex: CH 2 I 2 ) - expect increase in absorption Vycor glass - surface area of internal voids

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What kinds of specimens?

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  1. What kinds of specimens? Examples from literature Catalysts - mask large pores by filling w/ medium of same electron density as catalyst support (ex: CH2I2) - expect increase in absorption Vycor glass - surface area of internal voids need precise data, absolute intensities - specimens precisely ground sub-mm in thickness

  2. Thickness? In transmission: Io I x I/Io = exp(-x) = exp(-x)  (= */ = mass attenuation coefficient * = linear attenuation coefficient  = density of specimen

  3. Thickness? In transmission: Io I x I/Io = exp(-x) = exp(-x)  (= */ = mass attenuation coefficient * = linear attenuation coefficient  = density of specimen  = wt. fract. A A + wt. fract. B B + wt. fract. C C + ........ Values for can be found in a number of tables (e.g., Intnl Tables for X-ray Crystallography)

  4. Thickness? I/Io = exp(-x) = exp(-x)  (= */ = mass attenuation coefficient * = linear attenuation coefficient  = density of specimen  = wt. fract. A A + wt. fract. B B + wt. fract. C C + ........ Also, scattering intensity built up by t2, so I ~ Io exp(-x) t2 dI = const. Io (exp(-x)) (2 - x) = 0 optimum x = 2/; more correct derivation gives 1/

  5. Thickness? I/Io = exp(-x) = exp(-x)  (= */ = mass attenuation coefficient * = linear attenuation coefficient  = density of specimen  = wt. fract. A A + wt. fract. B B + wt. fract. C C + ........ optimum x = 1/ Examples (for CuK: Pure Ni - optimum x = 1/(49.3cm2/gm x 8.90gm/cm3) = 0.023mm

  6. Thickness? I/Io = exp(-x) = exp(-x)  (= */ = mass attenuation coefficient * = linear attenuation coefficient  = density of specimen  = wt. fract. A A + wt. fract. B B + wt. fract. C C + ........ optimum x = 1/ Examples (for CuK: Pure Ni - optimum x = 1/(49.3cm2/gm x 8.90gm/cm3) = 0.023mm Pure Al - optimum x = 1/(48.7cm2/gm x 2.70gm/cm3) = 0.076mm

  7. Thickness? I/Io = exp(-x) = exp(-x)  (= */ = mass attenuation coefficient * = linear attenuation coefficient  = density of specimen  = wt. fract. A A + wt. fract. B B + wt. fract. C C + ........ optimum x = 1/ Examples (for CuK: Pure Ni - optimum x = 1/(49.3cm2/gm x 8.90gm/cm3) = 0.023mm Pure Al - optimum x = 1/(48.7cm2/gm x 2.70gm/cm3) = 0.076mm NiAl - optimum x = 1/(((58.69/85.672) x 49.3cm2/gm + 0.315 x 48.7cm2/gm) x 5.86gm/cm3) = 0.035mm

  8. Thickness? I/Io = exp(-x) = exp(-x)  (= */ = mass attenuation coefficient * = linear attenuation coefficient  = density of specimen  = wt. fract. A A + wt. fract. B B + wt. fract. C C + ........ optimum x = 1/ Examples (for CuK: Polyethylene - optimum x = 1/(((12.011/14.077) x 5.50cm2/gm + 0.147 x 0.44cm2/gm) x 1.0gm/cm3) = 2.1mm

  9. Thickness? I/Io = exp(-x) = exp(-x)  (= */ = mass attenuation coefficient * = linear attenuation coefficient  = density of specimen  = wt. fract. A A + wt. fract. B B + wt. fract. C C + ........ optimum x = 1/ Examples (for CuK: Quartz - optimum x = 1/(((28.086/60.086) x 60.3cm2/gm + 0.533 x 12.7cm2/gm) x 2.65gm/cm3) = 0.11mm

  10. Thickness? I/Io = exp(-x) = exp(-x)  (= */ = mass attenuation coefficient * = linear attenuation coefficient  = density of specimen  = wt. fract. A A + wt. fract. B B + wt. fract. C C + ........ optimum x = 1/ Examples (for CuK: Quartz - optimum x = 1/(((28.086/60.086) x 60.3cm2/gm + 0.533 x 12.7cm2/gm) x 2.65gm/cm3) = 0.11mm Water - optimum x = 1/(((16/18.016) x 12.7cm2/gm + 0.112 x 0.44cm2/gm) x 1gm/cm3) = 0.88mm

  11. Thickness? Metals & alloys optimum x = 10-500.01-0.05 mm generally cut, ground, & polished very carefully - avoid poor surface finish polycrystalline matls - grain size should be small

  12. Thickness? Metals & alloys optimum x = 10-500.01-0.05 mm generally cut, ground, & polished very carefully - avoid poor surface finish polycrystalline matls - grain size should be small Polymers optimum x = 1-2 slice, microtome Water solutions ~ 1mm thick

  13. Thickness? Metals & alloys optimum x = 10-500.01-0.05 mm generally cut, ground, & polished very carefully - avoid poor surface finish polycrystalline matls - grain size should be small Polymers optimum x = 1-2 slice, microtome Water solutions ~ 1mm thick Note: for sans, specimen prepn much easier…much larger specimens

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