The document discusses various sample preparation and presentation techniques for X-ray diffraction (XRD) analysis. An ideal powder sample consists of many randomly oriented crystallites between 40-1 micrometers in size. Proper grinding and sieving can achieve the desired particle size. Back loading and using a zero-background holder are common techniques to present samples as flat plates for analysis. Special cases may require protecting samples in reaction chambers or capillaries to avoid contamination or preferred orientation.

1. Sample preparation and
Presentation
XRD Webinar June 19 2012

2. Contents
The goal of sample preparation
Different analytical questions may
require different sample preparation
techniques
Sample related issues in X-ray
diffraction
An overview of various sample
preparation and presentation
techniques
Some Special cases

3. An ideal ‘powder’
Consists of very many, randomly
oriented crystallites
Depending on the analytical needs the
optimal crystallite size may vary from
40µm down to <1µm
Crystallites too big
Unreliable intensities
Crystallite size of 40µm only 12 crystals
contributing to the intensity profile at any
time
To obtain a 1% you need about 53000
contributing crystals

4. An ideal powder
Particles too small, or wrongly ground
Peaks get broader at the cost of the
maximum intensity
Crystallites not randomly oriented
(preferred orientation, or texture)
Deviating relative intensities
One very dominant orientation
Sometimes just one reflection is visible
(Mica and Muscovite, for example)

5. Need a fine powder? Grind!

6. Coarse powder

7. Effect of spinning

8. Effect of spinning

9. Grinding devices

10. Swing Mill

11. Planetary Ball Mill

12. Effect of grinding

13. Issues to pay attention to
Take care that you grinding doesn’t
affect the crystal structure, or
induces strain into the crystallites
(pharmaceuticals, but also cryolite;
the solvent of alumina for the
elctrolysis must be dealt with
carefully)
The material of the grinding vessel
is of paramount importance
(Cross) Contamination

14. Sieving
80
Effective Particle Size (µm)
70
60
50
40
30
20
10
0
0 200 400 600 800 1000 1200
Mesh

15. Preparing a flat specimen
Cavity front loading
Cavity Back loading
Spray (atomizing) (on a zero
background holder)
Suspending (on a zero background
holder)
Side drifting

16. The specimen holder
Reference surface must
be flat within 13µm

17. Cavity Front Loading

18. Cavity Back loading

19. Cavity Back Loading

20. Effect of Back Loading
Equant
Elongate
Tabular
Bladed

21. Effect of Back loading
For Equant particle shape the effect
of Back Loading versus Front
Loading is small and BL is usually
not needed
For Elongate and Tabular shapes
the effect of BL is not always
sufficient
Most effect of BL is expected for
Bladed particle shape

22. Effect of Back Loading

23. Zero Background holder
Needed when:
Sample is transparent to X-rays
Very small amount of sample is
available and the specimen must be
presented as a flat plate
Sample cannot be packed properly

24. Zero Background Holder
Obliquely cut single crystal
Most commonly either Si, or Quartz
Direction of the cut is chosen to
avoid any reflections occurring in
the reflection sphere (i.e. no
reflecting lattice planes parallel to
the crystal surface)

25. Zero Background Holder

26. Dusting on a 0-BG holder

27. Compare with Back Loading

28. Compare with Back Loading

29. Alternative Presentations
Protect the specimen during the
measurement
Specimen presentation for
transmission measurements
Capillaries

30. Protecting your specimen
Mount your specimen in a reaction
chamber (the Anton Paar XRK900,
for example) and flush with an inert
gas
Cover your specimen with a
transparent foil, which does not
give a diffraction pattern
Mount the specimen inside a glass
capillary tube (Mark tube)

31. Transmission
Het monster wordt in een holle ring
tussen twee folieën geklemd
De folieën worden m.b.v. drie in
elkaar passende ringen (vaak teflon)
gespannen
Of het monster wordt in een capillair
gemonteerd

32. Capillair
Gebruikt erg weinig monster
Voorkomt meestal
voorkeursoriëntatie
Beschermt tegen invloeden
van buitenaf
Is lastig te vullen