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Schematic diagram showing the principles behind the DCT technique. Please click here for a fuller technical description.

Sample constraints:

For successful DCT data acquisition a number or sample conditions must be respected:

  • The grains within the sample should be in an unstrained state with low mosacity (plastic deformation) to reduce overlap and distortion of the diffraction spots. This should be checked with EBSD before submission of an experimental proposal.
  • The sample dimensions must fulfil the constraints shown in the table below (from Reischig et al. 2013).
  • A sufficient proportion of the beam must be transmitted through the sample to the detector, so consideration must be given to the z number vs sample dimensions.

 

Parameter

Practical limits

Typical range

Effective pixel size (microns)

0.3-50

1-10

Grain size (microns)

10-5000

20-200

Sample diameter (mm)

0.05-10

20-200

Rotation axis-detector distance (mm)

0.5-100

3-10

No. of pixels in sensor

1024x1024 to 4096x4096

2048x2048

Rotational increment (o)

0.01-1

0.05-0.5

Width of 2theta range (o)

5-45

10-30

Accessible 2theta range (o)

0-180

10-30

Accessible energy range (keV)

6-100

15-50

 

Data reduction

The DCT "grain tracking" code is written in Matlab with some parts optimized for fast calculation implemented in "c". It is a complete package, capable of generating DCT maps from raw diffraction data but does require the user to have a basic knowledge of Matlab to run it. The complexity of the data reduction (and therefore of the degree of user 'involvement')  is very much dependant of the condition of the sample, and it adhering to the specifications layed out above. A link to the DCT analysis code can be found here).

 

Image of High-resolution DCT grain map of a UO2 sample containing 119 grains (from Reischig et al. 2013). Please click here for a fuller experimental description.

 

Click here for a list of relavent publications to DCT at ID11

 

Ludwig,W., Schmidt, S., Lauridsen, E.M. and Poulsen,H.F. (2008). X-ray diffraction contrast tomography: A novel technique for three-dimensional grainmap ping of polycrystals. 1. Direct beam case, J. Appl. Crystallogr., 41, 302–309.

P. Reischig, A. King, L. Nervo, N. Vigano, Y. Guilhem, W. J. Palenstijn, K. J. Batenburg, M. Preuss & W. Ludwig. Advances in X-ray diffraction contrast tomography: flexibility in the setup geometry and application to multiphase materials. Journal of Applied Crystallography 46, 297--311 (2013).