Sample preparation

Source:  Sample preparation    Tag:  x ray diffraction sample preparation


Important! We will not accept any samples that are in form of solution, sol gel type or liquid types!
Any special sample such as small amount sample, thin film, not crystallited sample or any sample that cannot match our sample holder, applicant are required to meet authorized person/group members to discuss in detailed due to the limitation of our XRD specification.

The sample preparation are very important to get a precise and high quality XRD result, here we shared several suggestions:

Preparing a powder specimen 

Characteristic of  an ideal powder sample
We suggest that the sufficient quantity in gram(g) for powder sample should not be less than 1.5 gram

An ideal powder sample should have many crystallites in random orientations and the grain size should be  
  less than 10 microns to get a good powder statistics
 - Large crystallite size and non-random crystallite orientations both lead to peak intensity variation :
    • The measured diffraction pattern will not agree with that expected from an ideal powder
    The measured diffraction pattern will not agree with reference patterns in the Powder Diffraction File 
      (PDF) database


• During preparation for powder sample, a flat and smooth surface are required :
   -If the surface is not smooth and flat, X-ray absorption may reduce the intensity of low angle     
    peaks   


The powder sample should be densely packed and 'infinitely' thick to a get a good powder statistic

 
Figure 4: Sample holder for powder sample with diameter of 25mm.

 Ways to prepare powder sample

• Top loading a bulk powder into a well
   - Deposit powder in a shallow well of the sample holder. Use a slightly rough flat surface to press down on       the powder, packing it into the well.
   - Using a slightly rough surface to pack the powder can help minimize preferred orientation.

Dispersing a thin powder layer on a smooth surface
   - powder may be gently sprinkled onto a piece of double-sided tape or a magic tape to adhere it to the   
     sample holder 
      • It is preferred  to use magic tape which can be bought at the stationary shop/Tesco because the  
        double-sided tape will contribute to the diffraction pattern (additional peak)


Preparing a solid sample

In order to meet the size of our sample holder and get a good XRD pattern result, XRD users are advised to be prepare an ideal solid sample with the dimension such as  :

Sample Height must be less than 8mm


Sample size should be as large as possible with diameter of 25mm

  - Small sample (less than 25mm) may contributed less desired diffraction peak because the X-ray target 
     may not shot exactly on the sample surface; or X-ray may shot on other spot that contribute additional   
     peaks, which is not related to the sample materials 


Figure 5: Sample holder for solid sample.