XRD limitation in detection of a second phase with low amount

  • Thread starter mah65
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  • #1
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I have performed heat treatment (aging) on my alloy. In this process fine precipitates form in the matrix of the alloy, which strengthen the alloy.

However, XRD spectrum could not show the peaks related to the fine precipitates.

1- Why the peaks are not detectable? Is it because of the very small size of the precipitates? Or, is it because of their low content? What is the X-Ray method limitation in detecting a phase?

(I would appreciate it if you also introduce a reference, because I need to mention it in my paper)

2- What solutions and especially what other X-ray methods can help in detecting the precipitates? Can "small step scan XRD" be helpful in this respect?

Thank you :)
 

Answers and Replies

  • #2
chemisttree
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If the second phase is poorly crystallized or amorphous, you won't get much signal. What do you know, exactly, about the second phase.
 
  • #3
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The second phase in totally crystalline. We know the approximate position of the peaks (= the related 2teta) in XRD spectrum. We detected no such peaks in those positions, however. What can we do?
 
  • #4
uby
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Signal to noise ratio will determine whether you see a peak (assuming the material is present). Signal will be proportional to the volume fraction of the phase present. If the domains are small (< ~300 nm), the signal will be diminished and broadened over a larger 2-theta range. The differential xray absorption behavior of the alloy and precipitate will also play a role in the relative signal.

XRD generally does not have robust lower detection limits. TEM would allow for direct characterization of the precipitates.
 
  • #5
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You can try performing slower measurements and if that does not help either, you can also try using synchrotron radiation.
 
  • #6
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XRD does not detect the presence of very small quantity of phase even though it is present in the materials.

Sometimes the peak is there, but get clouded with background radiation. This maybe due to the intensity of the peak is too low. In certain XRD software (X`pert Highscore Plus), you can remove/reduce the background radiation.

Alternatively, you can use SEM to identify the precipitate, but I never done that before.

My research involves the addition of MgO into Al2O3, the presence of Al2O3 only detected when the amount of MgO reach 0.9 wt %. The result is here - http://www.sciencedirect.com/science/article/pii/S0925838810005347.

Hope it helps.
 

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