I have scanned neat PA6 (Nylon 6) sheet samples using D2 Phaser, and the obtained XRD pattern is attached. I would appreciate it if someone could help with the procedure for curve fitting (deconvolution) of the crystalline structure and the amorphous halo?
I am not certain what is the correct way of defining background and amorphous halo for such patterns. I suppose the position of the amorphous halo and its intensity could significantly affect the crystallinity measurement. But how is best to define and characterize it?
I tried the automated "search peak" option and then "Default profile fitting", but not sure if this is the correct approach. In the end, I need to measure the area below each crystalline/amorphous peak to calculate the degree of crystallinity.
Thanks in advance for any help or suggestion you could provide.
Statistical analysis of XRD pick analysis by origin pro can solve the problem of degree of crystallinity measurement. By assuming zero width for perfect single crystal and infinite for amorphous (highest entropy) material for a plane.
Thank you Kankan Mandal for your reply.
Indeed there are options in Origin for such calculations. But first, we don't have a license for that. Plus, I suppose there should be a similar approach for the deconvolution of crystalline peaks/amorphous halo in Xpert HighScore for semi-crystalline polymers. Hence, I would greatly appreciate it if someone can share similar experiences.
Hello Sepehr Simaafrookhteh what exactly do you want to achieve?
Because if you want to know the crystallinity of your sample then you need something to compare to. Now you don't know how much of your "background" is due to instrumental contribution (air scatter etc) and how much is caused by the amorphous compound.
Dear Thomas Degen Thanks for your reply. I want to measure the percentage (area below) of each individual peak as well as the amorphous halo. Using this information, I can also calculate the crystallinity.
You are correct that I don't know the background at the moment. But how can I measure it accurately so I can distinguish between the instrumental contribution and the amorphous region?
Hi Sepehr Simaafrookhteh
when you know what your Instrumental background contribution is AND when the amorphous phase(s) has the same scattering power as the crystalline phase(s), then it gets easy.
You don't need to fit peaks, you just have to find/set a background line that separates the crystalline portion from the (amorphous material caused) background. Then you compare the counts above the background line to the counts below the background line MINUS the known Instrumental background. Like this:
Crystallinity[%] = 100 * SumNetIntensity / (IntensityTotal - InstrumetBackground)
It's approximately like this, and there is a practical in the HighScore Help:
Assuming an Instrumental background contribution of 1700 Counts and the background line as shown, you get 50% crystallinity. Since I did a lot of assumptions here this is for sure off. But if you do multiple experiments this method will allow you to see any changes in crystallinity, when you use the same measurement conditions and the same background parameters etc.
Thank you so much Thomas Degen
I have used the same procedure recommended in HighScore help before. But there are several unknowns here. Where to put the "constant background" line? You selected 1700 counts, but I can go as high as 2700 counts in the same scan (minimum value of the recorded pattern).
The selection of the amorphous halo (background) is also a manual process and prone to lots of errors. Maybe it is simpler for metals, ceramics, and other materials with sharp peaks and low percentages of amorphous regions. But here, in the semicrystalline polymer (PA6) it is unclear "where" and "at what intensity" we should position the peak of the amorphous halo.
Please see figs. 1 and 2 above. If we go a bit higher in intensity with the background green curve, that would significantly increase the amorphous content and lowers the crystallinity.
That's why I think we need a peak fitting/deconvolution procedure. Please see the result attached from the work of Uematsu et al. 2022 (Article Fracture Properties of Quasi-Isotropic Carbon-Fiber-Reinforc...
) for CF-reinforced PA6.Thank you again for your time and help.
Hello Sepehr Simaafrookhteh , just Peak fitting doesn't give you any new/additional information (There is no magical bullet for this). You either need to measure a Standard sample with a known crystallinity, then from that, you can deduce the instrument contribution. Or you need to work with an Internal or External (100 crystalline) standard and use a Rietveld / PONKCS like approach. Without that, your crystallinity numbers are just relative and not absolute. For many applications, relative numbers are good enough. That's what I said before. If you do multiple experiments you still can see if the Crystallinity increases or decreases.
Hello dear Sepehr Simaafrookhteh
If you want, send me one of your xrd patterns, and I will analyze it for free.
My email is [email protected]
Regards
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