I use X-ray diffraction (XRD) techniques to quantify the degree of crystallinity in my samples, referring to the following formula (CrI=Acrystal-Aamph/Atotal ). using deconvolution area methods ( Gaussian fitting ), according to literature the amorphous peak is between 2θ=18°-19°. I couldn't find the area of this peak.
my question is what are the crystalline and amorphous regions? if there are calculation details?
Hello Sabrina Ahmima
In a XRD pattern, there is no specific "region" for amorphous. Crystal is an solid with ordered atomic structure, and amorphous is a solid with non-ordered atomic structure. The structure of a crystal is represented by that specific peaks you see in the XRD pattern, and amorphous are represented by "bumps". You can have both represented in the XRD pattern, peaks or bumps, and they can overlap, so our job is to determine what peaks are the ones we are interested.
Eg: You have cellulose XRD pattern, with peaks of cellulose, but then you have other peaks, that are not from cellulose. These peaks are from another crystalline structure, of course, but they will not contribute to the "crystallinity" percentage of the cellulose, because they are not from the cellulose structure.
In order to calculate the crystallinity of your sample, you can follow the method described in this video produced by Dr. Shahid Ali:
https://www.youtube.com/watch?v=D65k1yHPKaM&t=905s
Feel free to reply if you have any questions about this topic.
Best regards,
Ricardo Tadeu
I think this paper will help you to find out the CI index. Article Comparison and assessment of methods for cellulose crystalli...
Dear Sabrina Ahmima ,
in addition to the remarks of Ricardo Tadeu Maia , I would like to add, that I could not either identify any amorphous area, as you already stated above by 'I couldn't find the area of this peak'.
There is a dip around 18 to 19° in your XRD patter going down touching the baseline. Thus there could not be any amorphous hump (or residuals) in that region.
The crystallinity of your sample is very close to 100.
Best regards
G.M.
Dear Ricardo Tadeu Maia
I appreciate your detailed response to my question. thank you so much for your recommendation.
Cellulose is a linear macromolecule, consisted of long and short chain structures. The macromolecular chains of cellulose start degradation and decomposition before melting takes place. It is amorphous materials. Two diffraction peakscorrespond to short and long chain structures respectively.
Lots of misunderstanding on crystalline and amorphous content of the materials contain macromollecules, e.g. polymers. Polymers all contain long chain structures with some residual fragments. The diffraction peaks belong to the long chain structures, but NOT to the crystalline structures.
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