Regarding Crystallinity -
 
As a technicality, the concept of "% crystallinity" is not only an x-ray 
analysis issue.  One can measure "% crystallinity" by other methods - and the 
findings (numbers) from the different techniques are not necessarily the same.  
I'm not sure if there is a technique which claims to give an absolutely correct 
number for "% crystallinity."
 
For an "absolute" figure, one needs a reference which is either "100 percent" 
crystalline (or 100% non-crystalline).  How does one prove that is the case?  
One must have an analytical standard......
 
When I have a researcher who wants an assessment of crystallinity by XRD, I 
provide a "crystallinity index" instead of a "percent".  It provides a relative 
estimate of crystallinity.
 
If one assumes a 100% crystalline reference, one might find the situation 
within a system of samples (in an environment where numerous samples are 
generated) that a sample calculates to be 110% crystalline.  Such a number is 
physically impossible.  However, using a reference which is assigned a 
crystallinity index equal to 1.00, it is perfectly reasonable to find a 
crystallinity index of 1.10 for a sample and report that figure relative to the 
chosen standard.  The higher figure merely illustrates the fact the original 
standard wasn't an end member along the amorphous-to-crystalline line.
 
There are many reasons for subsequent encounters of a crystallinity index 
greater than 1.00.  That might be the subject of another posting if you want it.
 
Obviously, there is no "foolproof" way to determine "percent crystallinity."
 
Frank May
Research Investigator
Department of Chemistry & Biochemistry
University of Missouri - St. Louis
One University Boulevard
St. Louis, Missouri  63121-4499
 
314-516-5098
[EMAIL PROTECTED]
 

________________________________

From: Von Dreele, Robert B. [mailto:[EMAIL PROTECTED]
Sent: Wed 2/27/2008 10:52 AM
To: rietveld_l@ill.fr
Subject: RE: % Crystallinity



John (& others),
The best way to determine %crystallinity (or %amorphous) is to do "spiking" 
experiments with material with known (preferably ~100%) crystallinity. The 
change in the apparent phase fractions by Bragg intensities as compared to that 
expected from the masses can be used to estimate the fraction that doesn't 
Bragg scatter (i.e. the amorphous content). The spiking material should also be 
chosen to have nearly matching absorption to avoid systematic effects (e.g. 
Brindley corrections). It does not have to be the same phase as the crystalline 
phase in your sample. There are literature references to this but I can't 
recall the exact ones to look at. Perhaps others might know them better. (BTW - 
this is not a PDF problem).
Bob Von Dreele

________________________________

From: john o callaghan [mailto:[EMAIL PROTECTED]
Sent: Wed 2/27/2008 5:58 AM
To: rietveld_l@ill.fr
Subject: % Crystallinity


Dear Users,
I'm trying to determine the percentage crystallinity in a crystalline/amorphous 
mixture, could someone point me in a foolproof direction.

Thanks,
John


________________________________




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