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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