Polymers are not a good example for the spiking method as it is difficult to find a standard with a good absorption match (although diamond and LiF are possibilities), people don't usually hand them to you as nice micron-sized powders (poor particle stats on a lab system), and a few other issues.
The business about getting a standard with a known crystallinity is an issue, but not as unsurmountable as it seems. Firstly SRM676 and SRM676a have certified crystallinity values with errors of +-1%. Given the likely errors in subsequent lab determinations is quite large this isn't as much of a problem as it first seems. If you need a standard with higher absorption than corundum there is SRM674a which has a range of materials. SRM674a has values listed as 'phase purity' as opposed to crystallinity, but as the values were determined from diffraction measurements they may be pretty much equivalent to the crystallinity (Bob might know more as I believe he was involved in the work). As far as paracrystalline materials I wouldn't bother with this technique as the concept of crystallinity becomes a bit arbitrary and almost meaningless in extreme cases. For a lot of these materials (layered ones especially) looking at microstructure in terms of density of stacking faults should get you a lot further in understanding what's going on. Pam From: May, Frank [mailto:[EMAIL PROTECTED] Sent: February 27, 2008 11:31 PM To: rietveld_l@ill.fr Cc: Barton, Lawrence; Spilling, Christopher; Fraundorf, Philip; Wilking, Janet B.; Liu, Jingyue; Corey, Joyce Y.; Rath, Nigam Subject: RE: % Crystallinity As Pamela Whitfield indicates below, this is not a straightforward issue. Reading the reference in Dr. DM's posting, one see that it is necessary to have "100% crystalline" or "100% amorphous" or "50% crystalline/50% amorphous" standards. The rub is that it is necessary to have a means to determine if something is precisely "100" or "50" or another amount. In order to do that, one must have a standard....which is circular logic....and which illustrates at least part of the problem. Further, the concept of "para-crystallinity" also includes materials which are not well-behaved and 3-dimensionally ordered substances. This is well-recognized in "high polymer" systems, but it also occurs in organic and inorganic materials. How does one assess the "crystallinity" of a material which is not 3-dimensionally ordered when a "reference" for that material has 3-dimensional ordering? 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Wed 2/27/2008 9:58 PM To: rietveld_l@ill.fr Subject: Fw: % Crystallinity (See attached file: XRD Percent Crystallinity Determination in Polymers.pdf) PERCENT CRYSTALLINITY DETERMINATION BY XRD THE MOST ACCURATE ONE AS IT CONSIDERS AMORPHOUS PART DURING CALCULATION , IN OTHER METHODS IT IS IGNORED , HAPPY TO GET VALUE ADDED COMMENT FROM ALL RESERACHER WHO ARE EXPERT ON THIS FIELD. Regards, Dr. DM ----- Forwarded by Debabrata Mukhopadhyay/hpl/IN on 02/28/2008 09:08 AM ----- This is a can of worms that keeps cropping up now and again. Rather than go into masses of detail I'd suggest looking at the Rietveld mailing list archive for some fairly detailed discussions on the subject. I'd go with Bob's route as it's applicable in a laboratory environment but foolproof it isn't and good sample preparation is vital. Pam ________________________________ From: Von Dreele, Robert B. [mailto:[EMAIL PROTECTED] Sent: Wed 27/02/2008 11:52 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 ________________________________ Free upgrade for your Windows Live Messenger! Click here! < http://get.live.com/> (See attached file: winmail.dat)
