Dear Jim, there was a discussion about the silicon standard a parameter some time ago, and the surprisingly high discrepancy between the results for single crystal and powder
543.11946(92) pm, NIST SRm640c (Si 4.9 µm) 543.101988(48) pm, Siegert & Becker 1984 (Si single crystal) d=0.017472 = 18*sum(esd) were adscribed, if I remember well, to the increased strain in the bulk and at the surface of small particles. So it looks like grain size modifies both peak width and peak position, and some material at the surface shouldn't contribute at all to Bragg diffraction. Do you have an idea to what extent the grain size is correlated to crystallinity, which in this thread is defined as mass ratio of crystalline to (crystalline+amorphous) material? regards Miguel On 28 Feb 2008 at 7:49, Jim Cline wrote: > Hi all, > > Please prepare for a shameless plug for the newly certified NIST SRM 676a: > > In order to measure amorphous content (via non-PDF diffraction methods) one > needs two things: > 1) An unbiased diffraction method for measurement of phase abundance > (laughter please) and 2) > A standard of known phase purity. A quantitative Rietveld analysis of data > from a divergent beam > powder diffractometer yields results that are consistently biased by a few > percent. The nature of > the bias appears dependent on the phases being measured and I don't really > know of the origin. > But by process of elimination, I think it is due to an over simplistic model > for the > Lorentz/polarization factor. Therefore, you are better off using > nonconventional sources, or > accepting that your results may be inaccurate to a few percent. For 10+ years > I/we have been > pursuing an experimental design to measure absolute phase purity. It has > taken several iterations > to obtain results I/we cared to talk about. SRM 676 was recertified ~2 years > ago for phase purity, > however, stocks of it were exhausted (the recertification is retroactive). > SRM 676a was released > for sale a week or two ago and offers improvements in both the phase purity > (99%) and the error > bounds on the certified value. > > See: https://srmors.nist.gov/view_detail.cfm?srm=676A > > I haven't written the work up yet (I'm working on it); but the experimental > design is described in the > certificate. > > Regards, > > Jim > > At 06:58 AM 2/27/2008, you wrote: > 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! > James P. Cline > Ceramics Division > National Institute of Standards and Technology > 100 Bureau Dr. stop 8520 [ B113 / Bldg 217 ] > Gaithersburg, MD 20899-8523 USA > [EMAIL PROTECTED] > (301) 975 5793 > FAX (301) 975 5334 -- Miguel Gregorkiewitz Dip Scienze della Terra, Università via Laterina 8, I-53100 Siena, Europe fon +39'0577'233810 fax 233938 email [EMAIL PROTECTED]
