Hi all,
Well, I thought I'd weigh in on this with a discussion of an aforementioned SRM project:
We are in the final stages of preparing an SRM for determination of crystallite size from line profile analysis. Through the course of his PhD work and NIST postdoctoral position, Nick Armstrong has developed a MaxEnt / Bayesian method specifically for the certification. The method can quantify, from the quality of the raw data, the probably that a proposed model for the crystallite size distribution is the true one. Thus, the certified values of the standard will include a valid measure of their uncertainty that, in our humble opinion, would not be obtainable with alternative methods. Details, and results of the method as applied to the RR CeO2, have been published. We are working at the production of ~kg quantities of "strain free" CeO2 and ZnO for use as the SRM feedstock; no small challenge.
We expect two outcomes: 1) The community will have a standard by which results from "mortal" methods may be readily tested and compared. 2) A high-intensity squabble will ensue as to whether or not we got the right answer.
With regards to the latter issue: Nick and I have been approached about another round robin. Forgive me, but: round robins don't have anything to do with accuracy. They test for uniformity of measurements in the field, the major premise being that, as a result of mature methodology, a narrow distribution is expected. Note the highly successful, Rietveld, QPA, and "instrument sensitivity" round robins. There is, however, no "mature" methodology here. Indeed, only a small number of operations worldwide can perform a credible microstructure analysis, and their methods certainly differ. It is our intention to make the data collected for the certification available to the community. But with regards to model testing for the more advanced, physical model, methods (with the use of simulated, bi-model data for instance), I would suggest that more of a collaborative effort be organized.
Regards,
Jim
James P. Cline [EMAIL PROTECTED]
Ceramics Division Voice (301) 975 5793
National Institute of Standards and Technology FAX (301) 975 5334
100 Bureau Dr. stop 8520
Gaithersburg, MD 20899-8523 USA
