Concerning the questions from L. Cranswick, I had an experience about the
comparison between the granulometry determined by laser and by SEM. My
powders were intermetallic compounds in the range 10-60microns and the
comparison worked quite well. But I have to say that the accuracy
(especially of the SEM method which is only estimation by visual method as
you say) is not so good. Secondly, you must keep in mind that you measure
different things by the two methods : for the laser method you measure the
radius of particles assumed as a sphere, for the laser you measure probably
the length of the particle, so depending on the particle shape you can
obtain different results.
Furthermore, for the micro-absorption correction the value that you need is
the crystal size ans as your particle could contain more than one crystal
you don't need perhaps more than an order of magnitude.
Finally,concerning the question about the micro-absorption correction for
quantitative analysis, I had an experience during my PhD thesis that I want
to report. I studied ternary intermetallic compounds with Zr, Ni and Cr. The
particles were quite large (20-40microns) and heavy absorbing especially
with copper radiation. Moreover the differents phases to quantify had very
different absorption coefficients depending on the chromium contents.
According to Brindley and some other authors, it had no sense to perform a
quantitative analysis on those samples. However the quantitative Rietveld
refinement without any correction worked quite well for test samples and for
real samples for which other quantitative methods were used and gave similar
results (standard deviations about 2%).
Any idea for this phenomena ?
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Jean-Marc Joubert E-mail : Jean-Marc.Joubert@cryst.unige.ch
Laboratoire de Cristallographie Phone : (41) (22) 702 64 50
24 quai Ernest-Ansermet Fax : (41) (22) 781 21 92
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