Thank you so much for the overwhelming response. I really
appreciated all the information, contacts and suggestions. There were
also requests for the references I mentioned. Here they are:
MANSOUTRE, S. and LEQUEUX, N (1996) Quantitative phase analysis of
Portland cements from reactive powder concretes by X-ray powder
diffraction, Advances in Cement Research, 8(32) 175-182
That was the one I excavated in my office. Then the Krupp work:
MOeLLER, H. (1995) Standardless quantitative phase analysis of
Portland cement clinkers, World Cement, September, 75-84.
What I find disturbing often reading papers on QXRD using
Rietveld particularly pertaining to cement materials, is that
people don't always specify which program they used or at least refer
to a paper referencing their own code. In most crystallographic
journals it is a requirement to state what software or code has been
used. I personally think it is pertinent information.
The other thing I find disturbing is that quantitative phase
analysis acquired by Rietveld methods on cement/clinker are compared
to Bogue results. This doesn't mean anything. Okay, if you somehow
consider impurity incorporations within each phase by virtue of what
one can infer from the fine structure of the peaks for the various
phases in the diffraction pattern, and know the thermodynamic
information of the kiln at hand, this calculation would be more valid
for comparative purposes. People insist on using Bogue, which is
simply a resynthesis of the chemical information. Why not use the
chemical information proper? Calculate what the chemical composition
should be from the Rietveld refined quantitative phase composition and
compare it to the real chemical composition and compare. Okay, this
doesn't prove that your quantitative phase composition is correct,
but at least this is more valid than comparing to Bogue. Bogue is
fine as an approximate online industry technique, but not to prove
the validity of a Rietveld calculation. It should rather be the other
way round, we should proof the Bogue method wrong with Rietveld
results.
And also a 'goodness-of-fit' doesn't prove accuracy of quantitative
results. You may be overestimating one phase at the expense of
another--something that I have discovered is exactly what is indeed
happening.
The only direct verification is that of point counting, which
indeed does not come without its limitations, but the Rietveld method
applied on cements also has limitations. But fortunately these two
methods compensate very well for the limitations of the other.
Any further ideas on this discussion would be very interesting.
Best wishes,
Quirina
"You cannot prove anything right in science. You can only prove
something wrong."
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Quirina I. Roode
PhD student: Cement Chemistry
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Department of Civil Engineering
University of the Witwatersrand
P O Wits, 2050, Johannesburg
SOUTH AFRICA
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ROODE@civen.civil.wits.ac.za ( )
Tel: +27-(0)11-716-2478 (w) ) /
Fax: +27-(0)11-339-1762 (w) (_/
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