Re: QXRD--cement

Jürgen Neubauer ( (no email) )
Fri, 28 Aug 1998 12:36:53 +0200

Hi all,
some notes to the statement on Rietveld Q-XRD of OPC:

Bogue calculation is the standard online industry technique. Therefor the
comparison of Bogue results and microscopic point counting is very valuable
in explaining the advantages of Rietveld Q-XRD to cement producers. In
constant kiln and cooler operating conditions changing in the chemical
composition of the raw meal (e.g. changing LSF) should influence the phase
distribution in the clinker. This means in constant operation conditions
there should be a correlation between Bogue values and Rietveld data (so
Bogue works fine for cement production purposes what is important for the
producers who used this methods for decades!!). The correlation breaks down
when the chemical composition of the clinker phases is changing due to
changing operating conditions (kiln starting periods, changing fuels,
cooling conditions .....). In this case there is only a correlation of the
phase content determined by microscopic point counting and Rietveld
refinement.
Beside microscopic point counting there is another method to prove the
accuracy of Rietveld quantitative phase analysis:
1. Extracting clinker main phases from technical clinkers
2. Synthesis of clinker like phases
3. Mixing of pure phases to artificial clinkers
4. Quantification by Rietveld refinement
5. Comparison of Rietveld data and actual phase content
6. Determination of the accuracy and reproducibility of the method

Best wishes

juergen

____________________________
Dr. Juergen Neubauer
Universitaet Erlangen
Lehrstuhl f|r Mineralogie
Schlossgarten 5a
91054 Erlangen
Germany

Tel. ..49 9131 853986
Fax ..49 9131 853734
email: jneubau@geol.uni-erlangen.de

----------
Von: Quirina Roode <ROODE@civen.civil.wits.ac.za>
An: rietveld_l@ill.fr
Betreff: QXRD--cement
Datum: Freitag, 28. August 1998 13:33

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
*-----------------------------*
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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