I would suggest that you use an internal standard to get a handle on your sources of uncertainty.
I would suggest Baikalox corundum CR1 - while I don't know its non-diffracting content, it is probably low.
I would suggest that you use the technique outlined in Pratapa et. al. Powder Diffraction 13(3) 166-170, and measure the diffractometer constant, then look at the relationship between s (scale factor) and phase concentration.
If you want more details, contact me directly.
regards,
Tony Raftery
At 02:59 AM 18/03/2007, you wrote:
My purpose is really quantification. And I´m getting erros of about 5% in each phase (in the quantification part).
I´m using samples that I made by mixing calcite, dolomite and kaolinite (18, 55 and 26 or near it). It is valid to mix the sample with a known standard if you are analysing a unknown sample (quantitatively). But I´d like to know more about this method to determine the amount of amorphous content using a standard.
I´m using now a beq. of 20 in all atoms, and they are fix. Could you discriminate each variable of the equation that you send to me?!
prm b 0 scale_pks = Exp(-b />D_spacing^2)
Does it give reasonable values!?
Regards,
Leandro
From: "AlanCoelho" <[EMAIL PROTECTED]>
Reply-To: rietveld_l@ill.fr
To: <rietveld_l@ill.fr>
Subject: RE: Problems using TOPAS R (Rietveld refinement)
Date: Fri, 16 Mar 2007 09:56:33 +1100
Leandro
Not sure what the purpose of your refinement is but if it's quantification
then your results would probably be in error to a large extent.
The references given by Alan Hewat and Lubo Smrcok is probably a good
starting point.
Data quality and model errors typically mean that atomic positions should
not be refined for clays; especially for Kaolinite. Also, use a common beq
value for all sites or take them from literature. A gobal beq could then be
superimposed using something like prm b 0 scale_pks = Exp(-b /
D_spacing^2);.
For quantification try spiking the sample with a standard to determine the
amorphous content.
It is possible to get the peak shapes without changing peak intensities; if
you need assistance then contact me off the list.
Cheers
Alan
-----Original Message-----
From: Leandro Bravo [ mailto:[EMAIL PROTECTED]]
Sent: Friday, 16 March 2007 9:15 AM
To: rietveld_l@ill.fr
Subject: Re: Problems using TOPAS R (Rietveld refinement)
Ok, I´m starting to have sucess in the kaolinite refinement, the
quantification is giving me reasonable values. I´m refining the thermal
factors, all the atoms positions in the kaolinite, the lattice parameters
and the cystallite size. Lattice parameters and crystallite size are giving
me very good numbers, with very low errors (about 0,09). In the thermal
factors, I realized that alll of them tend to 20, so after all refinements I
put them to 20, and refine all over again. I don´t care that much for atoms
positions, I´m only using them because refining only lattice, thermal and
cry size wasn´t enough to make a good calculated pattern to compare with the
measured one.
In the calcite and dolomite I refine: lattice parameters, cry size and
thermal factors. And use on both a preferred orientation correction
(spherical harmonics 4 th order). The RWP is about 16.
I´d to hear some opinions about this strategy of refinement, if you think
that I can spare some refining cycles or even fix some values to reduce
erros in the refinement.
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