Leandro,
the refinement/profile fitting of kaolinite-bearing samples is strongly
affected by disorder of natural kaolinites. The atomic coordinates in
ICSD (for example Bish and von Dreele) have been derived from the best
ordered samples known on earth, mainly Keokuk site. "Real-world"
kaolinites from deposits are disordered by several types of stacking
faults, see the textbook
Brindley, G.W. (Ed.) Crystal structures of clay minerals and their X-ray
identification. Mineralogical Society, London, 1980.
see several detailed works done by Alan Plancon,
and a very good general treatment
Drits, V.A. and Tchoubar, C. X-ray diffraction by disordered lamellar
structures. Springer, 1990 ISBN 3-540-51222-5
Thus, Rietveld refinement of such structures needs for a model what can
treat the "anisotropic line broadening" and all the other diffraction
effects caused by the stacking faults. Until now, no general model
suitable for Rietveld refinement of all varieties of disorder in
kaolinite does exist. There are not so much trials published to find a
working solution for practical Rietveld quantification of clays. One
would be a self-citation of a paper, so I can't do this here in the list.
Nevertheless, even with the best models available you will not be able
to refine "true" temperature factors of kaolinite from powder data of
disordered kaolinites. I would recommend to keep the temperature factors
fixed in phase quantification work, and to think about a "reasonable"
model for the description of disorder in your actual kaolinite.
Reinhard
Leandro Bravo schrieb:
Ok... another problem...
I don´t think that the kaolinite CIF that I´m using is working well,
I´m refining the temperature factors and it´s giving me non realistic
numbers. Can somebody send me a trustable kaolinite CIF, with good
temperature factors?!
Other doubt... I´m making my scans from 5 (2-theta) to 120 (2-theta),
and I´m realizing that above 80° I´m getting unecessary data
(basically just backgorund). The question is how this ´´unecessary
data`` affect the quantification?!?!
From: "Leandro Bravo" <[EMAIL PROTECTED]>
Reply-To: rietveld_l@ill.fr
To: rietveld_l@ill.fr
Subject: Re: Problems using TOPAS R (Rietveld refinement)
Date: Mon, 12 Mar 2007 13:35:54 -0300
I think that I just did a good job in my quantification: 50,2%
calcite and 49,8% dolomite. Now I´m moving foward to a sinthetic
mixture of calcite, dolomite and kaolinite.
I have other questin, how can I determine a trustable value to the
Full Axial Model?! Especially the these paramters: sample lenght,
source lenght and RS lenght?!?!
I´m starting to realize that the temperature factors are the key to
the refinement! They change the calculated pattern so much!!!
From: "jilin_zhang_Houston" <[EMAIL PROTECTED]>
Reply-To: rietveld_l@ill.fr
To: "rietveld_l@ill.fr" <rietveld_l@ill.fr>
Subject: Re: Problems using TOPAS R (Rietveld refinement)
Date: Mon, 12 Mar 2007 10:39:41 -0600
Leandro :
here is an example of calcite I used. You can use min and max to
confine the parameters.
One way to know whether it is right is to mix a known fraction of a
compound, e.g. ZnO with a ratio of original sample/ZnO=100/15.
At the end of the refinement, you have N components with N
corrected(with volume and density) scalefactor, S(i),
Weight(i)=S(i)/S(ZnO)*15
the sum of all weight(i) should be close to 100 if the whole thing
is crystalline.
str
phase_name calcite
scale sc_calcite 0.0001813894308
space_group R-3c
r_bragg 5.769971925
Crystallite_Size(cs_calcite, 100 min =100; max =1000;)
Trigonal(a_calcite 4.995096119 min =4.95; max =5.2;,c_calcite
17.08621648 min =16.9; max =17.1;)
site Ca num_posns 6 x 0 y 0 z 0 occ Ca+2 1 beq 0.95
site C num_posns 6 x 0 y 0 z =1/4; : 0.25 occ C 1 beq 0.9
site O1 num_posns 18 x 0.257 y 0 z =1/4; : 0.25 occ O-2 1 beq
0.94
PO_Spherical_Harmonics(sh_calcite, 2 )
Cheers
J
Hi, guys,
I´m having some trouble using the Bruker software TOPAS R, right now
I´m
quantifying a sinthetic sample with 50% of calcite and 50% of dolomite.
Check the following questions an help me if you can.
1) I´m using the CIF files from ICSD, but when I put it in the
software it
gives me a temperature factor (beq.) of 1. Is there anyway I can
check some
good temperature factors?! When i put then to refine, sometimes they
become
negative, but the calculated - observed pattern is just good.
2) I´m using Fundamental Paramaters and for these I must have
acknowledge of
my instrument, well I have, minus sample lenght... and stuff like
that... is
there anyway I can determine these values with accuacy and use them
with
sure?!
3) In TOPAS how do I know if the refinement is good?! Because each
time I
refine the 50%/50% mixture I have different results and I don´t know
wich
one gives me a result that I can trust.
Thank ou in advance,
Leandro Bravo Ferreira da Costa
Student, UFRJ - Universidade Federal do Rio de Janeiro - BR
CETEM - RJ
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begin:vcard
fn:Reinhard Kleeberg
n:Kleeberg;Reinhard
org;quoted-printable:TU Bergakademie Freiberg;Institut f=C3=BCr Mineralogie
adr:;;Brennhausgasse 14;Freiberg;Sachsen;D-09596;Germany
email;internet:[EMAIL PROTECTED]
title:Dr.
tel;work:(+49) (0)3731 393244
tel;fax:(+49)(0)3731 393129
url:http://www.mineral.tu-freiberg.de/mineralogie/roelabor/
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