Even in case of a "really random sample", the intensity of 00l peaks of
smectites is biased by a number of unknowns, like site occupation of
tetrahedral positions, interlayer cation and its hydratation stage, and
the usual instrumental and preparation effects at low angles like beam
overflow and sample roughness. Therefore, in clay mineralogy, it is well
established practice to use primarily the hk0 of "random" samples for
quantification purposes, see
Srodon et al., (2001) Clays and Clay Minerals, 49 (6) 514-528
Fig. 9 shows the popular 06,33 region of dioctahedral clay minerals.
The other idea is full profile modelling of the turbostratically
disordered smectites, see
http://www.bgmn.de/smectite.html
Both approaches are more or less successfully in use for quantification
purposes, whereas the use of 00l reflections often failed, see
Omotoso, O., McCarty, D.K., Hillier, S., Kleeberg, R. (2006) Some
successful approaches to quantitative mineral analysis as revealed by
the 3^rd Reynolds Cup contest. Clays and Clay Minerals, 54 (6), 751-763.
Reinhard
Lubomir Smrcok schrieb:
Just few words of warning : think of preferred orienatation in your
samples... Moreover, from the vast majority of montmorilonites one
gets only few so called "00L" diffractions what means that the
results of quantitative phase analysis can be better obtained by a
random numbers generator :-)
Enjoy !
Lubo
comparison with "calculated" patterns gives the numbers whose accuracy
is not worth the time you spend with
On Sat, 15 Mar 2008, Alan Hewat wrote:
the cif-file below was created from the AMCSD...
The I/Ic value calculated by Match! is 20.5
The only ICSD entry has an RIR of over 23, so does
vermiculite. Why is that so high?
I guess these differences in I/Ic are not very significant, since the
exact same montmorillonite entry is in ICSD, from which you can
export the
CIF directly. (In fact I doubt that there are any AMCSD entries that
are
not also in ICSD).
Clays, micas etc are highly layered structures, often with variable
amounts of intercalates, and usually not well ordered. They are
therefore
difficult to model, so the profile fit will be relatively poor.
______________________________________________
Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
<[EMAIL PROTECTED]> +33.476.98.41.68
http://www.NeutronOptics.com/hewat
______________________________________________
