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[sdpd] NIST SRM 1976: questions
Hi everybody,
We are using the SRM 1976 "/XRD Flat Plate Intensity Standard/" in order
to check our diffractometer (1976 and not 1976a).
This plate was new and immediately inserted on to the diffractometer
sample holder (clean !) as soon as its exit from the NIST box.
We observe two "problems":
a) The NIST certificate that is delivered with the Al2O3 plate claims
that the alumina is pure. We were a little surprised when we observed
systematically (with several different diffractometers) one impuritie
that I suppose (I am not sure !!) to be 3Al2O3-2SiO2 (Mullite). I do not
understand why do one observe that...
I downloaded data on NIST SRM 1976 from Armel Le Bail site "Summary on
the Subject Low FWHM and Rp
<http://www.cristal.org/powdif/low_fwhm_and_rp.html#t2>" and this
impuritie does not appear (even with quite recent detectors such as
X'Celerator).
Could you help me to understand the presence of such Mullite phase (PDF
N°00-015-0776) inside a so called "reference material" ?!
b) Data were recorded with a proportional gaz filled detector, a rear
Graphite monochromator, Cu for the radiation. Because of the rear
monochromator I did not used any Ni filter (rear Cgr monochromator is
better in this aim than Ni filter, or not ?). It is surprising to
observe something like "step" in the left part of the tail of some peaks
(not all of them). These "steps" are like the Ni absorption edge that
can be observed with such a filter.
I do not understand at all why such steps are present in my data because
I did not use any Ni filter... Do you have an idea ?
Many thanks in advance for your help.
JM
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