Hi All,
I have been following this discussion with much interest. For what it's worth,
I think that you also need to consider issues to do with the data collection
strategies used. Periclase has a small cubic unit cell and hence has very few
reflections in a typical scan rang used for QPA in a production environment.
If we assume Cu Kalpha radiation and a scan range up to 90deg 2theta, periclase has only 5 reflections (and only 2 of these have intensity > 10% I/Io). If Co Kalpha is used, then the total number of reflections is 4. In a Rietveld based analysis, this is too few reflections to ensure stable refinement of many parameters related to periclase. Any minor errors in the periclase model have the potential to be reflected in the QPA.
For example - if there is a little solid solution of Fe in periclase (quite possible in this environment) then the relative intensities will vary - try doing a calculated pattern in your favourite Rietveld program - below are some values for F^2
h k l MgO (Mg0.95Fe0.05)O % change
1 1 1 10.99 14.86 35.2
0 0 2 170.20 181.39 6.6
0 2 2 202.72 215.33 6.2
3 1 1 38.82 45.46 17.1
While there is an overall increase in calculated F^2 by the inclusion of Fe,
more important is the change in relative intensities.
To assess whether there is any solid solution present try collecting a pattern to
the limit of the diffractometer (> 140 deg 2Theta if possible) and refine the
unit cell parameter for periclase. Then simply apply Vegard's Law. If the cell is
indistinguishable from the reported periclase cell, then all of these ramblings
have been in vain!
The issues relating to crystallite size already discussed in this thread are
especially important since there are too few reflections from periclase to
'average out' the impact of any intensity abberations - at he very least, spin
the sample to help minimise this.
You can see I have too much time on my hands, but this seems like a good way to fill in time in the small hours of the morning while waiting for data to collect ( we have some beamtime on the powder diffractometer at the Oz Synchrotron)
Cheers
o----------------------oo0oo---------------------------o
Ian Madsen
Team Leader - Diffraction Science
CSIRO Minerals
Box 312
Clayton South 3169
Victoria
AUSTRALIA
Phone +61 3 9545 8785 direct
+61 3 9545 8500 switch
+61 (0) 417 554 935 mobile
FAX +61 3 9562 8919
Email [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
o----------------------oo0oo---------------------------o
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Sent: Sat 31/05/2008 3:37 AM
To: Whitfield, Pamela; Kurt Leinenweber; [EMAIL PROTECTED]; rietveld_l@ill.fr
Cc:
Subject: RE: RES: ADS
Hi all, in this long and interesting discussion I think that Prof.
Leinenweber has indicated where it is one of the problems in
quantitative phase analysis. Regards,
--
********************************
Jose M. Amigo
http://www.uv.es/~amigo/
********************************
> Interesting thought and probably worth following up, although it
sounds like a meticulous and possibly time-consuming study for
someone or other - any volunteers? :-)
> Following Deane Smith's methodology you should be able to calculate
the number of diffracting crystallites per phase for particular
crystallite sizes and fraction (assuming some sampling volume - I
vaguely remember his being 20mm^3 or something). I suppose that
whether you're using a PSD or 2D detectors as opposed to point
detectors and the geometry would also have to be taken into account.
>
> In our cement experiment the % difference between 0.1% and 2%
periclase is quite large to say the least. In terms of practical
versus theory, we did find that up to a point, the 'real' standard
deviation from repeated experiments with micronized samples can be
smaller than the esds calculated by the Rietveld program - a happy
note for repeatability! On a less happy note that doesn't mean that
something like severe microabsorption doesn't come along and mess up
your accuracy.
>
> Pam
>
> -----Original Message-----
> From: Kurt Leinenweber [mailto:[EMAIL PROTECTED]
> Sent: May 30, 2008 11:11 AM
> To: Whitfield, Pamela; [EMAIL PROTECTED]
> Cc: rietveld_l@ill.fr
> Subject: RE: RES: ADS
>
> Hi all,
>
> This is an interesting discussion of quantitative phase analysis.
It sounds to me from what Pam is saying that we can calculate an esd
for each phase if we know its particle size, and that the relative
error would be larger for phases in smaller abundance. If this is
correct, then you could also repeat the physical experiment several
times and get a variation of similar magnitude to the one that is
calculated. Is this what happens? Pamela refers to the errors as
being "worse" for minor phases, but they are what they are, and why
not estimate them?
>
> - Kurt
>
> -----Original Message-----
> From: Whitfield, Pamela [mailto:[EMAIL PROTECTED]
> Sent: Friday, May 30, 2008 7:30 AM
> To: [EMAIL PROTECTED]
> Cc: rietveld_l@ill.fr
> Subject: RE: RES: ADS
>
> Hi Rheinhard
>
> The comments weren't aimed at you in particular! We've been
banging our heads against a brick wall about this stuff for some
time, but not many in the cement community seem to be listening.
>
> Anyway - there is a fundamental statistics problem with quantifying
minor phases (of any symmetry) as the stats get worse with fewer
diffracting crystallites.
> The numbers that Deane Smith produced in terms of reproducibility
of the quartz reflection dealt with a single phase system. It
doesn't take much to imagine (or at least I do) that things rapidly
get worse in a multi-phase system where theoretically every phase
should consist of a nice random powder, reducing the required average
particle size even further. It should follow then that the errors
obtained with minor phases will be worse than major phases where the
stats are better even without any other effects. Maybe my logic is
flawed but I don't think so! Having said that it has been
demonstrated that the situation isn't quite as bad practically as it
is theoretically.
>
> Pam
>
> -----Original Message-----
> From: Reinhard Kleeberg [mailto:[EMAIL PROTECTED]
> Sent: May 30, 2008 10:10 AM
> To: Whitfield, Pamela
> Cc: rietveld_l@ill.fr
> Subject: Re: RES: ADS
>
>
> Hi Pam,
> maybe a misunderstanding: I did not try to discuss the amount of
> "amorphous" material in cements. I'm aware of the problem, but a
> careful Rietveld analysis with an internal standard should be able
to
> determine at least the magnitude of the amorphous part. Even if not
> (e.g. if profile errors or structural uncertainties of the clinker
> phases do prohibit a reliable quantification of the amorphous), a
> systematic error of 7 instead of 5 wt% for a highly symmetric phase
with
> well resolved peaks like periclase is neither acceptable nor
> unavoidable. And in my opinion a careful sample prep, measurement
and
> Rietveld analysis (maybe with internal standard) should be able to
> perform better. I only tried to relativise Lubo's general denial of
the
> potential of quantitative phase analysis to reach an accuracy of
about 1
> wt%. Maybe I'm simply more optimistic than Lubo ;-)
> Reinhard
>
> Whitfield, Pamela schrieb:
>
> > Hi Reinhard
> >
> > Saying the words amorphous content and cement in the same breath
is
> > heresy in many circles! Personally I think that it's a case
of 'see
> > no evil, hear no evil'!
> > Anyway, many moons ago we did yet another study on the amorphous
> > content in clinkers/cements and they can vary alot - we found up
to
> > 20wt% in some. The amount probably depends on the kiln
conditions,
> > alkali metal content and quenching rate.
> > Anyway don't take my word for it, Lerch and Brownmiller did a
lovely
> > bit of work (sadly forgotten) in 1937 using quenching in mercury
(?!)
> > and calorimetry yielding amorphous contents in clinker between
> > 10-28%. The Ruland method has also been used to show significant
> > amorphous contents in the various components of cement.
> >
> > In my opinion the cement companies are probably more interested in
> > consistency rather than accuracy to track changes in their
process.
> > Case in point - strictly speaking the XRF samples should be
micronized
> > (or fused) as well as the XRD ones - the XRF errors from the
matrix
> > effects of a 30micron cement in a pressed pellet are not exactly
ideal.
> >
> > I would agree that it's worth trying to push the boundaries of
QPA.
> > All is not lost for cements though - I saw the results of a test
that
> > Mati Raudsepp did with a very messy synthetic mineral mixture
that
> > looked completely ridiculous with the number of phases, but the
result
> > matched the weighing figures quite nicely.
> >
> > Pam
> >
> > ------------------------------------------------------------------
----
> > --
> > *From:* Reinhard Kleeberg [mailto:[EMAIL PROTECTED]
> > *Sent:* Fri 30/05/2008 5:36 AM
> > *To:* rietveld_l@ill.fr
> > *Subject:* Re: RES: ADS
> >
> > Hi Lubo,
> > the difference between 6 and 7 % MgO is bigger than 15 %
relatively,
> > thus the error by wrong re-scaling (e.g. if 10 % "amorphous" are
> > missing) is smaller than the error discussed. And, if the "true"
> > content of periclase should be about 5 %, than a measured value
of 7 %
> > is worth to be discussed to be a real systematic error. This is
an
> > over-estimation by 40 %. In the very past (30 years and more ago)
> > people who applied single line methods carefully have been able
to
> > determine "simple" phases like free lime, quartz, anatase in low
> > concentrations very accurate (of course after optimizing their
> > technique), and I believe that such methods are still in use in
> > routine product control. So I feel it is worth to think about why
a
> > Rietveld refinement should perform worse. I agree with you that
the
> > cement business is full of dubious advertisement for machines and
> > methods for accurate QPA. But this is not a reason to finish
thinking
> > about how to improve QPA methods. Best
> > Reinhard
> >
> > Lubomir Smrcok schrieb:
> >
> > > Hi,
> > > I really wonder why do you bother about 1% difference when the
error
> > > of the method (XRD, quantitative phase analysis) could reach 10%
> > > (absolute) ...
> > > People in the discussions appearing here seem to forget about
two
> > things:
> > >
> > > i) "quantitative" phase analysis done by rietveld method is
always
> > > re-scaled to 100%, i.e. the accuracy of % attributed to the
> > > individual phase directly depend on %'s attributed to the
another
> > > phases present in the mixture (i.e. when you forget or ignore
one
> > > phase having 10% share, those %'s are redistributed among the
other
> > > phases);
> > >
> > > ii) this method completely ignores any amorphous parts (i.e.
those
> > > not providing Bragg peaks, to be more exact) - ignores, because
it
> > > cannot do anything else about it. Obviously, when you compare
XRF
> > > and XRD you can find yourself in troubles as XRF dos not bother
> > > about the state of the compounds.
> > >
> > > Finally, my personal advice. If someone tells you you can
analyze
> > > clinkers or even cements by XRD accurately, do not trust him.
He,
> > > most probably, thinks of selling you a machine you can hardly
use
> > > for this purpose :-) Bad luck if you have already bought it ...
> > >
> > > Best,
> > > Lubo
> > >
> > >
> > >
> > > On Thu, 29 May 2008, [iso-8859-1] José Carlos Cordeiro wrote:
> > >
> > >> My samples are cements (fine samples with 30 microns) and
don't
> > >> need micronize its. The problem in my refinements is that
periclase
> > >> quantified with fixed slit is bigger than MgO by Fluorescence,
and
> > >> its impossible. Ex:
> > >>
> > >>
> > >>
> > >> Periclase with fixed slit: 7,14%
> > >>
> > >> MgO by XRF = 6,84%
> > >>
> > >>
> > >>
> > >> We know that part of MgO (1,5-2,0%) go to the structure of C3S
an
> > >> C2S phases, so periclase expected in this sample is 4,8% -
5,3%. If
> > >> we consider this, the errors of refinement is not very slim.
> > >>
> > >>
> > >>
> > >> Sorry for my bad English!!!
> > >>
> > >>
> > >>
> > >> regards
> > >>
> > >>
> > >>
> > >> ===========================================
> > >>
> > >> José Carlos Cordeiro
> > >>
> > >> Diretoria Técnica - Laboratório Central
> > >>
> > >> Centro Técnico - Curitiba
> > >>
> > >> Rodovia PR-092, 1303, Abranches, 82130-570 Curitiba-PR
> > >>
> > >> Votorantim Cimentos
> > >>
> > >> [EMAIL PROTECTED]
> > >> <mailto:[EMAIL PROTECTED]>
> > >>
> > >> www.votorantimcimentos.com.br
> > >>
> > >> Fone: + 55 041 3355-1380
> > >>
> > >> Fax: + 55 041 3355-1358
> > >>
> > >> ===========================================
> > >>
> > >> -----Mensagem original-----
> > >> De: Whitfield, Pamela [mailto:[EMAIL PROTECTED]
> > >> Enviada em: quinta-feira, 29 de maio de 2008 17:40
> > >> Para: José Carlos Cordeiro; rietveld_l@ill.fr
> > >> Cc: Mitchell, Lyndon
> > >> Assunto: RE: ADS
> > >>
> > >>
> > >>
> > >> Hi Jose
> > >>
> > >>
> > >>
> > >> Errors in the region of 1wt% aren't unheard of in complex
mixtures
> > >> (and the liklihood of the second decimal place being
meaningful is
> > >> very slim). However there are other possible explanations and
one
> > >> in particular comes to mind.
> > >>
> > >> Did you micronize your sample? If yes then feel free to
ignore the
> > >> following! If not then it might be worth thinking about.
> > >>
> > >>
> > >>
> > >> We did a systematic study on the effect of particle statistics
on
> > >> the repeatability of quantitative analysis on one of the NIST
> > >> cements last year (presented at the ICCC in Montreal - should
> > >> really go somewhere more accessible). We compared different
> > >> divergence slits, micronized and unmicronized samples, spun
and
> > >> static, and remounted/repeated the experiments 3 times each
for
> > >> real statistics as opposed to esds.
> > >>
> > >>
> > >>
> > >> Funnily enough the phase that showed the biggest anomaly in
one of
> > >> the unground sample was the periclase - obviously a big (by XRD
> > >> standards) lump fell into the sample from the kiln that made
up the
> > >> NIST batch and made it through the mill at the plant. Without
> > >> grinding it we got 0.1, 0.1 and 2wt% one series of 3, versus
0.6,
> > >> 0.6 and 0.6 wt% (this is from memory so don't don't quote me!)
for
> > >> the micronized sample.
> > >>
> > >> This was the result that we should have got theoretically but
it
> > >> was nice to see it work in practice, and the periclase did
such a
> > >> nice job for us by sticking out like a sore thumb even without
a
> > >> Rietveld analysis! BTW there was no statistically significant
> > >> difference (95%
> > >> limits) in the results of the C3S and C2S phases between
ground and
> > >> unground samples - mostly because the errors in the unground
samples
> > >> were so large! The minor phases were another matter. In the
> > >> micronized samples the choice of divergence slit size made
little
> > >> difference, but with the unground samples they made a
significant
> > >> difference.
> > >>
> > >>
> > >>
> > >> To cut a long story short it all comes down to particle
statistics
> > >> - with an ideal powder the choice of fixed versus variable
slits
> > >> (or even different fixed slits) should make no difference
(assuming
> > >> that the Rietveld software can handle the difference in
profiles).
> > >> Moral of the story - sample prep, sample prep and more sample
prep!
> > >>
> > >>
> > >>
> > >> Pam
> > >>
> > >> -----Original Message-----
> > >> From: José Carlos Cordeiro
[mailto:[EMAIL PROTECTED]
> > >> Sent: May 29, 2008 3:53 PM
> > >> To: rietveld_l@ill.fr
> > >> Subject: ADS
> > >>
> > >> I have a Programmable Divergence Slit (incident beam) in
my
> > >> difratctometer, that can work in automatic mode (irradiated
length)
> > >> or fixed mode (0.5 degree or 1.0 degree etc). What is the best
> > >> collect mode for Rietveld Refinament??
> > >>
> > >>
> > >>
> > >> I did refinement two difractograms collected in booth
> > >> configuration (fixed 0.5 degree and automatic mode), the
results in
> > >> the fase "Periclase" (cement fase) changed, see below:
> > >>
> > >>
> > >>
> > >> Periclase with 0.5 degree = 6.08%
> > >>
> > >> Periclase wich automatic mode = 7.14%
> > >>
> > >>
> > >>
> > >> Note.: The refinement of the difractograms collected with
> > >> automatic mode went converted to fixed mode by software.
> > >>
> > >>
> > >>
> > >>
> > >>
> > >>
> > >>
> > >> What do you think about this?
> > >>
> > >>
> > >>
> > >> regards
> > >>
> > >>
> > >>
> > >> ===========================================
> > >>
> > >> José Carlos Cordeiro
> > >>
> > >> Diretoria Técnica - Laboratório Central
> > >>
> > >> Centro Técnico - Curitiba
> > >>
> > >> Rodovia PR-092, 1303, Abranches, 82130-570 Curitiba-PR
> > >>
> > >> Votorantim Cimentos
> > >>
> > >> [EMAIL PROTECTED]
> > <mailto:[EMAIL PROTECTED]>
> > >>
> > >> www.votorantimcimentos.com.br
> > >>
> > >> Fone: + 55 041 3355-1380
> > >>
> > >> Fax: + 55 041 3355-1358
> > >>
> > >> ===========================================
> > >>
> > >>
> > >>
> > >>
> >
> >
>
>
>
>
>
