Hi Elena,
Internal standard method means physically mixing sample with the internal
standard.
Adding two data together won't work as their mass absorption coefficients are
different, hence cannot be cancelled out.
>"Why I'm getting negative amorphous in Topas using IS internal method?"
If correct weighings and homogenous mixing have been done (scaresly by
students), "negative amorphous" generally mean your sample is more crystalline
than your internal standard.
>In DIFFRAC.EVA, any powder will show some %-Amorphous if we compute
>crystallinity using the Default Bg model parameters (Curvature=1,
>Threshold=1 and No Enhancement).
EVA's automatic background if just a boundary line between sharp peaks and
board humps, for the purpose of Phase ID only.
It is neither true instrument background, nor amorphous hump. Please do not
abuse this background for Rietveld.
>However, even if the powder is known to have an amorphous phase, the
>%-Amorphous would be =0% if we use a flat Bg with curvature=0.
The amorphous hump area are between your "boundary line" and the flat Bg with
curverture=0.
If you adjust the "boundary line" to the "flat Bg with curvature=0", you are
basically telling EVA that you have 0% amorphous, which is what you get.
I don't know why do you so though, as EVA tutorial tells users to adjust the
"boundary line" to cover the amorphous hump.
This Degree of Crystalline function is just a simple ratio between area under
sharp crystalline peaks and Amorphous board humps. It can be used in pharma or
ploymer samples, in which the amorphous part and crystalline part have similar
chemistries. It cannot be used in multi-phase samples like geological samples,
becasue their scattering form factors are different.
>refinement is instrument sensitive...run reference materials....model it as an
>hkl phase
Refinement results from data measured on different machines can be compared if
both machine's geometric contributions are accounted correctly.
I would not use "calibrated hkl_Is" model for internal standard, which will
give others another degree of uncertanity.
In RR assessment, people even tend to use same .cif structure to compare
results.
Hope these helps.
--
Dr. Tony Wang
Senior Research Infrastructure Specialist (XRD)
Central Analytical Research Facility (CARF) | Queensland University of
Technology
Address: Level 6, P Block, Gardens Point campus, 2 George St Brisbane QLD 4000
Tel: +61 7 3138 1904 | Mob: 0452 571 680
Email: tony.w...@qut.edu.au | Web: www.qut.edu.au/ife/carf
At 2022-05-02 18:39:08, "Elena Lounejeva" <elena.lounej...@utas.edu.au> wrote:
Good day everybody,
I agree with Holger. I'd be happy to help organise a RR for amorphous content
quantification if somebody takes over. Count me in.
Hi Matthew,
I came back to your question after your last message on April 30th. I only know
how to estimate amorphous using the internal calibration in Topas; therefore, I
made an approximate estimation. I summed both of your XY files below and put
them into the attached .pro file. Doing that, I have noticed a couple of
things. First, I have noticed that the Bg is a bit convex, and you probably
would like to double-check your instrumental setup (was it the silicon holder?
0.5 or 3 mm air screen? A narrow incident slit? Or something else). Second,
please review the instrumental parameters in the attached *.pro file as I use
D2 and am not familiar with D8 details. Third, I'm not sure how to improve
refinement for Corundum, but it is definitively deficient, as you can see on
the residual curve and high Rwp ~7.
I firstly ran refinement of the mixture with three structures and got ~55% of
Corundum which is logical given the uncertainty introduced by summing the BGs.
Then I fixed it as an internal standard at 55%, and obviously, Amorphous
content was very low (try and see the result). So I tried several values down
to 50% for Corundum and got the best match for Corundum ~52.5% with Rwp~6:
|
Phase
|
Wt% in mixture
|
Wt% in original
|
|
Cor
|
52.5
|
|
|
Alpha
|
41.47
|
87
|
|
Beta
|
1.16
|
2.5
|
|
Amor.
|
4.87
|
10
|
You probably can improve it.
https://www.dropbox.com/s/r0stzrl8so0h43x/ROW.pro?dl=0
A proper calculation should be much better after running a physical mixture
with ~10-20 wt% of Corundum by weight rather than simply summing the data and
using each simple structure refined for the instrument setup (I agree to DO NOT
refine Beq) before refining the mixture. I'd be relatively happy with the
result, but the problem remains with the "unknown" samples…
Please review and share your thoughts. Bets wishes,
Elena
PS
"Why I'm getting negative amorphous in Topas using IS internal method?" - is
the most off-putting question from our students. In DIFFRAC.EVA, any powder
will show some %-Amorphous if we compute crystallinity using the Default Bg
model parameters (Curvature=1, Threshold=1 and No Enhancement). However, even
if the powder is known to have an amorphous phase, the %-Amorphous would be =0%
if we use a flat Bg with curvature=0. In Topas, the "Amor" accounts for the
difference between what is identified, refined and weighted relative to
internal standard; thus, Amor includes all the unknown phases, either amorphous
or not-identified crystalline) and it is also Bg and many other things
-sensitive. My understanding of the matter so far: refinement is instrument
sensitive; therefore, it is essential to run reference materials and calibrate
each instrumental setup for the purposes, model background or amorphous and
save it as a scan, load in Topas, model it as an hkl phase, estimate
proportions as semi-quant for the known SRM and only if a general refinement
gives a reasonable amount (+-1%?) we could use it with the internal std. Also,
the external method should give better results when you have a mixture of
well-known references in several proportions, a kind of calibration curve. This
is what Matt is going through, although this approach is time-consuming.
From:rietveld_l-requ...@ill.fr <rietveld_l-requ...@ill.fr> On Behalf Of Matthew
Rowles
Sent: Tuesday, 19 April 2022, 4:20 PM
To: Holger Kletti <holger.kle...@uni-weimar.de>
Cc: RIETVELD_L Distribution List <rietveld_l@ill.fr>
Subject: Re: NIST SRM656 Analysis
Hi Holger
There is a good paper by Ian Madsen, Nikki Scarlett, and Arnt Kern about the
quantification of amorphous materials - https://doi.org/10.1524/zkri.2011.1437
On the RR, I'll let the CPD know!
Matthew
On Thu, 14 Apr 2022 at 16:51, Holger Kletti <holger.kle...@uni-weimar.de> wrote:
an actual RR on amourphous contents like thos on crystalline mixtureswould
really be appriciable, i don't know any publications therewith. The problem
seems to exist as can be seen here, but also with internal standard method, as
in personal discussions the question on achieved negative amorphous contents
(internal as well as external standard method) arises from time to time. And
not alway this can be solved just by variation of background polynoms or other
structure related parameters.
So if "anyone" would initiate such a RR i would like to join it ....
Holger
Am 14.04.2022 um 09:49 schrieb Julian Richard Tolchard:
I confess that this discussion seems to validate my personal choice to treat
Rietveld quantification (and especially amorphous quant) as something lying
between a quantificational and semi-quantificational technique.
Has anyone done a proper round-robin on amorphous quant (by any methods
actually)? There have been some RR’s for crystalline mixtures I know, but I
can’t remember seeing one for crystalline+amorphous samples.
jools
From:rietveld_l-requ...@ill.fr<rietveld_l-requ...@ill.fr>On Behalf Of Matthew
Rowles
Sent: torsdag 14. april 2022 09:03
To: Jonathan WRIGHT <wri...@esrf.fr>
Cc: RIETVELD_L Distribution List <rietveld_l@ill.fr>
Subject: Re: NIST SRM656 Analysis
Hi Jon
The data is put on an absolute scale through the external standard approach.
The calculations assume that the QPA for corundum in NIST SRSM676a is 99.02
wt%. This scaling factor is then applied to the silicon nitride pattern.
re surface roughness: The samples were backpacked against a glass surface, and
the powders used as-received. I've never measured the particle size
distribution of either (any!) SRM, but the certificates describe 676a as "fully
disaggregated" and "grains are sub-micrometer in size and equi-axial in shape"
and the 656 certificate has a particle size distribution by laser scattering,
with 100% less than 5 um. In our other work, we aim to micronise to less than
10 um. Our grinding checks show that we get 100 vol% <15 um and 95 vol% <6 um.
I've never used the Pitschke or Suortti roughness corrections available in
Topas, and have no intuition as to the magnitude of their correction or what
"proper" values should be.
Matthew
On Wed, 13 Apr 2022 at 18:11, Jonathan WRIGHT <wri...@esrf.fr> wrote:
Maybe a silly question: are you assuming you have the data on an absolute scale
in order to do these calculations? Do things like surface roughness somehow not
matter?
Best
Jon
On 13/04/2022 11:56, Matthew Rowles wrote:
> Thanks Tony
>
> When I add the absorption edge correction to the silicon nitride model (and
> add
> beta-silicon nitride), it becomes -2.8 wt% amorphous; up a little due to the
> added correction and down a little due to the extra phase.
>
> If I change your al-SN thermals from 1 to those given in ICSD 77811, I get
> +4.8
> wt% amorphous. Your atoms were already neutral, so I left them as-is.
>
> If I make all the Si-nitride phases' thermal parameters == 0, then I can get
> up
> to 8.5 wt% amorphous.
>
> In all of this, corundum is staying as charged atoms, with Al and O beqs fixed
> at 0.334 and 0.278.
>
> I'll have to have a go at applying the absorption edge correction; I always
> forget which parameter is which thing and have to rederive my understanding of
> it everytime...
>
>
> Thanks
>
> Matthew
>
> On Wed, 13 Apr 2022 at 13:58, iangie <ian...@126.com <mailto:ian...@126.com>>
> wrote:
>
> Dear Matthew,
>
> I tried your data and get ~-1% amorphous. My .pro is in below link.
>
> https://www.dropbox.com/s/xuw13c91l9gq5m5/ROW.pro?dl=0
> <https://www.dropbox.com/s/xuw13c91l9gq5m5/ROW.pro?dl=0>
>
> I normally do not refine Beq, which I believe gives biggest source of
> error
> in QPA...
>
>
> Cheers!
>
> --
>
> *Dr. Xiaodong (Tony) Wang*
> *Senior Research Infrastructure Specialist (XRD)*
> Central Analytical Research Facility (CARF) | Queensland University of
> Technology
> *Address:* Level 6, P Block, Gardens Point campus, 2 George St Brisbane
> QLD 4000
> *Tel:*+61 7 3138 1904 | *Mob:*0452 571 680
> *Email:* tony <mailto:stephen.blank...@qut.edu.au>.
> <mailto:stephen.blank...@qut.edu.au>w...@qut.edu.au
> <mailto:stephen.blank...@qut.edu.au> | *Web:* www.qut.edu.au/ife/carf
> <http://www.qut.edu.au/ife/carf>
>
>
> At 2022-04-13 13:00:44, "Matthew Rowles" <rowle...@gmail.com
> <mailto:rowle...@gmail.com>> wrote:
>
> Hi all
>
> Thanks to those that have replied off-list.
>
> I've managed to jiggle things around and get various answers. If you
> want an answer between -14 and +6 wt% amorphous, I can make it
> happen. I
> can either use charged atoms or not, or use thermal parameters or not.
> Combining those between the corundum and Si3N4, you get the following:
>
>
> image.png
> This is using the scattering factors defined with 11 gaussians.
>
> If you use the ones defined by 9 gaussians, you get
> image.png
>
> The structures I used are below. In the certificate for 656, the
> structures are referenced, but those structures have no thermal
> parameters. Does anyone know what was used in the NIST determination?
>
>
>
> phase_name "Aluminium_oxide_alpha_10425_icsd"
> Hexagonal( 4.759355, 12.99231)
> space_group "R -3 c H"
> site Al1 num_posns 12x 0 y 0 z 0.14772 occ Al+3 1. beq 0.318
> site O1 num_posns 18x 0.3064 y 0 z 0.25 occ O-2 1. beq 0.334
>
> phase_name "ALPHA_Marchand_ICSD_26191"
> Hexagonal( 7.75411, 5.62034)
> space_group "P31c" 'atom positions from Marchand. Thermals from ICSD
> 77811
> site Si1 num_posns 6x 0.0806 y 0.5095 z 0.3020 occ Si+4 1 beq 0.25
> site Si2 num_posns 6x 0.1675 y 0.2560 z 0.0070 occ Si+4 1 beq 0.29
> site N1 num_posns 2x 0 y 0 z 0 occ N 1. beq 0.88
> site N2 num_posns 2x =1/3; y =2/3; z 0.3500 occ N 1. beq 0.46
> site N3 num_posns 6x 0.0390 y 0.3860 z 0.0310 occ N 1. beq 1.06
> site N4 num_posns 6x 0.3190 y 0.3210 z 0.2660 occ N 1. beq 0.17
>
> phase_name "BETA_Billy_ICSD_35566"
> Hexagonal( 7.60633, 2.90778)
> space_group "P 63/m" ' structure from Billy, thermals from ICSD 170004
> site Si1 num_posns 6x 0.2323 y 0.4096 z 0.25 occ Si+4 1 beq 0.231
> site N1 num_posns 2x =1/3; y =2/3; z 0.25 occ N 1 beq 0.326
> site N2 num_posns 6x 0.3337 y 0.0323 z 0.25 occ N 1 beq 0.314
>
>
>
>
>
>
> On Tue, 12 Apr 2022 at 17:13, Matthew Rowles <rowle...@gmail.com
> <mailto:rowle...@gmail.com>> wrote:
>
> Hi all
>
> I've collected some more data, and am still getting spurious
> results, and by spurious, I mean -5 wt% amorphous in SRM-alpha-656
> when quantified by the external method against SRM 676a.
>
> We had some SRM-656alpha (couldn't find any of the beta) stored
> in a
> drying oven, and some SRM676a stored in a cupboard. I collected
> some
> data using a D8 with Ni-filtered Cu and a lynx-eye detector (0.25°
> fixed divergence, 250 mm radius, 2x2.5° sollers). The patterns
> were
> collected consecutively (using the same program), with a single
> peak
> from SRM1976 (b, I think), acting as an intensity calibrant (the
> intensity didn't appreciably change), collected before, after, and
> between.
>
> Does anybody want to have a look at the data and see what I'm
> doing
> wrong? Data available at:
>
> https://raw.githubusercontent.com/rowlesmr/pdCIFplotter/changing-str-to-float-conversion/data/row_Cu_676a.xy
>
> <https://raw.githubusercontent.com/rowlesmr/pdCIFplotter/changing-str-to-float-conversion/data/row_Cu_676a.xy>
>
>
> https://raw.githubusercontent.com/rowlesmr/pdCIFplotter/changing-str-to-float-conversion/data/row_Cu_al656.xy
>
> <https://raw.githubusercontent.com/rowlesmr/pdCIFplotter/changing-str-to-float-conversion/data/row_Cu_al656.xy>
>
>
> Thanks
>
> Matthew
>
>
>
>
>
> On Wed, 16 Mar 2022 at 21:13, Matthew Rowles <rowle...@gmail.com
> <mailto:rowle...@gmail.com>> wrote:
>
> Hi List People
>
> Do any of you use NIST SRM656 in your quantitative analysis
> quality control?
>
> I've recently started at a new lab, and am finding it
> impossible
> to make a physically realistic model (in Topas) that gives
> results anywhere near correct (or at least, close to the
> certificate values).
>
> As an example, using the external std approach with SRM676,
> I've
> managed to calculate there is -11 wt% amorphous in the
> beta-656
> standard.
>
> I've tried using the silicon nitride structures given in the
> SRM
> certificate, but the papers and the ICSD entries don't list
> any
> thermal parameters.
>
> I can get the same results as given on the certificate using a
> siroquant model, but I don't know the provenance of the HKL
> files used in the analysis.
>
>
> Thanks in advance
>
>
> Matthew Rowles
>
>
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