Does anyone know if it is possible to calculate amorphous phases in weight percent in a whole rock geological sample using Bruker Topas software?
I have a sample whole rock sample that has about 6 different crystalline minerals, but based on the background (hump), I can tell there is some amorphous material in the sample. When I calculate the mineral weight percent of the sample, the software only considers the 6 crystalline phases. Is there a way to calculate the amorphous content wt. % included with the other 6 crystalline phases?
Thank you in advance for your assistance.
Dear Sir Hector Garza for the topas software I have no idea. However, you can find the weight per cent of the amorphous phase in Fullprof software. In this software, you can run 8 different phases at a time
In addition to the answer by Haobam Samananda Singh , to determine the weight percentage for an amorphous materials, a reasonable approach would be:
first determine proper instrumental resolution function values for your instrument from a standard like LaB6
then refine the crystalline phases as done conventionally and try to add a "quartz" phase that you describe as a very small nanoparticle. I think Topas has a crystal size parameter that you can try to fix to say 2 to 3 nm. This should result in a very broad diffraction background that corresponds to the "amourphous" phase.
Depending on your rock type you might try "quartz" , "illite", "kaolinite" or other clay/mica as substitute for the amorphous background.
You could verify this approach by mixing known weight percentages of say feldspar and finely ground glass.
Dear Hector Garza,
When you have 6 different phases, this can be challenging.
The Rietveld refinement in TOPAS can simultaneously fit a mixture of phases described by one of three different methods: Single Line Fitting, Whole Powder Pattern Fitting/Decomposition - cell parameter fitting without atomic coordinates, and Pattern Fitting based on crystal structure. For each of them, Wt % Rietveld / Wt% of Spike can be calculated if you turn it on. You can find it in the GUI or somewhere in some of the files generated by TOPAS.
(See pages 39-40 and 49-50 in the TOPAS User's Manual DOC-M88-EXX065 V4.2 - 01.2009, e.g.: http://algol.fis.uc.pt/jap/TOPAS%204-2%20Users%20Manual.pdf ).
You can get close to solving your problem by marking the background as a straight line and using the 7th phase as a broad peak with a maximum at about 27 deg. ("amorphous hump").
See an example in the free online supplementary material (Fig. S8 on page S10): https://pubs.rsc.org/en/content/articlelanding/2012/dt/c1dt10744e
The direct link is:
https://www.rsc.org/suppdata/dt/c1/c1dt10744e/c1dt10744e.pdf
There is also an "amorphous hump". I hope this has shown you the possibilities and is helpful. On the other hand, I cannot tell you if the Wt % results are correct and how close it is to reality. Maybe @R. B. Neder 's idea makes more sense.
Best of luck.
For calculating amorphous phases in weight percent using Rietveld based software's publication from this group may be helpful in quantification:
https://www.researchgate.net/profile/Ian-Madsen-2
https://www.researchgate.net/profile/Nicola-Scarlett-2
Thank you so much for your responses. I really appreciate it. Based on all of your responses, there is no doubt that spiking the powder with a known amount is the best way to go, but unfortunately, the XRD scan I was working with was scanned years ago. Using the Topas tutorial document and with the help of one of Bruker's software engineers, we calculated the amorphous content when the sample was not spiked. I am putting images of the tutorial in case anyone is interested or it helps someone in the future.
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