seyed-rookie
Hey Everyone,
I have a delicate problem with using Topas for Phase Quantification of Retained Austenite. I have done a couple measurement on a high carbon steel with our recently purchased Göbel Mirror at 1-degree with a Cr-source. My intention is to quantify the amount of retained austenite (RA%) with topas. The difficult part is that I have overlapping peaks for hkl - 110-alpha and 111-gamma. When I perform peak fitting the amount of RA% is given to the right in software after the run is finish, but depending how the peak fitting is done and how the parrameters are set the value can alter from 10 - 30 % indicating an unstable peak fitt.
Have anyone experience solving similar problems?
See my XRD-Pattern below.
ps. I tried to add a Image of my XRD pattern but it did not work! sorry.
Thanks
Seyed
alancoelho
>The difficult part is that I have overlapping peaks for hkl -
>110-alpha and 111-gamma.
A peak that is overlapped 100% with another of similar shape will have a 100% correlation with the other peak.
I dont know the pattern but if there's not a 100% overlap between the phases then try:
- fix/constrain lattice parameters to within expected ranges.
- rescan at higher resolution
iangie
Rietveld quantification is a method purely based on pattern fitting.
If the only peaks of your two phases all overlap, then Rietveld can't help you.
That's why you need crash your sample into powder, and try to record peaks for each phase not overlapping, where Rietveld quant result derived from.
iainoswald
Dear All,
Sorry if this has been mentioned on another thread but I can't find it.
I have data from PEARL at ISIS that has four phases, my compound, Fluorite, alumina and zirconia. My compound and fluorite are mixed together and should be illuminated to the same extent all the way through the experiment so could be used to calibrate (I have not weighed any of the compounds); the other two phases may have more or less.
I would like to see if there is still the same quantity of my material at the end of the experiment as at the beginning. I have not weighed the compound and so would only be looking for a relative decrease or not. The phase mixture is showing a difference but I am not sure whether I can believe or report it given the variation in the other two 'non-important' phases.
e.g at beginning my compound 50%, flurorite 26%, Alumiona 19% and Zirconia 3%
At end of exp these change to 21, 43, 31, 4 (these are rounded and may not add to 100%).
Best wishes,
Iain
rowlesmr
Hi Iain
What was your experiment? If you mixed fluorite and your compound, where did the alumina and zirconia come from? ie: What is in the beam, where does it come from, how does it change during your experiment?
Matthew
iainoswald
Hi Matthew,
The fluorite is contained in the TiZr gasket and will be illuminated to the same extent as the sample (organic acid). The alumina is is part of the experimental set-up and as pressure is applied to the system the amounts of alumina and zirconia (from the anvils) in the beam can change.
Therfore I have an internal reference in fluorite but the weight percent but I am wondering how I can perhaps use this to see if I have lost crystallinity.
Best wishes,
Iain
rowlesmr
I think that you can.
If you ignore the contribution to the quant from corundum and zirconia, you have 34 wt% fluorite and 66 wt% acid before (assuming everything is 100% crystalline, and you aren't missing anything else, and all of the other caveats).
If you assume that the fluorite doesn't take part in the experiment, and everything else stays the same, you should have 34 wt% of it left in the end, so you can use it as an internal std.
The Rietveld wt% after, are 33 wt% acid and 67 wt% flu. Flu should be 34 wt%, so it is 1.97x what it should be. Reduce the acid by this fraction, and you get 17 wt% acid, and then by difference, you have 49 wt% "amorphous" (or otherwise unaccounted for stuff).
iainoswald
Many thanks for your help.
Iain
mfisch
The most easy way may actually be to put in your phase and CaF2 as "str" and the other two as "hkl_Is". then they don't contribute to the quantification at all. Define your initial amount of fluorite as internal standard et voila... ;-)