I have a slag sample with following elemental oxide composition:
CaO, SiO2, Al2O3, MgO, SO3 and also contains carbon (in calcite). I have managed to identify the following phases:
Gypsum (CaSO4.2H2O) , Aragonite (CaCO3); Calcite (CaCO3), Calcium silicate (Ca2SiO4) but I am struggling to find Mg bearing phase. XRF shows about 4% of MgO content.
I would highly appreciate if somebody can have a look at the XRD file and throw some light on possible Mg bearing phase present.
I have attached the XRD file, compressed in .rar format
Hello Rajeev,
Your crystalline component is explained fully by gypsum, calcite and aragonite. I am not convinced that you have any C2S as the overlap with gypsum is is severe.
So the Mg must be in the significant amorphous component. Being amorphous its structure would be unknowable.
PS thanks for compressing the file - it saved 18 bytes ;-)
Thanks Ian for your help with the data analysis.
I used to upload the xrd .raw file previously but for some reason it doesn't show up, so now a days if I have to upload xrd data I just compress it in WinRAR, so that it is uploadable, no doubt it saves space on Researchgate servers as well (:->)
Magnesium can also incorporate into the crystalline structure of calcite and gypsum through replacing calcium in their lattices. This does not happen in any significant amounts with aragonite.
I would conclude an amorphous phase exists in your experiment if there is any additional evidence for this (e.g. FTIR, electron microscopy + EDX, etc.), not from just the absence of crystalline idealized Mg containing mineral phases.
Pieter, I don't think this can be explained by Mg-calcite. There is very large (80%) proportion of amorphous in this sample (not accounting for the low angle hump which I believe is due to air scatter/sample holder issues). See image below.
A quant analysis (second image and below) shows the possibility of 2.6% Mg-calcite. But since the crystalline total is 20% then this reduces to 0.5% of the total. The weight of the Mg in the Mg-calcite again reduces the amount.
I do not have a structure file of Mg bearing gypsum so I am not able to model that. If you have one then I can explore this further.
So I still think the likelihood is that the Mg content resides in the amorphous component.
Perhaps Rajeev can do chemical balance comparing these mineral data with the XRF values and see what is left over - that would be the composition of the amorphous.
----------
R-Values
Rexp : 2.09 Rwp : 3.06 Rp : 2.26 GOF : 1.46
Quantitative Analysis - Rietveld
Phase 1 : Gypsum 67.215 %
Phase 2 : Calcite 13.471 %
Phase 3 : Aragonite 16.665 %
Phase 4 : "Calcite magnesian" 2.649 %
I suggest to measure the sample with internal standard to check amorphous phase content and calcinate the sample. After heat treatment you should see Mg-phase.
Check also cell parameter of calcite, if you see reduction it may be confirmation of the presence of Mg-calcite phase
Sorry, couldn't easily look at .rar files, and have no way of opening .raw files at my desktop. If the amorphous phase makes up 80% of the sample, then definitely more information is needed, because with only 4% Mg, if all Mg is in the amorphous phase, other elements also need to be incorporated in the amorphous phases and definitely more information is needed for this. especially because of potential formation of solid solutions and potential artificial "amorphous" background scattering because of sample morphology and holder or machine artefacts.
Thanks Pieter / Ian / Bartlomiej, for your valuable responses. I highly appreciate your help.
I did thermogravimetric analysis on the slag sample and have attached the derivative TG curve. It shows a mass loss between ~330 to ~480 deg centigrade temperature, which as per past literature is of Mg(OH)2. The loss of chemically bound water was 0.22% of the initical fully dired mass, that equated to about 0.7% of Mg(OH)2.
I agree with Bartlomiej's suggestion, i.e. do an xrd of the sample after heating and getting rid of the CO2 content, to see if the leftover contains MgO.
After bit of more digging into the analysis i'll check with mass balance as well as rightly suggested my Ian.
Thanks Ian / Pieter / Bartlomiej for all your help
Dear Ian,
Could you please email me the TOPAS project file that you have analysed. My analysis is throwing totally different results. The amorphous content I'm getting is about 65%. Just wanted to check what parameters were different in your analysis that shows this difference in analysis.
Rajeev, I did the amorphous quant in EVA by simple areas under the curve for total and crystalline components. As in my first document above. The TOPAS was for quant of crystalline only. I was able to obtain a value of 19% crystalline in TOPAS, but it was not reproducible in multiple refinements, I think the background modelling was not quite correct and it was being interfered with by the low angle humps which we have discussed previously.
Thanks Ian,
I tried mass balance approach as you suggested earlier, with the help of thermogravimetric analysis, that helped a lot in working out the crystalline and amorphous phases.
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction