The attached image shows a 28 day XRD spectra of a mix containing Cement, Fly ash, nano silica and alumina powder. There is an amorphous hump between 5 and 10 deg 2theta. The peak that i have identified in search/match option central to that hump is tobermorite. Just wondering if tobermorite shows a sharp peak or an amorphous hump and if the selection made is right. Also, at 29.4 deg 2theta another C-S-H peak is identified with a broad peak i.e. Rosenhahnite. Could anybody please help me in checking if the selections made are correct? The search/match was done with PDF2-2001 database using Bruker's Diffrac.eva software. The instrument used for data collection was Bruker's Endeavor D4 with X-ray source of CuKa.
Dear Rajeev,
Please do an empty scan of your sample holder with any glue, wax or solvent that you might have used and see if you reproduce some of the low angle scattering. The low angle scattering is most of the time organics, air (with particles) and similar non-crystalline materials.
Regards,
Dear Rajeev,
Please do an empty scan of your sample holder with any glue, wax or solvent that you might have used and see if you reproduce some of the low angle scattering. The low angle scattering is most of the time organics, air (with particles) and similar non-crystalline materials.
Regards,
Most probably your humps are came from sample holder. I agree with Riza: scan of sample holder can answer if the hump is really sample holder or it is from sample.
Tobermorite even in autoclaved samples often doesn't show really sharp peaks (like e.g. your quartz-peak). On the other hand the shape of your hump seems not to beexplained with just one phase. Keep in mind that tobermorite is just one kind of C-S-H phase, to get an overview have a look at :
I. G. Richardson: The calcium silicate hydrates. Cem. Concr. Res. 38 (2008) 137–158.
And without having more than just a hump instead of an unsharp peak it is not possible to identify a phase. Still your guess might be a good starting point, but there could also be multiple C-S-H phases contributing to that shape.
A peak at an angle of ~29.4° 2 theta using Cu radiation is in such systems often calcite, if you did not work under CO2 free atmosphere (e.g. a glove box).
For further identification of phases a look in the SEM would be of great help, even though very small, C-S-H phases show typical shapes. And o course as already mentioned, you should give some information of the sample preparation, especially on any additional components like wax or preparation on a low background sample holder (Si).
Do you jast need to identify these phases, or do you plan futher work like Rietveld refinements for quantification ? Then i would suggest doing it with the PONKCS method.
Are you using capton foil or similar to cover/keep your powder in the sample holder? If so, my guess is that it is the capton or whatever you are using, Definitely not originating from the sample, I would say. Phase identification looks ok, provided you don't need a more precise info.
Thanks Helen, Riza, KArina, Holger and Wolfgang for your valuable answers.
Dear Holger,
No wax was used in sample preparation. The sample holders were made of some metal probably bronze, i don't think they were low background sample holders. I plan to do rietveld refinement quantitative analysis. I will go through the article you suggested. That might be of help in the analysis part
I notice that your background levels are very high - 5000 counts, I wonder if the iron in the fly ash is causing you some fluorescence problems here with CuKa radiation. You might want to try adjusting the discriminator level in your detector. Which detector do you have?
Thanks for your reply Ian, we have Lynxeye linear strip detector installed on Brukers D4 Endeavor instrument.
Ok. try setting the Lower Level discriminator to 0.18 instead of 0.11, leave the window setting, double the count time to regain the lost signal, and see if this brings the background down. I doubt that it will have much effect on the amorphous hump you see, but it may help bring out smaller peaks from the background.
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