I did an XRD test for gypsum crystals which have a needle shape. One peak has much more intensity than others. I have other kinds of gypsum crystals which have been produced in other conditions and are very thin and more elongated. I did an XRD test but all of the peaks intensity were increased. In papers to prove this elongation which might be in (010) direction, they have showed that just the intensity of this peak (010) has increased. Why did the intensity of all of the peaks in my XRD patterns increase?
Do you have better suggestions?
The first effect is certainly caused by texture of your powder sample although I am a bit surprized about the statemant that only one has a higher intensity. Comparing with a simulated diffractogram all should be somehow affected by texture...
The second observation: you are talking about the counts, right? Same preparation? same crystal size? Chemically exactly the same phase?
You perhaps only observe another texture which decreases your big 020 reflection and increases all other. Ideal conditions assumed you can expect that the integrated diffraction intensity keeps (more or less) constant. There is no intensity which "disapears" somewhere.
But don't forget the background which can be enormous.... Are the backgrounds in both measurements comparable?
While I would like to see your XRD patterns, I can say that increase in peak intensity at the expense of other diffraction peaks is clearly an indication for crystallographic texture (preferred orientation). All peaks intensity increasing is an indication for "abundance" (quantitative - diffracting planes) effect. On the premise that all your gypsum samples have needle-like crystals and that what XRD "sees" is the cross section (in the smaller dimension) of the needle-like crystals then the diffraction peak width and not the peak intensity should provide information about crystal size effects. These size effects can be deduced qualitatively by merely comparing the peak widths (integrated peak breadth or FWHM) of the XRD peaks or quantitatively using rigorous line profile analysis. Both will provide you with information about the size (X-sectional) effects in the needle-like crystal gypsum samples and not effects due to length changes of the needle-like crystals....except the lengths of the needle are below 150 nm and changing within the range 2 nm and 150 nm. I can also say that optical microscopy is certain to reveal and confirm any elongation of the needle-like crystals in your gypsum samples. ....(are the samples in powdered form?)
To get the most and best out of the RG network, please post the subject data along with all the material details including sample morphology and other relevant data (SEM, TEM etc.).
Dear Taher,
Could you upload your XRD data to get elements on which to base an appropiate comment about your results?
Regards,
Jose Elizalde
I think it is an orientation effect. Your needles are oriented in your capillary, if you use capillary for instance.
Thus, try a better grinding.
"How can I prove elongation of gypsum crystals by XRD?"
Since the question has some fundamental connotations, I'm interested despite the originator MIA. Knowingly introducing "preferred orientation" may be an idea to establish your hypothesis as well. It may even be possible to estimate the "aspect ratio" of the "needle" like elongated constituents in these cases using XRD.
NDE! Simple! In situ (grinding may break the "needles") 2D Transmission Laue diffractogram with the powder sample on scotch tape or Aluminum foil. The Laue transmission method allows the observer to acquire "+" & "-" 2Theta simultaneously. This helps eliminate several instrumental errors including alignment of sampling VOXEL with the diffractometer axis. You may use photographic film to acquire such data and digitize with a ubiquitous (thanks to the Chinese) scanner. See example below of Kevlar fibers and Al foil using a real time 2D XRD Microscope. It is a "no brainer". The conventional diffractogram would be a convoluted, time prohibitive & imprecise method to use for your objective. Punny!
http://www.flickr.com/photos/85210325@N04/7975835813/in/set-72157632728981912
Here's Al foil by itself: http://www.flickr.com/photos/85210325@N04/7944785794/in/set-72157632728981912
Other examples:
http://www.flickr.com/photos/85210325@N04/8012716332/in/set-72157632728981912
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