I need to measure the lattice constants of graphite fiber using xrd. Based on the xrd spectrum, only 002 peak is clearly visible. The 004, 110, 112 & 006 peaks are so weak. Any suggestion to improve these weak peaks? Fyi, the parameters were 40 kV, 30 mA, scan speed 0.25 deg/min, step 0.02 deg, plus Ni filter Installed. Thank you in advance for your suggestion(s).
pLEASE CX THE ARTICLE: HP Klug, LE Alexander - 1954 - tocs.ulb.tu-darmstadt.de
XRD would be most practical way of measuring lattice parameter.
XRD analysis of graphite materials always give stronger 002 peak due to preferred orientation of graphite. The broadening of peaks also appear greater than normal due to transparency of graphite to Xrays. Disperse graphite fibres in ethanol or acetone by sonication and then drop a tiny amount of solution with micro pippette onto single crystal zero background silicon sample holder/substrate. Then perform XRD as usual and use 002 peak to calculate crystallite thickness using Scherrer equation, if below 200 nm, and use other peaks to calculate lattice constants. Perform rietveld refinement of your data to calculate lattice constants.
Thank you all for your input, but I believe I didn't make myself clear on this one.
My problem is not on how to measure the lattice constants and crystallite size but rather on how to make the peaks clear or how to properly prepare the graphite fiber for xrd analysis. Without clear peaks, the calculation of lattice constants and crystallite size by using bragg's law and scherrer's equation will produce very high error.
Mr Ravikumar, I did not do capillary setup because I don't have the capability to do so. Any other option?
Mr Mohsin, I agree with you the difficulty is due to the low absorption coeff of graphite for xray that it penetrates deep into the sepcimen. I can get 002 peak easily, but the other peaks are the problem. They are too weak.
You can try XRD in transmission mode rather than using conventional Bragg-Brentano geometry. You will definetly loose some resolution in this geometry, however, you have larger pathlength in transmission geometry.
Disperse fibres in the binder and then try XRD or increase time per step or reduce scan speed
Neutron diffraction is the best choice. But if u dont have the access, transmission cud be the first to pick, In-plane GIXRD, but if there's only BB geometry than zero background is the one. Use 0D detector or reduce the linear length detector.
Well it's all described by Mohsin and Ravikumar...
If it's nano fiber along 001, then the size is directional dependent, it has anisotropic broadening .
I agree that the best was is a transmission gemoetry with a home diffractometer. If you don't have, you can try to enhance the low intensity peaks by using a low background sample holder. Si (510) is the best but you can also use a piece of Si wafer (100) . If you use Si (100), stop the measurement at 60º 2theta (with copper radiation) to avoid the 400 peak of Si. You must increase the time per step to reduce the noise and thus enhance the low intensity peaks. You can reduce the sample orientation (if it is present) by sieving the powder onto the low background sample holder.
Dear Maykel, thank you for your jnput especially on the anisotropic broadening issue.
Francesc, great idea on using Si wafer for reference. Fyi, I used Si powder (electronic grade 99.999%) for the xrd. Should try using Si wafer after this. Thanks a lot!
The basic challenge you have is the "spatial blindness" of the conventional XRD techniques you are using. This method neglects the rich 2D XRD signal ever present in all XRD observations. This conventional method is limited to only the equatorial scan with a 0D point counter. The antiquated Debye-Scherrer film technique would serve better perhaps in this case of your graphite fiber sample.
Here are some examples of transmission XRD images elucidating "preferred orientation" in Kevlar fibers and aluminum foil. The examples also include a comparison between conventional linear diffractograms as you are using and 2D transmission imaging for aluminum foil. Just by lining up the graphite fibers to maximize your signal you are unquestionably introducing "preferred orientation". The Kevlar fibers were only loosely bunched together in the beam to maximize diffracting volume.
Just imagine trying to precisely determine the lattice parameter without visualizing the whole Debye-Scherrer ring :-) Not trivial!
https://www.flickr.com/photos/85210325@N04/7975835813/in/album-72157632728981912/
https://www.flickr.com/photos/85210325@N04/7944785794/in/album-72157632728981912/
Mr. Ravi,
Thanks for the hi-light on the preferred orientation issue. The old conventional xrd equipment is the only option I have, guess I have to live with it.
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