I have the XRD of pod and husk from one tree, the materials present amorphous halo in 16 and 22º, and two sharply peaks in 36,4 and 42,7º. How can I attribute these peaks? I don´t find any XRD with similarity in the literature.
If the sample holder is Aluminum one would expect sharp reflections with Copper radiation at:
38.47 100
44.72 48
65.095 31
78.23 36
where the second column indicates the relative intensities.
Marcelas angles of 36,4 and 42,7 are rather far away for a good (?) diffractometer. As both reflection are off by 2 degrees, Aluminium seems unlikely to me. Of course, if the sample does not absorb the x-rays very well the sample holder is hit at a lower position compared to the sample. this will shift the observed reflections to lower angles. In my experience though, a shift of 2 degrees would go along wiht a widening of these reflections.
Marcela, you need to specify more accurate information:
What are the relative intensities of these reflections?
What is their width expressed as full width at half maximum. For a good diffractometer these width should be around 0.2 degrees.
Are there further sharp reflections?
If so do they match the Aluminium positions with similar shift and relative intensities
il faut faire une analyse élémentaire par XRF ou EDS et essayer de voir si les pics correspondent a un ,deux éléments ou bien à la combinaisons des ces éléments.si ça marche pas envoyer moi la collecte et je vais essayer de l’interpréter .
What are these values in terms of reciprocal nano meters?
May be the sample is mixture of two materials. Once you get sharp peaks you cannot say your material is totally amorphous. These peaks may be from unintentional crystalline impurities or you sample is not amorphous. Impurities may be due to improper handling during sample collection and analysis.
Hi Marcela,
up front I am not that familiar with minerals or crystalline material observed in tree material.
However, two sharp reflections are rather few to pin point the pattern down to a unique solution. You did not specify, which radiation you used for the diffraction experiment. This is absolutely necessary to look up the diffraction peaks in a data base.
A quick search with Copper radiation yields too many possibilities, Common minerals that the search finds are feldspars and pyroxenes. Beats me if these are ever found in tree mater???
As you state that the peaks are sharp, I would be surprised if there were not many further ( possibly weak but sharp) peaks. Your best bet is to run the experiment again, with some 5 to 10 times the exposure time. Such a pattern one can then run through a search program to identify the phases. I am not in the lab next week, but if you sent me the long exposure pattern, I can run it through our programs.
Ideally, you need to atleast guess what are the elements present in your sample. If you can dissolve your sample in a medium, you can do an ICP (induction coupled plasma) analysis and semi-quantitatively find out the elements. The inorganic material present might give you a clue into the XRD peaks. Alternatively, you can put your biomass in and conc HCl solution to see if there is any metal value which leaches out (change in colour). Dilute the solution and do an ICP analysis to see of any metal is present.
What is the sample holder made of? Those two peaks are close to aluminum
What is your sample holder made of? Those two peaks are close to aluminum.
I agree that you are probably seeing your sample holder. The amorphous halos correspond to cellulose, PDF 030289
If the sample holder is Aluminum one would expect sharp reflections with Copper radiation at:
38.47 100
44.72 48
65.095 31
78.23 36
where the second column indicates the relative intensities.
Marcelas angles of 36,4 and 42,7 are rather far away for a good (?) diffractometer. As both reflection are off by 2 degrees, Aluminium seems unlikely to me. Of course, if the sample does not absorb the x-rays very well the sample holder is hit at a lower position compared to the sample. this will shift the observed reflections to lower angles. In my experience though, a shift of 2 degrees would go along wiht a widening of these reflections.
Marcela, you need to specify more accurate information:
What are the relative intensities of these reflections?
What is their width expressed as full width at half maximum. For a good diffractometer these width should be around 0.2 degrees.
Are there further sharp reflections?
If so do they match the Aluminium positions with similar shift and relative intensities
As suggested in some previous answers the most likley explanation is that the two sharp peaks are from a metal, most likely the holder material (high symmetry phases such as metals have few peaks). Since your sample is organic it will have low mass attenuation so its not uncoomon to "see" the metal of the holder, although your peaks are considerably displaced from the expected positions for aluminium (with Cu radiation, but close to W lines for Al) displacement could result from the above scenario sinnce the base of a metal holder is not on the focusing circle. Try runiing an empty holder for comparison.
Mineral inclusions are also not uncommon in wood. The common is silica but I have seen many others.
These peaks are due to some crystallites of lignocellulose polymer in plants
I agree with Abhishek Lahiri & Stephen Hillier.The peak may be due to silica.
Marcela, Have you treated your sample (pod and husk) before the XRD such as heating / acid digestion. If heat treated you must look for peaks of silicates (SiO2). Sharp peaks may be due to some metal/oxide contamination during pre-treatment or sampling (eg., grinding/milling). This is apart from the chance of interference due to sample holder (as said by others) or contamination from sample holder too. Give a thought about sampling process for possible contamination and you may find a clue.
Marcela, if you have only two peaks and you have no information on a chemical composition and other additional data (for example, what are chemicals, which were used as fertilizers) your attempts of phase identification using only XRD data will be chiromancy.
Marcela, you can see from this discussion that two peaks in a XRD diffraction pattern are not enough to identify the material. In the discussion many hints came up how you should proceed.
As you have observed two peaks only at this time at fairly high angular positions, a material with small lattice constant like a metal is a likely culprit. Silica has its strongest reflection at 26.638 degrees, If you do not see that peak your phase is not silica.
To identify the material do the following steps:
Check the current pattern, are there further weaker reflections? If you find some five in total the search programs might find the material.
What are the relative intensities,
what are the peak width?
Rerun the experiment with a different sample holder (Brass versus Aluminium, or even a polymer holder) and much longer exposure.
Check the sample preparation routine to ensure that no impurities can contaminate the sample.
In a report to this discussion, include info on the experiment like
Diffractometer geometry, Radiation, type of sample holder, sample thickness, Sample preparation routine.
Phase identification from a list of diffraction angles alone is tedious, you will need somebody who can run the diffraction pattern through a phase identification program. At least post peak positions and relative intensities.
Dear Madam,
Make a diffraction of the support itself. Substract possible peaks from the diffractogram and see what happens.
Professor George Arghir
Most likely reason for these peaks are the sample holder. As suggested by others, make an empty sample holder run and it will clear the picture.
I agree that the metal support is a possibility. However, I have been doing XRD of biomass for a while, with samples in a capillary tube (fiber diffraction, no metal support), and sometimes strange sharp peaks appear. I already found quartz that could be attributed to soil residues, wax from the plant epidermis, and metal residues from biomass processing machinery. Sometimes just moving a bit the sample position makes the XRD peaks disappear, because the few contamination particles may move outside of the area that is being analyzed.
Carlos, It is interesting to note that by moving the sample position you are able to get rid of such peaks ! Just for a clarification, are you spinning your capillary while doing XRD to avoid any possible orientation effects ?
Why dont you try for carbonates? Further generally the material may contain Ba, and any 3d elements while grwoing the plant. There is little bit chance for silicates and mostly for carbonates.
These two peaks sound very much like aluminum. Do you have an aluminum sample holder?
Please do the following:
1. Mount your sample on glass sample holder so that you do not get extra crystalline peaks from the sample holder or you can take pattern of sample holder alone to excluse the contributions from sample holder.
2. If you are using any adhesive, make sure that gives only amorphous peaks.
3. As mentioned by EL.Aleem, specify the target you are using.
4. Yes, you should upload the diffractogram.
5. You should check whether any kind of impurity introduced in the process before taking pattern.
Marcela, many people believe that peaks appeared from a bottom of your aluminum cuvette. If it so, you can estimate the value of shift of a peak positions with using following formula:
∆2θ=(-114.6∙s∙cosθ)⁄R
where s is displacement, R is goniometer radius, and θ is peak position.
In your case ∆2θ is about 2°and depth of aluminum cuvette is about 3-4mm (for goniometer radius about 150mm and 217.5mm)
Hi Marcela,
These values (if in Cu radiation) are very close to titanium nitride (TiN). Although this would be very rare in nature, is it possible that you contaminated the samples during collection? Maybe using titanium drill bits? Or while grinding? If you have a 3rd peak at ~61.8 that may be worth considering.
I want to thanks for all!
I´m pos-doc researcher, and I´m working with some data that it´s not my work, but they are data obtained by other alumn...I dont´have so much informations...but the lamp is Cu...and the sample holder is made by quartz...
Than, I think those peaks are due for quartz...
Because I did XRD for the same samples in another equipment , and these peaks dont appear.
Thanks for all!!!
Those peaks are not due to quartz. Have you tried to match them to Graphite or turbostratic graphene? Is this bio-char?
If the peaks disappear when the quartz is removed, then the conclusion should be correct. Right?
Why don't you post the two diffractograms in question along with that from a "known standard" using identical apparatus?
R. B. Neder! "angles of 36,4 and 42,7 are rather far away for a good (?) diffractometer. As both reflection are off by 2 degrees, Aluminum seems unlikely to me."
It would be tough to preclude Aluminum without reviewing the diffractogram. The example below illustrates a series of linear conventional diffractograms from a well aligned Rigaku MiniFlex desk top unit. The diffractograms were aligned using the Aluminum holder diffraction peaks at 38 and 45 degrees (approx.) as the "known standard". https://www.flickr.com/photos/85210325@N04/10888339173/in/photostream/lightbox/ If you observe the "off-set" needed to attain this match, you'll notice the variation of 1-2 degrees. So unless we have the sample diffractogram and one from a "known standard" for identical settings of the diffractometer, we would still be guessing.
For more details and specifics regarding the figure below see:
https://www.researchgate.net/post/Is_this_a_reasonable_way_to_eliminate_effects_of_sample_surface_misalignment_with_the_diffractometer_axis_Theta-2Theta_Diffractograms?_tpcectx=home_feed
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