I need to know about element percentage of fly ash. Is it SEM-EDX results is sufficient or should I go for XRF? Can anyone tell me which analysis is most important?
Thanks in advance for your valuable answer.
I guess the answer depends on the kind of element percentages. I think that for SEM-EDX, most quantitative results are from point counts (of an EDX map) and thus proxies volume percentages. So this method requires that you have a elemental map where you have a spectrum for each point so you can calculate area percentage for each major element. On the other hand, to get weight percentages requires calibration with standards which is difficult for SEM scale.
Dear Siva,
Matthew is right. But also using XRF (fluorescence excitation by x-rays) is very useful; however also here you have to calibrate your system carefully. The choice depends on which elements you are looking for and which type of system is available to you. With respect to precision I would have no real preference for one of the systems except the aspect of preferably avoiding having ash as a sample in a vacuum system such as in the case of SEM-EDX.
Respected Mr. Matthew Wehner and Mr. Gerhard Martens, Thank you, sir, for your valuable information.
Dear Siva Mani,
Go for ICP-MS(Inductively coupled Plasma) technique. It can even show you the heavy metals present. It gives you the complete profile.
EDX on SEM or on TEM is agood one for that if you need the accurate percentage
If your main concern is 'accuracy', then it really comes down to how well you have calibrated your systems. XRF can achieve higher precision and sensitivity than EDS but if it is poorly calibrated, the accuracy could be poor. Similarly with EDS if it well calibrated then even though the results may have less precision and sensitivity, the results could be more accurate. You also need to consider if you are looking at ED-XRF or WD-XRF. And again what type of detectors you have available in your EDS system.
One of the biggest issues is the sample preparation. As has been mentioned it is not wise to put ash into a SEM unless it is stabilised in some way. Consider also that for EDS the sample has to be homogeneous within the interaction volume. There should be no porosity, so no gaps between grains. The sample needs to be flat and polished to remove all topography as this would affect the geometry and therefore the results. Trying to do 'accurate' EDS on particles of ash is fraught with problems. However, if you can overcome them and get a good sample then it should be possible. Another approach might be to make a glass out your ash and analyse that rather than trying to get the powder in a suitable form. I would set up a grid of points and measure all then you can check for repeatability. Remember also to measure your own standards under similar conditions rather than rely on standardless analysis, in this way you can achieve a non-normalised semi-quant.
For XRF there are two ways to proceed with preparation, pressed powders or glass fusion, for fused beads it would give you major elements only as the dilution is high; the advantage is that the matrix corrections are less complex. Pressed powders would give you a wider range of elements, but the sample surface has to be perfect, the overlap and matrix corrections are more involved. Here is it essential to have measured your own standards and created a suitable calibration. You can then back analyse the standards to check that you are achieving your required 'accuracy'.
Ash will most probably be non-homogenous, so ED(x)S in SEM or TEM (not EDAX, as stated numerous times already) will be time-consuming and due to small size of the particles will demand some (enhanced) knowledge of the operator / intepretor. All instant analyses through recipies will most probably result in GIGO effect (garbage in - garbage out). But you can always get some % (weight or atomic), although with only little relation to your real sample's composition.
Read Ian's reply twice.
Ian J Slipper can you kindly guide me on analysis and interpretation of XRD and SEM analysis ?
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