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XRF and XRD Combined Application (2 replies)

Tony Verdeschi
11 months ago
Tony Verdeschi 11 months ago

One XRF manufacturer has had a combined XRF and XRD for the cement industry for a long time and I think there are a now few others. I am curious about peoples experience with these combo instruments. There must certainly be trade offs. Please keep your responses non vendor specific. The aim is to start a conversation about the technology not a conversation about a vendor.

Alan Carter
11 months ago
Alan Carter 11 months ago

My experience is not with a combo instrument, but with separate instruments running the same sample independently. XRF gives you elemental information, but can tell you nothing about structure. It may be valuable to a corrosion scientist to know if he has FeO, Fe2O3, or Fe3O4. Your assumed normallization can be off in XRF if you don't know the exact matrix, but this is where XRD data can help identify what materials make up your matrix, if there is confusion. (For example, you might have a water-oil mixture and the diffraction pattern can help identify whether the majority of the matrix is water or oil. Some venders may allow you to split the matrix.) XRD can only tell you structures, not elements. I can have two very similar diffraction patterns but not be able to identify the compound (especially if it is mixed with a large number of other compounds) without elemental data. Or the lattice parameter for calcium carbonate may be off slightly, but one does not know if this is due to sample mounting/alignment or perhaps there is magnesium substitution, causing a shift in the lattice parameter.

I am not sure about specific vendor's combo instruments, but I suspect that one of the most common tradeoffs is time versus information. Both XRD and XRF data can be collected at the same time, but some of these instruments cannot identify anything lower on the periodic table than say Ti, if the sample is not housed in a vacuum environment.

John Koenig
11 months ago
John Koenig 11 months ago

We sometimes use coupled XRF/XRD analyses in my university teaching and research. For XRD I have a large lab XRD and a transmission geometry benchtop system. The benchtop XRD has a small EDXRF built into it, which has some capability, but it's best for Row 4 of the periodic table.

The large XRD is used for structural determinations, and so far we haven't needed to couple XRF/XRD analyses that often. The main research it has been used for over the past 5 years has been >1100 analyses of deep sea organisms (for ocean acidification research), and about the same number for heavy metal stabilisation research. Then the physics people use it for whatever they do (diamonds, optic fibres etc) and of course the geologists to help with rock identifications.

The small XRD is mainly for teaching soils, mineralogy and environmental chemistry, and we use the EDXRF in it to help with mineralogical ID's. The small XRD is wonderful in this role, because students can prepare and run samples easily and cheaply, and they can learn about mineralogy and elemental composition in one measurement. I'm just back from a two week teaching field trip, where my 2nd year students prepared and ran 60 soil samples, combined with a whole lot more work in sedimentology.

So, regarding combo instruments, I do occasionally use XRF/XRD in combination, but I don't really have a great *need* for a combo instrument. If I had one, I'd use it - but right now I can run powders in both my regular XRD and then EDXRF sequentially - and high sample throughput isn't so much of a problem. I put about 2000 samples/year through my EDXRFs and only about 500/year through my XRDs - so combo machines are more of a curiosity, at least for my purposes.