A potential pitfall is preferential orientation by sample inhomogenity (e.g., not well enough grinded crystals) when filling a capillary sample holder/transmission geometry (sample is between X-ray source and detector) vs. Though the blue trace looks like to be better in terms of signal/noise ratio than the green one, the two traces include differences (presence/absence of signals) which can not fully attributed to variation of Cu/Co only. There equally are many mathematical methods to discern the pattern of noise from pattern of signals and dedicated programs (e.g., fityk) before one even starts to assign the diffraction peaks. An other plausible reason that green and blue trace in your superimposed diffraction pattern appear moved against each other are different strategies to counter (as in exclude a priori by experimental design) e.g., by variation of the time of exposure to collect intensities, averaging multiple single recordings to cancel out noise in intensity while varying along the $2\theta$ scale. They differ in their sensitivity for X-ray radiation (which equally depends on the wavelength used in the experiment). Again, depending on the target material of the X-ray tube and thus characteristic emission spectrum, both design and material for the monochromator varies (e.g., for Mo radiation, graphite) widely.Ģ.) To record the diffraction signal, you either a point detector (similar to a Geiger counter which moves in respect to X-ray source and sample), or a fixed CCD array (similar to a blown-up camera, horseshoe like bent around your sample). (It just so happens that these interplane distances are about of the wavelength of X-ray radiation given a well suited repetitive pattern, diffraction equally may be observed with visible light (say scale of about $\ce$), or even sound.)īoth single crystal (XRD) as well as powder (PXRD) diffractometers go great lengths to pick and select only the characteristic wavelength for the experiment. The underlying principle for the diffraction experiment is the Bragg equation, $n\lambda = 2d \sin(\theta)$ where $n$ is an integer, $\lambda$ the wavelength of the X-ray radiation, $\theta$ the glancing angle of the diffraction experiment, and $d$ the distance of the lattice planes characterized. You don't need to use solid metals, indeed liquid metal target like molten Ga or In offer X-ray sources of high brilliance (though smaller in diameter than conventional tubes). This is why you read experiments described as using e.g., Cu $K\alpha$, or Mo $K \alpha$ radiation. On top of this you have a number of sharp emissions which are characteristic of the element's relaxation of inner (non-valence) electrons. Is it reasonable to presume that the instruments have been mixed up in the naming files because the blue trend (Co emission XRD2) is lower than the green trend (Cu emission XRD1)?ġ.) Assuming you use a cathode tube as source for the X-ray radiation, the target material emits bremsstrahlung what (on first approximation)* looks like a continuous emission (: How could I know quantitatively if an XRD emission source is good/suitable or bad/unsuitable for analysing samples containing iron (or any other element) components? How do the different emission profiles affect the diffraction patterns for this sample and what is going on physically?ĭoes the difference in emission profiles explain the higher background, translated 2 $\theta$ positions, both, neither, or only one of the differences seen between the patterns? Looking at the following diffractograms where the blue trend is from XRD1 (D8A) and the green trend is from XRD2 (D8D) I am surprised by the stark differences in pattern, namely the transpositions of the background (overall elevated intensities) and 2 $\theta$ positions (there seems to be a lag between the patterns). Assuming I've read and analysed the bulk XRF analytics right, the sample seems to contain mostly phosphorus at 45.2 wt% and manganese at 23 wt% (which I presume comes from the clay and soil covering used to contain tailings etc.) with only 1.3 wt% coming from the iron itself.
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