XRD for analysing powders

31st December 2015

Posted By Paul Boughton

Analysis of a pure mineral. The top hit for this sample is Heazlewoodite, a nickel sulphide mineral
The upper scan is identified as albite. The lower scan has the same albite peaks, as well as a number of peaks from a second phase, identified as microcline
A multiphase sample. This sample was run more slowly than the others to get higher intensity, which makes it easier to effectively identify many of the peaks. Major phases include quartz, halite, clinochlore and either illite or muscovite

Fast phase analysis of powders by X-ray diffraction. By Robert C Tisdale

X-ray diffraction (XRD) is an effective method for determining the phase composition of unknown crystalline and amorphous materials. In this study, data analysis was performed by comparing diffraction peak positions and intensity values obtained with a Rigaku MiniFlex diffractometer, with the reference patterns of known compounds maintained in the International Centre for Diffraction Data (ICDD) Powder Diffraction File (PDF). Routine characterisation is performed quickly with a minimum of operator involvement. Subsequent analyses, including quantitative analysis of identified phases, were easily accomplished.

The goal of this work was to quickly identify the major phases in a series of unknown mineral powders. Data reduction and Search/Match analysis was performed using the standard software package. Bulk samples were ground into fine powders using a mortar and pestle. Specimens were prepared from the samples by smearing them on glass slides coated with a thin layer of petroleum jelly. No special effort was made to control the preferred orientation in the grains.

The diffractometer software was able to identify the major phases of the minerals after little sample preparation and a short analysis time. The total time for the first two scans presented was 10 minutes. Increased analysis time would significantly increase the signal-to-noise ratio and would thus improve the detection limits of minor phases.

Data set 3 required a longer data collection time, since the peaks were not as intense as in the other samples. The data presented has been smoothed and background corrected. The stick patterns of the best search/match results from the PDF file are printed below each scan. ‘Good’ Search/Match results match both the position and the intensity of peaks, and there will be no unidentified peaks. Since many compounds have similar crystal structures, Search/Match results will list several ‘good’ matches. Additional information about the sample may be needed to definitively identify a phase.

A modern benchtop X-ray diffractometer such as the Rigaku MiniFlex, combined with a modern analytical software package, is an effective tool for phase identification of unknown mineral samples. Clear interpretation of the presence or absence of various phases may be performed quickly and with a high degree of confidence. Phase identification was easily performed, even with quick data collection scans that have high statistical noise. Specimen preparation for most standard materials was minimal since chunk materials – as well as powder samples – can be analysed.

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Robert C Tisdale is with Rigaku





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