International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.9, pp. 368-369

Section 3.9.10.3.5. Element analytical standards

I. C. Madsen,a* N. V. Y. Scarlett,a R. Kleebergb and K. Knorrc

aCSIRO Mineral Resources, Private Bag 10, Clayton South 3169, Victoria, Australia,bTU Bergakademie Freiberg, Institut für Mineralogie, Brennhausgasse 14, Freiberg, D-09596, Germany, and cBruker AXS GmbH, Oestliche Rheinbrückenstr. 49, 76187 Karlsruhe, Germany
Correspondence e-mail:  ian.madsen@csiro.au

3.9.10.3.5. Element analytical standards

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XRD-based derivation of elemental abundances relies on (i) the QPA abundances, and (ii) the assumed or measured stoichiometry of the crystalline phases. The accuracy of the QPA result may then be evaluated by comparing the calculated elemental abundances with those determined by traditional chemical-analysis techniques. However, for the best level of agreement, this method requires that the composition of the crystalline phases be well defined. A complication, in particular for minerals, is that idealized compositions may be reported but do not necessarily match the actual composition of the species present in the sample. Where possible, detailed phase analysis using microbeam techniques should be undertaken to establish the true composition for each phase. A complication that serves to decrease the agreement is that chemically based compositional analysis does not distinguish between crystalline and amorphous phase content, while the diffraction-based QPA usually measures only the crystalline phases. Generally, the composition of amorphous phases may not be known accurately and even highly crystalline material can contain amorphous components because of non-diffracting surface layers of the grains (Cline et al., 2011[link]).

An example demonstrating the level of agreement that can be achieved is that of the iron-ore certified reference material SX 11-14 from Dillinger Hütte (Fig. 3.9.22[link]). The material is moderately complex and consists of nine distinct mineral species. The data were measured with Co Kα radiation and analysed using Rietveld-based QPA in TOPAS (Bruker AXS, 2013[link]). The phase abundances are converted to elemental and oxide compositions for comparison with the certified elemental analyses (Table 3.9.6[link]). There is excellent agreement between the XRD results and the chemical analysis with bias values better than ±1 wt%.

Table 3.9.6| top | pdf |
Compositional analysis of the Dillinger Hütte iron-ore certified reference material SX 11-14, (i) derived from QPA results, taking into account the nominal stoichiometry of the phases (XRD) and (ii) the certified analyses (Cert) (Knorr & Bornefeld, 2013[link])

Phasewt% FeFeOSiO2Al2O3MgOCaOK2ONa2OC
Haematite 0.37   0.26
Goethite 3.86   2.43
Magnetite 85.97   62.21 26.68
Quartz 5.73   5.73
Gibbsite 0.71   0.46
Talc 1.79   1.13 0.57
Orthoclase 0.30   0.19 0.05 0.05
Albite 0.89   0.60 0.18 0.10
Calcite 0.40   0.22 0.19
      Fe FeO SiO2 Al2O3 MgO CaO K2O Na2O C
    XRD 64.89 26.68 7.66 0.70 0.57 0.22 0.05 0.10 0.19
    Cert 65.55 27.20 7.47 0.27 0.56 0.42 0.06 0.08 0.12
    Bias −0.66 −0.52 0.19 0.43 0.01 −0.20 −0.01 0.02 0.07
[Figure 3.9.22]

Figure 3.9.22 | top | pdf |

Output of Rietveld refinement and results of QPA for the iron-ore certified reference material SX 11-14 from Dillinger Hütte. The data were measured with Co Kα radiation.

References

Bruker AXS (2013). Topas v5: General profile and structure analysis software for powder diffraction data. Version 5. https://www.bruker.com/topas.Google Scholar
Cline, J. P., Von Dreele, R. B., Winburn, R., Stephens, P. W. & Filliben, J. J. (2011). Addressing the amorphous content issue in quantitative phase analysis: the certification of NIST standard reference material 676a. Acta Cryst. A67, 357–367.Google Scholar








































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