Combined analysis: general principles and theory. Luca Lutterotti

Transcription

1 Combined analysis: general principles and theory Luca Lutterotti

2 Needs SOLSA project (EU H2020): mining/raw materials mineralogy and composition of drill cores (phases + elements) automatic scanner (hyperspectra + XRD + XRF + Raman) automatic analysis, no operator clouds operating

3 tween the second half of the fifth and the first half of the sixth century AD. In the nearby area also, animal bones have been found. As to these latters, no conclusive hypotheses have been made on their origins, for the lack of a reliable archaeological context consequent to the already mentioned, uncontrolled disruptions of the site. In association with the undamaged tombs, several objects from funeral ornaments have been found. The interest of the present study is concentrated on two of them, featuring as a common aspect, the use of gilding to decorate part of their surfaces with a gold layer. These items turned out to be made of a copper and silver alloy, respectively. Of the different gilding procedures [3], fire gilding [4] seems to be the one used for the selected items. A common aspect of such approach is the usage of a gold amalgam, a paste made of Au and Hg, whose consistency can be varied by suitable additions or subtractions of mercury. In all cases, the final step of archaeological samples. Macrographs of the archaeological artefacts considered in the present Fig. 3. The investigated have been conducted on the face/side of the specimen appearing in the relevant picture. a) ID 1122; b) ID the manufacturing is a thermal treatment of investigations a few minutes, conducted at an estimated temperature of C, thus below the boiling point of mercury, equal to 357 C. The main reason why these finds have been selected is evidences in the perspective of further systematic investigations of the In Table 1 the res that, from an archaeological point of view, many they belong artefactstofound in the site in view of a reliable archaeological inwere conducted in a well established types, both having a broad terpretation distributionand in contextualisation. tefact in the experim Italian and European contexts [5], as concerns the respective relevant periods. The investigation presented herewith, regarding technological and materials aspects, is thus meant to set the basis for the application of a similar approach to a broader number of specimens available in several European collections that have not been analyzed from this point of view as yet. Needs Cultural heritage objects: non destructive analysis phases and chemical compositions fabrication processes, history 2 Sample description One of the finds that has been investigated is a buckle, code-

4 general principles and theory

5 Pattern fitting: the Rietveld method Least squares minimization of:

6 Combined techniques analysis XRD XRF/EDS Reflectivity 15 nm 25 nm CAP BUFFER SUBSTRATE

7 Combining XRD/XRF/XRR Goal: one structural model to fit XRD/XRF/XRR Composition, properties (refraction index, absorption etc.) are computed from the phases crystallography and layer structure Main advantages: In XRF: correct absorption calculation (matrix), intensities from XRD or XRR (for GIXRF) In XRD: more sensitivity to composition, mixed site occupations In XRR: unique solution

8 Theory For GIXRF we start from De Boer formulation: AuLα Au/Si multilayer SiKα

9 Multilayer example (Leti, Grenoble) Å In2O Å Ag Å In2O3 Stress GIXRF Si wafer XRR XRD

10 Fluorescence spectra calculation In Ag Si

11 Cement: XRD-XRF combined analysis (and experiment) INEL Equinox + Si drift XRF detector, Cu radiation + Ca Si Ar K Ti Cr Mn Fe Combined Rw(%): 4.8 (3.9 for XRD, 6.9 for XRF) Wt(%): C 3 S=43.5±1.4, C 2 S=27.2±1.4, C 3 A=11.0±1, C 4 AF=8.8±0.3, Calcite=2.5±0.5, Rutile=0.4±0.02, Al 2 MgO 4 =6.6±0.4 Chemical analysis: Ca/K=0.9836(8)/0.0164, Mn(C 4 AF)=0.0354(5), Cr(C 4 AF)=0.0101(3)

12 Equinox 3500 in Trento θ/θ INEL goniometer Mo microfocus tube ImXPAD detector Si drift X123 detector

13 Alpes coin Cu K lines Ag L lines Fe K lines Pb L lines

14 Dolomite rock

15 Kaolinite: modulated disorder Kleeberg, The reality: Ufer, Bergmann, CMS 05 C * b * l = 3 l = 2 l = 1 h = 0 h = 1 l = 0 h = 2 k = 3 k = 2 k = 1 a * k = 0 28 Kogure & Inoue, 2005

16 Kaolinite XRD (Mo X-ray)

17 Kaolinite XRF (Mo X-ray)

18 Depth profiling data fit θ/2θ

19 New instrument configuration Added: INEL CPS 120 Monochromator 1D

20 Calibration XRD: channel-2theta calibration XRF: filters and air path absorption Dair~2.5 cm

21 Detector absorption/efficiency Ar absorption Energy (KeV)

22 Old calibration: Si-PbTiO 3 XRD with Cu radiation Mo with no monochromator

23 75%Si-25%PbTiO 3 milled 14h Al sample holder Dair=2.395 cm 16.6(2)wt%PbTiO3 hybrid (custom+xraylib) Si Ti Fe,Cu W

24 Bad news: XRF is affected by absorption contrast too Good news: quantitatively is the same as XRD

25 Absorption contrast The largest source of residual error in QPA by XRD is due to microabsorption Occurs when sample contains a mix of low & highly absorbing phases and grains in one of the phases are bigger than a critical value (~1 micron) High absorbers: Beam absorbed in surface of grain Only a fraction of the grain diffracting Intensity under-overestimated low QPA Low absorbers: Beam penetrates further into grain Greater likelihood of volume diffraction occurring Intensity over-estimated high QPA

26 The Brindley correction The correction equation: where τi is given by Brindley in a table and the following formula is fitting it well (spherical particles): Brindley G. W.: A theory of X-ray absorption in mixed powders. Philos. Mag. 36, (1945)

27 In Maud For each phase: Edit and under microstructure: Select the Brindley microabsorption model In Options select the proper Brindley model Set the Grain Size for micro absorption correction to your estimated grain size (not the crystallite value), don t refine it Run again the refinement for quantitative phase analysis and check if the volume fractions have changed