Quantification of iron redox ratios in silicate glasses and melts by Raman spectroscopy

Transcription

1 Quantification of iron redox ratios in silicate glasses and melts by Raman spectroscopy B. Cochain 1,2, D. R. Neuville 1, V. Magnien 1,2, G. S. Henderson 4, and P. Richet 1 1 Physique des Minéraux et des Magmas, CNRS-IPGP, 4 place Jussieu, Paris Cedex 5, France cochain@ipgp.jussieu.fr 2 SCDV-LEBV, CEA Valrhô, Centre de Marcoule, 327 Bagnols-sur-cèze, France 3 Laboratoire Structure et Propriété de l Etat Solide, Université de Lille 1, Villeneuve d Ascq, France 4 Dept of Geology, University of Toronto, Toronto, Canada

2 Determination of iron redox equilibrium Geological interest Iron, most abundant transition element Corning, Inc. Th Staudacher IPGP

3 Determination of iron redox equilibrium Industrial interest : - glass production - nuclear waste storage glass

4 Determination of iron redox Lack of in situ data Knowledge on iron redox kinetics =>XANES spectroscopy (limited access) Raman spectroscopy Calibration to quantify iron redox ratios In situ experiments possible Ready access

5 Compositions investigated SiO2 Al2O3 B2O3 Fe2O3 FeO CaO MgO Na2O Li2O Pyroxenes based Pyrox PyrNa PyrLi Borosilicates NB67.18Fe NB67.18Fe NB67.18Fe Alumino-borosilicate FAMA , , 2, Synthesis under different oxygen fugacities redox ratios Iron redox ratios : Wet chemical analysis Mössbauer spectroscopy Electron Microprobe analysis

6 Experimental conditions Effect of focus on Raman spectra 1 8 Bas-O Bas-3 Bas-6 Intensity, a.u. 6 4 With iron-bearing glasses : Strong decrease in intensity with the focus depth due to absorption Wavenumber, cm -1 Need to focus on the surface of the glass

7 Raman spectra analysis NB67.18 Raman spectra correction and normalization 'NB67.18' baseline Intensity Raman spectra Intensity Long correction (1977) Wavenumber cm -1 I = I obs " R Avec R = f(ν,ν, et T) Wavenumber cm 'NB67.18'! Baseline subtraction 'NB67.18' Normalized Intensity Intensity Normalization Normalized Intensity Wavenumber cm Wavenumber cm -1

8 Evolution of Raman spectra with mol% Feo Case of borosilicates.35.3 Fe 2 O 3 /Fe tot =,85 Normalized Intensity FeO content mol% FeO Wavenumber cm -1 With increasing FeO content : Apparition and increase of a band at 98cm -1 in borosilicates Shift to lower frequency of the 98 cm -1 band => [4] Fe 3+ -O bonds shared with Si

9 Evolution of Raman spectra with iron redox ratio borosilicates : NB67.18Fe5.16 Fe 2 O 3 /Fe tot Normalized Intensity Wavenumber cm -1 NB67.18Fe5 NB67.18Fe5R5 NB67.18Fe5R17,85,78,57 Normalized Intensity Fe 2 O 3 /Fe tot Wavenumber cm -1 With increasing Fe 3+ content: Evolution of the 98 cm -1 band Clear changes in Raman spectra for a given composition

10 Evolution of Raman spectra with iron redox ratio PyrNa.4 [4] Fe 3+ Normalized intensity Fe 2 O 3 /Fe tot Wavenumber cm With increasing Fe 3+ content: Evolution of the 915 cm -1 band in based pyroxenes Clear changes in Raman spectra for a given composition

11 Validity of the method : band assignement.5 NS 2, NS 2 Ti 1, NS 2 Fe 1.4 NS2 NS2Fe1 NS2Ti1 Normalized intensity [5] Ti Wavenumber cm -1 [4] Fe 3+ Distinct bands appear for Ti and Fe : - around 885 cm -1 for NS 2 Ti 1 => attributed to Ti (Mysen & Neuville,1995, Reynard & Webb, 1998) => Ti in five fold coordination according with XANES and Raman (Henderson & Fleet, 1995, Farges et al 1996, Reynard & Webb, 1998) - around 92 cm -1 for NS 2 [4] Fe 3+ 1 (Mysen et al.,1985; Magnien et al., 26)

12 Evolution of Raman spectra with iron redox ratio Deconvolution of Raman spectra Mysen et al. (1982) : Intensity, position, width : unconstrainded and independent parameters NB67.18Fe5 1.5 Increasing [4] Fe x1-3.5 [4] Fe Bands of Q n species (T = Si,, Al) NBO T NBO NBO BO Q NBO Q 1 NBO T NBO NBO Q 2 NBO T BO BO NBO NBO T BO BO Q 3 BO BO Q 4 BO T BO BO

13 Evolution of Raman spectra with iron redox ratio Alumino-boro-silicate : FAMA Proportions of diverse structural entities: Area ratio of individuel bands (Mysen et al.,1892; Mysen et al.,1984) 1.2 Fe O 3 /Fe tot =,83 Fe 2 O 3 /Fe tot =, x x Fe 3+ Fe Fe 2 O 3 /Fe tot = A( [4] Fe 3+ )/A tot Calibration equation Fe 2 O 3 /Fe tot = 6 *A( [4] Fe 3+ )/A tot -,34

14 Evolution of Raman spectra with iron redox ratio borosilicates : NB67.18Fe5 Proportions of diverse structural entities : Area ratio of individual bands (Mysen et al.,1892; Mysen et al.,1984) NB67.18Fe x1-3.5 [4] Fe 3+ Fe 2 O 3 /Fe tot y = x R= Fe 2 O 3 /Fe tot = A( [4] Fe 3+ )/A tot Area 97 / Area tot

15 Evolution of Raman spectra with iron redox ratio 1.8 Fe 2 O 3 /Fe tot PyrNa Pyrox FAMA NB67.18Fe5 NB67.18Fe Calibration : Area (Fe 3+ )/ Area tot for each composition => need to know two redox ratios (ideally the most reduced and most oxidized) and after we can determine intermediate redox states

16 Fe 3+ / Fe tot (autres techniques) Fe 3+ /Fe tot Kress and Carmichael Wet Chemical Microsonde XANES Raman Fe 3+ / Fe tot (Spectroscopie Mössbauer) Mössbauer spectroscopy Magnien et al. (24) Chem Geol et Magnien et al. (26) J Nucl Mat; Cochain et al., (28)

17 Evolution of Raman spectra with iron redox ratio 1.8 Fe 2 O 3 /Fe tot PyrNa Pyrox FAMA NB67.18Fe5 NB67.18Fe Area (Fe 3+ )/ Area tot => follow all other redox, and especially redox variation in T

18 Application : In situ determination of Iron redox ratio Normalized Intensity (a.u.) PyrNa RT 3s 6s 9s 12s 15s 18s 24s 3s 6s 9s 12s 18s 372s PyroxNa Wavenumber (cm -1 ) At 75 C => evolution of the 915 cm -1 band => progressive oxydation

19 Conclusion Clear changes in Raman spectra visible with the evolution of iron redox ratio for a given composition Gaussian band around 95 cm -1 assigned to the vibration of [4] Fe 3+ -O bonds, and not to T-O bonds (T= [4] Ti, [5] Ti or all other network formers) Empirical calibration between the area ratio of the bands in the Raman spectra and wet chemical analysis In situ determination of iron redox ratio

20 Thank you for your attention