Determination of iron redox

Quantification of iron redox ratios in silicate glasses and melts by

Raman spectroscopy

B. Cochain^1,2, D. R. Neuville¹, V. Magnien^1,2, G. S. Henderson⁴, and P. Richet¹

1Physique des Minéraux et des Magmas, CNRS-IPGP, 4 place Jussieu, 75252 Paris Cedex 05, France E-mail : cochain@ipgp.jussieu.fr

2SCDV-LEBV, CEA Valrhô, Centre de Marcoule, 30207 Bagnols-sur-cèze, France

3Laboratoire Structure et Propriété de l’Etat Solide, Université de Lille 1, 59655 Villeneuve d’Ascq, France

4 Dept of Geology, University of Toronto, Toronto, Canada

Corning, Inc.

Determination of iron redox equilibrium

Geological interest

Iron, most abundant transition element

Th Staudacher IPGP

Determination of iron redox equilibrium

Industrial interest : - glass production

- nuclear waste storage glass

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

Compositions investigated

SiO2 Al2O3 B2O3 Fe2O3 FeO CaO MgO Na2O Li2O

Pyroxenes based

Pyrox 53.17 12.71 19.85 14.27

PyrNa 52.53 12.56 17.16 12.33 5.42

PyrLi 54.04 12.92 17.65 12.69 2.69

Borosilicates

NB67.18Fe1 64.78 20.44 1.16 13.63

NB67.18Fe5 61.78 19.49 5.74 12.99

NB67.18Fe10 58.07 18.32 11.39 12.22

Alumino-borosilicate

FAMA 46.5 10,00 18.5 5,00 20,00

• Synthesis under different oxygen fugacities

≠ redox ratios

• Iron redox ratios :

• Wet chemical analysis

• Mössbauer spectroscopy

• Electron Microprobe analysis

Experimental conditions

Need to focus on the surface of the glass

Effect of focus on Raman spectra

With iron-bearing glasses : Strong decrease in intensity

with the focus depth due to absorption

0 2000 4000 6000 8000 10000

200 400 600 800 1000 1200

Bas-O Bas-30 Bas-60

Intensity, a.u.

Wavenumber, cm^-1

0 1 10⁴ 2 10⁴ 3 10⁴ 4 10⁴ 5 10⁴

0 200 400 600 800 1000 1200 1400 1600

NB67.18

Intensity

Wavenumber cm^-1

0 2 10⁴ 4 10⁴ 6 10⁴ 8 10⁴ 1 10⁵ 1.2 10⁵ 1.4 10⁵

0 200 400 600 800 1000 1200 1400 1600

'NB67.18'

Intensity

Wavenumber cm^-1

Raman spectra analysis

Raman spectra correction and

normalization

Raman spectra

Baseline subtraction

Normalization

Long correction (1977) Avec R = f(ν₀,ν, et T)

!

I = I_obs " R ⁰

2 10⁴ 4 10⁴ 6 10⁴ 8 10⁴ 1 10⁵ 1.2 10⁵ 1.4 10⁵

500 1000 1500

'NB67.18' baseline

Intensity

Wavenumber cm^-1

0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016

500 1000 1500

'NB67.18'

Normalized Intensity

Wavenumber cm^-1

0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016

500 1000 1500

'NB67.18'

Normalized Intensity

Wavenumber cm^-1

0 1 10⁴ 2 10⁴ 3 10⁴ 4 10⁴ 5 10⁴

0 200 400 600 800 1000 1200 1400 1600

NB67.18

Intensity

Wavenumber cm^-1

Evolution of Raman spectra with mol% Feo

• Shift to lower frequency of the 980 cm ^-1 band => ^[4]Fe³⁺-O bonds shared with Si

mol% FeO

With increasing FeO content :

• Apparition and increase of a band at 980cm^-1 in borosilicates

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035

500 1000 1500

Normalized Intensity

Wavenumber cm^-1

Case of borosilicates

Fe₂O₃/Fe_tot = 0,85

0 1 5 10

FeO content

0 0.0004 0.0008 0.0012 0.0016

850 900 950 1000 1050 1100 1150 1200 1250

Normalized Intensity

Wavenumber cm^-1

Fe₂O₃/Fe_tot 0.85 0.78 0.57

Evolution of Raman spectra with iron redox ratio

With increasing Fe³⁺content:

• Evolution of the 980 cm^-1 band

• Clear changes in Raman spectra for a given composition

0 0.0004 0.0008 0.0012 0.0016

500 1000 1500

NB67.18Fe5 NB67.18Fe5R17 NB67.18Fe5R5

Normalized Intensity

Wavenumber cm^-1

Fe₂O₃/Fe_tot 0,85 0,78 0,57

borosilicates : NB67.18Fe5

0 0.001 0.002 0.003 0.004

200 400 600 800 1000 1200 1400

Normalized intensity

Wavenumber cm^-1

Evolution of Raman spectra with iron redox ratio

Fe₂O₃/Fe_tot 0.99

0.83 0.82 0.56 0.27 0.17 [4]Fe³⁺

PyrNa

With increasing Fe³⁺ content:

• Evolution of the 915 cm^-1 band in based pyroxenes

• Clear changes in Raman spectra for a given composition

0 0.001 0.002 0.003 0.004 0.005

200 400 600 800 1000 1200

NS2NS2Fe10 NS2Ti10

Normalized intensity

Wavenumber cm^-1

Validity of the method : band assignement

Distinct bands appear for Ti and Fe :

- around 885 cm^-1 for NS₂Ti₁₀ => 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)

NS₂, NS₂Ti₁₀ , NS₂Fe₁₀

- around 920 cm^-1 for NS₂ ^[4]Fe³⁺₁₀ (Mysen et al.,1985; Magnien et al., 2006)

[5]Ti

[4]Fe³⁺

1.5

1.0

0.5

0.0

x10-3

1200 1100

1000 900

Evolution of Raman spectra with iron redox ratio

Deconvolution of Raman spectra Mysen et al. (1982) :

Intensity, position, width : unconstrainded and independent parameters

Bands of

Bands of QQ^{n n} species species (T(T = Si= Si, Al), Al)

BO

BO BO BO

T

QQ⁴⁴

NBO

BO BO BO

T

QQ³³

NBO

NBO BO TBO

QQ²²

NBO

NBO BO ^TNBO

QQ¹¹

NBO

NBO NBO TNBO

QQ⁰⁰

NB67.18Fe5 Increasing ^[4]Fe³⁺

[4]Fe³⁺

1.5

1.0

0.5

0.0

x10-3

1600 1400

1200 1000

800 600

400 200

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

x10-3

1600 1400

1200 1000

800 600

400 200

Evolution of Raman spectra with iron redox ratio

Proportions of diverse structural entities:

Area ratio of individuel bands (Mysen et al.,1892; Mysen et al.,1984)

Fe₂O₃/Fe_tot= A(^[4]Fe³⁺)/A_tot

Calibration equation Fe₂O₃/Fe_tot= 6 *A(^[4]Fe³⁺)/A_tot - 0,34

Alumino-boro-silicate : FAMA

Fe₂O₃/Fe_tot = 0,83 Fe₂O₃/Fe_tot = 0,27

Fe³⁺ Fe³⁺

1.5

1.0

0.5

0.0

x10-3

1200 1100

1000 900

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)

[4]Fe³⁺

Fe₂O₃/Fe_tot= A(^[4]Fe³⁺)/A_tot ^0.55

0.6 0.65 0.7 0.75 0.8 0.85 0.9

0.56 0.58 0.6 0.62 0.64 0.66 0.68 0.7

NB67.18Fe5

y = -0.78775 + 2.3539x R= 0.99523

Fe 2O 3/Fe tot

Area₉₇₀/ Area_tot

0 0.2 0.4 0.6 0.8 1

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

NB67.18Fe10 NB67.18Fe5

FAMA PyrNa Pyrox

Fe 2O 3/Fe tot

Area (Fe³⁺)/ Area_tot

Calibration :

for each composition => need to know two redox ratios

(ideally the most reduced and most oxidized) and after we can determine intermediate redox states

Evolution of Raman spectra with iron redox ratio

Magnien

Magnien et al. (2004) et al. (2004) Chem Geol Chem Geol et et Magnien Magnien et al. (2006) J et al. (2006) J Nucl Nucl Mat; Mat; Cochain Cochain et al., (2008)et al., (2008)

0 0.2 0.4 0.6 0.8 1

Kress and Carmichael Wet Chemical

Microsonde XANES Raman

0 0.2 0.4 0.6 0.8 1

Fe3+ / Fe tot (autres techniques)

Fe³⁺/ Fe

tot (Spectroscopie Mössbauer)Mössbauer spectroscopy

F e

/F e

Evolution of Raman spectra with iron redox ratio

=> follow all other redox, and especially redox variation in T

0 0.2 0.4 0.6 0.8 1

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

NB67.18Fe10 NB67.18Fe5

FAMA PyrNa Pyrox

Fe 2O 3/Fe tot

Area (Fe³⁺)/ Area_tot

Application : In situ determination of Iron redox ratio

-20 0 20 40 60 80 100

700 800 900 1000 1100 1200 1300

RT30s 60s 90s120s 150s180s 240s300s 600s900s 1200s 1800s 3720s

PyroxNa750

Normalized Intensity (a.u.)

Wavenumber (cm^-1)

PyrNa

At 750°C => evolution of the 915 cm^-1 band => progressive oxydation

Conclusion

• Clear changes in Raman spectra visible with the

evolution of iron redox ratio for a given composition

• Gaussian band around 950 cm^-1 assigned to the

vibration of ^[4]Fe³⁺-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

Thank you for your attention