Green rusts and the corrosion of iron based materials J.-M. R. Génin et al. Institut Jean Barriol Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, UMR 7564 CNRS- Université Henri Poincaré-Nancy 1, Département Matériaux et Structures, ESSTIN, 405 rue de Vandoeuvre, F Villers-lès-Nancy, France. “Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal 2009”

Green rusts, i.e. Fe II-III hydroxysalts, are layered double hydroxides (LDH) constituted of [Fe II (1-x) Fe III x (OH) 2 ] x+ layers and [(x/n)A n-  (mx/n)H 2 O] x- interlayers. Anions can be Cl -, CO 3 2-, SO 4 2-, HCOO -, C 2 O 4 2-,, SeO 4 2- … For Chloride[Fe II 2 Fe III (OH) 6 ] +  [Cl -  2H 2 O] - Sulphate[Fe II 4 Fe III 2 (OH) 12 ] 2+  [SO 4 2-  8H 2 O] 2- Carbonate[Fe II 4 Fe III 2 (OH) 12 ] 2+  [CO 3 2-  3H 2 O] 2- Two types of stacking by XRD: GR1 [R(-3)m] and GR2 [P(-3)m1] XRD pattern of hydroxycarbonate GR1(CO 3 2- ). ( thesis of Omar Benali 2002). R-3m XRD pattern of hydroxysulphate GR2(SO 4 2- ) (thesis of Rabha Aïssa 2004). P-3m1

GR1(Cl - ) GR1(CO 3 2- ) GR1(CO 3 2- ) GR2(SO 4 2- ) x   RA   RA  RA   RA mm s -1 % mm s -1 % mm s -1 % mm s -1 % D D D Transmittance % D3D3 D1D1 D2D2 78 K Velocity (mm s -1 ) Transmittance % (c)(c) GR1(CO 3 2- ) x = 0.33 D1D1 D3D3 D2D2 Velocity (mm s -1 ) Transmittance % GR1(CO 3 2- ) x = K (b)(b) D3D3 D1D1 GR2(SO 4 2- ) x = 0.33 Transmittance (%) Velocity (mm s -1 ) K (d)(d) GR1(Cl - ) x  K (a)(a) Velocity (mm s -1 ) D2D2 D3D3 D1D1 Transmission Mössbauer spectra measured at 78 K of various Green Rusts 2 ferrous doublets D 1 & D 2 (large  ) 1 ferric doublet D 3 (small  ) x = Fe III / Fe total is obtained directly from the spectrum (RA of D 3 ) Experimentally 0.25 < x < 0.33

S1S1 S2S2 after t f Transmittance (%) V (mm s -1 ) D3D3 D2D2 D1D1 Transmittance (%) V (mm s -1 ) 15 t1t1 Most of the time the corrosion of iron ends into a ferric oxyhydroxide FeOOH that is the result of the oxidation of the green rust by dissolution-precipitation V (mm s -1 ) S2S2 S1S1 D3D3 D1D1 Transmittance (%) V (mm s -1 ) t2t D2D2 D3D3 D1D1 Transmittance (%) V (mm s -1 ) tgtg Transmittance (%) 15 t3t3 D4D4 S1S1 S3S3 S2S2 pH EhEh t2t2 pH EhEh t3t3 t1t1 tgtg time (mn) tftf (a) D 1, D 2, D 3 : GR1(CO 3 2- ) doublets S 1 : ferrihydrite sextet S 2, S 3 : goethite sextets D 4 : ferrihydrite doublet t g : GR1(CO 3 2- ) alone t 1 : GR1(CO 3 2- ) + some ferrihydrite t 2 : GR1(CO 3 2- ) + goethite + ferrihydrite t 3 : goethite + ferrihydrite After t f : goethite alone Carbonate containing medium E h and pH monitoring of the solution with time Mössbauer spectra during the oxidation by dissolution- precipitation (O. Benali)

H2O2H2O2 Quadrupole splitting  (mm s -1 ) x = x = 1 78 K (e)(e) Transmittance % Velocity (mm s -1 ) Velocity (mm s -1 ) x ~ K (d)(d) Transmittance % D3D3 D1D1 D2D2 78 K Velocity (mm s -1 ) Transmittance % (a)(a) x = 0.33 Quadrupole splitting  (mm s -1 ) x ~ 0.50 D 3 33 % D % 78 K Probability density (p) (b)(b) 0123 D 1 38 % D % x = 0.33 D 3 33 % 78 K Probability density (p) (a)(a) 0123 D 1 50 % D 2 17 % Quadrupole splitting  (mm s -1 ) Transmittance % (b)(b) x ~ K Velocity (mm s -1 ) Quadrupole splitting  (mm s -1 ) D 3 32 % D 4 31 % 78 K Probability density (p) (c)(c) 0123 D 1 28 % D 2 9 % x ~ 0.63 (c)(c) Transmittance % 78 K Velocity (mm s -1 ) E h (V) {2 × [n(H 2 O 2 ) / n(Fe total )] + (1/3)} Quadrupole splitting  (mm s -1 ) D 3 35 % D 4 43 % 78 K Probability density (p) (d)(d) 0123 D 1 + D 2 22 % x ~ 0.78 D 3 33 % D 4 67 % 78 K (e)(e) 0123 Probability density (p) with H 2 O 2 a b c d e Fe II 6(1-x) Fe III 6x O 12 H 2(7-3x) CO 3 The in situ oxidation of green rusts by deprotonation Use a strong oxidant such as H 2 O 2, Dry the green rust and oxide in the air, Violent air oxidation, Oxide in a basic medium… Fe II-III oxyhydroxycarbonate 0 < x < 1 “Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal 2009”

µm (a)(a) GR(CO 3 2- ) x = µm (b)(b) H 2 O 2 x = 0.50 (c)(c) 0.5 µm H 2 O 2 x = 1 (d)(d) 0.5 µm Aerial x = Intensity (arb. unit) Diffraction Angle (2  (c)(c) (a)(a) (b)(b) (d)(d) Intensity (arb. unit) Diffraction Angle (2  TEM and XRD patterns of the Fe II-III oxyhydroxycarbonate due to the in situ deprotonation

G G G 2  (°) (b)(b) K  (Mo  G G G Velocity (mm s -1 ) 293 K GR* Velocity (mm s -1 ) 293 K Goethite (G)  -FeOOH K  (Mo  00.3 GR* 00.6 GR* 01.2 GR* 01.8 GR* (c)(c) 01.5 GR* 2  (°) Intensity (u. a.) (a)(a) G M G M M M M M G  (°) Velocity (mm s -1 ) 293 K Magnetite (M) + Goethite (G) tftf x(O 2 ) = 20% (750 rpm) 20% …13,3%...6,7% ………. 2,7% (375 rpm) E C B M + G G G G GR1(CO 3 2- )* Reaction time (min) tgtg E h (mV) (c)(c)(a)(a)(b)(b) End products of oxidation (A.Renard) Oxidation by oxygen (a) & (b) Dissolution- precipitation (1)Fe II 4 Fe III 2 (OH) 12 CO 3 + 3/4 O 2 → 5 Fe III OOH + CO Fe /2 H 2 O (2) 3Fe 2+ + (1/4)O 2 + (3/2) H 2 O   -Fe III OOH + 2 Fe 3+ + H 2 (3) Fe II 4 Fe III 2 (OH) 12 CO 3 + 1/3 O 2 → 5/3 Fe II Fe III 2 O 4 + CO Fe H 2 O (c) In situ deprotonation (4)Fe II 4 Fe III 2 (OH) 12 CO 3 + O 2 → Fe III 6 O 12 H 8 CO H 2 O Both modes of oxidation exist depending on the rate of oxygen B C D C D

D 1 +D 2 D3D3 CEMS spectrum at room temperature of a steel disk dipped 24 hours in a 0.1 M NaHCO 3 solution.  -Fe Dissolution and Precipitation CORROSION In situ deprotonation of GR1(CO 3 2- ) PASSIVATION pH  -FeOOH H 2 CO 3 HCO 3 - CO Fe ++ FeOH + FeOOH - Fe(OH) 2 Fe E h (V) Fe(OH) 2 + GR(CO 3 2- ) The first step of corrosion: the green rust layer [Fe 2+ ] is M E h -pH Pourbaix diagrams of GR(CO 3 2- ) Aqueous corrosion of iron Iron, Steels Ferrous hydroxide Agressive anions (Cl -, CO 3 2-, SO 4 2- ) Green rusts Common rustsFerric green rusts including anions Fe0 Fe II Fe II-III Fe III Dissolution-precipitationIn situ deprotonation Goethite, Magnetite, Lepidocrocite, Akaganeite,  -FeOOH, Ferroxyhite

20 µm (e)(e) (A. Zegeye) (G. Ona-Nguema) (a)(a) (b)(b) 5 µm (d)(d) (a)Production of Fe(II) and consumption of methanoate during culture of Shewanella putrefaciens in presence of lepidocrocite  FeOOH. The initial amount of FeIII (as lepidocrocite ) and of methanoate were respectively 80 mM and 43 Mm. (b) X-ray pattern of the solid phase of incubation experiments with S. putrefaciens: mixture of green rust (GR1) and siderite (S) obtained after 15 days of incubation. (c) Mössbauer spectrum after 6 days of bioreduction. (c) TEM observations and (d) optical micrograph of GR crystals obtained by reduction of lepidocrocite by S. putrefaciens; One sees the bacteria that respirate GR* Intensity (a.u.) 2  GR1 (012) GR1 (015) GR1 (018) GR1 (003) GR1 (006) S (104) S (018) Time (days) Fe(II) Methanoate Abiotic control Methanoate (mM) Fe(II) (mM) 80 GR* is also obtained by bacterial reduction x ~ 0.50 (c)(c) Six days Velocity (mm s -1 ) Transmittance (%) D2D2 DD D’ 3 D1D1 78 K bioreduction

( a) SEM micrograph showing hexagonal shaped crystals of GR(SO 4 2− ) upon corroded steel sheet left 25 years in seawater, (b) sequence of the rust layers: metal–magnetite–lepidocrocite–GR(SO 4 2− ), (c) Raman spectrum of the outer part of the marine corroded layer. (A. Zegeye) Marine corrosion of steel and Microbially influenced corrosion Formation of GR2(SO 4 2- ) during the reduction of  -FeOOH by a dissimilatory iron-respiring bacterium, Shewanella putrefaciens. Reduction was performed in a non-buffered medium without any organic compounds, K Transmittance (%) Velocity (mm s -1 ) D3D3 D2D2 D1D1 DD Global computed GR: Fe(II) = D 1 GR: Fe(III) = D 3 GR: Fe(II) = D 2 Lepidocrocite = D  Experimental Fe 0  -FeOOH GR(SO 4 2- ) Fe II S DIRB SRB GR(SO 4 2- ) Fe II Microbially induced corrosion in marine sediments is due to the reduction of oxyhydroxides by dissimilatory iron reducing bacteria that respirates Fe III producing Fe II-III oxyhydroxysulphate followed by its reduction into sulfides in acidic conditions due to sulphate reducing bacteria. Mössbauer spectroscopy allowed us to study the family of Fe II-III hydroxysalts known as green rusts, which are intermediate compounds during the corrosion of iron-based materials. There exist two modes of oxidation of the green rusts, either by dissolution-precipitation that leads to corrosion, or by in situ deprotonation giving rise to a ferric oxyhydroxysalt, e.g. Fe III6 O 12 H 8 CO 3, that leads to passivation of steels. (c)(c) (Refait, Génin)