57 Fe Mössbauer Spectroscopy Enver Murad Marktredwitz, Germany Enver Murad Marktredwitz, Germany : a Tool for the Remote Characterization of Phyllosilicates?

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  • Slide 1
  • 57 Fe Mssbauer Spectroscopy Enver Murad Marktredwitz, Germany Enver Murad Marktredwitz, Germany : a Tool for the Remote Characterization of Phyllosilicates?
  • Slide 2
  • Basic principles of Mssbauer spectroscopy
  • Slide 3
  • Free emitting and absorbing atoms Energy of recoil -ray energy Mass of atom
  • Slide 4
  • Emitting and absorbing atoms fixed in a lattice Mass of particle Mssbauer spectroscopy is the recoil-free emission and absorption of gamma rays
  • Slide 5
  • Appearance of Mssbauer spectra Depending on the local environments of the Fe atoms and the magnetic properties, Mssbauer spectra of iron oxides can consist of a singlet, a doublet, or a sextet. Symmetric charge No magnetic field Asymmetric charge No magnetic field Symmetric or asymmetric charge Magnetic field (internal or external) B hf Isomer shift Quadrupole splitting Magnetic hyperfine field
  • Slide 6
  • Fe 3+ Fe 2 +
  • Slide 7
  • Slide 8
  • Use of Mssbauer spectroscopy as a fingerprinting technique Isomer shifts and quadrupole splittings of Fe-bearing phases vary systematically as a function of Fe oxidation, Fe spin states, and Fe coordination. Knowledge of the Mssbauer parameters can therefore be used to fingerprint an unknown phase.
  • Slide 9
  • Hyperfine parameters of Fe 3+ oxides Mineral Ordering temperature (K) Magnetic hyperfine fields RT: B hf (T) 4.2 K: B hf (T) (mm/s) Hematite 950 51.8 53.5 -0.20 / 54.2 +0.41 Magnetite 850 49.2 + 46.1 50.6 { + 36 52 } Maghemite ~ 950 50.0 + 50.0 52.0 + 53.0 |0.02| Goethite 400 38.0 50.6 -0.25 Akaganite 299 47.3 + 47.8 + 48.9 Lepidocrocite 77 45.8 0.02 Feroxyhyte 450 41 53 + 52 ~0.0 Ferrihydrite 25 115 47 50 -0.02 -0.07 Bernalite 427 41.5 56.2 |0.01| * Magnetic blocking temperature # several B-site subspectra below 120 K * #
  • Slide 10
  • Iron in phyllosilicates
  • Slide 11
  • 1:1 phyllosilicates 2:1 phyllosilicates Fe 2+, Fe 3+ Fe 3 +
  • Slide 12
  • Classification of clay-sized phyllosilicates (clay minerals sensu stricto) Layer type Octahedral occupancy Octahedral charge 1 Central cation(s) GroupCommon species 1 : 1Di 2 0AlKaolinKaolinite, halloysite 1 : 1Tri 3 0MgSerpentineLizardite, chrysotile 2 : 1Di< 0.2AlPyrophyllite 2 : 1Tri< 0.2MgTalcTalc, minnesotaite 2 : 1Di / Tri0.2 0.6Al, Mg, FeSmectiteMontmorillonite, nontronite 2 : 1Di / Tri0.6 0.9Al, Mg, FeVermiculite 2 : 1Di / Tri> 0.9Al, Mg, FeMicaIllite, glauconite 2 : 1 (: 1)Di / TriAl, Mg, FeChloriteClinochlore, chamosite 1 Per formula unit [O 10 (OH) 2 ], 2/3 Dioctahedral/Trioctahedral, (Fe)
  • Slide 13
  • Mssbauer spectra of selected simple (pure) clay minerals
  • Slide 14
  • The simplest clay mineral: kaolinite [Al 2 Si 2 O 5 (OH) 4 ] Kaolin / Jari @ 295 K
  • Slide 15
  • Kaolin / Jari @ 4.2 K
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  • Mssbauer parameters of clay minerals MineralTemp Isomer shift (/Fe) Quadruple splitting () KaoliniteRT0.350.51 ** * Average values. Isomer shift relative to Fe at room temperature. Only Fe 3+ considered.
  • Slide 17
  • Illite : (K,H 3 O) x+y (Al 2-x M x )(Si 4-y Al y )O 10 (OH) 2 Illite OECD #5 Fe 3+ : 2 Fe 3+ : P()
  • Slide 18
  • Mssbauer parameters of clay minerals MineralTemp Isomer shift (/Fe) Quadruple splitting () KaoliniteRT0.350.51 IlliteRT0.350.59 0.73 * Average values for Fe-poor ( 3% Fe) and Fe-rich (> 5% Fe) samples, respectively *
  • Slide 19
  • Nontronite : M x Fe 2 (Si 4-x Fe x )O 10 (OH) 2 3+ RT Nontronite API H33a 23.46 % Fe 1.44 % Fe d 2.3 % Gt From A sext 1.4 % Gt 77 K
  • Slide 20
  • Nontronite : M x Fe 2 (Si 4-x Fe x )O 10 (OH) 2 3+ Nontronite API H33a Fe 2+ /(Fe 2+ +Fe 3+ ) = 0.15 Reoxidized 644 days in air no Fe 2+ DCB
  • Slide 21
  • Mssbauer parameters of clay minerals MineralTemp Isomer shift (/Fe) Quadruple splitting () KaoliniteRT0.350.51 IlliteRT0.350.59 0.73 NontroniteRT0.35
  • Slide 22
  • Complex natural clays : The real world
  • Slide 23
  • Physics Today 61 (8) Phyllosilicate with intercalated interlayer Na + CH 4 H2OH2O Note: Fe-containing interlayer must be frozen to show Mssbauer Effect Phyllosilicate with intercalated interlayer: Natures trashcan Fe 2 + Fe 3+
  • Slide 24
  • Kaolin Wolfka @ 4.2 K DCB-treated0.11 % goethite
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  • Bauxite
  • Slide 26
  • Red soil
  • Slide 27
  • Extraterrestrial Mssbauer spectroscopy Lunar samples In situ Mssbauer spectroscopy on Mars
  • Slide 28
  • S.S. Hafner, 1975: The data should not... be interpreted in an isolated form, but... correlated with the results of other techniques.... Lunar soil 10084 For lunar samples, this is possible !
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  • Slide 30
  • The data should not... be interpreted in an isolated form, but... correlated with the results of other techniques... (S.S. Hafner 1975) we assign the broad doublet present in Mssbauer spectra of [Mars] soils to be due to Fe 2+ sulfates rather than olivine (Bishop et al. 2004) Fe 2+ sulfate ? NASA/JPL/University of Mainz ??
  • Slide 31
  • Summar y
  • Slide 32
  • Strengths and weaknesses of 57 Fe Mssbauer spectroscopy Sensitive only to 57 Fe (no matrix effects) Sensitive to oxidation state Allows distinction of magnetic phases Very sensitive towards magnetic phases Non-destructive Resolution limited by uncertainty principle Sensitive only to 57 Fe (sees only 57 Fe) Coordination ? to Paramagnetic phase data often ambiguous Diamagnetic element substitution & relaxation Slow If possible, use other techniques as well StrengthsWeaknesses Often a combination of Mssbauer spectroscopy with other techniques can help solve problems that cannot be resolved using Mssbauer spectroscopy alone.