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  • 1990-1994  (11)
  • 1994  (5)
  • 1990  (6)
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  • 1990-1994  (11)
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  • 1994  (5)
  • 1990  (6)
  • 1992  (10)
  • 1
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Cathodic hydrogen charging at low current density at room temperature in acidic medium is carried out on an austenitic 1.9 wt% C iron alloy. This induces the martensitic transformation as checked by Mössbauer spectroscopy and the spectra observed at room temperature present all the features of an already aged martensite. Further ageing at higher temperatures up to 390 K clearly demonstrates that the ageing kinetics is stopped compared to that of uncharged martensite of a similar alloy. Further, in situ transformation of extended multiplets into ε-η carbide precipitates resumes at the same temperature in both cases.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The kinetics of the isochronal ageing of 1.7–1.9 wt% C iron martensite made from 200 K to 450 K is done by following the Mössbauer spectra run at 10 K intervals for varying ageing times of 1, 10 and 100 hours. A new analysis, similar to that used in constant heating rate measurements of resistivity, calorimetry and dilatometry, is made here and shows that the two steps of clustering and ordering prior the in situ transformation into ε-η carbide have exactly the same activation energy of 75±2.5 and 74±1.5 kJ.mol−1, respectively. The clustering-ordering synergy is discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Green rust 2 is usually obtained by oxidizing an initial mixture of FeSO4 and NaOH solutions and a complete oxidation leads mainly towards γ oxyhydroxide known as lepidorocite. By adding some NiSO4 one can stop at the first stage and Mössbauer spectra reveral only ferric doublets. This implies that the initial formula 4Fe(OH)2, 2FeOOH, FeSO4 of green rust 2 must be replaced byxNi(OH)2, (6−x)FeOOH, NiSO4, wherex scans from 2 to 4. It also means that all initial ferrous ions become oxidized into the ferric state leaving the Ni2+ ions unchanged. Therefore the end product of oxidation is the nickel containing green rust 2 at the place of the usual lepidocrocite.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 93 (1994), S. 1783-1788 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The mechanism of oxidation of ferrous hydroxide precipitated by mixing FeSO4 · 7H2O and NaOH solutions depends on the ratioR=[FeSO4]/[NaOH]. The study presented here concerns values ofR ranging from 0.38 to 0.43, i.e. Fe(OH)2 is precipitated in the presence of an excess of caustic soda. The analysis made by Mössbauer spectroscopy of the final compounds of oxidation shows that the valueR=5/12 is particular. At this value, 8FeOOH is the main product of oxidation. Its formation is assumed to take place through an intermediate compound, which formula is deduced from the value R=5/12 to be: 3Fe(OH)2 · 2Fe(OH)3 ·nH2O. This compound could be considered as a green rust one compound including excess OH− ions in theAcB i BaC j CbA k stacking, whereA, B andC are the OH− planes,a, b andc the iron planes, andi, j andk layers made of the excess OH− ions and water molecules.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An unusual low-water corrosion of steel sheet piles has been systematically investigated in a channel harbour (Boulogne sur Mer, France). An analysis of the environment reveals that all sampling of dark rust taken at different heights above marine sediments and kept in anaerobic conditions present unusual concentrations of sulfate-reducing bacteria. The rust products have been characterized by Mössbauer spectroscopy and X-ray diffraction, comprising the ferrous—ferric sulfated compounds of formula 4Fe(OH)2 · 2FeOOH · FeSO4 ·nH2O, called green rust 2, mixed sometimes with magnetite and a small amount of ferrous sulfide.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 90 (1994), S. 389-394 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The oxidation of Fe(OH)2 in the presence of Cl− or CO 3 2− ions leads, in the first stage of the reaction, to chloride-containing green rust one (GR1), 3Fe(OH)2· Fe(OH)2Cl·nH2O, or carbonate-containing GR1, 4Fe(OH)2·Fe2(OH)4CO3·nH2O, respectively. These GR1 compounds give the ferric oxyhydroxides by further oxidation. If a hydroxide Ni x Fe1−x (OH)2 is initially precipitated, the reaction leads to a nickelous-ferric compound isomorphous to the ferrous-ferric GR1, but stable with respect to the oxidizing action of air. Similarly, the oxidation of a nickelous-ferrous hydroxide, in the presence of excess OH− ions, leads to a nickelous-ferric GR1, a layered hydroxide with anionic interlayers made of OH− ions and water molecules. The Mössbauer spectra of these nickelousferric GR1 display two ferric doublets, D0 withIS=0.34 mm/s andQS=0.45 mm/s and D1 withIS=0.36 mm/s andQS=0.86 mm/s. The existence of a ferrous-ferric GR1 incorporating OH− ions, a compound never observed so far, is strongly suspected.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 90 (1994), S. 395-400 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Sodium carbonate Na2CO3 is added to a solution containing an Fe(OH)2 precipitate in order to study the influence of CO 3 2− ions on the oxidation of ferrous hydroxide. The first stage of the reaction leads to a ferrous-ferric compound, the carbonate green rust one (GR1), identified by its X-ray diffraction pattern. The Mössbauer spectrum at 78 K of this GR1 displays two ferrous doublets and one ferric doublet in the 3∶1∶2 abundance ratio. The quadrupole splittingsQS are 2.91, 2.58 and 0.42 mm/s, respectively, and the isomer shifts 75 are 1.25, 1.25 and 0.47 mm/s respectively. These values are very close to those of the three doublets of the chloride GR1, 3Fe(OH)2Cl·Fe(OH)2Cl·nH2O. This fact confirms that the crystallographic structures of these two GR1s are similar, formed by the stacking of hydroxide layers and interlayers containing the considered anions (Cl− or CO 3 2− ) and water molecules. The chemical formula of carbonate GR1 is Fe 4 (II) Fe 2 (III) (OH)12CO3·nH2O, and its standard chemical potential -853 900 cal/mol ifn=0. The second stage of the reaction is the oxidation of GR1, which leads to α-FeOOH goethite.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 92 (1994), S. 981-986 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The clustering-ordering synergy which forms Fe6C precipitates by aging Fe-C martensite is compared to the long-range ordering which forms Fe16N2 by aging Fe-N martensite.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 57 (1990), S. 2029-2035 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The kinetics of formation of green rust 2, 4Fe(OH)2.2FeOOH.FeSO4.nH2O, called “GR2, was followed by Mössbauer spectroscopy in the controlled aeration of a mixture of 0.4 M FeSO4 and 0.4 M NaOH. Mössbauer spectra run at 78 K of the reaction products taken at different time intervals display an average of seven doublets. The initial products of reaction consists of a badly crystallized ferrous hydroxide, FE(OH)2., called “FH”, which disappears first at about 1/3 of the total time of formation of GR2, and sulphated ferrous hydroxide, 4Fe(OH)2.FeSO4.nH2O, called “SFH”. The kinetics of oxidation of SFH into GR2 can be described by a linear growth reaction and the transformation is considered to be in situ.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 57 (1990), S. 2037-2043 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The formation of goethite is simulated by stirring up in the presence of air a mixture of FeSO4, 7H2O and NaOH in the 1∶5 ratio at different initial concentrationC of ferrous ions. Mössbauer spectra of the oxidation end products display the sextet of goethite (αFeOOH) and a paramagnetic ferric doublet increasing whenC decreases; the crystal structure of goethite is also being modified. At a critical low concentration, the orthorhombic structure is no longer justified; inactive α′-FeOOH, which has a similar X-ray diffraction pattern as δ-FeOOH is obtained. All these compounds are crystallographically related.
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