Synthesis and characterisation of the Fe(II–III) hydroxy-formate green rust

A new methodology was envisioned in order to prepare green rust compounds build on organic anions that could intervene in microbiologically influenced corrosion processes of iron and steel. The formate ion was chosen as an example. The formation of rust was simulated by the oxidation of aqueous suspensions of Fe(OH)₂ precipitated from Fe(II) lactate and sodium hydroxide, in the presence of sodium formate to promote the formation of the corresponding green rust. The evolution of the precipitate with time was followed by transmission Mössbauer spectroscopy at 15 K. It was observed that the initial hydroxide was transformed into a new GR compound. Its spectrum is composed of three quadrupole doublets, D ₁ (δ?=?1.28 mm s^?1, Δ?=?2.75 mm s^?1) and D ₂ (δ?=?1.28 mm s^?1, Δ?=?2.48 mm s^?1) that correspond to Fe(II) and D ₃ (δ?=?0.49 mm s^?1, Δ?=?0.37 mm s^?1) that corresponds to Fe(III). The relative area of D ₃, close to the proportion of Fe(III) in the GR, was found at 28.5?±?1.5% (～2/7). Raman spectroscopy confirmed that the intermediate compound was a Fe(II–III) hydroxy-formate, GR(HCOO^?).     

Synthesis by Coprecipitation of Al-Substituted Hydroxysulphate Green Rust FeII 4FeIII (2−y)AlIII y (OH)12SO4,nH2O

Al-substituted hydroxysulphate green rust (Al-GR{SO₄}) were synthesised by the coprecipitation of Fe^II, Fe^III and Al^III cations. The Al-GR{SO₄} crystals (～50 nm) are significantly smaller than the hydroxysulphate green rust GR{SO₄} crystals (～500 nm). The Mössbauer spectrum of Al-GR{SO₄} was adjusted with two ferrous doublets D₁ and D₃ and one ferric doublet D₂. Doublet D₃ is attributed to Fe^II ions that have Al^III ions as a first neighbour.

     

The oxidation of Fe(OH)2 in the presence of carbonate ions: Structure of carbonate green rust one

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 312 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 -FeOOH goethite.     

The structure of Ni(II)−Fe(III) hydroxy-chloride green rusts by Mössbauer spectroscopy and X-ray diffraction

The crystallographic structure of Ni(II)?Fe(III) hydroxy-chloride green rusts obtained by oxidation of a Fe_xNi_1?x(OH)₂ precipitate is isomorphous with that of the ferrousferric green rust one and independent of the value of P=Fe/Ni. Mössbauer spectra exhibit two quadrupole doublets after further oxidation of the compounds which correspond to a formula (3-x)Ni(OH)₂ · xFeOOH · Fe(OH)₂Cl. The Fe³⁺ ions are found to occupy preferentially the sites close to the Cl^? ions and the Ni²⁺ those far from them. However the ordering of the Fe³⁺ ions is not perfect.     

Mössbauer study of ionic and metallic states of electrodeposited Fe−Ni−P amorphous alloys

In this contribution we report cases in which we found ionic character of the amorphous state in electrodeposited Fe?Ni?P samples electroplated in a similar way but with different parameters to those exhibiting metallic amorphous character in their Mössbauer spectra. In particular, the room temperature transmission spectrum of an X-ray amorphous electrodeposited Fe₆₈Ni₂₃P₈ sample consists of two doublets with IS1=0.27 mm/s, QS1=0.51 mm/s, IS2=1.22 mm/s and QS2=2.54 mm/s parameters, where the latter is characteristic for Fe²⁺ state.     

The substitution of Fe2+ ions by Ni2+ ions in green rust one compounds

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 Fe_1–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.     

Ordering in FeII–III Hydroxysalt green rusts from XRD and Mössbauer analysis (chloride, carbonate, sulphate, oxalate...); about the structure of hydrotalcite-like compounds

The domain of existence of Fe^II–III hydroxysalt green rusts (GR) is characterised by the ratio x = [Fe^III]/[Fe_total] lying in [1/4, 1/3] as it is for any layered double hydroxide (LDH). Since Fe^III cations balance the charges of intercalated anions, cation and anion distributions are correlated. However, the distribution of anions depends on their charge, shape and size. For Cl^? and CO₃ ^2?, x belongs to the complete range whereas for C₂O₄ ^2? and SO₄ ^2? it is limited to x = 1/4 and 1/3, respectively. Mössbauer spectra present in all cases two ferrous and one ferric doublets, which characterise each GR by their relative abundance. Intermediate values of x are in fact obtained by intrincate domains of two types, one where the cation periodicity is 2×a ₀ and the other one √3×a ₀ if a ₀ is the lattice parameter.     

Search for Fe3 trimers in an argon matrix

Mossbauer effect studies of ⁵⁷Fe embedded in solid argon (Fe at° = 0.5 at 16K depict the presence of a non-magnetic component with IS = 0.38(4) mm.s^-1 and QS = 1.08(7) mm.s^-1 which was assigned to Fe₃. The relatively large abundance of Fe₃ with respect to the larger clusters characterized by their magnetic splitting is attributed to the fast quenching of surface diffusion. This is manifested by the presence of Fe₂ dimers highly oriented parallel to the surface. From the relatively small value of QS and the IS it is concluded that the Fe₃ has a triangular structure.     

Kinetics of formation of green rust 2 in the steady acidic sulphated medium

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.     

The study of Mössbauer effect in EuBa2Cu3O7-y

EuBa₂(Cu_1-xFe_x)₃O_7-x has been investigated by the⁵⁷Fe and¹⁵¹Eu Mössbauer effect. The⁵⁷Fe Mössbauer spectra of the EuBa₂(Cu_1xFe_x)₃O_7-y without or with DC electric current (the current strength I=0.5A) around the superconducting transition temperature have been measured. The results indicate that the isomer shift (IS) and the quadrupole splitting (QS) of the Fe replacing the Cu(2) vary neither with increasing the Fe content nor with the small DC eletric, current passing the superconductor and that the IS and the QS of the Fe replacing the Cu(1) vary with the Fe content. Especially, the IS and the QS of the Fe (D3) replacing the Cu(1) are changed when the small electric current passes the superconductor at 80K.     

Variable temperature Mössbauer spectroscopic studies of oxo-centered trinuclear mixed-valence iron succinate, mesaconate and isophthalate complexes

Three new oxo-centered trinuclear mixed-valence iron complexes, iron succinate, iron mesaconate and iron isophthalate have been prepared. Temperature dependent valence delocalization processes were observed for all the complexes on variable temperature Mössbauer spectroscopic studies. Two clear quadrupole split doublets attributed to high-spin Fe(III) and high-spin Fe(II) states were existed for the complexes at liquid nitrogen temperature. At room temperature a nearly averaged singlet peak was observed for mesaconate complex and averaged doublet peaks were observed for succinate and isophthalate complexes with IS values 0.68 and 0.68 mms^?1 and QS values 0.44 and 0.48 mms^?1 respectively.     

57Fe Mössbauer spectroscopy study of phlogopite megacrysts from an evolved carbonatitic kimberlite in the northeastern Oman Mountains

The Fe oxidation degree determined by ⁵⁷Fe Mössbauer spectroscopy and microprobe was used to characterize fresh and altered phlogopite megacrysts from an evolved carbonatitic kimberlite from northeastern Oman. The Quadrupole splitting (QS) varies between 2.19 and 2.48 mm/s (Fe^2?+?) in the fresh phlogopite samples and between 2.40 and 2.47 mm/s in the altered phlogopite samples. The quadrupole splitting of the Fe^3?+? doublets varies between 0.66 and 0.85 mm/s in the fresh samples. The altered phlogopite samples show three Fe^3?+? doublets; the first show a quadrupole splitting between 0.97 and 1.13, the second quadrupole splitting varies between 0.24 and 0.46 mm/s and the third varies between ??0.23 and ??0.35 mm/s. The phlogopite was observed to have an average Fe^3?+?/Fe_total of 35% to 37%, and corresponds to fresh phlogopite. The second one results from the alteration of the first type, and the Fe^3?+?/Fe_total ranges between 40% and 57%. Tetrahedral Fe^3?+? ions were confirmed in the altered phlogopite samples. Quantitative Fe site distributions can be obtained from room-temperature Mössbauer data if the different recoilless factors for octahedral Fe^2?+? and tetrahedral Fe^3?+? are considered. The observed isomer shifts are consistent with Mössbauer temperatures of 330 K, reported in the literature for tetrahedral and octahedral Fe^3?+? and Fe^2?+? in phlogopite. The results are compared to those obtained for natural and synthetic phlogopite from worldwide.     

Green Rusts and Their Relationship to Iron Corrosion; a Key Role in Microbially Influenced Corrosion

Mössbauer spectroscopy (MS) has often been used to characterise double-layered hydroxysalts usually named green rusts (GR) and to follow their Fe(II)/Fe(III) ratio during the oxidation process of Fe(OH)₂ in the presence of aggressive anions such as Cl^–, SO ₄ ^2– , CO ₃ ^2– ,.... They are intermediate compounds between the initial metal Fe(0) via the Fe(II) and the final Fe(III) (oxyhydr)oxides constituting the usual rusts. E–pH Pourbaix diagrams of iron for predicting the aqueous corrosion conditions of iron-based materials are determined by monitoring the electrode potential E _h and pH vs. time. The crystal structure of GRs, in any case constituted of layers of [Fe^II _(1–x)Fe^III _x (OH)₂] ^x+ that alternate with interlayers [(x/n)A ^n–(mx/n)H₂O] ^x– made of A ^n– anions and water molecules, are presented. Several examples of the role of GRs are discussed, from chloride pitting of concrete reinforcing bars to bacterial corrosion of cast iron in water pipes or steel sheet piles in harbours. The efficiency of corrosion inhibitors like phosphate and their relationship to the oxidation of GRs are presented from basic MS studies. But most importantly, the evidence by MS of the dissimilatory reduction of a common ferric oxyhydroxide, -FeOOH lepidocrocite, into a GR by the action of a bacterium, Shewanella putrefaciens, opens the path through which microbially influenced corrosion (MIC) operates. A cycling of aerobic and anaerobic conditions is necessary where GRs but also magnetite play likely the key role.     

Mössbauer spectroscopy of the Zr-rich region in Zr–Nb–Fe alloys with low Nb content

Intermetallic phases and solid solutions in the Zr-rich region of the Zr–Nb–Fe system with low Nb content are studied by Mössbauer spectroscopy complemented with X-ray diffraction, optical and scanning electron microscopy and electron microprobe analysis. The phases found in each sample were those expected from the corresponding binary Zr–Fe system. Furthermore, one of the samples showed a ternary cubic Ti₂Ni type phase with a similar stoichiometry to the tetragonal Zr₂Fe compound. Mössbauer parameters were suggested to this phase (IS: - 0.12 mm/s, QS: 0.30 mm/s), to the bcc Zr(β) phase (IS: (-0.11 α 0.01) mm/s, QS: (0.23 α 0.02) mm/s), and to the hcp Zr(β^T) phase (IS: (-0.24 α 0.02) mm/s, QS: (0.45 α 0.02) mm/s).     

57Co emission studies of cupric oxide

Results on the incorporation, valence and spin states of Fe(Co) in CuO (with reference to similar studies on high temperature superconductors) and coupling of the Fe(Co) moment to the Cu magnetism in CuO are presented. Freshly prepared⁵⁷Co: CuO shows two quadrupole doublets D₁ and D₂ withQ.S. of 2.49 and 1.52,I.S. of 0.35 and 0.70 mm/s and relative abundance of 74% and 26%, respectively at room temperature, the abundance being dependent on time in a sample exposed to ambient conditions and reaching 38 to 62% fifteen months after preparation. Below,T _N=225¹K, a typical combined magnetic-quadrupole interaction pattern is observed with a single saturation magnetic hfs of 25.6 T, central shift of 0.82 mm/s and a single |E _Q|=1.62 mm/s at 4.2 K. External magnetic field spectra reveal an antiferromagnetic behaviour of the Fe(Co) ion. Temperature dependence of the magnetic hfs is fitted in the framework of the molecular field approximation allowing different spins and coupling constants for Cu and Fe(Co).     

Study on decays of DsJ *(2317) and DsJ(2460) in terms of the CQM model

Based on the assumption that D_sJ ^*(2317) and D_sJ(2460) are the (0⁺,1⁺) chiral partners of D_s and D^* _s, we evaluate the strong pionic and radiative decays of D_sJ ^*(2317) and D_sJ(2460) in the constituent quark meson (CQM) model. Our numerical results of the relative ratios of the decay widths are reasonably consistent with the data. PACS 13.25.Ft; 12.38.Lg; 12.39.Fe; 12.39.Hg     

57Fe Mössbauer Spectroscopic Investigation of Low-Iron Coals and Their Flyash

Trends in the speciation of iron and sulfur in high iron/sulfur coals are well-established. Less is known concerning iron and sulfur speciation in low sulfur coals such as those investigated in this study. Low sulfur coals and their flyash from Thunder Bay, Ontario, Canada and Atikokan, West Virginia, U.S.A. have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy, X-ray diffraction and X-ray fluorescence. Virgin coals, containing approximately 0.1% Fe, exhibited Mössbauer spectra too low in intensity to characterize the phases present. The flyash exhibited well-resolved, simple doublets with ΔE_Q=1.16 mm s^?1 (Canada) and 1.26 mm s^?1 (U.S.A.) and isomer shift values (w.r.t. Fe) of 0.22 mm s^?1 and 0.23 mm s^?1, respectively, characteristic of Fe³⁺. The linewidths of ～0.80 mm s^?1 are unusually large. Treatment of the flyash with cold, hydrofluoric acid resulted in a sample that exhibited very little absorption in its ⁵⁷Fe Mössbauer spectrum. This result, in conjunction with the linewidths, indicates that the Fe is present in the flyash mainly as a silicate glass.     

The substitution of Fe2+ ions by Ni2+ ions in the green rust 2 compound studied by Mössbauer effect

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.     

Mössbauer investigation of iron uptake in wheat

Iron uptake and distribution in wheat roots were studied with ⁵⁷Fe Mössbauer spectroscopy. Plants were grown both in iron sufficient and in iron deficient nutrient solutions. Mössbauer spectra of the frozen iron sufficient roots exhibited three iron(III) components with the typical average Mössbauer parameters of δ?= 0.50 mm s^???1, Δ?= 0.43 mm s^???1, δ?= 0.50 mm s^???1, Δ?= 0.75 mm s^???1 and δ?= 0.50 mm s^???1, Δ?= 1.20 mm s^???1 at 80 K. These doublets are very similar to those obtained earlier for cucumber [0], which allows us to suppose that iron is stored in a very similar way in different plants. No ferrous iron could be identified in any case, not even in the iron deficient roots, which confirms the mechanism proposed for iron uptake in the graminaceous plants.