Mössbauer study of Japanese ancient iron slag

Mössbauer spectroscopy was applied to an investigation of ancient iron slags, excavated at the ancient ruins for iron manufacturing in order to deduce the raw materials and operative conditions of the furnace. From the Mössbauer spectra, it was found that the slags consisted of fayalite, wüstite, ulvöspinel and magnetite.     

Degradation of passive layers of iron studied by conversion electron Mössbauer spectroscopy

Integral electron Mössbauer spectroscopy (ICEMS) and additionally some electrochemical methods were used to characterize the passivation process of iron (low carbon steel) in sulfate, sulfate+sulfite (a possible model solution of acid rain) solutions and in phospate buffer. The phase compositions and thicknesses of the passive layers formed due to the electrochemical polarizations were analyzed in dependence on the duration of the anodic passivations and on the pH of the used electrolytes. The passive layer, as determined from the Mössbauer spectra, consists mainly of -FeOOH, however in sulfite containing sulfate aqueous solution at pH 3.5 Fe₃C and despite ex-situ circumstances FeSO₄·H₂O was detected after the shortest polarization time. The film thickness, which was found to grow nearly linearly with polarization time in pure sulfate solution and in phospate buffer, reached a maximum of 60–160 nm (depending on pH) in sulfate+sulfite solution after a passivation time of about 4 hours. It has been proved, that HSO₃ ^–-ion, which is contained by acid rain, initiate pit formation under acid conditions and so enforces the corrosion of iron. The experimental results furthermore suggest, that not the whole oxidic layer is responsible for the passivity but only a very thin intermediate layer formed between an inner oxide layer of a cubic structure and the rhombic oxide (-FeOOH) cover.     

Mössbauer measurements on iron phthalocyanines

Monomeric and polymeric iron phthalocyanines (FePc) with and without carbon support and subjected to various heat treatments have been studied by Mössbauer spectroscopy. Dispersing FePc on carbon changes the electronic state of the monomer to low spin (S = 0) while the electronic state of the polymer remains unchanged (S = 1). It is suggested that the bonding between polymeric FePc and carbon takes place through the side groups present on the peripheral parts of the polymer and/or through suitable chemical groups present on the carbon surface. The electron-attracting ability of the side-groups deduced from the Mössbauer spectra is discussed. The results will form a basis for a comparison with data from electrochemical measurements.     

Mössbauer study of iron-containing atmospheric aerosols

The Mössbauer technique was applied to study the seasonal variations of iron concentration in atmospheric air. The concentration of iron in air was calculated by the area method from the experimental spectra obtained. From the shapes of the Mössbauer spectra it was concluded that iron appears as Fe₂O₃ in the form of ultrafine particles in the superparamagnetic state. The measurements as a function of temperature [from 300 to 75 K) made it possible to estimate the size of iron-containing aerosol particles. Correlation of the seasonal variations of iron concentration with meteorite activity was discussed. This method was applied also in investigations of iron concentration variations with air radioactivity due to nuclear explosions performed in the atmosphere. Attempts were made to find a relation between air pollution and the concentration of iron in the air.     

Infrared and Mössbauer spectroscopic study of the metal-insulator transition in some oxides of perovskite structure

The IR spectra of some LaNi_1−xB_xO₃ (B = Cr, Fe, and Co) compounds having perovskite structure have been studied in the range 1000−300 cm⁻¹. An investigation of the changes in the metal-oxygen stretching frequency as x → x_c from the insulating side has been carried out. An important feature is that as x → x_c the vibrational features in the infrared spectra disappear when the resistivity is ∼10⁻¹ Ω cm which is of two orders of magnitude more than the value of ϱ₀ at which the temperature coefficient of resistance changes sign. Mössbauer studies on Fe-containing samples with various conductivities show that the isomer shift decreases as conductivity increases which is indicative of larger FeO overlap.     

Mössbauer spectroscopic study of an iron(III) complex with crown porphyrin

A complex of ⁵⁷Fe with 5-{4-[((4′-hydroxybenzo-15-crown-5)-5′-yl)diazo]phenyl}-10,15,20-triphenylporphyrin was studied by Mössbauer spectroscopy. The presence of signals of two types in the spectra (a doublet and an extended absorption band over a wide velocity range) suggests that the Fe atoms occupy two structurally different positions in this complex. The dependences of the doublet asymmetry on temperature and the angle between the normal to the sample plane and the γ-ray beam were studied. The isomer shift δ of the doublet in the temperature range from 360 to 5 K changes from 0.25 to 0.41 mm/s, while the quadrupole splitting remains virtually unchanged (Δ ≈ 0.65 mm/s). The relaxation-type absorption over a wide velocity range, the relative area of which strongly varies with temperature, can be described by a broad singlet with the following parameters: δ = 0.30–0.44 mm/s and Γ = 2.8–3.38 mm/s. According to the δ values, both signals are due to Fe(III) derivatives.     

Mössbauer study on thermal decomposition of some hydroxy iron(III) carboxylates

Thermal decomposition of some hydroxy iron(III) carboxylates, i.e., iron(III) lactate, Fe(CH₃CHOHCOO)₃, iron(III) tartrate, Fe₂(C₄H₄O₆)₃ and iron(III) citrate, Fe(C₆H₅O₇) · 5H₂O has been studied in static air atmosphere in the temperature range 298–773 K employing Mössbauer, infrared spectroscopies and themogravimetric methods. The compounds directly decompose to -Fe₂O₃ without undergoing reduction to iron(II) intermediates. An increase in particle size of -Fe₂O₃ has been observed with increasing decomposition temperature. The thermal stability follows the sequence: iron(III) tartrate > iron(III)citrate > iron(III)lactate.     

Mössbauer study of some Fe-containing M6 and M5 clusters

Isomer shift (δ) and quadrupole splitting (Δ) parameters have been assigned to the iron sites in [FeRh₅(CO)₁₆]⁻, trans- and cis-[Fe₂Rh₄(CO)₁₆]²⁻, [Fe₃-Rh₃(CO)₁₇]³⁻, [FeRh₄(CO)₁₅]²⁻, [Fe₃Pt₃(CO)₁₅]²⁻ and [Fe₄M(CO)₁₆]²⁻ (M = Pd or Pt) from ⁵⁷Fe Mössbauer spectra recorded at 78 K. The data for the closo compounds [FeRh₅(CO)₁₆]⁻ and [Fe₂Rh₄(CO)₁₆]²⁻ are compared with those for [Fe₆(CO)₁₆C]²⁻. In [Fe₃Rh₃(CO)₁₇]³⁻, the three major Fe sites were identified. For both [Fe₄M(CO)₁₆]²⁻ compounds two isomers were shown to be present in the solid state.     

Variable-temperature 119Sn Mössbauer study of tin phthalocyanines

Variable-temperature ¹¹⁹Sn Mössbauer spectroscopic (VTMS) data for six tin phthalocyanine (pc) derivatives have been collected in order to ascertain the restrictions imposed by the macrocyclic ring on the vibrational motion of the tin atom. Thermal condensation of [(t-Bu)₄pc]Sn(OH)₂ yields the co-facially stacked polymer {[(t-Bu)₄pc]SnO}_n which can be distinguished in the VTMS experiment by the enhanced rigidity of its structure.     

A study of XeFeF9 from Mössbauer spectra

A study of the new antiferromagnetic complex XeFeF₉ by the Mössbauer effect has contributed experimental data on the temperature dependence of hyperfine splitting parameters of ⁵⁷Fe. There is evidence that the relative intensity of the lines is affected by the texture. The anomalous spectra in the range 85 – 100 K might be interpreted as superparamagnetism; the corresponding blocking temperature being obtained near 98 K.     

A study of carbonic anhydrase using Mössbauer spectroscopy

The preparation and characterization of an Fe(II) bovine carbonic and human carbonic anhydrase are presented. Results of Mössbauer spectroscopy measurements indicate that the Fe(II) (low spin) is bound at the enzymatically active site. The results are compared with previous studies which had used the technique of perturbed angular correlations of γ-radiation.     

57Fe-Mössbauer study of electrically conductive alkaline iron vanadate glasses

A relationship between local structure, thermal stability and electrical conductivity (σ) of xR₂O·10Fe₂O₃·(90 ? x)V₂O₅ glasses (abbreviated as xRFV glasses, where R = Li, Na, K; x = 20 and 40 in mol %) was investigated by ⁵⁷Fe-Mössbauer spectroscopy, X-ray diffractometry, differential thermal analysis (DTA) and DC two- and four-probe method. From DTA study, thermal stability of 20RFV glasses is lower than that of 40RFV glasses by evaluating Hruby parameter (K _gl). Constant activation energy for crystallization (E _a) of 2.5 eV obtained from both 20RFV and 40RFV glasses indicate that the crystallization proceeds with the cleavage of Fe–O bond having the energy of 2.6 eV. Isochronally annealed 20RFV glass at 400–450 °C resulted in the increase in electrical conductivity (σ) from the order of 10^?3 to 10^?1 S cm^?1, whereas slight decrease in σ was observed for 20RFV glass annealed above 460 °C. A paramagnetic doublet with an identical isomer shift (δ) of 0.39 mm s^?1 was observed in the ⁵⁷Fe-Mössbauer spectra of 20RFV glass after isothermal annealing conducted at 400–450 °C for 100 min, which caused a decrease of quadruple splitting (Δ) from 0.67 to 0.52 mm s^?1 for 20LiFV glass and from 0.66 to 0.53 mm s^?1 for 20NaFV glass. On the other hand, three paramagnetic doublets with δ and Δ of 0.40 and 0.25, 0.38 and 0.60, and 0.31 and 1.11 mm s^?1 respectively were observed for 20RFV glass annealed at 460–550 °C, reflecting precipitation of semiconducting FeVO₄ phase having σ of 6.0 × 10^?7 S cm^?1. It can be concluded that isochronal annealing of 20RFV glass below 450 °C resulted in increase in σ due to the structural relaxation, while annealing above 500 °C resulted in the decrease of σ due to the precipitation of FeVO₄ phase.     

Mössbauer and infrared study of the thermal decomposition of iron and nickel compounds impregnated in alumina

In this work, studies of Fe₃(CO)₁₂ and a mixture of Fe₃(CO)₁₂ and Ni (acac)₂ impregnated in Al₂O₃ were undertaken using Mössbauer and i.r. spectroscopies. In freshly prepared samples, low oxidation species were shown to be present. After thermal decomposition, the data indicate the appearance of aluminum compounds of Fe^II and Fe^III plus superparamagnetic Fe^III. No Fe° species were detected, even under H₂ atmosphere.     

Local structure and valence of impurity ions in oxides by TDPAC and Mössbauer emission spectroscopy

The features of time-differential perturbed angular correlation (TDPAC) in studies on local chemical structures around impurity atoms are described in comparison with those of Mössbauer emission spectroscopy with four typical examples of recent applications to metal oxide systems, namely,⁹⁹Rh⁹⁹Ru in -Fe₂O₃ and YBa₂Cu₃O_7– and¹¹⁷Cd¹¹⁷In in MO (M=Mn, Co, Ni) and BaRu_2/3Cd_1/3O₃.     

Mössbauer study of the effect of boron and iron contents on the dynamic behavior of iron in sodium phosphate glass system

Mössbauer measurements were performed at different temperatures in order to examine the dynamic behavior of iron in the glass system: 42.5% P₂O₅, 42.5% Na₂O, 15% Fe₂O₃. Variation of the dynamic behavior was traced by substituting B₂O₃ for P₂O₅ [30 P₂O₅, 12.5 B₂O₃, 42.5 Na₂O, 15 Fe₂O₃] and by increasing the amount of iron at the expense of Na₂O [42.5 P₂O₃, 15 Na₂O, 42.5 Fe₂O₃]. The Mössbauer measurements gave the values of Debye temperature (_D), mean square displacement <²>, mean square velocity <v ² > of oscillation, the lattice time () and the strength parameter (B) for each glass. These values were discussed with the results of DTA, density, hardness and D. C. conductivity.