Mössbauer Spectroscopic Studies of Supported α-Fe2O3 and Fe Catalysts I: Particle Size Determination and Support Effect

The chemical state of particles of 5wt% Fe in α-Fe₂O₃ and the subsequently reduced iron particles supported on different particle size (50–200 mesh) of silica (SiO₂), alumina (Al₂O₃), magnesium oxide (MgO) and carbon (C) was examined by Mössbauer spectroscopy at various stages of calcination and reduction. The particle size of the α-Fe₂O₃ supported on different mesh sizes (50, 100, 140, 200 mesh) of SiO₂ has been determined. The strength of metal-support interaction with respect to the kind of support was found to be MgO>SiO₂>Al₂O₃>C.     

Mössbauer Spectroscopic Studies of Ferrocenylaldimines and their TCNQ Complexes

A series of ferrocenylaldimines (Fc-CH=N-R) has been prepared by Schiff base condensation of formylferrocene with polyacenylamines RNH₂ where R = naphthyl, 5,6,7,8-tetrahydronaphthyl, anthracenyl, and pyrenyl groups. This step was followed by oxidation with TCNQ to give [Fc-CH = N-R][TCNQ]² salts. The electronic state of iron in these compounds was investigated by means of⁵⁷Fe Mössbauer spectroscopy.     

Mössbauer Spectroscopic Studies of the Hydroxofluorostannate(IV) Complexes

Mössbauer isomer shifts of ¹¹⁹Sn in a series of complexes K₂Sn(OH)_6-mF_m observed at 78 K were ?0.05, ?0.05, ?0.24, ?0.27 and ?0.40 mm s^?1, respectively, for m=0, 2, 4, 5 and 6. These IS values were linearly related to both m and (the average Pauling electronegativity of the ligands): . The IS straight line was compatible within experimental error with the one reported by Parish and Row-botham for the hexahalogenostannate complexes SnX₄Y₂², namely, The revised IS straight line including both series of complexes could be expressed by the equation Quadrupole splittings observed in the complexes of m = 2,4 and 5 were 1.16, 0.80 and 0.73 mm s^?1 respectively. They were linearly related to both m and .     

Mössbauer Spectroscopic Studies of Chlorostannate(II) Complexes in Frozen Aqueous Solutions

Mössbauer parameters of frozen aqueous solutions of Sn(ClO₄)₂ in 0.5 M HClO₄ did not change with the concentration of NaClO₄, so that it was used to keep the ionic strength at the desired level. When NaCl was added into Sn(ClO₄)₂ solutions, isomer shift did not change, but quadrupole splitting did. Therefore, stability constants were calculated from the quadrupole splitting data, which were in good agreement with the published values. The observed spectra could be resolved into components.     

Mössbauer Spectroscopic Studies of Bromostannate(II) Complexes in Frozen Aqueous Solutions

Mössbauer spectra of KSnBr₃·2H₂O were very broad and could not fit Lorentz equation, suggesting unresolvable quadrupole doublets. Its quadrupole splitting was estimated to be about 0.25 mm/s from the separate experiments on frozen aqueous solutions of Sn(II)-Br^? systems. Stability constants of bromostannate(II) complexes were determined at μ = 3.5 from the Δ-c_L curve by the approximation method, which were in agreement with the literature values.     

Mössbauer Spectroscopic Determination of Stability Constants of Fluorostannate(II) Complexes

Stability constants of fluorostannate(II) complexes were determined Mössbauer spectroscopically by rapid freezing technique. The observed isomer shift values suggested that these complexes were hydrogen bonded in perchloric acid solutions.     

Magnetic Hyperfine Mössbauer Spectra of Ferrocenyaldimines-FeCl3 Adducts

Ferrocenylaldimines (Fc-CH=N-R) were prepared by condensation of Schiff base of formylferrocene with polyacenylamines RNH₂; R = naphthyl, anthracenyl and pyrenyl groups. This step was followed by oxidation with FeCl₃ to give [Fc-CH=NR]-FeCl₃ adducts. The electronic state of iron in these adducts was investigated by means of ⁵⁷Fe Mössbauer spectra except for [Fc-CH=N-Pyr]-FeCl₃ showed that only a doublet was observed at ambient temperature. As the temperature was decreased below 200 K, additional magnetic hyperfine splitting was observed characteristic of ferric oxide.     

Mössbauer and Electrochemical Studies of Bridged Biferrocenes and Biferrocenylenes

A series of neutral and oxidized π-bridged biferrocenes (Fc—x—Fc) and biferrocenylenes (FC(—x—)₂Fc) (x= —CH=CH—, —CH₃,C=CCH₃—) were prepared and their physical properties have been studied by means of Mössbauuer and cyclic voltammetry. The electrode reaction of these bridged ferrocene derivatives appears to involve a consecutive two-step oxidation process. The results also show that the voltage difference between the first and second oxidaton potentials of the bridged biferrocenes was found to be largely exceeded that founded for the corresponding the bridged biferrocenylenes. The Mössbauer data show that the oxidation of doubly bridged Fc(—x—)₂Fc with iodine, DDQ, and TCNQ given the corresponding dioxidized salts only and no stable mixed-valence compounds were found.     

Mössbauer Spectroscopic Studies of K2SnCl6 and SnCl4·5H2O in Frozen Aqueous Solutions and in Ion Exchange Resins

Concentration dependence of isomer shift of K₂SnCl₆ and tin(IV) chloride was studied. Tin was hydrolyzed in both cation and anion exchange resins after water washing. Two pairs of these two solutions showing the same isomer shift values, and therefore the same , were selected for further studies in HCl solutions and in anion exchange resins. The first pair was 0.04 M K₂SnCl₆ and tin(IV) chloride solutions (δ=0.00 mm/s; =0): Their δ-[HCl] curves coincided each other. Tin was sorbed on anion exchange resin as pentachlorstannate(IV) at (HCl)≤6 N, and chiefly as hexachlorostannate(IV) at [HCl]≥7 N. The both complexes were sorbed when 6 N < [HCl] < 9 N. The δ-[HCl] curves of the second pair, 0.4 M K₂SnCl₆ and 3 M tin(IV) chloride(δ =0.23 mm/s; =3), also coincided each other, and tin was sorbed as pentachlorostannate(IV) from K₂SnCl₆ solutions in the HCl concentration range studied (≥5 N).     

Fifty Years of Mössbauer Spectroscopy in Solid State Research – Remarkable Achievements,Future Perspectives

Mössbauer spectroscopy was founded more than fifty years ago based on an outstanding discovery by the young German physicist Rudolf Ludwig Mössbauer while working on his Ph.D. thesis. He discovered the recoilless nuclear resonance fluorescence of gamma radiation and was awarded the Nobel Prize in Physics in 1961 as one of the youngest recipients of this most prestigious award. His discovery led to the development of a new technique for measurements of hyperfine interactions between nuclear moments and electromagnetic fields. This method, with highest sharpness of tuning of 10^–13, yields information on valence state, symmetry, magnetic behavior, phase transition, lattice dynamics and other solid state properties.     

An in‐situ Mössbauer Study of the Formation of Cementite,Fe3C

The formation of cementite, Fe₃C, from thin iron foils has been studied at 550 and 650 °C by means of in‐situ Mössbauer spectroscopy. At 550 °C, the kinetics of the reaction have been determined from time‐resolved experiments performed at different carbon activities. The product formation follows a two‐step process exhibiting two different kinetic regimes. The slow initial stages of the reaction as well as its rapid final part can be described by an Avrami‐type kinetics with a characteristic parameter of n = 3/2.     

Mössbauer Line Shape of Frozen Aqueous Solutions

Isomer shift of simple lines of the frozen mixture solutions of SnCl5H₂O and K₂SnF₆ were linearly related to mole fraction and, therefore, to average ligand number, ñ. These spectra corresponded to Sn(H₂O)_6-ñF_ñ^{(- ñ)+}. Assuming that quadrupole splitting was also linearly related to ñ, Mössbauer spectra of Sn(ClO₄)₂ solutions containing different amount of HF could be resolved into components.     

Electrodeposition and Mössbauer Spectra of Fe-Zn Alloys on Aluminum Foil

By controlling the current density, pH and temperature of the electrodepositing iron-zinc bath, various compositions of electrodeposited Fe_1-xZn_x (0.95 > x > 0.15) alloys on Al-foil have been prepared. The electronic state, intermetallic phases and magnetic hyperfine interactions have been studied by means of ⁵⁷Fe Mössbauer spectroscopy at 298K for these electrodeposited Fe-Zn alloys. The isomer shifts obtained from the Mössbauer spectral of the alloys increased with increasing Zn content. An alloy containing above 50% Fe, exhibits a linear dependence of the internal magnetic field, Hin, on the Zn content.     

Mössbauer Spectra and Magnetic Properties of Polydiimine Complexes of Iron(II) Sulfate

A new series of polynuclear iron complexes with polydiimine ligand have been prepared from the Schiff-base condensation of pyridine-2, 6-dialdehyde or 2, 6-diacetylpyridine with aliphatic diamines. The structures of the complexes are represented by [?N = CR-Py-CR = N-(CH₂)_n-]₂FeSO₄·xH₂O; where R = H, CH₃; n = 4?10, × = 5～8. Mössbauer spectra and magnetic measurements show several complexes have unusual magnetic properties.     

Concentration Dependence of Mössbauer Parameters of SnCl−3 and SnBr−3 Complex Ions

Mössbauer parameters of frozen salt solutions could be correlated with apparent degree of dissociation, γ. KSnCl₃ and KSnBr₃ were dissolved in 0.5 M H₂SO₄, whereas NH₄ SnCl₃ was dissolved in 0.5 M HClO₄. Mössbauer studies were made at different concentrations.     

The Effect of Perchloric Acid on the Mössbauer Parameters of tin-119 in Frozen Solutions

The Mössbauer parameters of frozen solutions of 0.05 M Sn(H₂O)(ClO₄)₂, Sn(H₂O)₃(ClO₄)₄, SnCl₄·5H₂O, SnBr₄ and Na₂SnBr₆ [designated as Sn(H₂O)_N-N, L^(x-N')+_N, in which N≤N; N' = N = 6 for SnBr^2?₆, N′=4 with N=6 for Sn(H₂O)₂(ClO₄₄ Sn(H₂O)₂Cl₄ and Sn(H₂O)₂Br₄ and N′=2 with N=3 for Sn(H₂O)(ClO₄₄)₂] were found to be linearly related to the concentration (c) of perchloric acid. These facts were attributed to a change in activity of water (a_w). At c=O, a_w=1, the Mössbauer parameters corresponded to Sn(H₂O)^z+_N, whereas at c=11.6 M (70%), they corresponded to the crystalline state of Sn(H₂O)_N-N, L^(z-N)+_N+. It was shown that even ClO^?₄ ion could coordinate to tin atom in perchloric acid. The degree of association at any given c could be estimated very easily through the relation . It was emphasized that the activity of water should be taken into account when equilibrium studies were carried out in perchloric acid solutions. Further corrections for perchlorate complex formation should be made, if a very weak ligand was added into metal perchlorate solutions.