Mössbauer study of iron carbide nanoparticles produced by laser ablation in alcohols

Iron carbide nanoparticles were synthesized by laser ablation of iron in alcohols (methanol and ethanol). A new cell, designed to allow the ablation to be conducted in a flowing solvent, enabled separation and collection of the nanoparticles immediately after production, thus preventing further photochemical reactions of the colloids. The nanoparticles were investigated using Mössbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. In methanol, they consisted of α-iron, γ-iron, iron carbide, and amorphous paramagnetic iron carbides, whereas in ethanol they consisted of iron carbides and amorphous paramagnetic iron carbides. The difference in products depending on the alcohol was attributed to the different carbon supplies for methanol and ethanol. For both solvents, the average particle size was found to be 16 nm, and the nanoparticles were dispersed in amorphous carbon. We also examined the effect of further laser irradiation of the colloids using stagnant solvent, and the particle size was found to increase and a very small amount of carbonization was observed.     

Mössbauer study of iron hydride produced under high pressure

The hexagonal iron hydride formed at a hydrogen pressure of about 7 GPa was studied by⁵⁷Fe Mössbauer spectroscopy. At 80 K its spectrum consists of two magnetic patterns with hyperfine fields of 33.6 and 29.0T, respectively. Both have an isomer shift of +0.50mm/s with respect to-iron. A tentative explanation for these results is that iron hydride is stoichiometric FeH with a dhcp crystal structure.     

Mössbauer effect study of the effect of gamma irradiation and heat treatment on montmorillonite

Mössbauer spectroscopy was used to study the effect of gamma irradiation and heat treatment on montmorillonite. Samples were irradiated to gamma-ray doses ranging from 10 Gy up to 30 MGy. Other samples were heated to different temperatures from 400 C up to 1350 C. The lattice distortion caused by gamma irradiation could be followed. The phase transformations which occurred through and above the dehydroxilation temperature range could be traced and identified. The Mössbauer results were confirmed by X-ray diffraction results.     

Mössbauer study of tektites

Room temperature ⁵⁷Fe Mössbauer spectroscopy has been used to investigate the structural and oxidation state of Fe in tektites from different strewn fields. Spectra have been analyzed in terms of two quadrupole splitting distributions corresponding to Fe^3?+? and Fe^2?+?. All tektites show similar distribution of quadrupole splitting. Each distribution has one peak. The Fe^2?+? sites show a narrow region of Mössbauer line shift (δ) and quadrupole splitting (ε), δ?= 1.02–1.10 mm/s and ε?= 0.85–1.00 mm/s relative to α-Fe. These values have been assigned to intermediate coordination between tetrahedral and octahedral. The Fe^3?+? sites show wider regions of hyperfine parameters: δ?= 0.25–0.45 mm/s and ε?= 0.65–0.90 mm/s. The Fe^3?+?/Fe^2?+? ratio was found to be 0.05–0.15.     

Mössbauer study of products of the thermocatalytic treatment of kerogen-containing rocks

To understand the mechanism of highly efficient catalyst formation from precursors, the active form of an iron-containing catalyst and kerogen samples from the Bazhen formation are studied by Mössbauer spectroscopy and X-ray diffraction analysis. It is established that as a result of phase changes, the multicomponent precursors are transformed into mixed transition metal oxides. It is found that the thermocatalytic effect on pyrite-containing kerogen leads to the formation of pyrrhotite FeS_{1 ? x} and mixed oxides of iron.     

Mössbauer study of natural wolframites

Natural Wolframite, (Fe _x Mn_1?x )WO₄ withx=0.95 to 0.41, obtained from seven different sites of two quartz-wolframites deposits of Degana and Sirohi in Rajasthan. India, have been studied by Mössbauer spectroscopy down to 20 K. X-ray diffraction studies with a monochromatic Cu radiation (λK_a-1.5405 Å), were carried out to determine the value ofx. The Mössbauer spectra of all seven samples were recored at 300, 200, 100, 50, 40, 30 and 20 K, and were least square fitted for different sites. The Mössbauer parameters are attributed to a high spin ferrous ion in a quite distorted octahedral symmetry, and only one sextet has been resolved below transition temperature.     

Mössbauer study of Hungarian phlogopites

Ultramafic xenoliths of mantle origin occur in Hungarian Cretaceous lamprophyres. The aim of the present work was to determine the iron positions and their occupancy in phlogopites originated from ultramafic xenoliths by the help of Mössbauer spectroscopy. On the basis of the evaluation of the Mössbauer spectra Fe _M1 ²⁺ , Fe _M2 ²⁺ , Fe _M2 ³⁺ and Fe _M1 ³⁺ (or in some cases Fe_tet) octahedral and tetrahedral iron sites were identified in the samples. Quantitative analysis was performed for all of the iron sites. We have observed large differences between the Fe²⁺/Fe³⁺ ratio in samples originated from 120–150 km deepness, which phlogopites having been existed at different erosion circumstances. We have found a significantly higher Fe²⁺/Fe³⁺ ratio in phlogopites which had been solidified in 120–150 km depth from the surface of Earth 70–100 million years ago, than those had been crystallized in 60–80 km deepness.     

Mössbauer study of Slovak meteorites

⁵⁷Fe Mössbauer spectroscopy was used as an analytical tool in the investigation of iron containing compounds of two meteorites (Rumanová and Ko?ice) out of total of six which had fallen on Slovak territory. In the magnetic fraction of the iron bearing compounds in the Rumanová meteorite, maghemite, troilite and Fe-Ni alloy were identified. In the non-magnetic fraction silicate phases were found, such as olivine and pyroxene. The paramagnetic component containing Fe^3?+? ions corresponds probably to small superparamagnetic particles. The Ko?ice meteorite was found near the town of Ko?ice in February 2010. Its magnetic fraction consists of a Fe-Ni alloy with the Mössbauer parameters of the magnetic field corresponding to kamacite α-Fe(Ni, Co) and troilite. The non-magnetic part consists of Fe^2?+? phases such as olivine and pyroxene and traces of a Fe^3?+? phase. The main difference between these meteorites is their iron oxide content. These kinds of analyses can bring important knowledge about phases and compounds formed in extraterrestrial conditions, which have other features than their terrestrial analogues.     

Mössbauer study of Brazilian soapstone

Steatite mineral rocks, soapstone, have been studied by X-ray diffraction, optical microscopic analysis (modal analysis), electron probe micro analysis and Mössbauer spectroscopy for characterization, mineral percentages and chemical composition. Mössbauer spectra show both, magnetic interactions corresponding to magnetite and doublets corresponding to talc. chlorite, dolomite and tremolite. The temperature dependence of the quadrupole splitting in dolomite has been explained in terms of crystal field interaction.     

M?ssbauer study of iron nitride films produced by pulsed laser deposition

Iron nitride films were produced by pulsed laser deposition of Fe onto an Al substrate in an N₂ atmosphere and their M?ssbauer spectra and powder X-ray diffraction patterns were measured. The nitrogen content of the iron nitride films varied depending on the N₂ pressure. Under high N₂ pressures, γ”-FeN (ZnS structure) and γ’”-FeN (NaCl structure) were obtained. The yields of these two phases could be controlled by varying the Al substrate temperature. γ”-FeN and γ’”-FeN were found to be paramagnetic and antiferromagnetic, respectively, at 5?K.     

Mössbauer study of Fe-Re alloys prepared by mechanical alloying

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for nanocrystalline iron-based solid solutions Fe _1?x Re _x , prepared by mechanical alloying with x in the range 0.01 ≤ x ≤ 0.04. The obtained data were analysed in terms of the binding energy E _b between two rhenium atoms in the Fe-Re system. The extrapolated value of E _b for x = 0 was used for computation of enthalpy of solution of rhenium in iron. The result was compared with that resulting from the cellular atomic model of alloys by Miedema as well as with value, derived from proper data for Fe-Re solid solutions obtained by melting in an arc furnace. From the comparison it follows that our findings are in agreement with the Miedema’s model predictions and previous Mössbauer studies.     

Mössbauer study of iron-doped lithium niobate

From Mössbauer spectra of LiNbO₃⁵⁷Fe(III) single crystals under external fields of 4.92 and 6.2 T, the crystal field and hyperfine parameters are determined. Transmission integral fits indicate a Boltzmann population of the Fe(III) electronic levels with a spin temperature equal to the sample temperature. Spectra at external fields of 0 T and 19 mT can be satisfactorily simulated using an effective spin 1/2,g-factors calculated from spin-expectation values and an internal averaged dipole field of 5.5 mT inclined 20 to thec-axis. The simulations indicate cross-relaxation between Nb and Li nuclear spins and the Fe(III) electronic spin.     

57Fe-Mössbauer study of electrically conducting barium iron vanadate glass after heat treatment

Local structure and thermal durability of semiconducting xBaO·(90?? x)V₂O₅ · 10Fe₂O₃ glasses (x = 20, 30 and 40), NTA glass ^TM, before and after isothermal annealing were investigated by ⁵⁷Fe-Mössbauer spectroscopy and differential thermal analysis (DTA). An identical isomer shift ( $\mathit{\delta}$ ) of 0.39 ± 0.01 mm s^???1 and a systematic increase in the quadrupole splitting (Δ) were observed from 0.70 ± 0.02 to 0.80 ± 0.02 mm s^???1 with an increasing BaO content, showing an increase in the local distortion of Fe^IIIO₄ tetrahedra. From the slope of the straight line in the T _g–Δ plot of NTA glass ^TM, it proved that Fe^III plays a role of network former. Large Debye temperature (Θ _D) values of 1000 and 486 K were respectively obtained for 20BaO · 70V₂O₅ · 10Fe₂O₃ glass before and after isothermal annealing at 400°C for 60 min, respectively. This result also suggests that Fe^III atoms constitute the glass network composed of tetrahedral FeO₄, tetrahedral VO₄ and pyramidal VO₅ units. The electric conductivity of 20BaO · 70V₂O₅ · 10Fe₂O₃ glass increased from 1.6 × 10^???5 to 5.8 × 10^???2 S cm^???1 after isothermal annealing at 450°C for 2,000 min. These results suggest that the drastic increase in the electric conductivity caused by heat treatment is closely related to the structural relaxation of the glass network structure.     

Mössbauer spectroscopy of grain boundaries in ultrafine-grained materials produced by severe plastic deformation

The applicability of Mössbauer spectroscopy in studying grain boundaries in ultrafine-grained materials produced by severe plastic deformation (SPD) is analyzed. It is shown that grain boundaries after SPD are in a nonequilibrium state that is characterized by excess free volume.     

Mössbauer study of CO-precipitated Fischer-Tropsch iron catalysts

Mössbauer spectroscopy studies of precipitated Fischer-Tropsch (FT) iron catalysts, viz. 100 Fe/5 Cu/4.2 K/x SiO₂, wherex=0,8, 16, 24, 25, 40, or 100, have shown that reduction of the oxide precursor in CO gives rise to -carbide Fe₅C₂ whose amount decreases with an increase of SiO₂ content. The -carbide is converted into magnetite Fe₃O₄ while catalyzing the FT synthesis reaction. A correlation between FT activity and the content of -carbide in the catalysts was found, which indicated that -carbide is active for FT synthesis reaction.     

Mössbauer study of the Cu-Zn alloy system

Using the 93.3keV transition in⁶⁷Zn, the Lamb-Mössbauer factor, the electron density and the electric field gradient at the Zn nucleus have been determined for pure Zn metal, the ^–, ^–, ^–, and -phases as well as pure Cu metal.     

Mössbauer and EPR study of nitrosyl hemoglobin

Nitrosyl hemoglobin was prepared by bubbling fresh⁵⁷Fe-enriched rat hemoglobin with NO. S- and X-band EPR spectra at 77 K are typical for anS=1/2 system with an anisotropicg-tensor and exhibit hyperfine interactions of¹⁴N with the electronic spin. Mössbauer spectra at 4.2 and 100 K consist of a superposition of spectra from high- and low-spin Fe(III), deoxygenated hemoglobin and a component corresponding toS=1/2,g=2, hyperfine constantsA _xx /g _{n n} =A _yy /g _{n n} =–19.6 T,A _zz /g _{n n} =6.8 T, quadrupole splitting E _Q=1.5 mm s^–1, isomer shiftI _s=0.42 mm s^–1 and linewidth 0.4 mm s^–1. The spin-lattice relaxation rate at 100 K is <2×10⁶ s^–1.     

Mössbauer study of carbon-supported α-Fe catalysts

Mössbauer spectra of carefully reduced carbon-supported iron catalysts show superparamagnetic -Fe at 80 K. The results indicate that the particle size depends on the reduction temperature. Effects of evacuation and CO chemisorption are discussed.     

Mössbauer study of internally oxidized silver-tin alloys

A Mössbauer study of internally formed oxides as a function of oxidation temperatures between 200 C and 850 C was performed on previously annealed 1 at%AgSn alloys. The oxide formed at high temperatures (t 500 C) consists in agglomerates of tin dioxide = 0.00 ± 0.01 mm/s, Q=0.50 ± 0.03 mm/s). The low temperature oxide (t 300 C) is characterized by = 0.29 ± 0.02 mm/s and Q=0.32 ± 0.03 mm/s, and could be in the form of one-Sn-atom oxide complexes in the silver matrix. From the measured isomer shifts in the range 400 t 550 C, the maximum contribution of the silver matrix to the effective number of electrons per Sn atom in oxide agglomerates has been estimated have a value of about 0.06. The effect of the cold work on the hyperfine parameters of the oxidized tin has also been investigated. As rolled samples were found to attain the same values of isomer shifts and quadrupole splittings as annealed specimens, but at lower temperatures.