Irradiation effects in amorphous alloy Fe80B20

The Mössbauer effect has been used to study the irradiation effects in the amorphous alloy Fe₈₀B₂₀ after 40 keV helium ion bombardment. Conversion electron Mössbauer spectroscopy reveals the eminent irradiation effects; α-iron phase appears in the damaged region of the sample.     

Stress-induced magnetic easy axis in amorphous Fe40Ni40P14B6

In a ribbon of amorphous Fe₄₀Ni₄₀P₁₄B₆ (Metglas 2826) the iron spins tend to be parallel to the plane of the ribbon, but the distribution of spin directions within the plane is nearly random. When a uniaxial tensile stress is applied to the ribbon the spins become almost completely aligned parallel to the applied stress. The technique of Mössbauer polarimetry was used to detect and measure this effect.     

The performance of iron-containing catalysts prepared at low temperature for carbon monoxide hydrogenation

The performance for carbon monoxide hydrogenation of amorphous- and crystalline-unsupported iron oxides following low temperature pretreatment in nitrogen, carbon monoxide and hydrogen has been examined. The phase compositions of the catalysts before and after catalytic evaluation have been determined by⁵⁷Fe Mössbauer spectroscopy. Pretreatment of amorphous non-potassium doped precipitates gave the formation of metallic iron catalysts which were catalytically active at low temperatures and which were shown by Mössbauer spectroscopy to be converted during evaluation to iron carbide and the iron oxide Fe₃O₄. Catalysts which were not pretreated were reduced during catalytic evaluation to Fe₃O₄. Pretreated potassium-doped catalysts composed of either iron carbide or a mixture of iron carbide and metallic iron gave hydrocarbon product distributions which showed a higher Schulz-Flory alpha value and a lower selectivity towards methane when the catalyst reached steady state as a result of an increase in carbon monoxide adsorption and/or a decrease in hydrogen adsorption. The used catalysts were shown by Mössbauer spectroscopy to contain iron carbide together with various proportions of metallic iron and the iron oxide Fe₃O₄. The activities of the pretreated amorphous and crystalline catalysts were comparable and may be related to the disintegration of the crystalline catalysts during pretreatment in carbon monoxide which induces the formation of particles with surface areas similar to those observed in the amorphous catalysts.     

Mössbauer spectroscopical investigation of amorphous Fe–Y alloy ribbons prepared by melt spinning

Fe–Y amorphous alloy ribbons were prepared by the melt spinning method and characterized by X-ray diffraction, Mössbauer spectroscopy and inelastic neutron scattering. X-ray diffraction demonstrates that the Fe_0.7Y_0.3 ribbons are completely amorphous, whereas the Fe_0.3Y_0.7 ribbons contain a small fraction of crystalline Y precipitates in the amorphous Fe–Y matrix. Mössbauer spectroscopy between 4.2 to 300 K reveals the amorphous nature of the Fe–Y matrix and the Fe_0.7Y_0.3 ribbons. The preliminary neutron scattering results S(Q, ω) show excess low energy vibrational modes which gives rise to the so called “boson peak” in this amorphous material.     

Crystallization of Fe-B amorphous alloy powders produced by chemical reduction

The crystallization behaviour of the Fe?B amorphous alloy powders prepared by the chemical reduction method has been investigated by Mössbauer spectroscopy. In comparison to amorphous ribbons prepared by melt-spinning, a different crystallization behaviour has been observed. After annealing the amorphous samples entirely crystallized into three crystalline phases: α-Fe, Fe₃B, and Fe₂B. In the case of Fe₈₀B₂₀ amorphous alloy ribbons produced by melt-spinning technique eutectic crystallization is commonly observed and results in the crystalline phases: α-Fe and Fe₃B. This kind of crystallization was not observed in the chemically prepared samples. The metastable tetragonal Fe₃B phase transformed completely into α-Fe and Fe₂B after annealing at 973 K for one hour.     

Mössbauer study of the in-plane anisotropy in annealed amorphous Fe81B13.5Si3.5C2 ribbons

Mössbauer spectra of amorphous Fe₈₁B_13.5Si_3.5C₂ ribbons (METGLAS 2605 SC) annealed in transverse magnetic field at 594 and 654 K were recorded for various orientations of the ribbons. It is determined that the in-plane projection of the anisotropy is 17° off the transverse axis for the 594 K annealed specimen and 10° off the transverse axis for the 654 K specimen.     

Hydrogen absorption in LaNi4.9Fe0.1

The magnetic properties of LaNi_4.9Fe_0.1 and its hydride have been studied by making Mössbauer and magnetic susceptibility measurements. ⁵⁷Fe Mössbauer spectroscopy shows a small increase in the isomer shift after hydriding. An increase in the magnetic susceptibility after hydriding was observed.     

Preferential substitution of 57Fe in Co1−χBχ glasses

The substitution of iron for cobalt in crystalline Co₃B and Co₇₈B₂₂ and Co₇₂Si₂B₂₆ glasses has been studied by Mössbauer spectroscopy. In both crystalline and amorphous states, iron preferentially replaces those cobalt atoms which have two boron nearest neighbours.     

57Fe Mössbauer study of amorphous Fe81B13.5Si3.5C2

The amorphous ferromagnet Fe₈₁B_13.5Si_3.5C₂ (Metglas^® 2605SC) has been investigated with Mössbauer spectroscopy. The hyperfine interaction parameters are studied between 80 and 300 K from which some characteristic properties are deduced. The behaviour of the amorphous alloy at higher temperatures has been studied by the room temperature spectra of annealed samples. After a structural relaxation process, a two step crystallization transformation is observed leading to Fe-Si alloy and Fe₂(B, C). X-ray diffraction of samples annealed at higher temperatures reveals the presence of an orthorhombic Fe-B-Si phase of which the structure changes slightly with annealing temperature.     

Hyperfine parameters of amorphous Fe64Cr16B20 particles dispersed in an alumina matrix

Mössbauer spectra of amorphous Fe₆₄Cr₁₆B₂₀ particles dispersed in an alumina matrix are compared to those of the corresponding amorphous ribbon. The slight variations between the hyperfine parameters of the granular samples are mainly assigned to disorders at the particle surface. The behaviour of the blocking temperatures versus frequency deduced from A.C. susceptibility measurements and Mössbauer spectroscopy is governed by particle interactions.     

Hyperfine field distribution in amorphous Fe40Ni40B20

From the Mössbauer investigation of amorphous Fe₄₀Ni₄₀B₂₀ and Fe₈₀B₂₀ alloys it was found that the substitution of Fe by Ni only shifts but does not influence the shape of the iron hyperfine field distribution contrary to that of crystalline f.c.c. Ni-Fe alloys suggesting a rather localized type of behaviour. The distributions of the linear combinations of isomer shift and quadrupole splitting are affected by this substitution.     

Mössbauer study of the effect of potassium on iron oxide catalysts

One kind of catalyst used for dehydrogenation of ethylbenzene to styrene was investigated by⁵⁷Fe Mössbauer spectroscopy. The results show that the area ratioS _B /S _A of two Mössbauer subspectra of Fe_3-vO₄ produced after catalytic reaction depends on the amounts of potassium added to the catalysts. A tentative conclusion is that the effect of potassium in iron oxide catalysts could be related to the reduction of Fe³⁺ to Fe²⁺.     

Preparation and Mössbauer study of a new Fe-rich amorphous alloy,Fe90Sc10

A new amorphous metal-metal alloy Fe₉₀Sc₁₀ has been prepared by single roller melt quenching. Mössbauer spectra above and below the magnetic ordering temperature of 99K have been analysed in terms of distributions of magnetic hyperfine fields and quadrupole splittings.     

Mössbauer and magnetic studies of BaVS3 and V5S8 doped with 57Fe

Iron can be easily introduced in BaVS₃ and V₅S₈. It is located at the vanadium sites and has been used as a probe to analyse by Mössbauer effect the magnetic properties of its surrounding matrix. The electronic state of iron in this matrix has also been studied. It was found that in BaVS₃, the iron is in a low spin Fe³⁺ configuration $\text{(S =}\text{1}\text{2}\text{)}$. In V₅S₈ at 4.2 K, the iron is in low spin Fe²⁺ configuration (S = 0). The rapid decrease of quadrupole splitting observed between 50 and 200 K is attributed to a thermally activated change in electronic structure. The high temperature configuration (above 200 K) seems to be neither pure low spin Fe³⁺ nor high spin Fe²⁺, but a mixture of configurations fluctuating at a rate which is faster than the characteristic time of Mössbauer measurements.     

Oxidation state and short range order at the surfaces of amorphous Fe40Ni40P14B6 ribbons

Conversion electron Mössbauer spectroscopy (CEMS) was used to study the oxidation state at the surfaces of amorphous Fe₄₀Ni₄₀P₁₄B₆ ribbons obtained by melt-spinning in air and vacuum heated at 583 K. Different concentrations of ferric and ferrous ions depend on the different behaviour of phosphorous diffusion towards the two surfaces during low annealing temperature.     

Mössbauer study of a ferromagnetic metallic glass: Fe74Co10B16

Amorphous Fe₇₄Co₁₀B₁₆ (METGLAS 2605CO) has been studied in the temperature range of 77 K – 700 K by Mössbauer spectroscopy. Its crystallization temperature is found to be 665 ± 5 K and Curie temperature is estimated to be 760±10 K. The observed rapid decrease in reduced hyperfine fields can be explained well by Handrich's model for amorphous ferromagnets if one assumes a temperature dependent δ, a measure of fluctuations in the exchange interactions in such solids.     

In situ characterisation of supported iron-iridium catalysts by iron-57 and iridium-193 Mössbauer spectroscopy

Some silica-supported iron-iridium catalysts with different iron to iridium ratios and formed by the incipient wetness technique have been examined in situ by⁵⁷Fe and¹⁹³Ir Mössbauer spectroscopy following pretreatment in hydrogen. The results show that the reduction of the iron component is enhanced by the presence of iridium metal. The pretreated catalysts were evaluated for the hydrogenation of carbon monoxide at 270°C and 50 atmospheres pressure. The presence of iridium, which was shown by Mössbauer spectroscopy to result in the formation of reduced iron, iridium, and iron iridium alloy in the pretreated catalyst, was found to increase the catalytic activity and also influence selectivity. However, the systematic variation of the iridium content which was shown by Mössbauer spectroscopy to determine the exact phase composition of the pretreated catalysts, appeared to have little effect on catalytic performance. The⁵⁷Fe Mössbauer spectra recorded from all the used catalysts showed the formation of large and small particle ε′-Fe_2.2C under the high pressure of the catalytic reaction. The results suggest that the formation of iron carbides on reduced iron, perhaps at the surface, and the adsorption of hydrogen on reduced iridium are important features of this catalytic system.     

Magnetic properties of nanocrystalline composite in the Nd--Fe--B system

Using ⁵⁷Fe Mössbauer spectroscopy, X-ray diffraction and magnetization measurements, magnetic properties of melt-spun Nd_4.5Fe₇₇B_18.5 ribbon have been investigated after the annealing treatments which make nanocrystalline composite from the as-prepared amorphous state. Specimen ribbon which shows coercivity and is suitable for a permanent magnet consists of the mixture of Fe₃B and Nd₂Fe₁₄B. Relative fraction of these phases in the ribbon have been determined.     

激光辐照非晶Fe73.5Cu1Nb3Si13.5B 9微量晶化的穆斯堡尔谱研究

在激光功率为40—160W、扫描速度为10mm/s、激光光斑为20mm照射条件下,用CO ₂激 光辐照非晶Fe_73.5Cu₁Nb₃Si_13.5B_{9< /sub>产生微量晶化.利用透射穆斯堡尔谱 （TMS）技术分析了原始态和晶化后样品的超精细结构.确定了穆斯堡尔谱的基本参数——化 学位移(IS)、四极分裂(QS)、内磁场(Hhf)随激光功率变化的规律.分析表明，CO2关键词： 激光辐照 微量晶化 73.5Cu1Nb3 Si13.5B9')" href="#">非晶Fe73.5Cu1Nb3 Si13.5B9 穆斯堡尔谱}     

On the iron valence states in B2O3-PbO-GeO2 glasses

The Mössbauer effect measurements performed on 20Fe₂O₃ 80 3B₂O₃ (1?x)PbO xGeO₂ glasses show that the ratio between the number of ferrous ions to the total number of iron ions decreases by increasing the GeO₂ content. The Curie constants calculated from the distribution of iron cations obtained by Mössbauer effect data are in agreement with the values determined from magnetic measurements. Finally, we discuss the influence of the glass composition and melting temperature on the iron valence states.