Conversion X-ray Mossbauer Spectroscopy Research Articles

Mössbauer Instrument Package MS-2000IP

The paper describes the Instrument Package MS-2000IP, which is based on some new technical ideas of the authors. It allows to increase essentially the productivity of Mossbauer measurements in transmission Mossbauer spectroscopy, in conversion X-ray Mossbauer spectroscopy (XMS), as well as in conversion electron Mossbauer spectroscopy (CEMS).

Photon and Ion-Beam Induced Processes in Materials Studied by Hyperfine Interactions

Laser nitriding and laser cementation are investigated by Mossbauer spectroscopy and complementary methods. It is demonstrated how the backscattering versions of Conversion Electron and Conversion X-ray Mossbauer spectroscopy can contribute to the investigation of surface processes, like the laser-induced formation of nitrides and carbides. Additionally, the formation of semiconducting iron disilicide can be achieved by ion-beam mixing and pulsed laser irradiation of Fe/Si bilayers. The results of both processes are compared.

Iron nitrides and laser nitriding of steel

Nitriding of iron and steels is well known to improve hardness, wear and corrosion resistance of surfaces. Recently, it has been found that a simple irradiation of iron and steel with pulses of an excimer laser in air or nitrogen leads to a significant nitrogen take-up into the surface and to improvements in the surface properties. The mechanisms of the laser-nitriding process are not yet understood but the nitrification will be proved by several methods. Among these, Mossbauer spectroscopy is very powerful, especially when Conversion Electron and Conversion X-ray Mossbauer Spectroscopy (CEMS and CXMS) are applied simultaneously. Nevertheless, only a combination of methods gives a satisfying overview of the laser induced nitriding processes: Rutherford Backscattering Spectrometry (RBS) and Resonant Nuclear Reaction Analysis (RNRA) were also used to characterize the treated surfaces. First measurements show an increase of the hardness and the wear resistance with the number of pulses. From the results of the CEMS analyses this should be correlated with the increase in the fraction of the e-phase. This may be important for industrial applications.

Laser nitriding investigated with Mössbauer spectroscopy

The effect of the nitrogen take‐up upon irradiation of iron or steel with excimer laser pulses in air or in nitrogen atmosphere is well established. The resulting phase compositions and nitrogen depth profiles were measured by a combination of simultaneous Conversion Electron Mossbauer Spectroscopy (CEMS), Conversion X‐ray Mossbauer Spectroscopy (CXMS), and Resonant Nuclear Reaction Analysis (RNRA) as a function of the nitrogen gas pressure during irradiation. A maximum nitrogen content and a maximum fraction of the ɛ-nitride was found at 0.1 MPa. This result is in accordance with hardness measurements performed by the nanoindentation technique.

Enhanced magnetization and cation distributions in nanocrystalline ZnFe/sub 2/O/sub 4/: a conversion electron Mossbauer spectroscopic investigation

The synthesis of nanocrystalline zinc ferrite (ZnFe/sub 2/O/sub 4/) has been accomplished by a variety of chemical and mechanochemical techniques. An enhanced magnetization, 4-5 times that of bulk zinc ferrite, is observed for the nanoparticles regardless of the synthesis method. The hypothesis that the enhanced magnetization is due to partially inverted nanocrystalline zinc ferrite has been examined by transmission /sup 57/Fe Mossbauer spectroscopy (TMS), conversion X-ray Mossbauer spectroscopy (CXMS) and conversion electron Mossbauer spectroscopy (CEMS). Both TMS and CXMS data indicate differences in local structure between bulk and nanocrystalline samples, however they do not suggest that the samples are partially inverted. CEMS data are similar for both bulk and nanocrystalline samples, indicating similar cation distributions near the surface of nanocrystalline and bulk particles.

Microstructure of nodular cast iron after excimer laser surface processing

Nodular iron of martensitic structure was treated by means of a XeCl laser prototype. The energy density varied from 0.3 to 5 J/cm2 and the number of shots from 4 to 40. Conversion electron Mossbauer spectroscopy, conversion X-ray Mossbauer spectroscopy and grazing incidence X-ray diffraction were used to characterize the irradiated surface. Some Rutherford backscattering spectrometry measurements were performed to control surface oxidation and carbon distribution. It is shown that after irradiation austenite formed in a rather deep heat affected zone (10–20 μm) compared to the thickness of the melted zone (∼ 1 μm). The austenite amount as well as its carbon content increase with energy density and number of shots up to a threshold of carbide formation. Beyond the threshold Fe2C, Fe3C and Fe5C2 formed only in the melted zone. The carbon content as a function of depth is constant in the melted layer, then decreases quickly from the melted layer-heat affected zone interface down its initial value. The carbon content is shown to govern the evolution of phases content in the melted layer depending on the laser treatment conditions.

CEMS, CXMS and X-ray investigation of the microstructure of the surface layer in plasma nitrocarburized steel

The microstructure of the compound layer formed by plasma nitrocarburizing of steels has been investigated by means of conversion electron, conversion X-ray Mossbauer spectroscopy (CEMS, CXMS) and X-ray diffraction. A carbon steel C35 was plasma nitrocarburized using a gas mixture of nitrogen, hydrogen and methane. The compound layer was mechanically removed in steps, followed by Mossbauer and X-ray investigations. It was found that this layer consists of different nitrides and carbides. Their concentrations vary with the depth below the surface.

Effect of heat treatment on the microstructure and magnetic properties of polycrystalline MnZn ferrites

The effect of heat treatment of commercially available polycrystalline MnZn ferrite slabs was studied for temperatures near typical recording head glassing temperatures. Toroid-shaped specimens were heated in atmospheres of varying levels of oxygen and the deterioration in magnetic properties was measured. The surfaces of the exposed specimens were inspected by means of optical and electron microscopy and the occurrence of ferrite instabilities such as grain growth, segregation of secondary phases etc. were observed. The degradation also appeared to be surface-driven. To investigate this further, some samples were heat treated in highly oxidizing and reducing atmospheres to induce gross ferrite instabilities. The near surface regions of these samples were then characterized by x-ray diffraction, x-ray photoelectron spectroscopy (XPS) and conversion electron and conversion x-ray Mossbauer spectroscopy (CEMS and CXMS). In addition to grain growth and other structural changes, the precipitation of extraneous phases appears to be a major mode of ferrite failure during such annealing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

CXMS study of mild steel laser alloyed with CrB2

Laser alloying of surfaces has attracted a great deal of attention for technical applications. By laser alloying of materials it is possible to improve hardness as well as wear and corrosion resistance of the surface without affecting the bulk material. The surface of a mild steel (C45) substrate was laser-alloyed with chromium-boride CrB2. The chromium-boride was added to the substrate surface by powder injection during laser surface melting with a high power continuous-wave CO2-laser. The resulting surface layers were studied by surface Mossbauer measurements. The backscattering geometry of Conversion X-ray Mossbauer Spectroscopy (CXMS) was used to study the phase formation in the laser alloyed surface. The results for the treated surfaces are discussed for different samples.