F. Aubertin

Simultaneous conversion electron, conversion X-ray and transmission Mössbauer spectroscopy

Abstract Mossbauer spectroscopy can be performed in transmission (TMS) and backscattering geometry. The backscattering geometry of conversion electron Mossbauer spectroscopy (CEMS) and conversion X-ray Mossbauer spectroscopy (CXMS) enables nondestructive surface analysis to be carried out. Because of the different sampling ranges in these variations of Mossbauer spectroscopy it is of interest to measure them simultaneously. An experimental setup for simultaneous CEMS, CXMS and TMS measurements is shown.

Simultaneous Triple Radiation Mössbauer Spectroscopy (STRMS)

The setup for Simultaneous Triple Radiation Mössbauer Spectroscopy (STRMS) is described. The arrangement allows an independent and simultaneous recording of conversion electron Mössbauer spectra (CEMS) and of conversion X-ray Mössbauer spectra (CXMS), both in backscattering geometry, and-in addition-of γ-ray absorption spectra in transmission (TMS). Due to the different escape or penetration ranges of the three radiations involved, the spectra give information on phases, depth and orientation. From a practical point of view the counter for γ-rays, X-rays and electrons must be separated and shielded to minimize the mutual perturbation.

Experience with a toroidal proportional detector for backscattered Mössbauer ψ-rays and X-rays

Because backscattering geometry in Mössbauer spectroscopy is particularly useful for non-destructive testing interesting technical applications arise. The reported toroidal proportional detector for backscattered Mössbauer ψ-rays and X-rays enables non-destructive testing of technical surfaces since no sample preparation is required. Improvements in assembling, shielding, wire-fixing and gas-filling-in comparison to the first version of the detector-are reported. The performance of the improved detector is demonstrated by measurements of steel surfaces which are modified by plasma nitriding and laser irradiation.

High spin (5T2)-low spin (1A1) equilibrium of iron (II) in M2FeSn3S8 thiospinels (M = Cu, Ag)

Abstract The compounds M2FeSn3S8 (M = Cu, Ag) represent, to our knowledge, the first example of an iron(II) high spin (5T2) ↔ ; low spin (1A1) transition in the spinel lattice. Additionally, these compounds are one of the rare cases where such a spin transition is observed for bivalent iron in an octahedral sulfur coordination. The (5T2) ↔ ; (1A1) transition in M2FeSn3S8 is of the continuous type as is shown by the present 57Fe Mossbauer study as well as by previous magnetic susceptibility measurements.

Application of Mössbauer spectroscopy to physical metallurgy: The role of light interstitial elements

Light elements like hydrogen, nitrogen, and carbon, residing on interstitial sites of the host lattice, are capable of inducing noticeable changes in the physical properties of the material affected by their presence. Hydrogen uptake by different intermetallic compounds can lead to completely different results, depending on the chemical affinity between hydrogen and the constituent elements of the compounds. In the cases of considerable hydrogen concentrations, several distinct hydride phases can usually be found and identified by Mössbauer spectroscopy. Alterations of the magnetic behaviour of the intermetallic hydride are frequently observed. Nitrogen and carbon serve as agents for solid solution and precipitation hardening in commercial steels. Among the various methods for alloying with these elements and for controlling their distribution, implantation and surface treatment by use of a laser beam are of particular interest.

Kinetics of the phase transformation and wear resistance of in-situ processed titanium matrix composites based on Ti–Fe–B

Abstract Thermodynamic considerations lead to the conclusion that commercially pure cp titanium and Fe–B are appropriate educts for producing a titanium alloy based metal matrix composite reinforced by an in-situ reaction technique. The aim of the present study was the increase in wear resistance in comparison with the unreinforced cp titanium. Samples were prepared by arc melting, by the blended elemental powder metallurgy method and by hot-isostatic pressing. Mossbauer spectroscopy and X-ray diffraction patterns of as cast samples reveal a complete transformation of the educts. Owing to the high cooling rate, metastable phases are found. The sintering parameters using the powder metallurgical route were improved with the aim of increased wear resistance. Depending on the production process and the related microstructure the wear resistance of the Ti–Fe–B cermets was characterized using a pin-on-disc type machine. Under the present conditions wear resistance to the 100Cr6-steel counterpart was observed when the TiB content exceeded 20 vol.%.

Mössbauer spectroscopy in amorphous metals: Failures and successes

Abstract Mossbauer spectroscopy is an “ideal” tool for probing the local surroundings of resonance atoms. Consequently it was thought that the atomistic structure of amorphous metals would be revealed by the hyperfine spectra. However, the effectively infinite number of environments produces an infinite number of spectral components. Thus, only distributions of hyperfine Mossbauer parameters are observed. Despite considerable efforts, Mossbauer spectroscopy met with the same fate as all other methods in its failure to elucidate the structure of any of the amorphous metals. However, Mossbauer spectroscopy became the most powerful tool for investigating o r tracing any type of ordering and also where and at what temperature crystallization commences and in what sequence crystalline phases precipitate. Very useful is the combination of conversion electron Mossbauer spectroscopy (CEMS) and γ-ray transmission Mossbauer spectroscopy, allowing the surface and the bulk to be scanned simultaneously.

Carbon and nitrogen in steel

The phase composition at the surface of plasma nitrocarborized carbon steel was measured in backscattering geometry. The hyperfine parameters of the various iron sites in cementite, γ′-iron nitride and ε-carbonitride reflect the variation of composition with distance from the sample surface in a similar way as in the fractional areas of the respective phases.

Characterization of the single phase region with spinel structure in the ternary system In2S3FeSFeS2

Abstract The limit of single-phase solid solubility in a spinel host lattice in the system In2S3FeSFeS2 has been determined. Mossbauer spectroscopy showed that all iron is bivalent and, for the major part, occupies the B-sites (δ = 0.81–0.89 mm/s, Δ = 3.16–3.25 mm/s). The fraction of tetrahedral iron depends on the sample composition and the thermal treatment. Mossbauer spectroscopy also showed the influence of tetrahedral vacancies by causing quadrupole splittings on tetrahedral subspectra (δ = 0.64–0.74 mm/s and Δ = 0.55–1.07 mm/s).

A study of HfNi, HfCo and their hydrides by means of Mössbauer spectroscopy

The influence of hydrogenation on the hyperfine interactions in the intermetallic compounds HfCo, in which a small amount of Ni and Co were substituted with57Fe, respectively, has been investigated by means of57Fe Mössbauer spectroscopy. Crystal structure and hyperfine parameter analysis provided information on the site occupation of hydrogen in HfNi and HfCo during hydrogenation. Since the chemical properties of Hf and are similar, the hydrogen behaviour in HfNi or HfCo resembles that ZrNi and ZrCo.