Mössbauer Spectroscopy and X-Ray Diffraction Studies of Fe-Ni Order-Disorder Processes in a 35% Ni Meteorite (Santa Catharina)

Abstract

The composition and structure of iron-nickel alloys in the Santa Catharina iron meteorite were investigated by metallographic techniques, electron microprobe analysis, Mossbauer spectroscopy and X-ray diffraction.The occurrence of an ordered Fe-Ni phase with non-cubic symmetry is demonstrated. This phase is present in large proportions in the Santa Catharina meteorite, and has been identified by its asymmetric Mossbauer spectrum, arising from the presence of a quadrupolar splitting superposed on the magnetic hyperfine splitting. The other major Fe-Ni phase in Santa Catharina gives rise to a single line Mossbauer spectrum with no hyperfine components.X-ray diffraction confirms the presence of the Fe-Ni Llo superstructure in this meteorite. Lattice parameter variations with temperature were found to be identical for the meteorite and for electron irradiated Fe-Ni alloys of the sample composition.Detailed Mossbauer spectroscopy studies from room temperature to liquid helium, and in the presence of external magnetic field show the presence of a smaller amount of another ferromagnetic Fe-Ni phase, probably with disordered structure.The destruction of the superstructure in the Santa Catharina meteorite Was investigated after heating the samples. Partial ordering seems to coexist with the disordered phase at intermediate annealing temperatures. At higher temperatures the samples are homogenous and similar to laboratory produced Fe-Ni alloys with 35% Ni.Orderdisorder transformations produced by shock waves and by mechanical treatment are also described.

A New Process to Produce Ordered Fe50Ni50 Tetrataenite

“…With the exception of QS the other parameters compare quite well with that for the ordered g 00 Fe 50 Ni 50 tetrataenite phase found in the Santa Catharina meteorite, see Ref. [4], where the authors have published their IS data in relation to the 57 Co:Rh source and their values are reproduced in their original form in Table 1. As demonstrated in [1] the higher the QS value the more ordered is the tetrataenite phase.…”

“…At around 50 at% Fe the presence of a chemically ordered g 00 Fe 50 Ni 50 phase is predicted, that in fact has a very small tetragonal distortion (c/a ¼ 1.0036) and is therefore called tetrataenite. This little distortion is not easily distinguished by X-ray diffraction [3] but is clearly detected by Mö ssbauer (MS) spectroscopy [4]. This ordered phase has an order-disorder transition temperature of 593 K [5] making its laboratory production by normal annealing from the disordered alloys impossible.…”

A Mössbauer effect study of the Soledade meteorite

“…Iron is appearing in the austhenitic phase and alloyed with nickel. An analysis of the Mössbauer spectra at room temperature indicates that the Fe-Ni phase is homogeneously distributed in the matrix, although variations in the composition between different regions are observed.Since the early studies of the microstructure and chemical composition of meteorites the formation of magnetic phases has attracted the attention of metallurgists [1][2][3][4][5][6][7][8][9][10][11]. Most of the metallic specimens presented high contents of nickel and iron as major constituents, and thus the Fe-Ni alloys formed under such special conditions have been the subject of several investigations with a variety of experimental techniques.…”

Willow Grove: A unique nickel‐rich ataxite from Victoria, Australia

“…Nor would they be expected from the Ni content projected on the low-temperature Fe-Ni phase diagram (Yang et al, 1996). They also appear to be absent from Tishomingo, based on Mossbauer experiments by Scorzelli and Danon (1985), although from the same lowtemperature Fe-Ni phase diagram, they might be expected. Perhaps Tishomingo cooled fast enough for the decomposition to be suppressed.…”