Characterization of iron meteorites by scanning electron microscopy, x-ray diffraction, magnetization measurements, and Mössbauer spectroscopy: Mundrabilla IAB-ung
M. V. Goryunov, G. Varga, Z. Dankházi, A. V. Chukin, I. Felner, E. Kuzmann, V. I. Grokhovsky, Z. Homonnay, M. I. Oshtrakh
MAPS
Version of Record online: 11 September 2023
“A fragment of Mundrabilla IAB-ung iron meteorite was analyzed using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), magnetization measurements, and Mössbauer spectroscopy. The polished section of meteorite fragment characterization by optical microscopy and SEM shows the presence of the γ-Fe(Ni, Co) phase lamellae, plessite structures and schreibersite inclusions in the α-Fe(Ni, Co) phase. EDS indicates variations in the Ni concentrations in the following ranges: (i) ∼6.3–6.5 atom% in the α-Fe(Ni, Co) phase and (ii) ∼22 to ∼45 atom% in the γ-Fe(Ni, Co) phase lamellae including the range of ∼29–33 atom% of Ni leading to the paramagnetic state of the γ-Fe(Ni, Co) phase. Schreibersite inclusions contain ∼23 atom% of P, ∼33 atom% of Fe, ∼43 atom% of Ni, and ∼0.7 atom% of Co. Plessite structure contains the average Ni concentration of ∼17 atom% while detailed EDS analysis shows: (i) the lowest Ni concentrations of ∼5 to ∼8 atom%, (ii) the intermediate Ni concentrations of ∼9 to ∼19 atom%, and (iii) the highest Ni concentration up ∼38 atom% (some individual micro-grains demonstrate up to ∼47 and ∼59 atom% of Ni) that may indicate the presence of the (i) α-Fe(Ni, Co), (ii) α2-Fe(Ni, Co), and (iii) γ-Fe(Ni, Co) phases. These may be a result of the γ-phase decomposition with mechanism γ → α + α2 + γ that indicates a slow cooling rate for Mundrabilla IAB-ung iron meteorite. The presence of ∼98.6 wt% of the α-Fe(Ni, Co) phase and ∼1.4 wt% of the γ-Fe(Ni, Co) phase is found by XRD while schreibersite is not detected. Magnetization measurements show the saturation magnetization moment of Mundrabilla IAB-ung of 188(2) emu g−1 indicating a low average Ni concentration in Fe-Ni-Co alloy. Mössbauer spectrum of the bulk Mundrabilla powder demonstrates five magnetic sextets related to the ferromagnetic α2-Fe(Ni, Co), α-Fe(Ni, Co), and γ-Fe(Ni, Co) phases and one singlet associated with the paramagnetic γ-Fe(Ni, Co) phase, however, there are no spectral components corresponding to schreibersite. Basing on relatively larger and smaller values of the magnetic hyperfine field, two magnetic sextets associated with γ-Fe(Ni, Co) phase can be related to the disordered and more ordered γ-phases. The iron fractions in the detected phases can be roughly estimated as follows: (i) ∼17.6% in the α2-Fe(Ni, Co) phase, (ii) ∼68.5% in the α-Fe(Ni, Co) phase, (iii) ∼11.5% in the disordered γ-Fe(Ni, Co) phase, (iv) ∼2.0% in the more ordered γ-Fe(Ni, Co) phase, and (v) ∼0.4% in the paramagnetic γ-Fe(Ni, Co) phase.”
