V.G. de Resende

Mössbauer spectroscopic study of synthetic leucophosphite, KFe2(PO4)2(OH)·2H2O

A Mössbauer study of synthetic leucophosphite, KFe2(PO4)2(OH)·2H2O is reported. The sample was prepared by the reaction of synthetic goethite (α-FeOOH) with a K-phosphate solution of pH 2 at 373 K for 20 days. The obtained cell parameters are a = 9.771(1), b = 9.675(2), c = 9.747(2) Å, β = 102.45(1)°. The Mössbauer spectra from 295 K down to 40 K show the existence of two Fe3+ doublets with ∆EQ1 ≈ 0.62 mm/s and ∆EQ2 ≈ 0.91 mm/s (at 80 K), respectively, whereas for lower temperatures the spectra are composed of two sextets with Hhf1 ≈ 48.3 T and Hhf2 ≈ 48.8 T at 4.2 K. The magnetic transition temperature was determined to be 36 K from a Mössbauer thermoscan experiment. The magnetic ordering is presumed to be antiferromagnetic. The temperature variations of the hyperfine fields cannot be explained by the simple molecular field approximation. Using a model that takes into account the exchange magnetostriction associated to a non-second-order transition, an excellent reproduction of the Hhf(T) curves was obtained.

Influence of the borohydride concentration on the composition of the amorphous Fe-B alloy produced by chemical reduction of synthetic, nano-sized iron oxide particles Part II. Goethite

Influence of the borohydride concentration on the composition of the amorphous Fe–B alloy produced by chemical reduction of synthetic, nano-sized iron-oxide particles Part I: Hematite V.G. de Resende a,b,∗, E. De Grave a, G.M. da Costa b, J. Janssens c a Department of Subatomic and Radiation Physics, University of Ghent, B-9000 Gent, Belgium b Universidade Federal de Ouro Preto, Department de Quı́mica, 35400 Ouro Preto (MG), Brazil c Department of Chemistry, University of Antwerpen, B-2020 Antwerpen, Belgium

Characterization by Mossbauer spectroscopy of Fe phases in highly weathered serpentinitic soil from southern Cameroon

Abstract Weathered soil material derived from tectonically emplaced serpentinized ultrabasic intrusive rocks of southern Cameroon has received considerable attention from mining companies due to its extractable-metal (i.e. Ni, Co) potential. As these cations can be incorporated into Fe oxides, it was deemed appropriate to study the mineralogical assemblage of a highly weathered serpentinite soil profile from the area. This study focuses on the different Fe-oxide phases, which were investigated using 57Fe Mössbauer spectroscopy, showing goethite and hematite as the dominant Fe oxides throughout the weathering profile. These minerals, in association with gibbsite and kaolinite, indicate an advanced degree of weathering. The clay fraction of the ‘Lower Limonite’ layer, above the saprolite and at a depth of 7 m, is very rich in goethite, whereas hematite and magnetite are almost absent. Above this layer, the hematite content in the fine-earth and clay fractions increases upwards, while the goethite content remains constant. The significant substitution and change in the particle size of the goethite and the poor crystallinity of hematite, as indicated by the hyperfine parameters and XRD, suggest that the upper material evolved under different pedological conditions compared to the deeper layers. The mixed composition of the upper layers (above 7 m), which contain muscovite and a relatively chaotic distribution of trace elements, suggests ancient mica-schist capping and possibly different cycles of erosion and pedimentation.

Surface Magnetic Properties and MÖssbauer Spectroscopy of As-Quenched FeNiMoCuB Ribbons

Combination of surface-sensitive magneto-optical Kerr effect (MOKE) methods with the conversion electron and the integral low-energy electron Mossbauer spectroscopy (CEMS, ILEEMS), and with the X-ray diffraction (XRD) is used for structural investigation of the near-surface regions of as-prepared Fe40Ni36Mo8Cu1B15 ribbons. Jumps observed at measured MOKE hysteresis loops indicate the presence of two magnetically different phases at both ribbon sides and enable to determine corresponding surface coercive fields. The grazing incidence XRD (GIXRD) results yield an existence of the crystalline FeMo2B2, FeNi and amorphous phases confirmed by both surface-sensitive Mossbauer spectroscopy methods.