mossbauer spectra
Recently Published Documents

AbstractMössbauer spectra of nonweathered ordinary chondrites consist of four main mineral phases: olivines, pyroxenes, metallic phase and troilite. These minerals represent more than 95% of the whole mass of an ordinary chondrite. Distribution of these mineral phases in micro-scale is not homogeneous. Nevertheless, preparation of representative sample of ordinary chondrite for Mössbauer measurements is possible. To do that a part of 1 g nonweathered material, selected from inside of meteorite without any specific intention is needed. The Warsaw group has been working on investigation of meteorites for 25 years and has analysed about 150 Mössbauer spectra of various meteorites. Among them we found 15 spectra, which could be suspected of being non-representative. These spectra were obtained from Baszkówka, Amber, Bjurböle, Krasnoi-Ugol and Chelyabinsk meteorites. The analysis of how the samples of meteorites were selected for investigation, has shown that the non-representativeness of samples may be due to: intentional choice of sample, preparation of sample from a too small part of material or the use of non-credible source of meteoritic samples. For confirmation of these assumptions, we used a new method of classification of ordinary chondrites – the 4M method. It turned out that this method is a very useful tool for investigation of non-representative samples of equilibrated ordinary chondrites.

An algorithm for mathematical processing of the Mössbauer spectra of supersaturated disordered solid solutions by the Tikhonov regularization method using a double convolution of the Lorentz function and two Gaussians is proposed. By the examples of spectra of supersaturated disordered solid solutions Fe100–xGex (x = 10—25 at.%) and Fe75Si15Al10, it is shown that the algorithm allows more correct processing, which provides a reliable distribution function of the hyperfine magnetic field. It is shown that to take into account the statistical ensemble of nonequivalent local atomic configurations of Fe atoms in disordered supersaturated solid solutions, it is necessary to use not only the convolution of two Gaussian functions, but also the projection scaling factor of the hyperfine magnetic field onto the velocity scale.

In this work, we studied the Mössbauer spectra of magnetite samples of various compositions. To protect magnetite from oxidation, the resulting particles are coated with protective shells, among which silanes are promising, which polymerize on the surface of magnetite nanoparticles, forming strong covalent bonds. The coating of nanoparticles protects them from aggressive environmental influences, evens out their size distribution, and also protects the environment from the possible toxic effects of the particles themselves. It was shown that the magnetite phase predominates in the sample of native particles, the coating of native particles with alkoxysilane does not lead to fundamental changes in the phase state of the sample particles, and oxidation with nitric acid leads to the complete transformation of magnetite into maghemite. It is obvious that the reason for the distortions of the relaxation nature in the Mössbauer spectra of the samples is the small sizes of the iron-containing domains, which allows us to consider the description of the spectra within the framework of the model of multilevel superparamagnetic relaxation.

Abstract Ferrihydrite often precipitates with humic acid in natural ways, affecting the fate of lead ions, the stabilization of humic acid and the aging process of ferrihydrite. A series of 2-line ferrihydrite-humic (Fh-HA) acid with varying C loadings has been prepared, the morphology and surface properties of Fh-HA organo-minerals have been characterized, the adsorption property of Pb ions onto Fh-HA has been studied. The results indicated a strong interference of HA to ferrihydrite. 2-line Fh dominated mineral phase in all samples, but with increasing C/Fe molar ratios the crystallinity gradually weakened, particles became smaller and SSA decreased significantly. The data of Mössbauer spectra confirmed C loading changed the unit structure of ferrihydrite. Fh-HA performed good adsorption properties to Pb(Ⅱ): high efficiency and big capacity, especially Fh-HA_2.0. pH had great effect on Lead uptake, the pH change not only affects the amounts of competitive ions in solutions, but also the dissociation and protonation of functional groups on the surface of Fh-HA. Sorption kinetics can be well modeled by a pseudo-second order model, and the process was controlled by film and intraparticle adsorption simultaneously. The adsorption isotherms can be well described by Freundlich isotherm model. The careful determination of Fe 2p, O 1s and Pb 4f spectra before and after lead adsorption showed mononuclear bidentate or binuclear bidentate ligands occurring on Fh-HA surface, forming stable inner-sphere complex. By comparison of Mössbauer spectra and TEM images, it revealed a slower evolution of iron oxide/oxyhydroxide phases in Fh-HA-Pb system compared to pure ferrihydrite with aging time, ferrihydrite transformed to a combination of ferrihydrite, goethite and hematite phases. in this study, the determination of C-Fe interaction, Pb fate influenced by Fh-HA and transformation of ferrihydrite would have a great implication to application of Fh-HA precipitates in remediation for soil or groundwater polluted by heavy metals.