Jozef Lipka

Contamination of quartz by iron in energy-intensive grinding in air and liquids of various polarity

Abstract The influence of mill power and grinding environment on the contamination of quartz by iron during vibration grinding was studied. It was found that the Fe content of ground powders increased with an increase in specific grinding energy that was independent of the conditions of energy supply, that is whether it was supplied by varying the mill power or the grinding time. The specific contamination expressed as the ratio of Fe content to newly created surface area depended upon the physical properties of the grinding environment. The influence of grinding conditions on the state of the iron in the products of grinder wear was investigated by Mossbauer spectroscopy and by measuring the magnetic susceptibility of the ground powders. It was shown that the iron produced from grinder wear is present in tow main forms: as a magnetically ordered form identical with the basic material of the grinder and in a form of finely dispersed iron/iron compound showing superparamagnetic behaviour. Based on the results obtained, the formation of a silica-supported iron or iron oxide catalyst was presumed. By this assumption, the catalytic decomposition of water and methanol that takes place during quartz at grinding by iron containing grinders can be explained.

A study of titanomagnetites in basaltic rocks from Nigeria

The magnetic fractions of basaltic rock samples from Nigeria have been studied by Mossbauer spectroscopy, X-ray powder diffraction, and magnetic susceptibility measurements. The relative areas of the magnetically split components in the Mossbauer spectra decrease with increasing temperature. It is shown that this is not because of superparamagnetic relaxation but rather due to inhomogeneous distributions of the iron atoms in the titanomagnetites which lead to a distribution in Curie temperatures. Heating of some samples in air results in an increase in the Curie temperature and an increase in the magnetic susceptibility at room temperature. For other samples the susceptibility had decreased after heating, and the Curie temperature was not affected. Mossbauer and X-ray studies of the heated samples showed a transformation of titanomagnetite into magnetite and titanium-oxides and a partial oxidation of magnetite into hematite. These observations can explain the changes in the magnetic susceptibility. The results suggest that Mossbauer studies of iron-titanium oxides can give information on the cooling history of rock samples.

First Mössbauer study of the slovak meteorite rumanova

The Rumanova meteorite which belongs to the H5 chondrite group was investigated for the first time using57Fe Mössbauer spectroscopy. In the magnetic fraction the magnetite, troilite and iron-nickel alloys were identified. In the non-magnetic fraction, the silicate phases such as olivine and pyroxene were found. The paramagnetic component containing Fe3+ ions corresponds probably to small superparamagnetic particles.

Influence of mechanical activation on the Mossbauer spectra of the sulfides

Abstract Mossbauer spectroscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, electron paramagnetic resonance and X-ray diffraction were used to identify changes of surface, structure and spectroscopic properties of sulfide minerals produced by mechanical activation. In the present study we report the results of chalcopyrite (CuFeS 2 ), pyrite (FeS 2 ), cinnabar (HgS), bornite (Cu 5 FeS 4 ) and zinc sulfide (ZnS). The influence of energy input to the mill and the nature of grinding environment have been investigated upon the Fe contamination of the materials.

A Mössbauer study of an impactite from the Monturaqui crater

The iron mineralogy of samples of the Monturaqui impactite has been studied by Mössbauer spectroscopy. Magnetite, maghemite, goethite and a ferrous glass phase were identified. In a magnetic separate a bcc-structured iron-nickel alloy was identified in addition to the oxide phases. The oxides have formed by weathering of iron-nickel alloys.

Crystallisation kinetics of amorphous Fe72.5−xCu1Nb4.5Si10+x+y B12-y alloy

Fe73.5Cu1Nb3Si13.5B9 and Fe72.5−xCu1Nb4.5Si10+x+y B12−y alloys are compared from the point of view of crystallisation behaviour and changes in the short-range order in the amorphous reminder. The increase in Nb to 4.5 at.% in the latter system slows down the formation of nanocrystals to approximately 40% even after 16 hours of anneal at 550 °C forx=0.5,y=3. Segregation-induced changes in the short-range order are manifested via hyperfine field distributions corresponding to the amorphous reminder.

Study of Fe−Ni−Cr−Mo−Si−B metallic glasses after neutron irradiation

Chromium containing metallic glasses are studied by transmission57Fe Mössbauer spectroscopy after neutron irradiation. Increasing number of nonmagnetic chromium atoms causes a compositional dependence of Curie temperature. The unirradiated samples are fully paramagnetic forx≥10 at. % Cr at room temperature. Radiation induced changes in the magnetic structure imply a decrease of the Curie temperature. Ferromagnetic-to-paramagnetic transition is observed at room temperature for 8 at. % Cr after the exposure with 1019 n/cm2. Using low temperature measurements, the Curie temperature for the sample containing 10 at. % Cr is estimated to be about 270 K.

Mössbauer study of FeCuNbSiB-type nanocrystals

Abstract Hyperfine magnetic fields (HMFs) of Fe 70.5+ x Cu 1 Nb 4.5 Si 16−3 x B 8+2 x ( x = 0, 2) nanocrystals are discussed as a function of annealing time and composition. Increase in the number of Fe atoms with Nb and Cu as their nearest neighbours is observed with rising annealing time. As a consequence, the average value of HMF distribution of the residual amorphous phase is decreased.

Hyperfine magnetic fields of disordered systems by /sup 57/Fe Mossbauer spectroscopy

The feasibility of /sup 57/Fe transmission Mossbauer spectroscopy in the study of hyperfine magnetic fields is described with emphasis on amorphous, nanocrystalline and quasicrystalline alloys. Distributions of hyperfine magnetic fields obtained are presented via three-dimensional projections where effects of sample composition, temperature and annealing time on magnetic structure are followed by changes in probability of the field values. This allows magnetic transitions as well as mixed electric-quadrupole and magnetic-dipole interactions to be observed. >

Joule heating of FeB metallic glasses

Abstract Amorphous Fe80B20 and Fe83B17 ribbons were heated in air and in vacuum, respectively, by a dc electric current passing through the specimen. During the Joule heating, 57Fe transmission Mossbauer spectra were recorded. Ribbons of the same geometrical dimensions, cut from a natural iron foil, were treated in the same way as a reference. The influence of the current-induced magnetic field in addition to the Joule heating is supposed to cause fluctuations in a short-range order observed. Changes in the hyperfine magnetic fields are compared with those obtained by a conventional heating in a vacuum furnace.