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1
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Positron Annihilation in Magnetite Nanopowders Prepared by Co-Precipitation Method

100%
Durak K., Wiertel M., Surowiec Z., Miaskowski A.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1593-1597
EN
Nanosized iron oxide powders are materials considered with regard to its application in medical therapy called hyperthermia. Magnetite nanopowders with crystallite size varying from 6.6 to 11.8 nm have been prepared by the co-precipitation method. In this study a change of a crystallite size is driven mainly by varying of initial pH of water ammonia solution in which a process of magnetite precipitation runs. Crystallographic structures and phase composition obtained samples and the size of magnetite nanoparticles were determined by X-ray diffraction method. Positron lifetime spectroscopy has been used to assess defectiveness of microstructure. Experimental positron annihilation spectra were successfully resolved into three lifetime components. It appears that from point of view of microstructure the defects concentrations in studied nanopowder samples are very high which causes a saturation of positron trapping.
2
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Effect of an Adsorbed Atom on Resonant Charge Exchange in Atom Scattering on Metal Surfaces

100%
Taranko R., Taranko E., Wiertel M.
Acta Physica Polonica A
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2003
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vol. 103
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issue 5
483-497
EN
A simple model describing resonant charge transfer between the free-electron metal surface and an atom colliding with it at some distance from another adsorbed atom is presented. The negative ionization probability of a scattered atom is studied within the time-dependent Anderson-Newns model and the time-evolution operator approach. With appropriate models for the considered system, the ionization probability is shown to oscillate with the distance between the adsorbed atom and the collision point of the scattered atom with the metal surface. These oscillations are results of the indirect interaction between the adsorbed and the scattered atoms due to the coupling of both atoms with the metal energy band.
3
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Mössbauer and X-ray Diffraction Studies of Zr_{1-x}Ti_xFe_2 Laves Phase Compounds

100%
Budzyński M., Sarzyński J., Surowiec Z., Wiertel M.
Acta Physica Polonica A
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2001
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vol. 100
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issue 5
717-722
EN
Mössbauer spectroscopy of ^{57}Fe and X-ray diffraction measurements in the Zr_{1-x}Ti_xFe_2 phase have been made. Our X-ray diffraction spectra revealed that the samples have the cubic C15 crystal structure for low Ti concentration and the hexagonal C14 structure for high Ti concentration. In the range of 0.2≤xࣘ0.5 a mixture of both structures occurs. The investigated compounds are paramagnetic at RT for x>0.80 and magnetic for x
4
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Charge Transfer Dynamics in Atom-Metal Surface Collisions

100%
Wiertel M., Taranko R., Taranko E.
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vol. 96
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issue 6
769-783
EN
We study the charge exchange in atom-metal collisions in the framework of the generalized time-dependent Anderson-Newns model. The electron correlations and correlated hopping are treated within the mean-field approximation. The resulting one-particle model with an effective spin-dependent atom-surface coupling is used to study the charge transfer in scattering of Na and Li atoms on metal surfaces. It is shown that the effective occupation dependent atom-surface coupling influences mainly the expectation values for producing positive, neutral, and negative particles for small work functions and high atom velocities. It is also shown that the temperature dependence of these expectation values is more visible, especially for magnetic solutions.
5
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Resonant Charge Exchange in Atom Scattering on Atoms Adsorbed on Metal Surfaces

100%
Wiertel M., Taranko E., Taranko R.
Acta Physica Polonica A
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2002
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vol. 101
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issue 6
837-855
EN
The ionization probability of an atom scattered from an atom adsorbed on a metal surface has been studied theoretically within the time-dependent Anderson-Newns model. The effect of the metal electron density of states, the band filling as well as the relative position of the scattered atom and adsorbed atom energy levels have been considered and the comparison with the results obtained for clean surfaces has been made.
6
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The Influence of Reduction Process on the Iron-Molybdenum Nanoparticles in Modified MCM-41 Silica

100%
Surowiec Z., Wiertel M., Gac W., Budzyński M.
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vol. 125
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issue 3
846-849
EN
Iron-molybdenum silica mesoporous materials were obtained by the application of direct hydrothermal method. The influence of high temperature samples reduction in the H_2 flow on their structural and magnetic properties was studied. Four samples with different metal contents relative to silica were investigated. The study was carried out by means of X-ray diffraction, ^{57}Fe Mössbauer spectroscopy and the temperature programmed reduction method. With an increasing metals content, primary pores of MCM-41 transformed into the bottle-like pores, and then into the slit-like ones. Reduction and heat treatment caused the α-Fe, Fe_2Mo, and Fe-Mo alloy formation. Iron and molybdenum atoms after being released into the silica matrix, where they were embedded, create clusters or crystallites. It was observed that the high temperature reduction caused partial transformation of highly dispersed Fe-Mo oxides species initially embedded in silica walls into crystallites big enough to give magnetic sextet component in the Mössbauer spectra.
7
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^{57}Fe Hyperfine Interactions in the Sc(Fe_{1-x}Ni_x)_2 Laves Phases Synthesized under High Pressure

100%
Wiertel M., Surowiec Z., Budzyński M., Tsvyashchenko A.
Acta Physica Polonica A
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2008
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vol. 114
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issue 6
1517-1527
EN
The structural and microscopic magnetic properties of the pseudobinary Sc(Fe_{1-x}Ni_x)_2 system prepared under high pressure of 8 GPa were studied by X-ray diffraction and Mössbauer measurements in the range of 0.0 ≤ x ≤ 0.60. The samples for 0.0 ≤ x ≤ 0.10 have the hexagonal C14-type structure and those for 0.30 ≤ x ≤ 0.60 crystallize in the C15-type structure. Both the magnetic hyperfine field on ^{57}Fe and the Curie temperature decrease with the increasing Ni content and the system becomes paramagnetic for x ≈ 0.60 at room temperature. The form and temperature dependences of the Mössbauer spectra for 0.40 ≤ x ≤ 0.50 indicate the coexistence of paramagnetic and ferromagnetic regions in the samples and occurrence of magnetic clusters with a wide distribution of the Curie temperatures. It is interesting that T_C for the compounds obtained under high pressure are by about 100 K smaller in comparison with those for the isostructural samples produced under normal pressure even though interatomic distances are practically equal in the both types of compounds.
8
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The Synthesis and Properties of High Surface Area Fe_{2}O_{3} Materials

100%
Surowiec Z., Gac W., Wiertel M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 1
18-20
EN
Two types of the silica materials were used for the preparation of iron oxides. The MCM-48 type silica support and wide-pore silica gel were impregnated with iron nitrates. The samples were investigated by the nitrogen adsorption/desorption method, X-ray diffraction, scanning electron microscopy, and ^{57}Fe Mössbauer spectroscopy. Redox properties were studied by the temperature programmed reduction method. Strongly dispersed hematite was evidenced on the supports. An application of the MCM-48 silica mesoporous materials led to the development of the oxide phases within the ordered porous structure. The detailed temperature programmed reduction studies evidenced slight differences of the redox properties of the species located within the silica templates and after their removal. Magnetic properties of iron oxides were related to the porous structure of the silica supports. The Mössbauer study of high surface area materials Fe/SiO_{2} and Fe/MCM-48 type silicate templates revealed existence of ferro- and superparamagnetic phases. The relative contribution of the superparamagnetic doublet component in Mössbauer spectra is 15% and 80% for Fe/SiO_{2}/c and Fe/MCM-48/c samples, respectively.
9
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Positron Annihilation in MnFe_2O_4/MCM-41 Nanocomposite

100%
Wiertel M., Surowiec Z., Gac W., Budzyński M.
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vol. 125
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issue 3
793-797
EN
In the paper results of studies of MnFe_2O_4/MCM-41 nanocomposites have been presented. The influence of manganese ferrite loading on changes of porous properties of mesoporous MCM-41 structure was studied by means of N_2 sorption/desorption method and positron annihilation lifetime spectroscopy. Disappearance of the longest-lived ortho-positronium component (τ_5) of pure MCM-41 mesoporous material in the positron annihilation lifetime spectra of MnFe_2O_4/MCM-41 measured in vacuum is a result of either o-Ps quenching or the Ps inhibition mechanism. Filling of pores in the studied nanocomposites by air at ambient pressure causes partial reappearance of the (τ_5) component except for the sample with maximum ferrite content. Both the (τ_5) component lifetime and intensity are suppressed together with increasing MnFe_2O_4 content by chemical quenching and inhibition of Ps formation occur. Observed anti-quenching effect of air is a result of two processes: neutralization of some surface active centres acting as inhibitors and considerably weaker paramagnetic quenching by O_2 molecules.
10
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Positron Annihilation Studies of Mesoporous Iron-Molybdenum Modified MCM-41 Silica

100%
Surowiec Z., Wiertel M., Gac W., Budzyński M.
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vol. 125
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issue 3
789-792
EN
Iron-molybdenum modified MCM-41 mesoporous materials were obtained by the application of direct hydrothermal method. An incorporation of iron and molybdenum ions in the synthesis stage led to structural changes of the MCM-41 support. With an increasing metals content, cylindrical pores of silica are destroyed. X-ray diffraction investigations indicated that both iron and molybdenum ions were first embedded in the silica walls and then formed highly dispersed species in the pores. The porous structure of the studied samples was examined by means of N_2 adsorption/desorption and PALS methods. The longest-lived o-Ps lifetime component remains constant but its intensity monotonically decreases, except for the sample with the highest metals content. These results indicate that an effect of o-Ps formation inhibition occurs.
11
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Impact of Impulse Shot Peening Parameters on Properties of Stainless Steel Surface

88%
Wiertel M., Zaleski K., Gorgol M., Skoczylas A., Zaleski R.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1611-1615
EN
Shot peening was applied to austenitic stainless steel 1.4541 (EN). The surface treatment was performed at various impact energies E, impact densities j and ball diameters D. This resulted in improved microhardness, which increases monotonically with the increase of E, j and 1/D. However, its changes with E and j achieve saturation at about 400 HV0.1. On the contrary, no saturation is observed in the investigated range for 1/D. In the un-shot peened 1.4541 (EN) steel, the lifetime component of low intensity was found with use of positron annihilation lifetime spectroscopy (PALS). It corresponds to positron annihilation from delocalized state of positrons in bulk. In the shot peened samples the bulk component is no longer observed. Instead, two types of defects can be identified: vacancy-like defects coupled with edge dislocations and vacancies or their small clusters (consisting 3÷5 vacancies). The results of PALS and hardness testing do not correspond very well, especially in the case of the samples shot peened with balls of varying diameters. The most probable reason for this are different depth profiles of both methods. It seems that the defects, which are responsible for the increase of static microhardness above 400 HV0.1 are located mostly below the surface layer penetrated by positrons.
12
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Magnetic Nanoparticles in MCM-41 Type Mesoporous Silica

88%
Surowiec Z., Bierska-Piech B., Wiertel M., Budzyński M., Goworek J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 6
1605-1613
EN
Structural phase transformations and magnetic properties of mesoporous MCM-41 template modified with iron and nickel salts were studied by nitrogen physisorption, X-ray diffraction, Mössbauer spectroscopy and transmission electron microscopy. The FeNi-oxide or the bimetallic crystal structure is formed for low and high Ni concentrations, respectively. The average size of nanoparticles is about 10 nm. About 70% of particles exist in a superparamagnetic state at room temperature.
13
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Mechanical Properties of the Stellite 6 Cobalt Alloy Implanted with Nitrogen Ions

88%
Budzyński P., Kamiński M., Wiertel M., Pyszniak K., Droździel A.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
203-205
EN
The effect of nitrogen ion implantation on Stellite 6 cobalt alloy was investigated. In this research, cobalt alloy was implanted with 65 keV nitrogen ions at the fluence of (1÷10)×10¹⁶ N⁺/cm². The distribution of implanted nitrogen ions and vacancies produced by them was calculated using the SRIM program. The surface morphology was examined and the elemental analysis was performed using scanning electron microscopy, energy dispersive X-ray spectroscopy and grazing incidence X-ray diffraction. The wear tests were conducted with the use of the pin-on-disc method. The results demonstrate that implantation with nitrogen ions significantly reduces the friction factor and wear. The friction coefficient of the implanted sample at the fluence of 1×10¹⁷ N⁺/cm² increased to the values characteristic of an unimplanted sample after 5000 measurement cycles. The depth of the worn trace was about 2.0 μm. This implies that the thickness of the layer modified by the implantation process is ≈2.0 μm and exceeds the initial range of the implanted ions by an order of magnitude. This is referred to as a long-range implantation effect. The investigations have shown that the long-range effect is caused by movement of not only implanted nitrogen atoms but also carbon dopant atoms towards the friction zone. Diffusion of carbon atoms has been documented here for the first time. Furthermore, the increased content of oxygen atoms on the track bottom indicates a dominant oxidative wear of the Stellite samples after nitrogen implantation with the energy 65 keV and the fluences of 5×10¹⁶ and 10¹⁷ N⁺/cm².
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