Vladimir Sepelak

Karlsruhe Institute of Technology | KIT · Institute of Nanotechnology

The presented publication is based on the interaction of the material core and its surface during the machining process with a hydro abrasive flexible cutting tool (AWJ). In the AWJ technology, a cold cut is generated; therefore, there are no thermal stresses on the newly formed surface and, consequently, no significant internal and residual stress...

Strontium ferromolybdate, Sr2FeMoO6, is an important member of the family of double perovskites with the possible technological applications in the field of spintronics and solid oxide fuel cells. Its preparation via a multi-step ceramic route or various wet chemistry-based routes is notoriously difficult. The present work demonstrates that Sr2FeMo...

SPD (several plastic deformations) methods make it possible to obtain an ultrafine-grained structure (UFG) in larger volumes of material and thus improve its mechanical properties. The presented work focuses on the structural and mechanical changes of aluminium alloy AlMgSi0.5 (EN AW 6060) during processing by repeated extrusion through the ECAP re...

Nanocrystalline mullite-type bismuth-bearing complex oxides Bi 2 (M 0.5 Al 0.5 ) 4 O 9 (M=Fe ³⁺ , Ga ³⁺ ) are prepared by high-energy ball milling of the corresponding microcrystalline counterparts. An unusual five-fold coordination of metal cations is revealed in nanostructured Bi 2 (M 0.5 Al 0.5 ) 4 O 9 by means of ²⁷ Al magic angle spinning nucl...

The datasets presented here are related to the research paper entitled “Disordered Gd6UO12-δ with the cation antisite defects prepared by a combined mechanochemical−thermal method” [1]. The datasets complement the findings [1] on the effect of the combined mechanochemical−thermal processing of the stoichiometric mixture of solid precursors (3Gd2O3...

ABSTACT The synthesis of the rhombohedral Gd6UO12-δ is reported via mechanochemical processing of stoichiometric Gd2O3/UO2 mixtures and their subsequent annealing. Rietveld refinement of XRD data reveals that the as-prepared material exhibits a remarkable degree of cation antisite disorder and oxygen deficiency. The simulations of intensities of th...

Electromagnetic properties of complex oxide solid solutions containing Ce and Y attract increasing interests due to their high application potential. Their properties are known to be dependent on many factors including grain size and crystal defects. Here we focus on unique features of nanocrystalline Ce1-xYxO2-δ (x ≤ 0.3) solid solutions prepared...

Lithium-iron methasilicate (LiFeSi2O6, LFS), a member of clinopyroxene family, is an attractive compound for its multiferroic properties and applicability in energy-related devices. Conventional preparative method requires heating at elevated temperatures for long periods of time, with inevitable severe grain growth. We demonstrate that α-FeO(OH) (...

Nanostructured nickel ferrite (NiFe₂O₄) is prepared via high-energy ball milling of the bulk counterpart at ambient temperature. The structure of the as-prepared nanoferrite is characterized by Raman spectroscopy and 57Fe Mössbauer spectroscopy. Due to the ability of these spectroscopic techniques to probe the local environment of ions, valuable co...

The continued decrease in water quality requires new advances in the treatment of wastewater, including the preparation of novel, effective, environmentally friendly, and affordable sorbents of toxic pollutants. We introduce a simple non-conventional mechanochemical synthesis of magnetically responsive materials. Magnetic lignite and magnetic char...

Starting from gelatinous aluminum chloride hydroxide, the transformation process toward α‐Al2O3 was examined using ²⁷Al NMR, both in the liquid and solid states, as a main analytical tool. By increasing the hydrolysis ratio (h, defined as [OH⁻]/[Al³⁺]) of the starting aqueous precursor up to h = 2.5, the transition temperature to the final product,...

Mechanochemical interaction of Fe powder with the liquid Ga–In eutectic in the Fe-rich concentration corner of the Fe–Ga–In phase diagram was studied and compared with binary Fe–Ga and Fe–In specimens. Slow formation of diluted solid solutions in the Fe–In system was confirmed. In the Fe–Ga system, the dominant concentrated A2 solid solution is for...

Two members of the pyroxene family, the germanate-type LiFeGe2O6 and the titanate-type LiFeTi2O6, are prepared for the first time via non-conventional one-step mechanosynthesis. The evolution of the as-prepared materials in the course of mechanosynthesis and their structural state on the long-range and local atomic scales are characterized by X-ray...

The mechanically triggered interactions in the Ti–C and Hf–C systems performed in a high-energy planetary ball mill are studied. The formation of carbides (TiC and HfC) in the course of mechanochemical synthesis at the different stages is followed by both conventional and synchrotron X-ray diffraction analyses and high-resolution scanning and trans...

Among the many types of preparation techniques, the non-conventional mechanochemical processing has been recognized as an alternative route to nanomaterials. It is integral to the preparation of ceramic materials, including magnetoceramics, such as spinels, garnets, and hexaferrites, among others. This technique imparts copious levels of kinetic en...

Samples of NiFe2O4 nanoparticles N1 (nonactivated), N2 (milled for 15 min) and N3 (milled for 30 min) were studied using X-ray diffraction, scanning electron microscopy with energy dispersion spectroscopy, isothermal magnetization measurement and Mössbauer spectroscopy with respect to analyze the effect of particle milling on their magnetic propert...

This work evaluates the possibility of identifying mechanical parameters, especially upper and lower yield points, by the analytical processing of specific elements of the topography of surfaces generated with abrasive waterjet technology. We developed a new system of equations, which are connected with each other in such a way that the result of a...

Spinel phase Li4Ti5O12 (s-LTO) with an average primary particle size of 150 nm was synthesised via a solid state route by calcining a precursor mixture at 600 °C. The precursor was prepared from a stoichiometric mixture of TiO2 nanoparticles and an ethanolic solution of Li acetate and activated by ball-milling. Effects of the calcination temperatur...

In many cases, limitations in conventional synthesis routes hamper the accessibility to materials with properties that have been predicted by theory. For instance, metastable compounds with local non-equilibrium structures can hardly be accessed by solid-state preparation techniques often requiring high synthesis temperatures. Also other ways of pr...

We review the results of the study of magnetite, maghemite and nickel ferrite nanoparticles (NPs), applying for magnetic fluids, using Mössbauer spectroscopy with a high velocity resolution and magnetization measurements. The Mössbauer spectra of these NPs were fitted using a large number of magnetic sextets reflecting NPs complicity. The presence...

Samples of (Bi1-xGdx)14W2O27 (x = 0 and 0.05) compounds were prepared via a combination of mechanochemical and thermal treatments upon a Bi2O3/WO3/Gd2O3 stoichiometric mixture of precursors. Phase evolution, as well as the determination of structural parameters in as-prepared compounds, were performed by XRD analysis. Rietveld refinement revealed t...

The paper solves the problem of the nonexistence of a new method for calculation of dynamics of stress-deformation states of deformation tool-material systems including the construction of stress-strain diagrams. The presented solution focuses on explaining the mechanical behavior of materials after cutting by abrasive waterjet technology (AWJ), es...

Interfacial reactions at the surface of SnO2 nanoparticles adjacent to the fluorocarbon solids (FCS) under mechanical stressing were compared in an attempt to their modification by introducing fluorine and carbon. Emphasis was laid on the comparison of the reactivity of 3 different species of FCS, i.e., polyvinylidene fluoride (PVdF), polytetrafluo...

Chromium doped mullite-type ferrite, Bi2(Cr0.1Fe0.9)4O9, is synthesized for the first time by a combined mechanochemical/thermal route. The microstructure of the as-prepared material on the long-range and local atomic scales, revealed by X-ray diffraction and 57Fe Mössbauer spectroscopy, respectively, is found to be quite different from that report...

Iron oxide (magnetite and maghemite) nanoparticles developed for magnetic fluids were studied using Mössbauer spectroscopy with a high velocity resolution at 295 and 90K. The recorded Mössbauer spectra have demonstrated that usual physical models based on octahedral and tetrahedral sites were not suitable for fitting. Alternatively, the Mössbauer s...

Zinc aluminate (ZnAl2O4) nanoparticles with an average size of about 10 nm are synthesized via one-step mechanochemical processing of the ZnO:γ-Al2O3 stoichiometric mixture at ambient temperature. The mechanochemically induced formation of the phase is followed by XRD and 27Al MAS NMR. High-resolution TEM studies reveal a non-uniform nanostructure...

Ba1–xLaxF2+x covering the whole range of compositions was synthesized by high-energy ball milling of mixtures of BaF2 and LaF3 at ambient temperature. The compounds obtained in this way crystallize in the cubic fluorite structure in the range from 0 ≤ x 0.775 which extends the range for the fluorite-type Ba1–xLaxF2+x covered up to now (0 ≤ x ≤ 0.55...

Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, CaFe2O4 and Ca2SnO4 nanopowders were prepared via single -step mechanosynthesis performed at room temperature. The mechanically induced formation of a nanooxide product phase was followed by XRD, Fe-57 Mossbauer spectroscopy, and NMR. It is demonstrated that the mechanosynthesis of the c...

Technological and scientific challenges coupled with environmental considerations have prompted a search for simple and energy-efficient syntheses and processing routes of materials. This tutorial review provides an overview of recent research efforts in non-conventional reactions and syntheses of oxides induced by mechanical action. It starts with...

Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilling and annealing of a titania–PTFE mixture. XPS, 19F MAS NMR, FT-IR, Raman spectra, TEM and EDX analyses consistently indicated the oxidative decomposition of PTFE, inducing partial fluorination of titania. Incorporation of fluorine into titania was una...

In this research work, ferrite nanoparticles with composition of SrFe12−x(Ni0.5Co0.5Ti)x/2O19 (x = 0-2.5 in a step of 0.5) were synthesized by a reverse micelle. Multiwalled carbon nanotubes (MWCNT) were also functionalized by employing poly(acrylic acid). Then the ferrite nanoparticles were deposited on the functionalized surface of carbon nanotub...

The bulk NiFe2−xBixO4 ferrites with various Bi3+ concentration (x=0, 0.1, 0.15) were synthesized via sol–gel procedure, starting from nickel, bismuth and iron nitrate powders, followed by the conventional thermal treatment. The structural and magnetic properties of the as-prepared ferrites were studied by means of X-ray diffraction, alternating gra...

Technological and scientific challenges coupled with environmental considerations have prompted a search for simple and energy-efficient syntheses and processing routes of materials. This tutorial review provides an overview of recent research efforts in non-conventional reactions and syntheses of oxides induced by mechanical action. It starts with...

In this research work, a low temperature in-field 57 Fe Mössbauer spectroscopy is used for investigation of anomalous magnetic properties of MnZn nanoferrite. Based on Mössbauer spectroscopy results, the reduced saturation magnetization of MnZn nanoferrite respect to that of bulk sample is due to nonequilibrium cation distribution and spin disorder...

Self-assembled Ni-Co-Sn substituted strontium ferrite dot array was formed on the outer surface of functionalized multiwalled carbon nanotubes (MWCNTs) by means of hetero-coagulation. The structural properties were evaluated by X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy, and field emission scanning ele...

Nanostructured fayalite (α-Fe(2)SiO(4)) with a large volume fraction of interfaces is synthesized for the first time via single-step mechanosynthesis, starting from a 2α-Fe(2)O(3) + 2Fe + 3SiO(2) mixture. The nonequilibrium state of the as-prepared silicate is characterized by the presence of deformed polyhedra in the interface/surface regions of n...

This paper, by no means exhaustive, focuses on high-energy ball-milling of oxides, on their mechanically induced changes and on the consequences of such changes on their physical and chemical properties. High-energy ball-milling offers a fortunate combination of technical simplicity and of complexity both of physical mechanisms which act during mil...

Zn1�xCoxFe2O4 (x¼0�1 in a step of 0.2) nanoparticles with different range of particle size including 5–10 nm and 200–250 nm have been prepared by sol–gel process. Mo¨ssbauer spectra at room temperature indicated that, with increasing cobalt content, there is a transition from paramagnetic to magnetically ordered-ferrimagnetic state. Magnetic proper...

Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by means of magnetic measurement and Mössbauer spectroscopy at various temperatures demonstrated differences in the saturation magnetization and Mössbauer hyperfine parameters which were related to the interactions of Copaiba oil polar molecules with iron...

Zinc stannate (Zn2SnO4) nanoparticles with an average size of about 26 nm are synthesized via single- step mechanochemical processing of binary oxide precursors (ZnO and SnO2) at ambient temperature, without the need for the subsequent calcination, thus making the synthesis route very simple and cost- effective. The mechanically induced phase evolu...

High-energy mechanical action applied to solid leads to destruction and diminution to the nanosize level. But on the other hand, it can induce structural changes at the nanoscale and at the atomic level which can result in novel materials properties. In this contribution, case studies will be presented concerned with the tailoring of magnetic prope...

We studied the electrochemical insertion of Li in mechanochemically prepared Zn(2)SnO(4). The mechanism of the electrochemical reaction was investigated by using X-ray diffraction, nuclear magnetic resonance spectroscopy, and Mössbauer spectroscopy. Changes in the morphology of the Zn(2)SnO(4) particles were studied by in situ scanning electron mic...

Substituted strontium ferrite (SrFe_12-x(Cr_0.5Al_0.5)_xO₁₉) thin films were formed along the surface of multiwalled carbon nanotubes (MWCNTs). Mössbauer spectroscopy indicates that the substituted cations preferentially occupy the 12 k sites. X-ray diffraction (XRD), transmission electron microsco...

This paper presents the results of the research on the fabrication and characterization of barium M-type hexaferrite and its influence on the properties of butadiene-rubber composites. Nanocrystaline barium ferrite particles were prepared by co-precipitation followed by defined mechanical milling in a high energy mill. The particle size, magnetic p...

AbstractThe studies on the mechanochemical synthesis and electrochemical characterization of orthorhombic calcium ferrite (CaFe2O4) are reported in this paper. Stoichiometric mixtures of α-Fe2O3 and granulated Ca metal were used as the starting materials for the synthesis process. The synthesized calcium ferrite was characterized by room-temperatur...

NiFe2−xBixO4 (x=0, 0.1, 0.15) nanopowders were synthesized via sol–gel method. The precursor gels were calcined at 773K in air for 1h to obtain the pure nanostructured NiFe2−xBixO4 spinel phase. The crystal structure and magnetic properties of the substituted spinel series of NiFe2−xBixO4 have been investigated by means of 57Fe Mössbauer spectrosco...

SrFe12−x(Sn0.5Zn0.5)xO19 thin films with x=0−5 were synthesized by a sol–gel method on thermally oxidized silicon wafer (Si/SiO2). The site preference and magnetic properties of Zn–Sn substituted strontium ferrite thin films were studied using 57Fe Mössbauer spectroscopy and magnetic measurements. Mössbauer spectra displayed that the Zn–Sn ions pre...

The response of the local structure of various types of spinel aluminates, ZnAl2O4 (normal spinel), MgAl2O4 (partly inverse spinel), and Li0.5Al2.5O4 (fully inverse spinel), to mechanical action through high-energy milling is investigated by means of 27Al MAS NMR. Due to the ability of this nuclear spectroscopic technique to probe the local environ...

A one-step synthesis of nanostructured bismuth ferrite (BiFeO3) via mechanochemical processing of a alpha-Fe2O3/Bi2O3 mixture at room temperature is: reported. The mechanically; induced Phase evolution of the mixture is followed by XRD and Fe-57 Mossbauer spectroscopy. It is shown that the mechanosynthesis of the rhombohedrally distorted perovskite...

We studied the local structural disorder and relaxation in different nanostructures of SnO2 by using 119Sn MAS NMR in combination with 119Sn Mössbauer spectroscopy. We investigated nanocrystalline powders with an average crystallite size of 8 nm as well as hollow spheres with a wall thickness of 3 nm and a diameter of 14 nm, and compared the result...

Highly pure nanocrystalline BaLiF3 (space group Pm (3) over barm, inverse perovskite structure) with a mean crystallite size of the order of 30 nm was mechanosynthesized from the binary fluorides LiF and BaF2. The source materials with mu m-sized crystallites were treated in a planetary mill for several hours at ambient temperature. The product is...

The magnetic nanoparticles of La0.75Sr0.25MnO3 perovskite manganite with a controlled size were prepared via sol–gel procedure, followed by thermal treatment and subsequent mechanical processing of the resulting raw product. The prepared materials were structurally studied by the XRD and TEM methods and probed by DC magnetic measurements. The nanop...

Atomic force microscopy and scanning electron microscopy were used to study the structure of metallic cements that are formed upon the interaction of Cu/Bi mechanocomposites with liquid gallium at room temperature. It has been established that the intermetallic compound CuGa2, which is the basic component of this metallic cement, is formed as tetra...

It is known that the action of mechanical forces on solids (mechanical activation and/or mechanochemistry) leads to changes of their properties and reactivity. We have studied the physico-chemical and sorption properties of magnetite Fe3O4 (Kiruna, Sweden) mechanically activated in a planetary mill. Several methods such as X-ray diffractometry, Mös...