Thermally stimulated iron oxide transformations and magnetic behavior of cerium dioxide/iron oxide reactive sorbents

Significance Statement

Considerable attention, for many years, has been focused on nanostructure materials owing to their unexpected and interesting properties that pave way to new possibilities in areas of chemistry, physics and biology. Most of these materials, including magnetite and hematite, exhibit magnetic properties differing from macrostructural materials. Nanostructure materials are used in mixed oxide systems forming structures with properties not exhibited by individual oxides. Cerium oxide finds various applications in novel foamed porous ceramics and exhibits ferromagnetic behavior at room temperature.

Researchers from the Technical University of Ostrava, Jan Evangelista Purkyně University in Ústí nad Labem and Institute of Physics of Materials, Academy of Sciences of the Czech Republic proposed to investigate thermally stimulated iron oxide transformations and magnetic behavior of cerium dioxide/iron oxide reactive sorbents. They analyzed the structural/compositional and magnetic properties directed predominantly to ongoing thermally induced iron oxide transformations in the presence of cerium oxide. Their work is now published in the peer-reviewed journal, Materials Characterization.

The magnetically separable sorbents were prepared by calcination from the precursor consisting of cerium carbonate on the surface of magnetic grains. The process was done in a muffle furnace by stepwise annealing at various temperatures in air. These resulted in the powdered samples with an active layer of cerium oxide precipitated on iron oxide nanoparticles. The marked changes observed after annealing between 773 K and 973 K became a driving force for detail investigations of the sample morphology and phase composition in close connection to magnetic behavior at room temperature supported by low temperature measurements.

Micro- and macrostructure sensitive experimental methods are applied for exact identification of iron oxides and their transformations Fe3O4 → γ-Fe2O3 (ε-Fe2O3) → α-Fe2O3 in dependence on calcination temperature which simultaneously influences also the room and low temperature magnetic characteristics and particles size distribution of the powdered samples.

Thermal treatment at 773K

This treatment does not change the irregular form of particles of the precursor but their size distribution 5-50 nm is on the contrary visibly narrower. The presence of ferrimagnetic oxide phases, magnetite and maghemite, determined by Mössbauer spectrometry influences the high values of the room temperature saturation and remnant magnetization. Non-zero hysteresis at low temperature indicates blocking state of the magnetic nanoparticles.

Thermal treatment at 873K

The increasing treatment temperature contributes to a slight increase in particle size and their size distribution broadening. A diminishing of maghemite and an increasing contribution of the weakly ferromagnetic hematite are determining factors of magnetic behavior with a substantial decrease in saturation magnetization.

Thermal treatment at 973K

The highest annealing temperature of 973 K produces well defined rounded particles of dominating size of 20 nm. According to high resolution transmission micrograph the small and medium-sized CeO2 particles occur on a surface of the larger hematite, α-Fe2O3 particles. The dominating presence of hematite is reflected in low saturation magnetization.

Thermally stimulated iron oxide transformations and magnetic behavior of cerium dioxide/iron oxide reactive sorbents - Advance in Engineering

Thermally stimulated iron oxide transformations and magnetic behavior of cerium dioxide/iron oxide reactive sorbents - Advance in Engineering

Thermally stimulated iron oxide transformations and magnetic behavior of cerium dioxide/iron oxide reactive sorbents - Advance in Engineering

About the author

Prof. Jiří Luňáček is a Head of Department of Physics, VŠB – Technical University of Ostrava. He obtained his Masters (1981) in Physics of Solid State at the Charles University in Prague, Czech Republic and PhD. (1996) in Physical Metallurgy and Limit States of Materials at the VŠB – Technical University of Ostrava. He was appointed Professor of Applied Physics (2011) at the Czech Technical University in Prague.

In his scientific work he deals with solid state physics, especially magnetic and optical properties of thin films, powders (nanopowders) and composites, recently particularly magnetically separable sorbents based on a cerium dioxide and iron oxides, respectively.

He is a member of Czech Society for New Materials and Technologies (CSNMT) and the Czechoslovak Association for Crystal Growth (CSACG).

About the author

Dr. Jiří Buršík is a senior researcher in the Institute of Physics of Materials of Czech Academy of Sciences and a lecturer at Masaryk University in Brno. He obtained his Masters (1985) and PhD. (1993) in Physics of Solid State at the Charles University in Prague, Czech Republic. He is an expert in application of advanced transmission and scanning electron microscopy techniques and accompanying analytical methods for microstructural studies in various materials including advanced steels, Ti alloys, Mg alloys and Ni-based superalloys, layered semiconductor structures, nanostructured coatings, nanoparticle powders and carbon nanostructures.

About the author

Professor Pavel Janoš received his M.S. degree (1981) at the University of Chemical Technology in Pardubice, Czech Republic, and a Ph.D. degree (1992) at the Charles University in Prague, Czech Republic. He started his R&D career at the Research Institute of Inorganic Chemistry in Ústí nad Labem. In 1994-1996 he worked at the Masaryk University in Brno, Czech Republic as an associate professor. Since 2002 he is a staff member of the Faculty of Environment at the Jan Evangelista Purkyně University in Ústí nad Labem.

Prof. Janoš is the author of more than 100 papers in international scientific journals, several patents and many oral and poster presentations. His scientific interests involve environmental analytical chemistry, chemical equilibria in the environment and advanced technologies for the environmental protection.

His current research activities are focused on a development of new (nano)materials for trapping and destruction of chemical pollutants and on an assessment of environmental impacts of nanomaterials and nanotechnologies.

About the author

Dr. Yvonna Jiraskova is a senior researcher at the Institute of Physics of Materials, Academy of Sciences of the Czech Republic. She obtained his Masters (1974) and Ph.D. degree at the P.J. Šafárik University Košice, SK (2003).

She is an expert in application of Mössbauer spectroscopy and magnetic methods supported by X-Ray diffraction for micro- and macro-structural studies of various iron-based materials in the bulk and powdered states. The main topics include phase transformations, order-disorder studies, crystallization and relaxation in the amorphous and nanocrystalline materials, defect studies, phase analysis, surface properties and mechanical alloying for material preparation.

About the author

Dr. Ondřej Životský is an associate professor in the Department of Physics, VŠB-Technical University of Ostrava. Also, he is the head of the scientific group Magnetic properties of materials (http://kf.vsb.cz/magnetic-properties-materials.html).

His research activities cover:

  • optics of thin films and surfaces, light propagation in systems containing thin and thick anisotropic films
  • magneto-optical ellipsometry, linear and quadratic magneto-optical effects
  • magnetic domain observations using the magneto-optical Kerr microscopy and magnetic force microscopy (MFM)
  • surface and bulk magnetic properties of materials (Fe, Co and Ni alloys; thin films; magnetic powders; permanent magnets)
  • magnetism of nanoparticle systems

Journal Reference

J. Luňáček1,2, O. Životský1,2, Y. Jirásková3,4, J. Buršík4, P. Janoš5. Thermally stimulated iron oxide transformations and magnetic behavior of cerium dioxide/iron oxide reactive sorbents. Materials Characterization 120 (2016) 295–303.

Show Affiliations

1 Department of Physics, VŠB – Technical University of Ostrava, 17, listopadu 15/2172, 708 33 Ostrava-Poruba, Czech Republic.

2 Department 606, VŠB – Technical University of Ostrava, 17, listopadu 15/2172, 708 33 Ostrava-Poruba, Czech Republic.

3 CEITEC IPM, Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62 Brno, Czech Republic.

4 Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62 Brno, Czech Republic..

5 Faculty of the Environment, University of Jan Evangelista Purkyně, Králova Výšina 7, 400 96 Ústí nad Labem, Czech Republic.

 

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