Volume 89, Issue 4

Iron-based metallic glasses (MGs) are typical representatives of disordered alloys. They exhibit amorphous structure that is lacking any long-range order. Appropriate chemical composition of MGs ensures soft magnetic properties suitable for variety of practical applications. Because the beneficial magnetic properties are closely related to structural features of MGs it is inevitable to understand the ways how and under which conditions is their original structure modified. Notably elevated temperature can induce formation of crystallites that alter the desired magnetic parameters. Here, we demonstrate the use of 57 Fe Mössbauer spectrometry and nuclear forward scattering of synchrotron radiation for the study of structural transformations in (Fe 2.85 Co 1 ) 77 Mo 8 Cu 1 B 14 MG which was chosen as an example. These techniques are based upon nuclear resonances that can scan evolution of hyperfine interactions acting upon nuclear levels of a stable 57 Fe isotope. Because iron is typical constituent element of MGs, any deviations from original structural arrangement including modifications of the chemical surrounding can be studied.

20BaO·5ZnO·5Fe 2 O 3 ·70V 2 O 5 glass annealed at 450°C for 30 min showed a marked decrease in the electric resistivity ( ρ ) from 4.0×10 5 to 4.8 Ωcm, while 20BaO·5Cu 2 O·5Fe 2 O 3 ·70V 2 O 5 glass from 2.0×10 5 to 5.0 Ωcm. As for the conduction mechanism, it proved that n-type semiconductor model in conjugation with the small polaron hopping theory was most probable. Since Zn II and Cu I have a 3d 10 -electron configuration in the outer-most orbital, Ga 2 O 3 - and GeO 2 -containing vanadate glasses were explored in this study. 20BaO·5Ga 2 O 3 ·5Fe 2 O 3 ·70V 2 O 5 glass showed a less remarkable decrease of ρ from 4.5×10 5 to 100 Ωcm, and 20BaO·5GeO 2 ·5Fe 2 O 3 ·70V 2 O 5 glass from 3.3×10 6 to 400 Ωcm. Activation energies for the conduction ( E a ) of GeO 2 - and Ga 2 O 3 -contaning glasses before the annealing were respectively estimated to be 0.42 and 0.41 eV. It proved that barium iron vanadate glass with a smaller E a value could attain the higher conductivity after the annealing at temperaures higher than the crystalization temperature.

We investigated the physicochemicаl properties, structure and optical properties of the Ge 25 Ga 9.5 Sb 0.5 S 65 : Er 3+ /Yb 3+ glasses. The Judd-Ofelt theory was used to calculate the intensities of the intra-4 f electronic transitions of Er 3+ ions. We observed the upconversion photoluminescence (UCPL) at 530, 550, 660 and 810 nm under 980 nm excitation. In the Ge 25 Ga 9.5 Sb 0.5 S 65 : 0.1 at.% Er 3+ , we found that the Stokes photoluminescence (PL) at the green spectral region excited by the 490 and 532 nm laser is only ≈5 times higher than the UCPL emission under 810 or 980 nm excitation making these materials attractive for UCPL applications. The addition of 0.1–1 at.% of Yb 3+ into Ge 25 Ga 9.5 Sb 0.5 S 65 : 0.1 at.% Er 3+ glass reduces the UCPL as well as the Er 3+ ≈1.5 μm emission intensity probably due to the reabsorption processes of the excitation light and concentration quenching. However, the observed Er 3+ : 4 S 3/2 → 4 I 13/2 (≈850 nm) emission in the Ge 25 Ga 9.5 Sb 0.5 S 65 : 0.1 at.% Er 3+ sample populates the 4 I 13/2 level, which promises the using of this material for the 1.5 μm optical amplification.

Spectroscopic ellipsometry study on spin-coated non-toxic Ge 25 S 75 thin films annealed at different temperatures were conducted. Multi sample analysis with two sets of samples spin-coated onto soda-lime glass and onto silicon wafers was utilized. Optical constants (refractive index n and extinction coefficient k ) of these films were determined from ellipsometric data recorded over a wide spectral range (0.05–6 eV). Different parametrization of Ge 25 S 75 complex dielectric permittivity which consists of a Tauc-Lorentz or Cody-Lorentz oscillator describing the short wavelength absorption edge, a Lorentz or Gauss oscillators describing phonon absorption or optically active absorption of alkyl ammonium germanium salts in the middle infrared part of spectra is discussed. Using a Mott-Davis model, the decrease in local disorder with increasing annealing temperature is quantified from the short wavelength absorption edge onset. Using the Wemple-DiDomenico single oscillator model for the transparent part of the optical constants spectra, a decrease in the centroid distance of the valence and conduction bands with increasing annealing temperature is shown and increase in intensity of the inter-band optical transition due to annealing temperature occurs. Intensity of absorption near 3000 cm −1 could be used as alternative method to evaluation of quality of prepared films.

Thermogravimetry (TG) and differential thermal analysis (DTA) are traditional, but still useful, experimental techniques for obtaining information in the realms of materials and solid state chemistry. This paper presents two case studies (many more could be cited) to illustrate the strengths (and limitations) of these techniques: (1) Iron doping of clinoptilolite (the most common zeolite): the typical parameters of both components appear clearly in the TG and DTA curves. The decrease of the T max value of the structurally-typical DTA effect of FeOOH by approximately 100°C is attributed to the weakening of chemical bonds in FeOOH due to the incorporation of the doping component into the structure of this zeolite. (2) Macrodefect-free (MDF) materials: the results of both TG and DTA unambiguously locate the typical temperature range of the decomposition of the P{4}–O–Al/Fe{6} cross-links within the interval of 200–300°C. The presence of cross-links is shown by the DTA data while the TG data can be used to measure the degree of cross-linking, which is valuable information when studying both raw mixes and the final materials for a variety of MDF materials.

Iron is one of the most abundant elements on Earth and also in Mössbauer research. The present study is a summary of our search for iron compounds that now play an important role in the development of specific areas of inorganic chemistry of iron, biological applications and pigment for various types of artworks. The different catalytic or biologically active systems were studied in particular of the Mössbauer spectrometry, including temperature dependencies of the biological tissue and the synthetic vivianite. Mössbauer spectrometry was chosen as the main investigation tool for identification of Fe 2+ and Fe 3+ . We are identified divalent and trivalent iron in the samples and we found their mutual ratio. The iron sandwich complexes exhibit a linear dependence between quadrupole splitting and number of methyl groups. We also determined temperature of transformation of divalent to trivalent iron for vivianite sample that are used in painting. The transformation temperature is about 90°C.

Relocation of iron ions in microporous Fe-FER, (Al+Fe)-FER, Fe-MFI (FER: ferrierite, MFI: silicalite) and in mesoporous Fe-MCM-41 ferrisilicate (MCM: Mobile Crystalline Material) samples was followed during redox treatments primarily by tool of the in situ Mössbauer spectroscopy. Coexistence of various Fe 3+ and Fe 2+ species is demonstrated. In microporous Fe-FER and Fe-MFI existence of combined μ-oxo iron dimers, Fe 3+ FW -O-Fe 2+ EFW can be proposed. The presence of these dimers can easily be correlated with catalytic effect shown in certain oxidation processes. Structural rearrangement can also be revealed in mesoporous Fe-MCM-41 which result in improvement of catalytic performance in CO oxidation.

The research focuses on study of guest phase effect on the surface area and pore volume of SBA-15 with the emphasis on elucidation of reasons for these changes. The changes of surface area and pore volume are evident from evaluated N 2 adsorption isotherms of VOx-SBA-15 even for samples with relative low content of supported guest phase, which is “atomically” spread on the surface in the form of anchored monomeric vanadyl species. These species cannot block the pore with diameter of 10 nm, nevertheless the presence of such phase causes decrease in adsorbed nitrogen during physisorption. Comparison of guest phase amount with differences in adsorbed amount of nitrogen led to conclusion that each vanadyl complex prevents adsorption of about one or two N 2 molecules in the layer and influences two adsorption layers. Significant pore blocking occurs in the VOx-SBA-15 materials only in the case of presence bulk oxide-like nanospecies. Re-structuralization of silica mimicking phase separation phenomena relying on spinodal decomposition of a system was observed by SEM/TEM analysis and adsorption isotherms inspection for materials with high vanadium content.

In the present study, mesoporous silica materials doped with metal ions (Al 3+ , Ti 4+ , Zr 4+ ) were synthesized and characterized by a combination of various techniques, such as small angle X-ray scattering (SAXS), nitrogen adsorption/desorption at 77 K, elemental analysis, transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). It was shown that the metal ion doped samples retained their porous structure, which was similar to that of parent SBA-15. The synthesized M-SBA-15 samples (M=Al 3+ , Ti 4+ , Zr 4+ ) were evaluated in terms of adsorption of carbon dioxide and methane at 303 K. It was observed, that metal doping enhances carbon dioxide adsorption in comparison with purely siliceous sample, while low effect of metal doping on methane adsorption was observed.

Structure and phase composition of titania aerogels can be substantially influenced simply by the process of drying their parent water colloid suspensions prepared by the reaction of hydrogen peroxide with suspension of precipitates obtained by neutralization of solution of titanyl sulfate with ammonia. Two methods of drying are compared: (1) lyophilization of fast frozen material immersed in liquid nitrogen, and (2) critical point drying using supercritical CO 2 under high pressure. Both methods of drying lead to yellow titanium peroxide aerogels consisting of nanometer-sized blocks. While lyophilization leads to foils consisting of nano-sized crystalline nuclei of peroxo-polytitanic acid dispersed in predominantly amorphous material, the critical point drying provides rather bulk highly porous composite consisting of randomly oriented flat nanoparticles (5–10 nm) composed of crystalline anatase and amorphous peroxo-polytitanic acid.

Chemical looping with oxygen uncoupling (CLOU) is the tendency of releasing gaseous oxygen of an oxygen carrier upon heating, which is the key property for the efficient and cleaner combustion of solid fuels for their wide exploitation for thermal power applications. The solvent-free, improved synthesis method was developed for the synthesis of pure bixbyite, FeMnO 3 ( Ia3 ̅, a=b = c =0.94 nm) as a low-cost, oxygen carrier by exposing of the abundantly available precursors (Fe 3 O 4 and MnO) under inert- or reduction- atmosphere followed by air at 900°C. The bixbyite FeMnO 3 showed the enhanced, stable multi-cycle CLOU performance than that of the physical mixture and it is converted into FeMn 2 O 4 after the complete exhaustion of reactive oxygen under CLOU conditions. FeMnO 3 showed the uniform elemental distribution of Fe, Mn and O, which facilitate the regeneration in air upon heating for multi-cycle performance. 3.2 wt.% of reactive oxygen can be obtained compared to the mass of FeMnO 3 which is almost equal to the theoretical value under CLOU conditions. The lattice of FeMnO 3 is altered linearly above 100°C with the increase of temperature, however; without the decomposition of the bixbyite phase and it was reinstated virtually upon cooling in air.

The phosphates M 0.5+ x M′ x Zr 2− x (PO 4 ) 3 (M–Ca, Mn, Co, Sr, Cd, Ba, Pb; M′–Mg, Mn, Co) were synthesized by sol-gel method with the following thermal treatment of reaction mixtures. X-ray diffraction, IR spectroscopy and electron microprobe analysis showed that the obtained phosphates crystallized in Sc 2 (WO 4 ) 3 (SW) and NaZr 2 (PO 4 ) 3 (NZP) structural types. Both types of crystal structures are based on a framework comprised of octahedra and tetrahedra, the difference between them is fragments orientation. Thermal expansion of the phosphates was studied in the temperature range 20–800°C. Some compounds were found to belong to low-expanding materials (α av ~2·10 −6 °C −1 ).

A relationship between the local structure and the visible-light activated photocatalytic effect was investigated in the glass and glass ceramics prepared by recycling waste slag, which was discharged from a Tokyo Household Garbage Combustion Plant. For the preparation of a homogeneous sample of waste slag recycled glass, (WSRG), 10 wt% of Na 2 CO 3 and 10–50 wt% of Fe 2 O 3 were added. 57 Fe-Mössbauer spectra of WSRG recorded at liquid nitrogen temperature showed three types of magnetic hfs ; one due to Fe II ( O h ) with δ of 1.21 mm s −1 and H int of 46.7 T, one due to Fe III ( O h ) with δ of 0.46 mm s −1 and H int of 44.1 T, and the other due to Fe III ( T d ) with δ of 0.38 mm s −1 and H int of 47.8 T. They were superimposed on a relaxation spectrum due to superparamagnetic hematite. Methylene blue (MB) degradation test with 40 mg of the heat treated WSRG (50 wt% Fe 2 O 3 ), under the visible-light irradiation for 6 h showed a marked decrease in the concentration of MB from 20 to 7.7 μmol L −1 with a rate constant ( k ) of 2.7×10 −3 min −1 which was close to the k , 9.26×10 −3 min − 1 , recently obtained in 15Na 2 O⋅15CaO⋅40Fe 2 O 3 ⋅ 11Al 2 O 3 ⋅19SiO 2 glass.

Nanocrystalline nickel is an interesting material for catalysis, and also, like all nanocrystalline metals, it has potential for structural application. Our aim was to develop a method for preparation of precursor materials for powder metallurgy. Because of this, selective leaching of binary alloy was chosen as it leads to production of nanocrystalline clustered (sub)micro particles. In this work, the preparation of Ni particles by selective leaching of Al matrix from Al-50 wt.% Ni in NaOH water solution is described. It was found that structure and magnetic properties were strongly dependent on leaching temperature, which was proven by characterization of Ni particles leached at −20, 0, 20, 40, 60 and 80°C. The microstructure of as-prepared particles was observed by HRTEM and also by small angle neutron scattering. Magnetic properties were characterized by measuring of saturation magnetization. It was proven that with increased leaching temperature the grain size of prepared nanocrystalline particles increased. Also the value of saturated magnetization follows the same trend. The amount of hydrogen stored in nickel particles is independent on leaching temperature.

Fe and Si films were tested as corrosion protection layers for Zr in nuclear industry applications. Surface chemistry of Zr in dependence on the preparation conditions and layout of the films was complexly investigated by various spectroscopic and microscopic techniques. Corrosion experiments were carried out in autoclave conditions with in-situ Electrochemical Impedance Spectroscopy. A clean Zr surface is characteristic with disposition to disorder and rough morphology demonstrated in facets, steps or terraces. Upon deposition of Fe and Si atoms in amounts in the order of single monolayers and subsequent annealing at 400°C, the original (1×1) Zr surface structure rearranges into (2√3×2√3)R30°. Corrosion experiments show that a thicker Si overlayer successfully suppresses oxygen uptake of the underlying Zr material by forming a diffusion barrier. The barrier effect of the films was also confirmed for hydrogen.

Graphene-based materials are extensively studied, due to their excellent properties and their wide range of possible applications. Attention has recently been paid to three-dimensional-like graphenic structures, such as crumpled graphene sheets and graphenic foams: these kinds of materials can combine the properties of graphene associating high surface area and porosity, what is particularly interesting for energy or catalysis applications. Most of the synthesis methods leading to such structures are based on graphite oxide exfoliation and re-assembly, but in this work we focus on the preparation of graphenic foams by a solvothermal-based process. We performed a solvothermal reaction between ethanol and sodium at 220°C, during 72 h, under 200 bar, followed by a pyrolysis under nitrogen flow. An extended study of the influence of the temperature (800°C–900°C) of pyrolysis evidences an unexpected strong effect of this parameter on the characteristics of the materials. The optimal conditions provide multi-layer graphene (10 layers) foam with a surface area of 2000 m 2 ·g −1 . This work is an important step for the understanding of the mechanisms of the thermal treatment. Post-treatments in different experimental conditions are performed in order to modulate the structure and properties of the graphenic foams.