Mössbauer studies of iron(III)-(indole-3-alkanoic acids) systems in frozen aqueous solutions

Summary This paper describes the M?ssbauer investigations of iron(III) salts in aqueous solutions in the presence of indole-3-alkanoic acid ligands. The measurements showed two parallel reactions between the ligands and ferric ions: a complex formation and a redox process. The oxidation process takes place in the ligands, and a part of Fe³⁺is reduced to Fe²⁺.     

Vorticity‐velocity formulations of the Stokes problem in 3D

This work studies the three‐dimensional Stokes problem expressed in terms of vorticity and velocity variables. We make general assumptions on the regularity and the topological structure of the flow domain: the boundary is Lipschitz and possibly non‐connected and the flow domain may be multiply connected. Upon introducing a new variational space for the vorticity, five weak formulations of the Stokes problem are obtained. All the formulations are shown to lead to well‐posed problems and to be equivalent to the primitive variable formulation. The various formulations are discussed by interpreting the test functions for the vorticity (resp. velocity) equation as vector potentials for the velocity (resp. vorticity). Of the five sets of boundary conditions derived in the paper, three are already known, but only for domains with a trivial topological structure, while the remaining two are new. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermal Decomposition of Hafnium Phosphate and Related Materials

The thermal decomposition of hafnium phosphate (both in amorphous and crystalline forms), molybdate and tungstate was investigated. Hafnium phosphate has a layered structure, that of molybdate and of tungstate are tetragonal one. On investigating these materials two main endothermic processes with mass loss were observed in the temperature range of 298–1023 K. These processes were identified as crystal and structural water loss of the materials. The total mass loss of hafnium phosphate, molybdate and tungstate was 11,35 and 6.0%, respectively. In the case of mixed hafnium-titanium salts various crystal water quantities were found, depending on the titanium content of the sample. This revised version was published online in July 2006 with corrections to the Cover Date.     

57Fe and119Sn Mössbauer study of Ti-Containing highT c superconductors

⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopy as well as X-ray diffractometry were used to study Ti?Ca?Ba?Cu?O high T_c superconductors (T_c=106K) in the 4 to 300 K temperature range. X-ray diffractograms showed the dominant phase of these supercondutors to be 2-1-2-2 type. Three main iron sites were found and associalted with Fe in Cu sites in the real crystal. The dopublet with IS=0.25 mm/s and QS=0.7 mm/s at RT was attributed to the regular Cu site. No magnetic splitting was observed either in Sn or in Fe spectra taken even at 4 and 5K.     

57Fe and57Co Mössbauer study of suppression of superconductivity in PrBa2Cu3O7−d

⁵⁷Fe and⁵⁷Co Mössbauer spectroscopy and X-ray diffractometry were used to study⁵⁷Fe- and⁵⁷Co-substituted PrBa₂Cu₃O_7–d samples. Our most striking result is that the isomer shifts belonging to both Co and Fe at four- and five-coordinated Cu(1) sites in the PrBa₂Cu₃O_7–d cuprate are significantly higher than those observed for the superconducting 1-2-3 compounds. This result is considered as being a consequence of suppression of superconductivity because the extra electrons from Pr fill in the holes in Cu-O planes due to the valence state of Pr higher than 3+ and due to hybridization of Pr-Cu-O orbitals, via the charge transfer mechanism between the Cu(2)-O planes and Cu(1)-O chains. Our results give evidence of the existence of the charge transfer mechanism between the planes and the chains, and of its important role in controlling the superconductivity with a charge reservoir behavior of the Cu(1)-O chains.     

Kinetics of α-γ Phase Transition of Fe-12Cr-4Ni Alloy Aged between 500–650 °C

Using Mössbauer spectroscopy and X-ray diffraction as analytical tools, an "anomalous" α-γ phase transformation observed previously in steels was studied. It was shown in this work that this phase transformation is a feature of the Fe-12Cr-4Ni ternary alloy, and the ageing-time dependence of the γ-phase formation follows Avrami kinetics representing a diffusion controlled process. The activation energy of the process was also determined. The equilibrium composition of the samples could be interpreted in terms of calculated phase diagrams of the Fe-Cr-Ni system. On the basis of the hyperfine-field distributions derived from the spectra it was shown that two processes take place in the ferromagnetic α-phase during the ageing at different rates in which the slower one is in accordance with a decrease of the chromium concentration in the α-phase owing to the γ-phase formation.     

Bioautographic Detection of Antimicrobial Compounds in the Edible Shiitake Mushroom (Lentinus edodes)

JPC – Journal of Planar Chromatography – Modern TLC - The shiitake mushroom is well known for its health-beneficial effects. In this study we examined its antimicrobial activity by use...     

Temperature-dependent interfacial stiffness of the disorder layer in a thin Cu3Au alloy film

Epitaxial silicon carbide thin films grown on a silicon substrate were examined by short wavelength ( 0.71 A from a molybdenum anode) x-ray diffraction to study their atomic distortion and internal layer roughness. Up to 5 order Bragg peaks along (100) were measured and crystallographic structure factors were obtained. Electron density distributions along the surface normal were reconstructed via Fourier transform. In comparing to the ideal situation, it was found that, due to the lattice mismatch, the silicon atoms are no longer fixed on the same atomic plane, thus the corresponding electron distribution maxima were broadened. Also, the maxima for carbon atoms are flattened, indicating the randomized locations.     

Multinomial distribution as the most likely distribution of the stoichiometric composition of stochastically formednmers

Multinomial distribution is presented as the most likely distribution of the stoichiometric composition of stochastically formednmers. The termnmer is used in a wide sense, meaning not only the usual species in polymer chemistry, but molecules or a well defined set of neighbouring atoms in a crystal lattice as well. As a practical example the authors present the statistical interpretation of the Mössbauer spectra of ferromagnetic FeCrNi alloys. The problem discussed may also serve as a model calculation for courses on statistical thermodynamics.