Authors:S. Arriola, E. Nava, G. Aguilar, and H. Armendariz
The Mössbauer parameters were determined on a series of catalyst mixtures of iron and zinc oxides with variable quantities of zinc. From these results, a change in the crystal structure of the iron oxide when introducing zinc into the samples was observed. The corundum structure of the -Fe2O3 phase was transformed into the spinel type of zinc ferrite when zinc oxide was present in any quantity. By means of these parameters a strong electronic interaction between the zinc ferrite and the zinc oxide present in excess was evident. The catalysts were analyzed using X-ray fluorescence /XRF/ and X-ray diffraction /XRD/.
A method of detecting inaccessible metallic corrosion is proposed, in which a gamma-emitting radionuclide added in aqueous solution to the contents of a pipe or vessel attaches itself selectively to corrosion products, and then may be detected from outside using a hand-held gamma detector. This was simulated in the laboratory in preliminary studies. Corrosion products studied were oxidised iron, FeS, goethite, magnetite, spinel and oxidised stainless steel.Kd values were derived for various radionuclides. Of the radionuclides studied,60Co,152Eu,214Pb,214Bi and226Ra seem potentially useful, but not22Na or137Cs.
Sol–gel auto combustion process was employed to synthesize nanosized Mn–Zn ferrite at different pH values (<1, 5, 6, 7, 8
and 10). Although self propagating combustion behavior of gel was noted at pH 5 but more effective combustion was observed
at pH 6. The smoldering effect was observed in gel prepared at pH 7, 8 and 10, whereas pH < 1 showed localized burning. Thermogravimetric
(TG) and X-ray diffraction (XRD) analyses were done to investigate the effect of pH on the combustion behavior, particle size
and the formation of desired magnetic (spinel) phase. From TG curves of burnt powders, activation energy of ignition reaction
at each pH value was calculated. The results showed that fuel to oxidant ratio and the amount of gel residuals decided the
value of activation energy required to further purify the burnt powders. Calcination parameters (time and temperature in air)
of powders P1 and P6 synthesized at pH < 1 and pH 6 were also determined. B–H loop results showed that calcined powder C6
was more ferromagnetic than C1 due to fully developed spinel phase and larger particle size.
Authors:N. Padmanaban, B. N. Avasthi, and J. Ghose
Thermal studies on aluminium substituted copper chromite spinel oxide, CuCr2−xAlxO4 (x=0.2 tox=0.8) by DSC show that with 20% replacement of Cr by Al, the phase transition temperature of the spinel is lowered but on further increasing the percentage of Al the phase transition temperature becomes higher than that of CuCr2O4. The enthalpy change for phase transition however decreases gradually with increasingx.
The objective of present research was to sinter nanosized Mn–Zn ferrites (MZF) at low temperature (≤1,000 °C) by avoiding
the formation of nonmagnetic phase (hematite). For this purpose, MZF powder was synthesized by sol–gel auto combustion process
at 220 °C and further calcined at 450 °C. In calcined powder, single phase (spinel) was confirmed by X-ray diffraction analysis.
Pellets were pressed, having 43% of the theoretical density and showing 47 emu gm−1 saturation magnetization (Ms). Various combinations of heating rate, dwelling time and gaseous environment were employed to meet optimum sintering conditions
at low temperature (≤1,000 °C). It was observed that sintering under air or N2 alone had failed to prevent the formation of nonmagnetic (hematite) phase. However, hematite phase can be suppressed by retaining
the green compacts at 1,000 °C for 180 min in air then further kept for 120 min in nitrogen. Under these conditions, spinel
phase (comprising of nano crystallites), 90% of theoretical density and 102 emu gm−1 of saturation magnetization has been achieved.
Authors:Z. Homonnay, P. Szilágyi, E. Kuzmann, K. Varga, Z. Németh, A. Szabó, K. Radó, J. Schunk, P. Tilky, and G. Patek
57Fe-conversion electron Mössbauer spectroscopy (CEMS) — a sensitive tool to analyze the phase composition of corrosion products
on the surface of stainless steel — was applied to study real specimens from the Paks Nuclear Power Plant, Hungary. The primary
circuit side of the heat exchanger tubes was studied on selected samples cut out from the steam generators during regular
maintenance. Mostly Cr-and Ni-substituted magnetite, amorphous Fe-oxides/oxyhydroxides as well as the signal of bulk austenitic
steel of the tubes were detected. The level of Cr-and Ni-substitution in the magnetite phase could be estimated from the Mössbauer
spectra. It is suggested that Cr-Ni substitution occurs simultaneously so that the inverse spinel structure of magnetite is
preserved up to a certain limit which appears to be roughly at [Fe3+]tet[Fe2+1/4Ni2+3/4Fe3+1/4Cr3+3/4]octO4. Further decrease of the iron content of this phase results in the formation of nickel chromite of regular spinel structure,
with very low Fe content. This transformation may be responsible for the hybrid structure of the protective oxide layer, being
substantially accelerated by previously performed, factory developed and proposed AP-CITROX decontamination cycles.
Authors:M. Bîrzescu, M. Niculescu, Raluca Dumitru, Oana Carp, and E. Segal
The homopolynuclear coordination compound [CoL · 2.5H2O]n with L=C2O42− was synthesized by a new unconventional method. It consist in the redox reaction between 1,2-ethanediol and cobalt nitrate
in presence of nitric acid. The coordination compound was characterized by chemical analysis, electronic and vibrational spectra
respectively, thermal analysis. In the coordination compound the Co(II) ion exists in a high spin octahedral configuration
and oxalate anion acts as double-bridge ligand, tetradentate, similar as in CoC2O4 · 2H2O obtained by the classical method. Nonstoichiometric oxide, Co3O4+0.25 with deficit in cobalt and normal spinel Co3O4 where identified as thermal decomposition intermediates. As final product of decomposition, the oxide CoO was obtained.
The physico-chemical characterization of magnesium-modified ZSM-5 zeolite catalysts has been performed by differential scanning calorimetry. Evidence has been found of the formation of magnesium oxide and the magnesium spinel phase in alumina-bonded ZSM-5 catalysts. DSC proved a suitable technique for characterization of these systems.
Authors:O. Carp, L. Patron, I. Mindru, and C. Suciu
A TG, DTG and DTA study of three polynuclear coordination compounds,
containing Al(III)-Mg(II), namely (NH4)4[Al2Mg(C4O5H4)4(OH)4]⋅2H2O,
has been reported together with the associated thermal decomposition mechanism
rationalized in terms of intermediate products. As decomposition end-product,
magnesium-aluminum spinel is obtained. The values of MgAl2O4
mean crystallite size depend on the anionic ligand contained by the precursor
compound, varying in the order: malate (143 Å) ligand contained by the
precursor compound, varying in the order: malate (143 Å)
The binary system Li2Se-In2Se3 was investigated in the range of 40 to 100 mol% In2Se3 by thermoanalytical and X-ray methods. The system is characterized by two eutectic points. Beside the two binary components
and the known ternary compound LiInSe2 another ternary compound crystallizes in this binary system at 83.3 mol% In2Se3. This compound was identified as LiIn5Se8. In contrast to (Cu, Ag)IB5IIIC8VI compounds such as CuIn5S8  it does not crystallize in the spinel structure. LiIn5Se8 shows a stratified structure. The melting point was determined to be at 810C. Starting from room temperature up to the melting
point no phase transitions were observed.