Authors:Shmuel Yariv, Isaak Lapides, and Mikhail Borisover
peaks do not appear in the diffractograms. Trace amounts of spinel and cristobalite are obtained from thermal recrystallization. Quartz is present as an impurity in the Wyoming bentonite and after the amorphization of MONT its X-ray peak becomes very
Authors:L. Gonsalves, S. Mojumdar, and V. Verenkar
The chemistry, structure, and properties of spinel ferrites are largely governed by the method of preparation. The metal carboxylato-hydrazinate
precursors are known to yield nanosized oxides at a comparatively lower temperature. In this study, we are reporting the synthesis
of one such precursor, cobalt nickel ferrous fumarato-hydrazinate which decomposes autocatalytically to give cobalt nickel
ferrite nanoparticles. The XRD study of this decomposed product confirms the formation of single-phase spinel, i.e., Co0.5Ni0.5Fe2O4. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric (TG), and differential scanning
calorimetric (DSC) analysis. The precursor has also been characterized by FTIR, EDX, and chemical analysis, and its chemical
composition has been determined as Co0.5Ni0.5Fe2(C4H2O4)3·6N2H4.
Authors:Po-Chen Chen, Teng-Shih Shih, and Juen-Shiou Chen
In this study, thermogravimetric analysis (TG) testing is used to measure the mass loss of polished Al–6Zn–XMg (X = 0 and 2 mass%) alloy samples heated at 773 K for 6 h in dry air or nitrogen gas. The progressive development of thermally
formed oxides on an Al–6Zn–XMg (X = 0 and 2 mass%) alloy as shown by X-ray diffractometer analyses is discussed. Zn-spinel and Mg-spinel are detected on the
Al–6Zn and Al–6Zn–2Mg alloy samples, respectively, and then heated in the dry air atmosphere; AlN and Mg3N2 are detected in alloy samples heated in nitrogen gas. The chain reactions that cause the serrated change in the mass loss
curve are proposed and discussed.
Authors:F. Kovanda, V. Balek, V. Dorničák, P. Martinec, M. Mašláň, L. Bílková, D. Koloušek, and I. Bountseva
Thermal behaviour of synthetic pyroaurite-like anionic clay with molar ratio Mg/Fe=2 was studied in the range of 60-1100C
during heating in air. TG/DTA coupled with evolved gas analysis, emanation thermal analysis (ETA), surface area measurements,
XRD, IR and Mssbauer spectroscopy were used. Microstructure changes characterized by ETA were in a good agreement with the
results of surface area measurements and other methods. After the thermal decomposition of the pyroaurite-like anionic clay,
which took place mainly up to 400C, a predominantly amorphous mixture of oxides is formed. A gradual crystallization of MgO
(periclase) and Fe2O3 (maghemite) was observed at 400-700C by XRD. The MgFe2O4 spinel and periclase were detected at 800-1100C. The spinel formation was also confirmed by Mssbauer spectroscopy.
Authors:S. Iijima, A. Nomura, F. Mizukami, S. Shin, and F. Mizutani
Spinel iron oxide (Fe3O4-γ-Fe2O3) particles were supported on microbeads of silica gel by the calcination of the silica gel base adsorbing citric acid and
Fe3+ ions. The X-ray diffraction patterns and the57Fe Mössbauer spectra measured for the spinel iron oxide indicated that the particle size of the oxide was regulated by the
mean pore diameter (4–82 nm) of the silica gel support employed. In the case of α-Fe2O3 particles prepared by using the same silica gel beads, it was revealed by the Mössbauer spectra and the electron micrographs
that there were relatively large particles of the oxide on the surface of the beads, in addition to the particles in the silica
Authors:T. Konvička, Z. Šolc, P. Mošner, and A. Kalendová
The paper deals with the possible application of various methods to follow the course of reaction between zinc oxide and Fe(III)
oxide with respect to various kinds of Fe(III) oxides used (Fe(III) pigments - red, yellow and black). Differential thermal
analysis and chemical analysis can be recommended as the most suitable methods for following reactions leading to spinel formation.
The possibilities of determining the activation energy of the studied processes are discussed. When Fe(III) red pigment is
used as a reactant and therefore no reaction occurs except spinel formation, conductometric thermal analysis was found to
be suitable and more sensitive for the evaluation of differences in reactivities.
It has also been observed that the kind of Fe(III) pigment, due to its individual reactivity significantly affects the colouring
properties of the final product (e.g., of the ceramic stain).
DTA study of an Indian Kaolinite has been performed by varying packing density and rate of heating. Both these two parameters
influence the intensities of both endothermic and exothermic peaks related to the dehydration, dehydroxylation and then crystallizations
of Al-Si spinel, mullite and cristobalite phases. Significantly, the study reveals that mullitization takes place by two separate
reactions as indicated by two exotherms in the 1200-1400C range of DTA trace.
Authors:R. Zboril, M. Mashlan, V. Papaefthymiou, and G. Hadjipanayis
The mechanism of the thermal decomposition of Fe2(SO4)3 in air has been studied at different temperatures (520-700 °C) using mainly 57Fe Mössbauer spectroscopy. Iron(III) oxides with corundum (), bixbyite (), spinel () and orthorhombic () structures were identified as solid products of this conversion. A significant influence of the heating temperature on the decomposition mechanism and on the phase composition of reaction products was found.
The thermal decomposition kinetics of nickel ferrite (NiFe2O4) precursor prepared using egg white solution route in dynamical air atmosphere was studied by means of TG with different
heating rates. The activation energy (Eα) values of one reaction process were estimated using the methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS),
which were found to be consistent. The dependent activation energies on extent of conversions of the decomposition reaction
indicate “multi-step” processes. XRD, SEM and FTIR showed that the synthesized NiFe2O4 precursor after calcination at 773 K has a pure spinel phase, having particle sizes of ~54 ± 29 nm.
Authors:R. Frost, A. Musumeci, J. Kloprogge, M. Weier, M. Adebajo, and W. Martens
The thermal decompositions of hydrotalcites
with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer have
been studied using thermogravimetry combined with mass spectrometry. X-ray
diffraction shows the hydrotalcites have a d(003)
spacing of 11.1 and 10.9 which compares with a d-spacing
of 7.9 and 7.98 for the hydrotalcite with carbonate or sulphate in
the interlayer. XRD was also used to determine the products of the thermal
decomposition. For the hydrotalcite decomposition the products were MgO, Fe2O3
and a spinel MgAl2O4. Dehydration
and dehydroxylation take place in three steps each and the loss of cyanide
ions in two steps.