Search Results

You are looking at 51 - 60 of 157 items for :

  • Chemistry and Chemical Engineering x
  • All content x
Clear All

Nanocrystalline Zn0.5Ni0.5Fe2O4

Preparation and kinetics of thermal process of precursor

Journal of Thermal Analysis and Calorimetry
Authors: Wenwei Wu, Yongni Li, Kaiwen Zhou, Xuehang Wu, Sen Liao, and Qing Wang

Introduction Polycrystalline spinel ferrites have many unique properties, such as high electrical resistivity, high Curie temperature, large magnetocrystalline anisotropy, high coercivity, mechanical hardness, chemical

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: C. Santos, B. Capistrano, F. Vieira, M. Santos, S. Lima, E. Longo, C. Paskocimas, A. Souza, L. Soledade, and I. Santos

Abstract  

In this work, spinels with the general formula Zn2−xCoxTiO4 were synthesized by the polymeric precursor method and thermally treated at 1,000 °C. The powder precursors were characterized by TG/DTA. A decrease in the DTA peak temperature with the amount of zinc was observed. After the thermal treatment, the characterizations were performed by XRD, IR, colorimetry and UV/VIS spectroscopy. The XRD patterns of all the samples showed the presence of the spinel phase. Infrared spectroscopy showed the presence of ester complexes for Zn2TiO4 after thermal treatment at 500 °C, which disappeared after cobalt addition, indicating that organic material elimination was favored.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: D. Gouveia, A. Souza, M. de Maurera, C. da Costa, I. Santos, S. Prasad, J. de Lima, C. Paskocimas, and E. Longo

Abstract  

Using the Pechini method, pigments with spinel structure (Zn7Sb2O12)were synthesized by substitution of the cation Zn2+ by Co2+, in compounds with different concentrations of Sb2O3. The doping resulted in CoxZn(7–x)Sb2O12 phases(x=1–7) that were isomorphs to spinel, denominated as samples A and B. After thermal treatment at 400C for 1 h, the powders were characterized by thermogravimetry(TG) and differential thermal analysis (DTA). The results indicate a different behavior whena higher amount of Sb2O3 is used, due to the presence of a secondary phase (ilmenite).

Restricted access
Reaction Kinetics, Mechanisms and Catalysis
Authors: R. Thinesh Kumar, N. Clament Sagaya Selvam, T. Adinaveen, L. John Kennedy, and J. Judith Vijaya

Introduction Nanostructured metal aluminate spinels constitute an interesting class of oxide ceramics with important technological applications such as lower temperature sinterability, greater thermal stability, increased

Restricted access

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

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: F. Kovanda, V. Balek, V. Dorničák, P. Martinec, M. Mašláň, L. Bílková, D. Koloušek, and I. Bountseva

Abstract  

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.

Restricted access

Abstract  

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 gel micropores.

Restricted access

Abstract  

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).

Restricted access

Abstract  

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.

Restricted access

Abstract  

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.

Restricted access