Authors:D. Gouveia, R. Rosenhaim, M. de Maurera, S. Lima, C. Paskocimas, E. Longo, A. Souza, and I. Santos
With the aim of obtaining materials with applications in pigments, CoxZn7-xSb2O12 spinels were synthesized using the Pechini method. This method consists in the formation of a polymeric net, where the metallic
cations are homogeneously distributed. In this work, two types of alcohol (ethyl glycol and ethylene glycol) were used for
the synthesis of a zinc antimoniate spinel, CoxZn7-xSb2O12 (x=0-7). The materials were characterized by termogravimetry (TG) and differential thermal analysis (DTA). TG results indicated
a decrease in total mass loss when cobalt was added to the solution substituting zinc, for samples prepared using the two
different alcohols. Decomposition temperatures, obtained by TG and DTA, presented a decreasing behavior as cobalt was added
to the material. In relation to the alcohols, all results indicated a better polymerization of the resin when ethylene glycol
was used, being the most indicated one for cation immobilization. X-ray diffraction did not show differences between the two
alcohols - both presented the spinel phase (Co, Zn)2.33Sb0.67O4. Samples with higher quantity of cobalt also presented ilmenite phase (Co, Zn)Sb2O6.
Soon after the discovery of the Mössbauer effect, studies were performed on spinels containing various transition metal ions (mostly Fe2+). This method proved very useful for investigating the local symmetry at transition metal ions. In spite of the numerous results, the correct interpretation of the complex quadrupole split spectra is still not given for numerous spinel structures. Since spectra of different shapes were measured for FeAl2O4 and FeCr2O4 by different authors, we performed new measurements on these spinels. The results on FeAl2O4 showed that the statistical distribution of another kind of ions in the positions A may influence the electric field gradient at the Fe2+ ions in the tetrahedral interstices. In FeCr2O4 and in the mixed Fe0.5Mg0.5Cr2O4, the electric field gradient exists at the Fe2+ ions at room temperature indicating that the degeneracy of the orbital doublet of the Fe2+ is removed.
Authors:Kia Angus, Paul Thomas, and Jean-Pierre Guerbois
Spinels are an important class of material due to their catalytic and magnetic properties. Ferrites are manufactured for their magnetic properties, in particular, for their high frequency response in high frequency
Authors:L. R. Gonsalves, S. C. Mojumdar, and V. M. S. Verenkar
Magnetic nanoparticles of spinel ferrites are of great importance not only for its application potential but also for fundamental research [ 1 – 4 ]. Understanding the structure and size dependent properties is the
Authors:Ming Han, Hailu Zhang, Yukou Du, Ping Yang, and Zongwu Deng
hydrocarbons [ 17 – 22 ] and unsaturated aldehydes [ 12 , 23 – 25 ], water–gas shift reaction [ 26 ], and many other processes [ 27 , 28 ] where the optimal carriers for platinum are a major issue. Magnesium aluminate spinel (MgAl 2 O 4 ) is a favorable
Authors:Marcela Stoia, Mircea Stefanescu, Mirela Barbu, Paul Barvinschi, and Lucian Barbu-Tudoran
In the recent years, research has been carried out on mixed oxides of transition metals, of the type A II B 2 III O 4 with spinel structure, which are active and thermally stable. In addition to this, there is
Authors:Rakesh K. Singh, A. Yadav, A. Narayan, Amrendra K. Singh, L. Verma, and R. K. Verma
crystallizes in cubic system, has a spinel structure, and has a low Curie temperature. The ternary metal oxide spinel has potential catalytic and chemical sensing applications [ 3 – 6 ]. Unlike ferrites, the chromite spinels have no B-site Fe 3+ . Still, these
The novel two-step synthesis method decreasing
the calcining temperature necessary for formation of spinel lattice and as
well for reaching of bright and clear hue of the pigments prepared were investigated.
This work aims to utilization of DTA for synthesis monitoring. Influence of
raw materials and temperature of calcination on color properties were observed.
The characterization of the samples was performed by X-ray diffraction and
colorimetry in the CIE L*a*b* system. It
was proved that the black spinel pigment Cu2.3Mn2.8Cr4.9Ox can be prepared at finally temperature 700C as one-phase system with
high quality black hue.
Authors:Rakesh K. Singh, A. Yadav, A. Narayan, Mukesh Chandra, and R. K. Verma
garnets and spinels. Many rare earth aluminate garnets are used as laser host when doped with Nd(III) or Yb(III) and also as scintillators and phosphors. Upon doping, interesting properties have been observed. Eu 2+ , R 3+ -doping for example, brings
The kinetics of reduction at relatively low temperatures with hydrogen of pure and doped metastable non-stoichiometric magnetite
with 1 at% Mn, Co, Ni and Cu and also with 5 at % Ni and Cu have been investigated by using isothermal thermogravimetry in
the temperature range 300–400°C. With increase in the concentration of the dopant (5 at% Ni and Cu), the reactivity increases.
The activation energies for pure magnetite varies from 7 to 9 kcal/mole with the preparation temperature of precursorf Fe2O3 (250–400°C), being the lowest for those prepared at the lowest temperatures. The corresponding activation energies for the
reduction of doped samples (Fe, M)3−zO4, it depends, apart from their porosity and surface areas, on the nature of the solute atom, amount of disorder, whether it
occupies the tetrahedral (A) or octahedral (B) sites in the non-stoichiometric spinel and possibly on hydrogen ‘Spill over’