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Abstract  

Synthesis of the green spinel pigment Co0.46Zn0.55(Ti0.064Cr0.91)2O4 by a novel two-step method of preparation have been investigated. Inorganic pigments are almost always prepared by a solid state reaction. It is classical ceramic method which used oxides, hydroxides or carbonates as precursors. The reaction is performed at temperature higher than 1300C and an agent of mineralization is usually present. The presented novel method of preparation decreases the calcining temperature necessary for reaching of bright and clear hue of the pigments prepared. Main attention was focused on the influence of two types of titanium raw materials on the temperature region of the spinel structure formation and on the colour properties of the pigments. The mixture of precursors with TiO2 gives a one-phase system when calcining at 1100C but the colour properties are more interesting at 1150C. Thermal stability of this pigment is limited by temperature 1300C. This temperature is connected with partial oxidation of Cr(III) to Cr(VI). Thermal analysis provided the first information about the temperature region of the pigment formation and determined the thermal stability of pigment.

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Nanoscale spinel ferrites prepared by mechanochemical route

Thermal stability and size dependent magnetic properties

Journal of Thermal Analysis and Calorimetry
Authors: V. Šepelák, P. Heitjans, and K. Becker

Abstract  

Among the many types of preparation and processing techniques, the nonconventional mechanochemical route has been recognized as a powerful method for the production of novel, high-performance, and low-cost nanomaterials. Because of their small constituent sizes and disordered structural state, nanoscale materials prepared by mechanochemical route are inherently unstable with respect to structural changes at elevated temperatures. Taking into account the considerable relevance of the thermal stability of nanoscale complex oxides to nanoscience and nanotechnology, in the present work, results on the response of mechanochemically prepared MgFe2O4 and NiFe2O4 to changes in temperature will be presented. Several interesting features are involved in the work, e.g., a relaxation of the mechanically induced cation distribution towards its equilibrium configuration, a disappearance of the superparamagnetism on heating, an increase of both the saturation magnetization and the Néel temperature with increasing particle size, and a core-shell structure of nanoparticles.

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Journal of Thermal Analysis and Calorimetry
Authors: V. Ramírez-Valle, M. Jiménez de Haro, M. Avilés, L. Pérez-Maqueda, A. Durán, J. Pascual, and J. Pérez-Rodríguez

Abstract  

Static and dynamic heating of vermiculite samples from Santa Olalla, Huelva, Spain, saturated with different cations, i.e. Na+, Cs+, NH4 +, Mg2+, Ca2+, Ba2+ and Al3+, have been studied. The characterization of the phases formed during heating has been carried out by X-ray diffraction. The phases formed depend on the cation present in the interlamellar position and the heating process. The phases identified in the vermiculite samples saturated with different cations and heated at different temperatures are the following: enstatite, forsterite, spinel, cordierite, anorthite, pollucite, nepheline, coesite, celsian and others various mixed silicates; also some dehydrated and amorphous phases have been observed. On static heating, at the maximum temperature reached in this work, the phases formed appear mixed with a glassy phase.

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Journal of Thermal Analysis and Calorimetry
Authors: M. R. S. Silva, S. C. Souza, I. M. G. Santos, M. R. Cassia-Santos, L. E. B. Soledade, A. G. Souza, S. J. G. Lima, and E. Longo
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Journal of Thermal Analysis and Calorimetry
Authors: S. C. Souza, M. A. F. Souza, S. J. G. Lima, M. R. Cassia-Santos, V. J. Fernandes Jr., L. E. B. Soledade, E. Longo, A. G. Souza, and I. M. G. Santos
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Journal of Thermal Analysis and Calorimetry
Authors: Márcia Silva, Lydianne de O. Miranda, Maria Cassia-Santos, S. Lima, L. Soledade, E. Longo, C. Paskocimas, A. Souza, and Iêda Santos

Abstract  

Undoped and/or doped with 1 mol% of Co2+ Mg2TiO4 andMg2SnO4 powders were synthesized by the polymeric precursor method. The influence of the network former (Sn4+ or Ti4+) on the thermal, structural and optical properties was investigated. The recorded mass losses are due to the escape of water and adsorbed gases and to the elimination of the organic matter. Mg2TiO4 crystallizes at lower temperatures and also presents more ordered structure with a smaller unit call and having more intense green color than Mg2SnO4 has.

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Abstract  

A series of LiMn2O4 samples with nominal Li/Mn molar ratio=1/2 has been synthesized at 700 and 750C by the ceramic procedure from Mn2O3 and several lithium sources. Lattice parameters determined from X-ray diffraction patterns are within a narrow range, from a c=8.238(1) to a c=8.245(1) , Da c/a c<0.1%. The study by differential scanning calorimetry (DSC) shows that the temperatures of the cubic (Fd3m)↔orthorhombic (Fddd) phase transition are spread off in a wide range, from -30 to -2C for the exothermic C→O phase transition, and from -21 to +13C for the endothermic O→C transformation. Relationships between the lattice parameter values, the temperature of the phase transformation, and the stoichiometry of the LiMn2O4 samples are pointed out. The DSC technique, which reveals more sensitive than X-ray diffraction to very small variations of composition, is put forward as an essential technique to characterize LiMn2O4 samples.

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