P.M. Botta

Synthesis of Fe-FeAl2O4-Al2O3 by high-energy ball milling of Al-Fe3O4 mixtures

Physicochemical and structural changes induced by mechanical activation of Al–Fe3O4 mixtures are studied. After 37 min, the system undergoes a self-sustained reaction with formation of α-Fe, FeAl2O4 and α-Al2O3. The evolution of the composition follows a three-step reaction. The solid solution spinel Fe[Al2−xFex]O4, (0.13<x<0.29), is obtained through a mechanochemical-thermal route.

Magnetic and structural study of mechanochemical reactions in the Al-Fe3O4 system

The solid state reaction between Al and Fe3O4 (magnetite) using mechanochemical activation of powder mixtures under Ar atmosphere is studied. The phase evolution during the reaction is analyzed by X-ray diffraction (XRD), vibrating sample magnetometry (VSM), differential thermal analysis (DTA) and scanning electron microscopy (SEM). At 37 minutes of high-energy ball-milling the disappearance of reactive phases and the production of α-Fe, FeAl2O4 and α-Al2O3 is observed, together with significant changes in the magnetic behavior of the system. The composition and properties of samples heated up to 1200°C are also investigated. The behavior of the saturation magnetization Ms is interpreted on the basis of the formation of a variable composition spinel phase Fe [Alx Fe2−x] O4 with 0 ≤ x ≤ 2 and a canting effect due to the presence of Al3+ ions in the spinel structure.

Mechanochemical effects on the kinetics of zinc titanate formation

In this work, mixtures Zn-TiO2 (anatase) in molar ratio 1:1 were mechanochemically activated in air atmosphere, and submitted to thermal treatments in order to study its thermal transformations. The behavior of the system during the milling was followed by X-ray diffraction (XRD), differential thermal analyses (DTA) and thermogravimetric analyses (TGA).Mechanochemical activation produces a progressive loss in crystallinity of the starting powders, with simultaneous oxidation of metallic Zn. However, the formation of neither ZnTiO3 nor Zn2TiO4 could be detected. At temperatures above 600°C, the thermal treatments resulted in the formation of ZnTiO3 and Zn2TiO4, at lower temperatures and shorter holding times for samples activated during longer times. The non-activated mixture exhibited a very different behavior, yielding Zn2Ti3O8 and Zn2TiO4 without evidence of ZnTiO3 formation. The obtained results are explained on the basis of reaction mechanisms taking place in the activated and non-activated samples.

Thermal and phase evolution of mechanochemical reactions in the Al–Fe3O4 system

Abstract The physicochemical and thermal behavior of mechanochemically activated Al–Fe 3 O 4 mixtures have been studied. The composition and structural changes undergone in the reaction system have been analyzed by DTA and XRD. Experimental evidence indicates that the nature of the products was dependent on the conditions of mechanochemical and thermal treatments. Under adequate experimental conditions, a self-sustained reaction was triggered, with the production of α-Fe and α-Al 2 O 3 . By varying the treatment parameters, it was possible, through an alternative reaction path, to obtain different products which show interesting properties in their application as functional materials.

Synthesis and magnetic properties of zinc ferrite from mechanochemical and thermal treatments of Zn-Fe3O4 mixtures

Abstract The preparation of ZnFe 2 O 4 from mechanochemically activated reactive mixtures Zn–Fe 3 O 4 is studied. The physicochemical and structural evolution of the system is analyzed by X-ray diffraction, vibrating sample magnetometry, differential thermal analysis and scanning electron microscopy. The activated mixtures reacted towards the formation of ZnFe 2 O 4 at lower temperatures than the non-activated ones. In addition, thermal treatments as a function of time revealed a non-expected magnetic behavior of some mixtures. In order to interpret this observation, a qualitative diffusional reaction model is proposed.

Transformations Induced by Mechanochemical Activation in the Al–Fe3O4 System

The physicochemical transformations induced by mechanochemical and thermal treatments of Al–Fe3O4 mixtures under Ar atmosphere have been investigated. This reaction system underwent a self-sustained reaction after 37 min of high-energy milling, yielding α-Fe and α-Al2O3. The mixtures activated for shorter times showed the same reaction when thermally treated in Ar atmosphere, at approximately 660°C. Depending on the heating conditions, the reaction did or did not occur in a self-sustained way. The influence of the processing parameters on the synthesis and properties of the different materials obtained has been analyzed.

Microestructura y propiedades de compuestos de Fe3O4/BaTiO3/epoxi

The influence of Fe3O4 and BaTiO3 on dielectric and magnetic properties of Fe3O4/BaTiO3/epoxy composites was studied. Initially, biphasic Fe3O4/epoxy and BaTiO3/epoxy composites were analyzed, and based on these results Fe3O4/BaTiO3/epoxy composite were conformed. In all the cases, dielectric properties were influenced by the frequency and filler concentration. In this way, Fe3O4/epoxy composites with high filler concentration showed high dielectric loss due to percolation effects and semiconducting properties of Fe3O4.