We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe12O19) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900 °C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe(3+), Fe(2+) and Sr(2+) ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe2O3) at 300 °C. At 500 °C, the intermediate species is converted to hematite (α-Fe2O3) by a topotactic transition. The final product of strontium hexaferrite (SrFe12O19) is generated at 800 °C. The obtained strontium hexaferrite shows a magnetization of 62.3 emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25 kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60 nm.
High-energy milling process on ceramic material was analyzed, it process generate modifications on morphology and particle size, the process showed the last one relation with the crystallite size, about of structural analysis Rietveld refinement let identify anisotropy with the variations on crystalline planes and deformations occasioned by milling process, the particle size decrease with the process, similar tendency was observed on the images obtained by Scanning Electronic Microscopy, an result in this study was the variation on magnetization without chemical reaction under non-stoichiometric conditions and the agglomerates sizes observed on samples it is by process.
Se propone que durante la síntesis de hematita dopada con estroncio, el ion Sr estructura cristalina de la fase magnetita y coexisten dos fases (hematita y magnetita). Para confirmar lo anterior se sintetizaron dos tipos de polvos, una fase pura de hematita y una fase de hematita dopada con estroncio empleando cantidades estequiométricas. En este estudio se presenta la caracterización de la estructura cristalina y las propiedades magnéticas sobre ambas muestras. Para la muestra sin estroncio, los resultados por Difracción de Rayos X muestran sólo la fase Fe₂O₃, pero al agregar estroncio se observan dos fases la hematita y magnetita. En la caracterización magnética de la muestra sin estroncio se observan una curva de histéresis correspondientes a un material ferrimagnético con magnetización relativamente baja (1 emu/g) típica de la hematita, pero con campo coercitivo amplio, para la muestra con estroncio, la curva de histéresis de la muestra con estroncio confirma la coexistencia de dos fases. Ninguna caracterización aporta información acerca del efecto del ion estroncio, sin embargo, se puede indagar que el estroncio se introduce en la fase magnetita. La técnica de espectroscopia Mössbauer del polvo sin estroncio, muestra únicamente un sextete correspondiente a la fase hematita.
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