In situ and time resolved study of the g/a-Fe2O3 transition in nanometric particles.

Influence of Grain Size, Oxygen Stoichiometry, and Synthesis Conditions on the γ-Fe2O3 Vacancies Ordering and Lattice Parameters

The soft chemistry method has been used to synthesize γ-Fe2O3 nanoparticles: various synthesis temperature were applied to obtain nanometric powders with crystallite size in the 9–14 nm range. Powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrophotometry, surface area measurements, and electron microscopy (TEM, SEM). It is clearly shown that these nanometric powders are very well crystallized as indicated by XRD and IR spectra which present substructural bands attributed to vacancies ordering (P4132). Based on these model materials and in the crystallite size range studied here, cell parameter appears to be not linked to crystallite size. It rat…

Suivi par diffraction de rayons X “in situ” de l'évolution du paramètre de maille du ferrite nanométrique γ-Fe2O3lors de l'isotherme d'adsorption d'eau

La methode de synthese par chimie douce a ete utilisee pour synthetiser des nanoparticules de maghemite γ-Fe 2 O 3 dans une gamme de taille allant de 9 a 14 nm. Ces poudres, parfaitement cristallisees en phase spinelle, exemptes d'impuretes, avec une stoechiometrie en oxygene parfaitement controlee, ont servi de materiaux modeles pour cette etude. Le parametre de maille de ce materiau (0,8346 nm) s'avere etre non dependant de la taille. Cependant, le suivi en Diffraction de Rayons X in-situ revele des variations de ce parametre avec la modification de la surface en presence de vapeur d'eau. Les phenomenes de chimisorption et de physisorption jouent un role preponderant dans les evolutions o…

In situ and time resolved study of the - transition in nanometric particles

In situ and real-time study of the {gamma} to {alpha}-Fe{sub 2}O{sub 3} transition is carried out on the H10 beamline at LURE (France). {gamma}-Fe{sub 2}O{sub 3} particles are synthesized by soft chemistry. These particles have an average diameter evaluated by X-ray diffraction of 9{+-}1nm and a specific surface area of 116m{sup 2}g{sup -1}. The size of produced {alpha}-Fe{sub 2}O{sub 3} particles is determined by in situ and time resolved X-ray diffraction measurements at different temperatures. An amazing evolution of size with time is revealed: an abrupt doubling of the {alpha}-Fe{sub 2}O{sub 3} particle size is observed whatever the heating temperature. Some assumptions are given in ord…

Structural variations as a function of surface adsorption in nanostructured particles

Macroscopic (adsorption isotherm and micro-calorimetry measurement) and microscopic (in situ X-ray diffraction and IR spectroscopy) approaches were used to study the influence of water adsorption on γ-Fe 2 O 3 nanoparticles. A nonmonotonic variation of γ-Fe 2 O 3 lattice parameter is revealed when the relative water pressure (p/p 0 ) increases from 0.03 to 0.96 with a maximum deviation for p/p 0 0.1. With IR spectroscopy, similar results were observed since a modification of γ-Fe 2 O 3 structural bands has been shown. In situ investigations as well as thermodynamics considerations lead to one important conclusion: the variation of the lattice parameter is in relation with the strains induce…