New evidences of in situ laser irradiation effects on γ‐Fe₂O₃ nanoparticles: a Raman spectroscopic study

Abstract

International audienceThe nature of the physical mechanisms responsible for the structural modification of the γ-Fe2O3 nanoparticles under laser irradiation has been investigated by Raman spectroscopy. In situ micro-Raman measurements were carried out on as-prepared γ-Fe2O3 nanoparticles about 4 nm in size as a function of laser power and on annealed γ-Fe2O3 particles. A baseline profile analysis clearly evidenced that the phase transition from maghemite into hematite is caused by local heating due to laser irradiation with an increase of grain size of nanoparticles. This increasing was clearly determined by X-ray diffraction from 4 nm in nanoparticles up to more than 177 nm beyond 900 °C in a polycrystalline state

Effect of Ce and Co Addition to Fe/Al2O3 for Catalytic Methane Decomposition

“…The used catalyst samples were reduced at 500 °C and subjected to a reaction at 700 °C for 180 min. A weak Raman band is observed at 475 cm −1 corresponding to Fe2O3 [23,[28][29][30] The Raman spectra of the spent catalysts are shown in Figure 13. A similar spectrum has been observed for the three catalysts 30%Fe/Al 2 O 3 , 30%Fe-15%Co/Al 2 O 3 , 30%Fe-15%Ce/Al 2 O 3 , which supports our speculation based on XRD and TPR results since there is no evidence of formation of any chemical compounds between Fe and Co/Ce.…”

“…The used catalyst samples were reduced at 500˝C and subjected to a reaction at 700˝C for 180 min. A weak Raman band is observed at 475 cm´1 corresponding to Fe 2 O 3 [23,[28][29][30] …”

“…The used catalyst samples were reduced at 500 °C and subjected to a reaction at 700 °C for 180 min. A weak Raman band is observed at 475 cm −1 corresponding to Fe2O3 [23,[28][29][30] Two types of carbon nanotubes are detected from the Raman spectroscopy. A band signal at 1354 cm´1 is corresponding to a polycrystalline and imperfect graphite structure [31,32].…”

Micro- to nano-scale characterization of martite from a banded iron formation in India and a lateritic soil in Brazil

“…The peak wave numbers were determined assuming a Lorentzian line shape. Laser-induced thermal effects are known to affect iron oxides and hydroxides, but sample degradation can be avoided using a laser power on the sample below 1 mW (Shebanova and Lazor 2003a;gehring et al 2009;El Mendili et al 2010). Thus, a low 500-µW power was used here, and moreover, we check for any possible degradation by acquiring several spectra at the same location for a total time of 8 min on a goethite patch in the Indian sample as shown in "Appendix".…”

El arte rupestre esquemático del Arroyo Barbaón (Parque Nacional de Monfragüe, Cáceres): contextualización arqueológica y caracterización de pigmentos

“…Teniendo en cuenta que el láser altera drásti-camente la estructura de los probables óxidos de hierro de los pigmentos (Shebanova y Lazor, 2003;El Mendili et al, 2011), su potencia fue reducida hasta un grado de 0,2mW, con 30 s de tiempo de exposición.…”