Control of the Crystal Phase Composition of Fe_xO_yNanopowders Prepared by CO₂Laser Vaporization

Abstract

Crystalline magnetic iron oxide nanopowders are prepared by CO 2 laser vaporization (LAVA) of a hematite (α-Fe 2 O 3 ) raw powder. Condensation at normal pressure leads to maghemite (γ-Fe 2 O 3 ) as the main phase in the nanopowders. With an increasing oxygen partial pressure in the zone of condensation, an increasing amount of Fe 2 O 3 polymorph ε-Fe 2 O 3 is found. The LAVA-prepared Fe 2 O 3 nanopowders are characterized by X-ray diffraction, transmission electron microscopy, and chemical analysis and with respect to their magnetic properties. A mechanism for the initial nucleation is proposed to explain the formation of ε-Fe 2 O 3 with an increasing oxygen content in the condensation atmosphere. The model is based on the evidence of ozone in oxygen-rich condensation atmospheres. Density functional theory calculations indicate that ozone facilitates the formation of 6-fold oxygen-coordinated Fe ions acting as building units for the emerging crystal structure during the solidification of the nanoparticles. This insight into early nucleation stages will be useful for the functional design and crystal engineering of either isostructural materials like alumina (Al 2 O 3 ) or, more generally, vapor phase synthetic routes for ceramic materials.

Crystal Structure and Magnetic Properties of ϵ‐RuxFe2‐xO3 Nanosize Hard Ferrite

“…[21] Additionally, e-Fe 2 O 3 shows various functionalities such as high-frequency millimeter wave absorption, optical transparency,n onlinear magneto-optice ffect, ferroelectricity,a nd catalytic properties. [21][22][23][24][25][26][27] Severals ynthetic methods have been developed using wet and dry processes. [2-7, 21, 28-31] Metal substitution on magnetic materials is effective to control the magnetic properties.…”

Risk and life cycle assessment of nanoparticles for medical applications prepared using safe- and benign-by-design gas-phase syntheses

“…Argon was used as an additional gas since it promotes the formation of maghemite. 24,25 CoLAVA synthesis and formation of these SiliFe nanoparticles were described in detail previously. 23 The ferromagnetic maghemite nanoparticles in this study were prepared by using the LAVA method starting from the same hematite raw powder and applying the same process conditions already used for the synthesis of the SiliFe nano- particles.…”

“…LAVA synthesis and formation of the maghemite nanoparticles were described in detail previously. 24 Physicochemical characterisation of the magnetic nanopowders. The nanopowders were characterised according to the technical specification document ISO/TS 17200.…”

Europium(III)‐Doped MgAl2O4 Spinel Nanophosphor Prepared by CO2 Laser Co‐Vaporization

“…The CO 2 laser vaporization technique has proven its versatility to prepare a broad range of functional, single or multiphase ceramic NPs with excellent properties . Briefly, a CO 2 laser beam is focused onto the surface of a coarse‐grained raw powder.…”

“…The CO 2 laser vaporization technique has proven its versatility to prepare a broad range of functional, single or multiphase ceramic NPs with excellent properties. [15][16][17][18] Briefly, a CO 2 laser beam is focused onto the surface of a coarsegrained raw powder. By absorbing the high-intensity laser radiation, the raw powder heats up, vaporizes, and forms a plasma.…”