Calorimetric study of maghemite nanoparticles synthesized by laser-induced pyrolysis

Oscar Bomatí-Miguel, Lena Mazeina, Alexandra Navrotsky, Sabino Veintemillas-Verdaguer

Research output: Contribution to journalArticlepeer-review

70 Scopus citations

Abstract

The thermodynamic properties of maghemite (γ-Fe2O 3) nanoparticles with size smaller than 10 nm had not been studied previously because of particle size limitations for samples synthesized by wet chemical methods. Laser-induced pyrolysis is a well-established method of producing maghemite with particle sizes smaller than 10 nm. Maghemite nanoparticles, obtained by this method and having a size range of 2-40 nm, were fully characterized and studied by solution calorimetry. The enthalpy of water adsorption was also measured. The surface enthalpy obtained from calorimetric data for the hydrated maghemite surface is 0.57 ± 0.10 J/m2 and is in good agreement with previously reported values. The surface enthalpy for the dry, water-free surface is 0.71 ± 0.13 J/m2 and is reported for the first time. The difference in the surface enthalpy for the dry surface between α- and γ-polymorphs of Fe2O3 is similar to that between α-and γ-Al2O3. This large difference in surface enthalpy (∼1.2 J/m2) creates an energy crossover so that fine-grained hematite is metastable relative to fine-grained maghemite at particle size <15 nm.

Original languageEnglish (US)
Pages (from-to)591-598
Number of pages8
JournalChemistry of Materials
Volume20
Issue number2
DOIs
StatePublished - Jan 22 2008
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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