Textural evolution of synthetic γ-FeOOH during thermal treatment by differential scanning calorimetry

• Published in: Journal of colloid and interface science 1984-01, Vol.101 (2), p.392-400
• Main Authors: Gómez-Villacieros, Rosario, Hernán, Lourdes, Morales, Julián, Tirado, JoséL
• Format: Article
• Language: English
• Subjects: Adsorbents; Chemistry; Exact sciences and technology; General and physical chemistry; Surface physical chemistry
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(84)90050-X

The thermal decomposition of lepidocrocite microcrystals has been studied by DSC and the textural and structural characteristics of the solid products obtained by interrupting the DSC measurements have been examined by the measurements of N 2 sorption isotherms, X-ray line broadening analysis, and electron microscopy. A new exothermal peak, located between the γ-FeOOH dehydration to γ-Fe 2O 3 and further transformation to hematite, has been detected in the DSC diagrams. On the basis of isotherm analysis by the BET and the de Boer methods, electron micrographs and crystallite size and microstrains of samples treated at 300 and 340°C, the energy released at the exothermic peak is ascribed to a decrease in surface area caused by sintering of micropores which accounts for the development of mesoporosity. When the partial transformation of maghemite into hematite begins, a complex textural system develops, which results in an increase in BET surface area. When the phase transformation is complete, a new decrease in surface area is detected.