Thermal decomposition of Prussian blue under inert atmosphere
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The thermal decomposition of Prussian blue (iron(III) hexacyanoferrate) under inert atmosphere of argon was monitored by thermal analysis from room temperature up to 1000 °C. X-ray powder diffraction and 57Fe Mössbauer spectroscopy were the techniques used for phase identification before and after sample heating. The decomposition reaction is based on a successive release of cyanide groups from the Prussian blue structure. Three principal stages were observed including dehydration, change of crystal structure of Prussian blue, and its decomposition. At 400 °C, a monoclinic Prussian blue analogue was identified, while at higher temperatures the formation of various polymorphs of iron carbides was observed, including an orthorhombic Fe2C. Increase in the temperature above 700 °C induced decomposition of primarily formed Fe7C3 and Fe2C iron carbides into cementite, metallic iron, and graphite. The overall decomposition reaction can be expressed as follows: Fe4[Fe(CN)6]3·4H2O → 4Fe + Fe3C + 7C + 5(CN)2 + 4N2 + 4H2O.
KeywordsInsoluble Prussian blue Iron carbide XRD Calcination
This study has been supported by the Operational Program Research and Development for Innovations—European Regional Development Fund (CZ.1.05/2.1.00/03.0058), the internal IGA grants of Palacky University (PrF_2010_010, PrF_2011_013), the projects of the Ministry of Education of the Czech Republic (1M6198959201 and MSM6198959218), and the project of the Academy of Sciences of the Czech Republic (KAN115600801). The authors would like to thank to Jan Filip for XRD measurements, Martin Heřmánek for TG measurements, Jana Ševčíkova for Mössbauer measurements, Oldřich Schneeweiss for his comments on carbide phases, and Jiří Tuček for language corrections.
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