1. Violeta Nikolic, Institut Nuklearnih Nauka Vinca , Serbia
Magnetic behavior of the magnetite nanoparticles synthesized by hydrothermal method was investigated in detail by SQUID measurements, established by Nikolić et al . To get better insight in behavior of the prepared sample subjected to the thermal treatment, a more detailed thermo-gravimetric analysis was performed (thermal analyzer TA-SDT 2090). TG and DTA curves were measured by standard protocol. Additional measurements of the sample dried under the lowered pressure were also performed. Results revealed that processes observed as a consequence of a thermal treatment has strong exothermic nature; the most intense DTA maximum is observed at T = 289 °C. Having on mind results of XRD and TEM analysis , as well that magnetite to hematite phase transformation presents exothermic process: Fe3O4+1/4 O2= 3/2 α-Fe2O3+∆H, ∆H=115 kJ〖mol〗^(-1) [2,3], observed exothermic process is ascribed to Fe3O4→α-Fe2 O3 phase transformation at low temperatures (<300 ℃). Conversion of Fe3O4→α-Fe2O3 at such low temperature is observed for the first time, and still presents open question.
The author is gratefully acknowledged Dr N. Cvjetićanin for thermogravimetric measurements.