1. Violeta Nikolic, University of Belgrade, Vinča Institute of Nuclear Sciences, Serbia, Serbia
The magnetic behavior of nanoparticles of magnetite coated with oleic acid (〖Fe〗_3 O_4/OA), synthesized by the hydrothermal method, was investigated in detail by SQUID measurements, performed by Nikolić et al. . In order to get a better insight into the behavior of the prepared sample subjected to heat treatment, a more detailed thermo-gravimetric analysis was performed (thermal analyzer TA-SDT 2090). TG and DTA curves were measured by a standard protocol. Additional measurements of the sample dried under the lowered pressure were also performed. The results revealed that the processes, observed as a consequence of heat treatment, have a strong exothermic nature; the most intense DTA maximum is observed around T = 289 ° C. Having in mind the results of XRD and TEM analysis , as well as that the transformation of the magnetite phase into hematite represents an exothermic process: 〖Fe〗_3 O_4+1/4 O_2= 3/2 α-〖Fe〗_2 O_3+∆H, ∆H=115 kJ〖mol〗^(-1) [2,3], the observed exothermic process is attributed to 〖Fe〗_3 O_4→α-〖Fe〗_2 O_3 phase transformation at low temperatures (<300 ℃). The observed behavior could be ascribed to the presence of cation deficiency in the magnetite crystal lattice.
The author is gratefully acknowledged Dr N. Cvjetićanin for thermogravimetric measurements.
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