Curing epoxy with electrochemically synthesized Ni_xFe_{3- x}O₄ magnetic nanoparticles

Fe₃O₄ magnetic nanoparticles (MNPs) were synthesized via cathodic electrodeposition in the form of undoped and Ni²⁺-doped MNPs, and their curing potential towards epoxy was discussed. Partial substitution of Fe²⁺ sites by Ni²⁺ cations in the general formula of Ni_XFe_{3- X}O₄ was confirmed by – X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), dispersive X-ray spectrometry (EDS), and vibrating sample magnetometry (VSM). Low-filled epoxy/Fe₃O₄ and epoxy/Ni²⁺-Fe₃O₄ nanocomposites containing 0.1 wt.% MNPs based on 100 parts by weight of epoxy resin were prepared and underwent nonisothermal differential calorimetry (DSC) at different heating rates (5, 10, 15, and 20 °C/min). The curability of the well-characterized nanocomposites of epoxy/Ni_0.11Fe_2.89O₄ was qualitatively studied by the use of Cure Index. Overall, structural changes in Fe₃O₄ atomic structure resulting from the replacement of Fe²⁺ cations with Ni²⁺ had effect on epoxy curing reactions, as reflected in a shift in curing state from Poor for epoxy/Fe₃O₄ to Good for epoxy/Ni²⁺-doped Fe₃O₄ systems. This phenomenon was explained on account of the fact that Ni²⁺ dopants with their laminar structure tend to locate in the top layer of Fe₃O₄, which dramatically increases the activity of Fe₃O₄ to take electron pair of epoxy to open epoxy ring.