Rapid, Temperature-Failsafe Magnetic Induction Processing of Adhesives Using Coprecipitation-Synthesized Mn−Zn Ferrite Nanoparticles

Abstract

Magnetic induction heating of Curie nanoparticles (CNPs), termed “Spinheat”, offers a rapid, temperature-failsafe alternative to conventional curing of adhesives, which consumes substantial energy and requires prolonged heating. Mn−Zn ferrite CNPs combine tunable Curie temperatures (Tc) with heat generation under an alternating magnetic field (AMF), making them suitable transducers. An aqueous coprecipitation route was developed to prepare Mn−Zn ferrite (MnxZn1−xFe2O4, 0 ≤ x ≤ 1) CNPs, achieving a recovered-mass yield of ∼98%. Across the series of Mn−Zn ferrites, Tc was tuned from 107 to 334 °C, and the dry-state specific absorption rate (SAR) was correlated with composition, structure, particle and crystallite sizes, and magnetic properties. As-synthesized Mn0.9Zn0.1Fe2O4 (particle size ∼12 nm) exhibited the highest dry-powder SAR of 11 W/g at 140 Oe and 400 kHz (intrinsic loss power of 0.22 nH·m2/kg), exceeding prior dry-powder reports by more than tenfold. Annealing increased saturation magnetization but markedly reduced the SAR in the Mn-rich compositions, accompanied by particle growth from ∼5−15 nm to 300−400 nm. CNPs with Tc near 190 °C enabled 5 min induction curing of a commercial epoxy adhesive, achieving ∼19 MPa lap-shear strength (vs ∼15 MPa for oven curing), no discoloration, and ∼1.6% of the oven energy. These findings highlight the potential of Mn−Zn ferrite CNPs prepared via coprecipitation for rapid, energy-efficient adhesive and resin processing.