Magnetic nanoparticles (mNPs)are used where localized heat is required, such as in induction cook tops, laser welding, nano-material welding, and hyperthermia therapy for cancer patients. It is known that mNPs can provide heat based on three mechanisms: hysteresis, Neel’s Relaxation, and Brownian (friction) motion. The studies have shown for biomedical applications that the mNPs generate heat based on frictional losses and do not exhibit hysteresis.1 It is not as thoroughly understood how the mNPs behave in rigid environments, particularly when dispersed throughout a material. The main goal of this paper is to understand the dominant mechanism of heating when mNPs are in a rigid structure and use this understanding to optimize mNPs for localized heat applications. We experiment with the mNPs, induction heat, and heat sensitive paint to demonstrate the mNPs ability to create heat when embedded in rigid matrices. A commercially available induction heater operating at 30 - 104 kHz is used to create a high strength alternating magnetic field to test whether the energy at these frequencies leads to heating when mNPs are present. Studies are done for powdered carbon and iron (Fe2O3) particles and for particles when embedded in polyurethane, rubber, and thermochromic paint. The results suggest that the mNPs exhibit hysteresis in rigid systems. We demonstrate this heating using thermochromic paint on mNP-infused solids.
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