Study Of Thermophysical Property Enhancement Of Magnetic Nanofluids With Fe-based Amorphous Nanoparticles

Profiting from the unique thermophysical characteristics of magnetic nanofluids(MNFs),they are widely applied in the fields of energy,biomedicine and electricity.Fe3O4 magnetic nanoparticles,owning to their simple preparation,superparamagnetism,excellent biocompatibility and biodegradability,have been extensively studied as the object of MNFs' thermophysical properties.However,their low saturation magnetization and thermal conductivity severely restrict the further enhancement of magnetic heating and heat transfer efficiency.Therefore,it is necessary to explore new systems of MNFs in order to meet the practical demand in the fields of energy and biomedicine.We synthesized FeZrB amorphous magnetic nanoparticles by chemical reduction method,and studied the preparation technology systematically.The results indicate that the addition method,concentration,temperature and atmosphere exert critical influence on the architecture,chemical constituen,thermostability and magnetism of FeZrB particles.In contrast to Fe-based amorphous belt,FeZrB amorphous particles exhibit excellent magnetothermal stability.Interestingly,the magnetization of FeZrB particles undergo a sharp fluctuation near the crystallization peak,namely the magnetization quickly drop followed by fastly increase.We prepared MNFs with FeZrB amorphous nanoparticles and researched their magnetic heating efficiency under alternating current(AC)magnetic fields.Under 50 kHz and 250 Oe AC fields,FeZrB MNF shows higher magnetic heating efficiency,and the specific adsorption rate(SAR)of FeZrB nanoparticles is about 2.4 times that of Fe3O4 nanoparticles.In addition,by setting the intensity of AC fields,the maximum temperature of FeZrB MNF could be limited in the hyperthemia range(42?47 ?).Compared with relaxtion heating mechanism in the Fe3O4 MNF,the magnetic heating in the FeZrB MNF originate from relaxtion loss,magnetic hysteresis loss and dipolar interaction between magnetic nanoparticles.We also researched the thermal conductivity(k)enhancement of MNFs by FeZrB amorphous nanoparticles.At low concentrations,the addition of FeZrB nanoparticles reduces the k of base fluids.With increasing the concentration of nanoparticles,the k of FeZrB MNF goes down firstly and then goes up.By measuring the k of MNFs with transient plane source method and transient hot wire method,we demonstrate that the Kapitza resistance between MNFs and sensor should be responsible for the k decrease at low concentrations.The k enhancement of 2 vol.%FeZrB MNF is up to 34.0%.Under external magnetic fields,although some dipolar chains are observed in the FeZrB MNF,there is no significant k enhancement.This investigation of MNFs with amorphous nanoparticles shall shed light on the potential of utilizing amorphous nanoparticles to fabricate MNFs for biomedicine or heat management applications.