The Synthesis And Properties Of Ferrite Composites

Magnetic materials as absorbing material are currently widely used,chiefly characterized by its high microwave absorption efficiency, andthin absorbing layer. In magnetic materials, ferrites occupy animportant position in the field of microwave absorption, because of itsadvantages of low cost and high absorption efficiency, ferrite as highresistivity can avoid skin effect of metal conductors under highfrequency, and can be composited with other absorbent to adjustelectromagnetic parameters of the coating. But at the same time, ferriteshave disadvantages of narrow strong absorption band and high density,which limit its wider use in the field of absorbing materials. At present,Mn-Zn and Ni-Zn ferrite have extensive research, However, study onNi-Mn-Zn ferrite by very few. The application range of both the ferrites,however, differs on account of the differences in their electrical andmagnetic characteristics. Ni-Zn ferrites are usually employed for highfrequency applications on account of their high resistivit y to countereddy current losses, while Mn-Zn ferrites are more suitable at lowfrequencies in keeping with their low resistivity and high permeability.Low-temperature combustion reaction route, microwavehydrothermal and sol-gel self-propagating combustion were used toprepare a nominal composition of Ni0.25Mn0.25Zn0.50Fe2O4ferriterespectively. At the same time, Ni0.25Mn0.25Zn0.50Fe2O4ferrite and flyash were recombined, and prepared fly ash/ferrite core-shell compositematerials. Differential scanning calorimetry-thermogravimetry analysis(DSC-TG), X-ray diffraction analysis(XRD), transmission electronmicroscope(TEM), energy dispersive spectrometer(EDS), scanningelectron microscope(SEM), and vector network analyzer(VNA) were used to systematically study reaction process, phase composition,microstructure and microwave absorbing property, and analyze thedifferent reaction condition on the preparation ofNi0.25Mn0.25Zn0.50Fe2O4ferrite and its composite material.Preparation Ni0.25Mn0.25Zn0.50Fe2O4ferrite via Low temperaturecombustion reaction, the results indicate that under the condition ofurea and metal nitrates mass ratio of1:1, and heated to400℃for6hours, obtained pure phase Ni0.25Mn0.25Zn0.50Fe2O4ferrite. The asfabricated particles are irregular flake with a crystallite size of~20nm.At a thickness of4mm, the reflection rate of less than-10dB was from5GHz to8GHz. In the frequency of7.96GHz, the minimum reflectionrate was-30.75dB.Synthesis of Ni0.25Mn0.25Zn0.50Fe2O4ferrite via microwavehydrothermal, When EDTA addition amount of45%, the reactiontemperatures below160℃for2hours, obtained ferrite phase. When themass fraction of EDTA reduced to15%, synthesized high content ofNi0.25Mn0.25Zn0.50Fe2O4ferrite at200℃for2hours. Additive of urea andhexamethylenetetramine respectively, synthesized pure ferrite phase at200℃for30mins, and adding hexamethylenetetramine was expectedto prepared ferrite hollow spheres.Synthesis of Ni0.25Mn0.25Zn0.50Fe2O4ferrite via sol-gelself-propagating combustion, when the pH value of1.0, after at600℃for1hour, synthesize pure Ni0.25Mn0.25Zn0.50Fe2O4ferrite. Processed flyash microspheres, namely after by ultrasonic cleaning with hydroxide,and surface modification with ethylene glycol, when the mass ratios ofthe fly ash and ferrite were1/99and0.5/99.5, prepared fly ash/ferritecore-shell structure composite materials with uniform coating.