Investigation On Preparation And Performance Of Spinel Ferrites And Their Composites

Spinel ferrite is a magnetic material with high resistivity,high initial permeability,low coercive force,low eddy current loss,good impedance matching and high dielectric loss,which is widely used in a variety of modern appliances and technologies,such as transformers,sensors,stealth coatings,magnetic drug delivery,and water treatment.The properties of spinel ferrite are researched from three aspects.First,the soft magnetic properties of ferrite are improved by element substitution.Second,the microwave absorption and electromagnetic shielding properties of ferrite are studied.Third,ferrite is coated with magnesium silicate to prepare magnetic magnesium silicate composite,and the dye adsorption capacity is studied.The main research contents and results are as follows:（1）In order to improve the soft magnetic properties of Ni-Zn ferrite,the Ni ions in Ni-Zn ferrite were replaced by Mo ions and Li ions.It was found that the moderate doping of Mo ions increased the saturation magnetization and initial permeability of Ni-Zn ferrite.The Li ions replaced the Ni ions in the Ni-Zn ferrite,which increased the initial permeability and Curie temperature of Ni-Zn ferrite,suggesting that the soft magnetic properties of Li-Zn ferrite can be better than that of Ni-Zn ferrite.In order to further optimize the structure and magnetic properties of Li-Zn ferrite,Mo ions and Cu ions were doped in the Li-Zn ferrite.It was found that the Mo ion doping can increase the Curie temperature of Li-Zn ferrite.The incorporation of Cu ions reduced the sintering temperature and improved the soft magnetic properties of Li-Zn ferrite.（2）The structure,magnetic properties and microwave absorption properties have been systematically studied for the Li-Zn ferrite doped with Ti ions.The doping of Ti ions can effectively regulate the Curie temperature of Li-Zn ferrite,which can be used as temperature control materials.The Li-Zn ferrite with the thickness of 5 mm exhibited better absorption properties,and could be used as a potential microwave absorbing material.A uniform mixture of carbon nanotubes and Li_0.3Zn_0.4Fe_2.3O₄ nanoparticles was obtained by a simple mechanical mixing method.It showed high shielding effectiveness（maximum value 92 d B）,which suggested that the composite can be used as an electromagnetic shielding material.（3）The magnetic magnesium silicate（Fe₃O₄@MgSi）composite with shell-core structure was prepared,it was used for the removal of methylene blue（MB）from aqueous solution.The results exhibited that the maximum adsorption capacities was581 mg/g.The adsorption equilibriums can be reached in only 15 min.Furthermore,the removal percentages for MB with initial concentration of 300 mg/L was as high as 97%by six consecutive adsorption-desorption cycles.Compared with most the known adsorbents,the Fe₃O₄@MgSi composite had higher adsorption capacity,adsorption rate and reusability,indicating that it can be used as a cost-effective adsorbent for MB removal from aqueous medium.In order to improve the specific surface area of magnesium silicate,the Ni_0.5Zn_0.5Fe₂O₄ hollow spheres were coated with magnesium silicate to prepare the hollow structural Ni_0.5Zn_0.5Fe₂O₄@magnesium silicate composite.It showed larger BET specific surface area with 437 m²/g,which provided a new idea for the development of adsorbent.