Research On Key Preparation Technologies Of W-type Barium Ferrite Materials

Due to the limitation of material properties,the existing X-band circulators need to add permanent magnets to provide indispensable bias magnetic field when working,which is contrary to the development requirements of small lightweight,integration and planarization for microwave devices.Therefore,the study and preparation of hexagonal ferrite materials for X-band self-biased circulators is of great significance.The work in this thesis is driven by the requirements of the practical application for X-band self-biased circulators.W-type barium ferrite was prepared by ceramic method.The relationship between the main formula system of W-type barium ferrite,composite additives and key preparation techniques and properties was analyzed.On this basis,BaW/BaM hexagonal ferrite composite technology was explored.Firstly,the microwave and magnetic properties of W-type barium ferrite were optimized by using different main formula.The results of study show that with the increase of Co²⁺ion substitution,the anisotropic field and coercivity decrease gradually,and the remanence and saturation magnetization are hardly affected.A moderate amount of iron deficiency can enhance the superexchange between ions,increasing the remanence and saturation magnetization.Iron deficiency has little effect on the average grain size,the remanence ratio and the coercivity.Finally,excellent comprehensive properties were achieved when iron deficiency was 0.4.Secondly,the grain growth of W-type barium ferrite was controlled by using a compound additive.The results of study show that the doping of low concentration of Ca CO₃ additive can inhibit the grain growth,while the excessive doping leads to promote the grain growth.The critical doping amount is 0.2 wt.%.With the increase of Si O₂additive doping,the remanence,saturation magnetization and coercivity all increase first and then decrease.Finally,when the doping content is 0.2 wt.%,excellent comprehensive properties are obtained.The average grain size,density,remanence,and saturation magnetization of the samples show an increasing trend with the increase of BaTi O₃additive doping.The dielectric constant,dielectric loss and dielectric loss tangent all show a trend of first decreasing and then increasing.Subsequently,the key preparation techniques of W-type barium ferrite were optimized.The results of study show that the coercivity of the sintered sample is the largest when the pre-sintering temperature is 1260?.When the time of secondary ball milling was 21 h,the particle size of the powder was mostly in a single domain with a narrow distribution range and the density,coercivity,remanence and saturation magnetization of the samples were the largest.As the sintering temperature increased from 1020?to 1120?,the average grain size,density,remanence and saturation magnetization increased.The porosity and coercivity decreased.Finally,the composite technologies of BaW/BaM type ferrites were explored.For the method of pre-sintering reaction,the phase is dominated by W-type ferrite.With the increase of pre-sintering temperature,both SEM and FORC show that the sample transforms from single-domain state to multi-domain state,and the porosity,average grain size,remanence,saturation magnetization and ferromagnetic resonance linewidth of the samples gradually increase,while the coercivity sharply decreases.For the physical mixing method of secondary ball milling,the addition of M phase improves the coercivity and remanence ratio of samples,and significantly reduces the ferromagnetic resonance linewidth of samples.