Basic Study On Applications Of M Type Barium Ferrites And Related Composites

Due to the stronge uniaxial anisotropy, high coericitivity, (BH)_max value andexcellent gyromagnetic performances, M-type barium ferrite (BaFe₁₂O₁₉) has beenfound extensive applications in the fields of permanent magnets, wave-adsorbing,high-density magnetic recording and microwave devices. As the sintering temperaturefor the material is always higher than 1000℃and could not be satisfied with chipcomponents manufacturing technology, low-temperature co-fired ceramics and ferrites(LTCC) process, the problems of how to realize the low-temperature firing andmultifunctions of barium ferrite are becoming the key technologies for the adaption tothe developments of electronic components to the directions of sub-miniaturization,greater multifunctionality and excellent reliability. In this dissertation, the investigationswere focus on the theories, composition technics, processes and applications of theabove mentioned subjects. The research mode that combined theoretical analysis,materials preparation and components application was adopted to develop highperformance low-fired barium ferrite and multilayer chip components.In the part of theoretical analysis, the key factors to determine the formation of thelow-fired barium ferrite were investigated firstly from the point of view of the kineticsand thermodynamics for the sol-gel method, which were very helpful to optimize theparameters of preparation process during experiments. Then the sintering kinetics of theferrite was analyzed to give directions to densify the ferrite under low sinteringtemperature. And in order to realize the multifuctions of the ferrite, after moleculardesign, the ferrte was endowed with conductivity and photosensitivity. Combined withthe deduce and data fitness means, the thermal kinetics equations for the compositeswere successfully got, which could direct the thermal stability of high temperatureperformances and the processing routes available for consolidating the composites.In the part of experiments investigations, the sol-gel method was adopted toproduce the barium ferrite. After adding anionic surface active agent and by the meansof ultrasonic dispersing, the ultra-fine ferrites powders could be obtained with diametersof 60～80nm. On the basis of the results for the M-type barium ferrite, the rod-shaped polyaniline (PANI)-barium ferrite nanocomposites possessing the conductive andmagnetic performances were obtained by in situ polymerization method for the firsttime. The structure, morphology and properties of the composite were measured by allkinds of testing techniques, which indicated that it is a new and easy way to involve themultifuctions of ferrites. It is also found that the NSA plays a very important role as thereaction controlling agent and the template, which will guarantee the directional growthof micelle, the encapsulation of ferrite particles in the polymer chains and formation ofa "core-shell" structural mixture. The conductivity of the composites varied withdifferent BaFe₁₂O₁₉ content with the trend of earlier increasement and later decrease. Itis believed that this is caused by the insulting behavior of the ferrite and partialblockage of conductive path by BaFe₁₂O₁₉ in the core of the nanoparticles. The Ms andHc values were both obviously decreased with the increasement of the content ofBaFe₁₂O₁₉. TG-DTG testing results showed that the apparent activation energies of thecomposites were higher than that of the pure PANI in a great degree with high thermalstability and the degradation mechanism is three-dimensional diffusion. According tothe principles of photochemistry and through the molecular design for organicfunctional materials, novel photosensitive diamines with the structure of cinnamoylgroup were designed and synthesized by the technology of the Aldol Condensation andprotection for amino group. And corresponding photosensitive PAA were prepared bythe means of solution polymerization with maximal absorption wavelength of UVspectrum at 365nm and weight-average molar mass of 3319. The heat-resistanttemperature of PI is over 400℃and the resolution can reach 4um. The magnetic arrayswere fabricated by the nano ferrites and the above photosensitive polyimide, whichsupply another method to involve the barium ferrites new multifuntions.In order to realize the low-temperature sintered ferrites, by the references offomula of the materials designing, the BBSZ was adopted to the system. And theinfluences of compositions on the sintering behaviors, microstructures and magneticproperties of the ferrite were investigated. It was confirmed that 2wt% BBSZ contentwas appropriate to give attention to both low-fired characteristic and good magneticproperties. Then the low temperature sintered Co/Ti doped barium ferrite Ba(CoTi)_xFe_12-2xO₁₉ were carefully researched after the comparing experiments and theoptimal doping mode was x=1+3wt% BBSZ. The permeability of the materials was 13.5 and the cut-off frequency could reach 800MHz.In the part of LTCC application research, a research of the additives influences onthe slurry performances was carried out and the dispersant, binder, plasticizer andorganic solvent were added to adjust the slurry formula. The formula is as following.The amount of toluene is 30.0g, the alcohol is 20.0g, the dispersant is 5.5g, theplasticizer is 0.7g and the binder is 33.0g for 100.0g ferrites. The slurry viscosity is2000cPs. The co-firing behavior of different multilayer ceramic and ferrite sampleprepared by tape casting method was carried out and an improvement on the co-firingmatch between barium ferrite and the ceramic was established through the method ofadjusting the composition of the slurry for the first time. The HFSS software was usedto design, stimulate and optimize the multilayer chip components. It was confirmed thatfor the 0805-type multilayer chip inductor with the cut-off frequency at 560MHz andinductance of 2.52uH, the width of the silver was 200um, the radius of via holes was100um and the thickness of ferrite layer and protective layer was 27um, 130um withtwenty three figure layers. For the low-pass filter with the cut-off frequency at 120MHz,the inductor was constructed by eleven figure layer under the conditions of 200umsilver width, 100um via hole radius and 20um protective layer thickness and thecapacitor was constructed by seven figure layer under the conditions of 200um silverwidth, 20um layer thickness and 200um protective layer thickness. Then the preparedbarium ferfite was chosen to produce the multilayer chip inductors and low-pass filtersby LTCC technical line. The cut-off frequency and the inductance of the as-preparedinductors were 548.3 MHz and 5.45 uH respectively. And the cut-off frequency of thelow-pass filters and the attenuation were 130MHz and beyond 20dB. The performancesof the inductors and the low pass filter were in good agreements with that of the forecast,which benefits for the high-frequency, miniaturization of electronic components and theaccuate stimulation.