Study On Dry-press And Preparation Of High Performance Strontium Ferrites Based On Compound Additives

Ferrite is one kind of compound oxides, ususually composed by iron group elements and the other one or several of the proper metal elements. Ferrite can be devided into two categories, soft magnetic ferrite and permanent magnetic ferrite in accordance with the size of the coercive force. As a kind of functional material that produces a magnetic field, permanent magnetic ferrite plays an important role in many fields such as the electronics industry, information industry and automobile industry. Strontium ferrite and barium ferrite belong to the M-type magnetic lead stone structure are currently used largely. It is mainly attributed to hexaferrite high uniaxial magnetocrystalline anisotropy, high coercive force, good tribological properties, high Curie temperature, excellent cost performance and good chemical stability. In recent years, in pursuit of technological innovation and to expand the demand of the market, it is very necessary to improve magnetic properties, such as research on the preparation process or formula optimization (including doping modification or ion substitution).The non-rare earth and non-precious metals doping M-type high performance permanent magnetic strontium ferrite based on the combination of compound additive (CaC03、SiO2、H3BO3、C12H22CaO14·H2O, et al) were prepared by ceramic techniques. XRD, SEM and B-H analyzer were applied to investigate the structure, microstructure and magnetic properties, explores the conventional additives and process conditions on the magnetic properties. The results showed that the right amount of chromium doping and compound additive can improve the comprehensive magnetic properties of strontium ferrite. For SrFe12O19, the compound additive in the second ball mill can make its magnetic at relatively low sintering temperature basically meet the requirements of FB 5B series [Br:420±10mT,Hcb:262.6±12kA/m,Hcj:266.6±12kA/m, (BH)max:33.4±1.6kJ/m3], namely it can get high remanence of M-type strontium ferrite on the effect of composite additive. Under a certain sintering temperature, the remance Br is reduced and the coercive force Hcj is increase with the increase of Cr content for SrFe(12-x)CrxO19 on the effect of compound additive. It can reach a balance on the magnetic. At lower sintering temperature (1135～1165℃), the effects of the compound additives on SrFe11.8Cr0.2O19:with the increase of sinterig temperature, remanence Br increased from 393.5mT to 402.4mT, and intrinsic coercive force Hcj reduced from 371.0kA/m to 353.1 kA/m, which reaches TDK FB 6H series [Br:400±10mT, HCb:302.4±12kA/m, Hcj:358.1±12kA/m, (BH)max:30.3±1.6kJ/m3]. To sum up, high magnetic M-type permanent magnetic strontium ferrite can be obtained by the use of non-rare earth and non-precious metal elements doping under lower sintering temperatures (1135～1165℃).The topic also made a brief introduction for the advances in the research about the high performance dry pressing anisotropic ferrite materials at home and abroad. Comparing the wet with dry pressing process of preparation of high performance strontium ferrite, reducing adverse impact factor of dry pressing, and making full use of the technical advantage of dry pressing molding, it can be achieved to prepare high performance dry pressing anisotropic permanent magnetic strontium ferrite.