Development Of High-Performance M-type Strontium Ferrite

Permanent magnetic materials are essential for modern electronic devices, auto motor, loudspeaker, etc, among which M-type strontium ferrite is widely applied for its raw materials efficiency, low price and high stability. Considering the higher requirements towards magnetic properties of permanent strontium ferrite with the development of science and technology, such methods as the second addition or ionic replacement are tried to be adopted to improve the properties of M-type strontium ferrite the internal defects of which make it unreachable to high magnetic properties.Although China ranks first in the output of strontium ferrite materials, many companies produce only M-type strontium ferrite with low properties, and those with high properties in quite small amount which fail to meet the demand of market and the core technology of which are controlled in the hands of large Nippon or Korean companies. There are lots of studies in the high properties of M-type strontium ferrite in China, most of which remain prepared in small amount in laboratory and cannot be widely applied to manufacturing production. The M-type strontium ferrite prepared in this dissertation is researched and developed in the company with many a production experiments in small quantities which plays an important role in the development of high magnetic properties of M-type strontium ferrite in our country.In this dissertation, based on the Y30H-1 powder produced by Bengang Huanyu Magnetic Materials Co., Ltd., the powder is studied with ceramic processing by the second additives including CaCO3, SiO2, Al2CO3; La-Co substituted M-Type strontium ferrites Sr1-xLaxFe12-xCoxO19 (x=0～0.25) were prepared, dispersant calcium gluconate to enhance the overall properties of M-type strontium ferrite. In the experiment, we control the proportions of the ball, feed, and water, grinding time, and sintering temperature in ball milling, and employ wet pressing and magnetic field size to attain high magnetic properties. The basic process of the experiment is as follows:raw materials-- the second addiction-- milling-- draining-- pressing-- sintering-- magnetization test. During the test, the samples are researched by the permanent magnetic material auto-measuring instrument and the different phases when x change by X-ray diffraction. Several aspects are studied including the impacts of the second addictives and dispersants in different proportions on the performance of the samples, and of the milling time and the particle size on the samples as well. The results are as follows:(1) Impacts of the second addictives and dispersants on the properties①With the addition of CaCO3, both Br and Hcj first increases and then decreases, while the former is at the peak when reaching 0.6wt%～0.8wt% and the latter about 0.8wt%.②With the addition of SiO2 and Al2O3, Br reduces and Hcj rises while reaching their maximums at about 0.4wt% and 0.3wt% respectively.③With the addition of dispersant calcium gluconate, Br somewhat elevates and Hcj has little change.(2)Sr1-xLaxFe12-xCoxO19 (x=0～0.25), is single M-phase in 1215℃, when x=0.15 performance is the best.(3)The milling time has great influence on particle size. The particle size reaches 0.72μm when milling time is 12.5h, which means the optimum of the properties of M-type strontium ferrite.(4) After alternate tests, finally it is found that when CaCO3, SiO2, Al2O3, dispersant calcium gluconate and the Sr1-xLaxFe12-xCoxO19 reach 0.87 wt%,0.4 wt%, 0.32 wt%,0.75 wt% and x=1.5 respectively, the magnetic properties rise to the optimum values that are Br=423.1mT,Hcj=320.8 kA/m, (BH)max=32.9kJ/m3 and achieves Japanese TDK corporation the FB6B series level.