Strontium Ferrite and rare-earth alternative to composites

Title: Strontium Ferrite and rare-earth alternative to composites and absorbing properties ofAuthor: Chen NaDegree-granting units: Shanghai Jiaotong UniversityKeywords: strontium ferrite;; rare earth ion substitution;; zinc ferrite;; composite ferrite;; microwave absorptionSummary:


 The rapid development of modern microelectronic technology to bring convenience to people's lives, but the impact of electromagnetic radiation on the environment increasing, therefore, absorb electromagnetic functional materials become a hot research Neodymium Magnets and application. Ideal absorbing coating material should have a strong absorption wideband, thin, light weight characteristics. But so far, have not found any kind of material can fully meet these requirements. Therefore, an appropriate modification of existing materials and design have become the focus of the study. Hexagonal strontium ferrite due to its high anisotropy field, high saturation magnetization, high magnetic loss, strong acid and alkali resistance and stable performance, etc., are widely used in microwave absorbing materials, but a single strontium ferrite still has a strong enough absorption, relatively narrow absorption band of shortcomings. This paper aims to develop a simple preparation process, the absorption band wider and more capable of absorbing new strontium ferrite matrix composites, and to study the scientific issues related to preparation and absorbing mechanism for absorbing materials, production and application provide technical and theoretical support.


 Paper first alternative method using rare earth ions, significantly improved the absorbing properties of strontium ferrite, in particular, to improve the absorption intensity. In this paper, the sol - gel technology and the Combination of self-combustion method of preparation of lanthanum, cerium, neodymium three kinds of ion substitution of strontium ferrite. The results show that rare earth ions in strontium ferrite in the alternative depends on its ionic valence and ionic radius. Is tetravalent cerium ions hardly enter the strontium ferrite lattice, and the light rare earth elements lanthanum and neodymium (III) ions are replaced, respectively, 0.15 and 0.1. The difference with a smaller radius of oxygen ion lanthanum ion substitution is higher. Ions substitute the strontium ferrite grain size becomes smaller, less granular level of reunion; decrease in saturation magnetization is not the case, the coercivity increased; absorbing properties greatly improved, especially for lanthanum ions, when the alternative volume of 0.15, the matching thickness decreases from 2.6mm to 2.3mm,-24dB return loss from the reduced to-37.7dB, 10dB bandwidth from 2.7GHz (6.4-9.1GHz) extended to 4GHz (6-10GHz). Mossbauer results show that: Although the substitution of rare earth ions in strontium is strontium ferrite bit, but the iron http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets hyperfine field, the electron density around, and the electron orbits are affected, when the trivalent lanthanide ion substitution of divalent strontium ferrite strontium ions after valence balance for the 4 f 1 and 2a-bit, a small part of the iron ions from the trivalent into divalent. Absorbing performance Sr ferrite alternative reasons: to increase the grain size decreases the interfacial loss; coercivity increases to increase the hysteresis loss; ion substitution caused by changes in iron valence increase the dielectric loss.


 In order to further expand the bandwidth of the absorption of strontium ferrite, coated with a two-step method and the step compound and strontium ferrite prepared zinc ferrite composite powder. The results show that the step composite method can effectively expand its bandwidth, two-step composite powder prepared by a small amount of α? Fe2 O 3 generation. When the quality of zinc ferrite content of 15%, the two composite methods can improve the absorbing properties, but when the mass ratio increased to 30%, absorbing performance degradation, because the study of zinc ferrite in the frequency within itself does not have absorbing properties, too much zinc ferrite to decrease the overall performance of composite materials. One-step preparation of composite materials more superior performance, the matching thickness in 2.3mm, the minimum reflection loss reach-35dB, 10dB bandwidth in excess of 4GHz, which is due to the composite materials prepared by this method particles smaller, more uniform composition, interaction interface more, and no α? Fe2 O 3 exists. And pure strontium ferrite and strontium ferrite different alternative is in addition to the existence of a composite powder with the thickness of the reflection loss peak; In addition, around 16GHz, there is a position does not change with sample thickness of the reflection loss peak, which interaction is due to two kinds of ferrite caused.


 Finally, in order to develop a kind of absorbing superior performance and can be applied in practice the absorbing material in front of study, based on the performance of the best alternative choice and better composite ferrite way to prepare lanthanum strontium iron replacement zinc ferrite and ferrite composite powder. And preparation of composite powders with more absorbing agent to select the more practical application of the epoxy resin as a matrix, prepared by absorbing agent and the base body, respectively 1,1.25,1.5 than composite materials. The results showed that when the absorbing medium and the base body ratio of 1.25, the absorbing properties of composite materials from the best, relatively pure strontium ferrite has greatly improved, reducing the matching thickness from 2.6mm to 2.2mm, the minimum reflection frequency is reduced from-24dB to-41dB, down 70%, 10dB bandwidth from 2.7GHz to broaden to 5.7GHz, widened more than doubled, demonstrating the material's application. Especially when the sample thickness is 1.5mm, they get a relatively good absorbing properties, which in practice are very important, absorbing coating materials to meet the requirements of strong absorption, frequency bandwidth, thin, light weight characteristics.


 Replaced by lanthanum strontium ferrite and zinc ferrite composite powder crystal structure, magnetic properties and Mössbauer spectroscopy study showed that substitution of lanthanum strontium ferrite and zinc ferrite composite materials, both the alternative and composite two advantages. Because the two ferrite composite, so is zinc ferrite spinel type of change to the spinel compound, and zinc ions in the case of lanthanum, strontium ferrite into the lattice, replacing the 4 f 1 position of iron ions, so that the lanthanum strontium ferrite lattice constant alternative larger, smaller lattice constant of zinc ferrite. This interaction makes two kinds of ferrite saturation magnetization increase, thereby increasing the magnetic loss. These theories conclude on the future of new composite ferrite absorbing material absorbing mechanism of development and has a certain reference value.Degree Year: 2009