Synthesis And Characterization OfSrFe₁₂O₁₉/AFe₂O₄ Nano With Core-shell Structure

In recent years, It has become the electromagnetic wave absorption material study and application of hot spots. On the material property requirements is a strong absorption, absorption spectrum width, material thickness thin, light weight characteristics etc. But so far, has not found any kind of material can meet these requirements. So to existing materials appropriate modification and design became the focus of research. Hexagonal crystal M type strontium ferrite because of its natural resonant frequency in high frequencies higher, not easy to generate hasten skin current, dielectric constant is lesser, can be mixed with other absorbing materials for absorbing coatings used to adjust the electromagnetic parameters etc and become a kind of very important electromagnetic wave absorbing agent. Its defect is absorbing properties on the preparation process is very sensitive. To further improve the single ferrite materials magnetic conductivity is difficult. But spinel ferrite absorbing material has good stability, the highest temperature of saturation magnetization intensity, the microwave magnetic conductance larger, the advantage very obvious. But spinel ferrite absorbing material in microwave frequency is restricted by "because skin effect" and granularity cannot too big, and distribution uniformity, volume fraction can not be too big. Thus, magnetic lead stone type ferrite absorbing material and spinel ferrite absorbing material electromagnetic characteristics have strong complementary, effectively combines the two may create efficient absorbing agent. In this paper a new dedicated to design and preparation spinel ferrite magnetic hard magnetic strontium coated the "nuclear shell mould manganese-zinc electromagnetic wave absorbing materials". Design and preparation such "core-shell type" composite particle starting point is to use both electromagnetic properties of complementary, and still hope to be able to play compound form also is "core-shell type" structure and "nuclear" and the "shell" of various special interface effect effect, make they can also contribute to the electromagnetic wave absorption.This paper first through the contrast between the different processing methods, it is concluded that the superiority of sol-gel method. Then in traditional preparation process methods improved, based on prepared the spinel ferrite and magnetic lead stone type ferrite nano powder; Later in two different materials respectively, nuclear power as in a different material as the shell, using modified sol-gel process, prepared the coated nanostructured composite particles. Samples by XRD, SEM of VSM, TEM and network analyzer and vector analysis method and means, of particle morphology and absorbing properties are tested and analyzed.Test and analysis results show:1. The total precipitation and traditional by sol-gel method of the two different methods of preparation out, its size will nanoparticle since the temperature increases and increase, however, sol-gel process) out of the samples of particle size is small, and distributes uniformly; In the process of sol-gel process), contrast nitrate as raw materials and acetic acid salt as raw material with a sample preparation, the latter size smaller.2. In sol-gel process) process, join acrylamide and glucose and preparing a magnetic lead stone type SrFe₁₂O₁₉ nanometer powder, although nanoparticles size will also increases with temperature rise, however, and improved compared samples before the grain size, particle size uniform, small, dispersion also get improved considerably.3. Using the improved polymer network sol-gel method, SrFe₁₂O₁₉ by magnetic lead stone type for nuclear, preparation of a series of SrFe₁₂O₁₉ / AFe₂O₄ core/shell structure nanoparticles, in experiments found in core/shell mass ratio of 1:2, annealing temperature of 1050℃conditions heat treatment 10 hours, heating rate remained in 10℃/ min, get a spherical shape, the granules dispersion of good size in 30 - about 45nm, distribution and evenly. With nuclear materials in composite materials SrFe₁₂O₁₉quality and decreasing quality of magnetic intensity (Ms) SrFe₁₂O₁₉ value from the core material emu/g per increased to SrFe₁₂O₁₉/NiFe₂O₄ nanocomposites emu/g am. And SrFe₁₂O₁₉/NiFe₂O₄ nanocomposites intrinsic coercive force (Hc) is SrFe₁₂O₁₉ (5395Oe 336Oe, in NiFe₂O₄ (160Oe) and in between. When SrFe₁₂O₁₉/NiFe₂O₄nano powder quality than for 1:2, 9dB maximum absorbing properties, is a fine performance absorbing agent.4. The AFe₂O₄/SrFe₁₂O₁₉ (A is Ni, Co, Zn) core/shell structure powders, which were prepared use spinel AFe₂O₄ as nuclear materials, have high purity, uniformity of particle size, small size, and good dispersion. The results show that particle high purity, spheroidization small, even, good dispersion particle degree. When the nuclear material change, quality magnetized intensity (Ms) and intrinsic coercive force (Hc) will also happen different trends and different degree of change, analysis found that, as the cause of the changes with core-shell attaches to replace the atoms concerned.