Dissertation > Excellent graduate degree dissertation topics show

Study on Lithium Zinc Ferrite Low-Frequency Microwave Absorbers and Its Dispersing Technology in Polymer

Author: CaoXiaoFei
Tutor: SunKangNing
School: Shandong University
Course: Materials Science
Keywords: Lithium - zinc ferrite Low-frequency microwave absorbing properties Cerium doped ferrite The whole picture analysis Reciprocating jet dispersion
CLC: TM277
Type: PhD thesis
Year: 2009
Downloads: 433
Quote: 3
Read: Download Dissertation

Abstract

In recent years, due to the rapid growth of electrical and electronic equipment in industrial, civil and military fields, making the resulting electromagnetic radiation become a kind of environmental pollution, electromagnetic radiation within the low frequency band of 0.5-3 GHz has been proven harmful to human tissues and organs to produce more serious harm. , Radiation absorption is a practical and effective way in existing electromagnetic radiation protection measures. Accordingly, the study and preparation for civil frequency absorbing material has a very important significance. Spinel ferrite and hexagonal ferrite radar absorbing layer thickness, effective absorption bandwidth advantages compared with other materials. However, the the microwave absorptive capacity of the high-quality nano ferrite by the sol - gel prepared mostly concentrated in the high frequency region. Studies have shown that lithium zinc ferrite prepared by solid state reaction in the low frequency region has good microwave absorbing properties, but solid state reaction method itself shortcomings limit the further application of this material. Therefore, the use of the sol-gel method combined with the late calcined lithium zinc ferrite prepared with good microwave absorbing properties in the low frequency region micron level. Firstly, by the sol - gel method combined with the late calcined successfully prepared micron pure lithium zinc ferrite, and the use of X-ray diffraction, scanning electron microscopy and vector network analyzer and other means to study their microstructure and microwave absorbing properties. With the reaction kinetics and the theory of ferromagnetic resonance, its low-frequency microwave absorbing properties of the heat treatment process parameters, found eventually calcination temperature to determine the particle size, the different heating rates the actual impact of the post-calcination process lithium and zinc vaporization loss impact, while pure lithium zinc ferrite grain size and phase composition of the low-frequency microwave it caused by ferromagnetic resonance absorption. Rose to 500 ° C calcined at 200 ° C / h and rose to 240 ℃ / h to 1200 ° C calcined obtained pure lithium zinc ferrite absorbing properties are in the 0.5-3 GHz band, while the latter absorbing better in the 2.8 GHz and 10 mm thickness of the absorbing layer has the highest reflection attenuation of up to -25.89 dB. The preparation process has not been reported. But pure lithium zinc ferrite mainly in the 2.5-3 GHz microwave absorption capacity, the effective microwave absorbing band still need to move to the low frequency region. This article using the same process parameters is enhanced the 0.5-3 GHz microwave absorbing ability as well as broaden its radar absorbing bandwidth, sol-gel method combined with the late calcined, magnesium, copper, lanthanum, lithium zinc ferrite and different amount of cerium doped. The detection of doping from lithium zinc ferrite microstructure and microwave absorbing properties compared with pure lithium zinc ferrite. The results showed that the doped with magnesium, copper, lanthanum and cerium, may change the distribution state of the metal ions in the lithium-zinc ferrite lattice doped lanthanum and cerium also cause lithium zinc ferrite magnetic anisotropy changes. These changes have led to corresponding equivalent magnetic field changes, and thus the impact on the ferromagnetic resonance caused by low-frequency microwave absorbing properties. In addition, magnesium, copper, lanthanum, cerium, lithium-zinc ferrite having a maximum doping amount. If the actual doping amount exceeding this limit value, resulting ferrite materials formed respectively of MgFe ₂ O ₄ the CuFe ₂ O < sub> 4 , LaFeO ₃ of CeO ₂. On the one hand, the MgFe ₂ O ₄, The CuFe ₂ O ₄ and the LaFeO ₃ the generator will cause the generator to reduce the amount of doped lithium-zinc ferrite. On the other hand, MgFe ₂ O ₄ CuFe ₂ O ₄ the LaFeO _{3 low-frequency microwave absorbing ability is relatively weak. Will make the actual ability of the low-frequency microwave absorbing ferrite materials weakened further. However, when the cerium doping amount exceeds the limit value of CeO ₂ formation does not affect the number of the actual proceeds ferrite lithium zinc ferrite. It is noteworthy that, when the cerium doped to a certain amount, the actual ferrite in CeO ₂ for enrichment and a dielectric loss of the material will obtain the composite ratio of the lithium-zinc ferrite enhanced, which greatly increases the low-frequency microwave absorbing ability. The obtained ferrite materials at 1.68 GHz and 10 mm thickness of the absorbing layer reflection blockade the the attenuation maximum value of up to -28.06 dB, and the effective microwave absorbing band distribution in the 1.25-2.25 band bandwidth of up to 1 GHz. Therefore, this actually prepared ferrite composite absorbing materials in the 0.5-3 GHz band is a very practical outlook. Calculated according to the effective electromagnetic parameters of the whole picture analysis and composite paper using MATLAB prepared composite absorber at different frequencies reflection attenuation, the relationship between the distribution ratio of microwave absorbing layer thickness and group characterization computational model. Applying this model lithium zinc ferrite / acetylene black composite absorbents data. Reap three component milling prepared lithium zinc ferrite / acetylene black composites, detection and absorbing properties. The results show that, according to the pre-analytical model design and the actual preparation of the composite material, the low-frequency microwave absorbing properties do better than pure lithium zinc ferrite. This suggests that the pre-analytical model and the pre-design method for the preparation of low-frequency absorbing materials helpful. Rapid and uniform dispersion of fine particles absorbing agent in the polymer for of coated absorbing material absorbing properties, mechanical properties and practical use, has a very important impact. For promoting the practical application of the absorbing coating is developed reciprocating jet dispersion method and corresponding apparatus, and an unsaturated polyester resin in the micron-level lithium zinc ferrite and carbon nanotube dispersed experiment. Detected scattered viscosity of the mixture of the precursor and its fracture surface of the composite material obtained by curing, with respect to the result of the processing of the ultrasonic dispersion, the reciprocating jet dispersion treatment after the lithium-zinc ferrite and carbon nanotube in the polymerization The property matrix showed a more uniform distribution of state, and the dispersion treatment time is shorter. The technology is not only the implementation of fast of micron-absorbing agent uniformly dispersed, and good dispersion of the nano-absorbing agent particles. Therefore, reciprocating jet dispersed absorbents for the fine particles of the polymer will be an effective dispersion techniques.}

Related Dissertations

CLC: > Industrial Technology > Electrotechnical > Electrical materials > Magnetic materials,ferrite > Ferrite,oxide magnetic materials
© 2012 www.DissertationTopic.Net Mobile