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Preparation and Microwave Absorbing Properties of Modified Carbonyl Iron Powder Composite Materials

Author: WangChao
Tutor: HanXiJiang
School: Harbin Institute of Technology
Course: Chemical Engineering and Technology
Keywords: Carbonyl iron powder Polyaniline Barium titanate Composite material Microwave absorbing properties
CLC: TB33
Type: Master's thesis
Year: 2008
Downloads: 150
Quote: 1
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Abstract


Three microwave absorb materials were chosen based on different loss mechanism. Carbonyl iron powder(CIP) is a kind of magnetic loss absorber with large imaginary part of permeability which shows excelent impedence matched property and intense absorption. Another kind of aborber is light polyaniline(PANI) for electric loss with wide-band absorption and easily controlled permittivity. BaTiO3 can be simply and cheaply prepared while with dielectric loss.CIP was surface modified by polystyrene(PS) and silane coupling agent(1202). PS couldn’t cover inorganic CIP completely during the preparation, however, CIP was oxidized and corroded in the process of coating PS/CIP with PANI, resulting in bad impedence matching and microwave absorbing ability. In contrast, CIP might be covered absolutely with 1202 which was beneficial to the connection between PANI and 1202/CIP and avoiding the agglomeration of CIP. PANI prepared by chemical oxidation method had high electric loss tangent, with largest loss of -13.3dB at 8.7GHz and the absorbing intensity between 7~12GHz was larger than -5dB. When An:1202/CIP=1:1 the absorbing peak value of PANI/1202/CIP was a little greater than PANI, displaying obviously wider frequency band than CIP and PANI with loss stronger than -5dB. The improved absorbing property of the composite was mainly attributed to the cooperation of magnetic and electric loss while the most evident improvement is the enlargement of frequency band.Spherical BaTiO3 with an average diameter of 43.37nm was synthesized by chemical cooperation method and the crystal phase was indentified as cubic by XRD. Magnetic loss and dielectric loss contributed equally to the absorbing peak of BaTiO3. CIP and BaTiO3 were used as microwave absorbing materials while polyurethane was used as matrix, and two-layer films I(10%), II(20%), III(30%) were scraped based on the mass content of BaTiO3. BaTiO3 modified by 1202 showed no agglomeration and the homogeneity of the composite film was improved. The layer of magnetic CIP placed toward the air was propitious to the impedence matching. A strong absorbing peak at 14GHz and a relative negative peak at 17GHz appeared both in obverse and inverse faces, and the two absorbing peaks were due to BaTiO3. The microwave absorbing intensity was enhanced as the mass content of BaTiO3 increased. The CIP’s magnetic loss and BaTiO3’s dielectric loss and film’s electric loss contributed to the loss mechanisms of films. The absorbing effect enhanced as the content of BaTiO3 increased from 10% to 30%, not only arising from improving impedence matching, but also repeated absorption for scattering and dielectric loss came from BaTiO3’s surface polarization induced by surface electric field of CIP.

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