Microwave Absorption Property Of PANI And SiC Coatings

The study of microwave absorbing materials applied to military, stealth information and environment protection is an important item. Polymers and ceramic materials are becoming more and more important in microwave absorbing materials. Conductive polyaniline (PANI) has lots of advantages such as excellent conductive properties, environmental stability, cheap raw materials, easy processing, etc.,which makes it become a hot research field. SiC can be used as "light, thin, wide, strong" microwave absorbing material, because SiC is a sort of mature preparation process, high temperature performance, low density and can be effectively coupled with electromagnetic waves at room temperature.In this thesis, HCl-PANI and CA-PANI were synthesized by chemical oxidation method. We discussed the dosage of oxidant and reaction time on the conductivity of PANI. Samples were then studied by SEM, FT-IR and XRD. HCl-PANI and CA-PANI coatings were prepared to research their microwave absorption property. SiC absorbing coatings were prepared to study the volume fraction of SiC and thickness on the microwave absorption property. Then we studied the high temperature property of SiC coatings. Finally, we discussed the microwave absorbing ability of SiC/PANI bilayer structure coating. The main results are as follows:1. The optimum synthesis conditions of HCl-PANI are shown as follows:When n(An)/n(HCl)=1:1, n(An)/n(APS)=1:1, reaction time is18h, we got the highest conductivity of HCl-PANI is2.20S/cm. And when n(An)/n(CA)=1:1, n(An)/n(APS)=l:1.25, reaction time is6h, the highest conductivity of CA-PANI is0.13S/cm. The productions have good doping and crystalline degree. And HCl-PANI have better doping raito and crystalline degree than CA-PANI, also a higher conductivity. Microwave absorption property becomes stronger gradually with increasing thickness of PANI coatings. At the same time, the peak position moves to a lower frequency. And HCl-PANI coating have a better absorbing performance at low frequency, while CA-PANI coating’s absorbing performance is better at higher frequency.2. Absorption peak position of SiC coating moves to a lower frequency with increasing coating’s thickness. Absorption peak position was moved to higher frequency by reducing volume content of binder.1mm-thickness-coating have better absorbing property. The coating which thickness is3mm have good wave absorbing property in two wave bands of4～6GHz and13～17GHz, shows the property with multi-band absorption.3. SiC coating can work for a long time at150℃. After be heat treatment at250℃for10h, the absorption property of a thin coating which volume fraction of SiC is low becomes weak. For example, the lmm-thickness-coating, which volume fraction of SiC is20%, absorption intensity reduced to-11.7dB from-20.5dB after heat treatment at250℃. The SiC coating can withstand250℃work environment if increasing volume fraction of SiC and coating’s thickness.4. The reflectance testing for SiC-PANI layer structure coatings showed that the absorbing property of composite coating is poorer than single SiC coating at low frequency, but has better performance at high frequency. Composite coating has stable absorption property in each band, this establish the foundation for preparation of wide absorption frequency coating.