Preparation And Properties Of Co-doped SiC Microwave Absorbers

As the key component in stealthy techniques, the properties of microwave absorbing materials depend on the ability of absorbers to dissipate the electromagnetic wave. The absorbers that can be employed at higher temperature are required for the stealthy weapon equipments and electromagnetic wave shielding under higher temperature. SiC is one of the materials with good properties at higher temperature,and has a wide application prospect in stealthy materials using at higher temperature.The B/Al, B/N and Al/N co-doped SiC powder aborbers were prepared by combustion synthesis(CS). The relationship between the preparation, structure and property of co-doped SiC powder absorbers were investigated in detail by X-ray diffraction(XRD), X-ray photoelectron spetroscopy(XPS), scanning electron microscope(SEM) and dielectric property measurement, and the effect and mechanism of co-doping on the microwave dielectric properties of SiC absorbers were discussed.The B doped SiC absorbers were synthesized using Si powder and carbon black as raw materials, B powder as the dopant, and PTFE as chemical activator. The effect of B doping content on SiC properties was studied. Results showed that all the values of real part ?? and imaginary part ??of permittivity and di electric loss tan? of the prepared powders decreased with the increasing B contents. Meanwhile, Al doped SiC powder with nano size were synthesized using Al powder as dopant. It was founded that when the content of Al increased to 10% and 15%, Al2O3 impurity phase appeared in the synthetic products.The powder doped with 10% Al had the greatest values of real part ?? and imaginary part ?? of permittivity and dielectric loss tan?, which were 5.2~5.5, 1.5~1.7 and 0.29~0.31, respectively.The B and Al co-doped SiC absorbers were synthesized using B powder and Al powder as the dopants. Results showed that all the ??, ?? and tan? of samples doped with 5% B and 5%, 10% and 15% Al were less than the undoped SiC. When the Al content was 10%, the prepared sample revealed the greatest values of ??, ?? and tan?, which were ??=3.5~3.6,??=0.375~0.4 and tan?=0.09~0.1. In the case of 5% Al and 5%, 10% and 15% B co-doping, all the values of ??, ?? and tan? decreased as the B content increased.The B and N co-doped SiC powders were sythesized by CS using NH4 Cl and B powders as solid nitridizing agent and dopant, respectively. The pure ?-SiC powders with nano size were prepared under all the different N doping contents. Results of microwave dielectric properties showed the ??, ?? and tan? decreased as the N content increased. The effect of different B doping content was also studied. The ??, ?? and tan? of the prepare d samples decreased with increasing B content. The B and N co-doped SiC powders were sythesized by CS using Si3N4 and B powders as solid nitridizing agent and dopant, respectively. XPS analysis demonstrated that B and N atoms successfully incorporated into SiC lattice. Results of dielectric properties showed that the ??, ?? and tan? of the prepared samples decreased first, and then increased with increasing N content under different N doping content. When B content was 5% and N content was 15%, the values of ??, ?? and tan? of doped sample were greater than the undoped SiC. But all the ??, ?? and tan? of co-doped samples were less than the undoped SiC powders with the different B doping content, which decreased first, and then increased as the B content increased.The Al and N co-doped SiC absorbers were sythesized by CS, using Si3N4 and Al powders as solid nitridizing agent and Al dopant, respectively. Results showed that all the values of ??, ?? and tan? of the samples doped with different content of N were less than the undoped SiC, when Al doping content was 5%, which decreased with the increasing N content. The effect of different doping content of Al and only 5% N doping were investigated, which indicated that Al2O3 impurity also appeared in produced powders when Al content were 10% and 15%, and that the values of ??, ?? and tan? of the samples decreased with increasing Al content in whole.