| The microwave absorbing materials has been considered as one of key approaches for stealthy and electromagnetic protection techniques, the properties of which depend on the ability of microwave to dissipate electromagnetic wave. Microwave absorbers employed at higher temperature have been required for the stealth of the weapon equipment and electromagnetic protection at higher temperature. Ti3SiC2 has the unique properties of both metal and ceramic materials, which enable it to develop into a new material for the absorbers used at higher temperature. In this paper, the relationship between synthesis, structure and properties of Ti3SiC2 and Al-doped Ti3SiC2 powder absorbers was investigated systematically by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and dielectric properties measurement, etc. The preparation and oxidation resistance of Ti3SiC2/SiC ceramics was also studied. The corresponding mechanisms were discussed.Ti3SiC2 powders were synthesized by high temperature solid-state reaction under the vacuum atmosphere, using Ti/Si/TiC=2:x:3(1.6<x<3) as raw materials. Results showed that the content of Si in the starting materials had a great influence on the phase. morphologies and elemental compositions. The higher purity of Ti3SiC2 powder was produced when x was 2, with better dispersibility and an average particle size of 5μm. The permittivities of the as-prepared powders showed that the powder sample synthesized with x=1.8 revealed the best dielectric properties as a whole, which decreased with the increasing Al content.TisSiC2 microwave absorber were prepared when the molar ratio of Ti/Si/TiC was 2:2:3, and the effect of temperature on the product structure, composition and property was studied. Results showed that the content of Ti3SiC2 in the synthesized product increased with the increasing temperature on the whole in 1300℃-1450℃ range and it was up to 99.8% when the synthesis temperature was 1400℃.EDS and XPS analysis showed that Ti3SiC2 had been completely synthesized at 1300℃. Dielectric test results showed that the real part ε’ and imaginary part ε" of complex permittivities and loss tangent tanδ of sample decreased as the Ti3SiC2 content increased. The content of impurity phase TiC and defects in crystal influenced on the dielectric properties of the samples.The effect of Si content, oxidizing time and oxidizing temperature on the oxidation resistance of Ti3SiC2 powders was investigated. It was found that the more Si content in raw materials, the better oxidation resistance of the synthesized powders when it was oxidized at 600℃ for 2h. When the sample synthesized by 2Ti/2Si/3TiC materials was oxidized at 600℃ for different oxidation time, it could be seen that the morphology character of surface fracture for the samples were more obvious and the oxidizing degree were more serious as the oxidizing time increased, which was demonstrated further by dielectric measurement results. In addition, the oxidation resistance of the samples synthesized with 2Ti/2Si3TiC was investigated under the different oxidation temperatures of 600℃,800℃ and 1000℃.It was found that Ti3SiC2 sample had been severely oxidized when the oxidizing temperature was 1000℃.Ti3SiC2 powders doped with different Al contents were synthesized by solid-state reaction at 1300℃ under vacuum atmosphere, utilizing Ti/Si/TiC powders as starting materials and aluminium powder as dopant. Results showed that Al doping with less amount could improve the purity of the synthesized Ti3SiC2 product. The prepared particle sizes increased with the increasing Al contents, and the resultant Al doping product was Ti3Si(Al)C2 solid solution. The results of dielectric properties measurement showed that the properties of Al doping samples declined with the increasing Al contents, in which 5% Al doped sample had the best dielectric properties. Additionally, Al doping could improve effectively the resistance oxidation of prepared samples, in which 5% Al doped sample also revealed the best property.Ti3SiC2 ceramics were prepared by hot-pressing sintering at 1400℃ for holding 2h under vacuum atmosphere, using the 3TiC/2Si/2Ti,3TiC/2Si/0.2Al/2Ti and 3TiC/2Si/0.2Al as the starting materials, respectively, and their oxidation resistance were investigated. Results showed that Ti3SiC2/SiC composite ceramic had the best oxidation resistance at high temperature and its thickness of surface oxidation layer at 1000℃ for 10h was only 7λm. The oxidation properties of Ti3SiC2/SiC ceramics sintered by different procedures were studied, using 3TiC/2Si/0.2Al as raw materials. Results showed that the ceramic prepared by two-stage sintering had better oxidation resistance. The mechanism of the oxidation resistance for Ti3SiC2/SiC ceramic was the fact that externally diffused Ti and Al atoms and internally diffused O atoms reacted to form the compact oxidation layer which hindered the further oxidation of Ti3SiC2 materials and efficiently improved the oxidation resistance of Ti3SiC2 materials. |
PDF Full Text Request