Preparation And Properties Of Ti₃SiC₂Microwave Absorbers

The ternary layered carbides Ti3SiC2have a potential application in microwaveabsorbing materials at higher temperature due to their unique combination of theproperties of both metals and ceramics. By X-ray diffraction(XRD), scanning electronmicroscope(SEM), energy dispersive spectroscopy (EDS) and the measurement ofmicrowave dielectric properties, the relations between preparation, structure andproperty of Ti3SiC2and Al-doped Ti3SiC2were investigated systematically, and thereflection loss of the as-prepared powders was calculated through transmission linestheory. The mechanism of Ti3SiC2powders to dissipate microwave were discussed. Theoxidation resistance of Al-doped Ti3SiC2ceramics at higher temperature was studiedalso.The Ti3SiC2powders were prepared by solid state reaction at higher temperature,using titanium powder, silicon powder and titanium carbide powder as starting materials.The effects of the molar ratio of silicon powder in starting materials, holding time andsynthesis temperature on the preparation of Ti3SiC2were studied. Results showed thatthe laminated Ti3SiC2powder with92.6wt%of Ti3SiC2and the mean grain size ofabout4μm was prepared at1325℃with2h when the starting materials were mixturedin the molar ratio of nTi: nSi: nTiC=2:2:3. The dielectric properties and reflection loss ofpreparated powders were studied in the frequency range of8.2-12.4GHz. Resultsindicated that the real part ε′and imaginary part ε" of permittivity and dielectric losstanδ of the powders preparated at1325℃were9.54、4.97and0.52in average,respectively. The sample synthesized at1325℃with2.5mm thickness showed a goodreflection loss, with the value below-14dB in the range of8.6-11.5GHz and a minimumvalue of-23dB.The Al-doped Ti3SiC2powders were prepared by solid state reaction at highertemperature, using titanium powder, silicon powder and titanium carbide powder asstarting materials, and aluminium powder as dopant. The effect of Al doping on thedielectric properties of Ti3SiC2powders was studied. Results showed that the synthesistemperature of Ti3SiC2decreased to1250℃with10%-20%Al doping, and that thepurity of Ti3SiC2in the prepared powder was more than99%. The microwave dielectricproperties of the preparated powders were studied in the frequency range of8.2-12.4GHz. Results showed that the samples had better imaginary part ε" of permittivity anddielectric loss tanδ synthesized at1325℃and the molar ratio of nTi: nSi: nAl: nTiC=2:1.8: 0.4:3in starting materials, which were5.4and0.64in average, respectively.Additionally, the20%Al doped sample had the best reflection loss and the impedancematching thick decreased to2.1mm.The Al-doped Ti3SiC2ceramics were prepared by hot-pressed sintering at1300℃for2h and with a pressure of20MPa, using titanium powder, silicon powder, andtitanium carbide powder as starting materials, and aluminum powder as dopant. Theprepared Ti3SiC2ceramics were oxidized in the air at800℃for2h,6h and10h. Resultsshowed that there did not exist continuous oxide layers in the2h and6h oxidationsamples’ surface, an oxidation layer about2μm thickness appeared for10h sample. Theeffects of temperature and Al content on the oxidation resistance of Ti3SiC2ceramicswere investigated, by10h oxidation at800,1000and1200℃. Results showed that thethickness of oxidation layer increased from10μm to25μm as the Al content increasedfrom0%to20%at the oxidation temperature of1000℃, respectively. However, whenthe oxidation temperature was1200℃, the10%Al doped samples had the minimumthickness of oxidation layer.