莫来石陶瓷的制备、微波介电特性及其对材料吸波性能的影响

采用热压烧结法,用SiO₂溶胶和Al₂O₃溶胶制备的莫来石溶胶制备了莫来石陶瓷,研究了莫来石陶瓷的微波介电特性与烧结致密度之间的关系。研究表明,当莫来石陶瓷的烧结致密度从91.4%升高到97%时,其复介电常数的实部ε从3.85增加到的5.87,虚部ε″从0.04增加到0.11。当添加MgO烧结助剂后,莫来石陶瓷复介电常数的实部和虚部明显升高。将莫来石陶瓷作为吸波材料阻抗变换层,能够大幅度提高材料的吸波性能。这主要是由于采用的莫来石阻抗变换层的波阻抗较高,为156Ω,减小了空气与吸收层界面上电磁波的反射,使更多的电磁波进入了吸收层而被损耗。

Preparation,Microwave Properties of Mullite Ceramic and Their Effects on Microwave Absorbing Materials

Mullite ceramic is prepared by hot-pressing method from a mixture of SiO₂ sol and Al₂O₃ sol and from a mixture of SiO₂ and Al₂O₃ powders, respectively. The relationships between permittivities and sintering conditions of mullite ceramic are discussed. The samples’ permittivities are measured in the frequency range of 8.2~12.4GHz. The results show that the real and imaginary parts of permittivities of the samples increase with the sintering densities. The real and imaginary parts of permittivity of the samples increase when additive MgO is used. Mullite ceramics with different permittivities can be obtained through varying their preparation condition. When the as-formed mullite ceramic is used as an impedance transfer layer of the microwave absorbing material, it greatly enhances the microwave absorbing efficiency of absorbing materials. The mechanism of the enhancement of absorbing efficiency is that the addition of mullite ceramic to and absorbing material lowers the interface reflection between air and the absorbing material, more microwave enters the absorbing material and is dissipated. There exist different effects from ceramics which are prepared under different conditions. So an exact preparation condition of the mullite ceramic is required for expected characteristics of the microwave absorbing material.