Aluminum Phosphate–Mullite Composites for High‐Temperature Radome Applications

An AlPO ₄ –SiO ₂ powder with a composition of Al:P:Si=1.5:1:0.1 was synthesized by the sol–gel method using aluminum nitrate, phosphate acid, and tetraethoxysilane. The structural evolution of this material was characterized by thermal gravimetric analysis‐differential scanning calorimetry, Fourier transform infrared, and X‐ray diffraction. By adding silica in AlPO ₄ , the sinterability of the AlPO ₄ was enhanced because of the reactions between excess alumina and silica to form mullite. The sintered composites have a high strength and good dielectric properties at 10 GHz. Because of the formation of mullite at high temperatures, the composites showed a hydrophobic property. These unique properties indicate that the sintered AlPO ₄ –mullite composites are suitable for the radome application.