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 10GHz. 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.