Porous AlPO4 ceramic with high strength and good acoustic performance prepared by direct foaming and gel-casting

Acoustic stealth of underwater vehicles demands sound insulation and decoupling materials (SIDM) with good acoustic performance, high strength, and relatively low acoustic impedance. To address this, low elastic modulus AlPO 4 was selected as the backbone material and porous AlPO 4 ceramics were fabricated by the direct foaming and gel-casting approach using AlPO 4 powders and propyl gallate. The microstructures, compressive strength, and acoustic performance were systematically analyzed. Microstructural control by modulating stirring duration and foaming agent concentration yielded specimens with low density (0.40–0.88 g cm −3 ), high porosity (61.6–82.5 %), and high compressive strength (1.23–3.20 MPa). Dual mechanisms of the viscous friction effect enhanced by micrometer pore sizes and the acoustic wave resonance effect brought about by interconnected pore-window structure endowed specimens with high sound absorption coefficients (0.66) and good sound insulation performance (37.5 dB) at 500–6300 Hz. The integrated high strength and good acoustic performance identify porous AlPO 4 ceramics as potential SIDM for submarines.