Aluminium metallic foams: A competitive candidate for noise control applications in construction

Regardless of pore shape, two kinds of metallic foams are existent: closed pores and open pores foams. "Closed pores" are surrounded by material wall and each pore is isolated, while "open pores" are pores connected to each other in space. The acoustic properties of the aluminium foams fabricated by the powder metallurgical technique (closed pores) and by the infiltration process (open pores) have been investigated. Their absorption coefficient at normal incidence of the aluminum foams has been measured in an impedance tube. The main objective of the work has been to analyze the possibilities of using these foams for noise control in construction. So during the measurements, the foam samples were placed either directly against the back plate, with an air gap to the back plate in the impedance tube and combined with a mineral fiber panel: two usual solutions used in controlling noise and reverberation time in rooms. The main inconvenient of the foams fabricated by the powder metallurgical technique is a structure very inhomogeneous and a difficult reproducibility during the fabrication process. The foams fabricated by the infiltration technique show a very homogeneous structure combined with a low cost production process that allows an easy fabrication with different pore size and so, with different thermal and acoustic properties. The aluminium foams offer a novel aesthetic that together with their sound absorptive capacities has drive to use these materials as roofs and walls in different kinds of construction. Other advantage of these materials is that are eco-friendly and recyclable.