Synthesis of Co3O4 Micro-needles on the Cell Walls and their Effect on the Sound Absorption Behavior of Open Cell Al Foam

Open cell Al foams usually show poor sound absorption performance due to excessively low flow resistance. In order to overcome this shortcoming, several measures have been taken including compression, cell surface erosion and modification, etc. In the present study, a cell surface modification process is adopted to synthesize needle like Co3O4 on the cell walls of open cell Al foams via hydrothermal method. The phase and morphology of micro-Co3O4 needles are characterized, and the airflow resistance as well as the sound absorption behavior of modified Al foams is examined. The Co3O4 needles have the diameter of around 5 μm and lengths of 10-50 μm. After the modification, the airflow resistance of the foams increases from 30Pa·s/m to 93Pa·s/m, and the height of sound absorption coefficient peak increases from 0.65 to 0.95. This demonstrates that the coverage of a rough Co3O4 needle layer can enhance the interaction between the air and the cell surface, not only the friction force but also the thermal exchange strength because Co3O4 needles possess both high thermal conductivity and high specific surface area, giving rise to increased flow resistance and increased sound absorption capability.