Refractory Open-Cell Foams:
Carbon, Ceramic, and Metal
Refractory foams are ideal for noise reduction in harsh environments because of their excellent attenuation characteristics and their ability to tolerate high temperature oxidizing environments.
Low-cost, reticulated vitreous carbon foam has demonstrated excellent noise attenuation capabilities when sound waves are propagating perpendicularly through the foam. In laboratory testing, the foam achieved noise reductions of 44 dB/m at 250 Hz and 64 dB/m at 1000 Hz. Silicon carbide foam, which is much stronger than reticulated vitreous carbon foam and can be used in high temperature oxidizing environments, showed a slightly better performance: 45 dB/m at 250 Hz and 69 dB/m at 1000 Hz.
Because Ultramet refractory foams create little pressure drop, they can be used in applications in which the noise is traveling down a conduit filled with flowing fluid, such as automobile mufflers.
For applications in which even the low pressure drop of refractory foam cannot be tolerated, the foam can be used to line the conduit or duct. In such a configuration, a 1" thick liner achieves noise reductions of 19 dB/m at 250 Hz and 41 dB/m at 1000 Hz. Because silicon carbide foam shows no loss of strength at temperatures up to 1800ºC, it is ideal in harsh environments, such as jet engines.