A Novel Production Method for Porous Sound-Absorbing Ceramic Material for High-Temperature Applications

Abstract

A new processing technique combining the freeze gelation process with sacrificial templating is used to create self‐supporting ceramic sound absorption structures for high‐temperature applications. The process leads to near‐net shape components with an open‐pored structure. Expanded perlite, acting as melting filler, increases the porosity up to 74%. The resulting properties of the microstructure such as porosity and airflow resistance are presented. Acoustical measurements in an impedance tube show high sound absorption coefficients up to 0.7. The measured sound absorption is compared with a mathematical simulation. In summary, this process allows the fabrication of temperature‐resistant ceramic sound absorbers.

Near‐Net‐Shaped Porous Ceramics for Potential Sound Absorption Applications at High Temperatures

“…The following sample produced with 14.00 g of template particles showed a reduction on the sound absorption properties, obtaining a maximum coefficient of 0.85. Compared to the material produced by Frank et al ., higher sound absorption coefficients could be obtained for the entire investigated frequency range from 50 up to 1400 Hz.…”

“…Sound absorbing materials represent a very important engineering material class and their uses involve a large range of applications, e.g., in architecture and thermo‐acoustic insulation of engines and pump chambers . Nowadays, much attention in industry and research is given for the development of new materials to be applied in equipment which includes a low noise emission level and damping of vibrations due to sound emissions . The use of porous ceramics is particularly interesting for applications where high temperatures, wear stresses, and corrosive media are involved due to their excellent combination of properties such as low density, high thermal, chemical and mechanical resistance .…”

“…Combustion chambers of gas turbines, water pumps, and thermal insulation of motors, require the damping and insulation of emitted sound waves. Whether for regulatory reasons or with the objective to reduce thermo‐acoustic instabilities due to vibrations, the use of sound absorbing materials results in the enhancement of the efficiency of the equipment …”

“…For obtaining promising sound absorbing properties, it is known that a microstructure with controlled airflow resistance (values generally between 1 and 200 kPa s/m²) and high interconnected porosity is necessary, because an open porous microstructure allows the penetration and propagation of the sound waves through the material . When the sound waves enter these special microstructures, their amplitude is decreased by friction when moving through the tortuous passages.…”

“…The addition of expanded polystyrene spheres acting as template particles was chosen to obtain large pores on a millimeter‐scale and to increase the porosity of the produced material. Another processing route to produce ceramic absorbers was presented by Frank et al . Here, the author combined freeze gelation with sacrificial templating of expanded perlite obtaining a sound absorption coefficient of 0.7 at frequencies of around 400 Hz.…”