Acoustical properties of nanoporous activated carbon felts, by Hugo Karpinski (University of Salford)

DENORMS Action’s Workshop “Modelling of high performance acoustic structures Porous media, metamaterials and sonic crystals”, Rome, 24-25th January 2017

Website of DENORMS Action

Programme of the Workshop

Session on New trends in traditional noise treatments – porous materials and microperforated plates

Speaker: Hugo Karpinski (University of Salford)

Abstract:

Activated carbon felt is a fibrous material used until now for filtration of air and water. It has demonstrated high acoustic sound absorption coefficients in articles of Shen and Jiang [1]-[2] for relatively thin layers. In this work, we aim at establishing the link between the microstructure of felts and their acoustical properties. Various kinds of measurements have been carried out to characterise several samples of activated carbon felts. Sound absorption coefficients have been measured in the impedance tube. The static flow resistivity, strongly linked to the mesoporosity (porosity between the fibres), has been measured in a standard set-up. Eventually, the the microstructure images have been obtained Scanning Electron Microscope (SEM) to identify the fibre size, their geometry and pore radii geometry. A fibre size distribution has been obtained from the analysis of the images. Activated carbon felts can be considered as a multi-scale material as the fibres itself contain pores of the nanometre size. This allows higher sound absorption coefficients at low and medium frequencies compared to foams or non-activated fibres. Sorption processes occur in the nanopores of the fibres. The molecules of air are either attracted or released by the surface (adsorption and desorption) due to weak Van der Vaal forces. To describe these phenomena, a porosity analysis and adsorption isotherm measurements have been performed. The ratio of adsorption and desorption constants has been now measured directly and used in the modelling. The model used in this study has been adapted from [3] to describe cylindrical fibres instead of spherical porous particles.

[1]Shen Y., Jiang G, Effects of different parameters on acoustic propertiesof activated carbon fiber felts, The Journal of The Textile Institute, Vol.105,No.4,392–397, 2014

[2]Shen Y., Jiang G, The influence of production parameters on sound absorption of activated carbon fiber felts, The Journal of The Textile Institute, Volume 107 2016 - Issue 9 ,2015

[3]Venegas R., Umnova O., Influence of sorption on sound propagation in granular activated carbon, JASMAN-vol_140-iss_2-755_1, 2016