Acoustical properties of granular silica aerogels

HAL Id: hal-03235452

https://hal.archives-ouvertes.fr/hal-03235452

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Acoustical properties of granular silica aerogels

Hasina Begum, Kirill Horoshenkov, M Conte, Wim Malfait, Shany Zhao,

Matthias Koebel, P. Bonfiglio, Rodolfo Venegas

To cite this version:

Hasina Begum, Kirill Horoshenkov, M Conte, Wim Malfait, Shany Zhao, et al.. Acoustical prop-erties of granular silica aerogels. Forum Acusticum, Dec 2020, Lyon, France. pp.3091-3092, �10.48465/fa.2020.0543�. �hal-03235452�

Acoustical properties of granular silica aerogels

H. Begum1_{, K. V. Horoshenkov}1_{, M. Conte}2_{, W. J. Malfait}3_{, S. Zhao}3_{, M. M. Koebel}3_{, P.} Bonfiglio4_{, R. Venegas}5

1_{Department of Mechanical Engineering, The University of Sheffield, S1 3JD, United}

Kingdom

2_{Department of Chemistry, The University of Sheffield, S3 7HF, United Kingdom}

3_{Laboratory for Building Energy Materials and Components, Swiss Federal Laboratories for}

Materials Science and Technology, Empa, Überlandstrasse 129, 8600, Dübendorf, Switzerland

4_{Materiacustica srl, Via C. Ravera 15A, 44122 Ferrara, Italy}

5_{University Austral of Chile, Institute of Acoustics, P.O. Box 567, Valdivia, Chile}

Received 30 October 2020

Limited published data are available on the fundamental acoustic properties of granular silica aerogels. The majority of previous work focuses on sound absorption performance, using a sample’s lateral dimensions or thickness to determine the sound absorption coefficient or transmission loss. This work highlights the key acoustic properties in terms of chemical composition, pore structure and particle size using materials characterisation and an advanced mathematical model to accurately predict the experimentally determined acoustical properties of silica aerogels. The silica aerogels were produced from polyethoxydisiloxane (PEDSP750) through a two-step, acid-base sol-gel process, with different sol silica concentrations and a select particle size of 2-3 mm. The pore structure was characterised by nitrogen sorption analysis and SEM. The acoustical properties were measured in a bespoke acoustic impedance tube. Inversion of the data enabled the prediction of key structural parameters based on the acoustical properties alone.

In this extended abstract we focus on one type of silica aerogel prepared with variable PEDSP750 content in the sol to produce an aerogel named PEDSP750E30. Fig.1 shows that the

particles are not spherical but angular with sharp edges.

Figure. 1. SEM image of PEDSP750E30 showing micrometric grains of the 2-3 mm fraction.

After inserting the key experimental parameters obtained from this study into the model, Fig. 2 shows there is agreement between the measured and predicted acoustical surface impedance spectra. The relative mean error between the data and predictions was generally less than 3.1%, this suggests that the model captures the acoustical behaviour of aerogel

PEDSP750E30 accurately.

Figure 2. Measured and predicted reflection coefficient for a hard-backed layer of aerogel

granulate PEDSP750E30.

The results found the values of the inverted parameters to make physical sense. Silica aerogels have close to 100% open porosity, however this is not reflected in the parameter values inverted using the proposed mathematical model. Our findings indicate that not all the aerogel's mesopores appear to contribute to the observed acoustical performance.

i

i _{This manuscript is currently under review for publication in the Journal of Applied Acoustics}