Long-Term Performance of Monolithic Silica Aerogel with Different Hydrophobicities: Physical and Color Rendering Properties after an Accelerated Aging Process

Costanza Vittoria Fiorini; Francesca Merli; Elisa Belloni; Mary K Carroll; Ann M Anderson; Cinzia Buratti

doi:10.3390/gels9030210

Long-Term Performance of Monolithic Silica Aerogel with Different Hydrophobicities: Physical and Color Rendering Properties after an Accelerated Aging Process

Gels. 2023 Mar 10;9(3):210. doi: 10.3390/gels9030210.

Authors

Costanza Vittoria Fiorini¹, Francesca Merli², Elisa Belloni², Mary K Carroll³, Ann M Anderson⁴, Cinzia Buratti²

Affiliations

¹ DIAEE Department of Astronautical, Electrical, and Energy Engineering, "Sapienza" University of Rome, Via Eudossiana 18, 00184 Rome, Italy.
² Department of Engineering, University of Perugia, Via G. Duranti 63, 06125 Perugia, Italy.
³ Chemistry Department, Union College, 807 Union Street, Schenectady, NY 12308, USA.
⁴ Mechanical Engineering Department, Union College, 807 Union Street, Schenectady, NY 12308, USA.

Abstract

Due to its excellent properties, monolithic silica aerogel is a promising material for innovative glazing systems. Since glazing systems are exposed to deteriorating agents during building service life, it is essential to investigate the long-term performance of aerogel. In the present paper, several 12.7 mm-thick silica aerogel monoliths produced by a rapid supercritical extraction method were tested, including both hydrophilic and hydrophobic samples. After fabrication and characterization of hydrophobicity, porosity, optical and acoustic properties, and color rendering, the samples were artificially aged by combining temperature and solar radiation effects in an experimental device specifically developed at the University of Perugia. The length of the experimental campaign was determined using acceleration factors (AFs). Temperature AF was evaluated according to the Arrhenius law using thermogravimetric analysis to estimate the aerogel activation energy. A natural service life of 12 years was achieved in about 4 months, and the samples' properties were retested. Contact angle tests supported by FT-IR analysis showed loss of hydrophobicity after aging. Visible transmittance values in the 0.67-0.37 range were obtained for hydrophilic and hydrophobic samples, respectively. The aging process involved optical parameter reduction of only 0.02-0.05. There was also a slight loss in acoustic performance (noise reduction coefficient (NRC) = 0.21-0.25 before aging and NRC = 0.18-0.22 after aging). For hydrophobic panes, color shift values in the 10.2-59.1 and 8.4-60.7 ranges were obtained before and after aging, respectively. The presence of aerogel, regardless of hydrophobicity, results in a deterioration in light-green and azure tones. Hydrophobic samples had lower color rendering performance than hydrophilic aerogel, but this did not worsen after the aging process. This paper makes a significant contribution to the progressive deterioration assessment of aerogel monoliths for applications in sustainable buildings.

Keywords: accelerated aging; acoustic performance; color rendering index; hydrophobicity; monolithic aerogel; optical properties.

Grants and funding

This research received no external funding.