Strengthening and aging of wet silica gels for up-scaling of aerogel preparation

Abstract

International audienceIn order to enhance the mechanical properties of wet gels for aerogel production, aging studies by using three different routes was performed. The wet gels were prepared from a polyethoxydisiloxane precursor by using HF as a catalyst. The three different aging routes studied were i) aging in sealed mould, ii) aging in solvent and iii) aging in simulated pore liquid, i.e. a solvent with small amounts of water and HF resembling the mother liquor. All aging processes gave stronger and stiffer wet gels however, a maximum in strength and stiffness was observed after a certain aging time. The simulated pore liquids allowed short aging time in the range of 8 h to achieve the maximum mechanical strength, however the maximum in strength was lower than for the other two aging routes. From the wet gels, monolithic and transparent aerogels were obtained by supercritical drying at small-, mid- and large-scale. The aging strengthening process was successfully transferred to larger scales giving both lower density and higher transparency compared to small-scale

Effect of aging on silica aerogel properties

“…A reduction in surface area with aging time and temperature was also observed in previous studies for silica xerogels/aerogels when exchanged into a silane precursor solution (TEOS or TMOS) before aging or when aged for very long times [38,44,46,55]. During the aging process, the strength and stiffness of the gel framework increase due to an increased degree of condensation reactions and siloxane cross linking within the gel network (^SieOH þ OHeSi^/^SieOeSi^), solution-precipitation of silica and attachment of unreacted oligomers from the gelation process (Fig.…”

“…In summary, most of these studies indicate that long aging times and several solvent exchanges before drying are typically employed during the synthesis of silica aerogels. The effect of both aging and drying processes on the final physico-chemical properties of silica aerogels was investigated for SCD TEOS based silica aerogels [55,57] and for APD water-glass based silica aerogels [52,58,59].…”

Cold Climate Building Enclosure Solutions

“…The total costs 21 to retrofit the wall of a baseline house 22 with conventional insulations and aerogels were estimated and compared using RS Means Cost Data [11]. The aerogel blanket cost 19 Exterior cladding installation cost is not included in the cost estimation.…”

“…Future reports need to employ energy performance to account for more comprehensive performance aspects of these insulations. 21 The total cost is the sum of the bare material cost, the bare labor cost, the bare equipment cost plus 10% for profit. 22 The baseline house is a two story average class residential house with 2,000 ft 2 floor surface area, 135 ft perimeter, and 2,700 ft 2 wall surface area as defined by RS Means Residential Cost Data (2011, page 42).…”

“…Another direction to reduce the cost is to minimize the aging time, which can be achieved by aging in a simulated pore solvent [21] or increasing the solvent temperature.…”