Water-induced highly transparent SiO2 porous ceramics with tunable visible transparency, anti-fogging and thermal insulation

To address the difficulties of continuous adjustment of visible transmittance of amorphous porous ceramics and their anti-fogging without treatment, this paper delicately combined “hydrochromism” and porous ceramics, and prepared water-induced SiO2 transparent porous ceramics (TPCs) with high strength and adjustable transparency. The effects of adding solvents to the silica sol on their visible transmittance, integrity and porosity were studied, and their multifunctional applications were also investigated. Results showed that the addition of EG, ammonia and acetonitrile mainly affected the gel integrity, the porosity of amorphous TPCs, and their gelation time and light transmittance, respectively. The compressive strength, porosity, visible transmittance after drying and water absorption of the optimal TPCs prepared at 600 °C by adding the above three solvents were 23.95 MPa, 54.7 %, 43 % and 81 %, respectively. The transparency of TPCs could be adjusted from 3 % to 81 % by controlling their water content, and they had excellent thermal insulation and anti-fogging ability without any treatment, and the excellent anti-fogging performance is related to their hydrophilicity and uniform nanopore structures. Overall, this paper provides new strategies for lightweighting, anti-fogging, and continuous adjustment of visible transmittance of transparent ceramics, and the resulting lightweight TPC is an ideal candidate for applications in daylighting design, as well as thermal insulation and anti-fogging in high humidity environments.