Thermal Insulation Monolith of Aluminum Tobermorite Nanosheets Prepared from Fly Ash

Abstract

A thermal insulation monolith of aluminum tobermorite nanosheets was prepared by a facile method of one-step hydrothermal reaction and molding of a high energy ball milled slurry of fly ash, sodium bentonite, calcium hydroxide, and sodium water glass, followed by drying at ambient pressure. The monolith was characterized by XRD, FTIR, TG-DSC, SEM, TEM, BET, mercury porosimeter, and AFM. The addition of both sodium bentonite and sodium water glass plays a crucial role in preventing shrinkage and improving the porosity of the monolith. The monolith has the microstructure of randomly oriented and multually interwoven aluminum tobermorite nanosheets among which there are numerous macropores. Interestingly, the aluminum tobermorite nanosheets can be exfoliated by ultrasonication treatment to provide single-layer ultrathin nanosheets of aluminum tobermorite with a thickness of 1.18 nm and an aspect ratio of ∼1000. The monolith of aluminum tobermorite nanosheets has low apparent density (0.077 g cm −3 ) and very low thermal conductivity (0.03793 W m −1 K −1 ). The low thermal conductivity of the monolith is attributed to its high porosity or pore volume due to the presence of numerous macropores among aluminum tobermorite nanosheets.

Incorporation of Al and Na in Hydrothermally Synthesized Tobermorite

“…Tobermorite [Ca 5 (OH) 2 Si 6 O 16 ·4H 2 O] is a type of crystalline C–S–H mineral synthesized in a hydrothermal environment . Recently, many studies have been carried out on tobermorite and Al‐substituted tobermorite, due to their good performance in applications such as thermal insulation and cation exchange . In our previous studies, we synthesized Al‐substituted tobermorite from alumina‐extracted fly ash in a dilute NaOH solution by a hydrothermal process.…”

“…30,31 Recently, many studies have been carried out on tobermorite and Al-substituted tobermorite, due to their good performance in applications such as thermal insulation and cation exchange. [32][33][34][35] In our previous studies, 35,36 we synthesized Al-substituted tobermorite from aluminaextracted fly ash in a dilute NaOH solution by a hydrothermal process. However, the incorporation mechanism of Al and Na in the samples was not investigated.…”

Ultrahigh-Temperature Insulating and Fire-Resistant Aerogels from Cationic Amylopectin and Clay via a Facile Route

“…More than 30% of the world’s energy consumption is used for comfortable interior environments. − Its corresponding energy efficiency in developing countries is 3–5 times worse than the developed countries, which leads to severe energy waste and sustainable development problems. A widely adopted partial solution is the installation of thermal insulation materials. − Currently, such materials are mainly petroleum based, with expanded polystyrene foam (EPSF) and polyurethane foam (PUF) being the predominant products.…”

Synthesis and Catalytic Properties of New Sustainable Aluminosilicate Heterogeneous Catalysts Derived from Fly Ash

“…In order to reduce the financial and environmental costs of its disposal, fly ash has been utilized mainly in construction applications such as extenders in concrete, asphalt fillers, and pavement base coursees. , However, the growing production of fly ash is outstripping the demands of the civil engineering sector; ∼50% of the fly ash produced in 2010 was globally utilized, with the reminder dumped into the sea or into landfills. Consequently, fly ash has been investigated for a range of other applications including as an adsorbent for flue gases and heavy metals from industrial wastewater, , recovery of valuable metals, , and as a precursor for materials such as ceramics, − antibacterial pigments, and thermal insulation monoliths …”

“…Consequently, fly ash has been investigated for a range of other applications including as an adsorbent for flue gases 7 and heavy metals from industrial wastewater, 8,9 recovery of valuable metals, 3,10 and as a precursor for materials such as ceramics, 11−13 antibacterial pigments, 14 and thermal insulation monoliths. 15 The utilization of fly ash in the field of heterogeneous catalysis has attracted much attention over the last few decades, 16,17 since it is mainly composed of SiO 2 and Al 2 O 3 and contains metals oxides such as Fe 2 O 3 , TiO 2 , CaO, and Na 2 O. In this context, fly ash has been investigated either as a support for catalytically active species 18−20 or as a precursor for active catalysts such as zeolites 21−23 and mesoporous molecular sieves.…”