Synthesis of aerogels, nanocomposites and lightweight silica aerogel superinsulation nanocomposites by ambient pressure drying method

Abstract

This thesis mainly investigates the improvement of the new ambient pressure approach used to synthesise aerogels by using a solvent comprising of sodium bicarbonate and water instead of a low surface tension solvent. Firstly, to improve the efficiency of thermal insulation, the sodium bicarbonate approach is utilised to synthesise cost effective ceramic blanket silica aerogels (CBSA) and short ceramic fibres silica aerogel composites (CSSA). To reduce the manufacturing cost and scalable of silica aerogels, we propose applying the sodium bicarbonate approach to synthesis silica aerogels from sodium silicate (water glass) precursor. In addition, the approach is used to synthesise alumina-based aerogel (dawsonite-sodium aluminium carbonate hydroxide) from Aluminium sec-butoxide precursor (ASB). To mimic the structure and thickness of the wings of the damselfly, which was the main source of inspiration for this study, multi-layered silica aerogel films with a thickness of 0.3 mm were synthesised using the bicarbonate approach. Finally, wavy nickel nanowires (NiNWs) were synthesise and immobilised on mesoporous silica (SiO2) aerogels by the sol-gel method. In addition, nickel nanoparticles (NiNPs) were immobilised in silica aerogels to do a comparative study between the catalytic activity of immobilised NiNWs and NiNPs in silica aerogels for CO2 hydration reaction (CHR) in gaseous phase. Dynamic vapour sorption (DVS) analysis is used for that purpose. The analysis is performed at levels of 50% CO2 and 50% H2O vapour for SiO2 aerogels, immobilised nickel nanoparticles (NiNPs) on silica aerogels and NiNWs-SiO2 aerogels composites. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), uniaxial compression test, Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods are used to characterise the synthesised materials.