Al-rich industrial waste as new alternative of fumed silica for the manufacture of vacuum insulation panels for building energy conservation

Abstract

Nano-structured fumed silica (FS) is the most used vacuum insulation panel (VIP) core material for building applications. However, the FS VIP core has the majority of the environmental burden associated with conventional VIP manufacture and FS-based VIPs are very expensive. This paper explores aluminium anodizing sludge (ALW), a residue from the aluminium industry, as a new substitute for FS in VIP cores. Al-rich sludge waste is thoroughly characterised, and 100%-based ALW and its hybrid core mixtures with FS are formulated to produce VIPs cores, which are then evaluated. ALW was observed as aggregated clusters of nanosized individual particles in round and smooth-shaped forms typical of hydrated gel-like pure amorphous materials. The microstructure system of the sole ALW VIP core is found to be dissimilar to that of an FS VIP core, with the pore size range of 0.1–0.8 μm for the former and 0.01–0.04 μm for the latter, but the overall volume of large pores being much higher for the FS than ALW cores. The hybridization of ALW and FS resulted in a restructure of the initial ALW core systems. While the thermal conductivity of the ALW VIP core is less proficient than that of the single FS core, the effective thermal conductivity of both ALW50FS50 and ALW25FS75 core compositions at 1 Pa even suppressed that of the sole FS core, presenting 5.8 mW m−1·K−1 against 6.3 mW m−1·K−1 respectively. A life cycle assessment (LCA) study of these hybrid core solutions was also conducted to illustrate the positive environmental benefit of ALW-based VIP compared to FS-based VIP production. The study highlights the potential of using industrial residue ALW in VIP production, contributing to developing more sustainable superinsulation materials.