Experimental Synthesis of Hollow Silica Nanospheres for Application as Superinsulation in the Buildings of Tomorrow

The path toward energy-efficient buildings with a low or zero carbon footprint, e.g. zero energy and zero emission buildings, involves the development of high-performance thermal insulation, aiming at reaching thermal conductivities far below 20 mW/(mK). Applying such superinsulation will allow the construction of relatively thin building envelopes yet maintaining a high thermal resistance, thus also increasing the architectural design possibilities. A vacuum insulation panel (VIP) represents a state-of-the-art thermal insulation solution with a thermal conductivity of typical 4 mW/(mK) in the pristine and non-aged condition. However, the VIPs have issues with fragility, perforation vulnerability, increasing thermal conductivity during time and lack of building site adaption by cutting as four cardinal weaknesses, in addition to heat bridge effects and relatively high costs. Therefore, the VIPs of today do not represent a robust solution. Hence, our aim is from theoretical principles, utilizing the Knudsen effect for reduced thermal gas conductance in nanopores, to develop experimentally a high-performance nano insulation material (NIM). This work presents the current status of the development of NIM as hollow silica nanospheres (HSNS) in our laboratories, from the experimental synthesis to the material characterization by e.g. thermal conductivity measurements. One attempted approach for tailor-making HSNS is the sacrificial template method and optimization of the sphere diameter and shell thickness with respect to low thermal conductivity. The results so far indicate that HSNS represent a promising candidate for achieving the high-performance thermal superinsulation for application in the buildings of tomorrow.

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