NANO INSULATION MATERIALS AND THE UTILIZATION OF HOLLOW SILICA NANOSPHERES

Bjørn Petter Jelle
Department of Civil and Transport Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway; Department of Materials and Structures, SINTEF Building and Infrastructure, NO-7465 Trondheim, Norway

Sohrab Alex Mofid
Norwegian University of Science and Technology (NTNU), Department of Civil and Transport Engineering, NO-7491 Trondheim, Norway

Tao Gao
Norwegian University of Science and Technology (NTNU), Department of Civil and Transport Engineering, NO-7491 Trondheim, Norway

Serina Ng
SINTEF Building and Infrastructure, Department of Materials and Structures, NO-7465 Trondheim, Norway

DOI: 10.1615/TFEC2017.prm.017743
pages 2203-2211

摘要

A promising pathway for developing high-performance thermal insulation materials is to exploit the Knudsen effect and hence make thermal insulation materials with a nanoporous structure, i.e. nano insulation materials (NIM). These NIMs are supposed to maintain their thermally insulating properties with nanopores filled with air at atmospheric pressure. As comparison, vacuum insulation panels (VIP) require voids at nearly vacuum and a protecting envelope consisting of a metallized foil to achieve a low thermal conductivity of e.g. 4 mW/(mK). When punctured or after complete air and moisture diffusion penetration ageing this will increase to typically 20 mW/(mK) for VIPs with fumed silica-based cores. Currently, we are attempting to make NIMs by synthesizing hollow silica nanospheres (HSNS) through a coating process using polyacrylic acid (PAA) or polystyrene (PS) as sacrificial templates, where the templates PAA and PS are being removed by a washing or a heating process, respectively (the template materials diffusing and evaporating through the silica shell). Thus, the removal of the templates results in the formation of silica shells around spherical voids, i.e. HSNS. Thermal conductivity has been measured for various powder samples of HSNS, where the conductivity values are typically in the range 20 to 90 mW/(mK), though some uncertainties in the Hot Disk apparatus measurement method have to be further clarified. The thermal conductivity is currently being attempted lowered by a parameter variation and optimization of the hollow silica sphere inner diameter and wall (shell) thickness.