Reduced thermal conductivity of nanoparticle packed bed by hybrid design

Abstract

Nanoparticle packed bed (NPB) as a kind of promising thermal insulation material (TIM) has drawn widely concern because of their lightweight and ultra-low thermal conductivities (k). In this paper, breaking through the conventional wisdom that the TIM adopts the amorphous morphology, we develop the hybrid NPB (h-NPB) with the crystal morphology for thermal insulating application. The hybrid design of crystal nanoparticle benefits the reduced k together with the enhanced mechanical strength. The lowest effective thermal conductivity (ke) as low as 0.018 W m−1 K−1 is achieved in (3:7) h-NPB, which is inferior to the k of the free air and most prevalent TIMs. The mechanism can be understood by the quite low solid-phase thermal conductivity (ks), negligible thermal conductivity of the confined air (ka) and small radiative thermal conductivity (kr). Neglecting the ka, the minimum ke occurs at the porosity where domination role changes from ks to kr. In addition, an excellent mechanical strength, nearly 40-50 % compared to bulk silica, is harvested in silica h-NPB, guaranteeing the practical application. This study is expected to supply some information for the design of next generation TIM characterized with the lightweight, high strength and low k.