Effective Thermal Conductivity of a Packed Bed of Hollow Zirconia Microspheres, under Vacuum and under 100 kPa of Argon

Measurements have been made of the effective thermal conductivity of a packed bed of hollow, yttria‐stabilized zirconia microspheres, under vacuum and under 100 kPa of argon gas. Above 1400 K the spheres begin to sinter together. Before this occurs, the conductivity is given under vacuum by A 1 T 3 + A 2 with A 1 = 2 × 10 −11 W · m −1 · K −4 and A 2 = 0.01 W · m −1 · K −1 . The thermal conductivity increases strongly with both the gas pressure and the degree of sintering of the spheres. The measured values can be fitted reasonably well by a model developed by Takegoshi et al. These results may have some applicability to the development of high‐temperature thermal insulation.