Thermal emissivity and high-temperature stability of thermal insulating materials produced by mixing powdered porous MgAl<sub>2</sub>O<sub>4</sub> ceramics with commercial insulating castable

Conventional industrial thermal insulating materials have a porous structure and provide resistance to thermal conduction. However, this structure permits heat transfer through radiation. Hence, they exhibit high thermal conductivity at temperatures higher than 1000 °C. To achieve high total-thermal-insulation efficiency, we recently developed new insulating materials, called THERMOSCATTTM, which greatly suppress radiation heat transfer. Their thermal conductivity was measured to be less than 0.3 W/(m·K) at 1500 °C. These insulating materials consist of porous MgAl2O4 ceramics having 1–5 µm pores which restrain heat transfer through radiation, which was consistent with the Mie scattering theory. From the thermal emissivity estimated from reflectance measurements, the porous MgAl2O4 ceramics had near-zero hemispherical spectral emissivity values in the wavelength range of 0.35–5 µm. Mixing these powdered porous MgAl2O4 ceramics with a conventional commercial insulating castable ceramics is shown to successfully reduce heat transfer through radiative Mie scattering. This report describes the experimental result of the powdered porous MgAl2O4 ceramics mixed into the commercial insulating castable.