Thermal Conductivity of Very Porous Kaolin-Based Ceramics
Résumé
A clay-based material exhibiting high pore volume fraction and
low thermal conductivity suitable for thermal insulation is
described. Starting with a commercial clay containing >75% kaolinite,
foams were made by mixing in water and methyl cellulose
as a surfactant then beating. After drying at 70°C, the pore volume
fraction >94% remains almost constant for treatments up
to 1150°C. In contrast, the phases constituting the solid skeleton
evolve strongly with removal of surfactant, dehydroxylation of
kaolinite, and formation of mullite. The latter leads to greater
mechanical strength but also an increase in thermal conductivity.
Thermal treatment of the kaolin foam at 1100°C yields a suitable
compromise between low thermal conductivity of 0.054
W.(m.K) – 1 at room temperature with a compressive yield stress
of 0.04 MPa. The radiation component in the effective thermal
conductivity is <10% at 20°C increasing to >50% at 500°C