Structure of SiO₂-TiO₂ Pillared Clays and Their Thermal Conductivity

Abstract

SiO₂-TiO₂ pillared montmorillonite clay, prepared by intercalation of SiO₂-TiO₂ sol into the clay layer, was subjected to two drying treatments of supercritical drying with CO2 and air heat drying. The thermal conductivities of the pillared clays under the two drying treatments are discussed in view of their structure. The rmal conductivity of the pillared clay under air heat drying didnot show lower thermal Conductivity than that of air. However supercritical drying treatment with CO₂ gave lower thermal conductivity than that of air. Thermal c onductivities of gas in pillared clays under both treatments are lower than conductivity of air, since both pillared clays have smaller pore size than the length of mean free path. Therefore the difference of thermal conductivities of both pillared clays was sug gested to be due to the change of conductivities of pillared clay solid structure. By supercritical drying, card-house structure was created at silicate layer, which has lower contact each other and results in low thermal conductivity. By the increase of SiO₂-TiO₂ sol, the thermal conductivity became lower. This indicates that the increase of card-house structure portion enhanced to give lower contact each other.