Effective blocking of radiative thermal conductivity in La2Zr2O7/LaPO4 composites for high temperature thermal insulation applications

Ceramics with low thermal conductivity have been widely used for high temperature thermal insulation applications, but their performance deteriorates rapidly at temperatures above 600–800 °C due to the significantly enhanced radiation heat transfer effect. We found that by addition of secondary phase of LaPO4 into a matrix of La2Zr2O7, the radiative thermal conductivity could be remarkably suppressed due to lower photon mean free path as a result of photon scattering or absorption by the secondary phase. By adding more than 20 wt.% of LaPO4, the radiative thermal conductivity of La2Zr2O7 can almost be completely blocked, as the LaPO4 phase has formed percolating interconnected network inside the matrix, resulting in remarkable reduction of infrared radiation transmittance. Furthermore, the mechanical properties of some composites were also optimized, including improved toughness and lowered elastic modulus, making the composites of particular interest for engineering applications, such as thermal barrier coatings for gas turbine.