Effect of composition on thermal conductivity of silica insulation media.

Nano-sized fumed silica-based insulation media were prepared by adding TiO2 powders and ceramic fibers as opacifiers and structural integrity improvers, respectively. The high temperature thermal conductivities of the fumed silica-based insulation media were investigated using different types of TiO2 opacifier and by varying its content. The opacifying effects of nanostructured TiO2 powders produced by homogeneous precipitation process at low temperatures (HPPLT) were compared with those of commercial TiO2 powder. The nanostructured HPPLT TiO2 powder with a mean particle size of 1.8 microm was more effective to reduce radiative heat transfer than the commercial one with a similar mean particle size. The insulation samples with the HPPLT TiO2 powder showed about 46% lower thermal conductivity at temperatures of about 820 degrees C than those with the commercial one. This interesting result might be due to the more effective radiation scattering efficiency of the nanostructured HPPLT TiO2 powder which has better gap filling and coating capability in nano-sized composite compacts.