Thermal management in ceramics: Synthesis and characterization of a zirconia-carbon nanotube composite

Abstract

An investigation is conducted into the reduction of thermal conductivity in a porous ceramic through the inclusion of small amounts (1--3wt.%) of dispersed nanotube bundles and nanofibers. The thermal properties and thermal stability of single walled carbon nanotubes (SWNT) are examined at high temperature, and their impact on the micro and nanostructure of the ceramic matrix is evaluated. An isotropic dispersion of SWNT bundles between small (∼100nm) ceramic particles results in thermal conductivity reductions by altering the nature of the porosity, contributing to an extended grain boundary region, and by serving as the basis for polycrystalline templates. Vapor grown carbon fibers (VGCF)---an order of magnitude larger in diameter than SWNT bundles---are used in low concentrations within the matrix as a comparison. Partially stabilized zirconia (PSZ) is selected as the matrix due to its extensive use in the gas turbine industry in thermal barrier coatings, and a tape casting technique is used to produce samples of varying compositions for the measurement of thermal diffusivity and calculation of thermal conductivity. Significant total thermal conductivity reductions (40--50%) are achieved in the PSZ composite and the results are compared with conventional models for porosity to evaluate the nature of the contributions.