Rules to determine thermal conductivity and density of Anodic Aluminum Oxide (AAO) membranes

Abstract

Extracting the thermal conductivity of single nanowires is greatly important in investigating the phonon scattering phenomena that can occur due to the reduction of the dimensions of the material. In order to extract the thermal conductivity of a single nanowire from a measurement of the whole nanowire array, the effective medium theory (EMT) is employed. To appropriately use EMT, the template thermal conductivity must be known. However, the values reported in literature vary greatly. In this work, the photoacoustic technique was used to determine thermal conductivity of different anodic aluminum oxide (AAO) membranes as a function of the pore diameter and type of electrolyte used. To accurately obtain the thermal conductivity, values for the porosity, skeletal density and specific heat of each AAO membrane were measured. These values are critically needed in the most mathematical models to obtain the thermal conductivity of nanowires/AAO composites and theoretical works. Values of 1.07 W m–1 K–1 for the skeletal AAO prepared in sulfuric acid and 1.32 W m–1 K–1 in oxalic and phosphoric acid membranes are obtained. Also, general equations to determine the thermal conductivity and density by determining its percentage of porosity are obtained.