Estimation of Mechanical and Thermal Properties of Porous Aluminosilicate Foam

Abstract

Aluminosilicates are naturally occurring minerals with low thermal conductivity due to the presence of variable size pores in their structure. Because they are found in abundance in nature, they could be an economical alternative for the fabrication of thermal insulators used in the buildings and underground mines. In this study, the thermal and mechanical properties of amorphous porous aluminosilicate structures (PAS) were investigated using computational and experimental methods. Molecular Dynamics (MD) simulation was used to characterize the thermal conductivity at the atomistic scale. MD simulations were performed to identify the suitable Al-Si ratio that yields the lowest possible thermal conductivity as well as high mechanical strength. The effect of density on the thermal conductivity of aluminosilicate structures was characterized. It was observed that the thermal conductivity of the Aluminosilicate structures has a linear dependence on the densities varying between 0.4 g/cc and 2.62 g/cc. In addition, for a given porosity, a larger distribution of smaller pores results in lower thermal conductivity. This observation is correlated with the presence of phonon-scattering centers in such systems. The data obtained from MD simulations were used to physically fabricate the foams with similar densities in laboratory, and their associated thermal conductivity was experimentally measured. MD simulations and experimental data show a high degree of agreement. The ultrasound non-destructive technique (NDT) was used to transmit wave energy in the 1 MHz frequency range to measure dynamic mechanical properties experimentally. Porosity was varied by changing the composition of the blowing agent and surfactant. P-wave and S-wave velocities were measured using the time of flight of the ultrasonic energy through the sample. The Finite Element Method (FEM) provided in the COMSOL Multiphysics platform was used to verify the bulk mechanical and thermal properties of the amorphous porous aluminosilicate materials. Acoustic and stress analysis were performed at different porosities to determine P-wave and S-wave velocities, and other elastic properties. Symmetric spherical pores were introduced to simulate porosity. We also generated a high-fidelity model of the foam using micro-CT scans. Volume meshing was created in the Simpleware ScanIp software and subsequently exported as a COMSOL supported file to perform the modeling. Next, FEM models were set up to determine the acoustic and elastic properties at different porosity ranges. The data produced in this analysis demonstrated a good agreement between numerical and experimental tests. The findings from this research project will be used to design and fabricate a cost-effective thermal insulator.