Effects of Al2O3 nanoparticles on the properties of glass matrix composites for sealant applications

Glass matrix composites (GMCs) have better mechanical properties than glass, which is beneficial for applications as sealants. This application scenario requires the GMCs sealants to withstand extreme service conditions for extended periods of time. In this study, a borosilicate glass as the matrix was filled with Al2O3 nanoparticles to prepare the GMCs through powder technology, and the effects of Al2O3 nanoparticles on the phase composition, thermal behavior, coefficients of thermal expansion (CTE), microstructure, wettability, viscosity and mechanical properties were systematically investigated. X-ray diffraction (XRD) patterns and thermal analysis results revealed that the Al2O3 particles, which were thermodynamically stable in the borosilicate glass after heat treatment, could be considered as rigid inclusions. As the mass fraction of Al2O3 nanoparticles increased, the CTEs of the GMCs and the wettability to metal surfaces gradually decreased, and an increasing viscosity was also observed with the addition of Al2O3 nanoparticles, which was attributed to the inhibition effect of the Al2O3 nanoparticles on glass viscous flow and apparently contributed to the residual voids. The mechanical properties of the heat-treated GMCs were enhanced by the Al2O3 nanoparticles but limited by structural defects such as residual voids and swollen bubbles, especially when the mass fraction of Al2O3 nanoparticles was large. The results thus demonstrate that an increased heat treatment temperature was expected to reduce the viscosity of the melts and promote the elimination of residual voids, but will inevitably cause the undesired bubble growth at the same time. Therefore, the content of Al2O3 nanoparticles in the glass matrix should be limited to a certain extent to ensure that the reinforcements can fully exert their strengthening effect.