Effect of high temperature on compression property and deformation recovery of ceramic fiber reinforced silica aerogel composites

Ceramic fiber reinforced silica aerogel composites are novel insulation materials in the thermal protection field for hypersonic vehicles. Before the aerogel composites are applied in load-bearing structures, it is necessary to investigate their mechanical properties including load-bearing and deformation recovery capabilities. High temperature from service conditions will have important effects on the mechanical properties of thermal protection materials. In this paper, compression tests including loading and unloading stages were conducted for ceramic fiber reinforced silica aerogel composites at room temperature and elevated temperatures (300°C, 600°C and 900°C). Influences of thermal exposure to high temperature and high temperature service environment on the compression property and deformation recovery were both investigated. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were applied to help understand the mechanisms of mechanical property variations. The experimental results show that the compression modulus and strength both increase with the increasing thermal exposure temperature and testing temperature, but the deformation recovery capability decreases. The microstructure changes caused by thermal sintering are considered as the main reason for the property variations. Viscous flow and matter transport due to high temperature resulted in the fusion of aerogel particles. This made the particle skeleton thicker and stronger, which led to higher stiffness and strength of the composites. However, matrix cracks induced by the formation and fracture of larger pores made unrecoverable deformation more serious. In the tests at elevated temperatures, the aggregation of aerogel particles in a fused state got more severe because of the addition of mechanical load. As a result, the degradation of deformation recovery capability became more significant.