Microstructure analysis of quartz fiber reinforced SiO2 matrix composites by X-ray computed tomography

This paper presents the microstructure of quartz fiber reinforced SiO2 matrix (SiO2f/SiO2) wave-transparent composites characterized by X-ray computed tomography (XCT) and the impregnation of silica sol by conducting permeability and pore network model analyses. Results show that in 2.5D woven structural preform silica gel mainly flowed along the extension direction of weft yarns during impregnation, and the permeability rate in this direction reached 368.49μm2. Attributing to the large pore size, large throat radius and good pore connectivity, impregnation of this preform was more uniform, resulting in a small final porosity of the composite (2.32%). Comparatively speaking, in stitched structural preform silica sol flowed primarily between the layers of fiber cloths, achieving a maximum permeability rate of 36.47μm2, but along the direction of stitching fiber yarns permeability rate was only 5.23μm2. Small throat radius and pore size of fiber preform led to poor impregnation effect and a total porosity of 11.85%. Preform structure plays a crucial role in the densification process of SiO2f/SiO2 composites prepared by sol-gel method. •Morphology characteristics and phase distribution of two types of SiO2f/SiO2 composites were observed.•Permeability and pore characteristics of fiber preforms were discussed.•Preform structure plays a crucial role in the densification process of SiO2f/SiO2 composites prepared by sol-gel method.•XCT has significant advantages in exploring the microstructure and anisotropy of fiber-reinforced composites.