Hydroxyl-induced fluorine substitution in low dielectric all-inorganic silica composites for high fidelity communication cables under extreme environments

Abstract

All-inorganic quartz fiber reinforced silica with high temperature stability is a promising low dielectric material for high-fidelity communication cables in extreme environments. However, its dielectric properties are constrained by the inherent polarizable -Si-O- and -Si-OH, driving the urgent exploration of silica-based low-dielectric materials that go beyond merely adjusting the porous structure. Herein, a fluorine-substituted silica/quartz fiber composite (FS–SiO₂) is generated by developing an in situ vapor fluorine substitution (termed VFS) strategy. During the substitution process, highly polarizable -Si-OH of fluorosilane-modified SiO₂ is replaced with low-polarizability -Si-F bonds through a simple thermal treatment at 600 °C. As a result, the dielectric constant and loss were highly reduced to be 1.74 and 1.00 × 10⁻² at 20 MHz. The communication cable with the FS-SiO₂ dielectric layer exhibited a significantly low attenuation of 0.74 dB/m at the frequency of 12 GHz, outperforming the cable using pure silica/quartz fiber composites with the attenuation of 1.55 dB/m. Furthermore, the cable's attenuation and VSWR remained nearly constant even after ten thermal cycles at 550 °C or 4 h of operation at 300 °C.