B2O3 Modulating Glass Network Structure and Medium Permeation Behavior: Long-Term Corrosion Protection Performance of a Glass-Ceramic/Fluororesin Laminated Coating on Steel Substrate

A B 2 O 3 -doped glass-ceramic/fluororesin (Gc/ECTFE) laminated coating was developed for long-term corrosion protection of steel substrates. The relationship between B 2 O 3 content, glass-network structure, and barrier performance was investigated through microstructural characterization, corrosion behavior tests, and molecular dynamics simulations. At the optimal B 2 O 3 content (5 wt%), B 3+ was predominantly incorporated into the siloxane network as [BO 4 ] tetrahedra, enhancing glass-network polymerization, densification, and SiO 2 crystallization to form a compact and stable barrier structure. In contrast, excessive B 2 O 3 (≥ 10 wt%) increased [BO 3 ] units, causing network loosening and reduced protection. After 90 days in 3.5 wt% NaCl solution, the 5-Gc/ECTFE coating exhibited the highest corrosion resistance, with R ct = 3.765 × 10 4 Ω·cm 2 , nearly three orders of magnitude higher than that of the undoped system. Simulations revealed the lowest diffusion coefficients for H 2 O and Cl − (2.743 × 10 −8 and 9.771 × 10 −9 m 2 ·s −1 ), confirming from diffusion kinetics that the dense glass network effectively suppresses corrosive-medium permeation and improves long-term barrier durability.