In-situ ZrB2@SiO2 core-shell construction for high oxygen-barrier ZrB2-SiC coatings with continuous oxygen-barrier networks at 1973 K

In situ SiO 2 shells pre-establish oxygen-barrier networks in ZrB 2 -SiC coatings. • Core-shell ZrB 2 @SiO 2 improves interfacial continuity and particle packing. • Pre-positioned SiO 2 accelerates early-stage oxygen-barrier formation. • ZrO 2 and ZrSiO 4 dispersoids stabilize the borosilicate glass matrix. • ZrB 2 @SiO 2 -SiC lowers mass gain by 69% and gives 99.82% protection. Conventional ZrB 2 -based coatings rely on amorphous phases generated during oxidation to seal coating defects, which delays the establishment of an effective oxygen barrier. Here, an amorphous SiO 2 shell was constructed in situ on ZrB 2 particles through a sol-gel process, and the resulting core-shell powders were combined with SiC to prepare ZrB 2 @SiO 2 -SiC coatings. SiO 2 -free ZrB 2 -SiC and mechanically mixed ZrB 2 -SiO 2 -SiC were used as reference systems to distinguish the effect of SiO 2 incorporation from that of the core-shell configuration. Compared with the mechanically mixed system, the shell-derived phase became interconnected along ZrB 2 particle boundaries during sintering, improving interfacial continuity and suppressing particle agglomeration. During oxidation, this pre-connected SiO 2 phase combined with B 2 O 3 and SiO 2 generated by the oxidation of ZrB 2 and SiC, respectively, to promote the rapid formation and subsequent replenishment of a borosilicate glass network, while dispersed ZrO 2 and ZrSiO 4 helped preserve the continuity and structural stability of the resulting oxide scale. At 1973 K, this structure reduced the maximum mass gain to 0.62 × 10 −2  g·cm −2 , about 69% lower than that of the SiO 2 -free ZrB 2 -SiC system, and decreased the initial oxygen permeability by 83.23%, with the protection efficiency ultimately reaching 99.82%. This work provides an interface pre-encapsulation route for constructing continuous oxygen-barrier networks in ultra-high-temperature ceramic coatings.