Hydrothermal Corrosion Resistance of Reaction-Bonded SiC Ceramic: Synergistic Enhancement by Homogeneous MoSi₂...

Reaction-bonded SiC (RBSC) ceramics exhibit limited hydrothermal corrosion resistance due to the presence of residual silicon. This study presents a strategy to enhance the corrosion resistance of RBSC through homogeneous incorporation of MoSi₂ and concurrent reduction in residual silicon content. Three material systems were fabricated via reactive melt infiltration: conventional RBSC with a SiC/C preform (SC), a SiC-MoSi₂ composite incorporating commercial Mo₂C powder via physical mixing (MC), and a SiC-MoSi₂ composite derived from a Mo₂C/C precursor synthesized by a molten salt method (MS). The Mo₂C/C composite synthesized at 1150 °C exhibited fine, uniformly distributed Mo₂C particles coated on carbon black, contrasting with the agglomerated distribution in commercial Mo₂C mixtures. During reactive sintering at 1600 °C, Mo₂C reacted with molten Si to form MoSi₂, reducing residual Si content. Sample MS achieved the lowest residual Si (8.77 ± 0.45 vol.%), followed by MC (12.43 ± 0.86 vol.%) and SC (19.17 ± 1.01 vol.%). All samples achieved near-full densification (open porosity < 0.1%), with bulk densities of 2.96 ± 0.05, 3.03 ± 0.03, and 3.07 ± 0.03 g/cm³ for SC, MC, and MS, respectively. Microstructurally, MS displayed homogeneous MoSi₂ dispersion, while MC showed partial MoSi₂ aggregation, and SC contained continuous residual Si regions. Hydrothermal corrosion tests at 345 °C and 15 MPa for 9 days demonstrated that corrosion resistance followed the order MS > MC > SC. After 9 days, weight loss was 22.3970 ± 1.2059 mg/cm² (SC), 17.6370 ± 0.8266 mg/cm² (MC), and 15.4347 ± 0.7807 mg/cm² (MS), with corrosion depths of 393.17 ± 27.46, 267.40 ± 24.44, and 224.60 ± 25.13 μm, respectively. The enhanced performance of MS arises from two synergistic factors: reduced residual Si minimizes large corrosion pores, while uniform distribution of MoSi₂ facilitates the formation of a stable, dissolution-resistant composite oxide layer composed of MoO₃ and SiO₂, in which MoO₃ restrains excessive dissolution of SiO₂ through a pinning effect. These findings demonstrate that combining residual Si reduction with homogeneous MoSi₂ incorporation via molten salt-synthesized precursors offers an effective strategy for improving hydrothermal corrosion resistance of reaction-bonded SiC-based materials for applications in high-temperature and high-pressure aqueous environments such as nuclear water reactors.