To achieve high oxygen blocking structure of the ZrB₂-MoSi₂ coating applied on carbon structural material, ZrB₂-MoSi₂ coating was prepared by spark plasma sintering (SPS) method utilizing ZrB₂-MoSi₂ composite powders synthesized by self-propagating high-temperature synthesis (SHS) technique as raw materials. The oxygen blocking mechanism of the ZrB₂-MoSi₂ coatings at 1973 K was investigated. Compared with commercial powders, the coatings prepared by SHS powders exhibited superior density and inferior oxidation activity, which significantly heightened the structural oxygen blocking ability of the coatings in the active oxidation stage, thus characterizing higher oxidation protection efficiency. The rise of MoSi₂ content facilitated the dispersion of transition metal oxide nanocrystals (5-20 nm) in the SiO₂ glass layer and conduced to the increasing viscosity, thus strengthening the inerting impact of the compound glass layer in the inert oxidation stage. Nevertheless, the ZrB₂-40 vol%MoSi₂ coating sample prepared by SHS powders presented the lowest oxygen permeability of 0.3% and carbon loss rate of 0.29×10^-6 g·cm^-2·s^-1. Owing to the gradient oxygen partial pressure inside the coatings, the Si-depleted layer was developed under the compound glass layer, which brought about acute oxygen erosion.

TaB₂-SiC coating modified by different content of MoSi₂ was fabricated on graphite substrate with SiC inner coating by liquid phase sintering to elevate the anti-oxidation capability of the TaB₂-SiC coatings. As compared to the sample with the TaB₂-40wt%SiC coating, the coating sample modified with MoSi₂ exhibited a weight gain trend at lower temperatures, the fastest weight loss rate went down by 76%, and the relative oxygen permeability value reduced from about 1% to near 0. More importantly, the large amount of SiO₂ glass phase produced over the coating during oxidation was in contact with the modification of MoSi₂, which was proved to be beneficial to the dispersion of Ta-oxides. A concomitantly formed continuous Ta-Si-O-B compound glass layer showed excellent capacity to prevent oxygen penetration. However, when the TaB₂ content was sacrificed to increase the MoSi₂ content, the relative oxygen permeability of the coating increased instead of decreased. Thus, on the basis of ample TaB₂ content, increasing the MoSi₂ content of the coating is conducive to reducing the relative oxygen permeability of the coatings in a broad temperature region.