Preparation of ZrB₂-MoSi₂ high oxygen resistant coating using nonequilibrium state powders by self-propagating high-temperature synthesis

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.