Synthesis and high-temperature oxidation of a polymer-derived Mo-SiN based ceramic composite

Si3N4 ceramics strengthened with molybdenum silicides seem to be potential candidates for (ultra-)high temperature applications. While Mo5Si3 exhibits a higher melting point and a better creep resistance than MoSi2, its oxidation resistance is inferior due to accelerated pest oxidation at 700 °C in air.In order to protect Mo5Si3/Si3N4 ceramic composites from pesting, in this work a composite material was developed using the inorganic precursor PHPS loaded with Mo particles as active filler. After pyrolysis, the resulting ceramic composite was coated with PHPS to generate a protective SiO2 layer before the oxidation of Mo5Si3 starts.The results demonstrated the in-situ formation of the silicide phase during pyrolysis at temperatures up to 1500 °C via solid-state reaction of the formed amorphous SiN phase and the Mo particles. As intended, the coated Mo5Si3/Si3N4 ceramic composites exhibit a remarkably increased oxidation resistance up to 700 °C compared to the uncoated material.