High-temperature oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 ceramics up to 1700°C in air

Abstract

The high-temperature oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 ceramics up to 1700°C in air has shown their high corrosion resistance. A five-stage nonisothermal oxidation mechanism is established for the samples when heated at a rate of 20°C/min: 1) oxygen adsorption–desorption; 2) formation of ZrO2 and B2O3 oxides; 3) formation of α-SiO2 cristobalite and ZrSiO4 zircon; 4) formation of amorphous SiO2; and 5) formation of upper protective borosilicate film with ZrSiO4 inclusions at less than 40 wt.% SiC. It is shown that small ZrSi2 admixtures (<6–8 wt.%) substantially slow down the oxidation of the ceramics in initial heating stages due to diffusion-hindered formation of ZrO2 and B2O3. The 67.3 wt.% ZrB2–26 wt.% SiC–6.7 wt.% ZrSi2 ceramics are characterized by the highest corrosion resistance since their upper scale layer represents borosilicate glass stabilized with ZrO2 (tetragonal) inclusions.