CeO2 as a novel additive for enhancing the oxidation resistance of ZrB2–SiC ultra-high temperature ceramics: role of Ce-mediated ZrSiO4 formation

We report CeO2 as an additive for tuning oxidation behaviour of ZrB2-SiC ultra-high temperature ceramics (UHTCs). Four compositions were compared: AlN-only, AlN-CeO2 co-doped, and two CeO2-only compositions with different SiC contents. Samples consolidated by spark plasma sintering (96-99% density) were oxidised in stagnant air at 1600 °C for up to 10 h. Ce-bearing compositions consistently outperformed the AlN-only reference. The co-doped sample showed the greatest improvement: mass gain reduced from 58 to 40 mg cm-2, oxide thickness from 1388 to 550 μm, and the SiO2-rich surface layer increased from ~5 to 82 μm. EDS-PhaSe analysis identified significant ZrSiO4 formation across Ce-containing samples. CeO2 appears to operate at two scales: enhancing borosilicate melt spreading to form a continuous surface barrier and promoting subsurface ZrSiO4 formation. CeO2, particularly combined with AlN, represents a promising strategy for improving oxidation resistance in ZrB2-SiC UHTCs.