Preparation and properties of situ-sintered SiC ceramics aided by ZnO-Al2O3-CaO

•ZAC (ZnO-Al2O3-CaO) sintering additives contribute to the low-temperature sintering of SiC matrix composite ceramic.•The SiC-ZAC composite ceramic is a potential material for immobilizing the simulated radioactive graphite.•The SiC-ZAC composite ceramics have a high chemical stability. The safe treatment and disposal of radioactive graphite waste is becoming an important issue worldwide. The objective of this paper is to prepare the SiC-ZAC (ZAC: ZnO-Al2O3-CaO) composite ceramic for immobilizing radioactive graphite, where ZAC is as sintering additives. The effects of the sintering system and ZAC content on the phase compositions, microstructure, and properties of SiC-ZAC composite ceramic are studied by XRD, SEM-EDS, TEM-EDS, linear shrinkage, Vickers hardness, and thermal conductivity. By vacuum hot pressing sintering at 1600 °C for 1 h, the results show that the S-35-1600 (65 wt% SiC, 10.5 wt% ZnO, 15.72 wt% Al2O3, 8.78 wt% CaO) sample is the potentially applicable formula composition due to its better performance, in which the Vickers hardness and the thermal conductivity are 165.2 HV10, 14.6 W m−1 k−1 respectively, and the normalized elemental mass loss of Si, Al and Ca are 0.0064–0.0108 g/m2, 21.4784–24.7837 g/m2, 56.9108–67.5637 g/m2 after 42 days at pH = 5/7/9 solution, respectively. Importantly, ZAC sintering additives can form the bond phases of CaAl4O7, CaAl2O4, Ca3Al2(OH)12, and Ca2Al2SiO7 under relatively low temperatures to reduce the sintering temperature for SiC ceramics. Meanwhile, the existing form of the Zn element is revealed: one part of the Zn forms glass phase, and the other part volatilized by carbothermic reduction.