Preparation and characterization of SiC-ZAC composite material for immobilizing the simulated radioactive graphite

Abstract For the safe treatment and disposal of radioactive graphite, SiC-ZAC (ZAC: ZnO-Al2O3-CaO glass-ceramic) composite materials were designed, in which ZAC is used as a sintering additive. The performance of ZAC was firstly studied by ASTM C1285 leaching test to obtain a formula composition with high chemical stability. Then, using the optimized formula of ZAC, the SiC-ZAC composites were prepared by vacuum calcination at 1350 °C–1410 °C for the immobilizing of simulated radioactive graphite, and the structure and compositions of SiC-ZAC composites were studied by XRD, SEM, EDS. The material Gibbs free energy function method was used to calculate the thermodynamics of SiC-ZAC composites to investigate the reaction ways among Si, C and ZAC. The results show the Z30 (30 wt% ZnO, 44.91 wt% Al2O3, 25.09 wt% CaO) glass-ceramic is the applicable formula composition due to its high chemical stability, in which the normalized elemental mass loss of Zn, Al, Ca are 10−6g/m2-10−5 g/m2, 10−1 g/m2, 10−1 g/m2 respectively. Calcined at 1350 °C for 2 h, the B-Z30(0)-1(70.05 wt% Si, 29.95 wt% C) sample can be obtained with the phase compositions of β-SiC, α-SiC and a small amount of residual graphite. Moreover, the formations of Ca2Al2SiO7 and CaAl4O7 crystalline phase had a negative effect on the immobilization of simulated radioactive graphite in SiC-ZAC composites.