Oxygen adsorption on ideal ZrB2 and ZrC surfaces

To understand the initial oxidation of ZrB2 and ZrC, the adsorption behaviors of an O-2 molecule on ideal ZrC (1 1 1) and ZrB2 (0 0 0 1) surfaces were investigated by first-principle calculation, and thermal gravimetric and differential scanning calorimetry test was executed. The results reveal that the initial oxidation temperature of ZrC was 210 degrees C, while that of ZrB2 was up to 500 degrees C since the adsorption energies of O-2 molecule on Zr-ZrC surface was higher than that on Zr-ZrB2 surface. Meanwhile, the adsorbed O-2 molecule affected the C atom bonding with the oxidized Zr atom in O-Zr-ZrC, while the B atom bonding with oxidized Zr atom in O-Zr-ZrB2 underwent little influence. Besides, the higher adsorption energy was obtained in O-C-ZrC than in O-B-ZrB2, implying that the C atom in C-ZrC might be oxidized more easily than the B atom in B-ZrB2. In addition, big holes (C vacancies) were formed when O-2 molecule adsorbed on the C-ZrC surface because of the generation of C-C dimer and C-O bond, which led to that the next O-2 molecule might penetrate the Zr atomic layer and react with the Zr atoms. While O-2 molecule doped into the B atomic layer in B-ZrB2, and more O-2 molecules might be adsorbed on the B-ZrB2 surface to generate a B2O3 structure to protect the inner material. (C) 2020 Elsevier B.V. All rights reserved.