In-situ oxide scale investigation of Sm-doped ZrB2/SiC Billets

Abstract

Samarium-doped zirconium diboride/silicon carbide (Sm-ZBS) ceramics possess an emittance of 0.9 at 1600 °C and develop oxide scales that have excellent ablation performance. This study investigates the oxide scale development of 3 mol% doped Sm-ZBS which contains 80 vol% ZrB2 and 20 vol% SiC when exposed to temperatures in excess of 1800 °C in an oxidizing atmosphere. Samples were prepared via chemical infiltration of samarium nitrate into spray-dried powders of 80 vol.% ZrB2/20 vol.% SiC; powders were then pressed into billets and sintered without pressure. Samples cut from these billets were then oxidized for 10, 60, and 300 s, respectively, using an oxyacetylene torch. A Sm-depletion region was observed and believed to form due to glass transport to the surface. X-ray diffraction was used to determine the sequence of oxidation of Sm-ZBS, beginning with the formation of ZrO2 and Sm2O3. The final oxide scale was determined to be c1-Sm0.2Zr0.8O1.9, with a melting temperature exceeding 2500 °C. SEM and EDS were also used to investigate microstructural formation due to the bursting of convection cells.