Ultra-High-Temperature Ceramic (UHTC) materials, because of their high temperature resistance, are suitable as thermal protection systems for re-entry vehicles or components for space propulsion. Massive UHTC materials are characterized by poor thermal shock resistance, which may be overcome using C or SiC fibers in a UHTC matrix (UHTCMC).\ud \ud The University of Naples “Federico II” has a proven experience in the field of material characterization in high-enthalpy environments. A hypersonic arc-jet facility allows performing tests in simulated atmospheric re-entry conditions. The Aerospace Propulsion Laboratory is employed for testing rocket components in a representative combustion environment. Ad-hoc computational models are developed to characterize the flow field in both facilities and perform thermal analysis of solid samples.\ud Current research programs are related to a new-class of UHTCMC materials, for rocket nozzles and thermal protection systems. The activities include design of the prototypes for the test campaign, numerical simulations and materials characterizations

Ultra-high temperature ceramic matrix composites based on a ZrB₂/SiC matrix have been investigated for the fabrication of reusable nozzles for propulsion. Three De Laval nozzle prototypes, obtained by sintering with either hot pressing or spark plasma sintering, were tested 2-3 times in a hybrid rocket motor for proving reusability. Sections were extracted after oxidation tests to study the microstructural changes and oxidative and thermomechanical stresses induced by the repeated tests. Compared to a reference graphite nozzle, no measurable erosion was observed for the UHTCMC-based nozzles. The oxidation mechanism consisted in the formation of a ZrO₂ intermediate layer, with a liquid SiO₂ layer on the surface that was displaced by the action of the gas flux towards the divergent part of the nozzle, protecting it from further oxidation. Both specimens obtained by HP and SPS displayed similar performance, with very slight differences which were attributed to small changes in porosity. These tests demonstrated the capability of complex-shaped prototypes made of the developed UHTCMC to survive repeated exposure to environments representative of a realistic space propulsion application, for an overall operating time up to 30 s, without any failure nor measurable erosion, making a promising step towards the development of reusable rocket components.