1 AN INVESTIGATION UPON THE CATALYTIC AND RADIATIVE BEHAVIORS OF ZrB 2 -SiC ULTRA HIGH TEMPERATURE CERAMIC COMPOSITES L. Scatteia (1) , G. Cosentino (1) , S. Cantoni (1) , M. Balat-Pichelin (2) , E. Beche (2) , J.L. Sans (2) (1) CIRA – Italian Aerospace Research Centre, Via Maiorise snc 81043 Capua (CE) Italy – l. scatteia@cira.it (2) PROMES-CNRS Laboratory, Font-Romeu Odeillo, 66120, France ABSTRACT In this paper, the results of an experimental investigation into the efficiency of sintered ZrB 2 -SiC compounds and of plasma-sprayed ZrB 2 -SiC coating for heat radiation and for the recombination of atomic oxygen are reported. Total hemispherical emissivity and recombination coefficient for atomic oxygen in the range 1000-1800 K were measured. The characterization campaign was conducted using the MEDIASE and MESOX facilities developed at the PROMES-CNRS laboratory. Microstructural analysis prior and after the high temperature exposure into the MEDIASE and MESOX apparati were also carried out using XPS, DRX and SEM. High emissivity values and low recombination coefficients were found in agreement with previous experimental studies performed on similar ceramic compounds but at lower temperatures using a different measurement technique. Samples post-analysis highlighted the oxidation-induced surface modification, and the dependence of the radiative behavior upon these modifications. 1. INTRODUCTION Emissivity and catalycity represent key parameters for the eligibility of non-conventional Ultra High Temperatures Ceramic materials in hot structures manufacturing. Reliable experimental evaluations of these parameters are required to feed aero-convective heating computations (that, in absence of experimental data, have to rely on extremely conservative theoretical values), and extrapolate the structure performance in real re-entry conditions from on-ground test data obtained in arc-jet facilities. Many studies on radiative properties and catalytic behavior have been performed on a variety of structural and thermal protection system materials. However, little data are available for UHTC materials and their oxides. In particular, in a work of Marschall et al [1], the catalytic atom recombination on ZrB 2 -SiC and HfB 2 - SiC of oxygen and nitrogen was evaluated, from room temperature up to 1000 K. In that study, the recombination coefficient was found non negligible (∼5⋅10 -2 ), and dependant upon the surface oxidation of the material. Within the frame of the Sharp Hot Structures project [2], promoted by Italian Aerospace Research Centre and aimed at demonstrating new hot structures concept based on UHTC materials, a dedicated research activity was conducted in cooperation with CNRS-PROMES centre to investigate the radiative properties and the catalytic efficiency related to atomic oxygen recombination reaction at high temperatures of sintered and plasma sprayed ZrB 2 -SiC designed for slender- shaped leading edges The study is focused on a high temperature regime (from 1000 to 1800 K) that was achieved using the solar furnaces and associated facilities “Moyen d'Essai et de DIagnostic en Ambiance Spatiale Extrême” (MEDIASE) and “Moyen d'Essai Solaire d'Oxydation” (MESOX) available at PROMES-CNRS laboratory in France[3,4]. Total hemispherical emissivity and recombination coefficient for atomic oxygen were characterized in the range 1000-1800 K. Supportive micro-structural analyses were carried out on post-test samples in order to correlate the obtained results to the surface modifications occurring in the material during high temperature exposure. 2. MATERIALS AND EXPERIMENTAL METHODS 2.1 Materials Dense sintered UHTC samples were obtained by hot isostatic pressing of ZrB 2 powders with SiC, using MoSi 2 as a sintering aid to lower the temperature of the process. The process was conducted by the National Research Council Institute for Ceramic Materials located in Faenza, Italy. The obtained material has a density of 5.61 g/cm 3 which, on the basis of the rule of mixture, is higher than 99 % of the theoretical density. The material was cut and shaped in billets of 25 mm diameter and 2 mm thickness for catalycity ________________________________________________________________ Proceedings 5 th European Workshop on Thermal Protection Systems and Hot Structures Noordwijk, The Netherlands, 17 - 19 May 2006 (ESA SP-631, August 2006)