Thermal Stress Analysis of Ceramic Pellets for Catalysis

One of the most critical phenomena that limits the lifetime of ceramic catalysts for H2O2 decomposition is represented by substrate break-up as a consequence of thermal shocking. In a recent experimental campaign conducted by Alta S.p.A., Pisa, Italy, fracture of the ceramic support occurred in a Pt/γ–Al2O3 catalytic bed. Because of the catalyst rupture, the onset of a number of flow instabilities and the marked increase of the pressure drop in the decomposition bed led to a severe decrease of the engine thrust. In order to take proper action for enhancing the thermal shock resistance of the catalyst bed it has been necessary to better understand the dynamics of the heat transfer between the decomposing propellant and the catalyst support. In this work a reduced order model of the thermal transient and the associated thermal stresses in the catalyst pellets is presented. The indications provided by the model have therefore been used for orienting the selection of a suitable catalyst carrier and the development of a new Pt/α–Al2O3 catalyst, here indicated as LR-III-127. Its strength and propulsive performance have been experimentally evaluated under realistic working conditions in a HTP thruster prototype. After the decomposition of 1.5 kg of H2O2 (90% by weight) the LR-III-127 catalyst displayed a low susceptibility to thermal cracking and outstanding performance in terms of decomposition efficiency.