Internal Catalyst Breakup Phenomena

The use of hydrazine catalytic reactors for a wide variety of extended life missions is presently limited by degradation of the catalyst particles as evidenced by breakup of the particles. Fracturing of a catalyst particle can be caused by large pressure gradients or thermal stresses within the particle which cannot be supported by the porous structure. In previous studies, wetting by liquid hydrazine had been shown to lead to gas pressure buildup in catalyst particles, followed, under some conditions, by particle fracture. In this experimental study, individual Shell 405 catalyst particles of various size and history were mounted in a flow reactor in which the effects of hydrazine temperature, flow velocity, and exposure time on wetting and breakup could be determined. Particle wetting has been found to be strongly controlled by liquid hydrazine temperature; greatest wetting and most frequent breakup occur in particles exposed to lowest hydrazine temperatures. Tests of catalyst exposed to contaminants or decomposition product poisons indicated that in most cases activity was decreased and breakage was increased. The effects of thermal shock and thermal cycling were examined in a series of screening tests by rapid heating and cooling of particles. Single and multiple cycles were applied to individual particles.