Novel Kinetic Model for Chemical Energy Accommodation on Silica Surface

Abstract

A new phenomenological catalysis model for silica surfaces has been developed, the main feature of which is the capability of accounting for chemical energy accommodation, i.e., the effective transfer of chemical energy to the catalyst surface by catalytically formed molecules. In this new model, the interaction time between just-formed molecules and the surface is comparable with the time of other processes. The efficiency of the interaction depends on the coupling between the molecules interaction time prior to desorption and the phonons frequency distribution (characteristic period of surface vibration). The features of this interaction should lead to coupling with surface vibration modes and thus, transfer energy from just-recombined species to the surface lattice via phonons. To this aim, a new three-dimensional model of the interaction potential between the surface atoms and the impacting atom has been built and used inside the bulk structure of crystalline silica. The evaluation of a suitable potential function is of fundamental importance; it defines the surface sites in correspondence of which the gas atoms will probably create a chemical bond with the surface, and most of the kinetic model parameters depend on them. Finally, the model has been validated using data collected during a test campaign in the SCIROCCO plasma wind tunnel on a full-scale spacecraft component.