SELF-CONSISTENT KINETIC-MODEL OF LOW-PRESSURE N-2-H-2 FLOWING DISCHARGES - II - SURFACE PROCESSES AND DENSITITES OF N, H, NH3 SPECIES

This work is the second of two companion papers devoted to the kinetic modelling of low-pressure DG flowing discharges in N-2-H-2 mixtures. White the first paper was mainly concerned with bulk discharge process es, the present one investigates surface processes involving dissociat ed N and H atoms, which are essential to understand the discharge prop erties. The kinetic model for surface processes developed here takes i nto account: (a) physical adsorption and desorption of N and H atoms; (b) chemical adsorption and desorption of both types of atoms at vacan t chemically active sites on the surface; (c) surface diffusion of phy sisorbed N-f and H-f atoms; (d) the reactions of chemisorbed N-s and H -s atoms with gas phase N and H atoms and with physisorbed N-f and H-f atoms, leading to the formation of gas phase N-2, H-2 and chemisorbed (NH)(s) molecules. The latter molecules can either be desorbed or rea ct with H, H-s, H-2 to produce gas phase NH, NH2 and NH3 molecules. Th e probability of wall losses for N, H, NH, NH2 and the rates for wall production of NH, NH2, NH3 have been obtained for Pyrex glass as a fun ction of the wall temperature and the relative concentrations of N, H, NH, NH2, H-2. A number of important parameters for surface processes have been estimated from detailed analysis of experimental data. Measu rements of relative changes in N, H and NH3 concentrations in N-2-H-2 discharges as a function of the H-2 percentage have been interpreted i n terms of the model.