NITROGEN-ATOMS IN AR-N2 FLOWING MICROWAVE DISCHARGES FOR STEEL SURFACE NITRIDING

High nitrogen atom densities (10(15)-10(16) cm-3) have been produced in high pressure (20-760 Torr) Ar-N2 flowing post-discharges. Gas ionization is performed by 2.45 GHz surfatron and surfaguide exciters with 100-200 W transmitted power. Nitrogen atoms have been measured by NO titration and by the absolute intensities of the first positive system of N2 in the afterglow. From kinetics analysis the nitrogen atom recombination rate coefficient has been found to decrease with gas temperature from (4 +/- 1) x 10(-33) cm6 s-1 at T0 = 296 K to 1.3 x 10(-33) cm6 s-1 at T0 = 600 K. The nitrogen atom density remains constant within a factor of 2 at T = 700 K. An increase of gamma'-Fe4N coating thickness with nitrogen atom density in the post-discharge reactor is reported.