Active species in microwave postdischarge for steel-surface nitriding

Production of nitrogen atoms has been studied in a 2.45-GHz flowing postdischarge in N/sub 2/ and N/sub 2/-H/sub 2/ gas mixtures with Ar as a buffer gas in the high-pressure regime (5*10/sup 3/ to 6.5*10/sup 4/ Pa). N atom densities have been measured by NO titration in the 10/sup 14/-10/sup 15/ cm/sup 3/ range and monitored by the first positive emission resulting from the N atom recombination. The rate coefficient of the N+N+N/sub 2/ recombination has been found to be /sub k/=6*10/sup -33/ cm/sup 6/ atom/sup -2/ s/sup -1/ at T/sub 0/=300 K, which agrees with previously published data. The N atom production (or degree of N/N/sub 2/ dissociation) in front of an Fe-0.1%C substrate correlates well with the thickness of a gamma ' Fe/sub 4/N layer produced by the postdischarge treatment. The H/sub 2/ gas was first introduced in the initial phase of treatment to remove surface oxidizing and then was cut off to keep high densities of N atoms. It is deduced that N atoms are more active nitriding species than NH-type radicals.<
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