Production of N, H, O, and C atoms in flowing microwave discharges

Abstract

Several optical diagnostic methods have been used to determine the N, H, O, and C atom densities in flowing microwave postdischarge reactors. By using TALIF laser diagnostics in the postdischarges, N atom densities of (1–5)×10 15 cm −3 in pure N 2 at 2600 Pa (20 Torr) and in Ar–10%N 2 up to 2.6×10 4 Pa (200 Torr) have been obtained after a microwave discharge of 100 W in a quartz tube of 5 mm i.d, with a flow rate of 2 slm and injection inside a stainless reactor of 70 l. In conditions of discharges at 100 W, 1.4 slm, and 1300 Pa (10 Torr), H atom densities of about 10 14 cm −3 in Ar–1%H 2O were obtained, which is 10 and 50 times higher than in Ar–H 2 and N 2–H 2O, respectively. By NO titration, densities of N and O atoms were measured in N 2– xO 2 gas mixtures, with x less than 10 at.%. In conditions of the best results of postdischarge sterilization: decrease of 12 log of E. coli bacteria inside a Pyrex reactor of 5 l with a N 2–5%O 2 gas mixture at 650 Pa (5 Torr), 1 slm, and 100 W, an O atom density of (2–3)×10 15 cm −3 and an emission intensity of the NO β–UV 320 nm band were measured. Densities of N and C atoms were also measured by NO titration and spectroscopy of chemiluminescent reactions in N 2– xCH 4 postdischarges, with x less than 1 at.%. Iron nitriding with an ɛ+ γ′ layer of 5–6 μm including 1 at.% of carbon atoms was obtained by using a N 2–0.05%CH 4 gas mixture at 4160 Pa (32 Torr), 1 slm, 150 W, a substrate temperature of 823 K, and a treatment time of 2 h. In these conditions, densities of about 2×10 15 cm −3 for N atoms and (3–4)×10 12 cm −3 for C atoms were measured in the postdischarge tube of 2.6-cm i.d., 60-cm length.