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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)×1015 cm−3 in pure N2 at 2600 Pa (20 Torr) and in Ar–10%N2 up to 2.6×104 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 1014 cm−3 in Ar–1%H2O were obtained, which is 10 and 50 times higher than in Ar–H2 and N2–H2O, respectively. By NO titration, densities of N and O atoms were measured in N2–xO2 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 N2–5%O2 gas mixture at 650 Pa (5 Torr), 1 slm, and 100 W, an O atom density of (2–3)×1015 cm−3 and an emission intensity of the NOβ–UV 320 nm band were measured. Densities of N and C atoms were also measured by NO titration and spectroscopy of chemiluminescent reactions in N2–xCH4 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 N2–0.05%CH4 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 2×1015 cm−3 for N atoms and (3–4)×1012 cm−3 for C atoms were measured in the postdischarge tube of 2.6-cm i.d., 60-cm length. |
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