Speaker
Description
The development of plasma nitrocarburizing processes for steel treatment is important for establishing of an environmentally friendly heat treatment process. One of the strategies is to apply the main discharge power on a so-called active screen (AS). The AS surrounding the workload provides heat and reactive species to the workload. The treatment conditions are controlled by the discharge power and feed gas composition. However, the chemical composition in the reactor is also influenced by the pre-history of the reactor due to undesired surface reactions on the reactor walls that might compromise the process control. The current work reports on the time evolution of $HCN$ production in an active screen plasma nitrocarburizing (ASPN) reactor with a steel AS. Three sets of measurements were performed. Each set starts with a discharge in a $N_2-H_2$ gas mixture with the addition of 10% of $CH_4$ for one hour. In the following three hours, the $CH_4$ flow was replace by 6% or 2% of $O_2$ flow in sets 1 and 2, and in set 3 a pure $N_2-H_2$ gas mixture was used. The concentration of $HCN$ molecules, which are assumed responsible for the nitrocarburizing effect, was determined inside the ASPN reactor by quantum cascade laser absorption spectroscopy. The stabilization of the $HCN$ production was characterized by three time-constants. The fastest time-constant (1-4 min) was associated with the gas residence time in the reactor, the second time-constant (about 20 min) was related to surface reactions on the AS and third one (about 3 hour) most probably reflects the surface reactions on the cold reactor walls. The work indicates the importance of monitoring the gas composition during a plasma nitrocarburizing process to maintain defined treatment conditions.
| Speaker Country | Germany |
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| Register for the Tom Bell Young Author Award (TBYAA)? | No |
