Effect of excitation states of nitrogen on the surface nitridation of iron and steel in d.c. glow discharge plasma

Abstract

The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow-discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N 2 * ) or nitrogen molecule ions (N 2 + ). The optical emission spectra suggested that the formation of N 2 * -rich or N 2 + -rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N 2 + -rich plasma had a much higher nitrogen concentration than that by a N 2 * -rich plasma, likely due to the larger chemical activity of the N 2 + species as well as the N 2 + sputtering bombardment to the cathode surface. The strong reactivity of the N 2 + species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N 2 + -rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N 2 * -rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination.

Parameter settings in a compact laser‐nitriding system for titanium composed of a focused pulsed Nd:YAG laser and nitrogen gas blow

“…Here, the flow rate of the nitrogen gas blow was set to 30 L min −1 . All the intense emission lines observed in the spectra can be assigned to Ti II, whereas the major lines corresponding to nitrogen molecules such as the band heads of N 2 * (337.1 nm) and N 2 + (391.4 nm) cannot be found . Laser‐induced plasma in air is made up mainly of singly ionized nitrogen (N II), whereas the corresponding emission appearing at 399.5 nm was not found in Figure .…”

“…All the intense emission lines observed in the spectra can be assigned to Ti II, 25 whereas the major lines corresponding to nitrogen molecules such as the band heads of N 2 * (337.1 nm) and N 2 + (391.4 nm) cannot be found. 26 Laser-induced plasma in air is made up mainly of singly ionized nitrogen (N II), 27 whereas the corresponding emission appearing at 399.5 nm was not found in Figure 3. We assumed that the effectiveness of the nitriding is mainly determined by the number density of Ti plasma, and hence, monitoring its behavior is important for controlling the resultant surface.…”

DABCO Derived Nitrogen-Doped Carbon Nanotubes for Oxygen Reduction Reaction (ORR) and Removal of Hexavalent Chromium from Contaminated Water

“…XRD was used to study the structure and chemical properties of Pd@NCNT-rGO and plotted in the top region of Figure 2 A, which is dominated by a sharp peak at 26.01 (indicated by #), which can be attributed to the (002) peak of disordered carbon [ 23 ], whereas the relatively weak peaks at 34.51 and 64.69 can be attributed to (112) and (220) peaks of palladium nitride [ 24 ] and whereas the peaks at 42.4, 54.9 and 60.4 correspond to (110), (112) and (103) of the palladium oxide (JCPDS No.75-16210). In the case of Fe@NCNT-CF, the carbon peak is observed at 25.5 (highlighted by #), which indicates a higher degree of graphitization, whereas the two iron peaks at 42.9 and 47.91 correspond to iron nitride [ 25 ] and iron carbide/iron oxide [ 26 ], respectively. The deconvoluted XPS spectra of the Pd 3d plotted in Figure 2 C show two major peaks [ 24 ] at 335.9 and 348.4 eV, corresponding to Pd 3d3/2 and Pd 3d5/2, regions, respectively.…”