3.1.2. Optical emission spectroscopy and plasma parameters
Fig. 6 (a) depicts the emission spectra of the glow discharge in 80%
H2+20% Ar and for the gas mixture containing 1.00% CH4. The spectra
present atomic emission lines of Ar and H, and molecular bands of
H2. The identification was done according to [28,29] and spectra are
similar to that presented by [30,31] in ArH2 and H2 discharges, respectively.
The addition of 1.00% CH4 in the glow discharge does not
imply in the appearance of new peaks or molecular bands due to
CH4, at least at sufficient intensity. So in the studied condition, the optical
emission spectroscopy cannot be applied to the process control,
as proposed by [32] for high temperature plasma carburizing.
Nevertheless, it is clear that the introduction of CH4 causes a global
reduction on the intensity of the peaks. In Fig. 6 (b) a detail of some
intense Ar and H atomic lines is presented. It can be noticed that
adding CH4 up to 0.50%, a reduction of the emission intensity is verified.
On the other hand, adding CH4 from 0.50 up to 1.00%, the intensity
reduction becomes insignificant.
As show in Fig. 7, it is necessary to increase tON to keep the treatment
temperature when additional CH4 is added to the gas mixture.
The RMS current remains approximately constant as expected, since
to keep the same temperature, the same mean power must be delivered
to the glow discharge. Considering that the excitation occurs
mainly be electron impact, the emission intensity reduction could
be attributed to a reduction on the plasma electron density and/or
3.1.2. Optical emission spectroscopy and plasma parametersFig. 6 (a) depicts the emission spectra of the glow discharge in 80%H2+20% Ar and for the gas mixture containing 1.00% CH4. The spectrapresent atomic emission lines of Ar and H, and molecular bands ofH2. The identification was done according to [28,29] and spectra aresimilar to that presented by [30,31] in ArH2 and H2 discharges, respectively.The addition of 1.00% CH4 in the glow discharge does notimply in the appearance of new peaks or molecular bands due toCH4, at least at sufficient intensity. So in the studied condition, the opticalemission spectroscopy cannot be applied to the process control,as proposed by [32] for high temperature plasma carburizing.Nevertheless, it is clear that the introduction of CH4 causes a globalreduction on the intensity of the peaks. In Fig. 6 (b) a detail of someintense Ar and H atomic lines is presented. It can be noticed thatadding CH4 up to 0.50%, a reduction of the emission intensity is verified.On the other hand, adding CH4 from 0.50 up to 1.00%, the intensityreduction becomes insignificant.As show in Fig. 7, it is necessary to increase tON to keep the treatmenttemperature when additional CH4 is added to the gas mixture.The RMS current remains approximately constant as expected, sinceto keep the same temperature, the same mean power must be deliveredto the glow discharge. Considering that the excitation occursmainly be electron impact, the emission intensity reduction couldbe attributed to a reduction on the plasma electron density and/or
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