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A laboratory scale plasma nitriding monitoring reactor (PLANIMOR) has been designed to study the basics of active screen plasma nitriding (ASPN) processes. PLANIMOR consists of a tube reactor vessel, made of borosilicate glass, enabling optical emission spectroscopy (OES) and infrared absorption spectroscopy. The linear setup of the electrode system of the reactor has the advantages to apply the diagnostic approaches on each part of the plasma process, separately. Furthermore, possible changes of the electrical field and of the heat generation, as they could appear in down-scaled cylindrical ASPN reactors, are avoided. PLANIMOR has been used for the nitriding of steel samples, achieving similar results as in an industrial scale ASPN reactor. A compact spectrometer using an external cavity quantum cascade laser combined with an optical multi-pass cell has been applied for the detection of molecular reaction products. This allowed the determination of the concentrations of four stable molecular species (CH4, C2H2, HCN, and NH3). With the help of OES, the rotational temperature of the screen plasma could be determined. [ABSTRACT FROM AUTHOR]

Low-pressure pulsed dc H2–N2 plasmas with admixtures of CH4 or CO2 used for conventional (CPN) and active screen plasma nitriding (ASPN) were studied by infrared absorption and optical emission spectroscopy (OES) techniques. The experiments were performed in two modes: (i) the plasma at an internal model probe, driven by a bias voltage operated only, representing a CPN approach, and (ii) the screen plasma operated only, which corresponds to an ASPN experiment. Combining in situ tunable diode laser absorption spectroscopy with ex situ Fourier transform infrared spectroscopy the evolution of the concentrations of the methyl radical and of eight stable molecules, C2H2, CH4, C2H4, CO, CO2, NH3, HCN and H2O was monitored. The degree of dissociation of the carbon-containing precursor molecules varied between 40% and 98%. The methyl radical concentration was found to be in the range 1011–1012 molecules cm−3. By analysing the development of molecular concentrations with changes in gas mixtures and plasma power values, it was found that (i) C2H2, HCN and NH3 were the main products of plasma conversion in the case of methane admixture and (ii) CO, HCN and NH3 in the carbon dioxide case. The fragmentation efficiencies of methane and carbon dioxide (RF (CH4) ≈ (0.5–4) × 1016 molecules J−1, RF (CO2) ≈ (0.5–3.4) × 1016 molecules J−1) and the respective conversion efficiencies to the product molecules (RC (product) ≈ 1013–1015 molecules J−1) were determined for different gas mixtures and plasma power values. With the help of OES the rotational temperature of the screen plasma could be determined, which increased with power from 600 to 850 K. Also with power the ionic component of nitrogen molecules, i.e. the intensity of the -(0–0)-band, increased strongly in relation to the intensity of the neutral component, represented by the N2-(0–2)-band. [ABSTRACT FROM AUTHOR]

Microwave (MW) H2 plasmas with small admixtures of CH4 and/or B2H6 used for doped diamond deposition have been studied by infrared absorption and optical emission spectroscopy (OES) techniques. The experiments were carried out in order to analyze the dependence of the plasma chemistry on several parameters in the MW discharges, such as power, pressure and gas mixture, at relatively high pressures, i.e. up to 300 mbar, and power values, i.e. up to 4 kW. The evolution of the concentrations of five stable molecules, CH4, C2H2, C2H4, C2H6 and B2H6, was monitored in the plasma processes by in situ infrared tunable diode laser absorption spectroscopy. OES was used simultaneously to gather complementary information about the concentration of the boron atom. One target was the determination of the precursors' fragmentation rates and the conversion rates to the molecular reaction products. The analysis of correlations between the power and pressure of the plasma and molecular concentrations, and the differences found with CH4 and B2H6 admixtures were another focus of interest. The degree of dissociation of the carbon containing precursor molecule CH4 varied between 35% and 75%, while the decomposition of diborane, the boron precursor, varied between 85% and 97%. By analyzing the development of the molecular concentrations with changes of gas mixtures, pressure and plasma power values, it was found that (i) C2H2 is the most abundant reaction product in the plasma in the case of methane admixture and (ii) the boron atom concentration depends strongly on the presence of hydrocarbons in the plasma. The fragmentation efficiencies of methane and of diborane (RF(CH4) ≈ (1–2) × 1015 molecules J−1, RF(B2H6) ≈ (0.4–1.4) × 1013 molecules J−1) and the conversion efficiencies to the molecular products (RC(product) ≈ 1013–1015 molecules J−1) have been determined for different gas mixtures and plasma power, and pressure values. The boron atom balance, in relation to the dissociated B2H6 molecules was found to vary between 10% and 40% depending on the discharge conditions. [ABSTRACT FROM AUTHOR]

• Investigation on the influence of inorganic species on wood pyrolysis. • Application of infrared laser absorption and laser-induced fluorescence spectroscopy. • Potassium leads to an overlap of cellulose and lignin decomposition with secondary reactions. • Total fluorescence intensity and exothermicity track the presence of secondary reactions. • Potassium influences the release of fluorescence-emitting species, yields and thermochemistry. The influence of inorganic species content on the slow pyrolysis of thermally thick wood particles has been investigated with the application of laser-based spectroscopic techniques. Infrared laser absorption and laser-induced fluorescence were used to characterize, on-line and in situ, the release of permanent gases (CO and CH 4) and of species emitting fluorescence, respectively. These advanced methods were combined with the continuous monitoring of mass and temperature and with off-line GC–MS analysis of the liquid fraction. The experiments were performed using spherical particles of beech, H 2 O- and HCl-washed beech, KCl-doped beech, and pine. The pyrolytic behavior of washed beech (with lower content in inorganic species) was found to resemble much closely the one of pine, rather than the one of beech, probably due to the pine low content in K. Both washed beech and pine showed a more clear separation between cellulose and lignin decomposition, being lignin decomposition, and potentially the presence of heterogeneous secondary reactions, shifted to higher temperatures. The release of species emitting fluorescence was also affected by the removal/addition of inorganic species. K was observed to catalyze the pyrolysis reaction. A strong exothermic behavior, coincident with the maximum of the TFI (tracking the release of fluorescence-emitting species -e.g. PAHs-), was observed, attributed to the presence of heterogeneous secondary (charring) reactions. Moreover, at the end of the pyrolysis process, reactions in the char matrix, enhanced by the presence of K, were detected, with no further significant mass loss or temperature gradient, leading also to the formation of fluorescence-emitting species (e.g. PAHs). Higher content in inorganic species (beech versus washed beech) resulted also in lower major carbohydrates yields and slightly higher guaiacols, syringols, and phenols yields. This indicates an enhancement of charring reactions, in good agreement with the higher exothermicity, as well as in fragmentation reactions and in lignin reactivity with higher presence of inorganic species. [ABSTRACT FROM AUTHOR]

Abstract: The active screen (AS) nitriding is an advanced technology for the plasma nitriding of steel components providing a number of advantages over conventional plasma nitriding. Developed in the last decade, the AS technology has found its industrial application, however the understanding of the fundamental mechanisms and their relationship is not complete. For the first time the mid infrared tunable diode laser absorption technique in combination with the quadruple mass spectrometry has been applied in this work. In-situ diagnostics of chemical phenomena in the N2–H2 plasmas under variation of the process conditions such as H2 to N2 gas ratio, process temperature and bias activation power provided valuable information about the concentration of active nitrogen species in the vicinity of the samples'' surfaces. The thickness of the compound layer representing the nitriding efficiency was used as a response to nitriding conditions for the evaluation of selected process parameters derived from the plasma diagnostic studies. A 1:1 gas mixture of the N2–H2 process gases seems to be most effective to get thick compound layers. [Copyright &y& Elsevier]