Plasma catalysis:distinguishing between thermal and chemical effects

\u3cp\u3e The goal of this study is to develop a method to distinguish between plasma chemistry and thermal effects in a Dielectric Barrier Discharge nonequilibrium plasma containing a packed bed of porous particles. Decomposition of CaCO \u3csub\u3e3\u3c/sub\u3e in Ar plasma is used as a model reaction and CaCO \u3csub\u3e3\u3c/sub\u3e samples were prepared with different external surface area, via the particle size, as well as with different internal surface area, via pore morphology. Also, the effect of the CO \u3csub\u3e2\u3c/sub\u3e in gas phase on the formation of products during plasma enhanced decomposition is measured. The internal surface area is not exposed to plasma and relates to thermal effect only, whereas both plasma and thermal effects occur at the external surface area. Decomposition rates were in our case found to be influenced by internal surface changes only and thermal decomposition is concluded to dominate. This is further supported by the slow response in the CO \u3csub\u3e2\u3c/sub\u3e concentration at a timescale of typically 1 minute upon changes in discharge power. The thermal effect is estimated based on the kinetics of the CaCO \u3csub\u3e3\u3c/sub\u3e decomposition, resulting in a temperature increase within 80 °C for plasma power from 0 to 6W. In contrast, CO \u3csub\u3e2\u3c/sub\u3e dissociation to CO and O \u3csub\u3e2\u3c/sub\u3e is controlled by plasma chemistry as this reaction is thermodynamically impossible without plasma, in agreement with fast response within a few seconds of the CO concentration when changing plasma power. CO forms exclusively via consecutive dissociation of CO \u3csub\u3e2\u3c/sub\u3e in the gas phase and not directly from CaCO \u3csub\u3e3\u3c/sub\u3e . In ongoing work, this methodology is used to distinguish between thermal effects and plasma-chemical effects in more reactive plasma, containing, e.g., H \u3csub\u3e2\u3c/sub\u3e . \u3c/p\u3

Chemical erosion of carbon at ITER relevant plasma fluxes:results from the linear plasma generator Pilot-PSI

\u3cp\u3eThe chemical erosion of carbon was investigated in the linear plasma device Pilot-PSI for ITER divertor relevant hydrogen plasma flux densities 10 \u3csup\u3e23\u3c/sup\u3e < Γ < 10\u3csup\u3e25\u3c/sup\u3e m\u3csup\u3e-2\u3c/sup\u3e s\u3csup\u3e-1\u3c/sup\u3e. The erosion was analyzed in situ by optical emission spectroscopy and post mortem by surface profilometry. The experiments indicate a threshold for the absolute carbon erosion rate as a function of plasma temperature T\u3csub\u3ee\u3c/sub\u3e around 0.7 eV, a peak of the surface temperature around 550 °C, and no dependence on plasma flux density. The latter implies a flux dependence of the chemical erosion yield as Γ\u3csup\u3e-1\u3c/sup\u3e. The value of the chemical erosion yield at the surface temperature of maximum erosion and Γ = 1 × 10\u3csup\u3e24\u3c/sup\u3e m\u3csup\u3e-2\u3c/sup\u3e s\u3csup\u3e-1\u3c/sup\u3e was 0.9% for T\u3csub\u3ee\u3c/sub\u3e < 0.5 eV as determined by surface profilometry.\u3c/p\u3

Plasma for electrification of chemical industry:a case study on CO\u3csub\u3e2\u3c/sub\u3e reduction

\u3cp\u3eSignificant growth of the share of (intermittent) renewable power in the chemical industry is imperative to meet increasingly stricter limits on CO\u3csub\u3e2\u3c/sub\u3e exhaust that are being implemented within Europe. This paper aims to evaluate the potential of a plasma process that converts input CO\u3csub\u3e2\u3c/sub\u3e into a pure stream of CO to aid in renewable energy penetration in this sector. A realistic process design is constructed to serve as a basis for an economical analysis. The manufacturing cost price of CO is estimated at 1.2 kUS$ ton\u3csup\u3e-1\u3c/sup\u3e CO. A sensitivity analysis shows that separation is the dominant cost factor, so that improving conversion is currently more effective to lower the price than e.g. energy efficiency.\u3c/p\u3

Mode resolved heating dynamics in pulsed microwave CO\u3csub\u3e2\u3c/sub\u3e plasma from laser Raman scattering

\u3cp\u3eEfficient CO\u3csub\u3e2\u3c/sub\u3e reduction is predicted for CO\u3csub\u3e2\u3c/sub\u3e microwave plasma by virtue of predominant excitation of the asymmetric stretch vibration. Although interpretation of ongoing research is generally based on this mechanism, direct measurement of the power partitioning to support the assumed preferential vibrational excitation in CO\u3csub\u3e2\u3c/sub\u3e microwave plasma is currently lacking. Here, such measurements are performed on a 100 μs pulsed microwave CO\u3csub\u3e2\u3c/sub\u3e discharge. The <1% duty cycle ensures low gas temperature conditions at the discharge onset. Raman and Rayleigh scattering are employed to reveal vibrational, rotational, and gas temperatures in a spatially and temporally resolved manner. A novelty in the approach is that asymmetric stretch excitation is determined from the bending - symmetric stretch Raman spectrum. During the first 40 μs a significant inter-vibrational non-equilibrium is observed with the symmetric stretch and bending temperature reaching 750 K and the asymmetric stretch temperature reaching 1150 K. A maximum rotational-vibrational non-equilibrium occurs after 60 μs when the rotational temperature is half of the 1150 K vibrational temperature. Rotational and translational modes are measured to be in equilibrium at all times. The power partitioning is analyzed to estimate the power consumed by vibrational excitation, which is used to estimate the reduced electric field in the discharge. This work confirms strong vibrational excitation in CO\u3csub\u3e2\u3c/sub\u3e microwave plasma albeit less predominant than often assumed.\u3c/p\u3

Power pulsing to maximize vibrational excitation efficiency in N\u3csub\u3e2\u3c/sub\u3e microwave plasma:a combined experimental and computational study

\u3cp\u3ePlasma is gaining increasing interest for N\u3csub\u3e2\u3c/sub\u3e fixation, being a flexible, electricity-driven alternative for the current conventional fossil fuel-based N\u3csub\u3e2\u3c/sub\u3e fixation processes. As the vibrational-induced dissociation of N\u3csub\u3e2\u3c/sub\u3e is found to be an energy-efficient pathway to acquire atomic N for the fixation processes, plasmas that are in vibrational nonequilibrium seem promising for this application. However, an important challenge in using nonequilibrium plasmas lies in preventing vibrational-translational (VT) relaxation processes, in which vibrational energy crucial for N\u3csub\u3e2\u3c/sub\u3e dissociation is lost to gas heating. We present here both experimental and modeling results for the vibrational and gas temperature in a microsecond-pulsed microwave (MW) N\u3csub\u3e2\u3c/sub\u3e plasma, showing how power pulsing can suppress this unfavorable VT relaxation and achieve a maximal vibrational nonequilibrium. By means of our kinetic model, we demonstrate that pulsed plasmas take advantage of the long time scale on which VT processes occur, yielding a very pronounced nonequilibrium over the whole N\u3csub\u3e2\u3c/sub\u3e vibrational ladder. Additionally, the effect of pulse parameters like the pulse frequency and pulse width are investigated, demonstrating that the advantage of pulsing to inhibit VT relaxation diminishes for high pulse frequencies (around 7000 kHz) and long power pulses (above 400 μs). Nevertheless, all regimes studied here demonstrate a clear vibrational nonequilibrium while only requiring a limited power-on time, and thus, we may conclude that a pulsed plasma seems very interesting for energy-efficient vibrational excitation.\u3c/p\u3

Correction of time-of-flight shifted polymeric molecular weight distributions in matrix assisted laser desorption/ionization Fourier transform mass spectrometry

Molecular weight distributions on an external injection matrix-assisted laser desorption/ionization Fourier transform mass spectrometer are subject to time-of-flight distortions as different ion velocities are probed with varied delay times between ionization and trapping (i.e., the trapping time). This phenomenon is used to advantage to reject low-mass matrix ions which would otherwise saturate the trapped ion cell; however, for accurate determination of molecular weight distributions of complex samples like polymeric systems, several mass spectra must be acquired at a series of different trapping times to compensate for this distortion. The spectra acquired should be superimposed (not summed) on the same m/z axis to yield the correct molecular weight distribution as summation of these spectra merely causes further distortions and can cause loss of signal/noise. Distortions due to TOF effects are probed with a calibration compound, poly(ethylene glycol) of peak mass (Mp) ∼1000 Da, as well as the more difficult to ionize polystyrene, which was obtained as a chromatographic molecular weight standard (MW 950). This polystyrene reference material was determined to have a ∼20% error in Mp

Heating of a magnetized high density hydrogen plasma column around the ICR frequency

\u3cp\u3eA single and double loop antenna system are investigated in the ICR frequency range (5-25 MHz) to enable control of the plasma temperature in a 1-10 cm diameter, 10 \u3csup\u3e20\u3c/sup\u3em \u3csup\u3e-3\u3c/sup\u3e hydrogen plasma column in B=0.8T Wave propagation is evaluated on basis of damping lengths derived from the dispersion relation. The antenna is numerically analyzed with the TOPCYL code. Simulation results are compared with measured loading resistances and good agreement was found for the vacuum and saltwater column cases. Hydrogen plasma loading resistances determined from network analyzer measurements are typically higher than those predicted from simulation. This points to coupling of RF power to additional loss mechanisms. High RF power operation (1 kW) of the antenna increased the power deposited on the plasma endplate and accelerated the plasma, but the plasma temperature near the endplate remained constant.\u3c/p\u3

Heating of a magnetized high density hydrogen plasma column around the ICR frequency

\u3cp\u3eA single and double loop antenna system are investigated in the ICR frequency range (5-25 MHz) to enable control of the plasma temperature in a 1-10 cm diameter, 10 \u3csup\u3e20\u3c/sup\u3em \u3csup\u3e-3\u3c/sup\u3e hydrogen plasma column in B=0.8T Wave propagation is evaluated on basis of damping lengths derived from the dispersion relation. The antenna is numerically analyzed with the TOPCYL code. Simulation results are compared with measured loading resistances and good agreement was found for the vacuum and saltwater column cases. Hydrogen plasma loading resistances determined from network analyzer measurements are typically higher than those predicted from simulation. This points to coupling of RF power to additional loss mechanisms. High RF power operation (1 kW) of the antenna increased the power deposited on the plasma endplate and accelerated the plasma, but the plasma temperature near the endplate remained constant.\u3c/p\u3

Endgroup analysis of polyethylene-glycol polymers by matrix-assisted laser-desorption ionization fourier-transform ion-cyclotron resonance mass-spectrometry

Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) by external injection of matrix-assisted laser desorbed and ionized (MALDI) polymers offers good possibilities for characterization of low molecular weight homopolymers (MW range up to 10 kDa). The molecular masses of the molecular weight distribution (MWD) components of underivatized and derivatized (dimethyl, dipropyl, dibutyl and diacetyl) polyethylene glycol (PEG) 1000 and 4000 were measured by MALDI-FTICR-MS. These measurements have been performed using a commercial FTICR spectrometer with a home-built external ion source. MALDI of the samples with a 2,5-dihydroxybenzoic acid matrix in a 1000:1 matrix-to-analyte molar ratio produces sodiated molecules in a sufficient yield to trap the ions in the ICR cell. The masses of the molecular weight distribution of PEG components were measured in broad-band mode with a mass accuracy of < 5 ppm in the mass range around 1000 u and within 40 ppm accuracy around 4000 u. From these measurements, the endgroup mass of the polymer was determined by correlation of the measured component mass with the degree of polymerization. The masses of the PEG endgroups have been determined within a deviation of 3-10 millimass units for the PEG1000 derivatives and 10-100 millimass units for the PEG4000 derivatives, thus confirming the identity of the distal parts of the model compounds

How the alternating degeneracy in rotational Raman spectra of CO\u3csub\u3e2\u3c/sub\u3e and C\u3csub\u3e2\u3c/sub\u3eH\u3csub\u3e2\u3c/sub\u3e reveals the vibrational temperature

\u3cp\u3eThe contribution of higher vibrational levels to the rotational spectrum of linear polyatomic molecules with a center of symmetry (CO\u3csub\u3e2\u3c/sub\u3e and C\u3csub\u3e2\u3c/sub\u3eH\u3csub\u3e2\u3c/sub\u3e) is assessed. An apparent nuclear degeneracy is analytically formulated by vibrational averaging and compared to numerical averaging over vibrational levels. It enables inferring the vibrational temperature of the bending and asymmetric stretching modes from the ratio of even to odd peaks in the rotational Raman spectrum. The contribution from higher vibrational levels is already observable at room temperature as g???\u3csub\u3ee\u3c/sub\u3e∕\u3csub\u3eo\u3c/sub\u3e 0.96∕0.04 for CO\u3csub\u3e2\u3c/sub\u3e and g???\u3csub\u3ee\u3c/sub\u3e∕\u3csub\u3eo\u3c/sub\u3e 1.16∕2.84 for C\u3csub\u3e2\u3c/sub\u3eH\u3csub\u3e2\u3c/sub\u3e. The use of the apparent degeneracy to account for higher vibrational levels is demonstrated on spectra measured for a CO\u3csub\u3e2\u3c/sub\u3e microwave plasma in the temperature range of 300–3500 K, and shown to be valid up to 1500 K.\u3c/p\u3