Synthesis and characterization of halogenated amorphous silicon via a novel glow discharge process
TL;DR: Amorphous silicon powder has been produced in a tubular glow discharge reactor as discussed by the authors, where reaction were done using SiCl4 discharges of a mixture of hydrogen and helium at atmospheric pressure.
Abstract: Amorphous silicon powder has been produced in a tubular glow discharge reactor. Reaction were done using SiCl4 discharges of a mixture of hydrogen and helium at atmospheric pressure. Chemical and p...
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TL;DR: In this paper, the decomposition of CO 2 in fan-type ac glow discharge plasma reactors coated with gold, copper, platinum, palladium, rhodium, and mixed rotor/stator systems (Au/Rh and Rh/Au) was investigated.
Abstract: The decomposition of CO 2 in fan-type ac glow discharge plasma reactors coated with gold, copper, platinum, palladium, rhodium, and mixed rotor/stator systems (Au/Rh and Rh/Au) was investigated. A high-voltage ac signal was used to produce a plasma between the fins of a turning rotor and an immobile stator, through which a 2.5% CO 2 in He mixture was passed. The analysis of the product gases was achieved using a mass spectrometer equipped with a partial pressure analyzer, and the decomposition of CO 2 was found to proceed to CO and O 2 with >80% selectivity. The percentage conversion of CO 2 increases with decreasing flow rate and increasing input voltage. The opposite trend is obtained when the energy efficiency is evaluated. Spectroscopic data indicate that the diluent gas plays a role in the dissociation of CO 2 , likely via charge and energy transfer from excited state He species to produce vibrationally excited CO 2 + intermediates. The order of reactivity for the different metal catalyst coatings is Rh > Pt ≈ Cu > Pd > Au/Rh ≈ Rh/Au ≈ Au. With the Rh-coated reactor, conversions as high as 30.5%, reaction rates of 8.07×10 −4 mol/h, and energy efficiencies of 3.55% could be obtained. There is a clear relationship between excitation temperature, T ex , of a pure He plasma and the conversion of CO 2 in a CO 2 /He plasma: decreasing T ex corresponds to increasing conversion.
94 citations
TL;DR: In this paper, the activation of small molecules, such as CO2, NO, and H2O, has been achieved at atmospheric pressure via ac glow discharge methods in the presence of metal catalysts coated onto the electrode surfaces.
Abstract: The activation of small molecules, such as CO2, NO, and H2O, has been achieved at atmospheric pressure via ac glow discharge methods in the presence of metal catalysts coated onto the electrode surfaces. A fan-type reactor having one rotating and one static electrode has been designed to diminish mass transfer effects. Time lapse photography of the emitting plasma intermediate species and optical emission studies have been used to monitor reaction pathways. Gas chromatography, mass spectrometry, and combined GC−MS methods have been used to monitor product distributions, selectivities, and activities. The effects of flow rate, input voltage, diluent gases, and metal coating have been systematically studied. Additionally, the mechanisms of CO2 decomposition and the role of the metal catalyst in that decomposition have been studied by optical emission spectroscopy.
58 citations
TL;DR: In this paper, the decomposition of CO2 in fan-type ac glow discharge reactors coated with platinum or rhodium was studied as a function of concentration of CO 2in the feed, frequency, and waveform shape.
Abstract: The decomposition of CO2in fan-type ac glow discharge reactors coated with platinum or rhodium was studied as a function of concentration of CO2in the feed, frequency, and waveform shape. The progress of the reaction was monitored with an ion-quadrupole mass spectrometer coupled with a partial pressure analyzer. CO was the main carbonaceous product with selectivities >80%. Mixtures of 2.5, 10, and 20% CO2in He were studied and the conversion is observed to increase with decreasing CO2concentration, although the power consumed by the reactor remains relatively constant. The reaction efficiency for the reaction (proportional to yield) is observed to increase with increasing CO2concentration. The frequency has little effect on the conversion of CO2in the plasma, but the plasma power consumption is observed to decrease as the frequency is increased at constant applied voltage, resulting in an increase in reaction efficiency with increasing frequency. The conversion of CO2increases with increasing input voltage in the range 411–2050 V root mean square (rms), then levels off up to 10.91 kV rms. The plasma power shows the same trend as conversion, whereas the efficiency and excitation temperature of the plasma are observed to decrease up to 2050 V rms and then level off. The effects of sine, square, and triangular waveforms were examined and found to yield similar conversions, plasma powers, and efficiencies. The order for conversion and power is square > sine>triangular and the order for efficiency is triangular>sine≈square. CO2conversion is maximized for a square waveform and low concentrations of CO2at input voltages near 2 kV rms. Conversion is independent of the ac frequency. Conversely, maximization of reaction efficiency occurs at low input voltages (
35 citations
Patent•
23 May 2006
TL;DR: In this article, a method for the production of silicon from silyl halides was proposed, which is based on a first-and-second-step process, with a plasma discharge and then with heating.
Abstract: The present invention relates to a method for the production of silicon from silyl halides. In a first step, the silyl halide is converted, with the generation of a plasma discharge, to a halogenated polysilane, which is subsequently decomposed to silicon, in a second step, with heating.
30 citations
TL;DR: In this article, a fan type reactor consisting of a movable rotor and immobile stator produced the highest yields in contrast to a tube type (silent discharge) reactor with a glass dielectric barrier.
Abstract: Methane conversions of 11.9%, yields of hydrogen as high as 23.3% and energy yields of 1.0 mol H2/kWh have been achieved from CO2 reforming of CH4 in non-thermal, atmospheric pressure plasma reactors with Pt coated electrodes. Two reactors have been studied. A novel fan type reactor consisting of a movable rotor and immobile stator produced the highest yields in contrast to a tube type (silent discharge) reactor with a glass dielectric barrier. Conversions, yields of hydrogen and energy yields (expressed as mol H2/kWh) were studied for CO2/CH4 concentrations of 1.1% and 5.0% in He as a function of flow rate and input voltage. Hydrogen yields are observed to increase as the input voltage is increased from 411 V to 911 V and the flow rate is decreased from 100 cc/min to 30 cc/min. Energy yields vary only slightly with input voltage and flow rate. Hydrogen yields show little dependence on CO2/CH4 concentrations, but energy yields are approximately five times greater for the 5.0% mixture than the 1.1% mixture. Selectivities to H2, CO, coke, and low molecular weight hydrocarbons were also evaluated and compared to data obtained without CO2 in the feed. Hydrogen selectivities of nearly 100% were obtained, with small amounts of ethane and propane as the only observed side products and the selectivites were approximately the same whether CO2 was present or absent in the mixture. However, the reaction proceeds much more cleanly when CO2 is present, producing CO. The syngas product has an H2 : CO ratio of 1.5 with the fan type reactor and 0.67 with the tubular reactor. In the absence of CO2, coke is the main carbonaceous product. Under all conditions studied the fan type reactor demonstrated higher methane conversions (up to 11.9%) and selectivities to hydrogen.
14 citations
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TL;DR: It is established that trichomic cyanobacterium-like microorganisms were extant and morphologically diverse at least as early as ∼3465 million years ago and suggests that oxygen-producing photoautotrophy may have already evolved by this early stage in biotic history.
Abstract: Eleven taxa (including eight heretofore undescribed species) of cellularly preserved filamentous microbes, among the oldest fossils known, have been discovered in a bedded chert unit of the Early Archean Apex Basalt of northwestern Western Australia. This prokaryotic assemblage establishes that trichomic cyanobacteriumlike microorganisms were extant and morphologically diverse at least as early as about 3465 million years ago and suggests that oxygen-producing photoautotrophy may have already evolved by this early stage in biotic history.
1,243 citations
TL;DR: In this paper, polycrystalline silicon films have been prepared using chemical transport in a low-pressure plasma in a temperature range 80-400 degrees C and at deposition rates up to approximately 3 AA s-1.
Abstract: Polycrystalline silicon films have been prepared using chemical transport in a low-pressure plasma in a temperature range 80-400 degrees C and at deposition rates up to approximately 3 AA s-1. Their Raman spectra show several features which are correlated with X-ray diffraction measurements and attributed to the presence of crystalline and amorphous-like components. Optical absorption, infrared spectra, preliminary data on dark conductivity and some further properties are reported.
128 citations
TL;DR: Optical emission spectroscopy in the visible and near UV of a silane plasma was performed in a low pressure hot cathode glow discharge bounded into a magnetized multipolar wall as mentioned in this paper.
Abstract: Optical emission spectroscopy in the visible and near UV of a silane plasma was performed in a low pressure hot cathode glow discharge bounded into a magnetized multipolar wall. Emissions from Si, Si+, SiH, SiH+ and H are shown to originate from the dissociative excitation of silane molecules by electron impact. The absolute cross sections for the various photoemissive processes were measured in the 17–68 eV range. The relevance of optical emission spectroscopy to silane plasma diagnostics is discussed.
95 citations
IBM1
82 citations
TL;DR: In this paper, the authors used a compact electron beam reactor and a pulsed corona reactor to study the effects of background gas composition and gas temperature on the decomposition chemistry and elecmcal energy efficiency.
Abstract: This paper presents experimental results on non-thermal plasma processing of atmospheric-pressure gas streams containing dilute concentrations of various volatile organic compounds (VOCs). This investigation used a compact electron beam reactor and a pulsed corona reactor to study the effects of background gas composition and gas temperature on the decomposition chemistry and elecmcal energy efficiency. The elecmcal energy consumption is characterized for the decomposition of a variety of VOCs, including carbon tetrachloride, mchloroethylene, methylene chloride, benzene, acetone and methanol. For most of the VOCs investigated, electron beam processing is more energy efficient than pulsed corona processing. For VOCs (such as carbon tetrachloride) that require copious amounts of electrons for its decomposition, electron beam processing is remarkably more energy efficient. For some VOCs the decomposition process is limited by their reaction rate with the plasma-produced radicals and/or by the occurrence of back reactions. In these cases, the energy consumption can be minimized by operating at high (but non- combusting) temperatures.
75 citations