Torr Plasma Research Articles

Optical and Mass Spectrometric Measurements of the CH4-CO2 Dry Reforming Process in a Low Pressure, Very High Density, and Purely Inductive Plasma.

This paper presents a study of a CH4-CO2 plasma-reforming process carried out in a high power density (5-50 W/cm3), using toroidal transformer-coupled plasma, and operated at low pressure (0.2-0.7 Torr). Using the intermediate between a thermal and nonthermal plasma (electron density, ne ≈ 3 × 1012 cm-3 and a maximum gas temperature of ∼4000-6000 K along the center line), the low-pressure study provides a unique set of conditions to investigate reaction mechanisms, where three-body reactions can be ignored. Reactive species in the plasma were identified by optical emission spectroscopy. End products of the reforming process were measured by mass spectrometry. Quite high conversions of CO2 and CH4 were found (90%), with selectivities for CO and H2 of 80% at 300 sccm feed gas flow rate in a 0.5 Torr plasma, with a mole ratio CO2-CH4 of 1:1. A detailed reaction mechanism is presented, taking into account the combined detection of reactive intermediates in the plasma (H, O, CH, and C2) and stable product downstream.

Optical absorption and emission spectroscopy studies of ammonia-containing plasmas

The chemistry of NH3/Ar/He plasmas was investigated, using a combination of ultraviolet (UV) optical absorption spectroscopy (OAS) and optical emission spectroscopy (OES). Absolute NH3 number densities in 1 Torr plasmas were measured by OAS as a function of inductively coupled plasma power and substrate heater temperature (Th). OES and actinometry were used to determine semi-quantitative H-atom density. A ‘self-actinometry’ method was introduced to measure the absolute number density of N2 that formed following the dissociation of NH3 and secondary reactions. In this approach, small amounts of N2 are added to the NH3-containing plasma, leading to an increase in the N2(C 3 Πu → B 3 Πg) emission intensity. This provides an accurate calibration factor for converting relative N2 emission intensities into absolute number densities. The number densities of NH3 were found to decrease with increasing power and Th, reaching >90% dissociation at 400 W and 900 K. N2 densities increased with power and Th. The majority of dissociated NH3 was converted to N2 (i.e. the total nitrogen content was conserved in the sum of these two species). The major hydrogen-containing species appeared to be H2; however, a substantial amount of H-atoms (comparable to H2) was present at the highest powers.

Plume dynamics of laser-produced aluminum plasma in ambient nitrogen

We report on the plume dynamics of pulsed laser ablated aluminum in ambient nitrogen pressure varying from 0.01 to 70 Torr using ICCD images of the expanding plasma plume. At pressures of 0.01 to 1 Torr plasma expansion followed shock model whereas at 10 and 70 Torr plasma expansion followed drag model. The difference in the values of vapor and shock temperatures calculated at 0.1 and 70 Torr has been used to understand the formation of AlN in vapor phase. At pressures ≥ 1 Torr and later times plasma–gas interface showed instability in the leading edge of the expanding plume attributed to Rayleigh–Taylor instability.

Characterization of laser-produced aluminum plasma in ambient atmosphere of nitrogen using fast photography

We report on the pulsed-laser ablation of aluminum in ambient pressure of nitrogen varying from 0.01 to 70 Torr using images of the expanding plasma plume. At pressures ⩾1 Torr plasma–gas interface showed severe distortion in the front of the expanding plume. The plasma expansion velocity showed oscillatory behavior with delay time beyond 260 ns and is attributed to Rayleigh–Taylor instability. The effect of background gas on inducing polarization in the ablated plasma is also reported. At low pressure of 0.1 Torr the degree of polarization of Al III transition 4s 2S1/2–4p 2P3/20 at 569.6 nm increased with delay time. At pressures ⩾1 Torr it showed an oscillatory behavior. The observed steep pressure gradient at the plasma–gas interface may result in strong self-generated magnetic field due to Rayleigh–Taylor instability.

Effects of temperature on acid-base balance and ventilation in desert iguanas.

The effects of constant and changing temperatures on blood acid-base status and pulmonary ventilation were studied in the eurythermal lizard Dipsosaurus dorsalis. Constant temperatures between 18 and 42 degrees C maintained for 24 h or more produced arterial pH changes of -0.0145 U X degrees C-1. Arterial CO2 tension (PCO2) increased from 9.9 to 32 Torr plasma [HCO-3] and total CO2 contents remained constant at near 19 and 22 mM, respectively. Under constant temperature conditions, ventilation-gas exchange ratios (VE/MCO2 and VE/MO2) were inversely related to temperature and can adequately explain the changes in arterial PCO2 and pH. During warming and cooling between 25 and 42 degrees C arterial pH, PCO2 [HCO-3], and respiratory exchange ratios (MCO2/MO2) were similar to steady-state values. Warming and cooling each took about 2 h. During the temperature changes, rapid changes in lung ventilation following steady-state patterns were seen. Blood relative alkalinity changed slightly with steady-state or changing body temperatures, whereas calculated charge on protein histidine imidazole was closely conserved. Cooling to 17-18 degrees C resulted in a transient respiratory acidosis correlated with a decline in the ratio VE/MCO2. After 12-24 h at 17-18 degrees C, pH, PCO2, and VE returned to steady-state values. The importance of thermal history of patterns of acid-base regulation in reptiles is discussed.