Optimum Gas Mixture Research Articles

Production of methanol from methane by methanotrophic bacteria

Methanotrophs can oxidize methane to carbon dioxide through sequential reactions catalyzed by a series of enzymes including methane monooxygenase, methanol dehydrogenase, formaldehyde dehydrogenase, and formate dehydrogenase. When suspensions of methanotrophic bacteria of Methylosinus trichosporium IMV 3011 were incubated at 32°C with methane and oxygen, there was an extracellular accumulation of methanol from methane oxidation in response to carbon dioxide addition. Maximal accumulation of methanol was achieved with 40% carbon dioxide in the mixed reaction gases. A continuous experiment was performed in a continuous ultrafiltration reactor. The optimum gas mixture containing 20% (v v−1) methane, 20% oxygen, 20% nitrogen and 40% carbon dioxide was used to provide substrates and to maintain the transmembrane pressure. The product (methanol) was removed in the eluate buffer. The initial methanol concentration in the eluate buffer was 8.22 μmol L−1. The bioreactor was operated continuously for 198 h without obvious loss of productivity.

Search of optimum gas mixture ratio as gas insulating medium by genetic algorithm

Genetic algorithm is applied to find the optimum gas mixture ratio as gas insulating medium substituting pure SF/sub 6/. Genetic algorithm is very useful to find the optimum solution from vast searching possibilities. Testing each gas mixture by experiment requires a long time. The present method is very efficient to preselect the candidates of gas mixtures before more thorough but time-consuming investigation via experiment is carried out. The gas mixture ratio is coded as a series of bits simulating a genetic sequence of a life form. Two-term Boltzmann equation is used to calculate the effective ionization coefficient of each gas mixture that is used to evaluate the degree of adaptation of each individual representing one set of mixture ratios. Two types of degree of adaptation are used to evaluate each individual, the effective ionization coefficient at the critical ratio of the electric field to the gas density of SF/sub 6/ of 359.3/spl times/10/sup 21/Vm/sup 2/, and the global warming potential. Based on the degree of adaptation, better individuals can be selected as parents of the next generation, leaving their genes to future generations. After some generations, the group of individuals converges into the optimum with the best degree of adaptation.

“Chlorine-based Reactive Ion Etching Process to Pattern Platinum for MEMS Applications”

AbstractWe have developed platinum (Pt) deposition and chlorine-based Reactive Ion Etch (RIE) processes that are needed to deposit, pattern and embed electrodes deep within a MEMS process flow. Various combinations of chlorinebased gases were tested to find the optimum gas mixture for RIE. A 1: 0.4 mixture ratio of pure chlorine to argon and 100-150 Watts of RF microwave power were found to be optimum conditions for the RIE of platinum metal. The addition of argon gas to chlorine was found to contribute to the anisotropic etching of platinum, obtaining vertical shaped sidewall patterns. A simple model of the platinum etching mechanism is proposed. Following the plasma enhanced formation of platinum and chlorine ions, volatile products of platinum chlorides were formed and driven away at elevated temperature. As a demonstration of our RIE process, micron-sized platinum patterns with vertical sidewalls were fabricated. Etch chemistry was investigated using ToF SIMS analysis. This etch technique will be useful to device developers intending to use the unique properties of platinum metal as an electrode that is deeply embedded within a MEMS process flow.

A planar excimer-halogen radiation source pumped by transverse RF discharge

We present the characteristics of a planar source of wideband shortwave radiation pumped by transverse RF (f=1.76 MHz) discharge in a Kr/Xe/Cl2 mixture (P≤500 Pa). The spectral characteristics of the plasma emission were studied in the wavelength interval of 130–600 nm. The oscillograms of the voltage, current, and output radiation intensity and the diagrams of the output power depending on the gas pressure, partial composition of the working gas mixture, and discharge power are presented. It is established that the source produces emission predominantly in the spectral interval of 170–330 nm, representing a system of the molecular emission bands XeCl(D, B-X), KrCl(B-X), Cl2(D′-A′), and Cl2**. For a maximum output power in the UV-VUV range, the optimum working gas mixture is Kr/Xe/Cl2 with the partial pressures P(Kr)/P(Xe)/P(Cl2)=150–200/150–200/20–40 Pa. The maximum power irradiated within a solid angle of 4π via two output holes with a total area of S≤ 100 cm2 reaches 30–40 W. In the region of a threshold with respect to the transverse discharge initiation, there are narrow peaks of plasma emission that are probably related to the jumps in the density of electrons and the positive and negative ions at the boundary between the plasma and the RF discharge layer.

Investigations on nitrogen addition in the CH 4–H 2 gas mixture used for diamond deposition for a better understanding and the optimisation of the synthesis process

In this study, we report on some investigations on the effects of nitrogen addition in the conventional CH 4H 2 gas mixture employed for diamond synthesis by microwave plasma assisted chemical vapour deposition process. Diamond films have been achieved for CH 4 concentrations ranging between 0.5 and 3%, and nitrogen amounts introduced in the feed gas between 0 and 3000 ppm, for an averaged power density of 15 W cm −3. The analysis of the deposited films has been carried out using SEM, micro-Raman spectroscopy, profilometry, XRD and electrical characterisations. For the experimental conditions employed we have pointed out that the main and conjugated effects of nitrogen are to enhance the secondary germination formation and the {100} faces development. Consequently, these effects widely depend on CH 4 and N 2 concentrations and the use of an optimal gas mixture composition leads to a maximal growth rate, chemical purity and surface electrical resistance, with a {100}〈100〉 surface global morphology. Furthermore, the achievement of thicker diamond films using the optimal gas composition has permitted to confirm few mechanisms forecasted for thin films. In particular, these mechanisms are related to the {100}〈100〉 morphology formation and to the influence of nitrogen atom incorporation in the films on the surface electrical properties. Finally, the interest of nitrogen addition has been discussed in terms of process optimisation for the production of good quality diamond films for specific applications.

Inductively coupled plasma etching of Pb(ZrxTi1-x)O3 thin films in Cl2/C2F6/Ar and HBr/Ar plasmas

Pb(ZrxTi1-x)O3 thin films were etched in an inductively coupled plasma by using various etch gases such as Cl2/Ar, C2F6/Ar, Cl2/C2F6/Ar and HBr/Ar. The etch rates and etch profiles for each etch gas were investigated. Fast etch rates were obtained in chlorine-containing etch gases (e.g., Cl2/Ar and Cl2/C2F6/Ar), and clean and steep etch profiles were achieved in Cl2/Cv2F6/Ar or HBr/Ar gases. The gas mixture of Cl2 and C2F6 was proposed to give a fast etch rate and a steep sidewall angle of etched patterns. The optimum gas mixture of Cl2C2F6/Ar was found by varying the gas ratio of Cl2 to C2F6. On the other hand, HBr/Ar gas as an alternative for etching of the Pb(ZrxTi1-x)O3 films was examined. Cl2/C2F6/Ar and HBr/Ar etch gases were compared with respect to etch rate, etch profile and electrical properties.

Growth and decomposition of bulk GaN: role of the ammonia/nitrogen ratio

Gallium nitride crystals grown via vapor-phase transport processes that incorporate ammonia as the only source of nitrogen below atmospheric pressures experience significant surface roughening and the eventual cessation of growth. Investigations of these phenomena in this research, and in the context of the discovery of a non-ceasing process route to larger GaN crystals, showed that the RMS values of the surface roughness of single crystal GaN (0 0 0 1) films exposed to pure ammonia flowing at 60 sccm for 2 h at 1130°C increased from the as-received value of 3.7–6.8 nm, 21.4 and 32.6 nm at 100, 430 and 760 Torr, respectively. Quadrupole mass spectrometry revealed that the concentrations of H 2 and N 2 measurably increased at pressures above 400 Torr. The primary reason for the increased roughness above 430 Torr was the enhanced etching of GaN via reaction with atomic and molecular hydrogen derived from the dissociation of the ammonia. At lower pressures, the decomposition of the GaN via the formation and evaporation of N 2 and Ga increased in importance relative to etching for enhancing surface roughness. Dilution with nitrogen reduced the amount of hydrogen generated from the dissociation of the ammonia. The GaN surface annealed at 1130°C and 430 Torr in ammonia diluted with 33 vol% N 2 maintained the smoothest surface with a nominal RMS value of 10.4 nm. Mixtures with higher and lower percentages of N 2 showed enhanced roughness under the same conditions. Use of this optimum gas mixture also allowed the seeded growth of a 1.5×1.5×2.0 mm 3 GaN crystal and a 2.3×1.8×0.3 mm 3 thick platelet with neither observable decomposition nor cessation of the growth over periods of 36 and 48 h, respectively.

Influence of sodium chloride and modified atmosphere packaging on microbiological, chemical and sensorial properties in ice storage of slices of hake (Merluccius merluccius)

Abstract The effect of an optimum gas mixture (50% CO 2 :45% N 2 :5% O 2 ) on hake slices ( Merluccius merluccius ) was studied when combined with a sodium chloride dip (5 min in 5% NaCl solution). Exudation, water binding capacity (WBC), microbial growth, as well as undesirable chemical (pH, total volatile bases, lipid oxidation), and sensory alterations (raw fish odour) cooked fish flavour), were monitored. Values were compared with those obtained for air-stored samples and for MAP-stored samples in the absence of NaCl. Sodium chloride dips showed a further inhibition of biochemical, microbiological and sensory deterioration of MAP-stored hake slices, so that total volatile bases and total viable counts values were significantly lower ( p

Single-electron longitudinal diffusion in helium-isobutane gas mixtures

The single-electron longitudinal diffusion has been measured in several helium-isobutane gas mixtures and compared with computations based on electron transport theories. A discussion on the transverse momentum resolution of a 200 Mev/c charged π as a function of its track length in a drift chamber is presented and conclusions are drawn on the choice of the optimal gas mixture.

Microstructure and electrical properties of YBCO films

YBCO thin films were fabricated in situ on R-plane sapphire with YSZ buffer layers by inverted cylindrical magnetron sputtering. The films with , transition width , surface microwave resistance at 10 GHz and critical current density at 77 K were routinely fabricated at optimum deposition temperature and gas mixture pressure. The relations between the growth conditions, microstructure and electrical properties of YBCO thin films were investigated for a wide range of deposition temperatures. The variation of the film properties with deposition temperature is substantiated by a thorough analysis of changes in the microstructure and state of Cu-rich particles on the surface YBCO thin films. The particle formation observed in our experiment can be described using the classical thin film nucleation and growth model based on the concept of capture zones.

The choice of the optimum gas mixture for high rate wire chambers

In this paper attention is paid to the experimental data on the use of Penning and non-Penning gas mixtures in different wire devices including proportional, drift, microstrip and microgap gas chambers. The properties of some SQS mixtures also are considered. The main conclusions are: the best time, space and energy resolution, and the minimum deposits on the wires are reached with 5–10% of the quencher addition to the principal gas; the gas gain in the MSGC is not large (less than 10 4); the phenomena may be connected with the design of this device, i.e. the deexcitation of the principal gas occurs on the substratum of the chamber without additional ionization effects.

Scaling of laser power with N/sub 2/ partial pressure in a convective-cooled CW CO/sub 2/ laser

Diffusion-cooled and convective-cooled CW CO/sub 2/ lasers have significantly different N/sub 2/ partial pressure in their optimum laser gas mixture. While in diffusion-cooled lasers the N/sub 2/ fractional concentration is normally within 20% of the total gas pressure, it ranges up to 60% in convective-cooled lasers. By considering various effects of N/sub 2/ and solving a simplified rate-equation model analytically, the large difference in the optimum N/sub 2/ concentrations in these two types of CO/sub 2/ laser is explained. >

Infrared spectroscopy of carbo-ions. IV. The A 2Πu–X 2Σ+g electronic transition of C−2

The infrared spectrum of the A 2Πu←X 2∑+g electronic transition of C−2 has been observed under high resolution and analyzed. Three bands (v′←v)=(0,0), (1,1) and (0,1) have been observed; the first two bands were observed by using the difference laser frequency system in the frequency range of 3960–3780 cm−1 and the last by using a diode laser in the frequency range of 2210–2120 cm−1. A gas mixture of 50 mTorr of acetylene and 7 Torr of He was used for the ac discharge in an air-cooled and a water-cooled multiple inlet–outlet discharge tube. The simplicity of the optimum gas mixture suggested that C−2 is produced directly by simple dissociative electron attachment of acetylene. Altogether 103 absorption lines have been observed and accurately measured. Most of them are P, Q, and R form branches of allowed F1↔F1, F2↔F2 transitions although some forbidden F1↔F2 transitions and O and S transitions have also been measured. The hot bands (1,1) and (0,1) have been observed with intensity which is less than that for the (0,0) by a factor of only 2 or 3, in spite of the fact that the Franck–Condon factors of these transitions are lower than that for the (0,0) by 2.0 and 3.2, respectively, indicating that the vibrational temperature of C−2 in the He plasma is extremely high. All observed transitions are simultaneously fit to the formula for a 2Πu←2∑+g transition. The formulation of Brown and Watson has been used for the Hamiltonian for the 2Πu state. Molecular constants for C−2 in the two electronic states have been determined from the least-squares fitting. The constants are compared with those of other species isoelectronic to C−2. A short discussion is given about the astrophysical implication of the spectrum.

Prediction of cost optimal gas feed mixtures for carburization

A program is presented which predicts the cost optimal input gas mixture required in a carburization process to achieve a desired carbon potential within the furnace atmosphere. The input gas blend used for this process is methane, propane, nitrogen and air, although the program may be easily modified for other common blends. The process has no endothermic generator, the input gas mixture is injected directly into the furnace and reacts therein. Thermodynamic calculations are based on the equilibrium composition of the reacted gas inside the furnace at specified temperatures.

One-Joule XeCl laser

Development is reported of a UV-preionized electric-discharge XeCI laser with emission energy e ≧ 0.8 J (λ = 308 nm). The energy and temporal characteristics of the laser are investigated, and the optimum gas-mixture composition for He as the buffer gas is determined. Ways of further increasing the XeCl-laser energy are indicated on the basis of the results.

Energy characteristics of gasdynamic lasers utilizing transitions between the symmetric and bending modes of the CO2molecule

Theoretical and experimental investigations were made of the energy characteristics of lasing due to transitions between the levels of coupled CO2 modes in gasdynamic lasers. The calculations were performed by solving the rate equations for the populations of the vibrational states. Conditions were found under which the collisional coupling between the levels enabled a considerable fraction of the vibrational energy to be converted into radiation. The optimal gas mixture compositions were determined for eight vibrational transitions in the wavelength range 16.4–21.2 μ. It was shown that the specific output energy from a number of transitions could be as high as several joules per gram.

Electron cloud sizes in gas-filled detectors

Electron cloud sizes have been calculated for gas mixtures containing Ar, Xe, CO 2, CH 4, and N 2 for drifts through a constant electric field. The transport coefficients w and D/ μ are in good agreement with experimental data of various sources for pure gases. Results of measurements, also performed in this work, for Ar + CO 2, Ar + CH 4, and Ar + Xe + CO 2 mixtures are in fair agreement with the calculated cloud sizes. For a large number of useful gas mixtures calculated electron cloud sizes are presented and discussed, most of which are given for the first time. A suggestion is made for an optimal gas mixture for an X-ray position sensitive proportional counter for medium and low energies.

Efficient Ar–N2laser pumped by a high-current ion beam

An experiment is described and the first results are presented of an investigation of proton pumping of a gas laser. Laser action was studied at lambda=357.7 nm in the 2/sup +/ system of nitrogen in an Ar--N/sub 2/ mixture pumped by a high-current proton beam. The lasing efficiency with respect to the total energy of the injected ion beam was 1.6--2%. The optimal pressure and gas mixture composition were determined.

Plasma Etching of Titanium for Application to the Patterning of Ti‐Pd‐Au Metallization

A study of plasma etching of filament evaporated Ti, in a radial flow reactor, using Pd (Au) as a mask is described. This work was prompted by recurrent problems with etch‐out of Ti from contact windows during wet chemical patterning of Ti for the Ti‐Pd‐Au metallization process. , , and plasmas were investigated. Details of some of the plasma chemistry and interaction of these plasmas with Au are given. Only plasmas were found to provide suitable selectivity for etching Ti in the presence of Au. tends to produce an unstable plasma. However, a stable, uniform plasma can be formed by the addition of a sufficient quantity of He. Oxygen was also added to enhance the amount of atomic bromine formed in the plasma since this was thought to be the active species for Ti etching. The optimum gas mixture was determined to be 63% , 25% He, and 12% . A relatively strong Arrhenius‐type temperature dependence of the etch rate was measured with an activation energy of ∼0.2 eV for this gas mixture. The range of process parameters (power, pressure, temperature) for which acceptable etching could be achieved was found to be quite broad and working conditions were chosen mainly on the basis of an arbitrary etch time of 4 min to clear 1000Å of Ti from a 3 in. wafer. These conditions are: 200W rf power, 0.35 Torr of the mixture, 150°C wafer platen temperature, and a 4.4 cm electrode spacing. No measurable etching of Au or Pd occurs, using these conditions, while the etch rate for CVD is ∼25 Å/min. Undercutting of Ti is negligible even with a 100% overetch. No change in MOS characteristics was observed after plasma exposure.

Stoichiometry of methane oxidation in the methane-oxidizing strain M 102 under the influence of various CH4/O2 mixtures.

In laboratory-scale experiments with growing cells of the obligate methane-oxidizing strain M 102, an overall molar gas turnover ratio of the order given below could be postulated: 1 CH4+1--1.2 O2=0.3 CO2+water. Expectations that the optimal gas mixture of methane and oxygen should lie within the range of this stoichiometric consumption ratio have been verified in fermenter 5 1 batch culture experiments. The optimal range of methane-oxygen mixture, found under the experimental conditions described, is based on the estimated growth parameters as generation and doubling times, yield coefficients related to methane and oxygen, and the efficiency of methane metabolism as indicated in the absolute amounts of CH4, O2, and CO2 turned over. The mentioned stoichiometric relation of 1 CH4:1--1.202 did not change with varying the composition, i.e. the partial pressures of CH4 and O2 introduced as a mixture to the cells. The efficiency of methane oxidation was obviously influenced and decreased markedly when deviating from the broad optimal range of CH4/O2 mixtures. With non-growing cells, on the other hand, the stoichiometric relation showed a considerable shift (1:1.4--1.8 CH4:O2) with a clear tendency towards more O2 consumption. The oxidation potential of growing cells, seems then to have a linear interdependence to the substrate concentrations, i.e. partial pressures.