The Pyrolysis Property of a Pulsed Plasma of Methane

This study examined the discharge property of methane in a pulsed plasma using single and sequential pulse modes. A pulsed corona discharge occurred, followed by a pulsed spark discharge. An equivalent single channel model (ESC model) for the pulsed plasma of methane was established. The maximum temperature of methane in the discharge channel was estimated. The pyrolysis property of the channel methane was estimated from Senkin simulation and single channel discharge experiment.     

Theoretical studies on microscopic and macroscopic nonuniformities in electric-discharge-excited XeCl lasers

The satbilit r of the pumping discharge for XeCI (Ne/Xe/HCI) lasers is investigated by using different one-dimensional models, considering both bulk discharge instabilities and filamentary ones. It is found that the bulk stability in a XeCl laser discharge can he improved, under certain conditions, due to the vihrational excitation of HCl molecules: this effect is studied by using different models for the HCl vihrational kinetics. It is established that the very short instability time found in experiments cannot he explained as a result of hulk instability of the discharge. On the other hand, a satisfactory comparison with experiments can he obtained by adding to the model a simplified microinstability which develops in the discharge.     

Spatial distribution of the neutral gas temperature in rf and dc magnetron sputter discharges determined by fitting rotational spectra of the N2+ using a two-temperature fit

The spatial distribution of the neutral gas temperature in a dc and rf magnetron sputter discharge (boron target) with pure nitrogen was estimated by fitting the rotational spectra of the first negative system of the nitrogen molecule ion. The rotational levels of the excited nitrogen molecule ion are populated mainly by two mechanisms. Only one of them leads to a rotational level distribution corresponding to the neutral gas temperature. Therefore, fitting of the spectra assuming a single Boltzmann distribution of the rotational levels often leads to unreliable and too high rotational temperatures and the spectra have to be fitted using a two-temperature model. Beside the neutral gas temperature the value of the second temperature as well as the contribution of the higher rotationally excited molecules to the spectra are studied in more detail. The dependence of the spatial distribution of the neutral gas temperature on pressure and discharge power was investigated. Additionally, the results are compared to rotational temperatures obtained by fitting the spectra assuming a single Boltzmann distribution of the rotational levels. These rotational temperatures often do not reflect the neutral gas temperature and wrong dependences would be concluded.     

碳纳米管在室温熔盐中的电容特性

研究了碳纳米管在室温熔盐二(三氟甲基磺酸酰)亚胺锂(LiTFSI)-乙酰胺中的电容特性. 将碳纳米管制成薄膜电极, 以LiTFSI-乙酰胺为电解液, 装配成模拟电容器, 用循环伏安和恒流充放电法研究其电化学性能. 结果表明, 碳纳米管在室温熔盐中表现出典型的电容特性, 其比电容为22 F•g^-1, 模拟电容器的工作电压可达2.0 V, 具有非常好的循环性能, 循环充放电1000次后容量损失仅10%, 表明室温熔盐是超级电容器非常有前景的新型电解液.     

Application of near-infrared spectra on temperature-controlled protein crystallization

Large, high-quality protein crystals are required for the structural determination of proteins via X-ray diffraction. In this article, we propose a technique to facilitate the production of such crystals and validate its feasibility through simulations. An analytical method for protein aqueous solution based on a Fourier transform infrared (FTIR) spectroscopy is combined with a temperature control strategy to manipulate the extent of supersaturation during crystal growth, thus impacting crystal quality. The technique requires minimal knowledge about the growth kinetics a priori. The simulations show that, under ideal conditions, the design can be as effective as predesigned temperature programs for crystallization based on known growth kinetics. Two kinds of errors might be encountered with this design. Error in the estimated number of seed crystals can result in a growth rate deviating from the desired one. Nevertheless, the deviation is usually tolerable and system instability is unlikely to occur. Based on the standard error of our FTIR method, errors in concentration measurement are simulated. Measurement error can result in system instability and impair the control algorithm. Such errors may be compensated by limiting the temperature change taken by the control action, or by improving the measurement precision through the use of regressed concentrations. Through simulations, it is shown that the proposed design is practical and represents a significant improvement over the commonly used isothermal crystallization technique.     

On the carrier effect mechanism in relation to mass transport processes in the arc discharge

The time of residence of impurity atoms in the arc discharge is calculated. Diffusion, ion motion in the electric field, and ambipolar diffusion are taken into account. It is shown for the first time that ambipolar diffusion contributes significantly to the total particle flow from the arc discharge zone. The effect of charge exchange on the speed of ion motion in the arc is estimated. The influence of a carrier on the residence time of atoms in the arc discharge zone is calculated. Attention is paid to the peculiarities of the mechanism of the carrier effect associated with halide compounds. An attempt is made to explain the influence of halide compounds on the residence time of atoms in the arc using the considered model of mass transport. The velocities of mass transport and the time of atoms in the discharge zone are calculated for the are with and without halide containing substances. The initial parameters of calculation (discharge temperature, electron density, degree of ionization, and coefficient of atom diffusion) are partly measured and partly taken from the literature. The results of the calculation are compared with experimental data published in the literature. The adopted mass transport model adequately accounts for the influence of a carrier on the residence time of atoms in the arc discharge zone.     

In situ NMR diffusion coefficients assessment of lithium ion conductor using electrochemical priors and Arrhenius constraint——A computational study

In situ NMR measurements of the diffusion coefficients,including an estimate of signal strength,of lithium ion conductor using diffusion-weighting pulse sequence are performed in this study.A cascade bilinear model is proposed to estimate the diffusion sensitivity factors of pulsed-field gradient using prior information of the electrochemical performance and Arrhenius constraint.The model postulates that the active lithium nuclei participating electrochemical reaction are relevant to the NMR signal intensity,when discharge rate or temperature condition is varying.The electrochemical data and the NMR signal strength show a highly fit with the proposed model according our simulation and experiments.Furthermore,the diffusion time is constrained by temperature based on Arrhenius equation of reaction rates dependence.An experimental calculation of Li_4Ti_5O_(12)(LTO)/carbon nanotubes(CNTs) with the electrolyte evaluating at 20 ℃ is presented,which the b factor is estimated by the discharge rate.     

Simplified and complex modeling of self-sustained discharge-pumped,Ne-buffered XeCl laser kinetics

Two simple kinetic models of a Ne-buffered XeCl laser discharge are presented based on different simplifications of the chemical kinetics of a complex model that recently appeared in the literature. When applied to the study of a small-volume XeCl laser, the results of both simple and complex models are in satisfactory agreement with the experiments. Shifting to a larger-volume laser, both models show problems due to loss of stability of the discharge. A one-dimensional modelling is performed, and it is found that different assumptions on the kinetics of the NeXe⁺ ion in the discharge lead to completely different results as regards the effect of a preionization-triggered instability.     

Algorithms for modeling and processing spatial information in heterogeneous plasma discharges

Procedures are described for modeling and analyzing optical phenomena in bilaterally symmetric plasma discharges. Discharge shape, emission, absorption, background subtraction, and spatial instability are considered, and provision is made for imperfect imaging properties of the observation system. Algorithms are presented for interconverting lateral, laboratory information concerning a plasma discharge and radial, chemical information concerning the discharge. Various non-idealities and non-emissive processes may be modeled. The assumptions made are that the discharge is cylindrically symmetric and is viewed in a manner which preserves this symmetry; that the optical system non-ideality is limited to depth-of-field distortions, which can be corrected; and that emission and absorption take place in concentric but segregated regions of the discharge, with emission occurring closer to the discharge core. There are known limitations to this model, and any seemingly inconsistent results in experimental applications will indicate that processes not accounted for are active.     

Comparison and validation of methods for estimating heat generation rate of large-format lithium-ion batteries

The heat generation rate of a large-format 25 Ah lithium-ion battery is studied through estimating each term of the Bernardi model. The term for the reversible heat is estimated from the entropy coefficient and compared with the result from the calorimetric method. The term for the irreversible heat is estimated from the intermittent current method, the V–I characteristics method and a newly developed energy method. Using the obtained heat generation rates, the average cell temperature rise under 1C charge/discharge is calculated and validated against the results measured in an accelerating rate calorimeter (ARC). It is found that the intermittent current method with an appropriate interval and the V–I characteristics method using a pouch cell yield close agreement, while the energy method is less accurate. A number of techniques are found to be effective in circumventing the difficulties encountered in estimating the heat generation rate for large-format lithium-ion batteries. A pouch cell, using the same electrode as the 25 Ah cell but with much reduced capacity (288 mAh), is employed to avoid the significant temperature rise in the V–I characteristics method. The first-order inertial system is utilized to correct the delay in the surface temperature rise relative to the internal heat generation. Twelve thermocouples are used to account for the temperature distribution.     

Ionized Physical Vapour Deposition combined with PECVD,for synthesis of carbon–metal nanocomposite thin films

Carbon–metal composite thin films were synthesized by a hybrid process combining magnetron sputtering and PECVD in an argon–methane plasma. Titanium was chosen as the target metal. The paper is focused on the impact of three types of deposition process (DC magnetron, RF magnetron or Ionized Physical Vapour Deposition – IPVD) on thin films' deposition and microstructure. The effect of the methane fraction in gas discharge was also studied. Films were analysed by EDX, XPS and XRD. Results indicate steady deposition conditions for RF or IPVD operation whatever the methane fraction in the discharge without any problem of discharge instability commonly observed in DC operation. The presence of TiC crystallites in a-C:H matrix was detected at intermediary methane fraction in discharge whatever the operating mode. Nevertheless, at constant methane fraction in discharge, strong difference between film microstructure and composition was observed according to the operating mode.     

Influence of the anode material on the characteristics of an analytical glow discharge cell

The energy transfer to the discharge gas due to various collision processes in the plasma and the heating of the sample are widely known effects in glow discharge (GD) spectroscopy. Despite of the considerable thermal effects and their serious influence on the performance of GD devices, measurements of the discharge gas and sample temperatures are not common at all. The gas temperature depends on the power absorption of the discharge as well as on the temperature of boundaries (sample and anode). In this work the influence of different anode materials in a Grimm-type source on the voltage–current characteristics, crater shapes and GD spectra is investigated. Anodes made of titanium and copper alloys, graphite, and steel with thermal conductivities covering a wide range of values are used. For a fixed voltage and pressure a decrease of the measured current is observed for bad thermal conductive anodes. Cooling of the sample results in an increase of the measured current. Both observations can be explained by changes of the discharge gas temperature. The temperature of the sample is measured from the back side and compared for different anodes. Further, it is found that the choice of the anode material (i) has no significant influence on the crater shape, (ii) results in slightly different sputtering rates and (iii) strong differences of the GD spectra.     

Rotational temperature of nitrogen glow discharge obtained by optical emission spectroscopy

Measurements of rotational temperature as low as several hundred Kelvin have been measured using optical emission spectroscopy (OES) in nitrogen direct current (DC) glow discharge. The strongest band of the first negative system of nitrogen was chosen to deduce the rotational temperature at four different positions in nitrogen DC glow discharge, the back of cathode; cathode sheath; positive column; and anode glow. In positive column the rotational temperature increased apparently with the increasing discharge voltage from 500 to 1000 V when the pressure was 10 Pa. But with pressure of 20 Pa the rotational temperature in positive column increased slightly with the increase of discharge voltage. On the contrary, the rotational temperature in cathode sheath took reverse tendencies when the discharge voltage varies from 500 to 1000 V. As regard the anode glow, the rotational temperature at 10 Pa decreased with the increase of discharge voltage, but that at pressure of 20 Pa increased. We attribute the different tendencies of the rotational temperature to the different discharge statues at different pressures. When the discharge voltage varies from 500 to 1100 V, the discharge with pressure of 10 Pa is normal glow and that with 20 Pa is abnormal glow.     

甲烷氧等离子体直接合成过氧化氢

本文利用介质阻挡放电(DBD)方法, 在室温和常压下将甲烷和氧气的混合气体进行等离子体活化, 通过甲烷和氧等离子体直接气相反应高收率合成H2O2. 该方法能有效克服氢氧直接法合成H2O2受到原料气配比严格限制的缺点.     

Experimental studies on performance augmentation of single hole cored brick sensible heat storage system using turbulence inducers

This article presents experimental analysis on performance augmentation of a single hole cored brick regenerator using turbulence inducers. Experiments were carried out for different velocities with air as the working fluid for both charging and discharging processes of a 455 mm long aluminum regenerator with inner and outer diameters of 26 mm and 40 mm, respectively. Two numbers of turbulence inducers of 1.5 mm diameter and 13 mm long were placed in ten different combinations and the results were compared with the trials wherein no inducers were used. The mean temperature of the cored brick, exit temperature during discharge, ratio of heat transfer rate to pressure drop, and exergetic efficiencies are the characteristics that were used to study the performance of the regenerator. Placement of inducers increased the mean temperature of the regenerator and the ratio of heat transfer rate to pressure drop by about 15% and a maximum of 40%, respectively, during charging. The exit air temperature during discharge exhibited maximum improvement of 18%. Increased exergetic efficiencies of more than 10% and 5% were estimated for charging and discharging, respectively. It was also observed that the addition of inducers does not necessarily result in an increased performance, and some of the combinations in fact deteriorated the performance of the regenerator.

     

丙烯和氧等离子体直接气相合成环氧丙烷

在室温和大气压下,在针板式反应器中,通过脉冲电晕放电等离子体对分子氧和丙烯直接合成环氧丙烷的活化作用,考察了放电电极间距、电晕放电脉冲电压以及电晕放电重复频率参数对丙烯转化率、环氧丙烷产率和其选择性的影响,反应物及各产物通过在线色谱法进行分析.实验结果表明,在室温和大气压下,用脉冲电晕等离子体法可转化丙烯和氧气直接生成环氧丙烷,适当调节上述各参数可提高环氧丙烷的收率.当反应气总流速为200mL/min,极间距为4mm,脉冲放电电压为18kV,放电频率为120Hz时,环氧丙烷的收率、丙烯的转化率及环氧丙烷的选择性分别为5.15%,19.15%和26.89%.     

Nonequilibrium effects in thermal plasma chemistry

Numerical calculations have been performed to assess the potential significance of nonequilibrium effects on chemical reactivity in thermal plasmas The calculations consider situations in which the electron temperature and/or the electron density are elevated above their equilibrium values corresponding to the local gas temperature. Such nonequilibrium may occur in the plasma torch itself or could be purposefully imposed by a controlled hybrid discharge in a downstream reactor region so as to augment reactivity over a longer residence time. The calculations account for finite ionization/recombination rates of atomic and molecular species, electron-impact dissociation, dissociative recombination, dissociative attachment, and predissociation effects, as well as thermal reactions between neutral chemical species. As an example of the possible nonequilibrium enhancement of molecular decomposition, initial consideration has focused on the dissociation rates of diatomic species where heavy particle reaction rates and cross sections can be reasonably estimated. The results show that for O₂ or H₂ in argon at moderate temperatures, electron-temperature elevation can give rise to a notable enhancement of the dissociation rate, in comparison with the equilibrium case. Depending on the situation, it is found that either relatively energetic electron-impact dissociation or dissociative attachment (for O₂) can dominate the enhanced dissociation rate—which can be more than a factor of 2 greater than in the absence of a discharge. Similar effects would be expected for the decomposition of more complicated molecules.     

Wachstum dünner Fluorkohlenstoffschichten auf der Anode einer Glühkathodenentladung

The polymerization of tetrafluorethylene on the anode of a hot glow discharge has been investigated. Rates of polymer deposition have been measured as a function of monomer pressure, discharge current density, and electrode surface temperature. A mechanism of polymer formation is suggested. The results are different from those obtained by polymerization of the same monomer in a glow discharge. It is concluded that negative ions have a great influence on mechanism of polymer formation. Additionally, monomer molecules adsorbed at the electrode are polymerized by electron bombardment.     

Molecular interactions in aqueous solutions: The role of random fluctuations of external parameters and of thermodynamic instabilities

A biological system usually operates under nonstable values of relevant parameters, such as pH, temperature, and ionic strength. The question therefore poses whether such fluctations do affect its relevant processes. Experimental studies on the role of random temperature fluctuations on functional encounters of biostructural polymer molecules, and consequent self-assembly of supramolecular structures, have evidenced an additional, noise-induced order of these structures. This type of effect is the result of nonlinearity in physical systems, and the case of a biosystem is especially interesting. As recent experiments have shown, spinodal decomposition resulting from thermodynamic instability may favor the onset of the supramolecular ordering process. If the random fluctuations of temperature are imposed in such conditions of thermodynamic instability, their ordering effect is further enhanced.     

Spectroscopic study of argon MIP discharge used for analysis of solutions

Microwave-induced plasma (MIP) is an attractive excitation source which seems to be competitive to ICP-AES discharge. Reduced requirements in power and amounts of carrier gas and solution are considerable in comparison with ICP-AES. However, some disadvantages (such as a partial atomization and instability of discharge) can arise from the reduced power. Fundamental studies of MIP could be a help for control and proper selection of operating parameters of this discharge type. The behavior of solutions sprayed into an argon plasma was studied in a commercial MIP under different experimental conditions (argon and aerosol flow rates, discharge power). Rotational and vibrational energy distributions on the basis of the OH A²Σ − X²π molecular spectra and electronic energy distributions on the basis of atomic spectra have been measured under operative conditions and discussed from the point of view of analytical applications of MIP.