双分子水和氨气催化CF3OH分子裂解的理论研究

利用G3和CBS-QB3的理论方法研究CF₃OH分子裂解成FCFO和HF,并考虑大气中双分子和氨气对CF₃OH分子裂解的催化作用. 理论计算表明：由于在G3的理论水平下,计算的能垒为188.52 kJ/mol,所以CF₃OH分子在大气条件下不可能发生单分子裂解;当氨气和双分子水被加入时,能垒都被降到25.08 kJ/mol,起了强的催化作用. 除此之外,应用过渡态理论对速率常数进行了计算,计算结果表明：氨气催化CF₃OH分子的速率常数是单分子和双分子催化CF₃OH分子裂解速率常数的10⁹和10⁵倍. 考虑到大气中这些物质的浓度,计算结果预测了氨气催化CF₃OH分子裂解在大气中起到重要的作用.     

Research on chemical and discharge oxygen-iodine lasers

Novel methods and device configurations for singlet oxygen and atomic iodine generation were proposed and investigated for operation of the chemical or discharge oxygen-iodine lasers (COIL/DOIL). A chemical centrifugal spray generator of singlet oxygen was developed, based on the conventional chlorine-basic hydrogen peroxide chemistry. Results of theoretical and experimental investigation of the generator parameters are presented and compared with parameters of other generator types. A design of experimental device for singlet oxygen generation by means of the hybrid DC arc and RF plasma jet is presented. An alternative method of atomic iodine generation by a radiofrequency discharge decomposition of iodine compounds like CH₃I or CF₃I is described employing advanced experimental configuration. Some representative experimental results of this investigation are presented.     

低压下直流电弧热等离子体射流电子密度的光谱法测量

采用原子发射光谱仪研究低压直流电弧热喷涂等离子体射流的特性。利用Stark展宽法采集H_β谱线,使用其Δλ_1/2来计算等离子射流中的电子密度,研究了氢气流量、输入功率和探测距离对等离子体射流中电子密度的影响。使用Saha方程计算热等离子体的电离程度,研究了功率/氢气流量与等离子体电离程度的关系。结果表明:电子密度和电离程度随着电流强度的增大而增加;氢气流量增加可以明显提高等离子体射流的能量,但对电离程度影响不大。     

Mass spectrometry of arcs in SF6 circuit breakers

Today, SF₆ is used to a great extent as insulating and arc-quenching medium in high-voltage gas-blast circuit breakers. The arcing in SF₆ during current interruption forms decomposition products. These can influence the arc-quenching properties of the circuit breaker. Furthermore, they can cause corrosion of the circuit breaker housing. In this comprehensive study we present results obtained for the first time from a direct mass spectrometric investigation of the exhaust gases of a high pressure SF₆ arc in a model circuit breaker. Our mass spectrometric system consists of a time-of-flight mass spectrometer (TOFMS) equipped with a molecular beam sampling systems. This device allows us to measure mass spectra of high pressure sources with a time resolution of up to 10,000 spectra per second. We have determined the formation rate of the most abundant decomposition products in a SF₆ arc at 1 bar. These products are SF₄, CF₄, WF₆, SOF₂, SO₂, CS₂ S₂F₂ and HF. The fast detection time inherent to our system permits also the determination of the formation of SF₄, which is 0.45–0.50 Vol. %/(kJ/1SF₆). In addition, we have studied the influence of water and oxygen impurities which are responsible for the production of highly corrosive HF. Finally, we have considered the influence of the thermal degradation of teflon (P.T.F.E.), which is used as nozzle and insulating material in circuit breakers. On this occasion we have demonstrated that CF₄, which exhibits dielectric properties similar to SF₆, is the main decomposition product formed from teflon. However, we have found that besides CF₄ also excess carbon is formed, which is deposited on insulators of the model circuit breaker.Our time-resolved mass spectra reveal that the CF₄ production from teflon is delayed by a few milliseconds with respect to the SF₆ dissociation in the arc. This delay can influence the interrupting process of the circuit breaker by changing the plasma composition during the arcing period. Although our experiments have been performed on a model circuit breaker we claim that the results presented in this study can be applied to real circuit breakers, since the arc current density and the energy dissipated per liter SF₆ are of the same order of magnitude in both devices.     

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采用焓探针对大气压力下热喷涂等离子体射流的焓和温度进行了测量和计算,研究了氩气流量变化、电流变化和喷涂距离对等离子射流的焓和温度分布的影响。结果表明,氩气流量不变的情况下,随着功率的增加等离子体的焓值和温度增加;电流保持不变时,随着氩气流量的增加等离子体的焓值和温度不断减小,随着距离喷嘴出口轴向距离的增加,等离子体的焓值和温度都大幅度的降低;氩气流量变化对喷枪热效率影响不大,功率增大时,喷枪热效率增加显著,喷枪热效率最高可达到60%。     

Plasma deposition of silicon-containing polymer and some of its physical properties

Silicon containing polymer was deposited in a high frequency plasma in a silica barrel reactor. Hexamethyldisilazan (HMDS) was chosen as the monomer; silicon atoms are bounded in the polymer by -NH-groups. An influence of different deposition conditions and subsequent processing of polymer on its properties were studied. We measured the etch rate in CF₄+O₂ plasma (barrel reactor), thermal stability to 400 °C, dielectric strength (irreversible breakdown), permittivity? and dielectric losses tanδ.     

使用发射光谱对H2稀释情况下的感应耦合H2/C4F8等离子体中碳氟基团的研究

在射频输入功率为400W，气压为0.8Pa的条件下，使用光强标定的发射光谱方法研究了感应耦合H₂/C₄F₈等离子体中CF, CF₂, H和F基团的相对密度随流量比R=H₂/(H₂+C₄F₈)的变化情况，而HF基团相对密度的变化由四级质谱仪探测得到。结果表明等离子体活性先随着R的增加而升高，然后随着R的进一步增加而下降。在流量比从0逐渐上升到0.625的过程中，CF和CF₂基团的相对密度不断降低。实验中测得的CF基团的相对密度[CF]与理论计算得到的[CF]有很好的一致性说明了电子与CF2基团的碰撞反应是CF基团产生的主要原因。文中还讨论了HF基团。     

Study of the fluid flow characteristics in a porous medium for CO2 geological storage using MRI

The objective of this study was to understand fluid flow in porous media. Understanding of fluid flow process in porous media is important for the geological storage of CO₂. The high-resolution magnetic resonance imaging (MRI) technique was used to measure fluid flow in a porous medium (glass beads BZ-02). First, the permeability was obtained from velocity images. Next, CO₂–water immiscible displacement experiments using different flow rates were investigated. Three stages were obtained from the MR intensity plot. With increasing CO₂ flow rate, a relatively uniform CO₂ distribution and a uniform CO₂ front were observed. Subsequently, the final water saturation decreased. Using core analysis methods, the CO₂ velocities were obtained during the CO₂–water immiscible displacement process, which were applied to evaluate the capillary dispersion rate, viscous dominated fractional flow, and gravity flow function. The capillary dispersion rate dominated the effects of capillary, which was largest at water saturations of 0.5 and 0.6. The viscous-dominant fractional flow function varied with the saturation of water. The gravity fractional flow reached peak values at the saturation of 0.6. The gravity forces played a positive role in the downward displacements because they thus tended to stabilize the displacement process, thereby producing increased breakthrough times and correspondingly high recoveries. Finally, the relative permeability was also reconstructed. The study provides useful data regarding the transport processes in the geological storage of CO₂.     

Photocatalytic performance of TiO2/V2O5 nanocomposite powder prepared by DC arc plasma

TiO₂/V₂O₅ nanocomposite powder was synthesized by the DC arc plasma, and its photocatalytic activity was examined by decompositions of Rhodamine B solution and toluene gas. In the synthesis of TiO₂/V₂O₅ nanocomposite powder, TiCl₄ and VOCl₃ precursors were introduced into thermal plasma flame with argon carrier gases through separated two gas bubblers. They were decomposed by Ar–N₂ thermal plasma generating Ti and V vapors, followed by the formation of oxides with the injection of additional oxygen into a plasma reactor. Nanocomposite composed of relatively small size V₂O₅ nanoparticles on a spherical TiO₂ nanoparticle which was about 250 nm in diameter was identified by X-ray diffractometry, electronic microscopy, and energy dispersive spectroscopy when the ratio of carrier gas flow rates for TiCl₄ to VOCl₃ was 1:4 or 1:5. In ultraviolet–visible absorption spectroscopy, the absorbed wavelength of light for synthesized TiO₂/V₂O₅ nanocomposite powder was wider than that for commercially available TiO₂ nanopowder. Therefore, Rhodamine B solution exposed to visible light was decomposed by TiO₂/V₂O₅ nanocomposite, whereas it was not decomposed by TiO₂ nanopowder. In addition, toluene decomposition in a dielectric barrier discharge reactor was carried out with nano-sized photocatalysts of TiO₂ nanopowder and TiO₂/V₂O₅ nanocomposite. Relatively higher removal rate of toluene was found in the case of TiO₂/V₂O₅ nanocomposite in virtue of improved photocatalytic performance.     

Zersetzung von CCl4 im HF-Niederdruckplasma für plasmachemisches Ätzen von Aluminium

After a brief summary of decomposition processes occuring in a plasma etching reactor investigations of CCl₄-decomposition by gaschromatography and time resolved emission spectroscopy are described. The decomposition takes place in a plasma tube with external r.f. electrodes. The qualitative identification of decomposition products of CCl₄ shows few main products only quite in contrast to plasma decomposition of hydrocarbons. These are CCl₄, Cl₂, C₂Cl₄, C₂Cl₆ and glow polymers. The dependence of the product distribution on power density and flow rate gives some hints for a rapid decomposition mechanism. The time resolved emission spectroscopy bases on a two channel method using a reference signal of an Ar line to eliminate the changing plasma conditions during the decomposition process. The limits of application of this method are discussed. Investigations of CCl-, Cl₂- and Cl-intensity-time-functions also reveal the existence of a the rapid decomposition mechanism for which a dissociative electron attachment is supported giving rate constants in the expected order of magnitude.     

Theoretical study on the interaction of heptafluoro-iso-butyronitrile decomposition products with Al (1 1 1)

Seeking environmentally friendly gas-insulated medium has become a research hotspot in recent years. At present, C₃F₇CN (Heptafluoro-iso-butyronitrile) is considered to be a potential SF₆ environment-friendly alternative gas and some achievements have been made in the study of its insulation and decomposition characteristics, but there are few reports on the compatibility between its characteristic decomposition products and materials. The investigation of compatibility between gas-insulated medium and material is an important part of evaluating its comprehensive performance. In this paper, we investigated the interaction between C₂F₅CN, CF₃CN, COF₂ and CF₄ with the aluminium widely used in electrical equipment. It was found that the interaction between C₂F₅CN, CF₃CN and Al (1 1 1) surface is strong. There are obvious charge transfer and electron orbital overlap between the C atom, N atom in CN group and Al (1 1 1). The interaction between COF₂, CF₄ and Al (1 1 1) surface is weak and van der Waal’s forces play the major role. Relevant results reveal the characteristics of C₃F₇CN decomposition products and provide theoretical guidance for evaluating the material compatibility between C₃F₇CN decomposition products and aluminium.     

洛伦兹力对自由燃烧弧和壁稳非转移弧流场的影响

通过耦合迭代求解流体力学方程和电磁场方程,数值模拟了转移式自由燃烧电弧和具有细长中间段及突扩阳极结构的壁稳式非转移直流电弧的流场,分析了洛伦兹力对这两种典型直流电弧流场的影响。结果显示:在自由燃烧电弧情况下,电流自感磁场的洛伦兹力对流场特性有显著影响,自磁压缩是约束电弧的主要机制;而在壁稳式非转移直流电弧情况下,相对于强壁面约束和气动力作用而言,洛伦兹力对流场的影响有限。特别在中间段出口以后,洛伦兹力与气动力的比值小于0.010,因此,当主要考虑壁稳式非转移直流电弧发生器出口参数时,为了提高数值模拟效率,可忽略洛伦兹力的作用。     

Conversion of tar in supercritical water/oxygen fluid with soot suppression

An autothermal mode of tar conversion was implemented in a vertical tubular reactor. The pressure was 30 MPa; the tar and water flows were 4.9 and 6.9 g/min, respectively; the oxygen flow varied: 0, 2.9, 4.5 and 5.8 g/min. The tar was supplied from above, at the first stage into a counter-flow of supercritical water (SCW) and at the subsequent ones into a flow of SCW/O₂ fluid. The high-molecular sedimentary layer (HSL) that formed at the first stage was replenished continuously at the subsequent stages, consisted of tar components depositing on the bottom of the reactor and was suppressing formation of soot. The autothermal mode of the process was achieved due to heat release in the combustion of the lower part of the HSL in the SCW/O₂ fluid. With increased O₂ flow, the power of ohmic heaters was reduced to zero and the reactor wall temperature increased from the initial 723 K to 818 K. Elemental and mass spectrometric analyses of the liquid and volatile conversion products collected at the outlet of the reactor, as well as of the solid conversion residue taken from the reactor, enabled determination of their amount and composition. This in turn allowed us to write down the gross reaction of tar conversion in the SCW/O₂ fluid and determine the characteristics of the equivalent fuel and the thermal effects of its oxidation     

Nanoparticle Microreactor: Application to Synthesis Of Titania by Thermal Decomposition of Titanium Tetraisopropoxide

The nanoparticle microreactor (NPMR) is a new concept that we have introduced to describe a very small-scale system capable of converting an aerosol precursor to solid particles. The liquid precursor of about 1 µl is injected by a syringe through a septum into a tubular evaporator of 1.0 cm³ in volume with stopcocks at both ends. The evaporator has been preheated by a heating tape to a temperature sufficiently high for vaporization to occur in half a minute. By opening the stopcocks, the vaporized precursor is transported by a carrier gas stream into a quartz tube which is mounted along the axis of a tubular furnace. The nanoparticle aggregates produced in the reactor are sampled by deposition on an electron micrograph grid at the reactor exit. The NPMR was applied first to the synthesis of TiO₂ particles by thermal decomposition of titanium tetraisopropoxide (TTIP) in a nitrogen carrier gas, with TTIP concentrations varying from 1.0 to 7.0 mol% or 2.35×10^–6 to 1.65×10^–5 in TiO₂ volume loading, and decomposition temperatures from 300°C to 1000°C. Studies were made with a 2 mm reaction tube and a 4 mm tube with sheath gas. With the 2 mm tube, a considerable fraction of the TTIP precursor was consumed at the wall by surface reaction, resulting in very small particles. With the 4 mm tube, the primary particle size was comparable to that reported in the literature for steady flow experiments using a 22.2 mm tube. Primary particle sizes ranged from 200 to 400 nm. Depending on TTIP concentration and reactor temperature, the particles exhibited a bimodal size distribution, probably due to a two-stage nucleation. A fourfold increase in the gas flow rate had little effect on particle size, indicating that particle growth ended early, within one-fourth the tube length. Residence time in the reactor was between 0.35 and 1.4 s, and total run time about 1 min. The NPMR has potential for rapid assembly of large databases and is adaptable to combinatorial discovery of nanoparticles with novel properties. Design requirements for an ideal aerosol microreactor are discussed briefly.     

Numerical investigation of the effects of polydisperse water sprays on extinction conditions of counterflow methane non-premixed flames

Water, sprayed in the form of tiny droplets, has emerged as a potential fire suppressant after the halon compounds such as trifluorobromomethane (CF₃Br, Halon 1301) were banned by the Montreal protocol. The size distribution of the water droplet plays a crucial role in the effectiveness of the water spray in fire suppression. A numerical investigation of the influence of size distribution of a polydisperse water spray on extinction of counterflow diffusion flames is presented in this paper. This study uses laminar finite rate model with reduced CHEMKIN chemistry for numerical simulations. The discrete phase, namely the water spray, is simulated using Lagrangian Discrete Phase Modelling approach. In this work, the polydispersity of water spray is taken into account in the numerical simulation by a suitable Rosin–Rammler distribution. Results obtained from numerical simulation are validated with the experimental results reported in the literature. This study demonstrates that the representation of the polydisperse spray by a monodisperse spray (with droplet diameter same as the SMD of the polydisperse spray) in numerical simulations is not always justified and it leads to deviation from the experimental results. The effects of number mean diameter and spread parameter on the efficacy of flame suppression are investigated for polydisperse sprays. A comprehensive comparison is done between the effectiveness of monodisperse and polydisperse water sprays. An optimum droplet diameter is obtained for monodisperse sprays for which the effectiveness of the spray is maximum. The effects of evaporation Damköhler number and Stokes number of water droplets on flame suppression have also been explained.     

Zur plasmachemischen Umsetzung von GaAs mit CCl4 und CF2Cl2 in Gegenwart von Sauerstoff

The halogen liberation and reaction with GaAs by a plasma discharge in a flow reactor, using CCl₄, CF₂Cl₂ and CCl₄/O₂, CF₂Cl₂/O₂ mixtures was measured. The yields were studied in dependence from the output of a 27 MHz radio-frequency generator and from the oxygen content of the etching gas. A simple model of the kinetics is introduced to discuss the experimental results.     

Very low pressure plasma sprayed alumina and yttria-stabilized zirconia thin dense coatings using a modified transferred arc plasma torch

As a novel thermal spray process, very low pressure plasma spray (VLPPS) process has been significantly used to deposit thin, dense and homogenous ceramic coating materials for special application needs in recent years. In this study, in order to enhance low-energy plasma jet under very low pressure ambience, a home-made transferred arc nozzle was made and mounted on a low-power F100 plasma torch to fully melt or evaporate powder feedstock. As a result, thin and dense alumina (Al₂O₃) and yttria-stabilized zirconia (YSZ) ceramic coatings with an average thickness of 30-40 μm were successfully elaborated by the VLPPS process below 1 mbar. An optical emission spectroscopy (OES) was used to analyze the plasma jet properties. The microstructures of the coatings were observed by means of a scanning electron microscopy (SEM). It was found that the YSZ coatings displayed a bimodal microstructure which was composed of splats formed by melted particles and a little amount of vapor condensation from evaporated particles. However, vapor condensation could not be observed in the Al₂O₃ coatings, and only lamellar splats were found. The mechanical properties of both coatings were also evaluated.     

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In order to optimize the process of plasma spheroidization of the lithium micro-powder, a 2-D model of inductively coupled thermal plasma torch is presented. The calculating domain of the electromagnetic field is extended to the air region outside the plasma discharge region and multi-physics coupling calculation was performed by using COMSOL software. The plasma electromagnetic field, temperature and velocity distributions are obtained. The physical mechanism of distributions is analyzed. The simulation found that there are two sets of symmetrical reflux vortices in the coil section of the plasma region. The velocity distribution which locates in the center of coil section and closes to the wall of confinement tube is in disorder. The plasma particles hit the wall along the radial direction. Disorderly flow may cause a rupture area along the circular tube wall. Based on the simulation results, it is proposed that in the process of inductively coupled plasma spheroidization, powder injection port can be moved down to avoid the upper reflux vortex.     

Thermal release of trapped deuterium from silica injected by 80-keV D+ ion implantation and RF D2 plasma

When silica is irradiated by 80-keV D⁺ ions or RF plasma of D₂ gas, deuterium is trapped in the silica forming Si-OD bonds. The deuterium, trapped as OD bonds, is desorbed from the silica upon heating to form some release products. The thermal detrapping process corresponds to decrease of OD bonds and was studied by measurement of infrared Fourier transform spectroscopy (FTIR). The release products HDO, D₂O, HD, and D₂ were measured by quadrupole mass spectroscopy (QMS). The detrapping and release processes of trapped deuterium were studied by simultaneous measurement of FTIR and QMS. Since the release spectra of HDO, D₂O, HD, and/or D₂ correspond to the decrease spectra of OD bonds, these release products are formed by thermal decomposition of OD bonds. The formation of water (HDO, D₂O) and hydrogen (HD, D₂) depends upon concentration of pre-existing OH bonds and deuterium injection methods (80-keV D⁺ implantation or RF D₂ plasma irradiation).     

基于COMSOL 的感应耦合等离子体炬多物理场研究

为了优化锂微粉等离子体球化的工艺,对感应耦合等离子体炬进行二维建模,将电磁场计算域扩展到等离子体放电区域之外的空气区域,利用COMSOL 软件进行多物理场模拟。得到了等离子体的电磁场、温度和速度分布,并对分布形成的物理机制进行分析。模拟发现等离子体区域线圈段存在上下两组对称的回流涡,线圈段中部靠近约束管处等离子体速度分布杂乱,有激烈的径向打壁现象,乱流预计会对约束管壁相应位置造成一条环状的破裂效果。基于模拟结果,提出在采用感应耦合等离子体球化锂微粉的工艺工程中,可以将注粉口下移,绕开上回流涡。