Study of partial discharge characteristics in HFO-1234ze(E)/N2 mixtures

HFO-1234ze(E)(trans-1,3,3,3-tetrafluoropropene, chemical formula: C₃H₂F₄) is an extremely environmentally friendly SF₆ alternative gas with high electrical strength. In this paper, the partial discharge (PD) characteristics of HFO-1234ze(E)/N₂ mixtures were studied using the gas insulation test platform. The PD inception voltage of insulating gas under positive and negative half cycles of power frequency was tested. Using SF₆/N₂ mixtures as a control group, the effects of electrode spacing, mixing ratio and pressure on the insulation performance of HFO-1234ze(E)/N₂ mixtures were explored. The test results show that the PD inception voltage of the negative half-cycle of pure HFO-1234ze(E) under short electrode spacing can reach 0.96–1.04 times of pure SF₆ under different pressures; the PD inception voltage of 40%HFO-1234ze(E)/60%N₂ mixtures at 0.3 MPa is 0.67–0.89 times that of SF₆/N₂ mixtures under the same conditions, which has great application prospect.     

The Electronegativity Analysis of c-C4F8 as a Potential Insulation Substitute of SF6

The density distributions related to gas electronegativity for c-C₄F₈ gas, including negative ion, electron number and electron energy densities in the discharge process, are derived theoretically in both plane-to-plane and point-to-plane electrode geometries. These calculations have been performed through the Boltzmann equation in the condition of a steady-state Townsend (SST) experiment and a fluid model in the condition of both uniform and non-uniform electric fields. The electronegativity coefficients a = n−/ne of c-C₄F₈ and SF₆ are compared to further describe the electron affinity of c-C₄F₈. The result shows that c-C₄F₈ represents an obvious electron-attachment performance in the discharge process. However, c-C₄F₈ still has much weaker gas electronegativity than SF₆, whose electronegativity coe?cient is lower than that of SF₆ by at least three orders of magnitude.     

Breakdown characteristics of CF_3I/N_2/CO_2 mixture in power frequency and lightning impulse voltages

Trifluoroiodomethane(CF_3I) and its mixtures are believed to be prospective alternatives to sulfur hexafluoride(SF6), which has been included as a greenhouse gas. In this paper, the breakdown properties of a CF_3I/N_2/CO_2 mixture with the volume fraction of CF_3I fixed at 10% are investigated under power frequency and lightning impulse voltages. The experimental result shows that N_2 possesses higher power frequency and negative lightning impulse breakdown voltages than CO_2, but the power frequency and more negative lightning impulse breakdown voltages of the CF_3I/N_2/CO_2 mixture do not increase with the content of N_2. For the purpose of explaining this abnormal phenomenon, the ionization energies and excitation energies of CF_3I,N_2and CO_2 are calculated. The computation results indicate that the ionization energy of CF_3I is lower than the first excitation energy of N_2, but higher than the lowest excitation energy of CO_2,which means that CF_3I molecules are easily ionized by metastable N_2 molecules. The first excitation energy of N_2 is too high, which hinders its application as the buffer gas of CF_3I.     

离心分离大质量数差混合物的实验研究方法

为探究混合物离心分离性能，提出了使用易于分离的气体介质进行实验研究的方法，选取全氟甲基环己烷（C₇F₁₄）/六氟化硫（SF₆）、C₇F₁₄/氙气（Xe）、一氟三氯甲烷（CCl₃F）/乙烯（C₂H₄）气体混合物作为离心分离介质，开展了分离实验。利用分馏装置分别得到了精、贫料中的各组分气体含量，结合质谱分析结果，得到了各组分气体的基本全分离系数与混合物的全净化系数。结果表明：此方法可方便分离轻重气体混合物，针对二元混合物离心分离，能给出全净化系数和各自组分的基本全分离系数，可用于混合物离心分离性能的实验研究。     

Surface charge accumulation behavior and its influence on surface flashover performance of Al2O3-filled epoxy resin insulators under DC voltages

Surface charge accumulation on insulator surface can have great influence on surface flashover performance. An experimental system is established to investigate surface charge accumulation and decay characteristics ofAl₂O₃-filled epoxy resin insulators in 0.1 MPa SF₆ under DC voltages. Surface potential is recorded by a Kelvin vibrating probe connected to an electrostatic voltmeter. By pre-depositing charges on insulator surface, the influence of surface charges on surface flashover performance is studied. The results reveal that surface charge distribution appearance is the combined effect of electrode injection, back discharge and gas ionization. Surface charge distribution has obvious polarity effect. It is concentrated near the HV electrode under positive voltages and dispersed under negative voltages. The difference in positive and negative surface flashover voltage is attributed to the difference in surface charge distribution under DC voltages of different polarities. Surface charge decay contains two stages, which satisfies the law of double exponential function. At first stage, surface charge decays fast, which corresponds to charges escaping from shallower traps. While it decays slowly at the second stage, which corresponds to charge escaping from deeper traps. Surface charge decay process is dominated by surface conductivity mechanism. The pre-deposited charges on insulation surface have great influence on surface flashover performance. The deposited positive charges can increase positive flashover voltage but decrease negative flashover voltage.     

Study of spatial and temporal evolution of Ar and F atoms in SF6/Ar microsecond pulsed discharge by optical emission spectroscopy

The study of sulfur hexafluoride (SF₆) discharge is vital for its application in gas-insulated equipment. Direct current partial discharge (PD) may cause SF₆ decomposition, and the decomposed products of SF₆, such as F atoms, play a dominant role in the breakdown of insulation systems. In this study, the PD caused by metal protrusion defects is simulated by a needle-plate electrode using pulsed high voltage in SF₆/Ar mixtures. The spatial and temporal characteristics of SF6/Ar plasma are analyzed by measuring the emission spectra of F and Ar atoms, which are important for understanding the characteristics of PD. The spatial resolved results show that both F and Ar atom spectral intensities increase first from the plate anode to the needle and then decrease under the conditions of a background pressure of 400 Pa, peak voltage of −1000 V, frequency of 2 kHz, pulse width of 60 μs, and electrode gap of 5–9 mm. However, the distribution characteristics of F and Ar are significantly different. The temporal distribution results show that the spectral intensity of Ar decreases first and then increases slowly, while the spectral intensity of F increases slowly for the duration of the pulsed discharge at the electrode gap of 5 mm and the pulse width of 40–80 μs.     

Investigation on pulsed discharge mode in SF6-C2H6 mixtures

The non-chain chemical HF(DF)laser is one of the most powerful electrically-driven lasers operating in mid-infrared,in which SF6-C2H6 mixtures are often used as lasering media.Due to the electronegativity of SF6,the discharge in SF6-C2H6 presents a complicated discharge mode.To achieve reproducible pulsed laser output,pulsed discharge in SF6-C2H6 mixtures is investigated for discharge mode using plane electrodes assisted by array pre-ionization spark pins in cathode surface.Firstly,two modes can be distinguished.One mode is called the selfsustained volume discharge(SSVD),which is characterized by spatial uniformity in the discharge gap and pulse to pulse repeatability.On the contrary,another mode includes random arc passages in the discharge gap and therefore cannot conduct lasering.By varying discharge conditions(gap voltage,gas pressure,etc)two discharge modes are observed.Secondly,the holding scope of the SSVD mode is analyzed for the optimal mixture ratio of 20:1,and the boundary tend of the holding scope of SSVD indicates there exists maximum gas pressure and maximum charging voltage for SSVD.Finally,the peak current of SSVD relates positively to charging voltage,while negatively to gas pressure,from which it is drawn that synchronous electron avalanches initiated by the sliding array overlap spatially into SSVD and thus SSVD is essentially an α ionization avalanche.     

Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas–liquid discharge generated in atmospheric N_2

In this paper,unipolar pulse (including positive pulse and negative pulse) and bipolar pulse voltage are employed to generate diffuse gas–liquid discharge in atmospheric N_2with a rumpetshaped quartz tube.The current–voltage waveforms,optical emission spectra of excited state active species,FTIR spectra of exhaust gas components,plasma gas temperature,and aqueous H_2O_2,NO_2~-,andNO_3~-production are compared in three pulse modes,meanwhile,the effects of pulse peak voltage and gas flow rate on the production of reactive species are studied.The results show that two obvious discharges occur in each voltage pulse in unipolar pulse driven discharge,differently,in bipolar pulse driven discharge,only one main discharge appears in a single voltage pulse time.The intensities of active species (OH(A),and O(3p)) in all three pulsed discharge increase with the rise of pulse peak voltage and have the highest value at 200 ml min~(-1)of gas flow rate.The absorbance intensities of NO_2and N_2O increase with the increase of pulse peak voltage and decrease with the increase of gas flow rate.Under the same discharge conditions,the bipolar pulse driven discharge shows lower breakdown voltage,and higher intensities of excited species (N_2(C),OH(A),and O(3p)),nitrogen oxides (NO_2,NO,and N_2O),and higher production of aqueous H_2O_2,NO_2~-,andNO_3~-compared with both unipolar positive and negative discharges.     

Dynamic dielectric recovery performance of serial vacuum and SF6 gaps in HVDC interruption and its regulation method

Vacuum gaps have rapid dynamic dielectric recovery speed while SF₆ gaps have high insulation strength. The series-connected vacuum and SF₆ gaps are used as the main switch (MS), which combines their advantages. The work aims to verify the feasibility of serial vacuum and SF₆ gaps in mechanical HVDC interruption. The test circuit of the dynamic dielectric recovery performance (DDRP) is set up. The DDRP is tested under free recovery condition by the high voltage pulse source. The DDRP of the vacuum circuit breaker (VCB) and SF₆ gas circuit breaker (GCB) in DC interruption with active current injection is analyzed and compared. The test results indicate that the dielectric recovery duration of the VCB is below 30 μs while that of the GCB is above 100 μs. In order to achieve the cooperation between the VCB and GCB, a novel hybrid HVDC circuit breaker (CB) based on series-connected vacuum and SF₆ gaps is proposed. The ‘voltage-zero’ duration is created by introducing the follow current loop and there more recovery time for the dielectric recovery of the MS. The voltage distribution is controlled by the voltage dividing method so that the VCB undertakes the initial transient recovery voltage (TRV) and the later TRV is took by the GCB. The theoretical synergy characteristic of the novel HVDC CB is obtained. The paper supplies a new method to improve the custom mechanical HVDC CB, which is useful to achieve the HVDC CB with less serial breaks.     

微型气相色谱法测定H2中杂质气体

为了满足氢同位素分离系统、 等离子体排灰气处理系统和贮存与供给工艺系统对进气品质的要求,需建立准确、快速、高精度的杂质气体分析方法。针对H₂中体积分数为10^-2~10^-3的气体组分He、Ne、N₂、Ar、CH₄、CO和CO₂,本研究首先采用配有1个Pora PLOT U通道和1个MS5- 通道的微型气相色谱仪,以H2为载气,建立H2中杂质气体的分析方法并优化测量参数。结果表明,杂质气体组分测量精密度优于0.2%,-0.5%<测量相对误差<0.5%,分离度>1.5,检出限为1.3×10^-6~8.5×10^-6,定量限为4.5×10^-6~36.3×10^-6,分析时间<2.5 min。在优化后的测量条件下探讨分别以He、Ne和Ar为载气测量H2中杂质气体的可行性,得到了标准气体色谱图。所建立方法能够满足工艺系统对进气的分析要求,并可拓展应用到其他氢同位素气体的杂质组分分析。     

The current pulses characteristics of the negative corona discharge in SF6/CF4 mixtures

This paper presents the results of numerical investigation of the current pulses characteristics in SF₆/CF₄ mixtures for the negative point-plane corona discharge. The pressure and the temperature of gas mixtures are 0.4 MPa and 300 K, respectively. The CF₄ content varies from20% to 80%. The 2D axisymmetric geometry with point-plane electrodes is investigated, and the three drift-diffusion equations are solved to predict the characteristics of the negative corona...     

Effect of ionizing radiation on the electrical characteristics ofpolyvinylidene fluoride (PVF2)

The influence of high-energy electron irradiation on the electrical properties of biaxially oriented polyvinylidene fluoride (PVF ₂) film was investigated. The film was irradiated in air with a 1-MeV electron beam at a dose rate of 10⁶ rad/min to different dose levels of up to 10⁸ rad. Electrical properties measured included dielectric permittivity and dielectric loss, AC and DC breakdown voltages, and DC volume resistivity, X-ray diffraction and IR spectroscopy measurements were also made. The most pronounced of the radiation-induced changes were a decrease in like AC breakdown voltage and an increase in dielectric loss, both corresponding to increasing total absorbed dose. DC breakdown voltage and volume resistivity also showed noticeable changes. These changes are believed to be associated initially with a radiation-induced crystal phase transformation. This was confirmed by the X-ray diffraction curve and the IR spectra, which showed an increase in the β-phase and a decrease in the α-phase peaks at higher dose levels     

Etching characteristics of thin SiON films using a liquefied perfluorocarbon precursor of C6F12O with a low global warming potential

Perfluorocarbon gas is widely used in the semiconductor industry. However, perfluorocarbon has a negative effect on the global environment owing to its high global warming potential (GWP) value. An alternative solution is essential. Therefore, we evaluated the possibility of replacing conventional perfluorocarbon etching gases such as CHF₃ with C₆F₁₂O, which has a low GWP and is in a liquid state at room temperature. In this study, silicon oxynitride (SiON) films were plasma-etched using inductively coupled CF₄ +C₆F₁₂O+O₂ mixed plasmas. Subsequently, the etching characteristics of the film, such as etching rate, etching profile, selectivity over Si, and photoresist, were investigated. A double Langmuir probe was used and optical emission spectroscopy was performed for plasma diagnostics. In addition, a contact angle goniometer and x-ray photoelectron spectroscope were used to confirm the change in the surface properties of the etched SiON film surface. Consequently, the etching characteristics of the C₆F₁₂O mixed plasma exhibited a lower etching rate, higher SiON/Si selectivity, lower plasma damage, and more vertical etched profiles than the conventional CHF₃ mixed plasma. In addition, the C₆F₁₂O gas can be recovered in the liquid state, thereby decreasing global warming. These results confirmed that the C₆F₁₂O precursor can sufficiently replace the conventional etching gas.     

Extraction behavior of Ga(III) and Pd(II) with 2-methyl-8-quinolinol derivatives into supercritical fluid CO2

The extraction behavior of gallium(III) and palladium(II) with 2-methyl-8-quinolinol (HMQ), 2-methyl-5-hexyloxymethyl-8-quinolinol (HMO₆Q) and 5-hexyloxymethyl-8-quinolinol (HO₆Q) from an acidic solution into supercritical fluid (SF) CO₂ were investigated. Furthermore, the pH of an acidic solution contacting with SF CO₂ was spectrophotometrically measured, and the distribution constants of HMO₆Q between SF CO₂ and water were also determined at I = 0.1 M (H, Na)NO₃, 45°C, and 8.6 – 20.4 MPa. Above pH 3, the pH of the aqueous phase in contact with SF CO₂ was levelled to about 3. On the other hand, below pH 3, the pH change is negligibly small. The distribution constant (K_{D,SF CO2} of HMO₆Q between SF CO₂ and water at 20.4 MPa was about one tenth of the K_D for heptane - water system, indicating that the solubility of HMO₆Q in SF CO₂ is remarkably smaller compared with that in heptane. The Ga(III)-HMO₆Q and Ga(III)-HO₆Q complex extracted into SF CO₂ were assigned to be Ga(OH)(MO₆Q)₂ and Ga(O₆Q)₃, respectively. Palladium(II) was extracted with HMQ as Pd(MQ)₂ from a weakly acidic solution. Even in the presence of HMQ, the Pd(II)-HMQ complex extracted from the higher HCl concentration should be H₂PdCl₄.     

ESR法研究Pt催化N2H4分解机制

采用电子自旋共振谱（ESR）法，研究了酸性条件下•NH₂的转化，HClO₄体系下反应时间对溶液中自由基产生的影响、pH值对N₂H₄断键的影响以及HNO₃中N是否对溶液中的•NH₂有贡献，确定了Pt催化N₂H₄分解的反应机理。结果表明：在酸性条件下•NH₂被DMPO捕捉时反应式为•NH⁺₃+HO-H+DMPO=NH⁺₄+DMPO(•OH)，硝酸在Pt催化N₂H₄体系中不会发生断键产生•NH₂，所产生的•NH₂是由N₂H₄断键形成的；在HClO₄体系中，随着Pt催化N₂H₄反应时间的延长，N₂H₄中N-N断键的趋势逐渐减小，N-H断键的趋势逐渐增大；随pH值的增大，N₂H₄中N-N断键的速率先快速减小，pH>3后缓慢增大；Pt催化N₂H₄分解反应中N-N断键和N-H断键两种方式共存，但N-N断键占优；反应体系中N₂H₄与H^＋浓度之比决定了N-N断键生成•NH₂的速率，而•NH₂与H^＋的浓度又决定了•NH₂转化成产物的速率，这两方面共同决定了N₂H₄分解的速率。     

Pt催化N2H4还原U(Ⅵ)制备U(Ⅳ)过程中N2H4断键机制研究

为优化硝酸介质下Pt催化N₂H₄还原U(Ⅵ)制备U(Ⅳ)的工艺条件，确定此反应过程的控制步骤，有针对性地提高控制步骤的反应速率，以确定N₂H₄还原U(Ⅵ)制备U(Ⅳ)过程中的反应历程以及反应机理，通过实验研究确定了N₂H₄在Pt催化剂上的断键方式和分解机理。采用气相色谱法、分光光度法、滴定法及排水法对硝酸介质下Pt催化N₂H₄还原U(Ⅵ)制备U(Ⅳ)过程中的产物进行分析，确定反应过程中N₂H₄的断键机制。结果表明，硝酸介质下Pt催化N₂H₄还原U(Ⅵ)制备U(Ⅳ)反应过程中没有叠氮酸、氮氧化物及氢气生成，产物主要是N₂，生成的N₂的量与消耗的N₂H₄的量接近1∶1；当存在U(Ⅵ)时，生成的NH⁺₄产量较低，当U(Ⅵ)反应完全后，NH⁺₄的产生速率急剧增大；N₂H₄以N-N断键和N-H断键两种方式共存；反应温度升高有利于加快由U(Ⅵ)制备U(Ⅳ)还原反应的进行。     

SF6示踪剂远程泄漏监测系统设计及性能

非放射性气体示踪技术是一种常用的泄漏检测技术,SF₆是常用的气体示踪剂。对一些特殊检测场所,如贮存放射性和有毒有害气体的容器的泄漏监测,建立示踪剂在线采样和分析系统十分必要。本文阐述了SF₆示踪剂多监测点在线监测系统的设计思路和主要功能模块流程。该系统的样品消耗量小,可通过压力控制减小样品消耗。实验证实,系统运行对色谱基线无影响,同一样品通过不同监测通道在不同时刻的分析结果的相对标准偏差小于1%,不同监测通道样品无交叉污染,采样点的温度、压力监测结果与就地仪表监测精度相当。     

LiH和LiT与H2O反应机理研究

氢材料在微量H₂O、CO₂、O₂和N₂存在下可能发生物理化学反应,使材料的物理品位下降。由于反应过程十分复杂,很难从实验上准确获取这类反应的最佳通道和具体产物信息,因此,从理论上研究氢材料分子的物理化学性质及其化学反应机制,了解化学反应过程具有十分重要的意义。本文使用Gaussian03软件包和Gaussview工具软件,在6-311G(d)全电子基函数水平上,应用二阶微扰理论优化得到了⁶LiH、⁶LiT与H₂O反应的中间体、过渡态及产物的结构,总能量,振动频率和零点能等。通过计算发现⁶LiH、⁶LiT均只有1个反应通道,⁶LiH与H₂O反应的焓变、活化能和反应速率常数分别为-156.99 kJ/mol、8.95 kJ/mol和3.75×10¹⁰(mol•dm^-3)^-1/s,⁶LiT与H₂O反应的焓变、活化能和反应速率常数分别为-159.02 kJ/mol、9.92 kJ/mol和1.72×10¹⁰ (mol•dm^-3)^-1/s。     

Ni-MOF-74制备及其对CO的吸附性能

通过水热合成法制备了Ni-MOF-74材料，采用全自动表面积吸附仪、PXRD、扫描电子显微镜、同步热分析仪对材料的孔隙结构、晶体形貌和热稳定性进行了表征，并采用静态吸附法测定了CO、N₂、CH₄和CO₂在Ni-MOF-74上的吸附等温线；采用挤压成型方法制备了Ni-MOF-74成型材料，并研究了挤压成型后Ni-MOF-74晶体结构和微孔结构的变化及对CO的吸附性能的影响。结果表明，制得的Ni-MOF-74材料比表面积达1 212.61 m²/g ，其孔径主要集中在0.8～1.0 nm之间，对CO的吸附量远高于相同条件下对N₂和CH₄的吸附量，具有良好的热稳定性；Ni-MOF-74对CO的吸附作用力明显高于对N₂、CH₄和CO₂的；挤压成型后Ni-MOF-74的完整晶体数量明显减少，且部分微孔结构遭到破坏，成型后对CO的吸附性能明显下降。     

Reactive ion etching of PECVD silicon nitride in SF6 plasma

The reactive ion etching of PECVD silicon nitride thin films has been investigated using SF₆ plasma. Effects of variations of process parameters such as pressure (50–350 mTorr), RF power (50–250 W), gas flow rate (3–130 sccm) and additions of O₂ and He (0–50%) in SF₆, on the PECVD silicon nitride etch rate and selectivity to the AZ 1350J photoresist were examined. An etch rate of 1 μm/min has been obtained under the condition of 150 mTorr, 100 W and 60 sccm. Experimental results also indicated a maximum etch rate at approximately 30% O₂ while addition of He showed only dilution effect. A nitride/photoresist selectivity ranging from 1 to 3:1 has been obtained.