CF3I Mixtures Research Articles

Simulation Analysis of Arc-Quenching Performance of Eco-Friendly Insulating Gas Mixture of CF3I and CO2 under Impulse Arc

Due to its superior insulating qualities, SF6 gas is extensively used in the power sector. However, because of its poor environmental protection properties, finding ecologically acceptable insulating gas has become a critical challenge in the power sector in the context of pursuing green electricity. This work simulates the arc-quenching performance of a gas mixture of CF3I and CO2, which is thought to be a workable substitute for SF6 gas. The COMSOL software is used to build a two-dimensional model of a single-pipe arc-quenching chamber based on the concepts of magnetohydrodynamics (MHD) theory. The lightning impulse current is made by applying electrical stimulation to pure CO2 gas, gas mixtures with 10% CF3I and 90% CO2, and gas mixtures with 30% CF3I and 70% CO2 in the single-pipe arc-quenching chamber. During the first stage of arc formation, the results show that CF3I/CO2 gas mixtures with 10% and 30% CF3I have lower electrical conductivity than pure CO2 gas. An 8/20 μs lightning impulse current waveform with a magnitude of 4 kA is used for this observation. The highest airflow velocity for pure CO2 is 1744 m/s, but the mixture of 10%/90% CF3I/CO2 has a maximum airflow velocity of 1593 m/s. The 30%/70% CF3I/CO2 mixture has the highest maximum airflow velocity at 1840 m/s. Airflow velocity increases and the overpressure in the arc-quenching chamber is prolonged when there is a greater concentration of CF3I gas in the gas mixture. Consequently, these factors greatly reduce the duration of the arc-extinguishing time. The arc-quenching chamber’s overpressure is extended when the amount of CF3I gas in the gas mixture is increased, which increases the velocity of the airflow. As a result, these factors significantly decrease the duration of the arc-extinguishing time.

A Prototype of Electric Discharge Gas-Flow Oxygen–Iodine Laser: 2. Simulation of the Parameters of the Active Medium Formed in a Gas-Flow Slab RF Discharge in O2 : He : CF3I Mixtures

A calculated analysis of the possibility of achieving the generation in a gas-flow electric discharge oxygen–iodine laser when it is excited by a transverse slab RF discharge for various conditions of passing of the CF3I : O2 : He gas mixture components along the gas duct was carried out: in subsonic flow without cooling the channel walls and with cooling of various sections of the channel walls down to 100 K. To do this, reactions involving CF3I iodide and the photon balance equation were added to the model. It was assumed that the active medium was formed in two ways: (i) all components of the gas mixture simultaneously passed through the RF excitation zone; (ii) oxygen and helium passed through the RF discharge zone, and the iodide-containing component (CF3I : He mixture) was introduced through an injector located downstream gas flow from the discharge zone. Calculations have shown that it is possible, in principle to achieve the laser generation mode under conditions implemented on the experimental setup.

Plasma Etching of SiO2 with CF3I Gas in Plasma-Enhanced Chemical Vapor Deposition Chamber for In-Situ Cleaning

Non-global-warming CF3I gas has been investigated as a removal etchant for SiO2 film. Thermally fabricated SiO2 films were etched by the plasma generated with a gas mixture of CF3I and O2 (CF3I/O2) in the plasma-enhanced chemical vapor deposition chamber. The etch rate of SiO2 films was studied along with the process parameters of plasma etching such as chamber pressure, etching gas flow ratio of CF3I to CF3I/O2, plasma power, and chamber temperature. Increasing the chamber pressure from 400 to 1,000 mTorr decreased the etch rate of SiO2 film. The etch rate of this film showed a minimum value at a gas flow ratio of 0.71 in CF3I to CF3I/O2 and then increased at a higher CF3I gas flow ratio. In addition, the elevated plasma power increased the etch rate. However, the chamber temperature has little effect on the etch rate of SiO2 films. When only CF3I gas without O2 was supplied for etching, polymerized fluorocarbon was formed on the surface, indicating the role of oxygen in ashing the polymerized fluorocarbon during the etching process.

Comparison of dielectric breakdown properties for different carbon-fluoride insulating gases as SF6 alternatives

As a widely used insulating medium, sulfur hexafluoride (SF6) is a greenhouse gas with very high global warming potential (GWP). Some carbon-fluoride gases have potential to replace SF6 in insulating applications. In order to reveal their different dielectric performance, this paper is devoted to a comparative study of dielectric breakdown properties for SF6 and four carbon-fluoride insulating gases i.e. CF3I, C2F6, C3F8, and c-C4F8 mixed with CO2, N2, and CF4 based on the numerical solution of Boltzmann equation. The electron energy distribution function (EEDF), reduced ionization coefficients α/N, reduced electron attachment coefficients η/N, and reduced critical electric field strength (E/N)cr are compared for various gas mixtures. Generally c-C4F8 presents the largest dielectric strength among the four carbon-fluoride insulating gases whichever buffer gas is mixed, while C2F6 presents the lowest dielectric strength. In terms of (E/N)cr and GWP, CF3I is a good eco-friendly insulating medium. However, with the addition of buffer gases, the (E/N)cr of CF3I mixtures declines more quickly than other mixtures. It is also found that the mixing of CF4 makes insulating mixtures depend more linearly on the proportions of buffer gas than CO2 and N2.

Experimental and theoretical study of RF capacitively coupled plasma in Ar–CF4–CF3I mixtures

Radio frequency capacitively coupled plasma (RF CCP) sustained at RF frequencies of 27 MHz in an Ar–CF4–CF3I gas mixture is studied experimentally and theoretically. The RF CCP in Ar–CF4–CF3I is simulated by using a 1D hybrid particle-in-cell–fluid numerical model. We pay special attention to the changes in plasma structure and fluxes to the electrode, negative ion and neutral radical production with admixture of CF3I in Ar–CF4 plasma. With CF3I admixture the plasma becomes strongly electronegative as a result of the high electron attachment rate to the CF3I molecule. The atomic fluorine density becomes extremely low with addition of CF3I molecules due to the large volume loss in the reaction CF3I + F → CF3 + IF. Optical emission spectrometry data on CF2 emission at the wavelength of 250 nm indicate the essential sources of CF2 in CF3I-containing plasma in the studied conditions, although direct dissociation channels for the CF3I molecule with CF2 production have not been studied. Evaluation of CF2 density in Ar–CF4–CF3I plasma was first carried out on the basis of the actinometry technique and numerical simulation. The possible mechanism of ultra-low-k film damage in the studied conditions is also discussed.

Analysis of the insulation characteristics of CF3I gas mixtures with Ar, Xe, He, N2, and CO2 using Boltzmann equation method

The present study is devoted to the calculation of electron swarm parameters, including the reduced effective ionization coefficient, electron mean energy, and electron drift velocity, for the gas mixtures of CF3I with Ar, Xe, He, N2, and CO2. These data are computed by employing the Boltzmann equation method with two-term approximation in the condition of steady-state Townsend (SST) discharge. For the purpose of evaluating the insulation strength of CF3I gas mixtures, values of the limiting field strength (E/N)lim for which the ionization exactly balances the electron attachment are determined from the variation curves of (α − η)/N. The results indicate that mixtures of CF3I–N2 present the greatest insulation strength among all the combinations for CF3I content varied from 20 to 90%. Furthermore, the gas mixture with 70% CF3I can achieve a very similar dielectric strength to that of SF6. The concerned liquefaction issues are also taken into account to fully assess the possibility of applying CF3I gas mixtures in power equipment as an insulation medium.

Analysis of the insulation characteristics of CF3I mixtures with CF4, CO2, N2, O2 and air

This paper investigates the insulation characteristics of CF3I mixtures with CF4, CO2, N2, O2 and air by Boltzmann equation analysis (with mole percentages), neglecting the influence of electron-vibrational superelastic collisions. The critical reduced electric field strength (E/N)cr of a electronegative gas can be considered as the value for which the reduced effective ionization coefficient (α − η)/N = 0. First, the reduced ionization coefficient α/N, reduced attachment coefficient η/N and (α–η)/N of CF3I mixtures with CF4, CO2, N2, O2 and air are calculated. Then the (E/N)cr of those mixtures are determined. The results indicate that CF3I–N2 and CF3I–air have a superior insulation performance than the other three mixtures. Further, the (E/N)cr of CF3I–N2 and CF3I–air are obviously higher than that of SF6–N2 at the CF3I concentration higher than 65%, and even higher than that of pure SF6 at the CF3I concentration higher than 70%. In addition, the calculated results of CF3I and CF3I–N2 are compared with the experiment values from other literature for confirming the validity of present calculation method and parameters.

The effective ionization coefficients and electron drift velocities in gas mixtures of CF3I with N2 and CO2 obtained from Boltzmann equation analysis

The electron swarm parameters including the density-normalized effective ionization coefficients (α−η)/N and the electron drift velocities Ve are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend (SST) experiment. The overall density-reduced electric field strength is from 100 Td to 1000 Td (1 Td = 10−17 V·cm2), while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%. From the variation of (α−η)/N with the CF3I mixture ratio k, the limiting field strength (E/N)lim for each CF3I concentration is derived. It is found that for the mixtures with 70% CF3I, the values of (E/N)lim are essentially the same as that for pure SF6. Additionally, the global warming potential (GWP) and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.

Transport properties of CF3I thermal plasmas mixed with CO2, air or N2 as an alternative to SF6 plasmas in high-voltage circuit breakers

This paper is devoted to the calculation of equilibrium compositions, thermodynamic properties (mass density, enthalpy and specific heat at constant pressure) and transport coefficients (viscosity, electrical conductivity and thermal conductivity) of air/CO2/N2–CF3I mixtures. These data are computed in the temperature range 300 K–50 kK and pressure between 1 and 32 bar. Results obtained for pure gases (CF3I, CO2, air and N2) are systematically compared with SF6. Transport coefficients for N2, CO2, CF3I and mixtures of CO2, N2 or air with CF3I are also confronted with previous published values. Particular attention is paid to the collision integral database by the use of the most accurate and recent cross-sections or interaction potentials available in the literature.

Is CF3I a good gaseous dielectric? A comparative swarm study of CF3I and SF6

This paper deals with the measurement of the electron drift velocity, the longitudinal diffusion coefficient and the effective ionisation coefficient in pure CF3I and CF3I mixtures. The E/N range covered was 100-850 Td (1 Td=10-17 V cm2). The present results were derived from a pulsed Townsend experiment. For pure CF3I, the values of the electron drift velocity and of the effective ionisation coefficient were found to increase steadily with E/N. The E/N value at which ionisation equals attachment, commonly referred to as the limiting field strength, was found to be E/Nlim=437 Td, which is higher than that of SF6 (360 Td), a widely used insulating gas. Moreover, the curve for the mixture of 70% CF3I with N2 is very similar to that of SF6 in the neighbourhood of E/Nlim. Thus, from the point of view of these coefficients, CF3I would seem to be superior in dielectric behaviour to SF6. Besides, CF3I is an environmentally friendly gas as opposed to SF6. Certainly, many more tests should be performed to regard CF3I as a good dielectric and possible substitute to SF6.

IR and UV Absorption Cross Sections, Vibrational Analysis, and the Molecular Structure of Trifluoromethyl Peroxynitrate, CF3OONO2

The synthesis of CF3OONO2 is accomplished by UV photolysis (254 nm) of a mixture of CF3I, NO2, and O2. The pure product is isolated after trap-to-trap condensation. The removal of byproducts is accomplished by treatment of the crude product with O3. To complement the known physical and spectroscopical properties of CF3OONO2, the IR and UV absorption cross sections are determined, and a complete vibrational analysis is performed. On the basis of the UV data, the photolytic half-life in the troposphere is calculated to be 30 days. The molecular structure of CF3OONO2 is determined by gas-phase electron diffraction and quantum chemical calculations (HF/3-21G, HF/6-31G*, and B3PW91/6-311+G*). The peroxide CF3OONO2 possesses a skew structure (C1 symmetry) with a COON dihedral angle of 105.1(16)° and an extremely long O−N bond of 1.523(7) Å, which is in accordance with its low O−N bond-dissociation energy. The HF/3-21G and B3PW91/6-311+G* methods reproduce the experimental geometry satisfactorily whereas the HF/3-31G* approximation predicts a much shorter O−N (1.390 Å).

The production of long-lived IF(B 3Π) emission in the 248 nm photolysis of a mixture of CF 3I and F 2

Emission from IF(B) with a decay time of ≈ 645 μs has been observed following the photolysis of a mixture of CF 3I, F 2 and He at ≈ 0.5 mbar by a pulsed 248 nm KrF excimer laser. The IF(B) is formed with vibrational and rotational temperatures of 800 and 300 K, respectively. It is suggested that the key reagents are spin-orbit excited iodine atoms, I ★, produced by the photolysis of CF 3I and ground-state fluorine atoms resulting from the reaction of CF 3 radicals with F 2. The rate of fluorine atom formation determines the timescaleof IF(B) production.

Chemical pumping of pure rotational HF lasers

Pure rotational laser oscillation has been observed in HF following flash photolysis of various mixtures of trifluoromethyl halide, acetylenic compound, and argon in the ration of 1:1:100. Specifically, mixtures of CF3I+C2H2, CF3I+CH3C2H, and CF3Br+C2H2 exhibit different patterns of laser intensity, and, further, are markedly different from patterns generated by the known photoelimination system CH2CF2. The above systems show laser intensity at lower rotational levels than could be explained by simple V→R collision induced mechanisms (as in the case of CH2CF2). Further, the intensities in these anomalously low rotational levels appear to be a function of the identity of the electronically excited halide (I or Br) produced photolytically. A computer simulation model has been constructed which relaxes nascent HF through V→R transfer (formed vibrationally and rotationally excited by elimination) but incorporates an additional pumping mechanism, that of quenching of I or Br by these relaxing HF molecules. Most of the experimentally observed laser intensities are explained on the basis of this new pumping mechanism.

Donor-acceptor complexes formed by perfluoro-organo bromides and iodides with nitrogenous and other bases. II. Band shapes and widths in the absorption spectrum of gaseous CF3I-N(CH3)3

The absorption band centred at c. 77 cm-1 in gaseous mixtures of CF3I and N(CH3)3 previously reported and attributed to the N-I stretching mode of the complex CF3I-N(CH3)3 has been carefully re-examined. This band is of interest as an example of a low frequency ?dissociative type? vibrational mode of a weak molecular complex. The band is asymmetric and apparently structureless with a half intensity width at room temperature of 28-30 cm-1. The width of the band may be accounted for as arising from transitions vi + vi+1 where vi is the vibrational quantum number of the N-I stretching mode with vi up to c. 10 making appreciable contribution to the intensity on the low wave-number side. Centrifugal distortion in the complex is considered. Centrifugal stretching and consequent weakening of the bond may shift the band envelope 2-3 cm-1 to lower wave numbers. Assessment of these and other factors affecting the band shape suggest that the fundamental frequency is probably c. 90 cm-1. The band shape of the vibrational mode of the complex at c. 272 cm-1 is briefly discussed. Many of the considerations presented in this paper should apply to vibration-rotation band shapes in other weak molecular complexes. Some general consequences of anharmonicity for the interpretation of the spectra of weak molecular complexes are discussed.