Freon Research Articles

Method for analyzing nitrogen trifluoride impurities in high-purity carbon tetrafluoride by gas chromatography

Method for analyzing nitrogen trifluoride impurities in high-purity carbon tetrafluoride by gas chromatography

Towards atomic-scale smooth surface manufacturing of β-Ga2O3 via highly efficient atmospheric plasma etching

Abstract The highly efficient manufacturing of atomic-scale smooth β-Ga2O3 surface is fairly challenging because β-Ga2O3 is a typical difficult-to-machine material. In this study, a novel plasma dry etching method named plasma-based atom-selective etching (PASE) is proposed to achieve the highly efficient, atomic-scale, and damage-free polishing of β-Ga2O3. The plasma is excited through the inductive coupling principle and carbon tetrafluoride is utilized as the main reaction gas to etch β-Ga2O3. The core of PASE polishing of β-Ga2O3 is the remarkable lateral etching effect, which is ensured by both the intrinsic property of the surface and the extrinsic temperature condition. As revealed by density functional theory-based calculations, the intrinsic difference in the etching energy barrier of atoms at the step edge (2.36 eV) and in the terrace plane (4.37 eV) determines their difference in the etching rate, and their etching rate difference can be greatly enlarged by increasing the extrinsic temperature. The polishing of β-Ga2O3 based on the lateral etching effect is further verified in the etching experiments. The Sa roughness of β-Ga2O3 (001) substrate is decreased from 14.8 to 0.057 nm within 120 s, and the corresponding material removal rate reaches up to 20.96 μm/min. The polished β-Ga2O3 displays significantly improved crystalline quality and photoluminescence intensity, and the polishing effect of PASE is independent of the crystal faces of β-Ga2O3. In addition, the competition between chemical etching and physical reconstruction, which is determined by temperature and greatly affects the surface state of β-Ga2O3, is deeply studied for the first time. These findings not only demonstrate the high-efficiency and high-quality polishing of β-Ga2O3 via atmospheric plasma etching but also hold significant implications for guiding future plasma-based surface manufacturing of β-Ga2O3.

Abatement of Volatile Organic Compounds (VOCs) and Fluorine gases by a Microwave Plasma Torch (MPT)

The use of microwave plasma torch (MPT) in the abatement of potent greenhouse and fluorinated (F-gases) gases is crucial due to their high global warming potential. The purpose of this study was the abatement of volatile organic compounds (VOCs) and carbon tetrafluoride (CF4) using specifically designed reverse vortex flow reactor (RVR) and pillar of fire reactor (POF). The RVR has properties that are crucial for their synergistic effects with the MPT, and the POF configurations showed high-efficiency combustion due to plasma radicals and a large contact area with the MPT. The study used Aspen Plus and COMSOL software to analyse the mass balance involved in the thermal decomposition of isopropyl alcohol (C₃H₈O) and CF4 and to design the RVR and POF reactors. Using MPT without hydrocarbon fuel, low-concentration C₃H₈O and CF4 were successfully destroyed in high-flow streams. The experiment on C₃H₈O showed that using a plasma power of 2kW and 1 cubic meter per minute (CMM) of bulk gas, a destruction removal efficiency (DRE) of 95% was achieved for a polluted C₃H₈O of 410 ppm. In a second experiment, a DRE of 94% was achieved for a polluted C₃H₈O of 370 ppm. The first CF4 experiment achieved a DRE of 93.3% with a 7kW plasma power and 1 CMM bulk gas polluted at 285 ppm. In the second experiment, the presence of highly reactive hydroxyl radicals (OH⁎) in steam plasma improved the DRE to 99.8% at 7kW plasma power and 100 LPM bulk polluted at 180 ppm.

Synergistic effect of reducing volume expansion and improving electrochemical performance through a LiF-based SEI formation on SiOx/C electrodes

SiOx/C electrodes are widely used due to their high lithium storage capacities and cycling stabilities. However, the SiOx/C electrode exhibits large volume expansion and unstable SEI layer formation during cycling. In this work, a carbon tetrafluoride (CF4) plasma was used to introduce C-F bonds onto the electrode surface to form a LiF-based SEI layer on a SiOx/C electrode (SGE) to improve its mechanical and electrochemical properties. The fluorinated SiOx/C electrode (FSGE) subjected to the CF4 plasma treatment for 10 min mitigated 2.5 times the volume expansion compared to the SGE by forming a LiF-based SEI layer to increase the mechanical properties. This mitigation of FSGE volume expansion resulted in excellent long-term cycling stability of 83 % for 100 cycles (1C). In addition, the LiF-based SEI layer formed on the FSGE increased the mobility of Li ions, resulting in 1.2 times better cycle stability than that of SGE at a high rate (10C). Thus, the improvement in the electrochemical performance achieved by reducing the volume expansion of SiOx in the electrode and enhancing the Li-ion conductivity was attributed to the stable LiF SEI layer formed with semi-ionic CF bonds introduced by the CF4 plasma.

Effect of fluorine functional groups introduced into activated carbon aerogel by carbon tetrafluoride plasmas in supercapacitors

Effect of fluorine functional groups introduced into activated carbon aerogel by carbon tetrafluoride plasmas in supercapacitors

Modelling of thermal plasma-assisted carbon tetrafluoride abatement

This study focuses on the numerical modelling of the decomposition process of carbon tetrafluoride (CF4, Freon R-14), the most stable perfluorinated gas with a significant global warming potential, as experimentally carried out using a thermal argon/steam plasma in a plasma-chemical reactor. The numerical modelling approach incorporates advanced computational fluid dynamics (CFD) techniques and the kinetics of a complex chemical reaction mechanism. A two-dimensional axisymmetric model, incorporating the conservation of mass, momentum, energy and chemical balances, has been developed to simulate the species distribution under the assumption of steady flow, including turbulence effects. In order to compare the species distributions and destruction efficiencies, two chemical reaction mechanism models of different complexity were implemented: a simplified model A with 196 reactions and a model B with 258 reactions. The simulations were performed for plasma generated by steam and argon stabilized DC plasma torch under three operating conditions for arc currents of 120, 150 and 200 A. The destruction and removal efficiency (DRE) of CF4 decomposition at a high feed rate was computed by both models, with an error of less than 6% compared to the experimental data. It can be concluded that both models accurately predict the residual CF4 concentration trends depending on the feed per input torch power. While model A overestimates process efficiency, model B, with a more balanced reaction mechanism, more closely aligns with experimental results. Model B provides an accurate prediction of the DRE and captures trends as a function of input parameters. Importantly and innovatively, the model presented in this study, unlike previous models, allows for the first time the inclusion of both high concentrations and a sufficiently large reaction mechanism for CF4 abatement. This model presents a novel opportunity to perform trend simulations of operating characteristics for the CF4 abatement problem at a quantitative level, allowing experimental design to be evaluated and optimised.

Diamond-like carbon (DLC)-coated titanium surface inhibits bacterial growth and modulates human alveolar bone cell responses in vitro

Modifying the titanium alloy (Ti-6Al-4V) surface plays a key role in improving biological responses. The present work aimed to determine the response of human alveolar bone cells to the diamond-like carbon (DLC) film and to evaluate the antibacterial effect of DLC-coated titanium. The alloys were deposited with different compositions, including C2H2 (DLC), carbon tetrafluoride (CF4:C2H2; F-DLC), and tetramethylsilane (Si(CH3)4:C2H2; Si-DLC). The surface morphology and wettability were measured using an atomic force microscopy (AFM) and a contact angle measurement. Titanium coated with DLC, F-DLC, or Si-DLC increased surface roughness and hydrophobicity. The ratio of spreading cells to initial rounded attaching cells at 20 min of all modified surfaces was higher than that of the control surfaces. F-DLC showed better cell spreading at 20 min compared to other conditions, as observed by scanning electron microscopy (SEM). The DLC, F-DLC, and Si-DLC coating significantly promoted cell proliferation compared to the Ti-6Al-4V control surfaces. ALP mRNA expression was significantly reduced on DLC surfaces compared to the control on day 14. Additionally, ALP and BMP2 mRNA expression increased on F-DLC-coated surfaces, but there were no statistically significant differences. However, DLC surfaces promoted higher mineral deposition than the control. The lower Staphylococcus aureus colony was observed on the surface of the DLC and F-DLC. In conclusion, the DLC-modified Ti-4Al-6V surface modulates cell attachment, proliferation, osteogenic marker gene expression, and bacterial growth. Herein, DLC-coated titanium alloys are still needed for continued development as an alternative biomaterial in dental applications.

Force-Based Characterization of the Wetting Properties of LDPE Surfaces Treated with CF4 and H2 Plasmas.

Low-density polyethylene (LDPE) films are widely used in packaging, insulation and many other commodity applications due to their excellent mechanical and chemical properties. However, the water-wetting and water-repellant properties of these films are insufficient for certain applications. In this study, bare LDPE and textured LDPE (T-LDPE) films were subjected to low-pressure plasmas, such as carbon tetrafluoride (CF4) and hydrogen (H2), to see the effect of plasma treatment on the wetting properties of LDPE films. In addition, the surface of the LDPE film was textured to improve the hydrophobicity through the lotus effect. The LDPE and T-LDPE films had contact angle (θ) values of 98.6° ± 0.6 and 143.6° ± 1.0, respectively. After CF4 plasma treatments, the θ values of the surfaces increased for both surfaces, albeit within the standard deviation for the T-LDPE film. On the other hand, the contact angle values after H2 plasma treatment decreased for both surfaces. The surface energy measurements supported the changes in the contact angle values: exposure to H2 plasma decreased the contact angle, while exposure to CF4 plasma increased the contact angle. Kinetic friction force measurements of water drops on LDPE and T-LDPE films showed a decrease in friction after the CF4 plasma treatment, consistent with the contact angle and surface energy measurements. Notably, the kinetic friction force measurements proved to be more sensitive compared to the contact angle measurements in differentiating the wetting properties of the T-LDPE versus 3× CF4-plasma-treated LDPE films. Based on Atomic Force Microscopy (AFM) images of the flat LDPE samples, the 3× CF4 plasma treatment did not significantly change the surface morphology or roughness. However, in the case of the T-LDPE samples, Scanning Electron Microscopy (SEM) images showed noticeable morphological changes, which were more significant at sharp edges of the surface structures.

Carbon Tetrafluoride, Oxygen, and Air RF Plasma Modified Low-Density Polyethylene and Polydimethylsiloxane

Carbon Tetrafluoride, Oxygen, and Air RF Plasma Modified Low-Density Polyethylene and Polydimethylsiloxane

Highly efficient and atomic scale polishing of GaN via plasma-based atom-selective etching

Plasma-based atom-selective etching (PASE) of GaN is conducted to realize the highly efficient planarization of the GaN surface. Inductively coupled plasma with high temperature and high concentration of radicals is used as the source of PASE. The non-toxic carbon tetrafluoride is chosen over chlorine as the reaction gas, and the volatility of the etching products will be improved at high temperatures in the PASE of GaN. After 2 min of PASE, the GaN surface roughness is reduced from Sa 135.8 nm to Sa 0.527 nm. The material removal rate of PASE of GaN is measured to be 93.01 μm/min, thousands of times higher than that of the conventional chemical mechanical polishing method. The crystal structure of the GaN subsurface is well-ordered without any damage or defects. PASE is thus proven to be a non-destructive etching method. In this study, the effects of radio frequency power and reaction gas flow rate on PASE are also investigated. Surface temperature and concentration of radicals are found to be the critical factors in the PASE of GaN.

Analysis of Impurities in Sulfur Hexafluoride Gas via Gas Chromatography Based on Enhanced Plasma Detector

An analytical method for detecting impurities in high-purity sulfur hexafluoride (SF6) gas is established by using gas chromatography (GC) based on the enhanced plasma detector (EPD). The concentration of impurities (hydrogen, oxygen, nitrogen, methane, carbon monoxide, carbon dioxide, carbon tetrafluoride, hexafluoroethane, and octafluoropropane) can be quantitatively detected through one-time sampling and external standard method, and the minimum detection limit of each component is calculated to be about 0.1ppm, the RSD of the test results is less than 3%. This method can meet the requirements of detecting the purity of SF6 gas used in electrical equipment.

Low-pressure plasma treated polycarbonate and polymethyl methacrylate (PMMA) sheets with different surface patterns to change their surface properties

Low-pressure plasmas of carbon tetrafluoride (CF4), oxygen (O2), and air were used to treat the surfaces of polycarbonate (PC) and polymethyl methacrylate (PMMA) to achieve a variety of surface attributes, such as hydrophilicity, hydrophobicity, and surface free energy. Patterns of straight line, triangular and square shapes with different sizes e.g., 0.5 mm, 0.75 mm, and 1 mm dimensions as templates were constructed from stainless-steel sheets with a thickness of 1 mm, via laser cutter, were used to induce the corresponding shape of the functionality on PC and PMMA surfaces during plasma gas treatment were also investigated. The untreated PC and PMMA surfaces have a contact angle (θ) value of 70°±0.47° and 77°±0.80°, respectively. As expected upon CF4 plasma treatment, their contact angle values were increased to 109.04°±0.35° and 105.76°±0.61°, respectively; whereas the air plasma treated surfaces became more hydrophilic with the contact angle values of 29.34°±0.14° and 43.99°±0.22°, correspondingly. Moreover, O2 plasma treated surfaces became more hydrophilic with the contact angle values of 25.32°±0.77° for PC and 39.94°±2.05° for PMMA. Also, surface free energy (SFE) values were decreased to 11±0.87 mN/m from 41.16±0.42 mN/m for PC and to 12.11±1.53 mN/m from 35.93±1.12 mN/m for PMMA upon CF4 treated surfaces. Furthermore, SFE values were increased to 57.59±1.12 and 62.13±1.15 mN/m for PC and PMMA after air plasma treatment. PC surface's, advancing and receding contact angles were determined as 101.48°±0.33° and 65.60°±0.11° respectively for 34.77°±0.50° slide-off angles. Moreover, the advancing and receding contact angles for PMMA were found as 93°±0.64° and 61.60°±1.19°, respectively with a sliding angle of 24.49°±1.14°. X-ray Photoelectron Spectroscopy (XPS) analysis results confirmed the fluorination and oxidation of both PC and PMMA after CF4 and O2 plasma treatments, individually. PC and PMMA surfaces were treated multiple times with CF4 and Air, Air and CF4, O2 and CF4, and CF4 and O2 plasmas in succession. After multiple treatment, PC and PMMA surfaces contact angle values were decreased as low as 10.62°±0.88° and 14.96°±0.2°, respectively.

Rapid preparation of nickel fluoride motif via solution-free plasma route for high-energy aqueous hybrid supercapacitor

New and more accurate nano-material fabrication technologies are necessary to tackle the limitations of a conventional solution-based synthesis procedure for an efficient, sustainable, and carbon-free energy future. We devised a rapid, room-temperature yet solution-free dry carbon tetrafluoride (CF4) plasma strategy to cultivate the self-assembled nickel fluoride (NiF) motif nanostructure for a high-energy hybrid supercapacitor (HSC). The high reactivity of the CF4 plasma permitted the low temperature and rapid foundation of the NiF motif directly on the 3D Ni foam. The developed NiF motif nanostructure on the Ni foam delivers high electrochemical activity in terms of the specific capacity (1.18 mAh/cm2 at 1 mA/cm2), cycling stability (89.58 % retentions over 10,000 cycles), and rate capability (84.22 % at 10 mA/cm2) in conventional aqueous electrolytes. The ordered growth of the NiF motif nanostructure linked with high fluorine concentration (51.33 at%) provides large electroactive accessible sites and high electronic conductivity for the facial and reversible charge transport process. To further explore the potential of the NiF motif nanostructure, an aqueous HSC cell was assembled by using the NiF motif and activated carbon (AC) as positive and negative electrodes, respectively. The constructed NiF//AC HSC brings an energy density of 0.96 mWh/cm2 at a specific power of 3.18 mW/cm2 with excellent cycling durability (87.98 % over 12,000 cycles) and rate capability (84.55 %). The superior electrochemical parameters of the NiF motif and developed HSC cell indicate that the described synthetic approach can be extended to prepare a wide range of electrode materials rapidly and solution-free dryly.

Electrophysical Characteristics and Emission Spectra of Carbon Tetrafluoride Plasma

Electrophysical Characteristics and Emission Spectra of Carbon Tetrafluoride Plasma

Plasma grown fluoride-rich artificial SEI for stabilizing Li metal anodes

The growth and detachment of lithium (Li) dendrites are regarded as the primary issues hindering the practical application of Li metal anodes, and constructing a stable solid electrolyte interface (SEI) is considered to be the most straightforward solution. Herein, carbon tetrafluoride (CF4) plasma growth instead of adding of additives into electrolyte is proposed to construct an artificial SEI. Highly reactive C- and F-containing species from the ionized CF4 react with the surface Li metal to form a stable fluoride-rich (i.e. LiF and CF) artificial SEI. Profit from the high chemical stability, low diffusion barrier and high mechanical strength of plasma-generated SEI, the distribution of lithium ions (Li+) on the surface of the prepared Li metal (F-Li) anodes is homogenized and the Li dendrites are inhibited. The symmetrical cells composed of F-Li can cycle stably for 1700 (1 mA cm−2, 1 mAh cm−2) and 1400 h (2 mA cm−2, 2 mAh cm−2) with minimum overpotentials of about 13 mV and 80 mV, respectively. The enhanced cyclability in the full cell system paired with NCM811 cathode further demonstrates its practical application. The mechanisms underlying the artificial SEI growth and its component evolution during electrochemical cycling were also discussed.

EC-QCL based photoacoustic spectroscopy for detection of SF6 decomposition components

The detection of multiple SF6 decomposition gases based on photoacoustic spectroscopy (PAS) has been a research hotspot in recent years. A highly sensitive sensor for the detection of sulfuryl fluoride (SO2F2), carbon tetrafluoride (CF4), and sulfur dioxide (SO2) in sulfur hexafluoride (SF6) was demonstrated by using PAS. The PA sensor is composed of an external cavity quantum cascade laser (EC-QCL) emitting between 1278 and 1360 cm−1, a Helmholtz differential resonant PA cell isolating the target gas from the surrounding environment, and an acousto-optic modulator (AOM) modulating the laser intensity. When the noise level was evaluated based on the PA signal noise of pure SF6 gas, minimum detection limits of 510 ppb, 9 ppb, and 69 ppb with 1 s integration time for SO2F2, CF4, and SO2 in SF6 were achieved at the characteristic absorption wavenumbers of 1282.8 cm−1, 1283.0 cm−1, and 1348.4 cm−1, respectively. Further, if the integration time was increased to the optimal integration time determined via Allan-Werle deviation analysis, the minimum detection limits were further improved to 70 ppb, 1.5 ppb, and 7 ppb for SO2F2, CF4, and SO2, respectively. The multilinear regression (MLR) statistical algorithm based on the least square method was utilized for discrimination of three-gas spectra and retrieving of three-gas concentrations from a three-gas mixture in SF6 despite the significant overlap between their absorption features.

Fiber-Enhanced Raman Spectroscopy for Trace-Gas Sensing in the High-Concentration Gas Background With an Anti-Resonant Hollow Core Fiber

In this article, with an anti-resonant hollow core fiber (ARHCF), fiber-enhanced Raman spectroscopy (FERS) for trace-gas sensing in a high-concentration gas background is demonstrated for the first time. The performance of the apparatus is verified by detecting trace-gas in the high concentration SF6 and gaseous impurities in the high concentration C2H6. With a 1.5 W laser source and 60 s exposure time, the limit of detection (LOD) of gases at tens of ppm levels is achieved, including carbonyl sulfide (COS), carbon tetrafluoride (CF4), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), acetylene (C2H2), ethylene (C2H4), propyne (C3H4), propylene (C3H6), and propane (C3H8). Quantification of multi-gas with great accuracy exceeding 94% is also realized. It shows that the FERS can demonstrate the ability of multi-gas sensing with high selectivity, sensitivity, and accuracy.

Single and double electron detachment absolute cross sections of H− and D− in collisions with SF6 and CF4

Collisional single electron detachment (SED) and double electron detachment (DED) absolute cross sections of H− and D− with sulfur hexafluoride (SF6) and carbon tetrafluoride (CF4) were measured by using the growth rate method. The energy used in the experiment ranged from 10 to 30 keV. By combining with the available data in references, it was found that SED absolute cross sections reach saturation in the experimental velocity range, while DED absolute cross sections continue to increase as the velocity increases. The SED absolute cross sections of CH4, SF6, and CF4 were proportional to their bond lengths and the radius of the incident anionic projectile within the error range in the present velocity region.

Total Ionization Cross Sections due to Electron Impact of Carbon Tetrafluoride from Ionization Threshold to 10 MeV

Modified Khare-BEB model has been used to calculate the electron impact ionization cross section for carbon tetrafluoride (CF4) from ionization threshold to 10 MeV. The collisional parameters CRP and also has been calculated. The calculations are compared with available experimental data . A good agreement is found among the present results, other previous calculations, and experimental data.

Safety evaluation of carbon tetrafluoride as an inert hyperbaric breathing gas in Sprague-Dawley rats

Carbon tetrafluoride (CF4) is an inert gas with higher molecular weight and lower water solubility than commonly used hyperbaric breathing gases. These inert gas properties decrease time required to decompress and avoid decompression sickness after deep dives. To assess CF4 toxicity, Sprague-Dawley rats were exposed to 8 atm absolute (ATA) air (10 males, 10 females) or 8 ATA 79% CF4/21% O2 (25 males, 25 females). Exposures were 30 min daily for 5 days. Rat behavior was normal throughout the testing period. There were no gross or microscopic pathology abnormalities following repeat dose exposure. Male body weight trends were similar between groups. Female body weight trends were 0.5 ± 0.8% day−1 for hyperbaric air exposure and − 0.2 ± 0.8% day−1 for hyperbaric CF4 exposure (P = 0.01) but remained within literature cited norms. Organ weights and hematologic indices remained within or near literature normal ranges. Clinical chemistry panels showed no signs of toxicity in renal or hepatic biomarkers. Polychromatic erythrocyte micronucleus frequency showed no chromosomal damage. Comet assay showed no DNA damage in lung tissue. Females exposed to CF4 had 2.5 times greater percent tail DNA in liver tissue than controls (P = 0.009). However this result remained within the normal range of local negative controls. A bacterial reverse mutation assay with exposure to 1 ATA 79% CF4/21% O2 for 72 h was nonmutagenic in four strains of Salmonella typhimurium and one strain of Escherichia coli. Overall, there was no evidence that CF4 caused organ toxicity or genetic toxicity.