Surface Modification of Silicone Rubber by CF<Subscript>4</Subscript> Radio Frequency Plasma Immersion

Silicone rubber samples were treated by CF₄ capacitively coupled plasma at radio frequency (RF) power of 60, 100 and 200 W for a treatment time up to 20 min under CF₄ flow rate of 20 sccm, respectively. Static contact angle, ATR-FTIR and XPS, and AFM were employed to characterize the changes of surface on hydrophobicity, functional groups, and topography. The results indicate the static contact angle is improved from 100.7 to 150.2°, and the super-hydrophobic surface, which corresponds to a static contact angle of 150.2°, appears at RF power of 200 W for a 5 min treatment time. It is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of surface roughness created by the ablation reaction of CF₄ plasma and the formation of [–SiF _x (CH₃)_2−x –O–] _n (x = 1, 2) structure produced by the direct attachment of F atoms to Si.     

Plasma fluorination of polyolefins

ESCA and contact angle measurements were used to characterize the surfaces of Polyethylene and polypropylene films exposed to SF₆, CF₄, and C₂F₆ plasmas. None of these gases polymerized in the plasma. However, all plasma treatments grafted fluorinated functionalities directly to the polymer surfaces. SF₆ plasmas graft fluorine atoms to a polyolefin surface. CF₄ plasmas also react by a mechanism dominated by fluorine atoms, but with some contribution from CF_x-radical reactions. Although C₂F₆ does not polymerize, the mechanism of grafting is still dominated by the reactions of CF_x radicals. For all gases studied, the lack of polymerization is attributed to competitive ablation and polymerization reactions occurring under conditions of ion bombardment.     

Mass-spectrometric investigation of the anions and cations in a hydrocarbon flame doped with sulphur/fluorine additives

A fuel-lean, premixed, CH₄O₂ flame at atmospheric pressure was doped with 0.2 mol% of SF₆ and 0.1 mol% of triflic anhydride (CF₃SO₂)₂O. Primarily the anions, but also the cations, occurring in the flame reaction zone and in the burnt-gas region downstream were observed by sampling the flame through a nozzle into a mass spectrometer. The main objective was to ascertain the ability of these sulphur/fluorine (S/F) additives and their combustion products to scavenge free electrons by forming negative ions in the flame gas. With either additive present, both total anions and cations increased in the reaction zone by a factor of between three and four. In the burnt gas, the total cations were essentially unchanged but the total anions showed a three-fold increase. With SF₆ additive only, major S/F cations were observed in the reaction zone (e.g.; SF⁺₃, SF₃O⁺, SF⁺₃, etc.) although H₃O⁺ with both additives was completely dominant downstream. Both additives produced major S/F anion signals in the flame reaction zone. Some of these were related to the individual additive structure (e.g. SF⁻₅ with SF₆; CF₃SO⁻₃ with (CF₃SO₂)₂O). Others were essentially unrelated but were observed with both additives (e.g. FSO⁻₃, HSO⁻₄, etc.) and persisted throughout the burnt gas. Some important features of the ion chemistry are discussed.     

Interaction of polynitro compounds with difluoroamine

Difluoroamine does not react with tetranitromethane and fluoro-, chloro-, and bromotrinitromethanes in DMF and in acidic media (CF₃COOH, ClSO₃H, FSO₃H, and oleum), but reacts with α-fluoro- and α-(difluoroamino)-α,α-dinitrotoluenes to give substitution products of the difluoroamino group for both the nitro groups,viz., PhC(NF₂)₂F and PhC(NF₂)₃, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1647–1649, August, 1998.     

Studies on atmospheric plasma abatement of PFCs

Microwave plasma at 2.45 GHz frequency operating at atmospheric pressure in synthetic gas mixtures containing N₂, CF₄, C₂F₆, CHF₃, and SF₆ were investigated experimentally for various gas mixture constituents and operating conditions, with respect to their ability to destroy perfluorocompounds. It was found that the destruction and removal efficiency (DRE) of the process is highly dependent on the total gas flow. DREs of up to 99.9% have been achieved using 1.8 kW of microwave power at 20 l/min total flow rate.     

Active Species Generated by a Pulsed Arc Electrohydraulic Discharge Plasma Channel in Contaminated Water Treatments

Pulsed arc electrohydraulic discharge (PAED) direct plasma technique was applied for various types of contaminated water treatment. The experimental system consists of a spark-gap switch type pulse power supply (0.5 kJ/pulse) and a 3 L stainless steel reactor with eccentrically configured rod-to-rod electrodes. The current and voltage waveforms are fundamentally different for different conductivity water. Double pulse current discharges were observed for pond water with relatively higher conductivity (637 mS/m) while a single pulse current discharge was observed for lake water with relatively lower conductivity (78 mS/m). From the optical emission spectrum and UV dosimeters, UV-A, UV-B, excited molecules and radicals including N₂*, O, H, OH, O₃ etc. were observed during the discharge period. Both optical emission and UV intensities in pond water are slightly lower than lake water. The decay time of the UV-A, N₂*, OH, H and O radicals were around 0.6 ms, where the discharge period ended around 0.4 ms. The results indicate that the radicals existed longer than the discharge period. The pH, dissolved oxygen and conductivity were changed during the course of PAED treatment. The ions and radicals such as H·, O·, H⁺, OH· etc. generated by PAED may cause alterations density decay time and the active species in water were present for a longer period. The reduction of total organic carbon (TOC) in pond water reached 80% after 5 min of PAED treatment. Based on local thermal plasma equilibrium (LTE) model, LTE thermal plasma chemical composition model for 1 mol water vapour was used to compare to present experiments. PAED discharge in contaminated pond water generated peak concentration of OH = 28% and O₂H = 0.012% mol in gas-phase and migrated to water-phase via gas–liquid interfaces generated by arc and micro-bubbles to form more stable O₃, H₂O₂, H₂ and O₂. The model suggested that the reduction of TOC occurred in gas/plasma phases or liquid-phase side of gas liquid interfaces.     

CCl<Subscript>4</Subscript> Decomposition in RF Thermal Plasma in Inert and Oxidative Environments

The decomposition of carbon tetrachloride was investigated in an RF inductively coupled thermal plasma reactor in inert CCl₄–Ar and in oxidative CCl₄–O₂–Ar systems, respectively. The exhaust gases were analyzed by gas chromatography-mass spectrometry. The kinetics of CCl₄ decomposition at the experimental conditions was modeled in the temperature range of 300–7,000 K. The simulations predicted 67.0 and 97.9% net conversions of CCl₄ for CCl₄–Ar and for CCl₄–O₂–Ar, respectively. These values are close to the experimentally determined values of 60.6 and 92.5%. We concluded that in RF thermal plasma much less CCl₄ reconstructed in oxidative environment than in an oxygen-free mixture.     

Nanocrystalline spinel zinc-substituted cobalt ferrite thick film an efficient ethanol sensor

This study considered Zn-substituted cobalt ferrite (Zn_xCo_1-xFe₂O₄ (x = 0.0–1.0) (ZCF)) thick films structural, morphological, and electrical properties; and gas sensing performance. The ZCF thick film sensor was screen printed on a glass substrate and tested for different analyte gases, including H₂, H₂S, CO₂, Cl₂, NH₃, LPG, and C₂H₅OH. We used X-ray photoelectron spectrometry to investigate composition, chemical state, iron/cobalt or zinc ratio, and cation distribution within Zn-substituted cobalt spinel ferrite tetrahedral and octahedral sites without impurities. FESEM and HR-TEM confirmed grain dimensions between 0.13 and 0.23 μm and porous, nearly spherical to flake-like morphology for the ZCF samples. Sample DC resistivity reduced with increasing temperature, confirming semiconductor nature. Thick film ZCF composition achieved highest the gas response and selectivity to 100 ppm ethanol at room temperature (30 °C). Overall results confirmed that flake-like ZCF sensors could be effective ethanol gas sensors.     

Net Emission Coefficients of Radiation in Air and SF<Subscript>6</Subscript> Thermal Plasmas

Net emission coefficients of radiation were calculated for isothermal plasmas of air and SF₆ as a function of the plasma temperature 5,000–30,000 K and the arc radius (0.01–10 cm) at various plasma pressures. Calculations take into account continuum and line radiations, special attention has also been taken to influence of molecular species in case of the air plasmas. It has been found that the molecular bands of O₂, N₂, N₂ ⁺, NO and NO⁺ have very strong effect on the net emission coefficients at low temperatures (below 10,000 K). In case of SF₆, effect of PTFE admixture on the net emission coefficients was also studied. It follows from the calculations that the net emission coefficients vary very little with various admixtures of PTFE. Values of net emission coefficients if SF₆ plasma calculated for various spectral regions were compared.     

Plasma fluorination of polystyrene

ESCA and contact-angle measurements were used to characterize the surfaces of polystyrene films exposed to SF₆, CF₄, and C₂F₆ plasmas. SF₆ plasmas cause loss of aromaticity in the polystyrene surface region via saturation of the phenyl ring and/or carbon-bond breakage and subsequent fluorination. C₂F₆ plasmas graft CF_x radicals directly to the polystyrene surface without necessarily destroying the aromaticity of the polymer. CF₄ plasmas appear to be intermediate in character between SF₆ and C₂F₆ plasmas.     

Kinetics of the radical reactions in pulse radiolyzed RHF — CO2(SF6)-O2-NO gaseous mixtures; RHF = CH3CH2F, CH3CHF2, CH3CF3, CH2FCF3

The kinetics of the peroxy radicals RHFO₂ reactions with NO has been studied by using pulse radiolysis and UV absorption spectroscopy. The rate constants of interaction of oxygen atoms with NO − k ₂ = 2.2±0.2·10⁻¹² cm³·s⁻¹ and NO₂ − k ₃ = 2.1±0.2·10⁻¹¹ cm³·s⁻¹ were found in agreement with the literature values. The bath gases (SF₆ or CO₂) have got minor effect on the rate constants of RHFO₂+NO→NO₂+prod. reactions; RHFO₂ = CH₃CH₂O₂, CH₃CHFO₂, CH₃CF₂O₂, CF₃CH₂O₂, CF₃CHFO₂. The obtained rate coefficients are in the scope of the literature values, although they are lower than those recommended in NIST database. The reasons are discussed.     

Fluorine absorption spectra and some fluorides in condensed state

The absorption spectra of liquid F₂, NF₃, N₂F₄, CF₄, BF₃, NF₃, SF₆ have been obtained at diminished temperatures in the near ultra-violet region of the spectrum. It is shown that the absorption spectrum does not differ from the spectra in the gaseous phase, therefore the elementary absorption act is characterized by the cross section of photon absorption by an individual molecule. The absorption cross sections of the above mentioned molecules are represented in the liquid phase, which do not differ strongly from absorption cross sections of these molecules in the gaseous phase. The dependence of the absorption cross sections of liquid fluorine on its concentrations in solutions with N₂, Ar, NF₃, O₂ at - 196°C has been studied. The cross sections of photon absorption by the fluoride molecule in different liquid media with small fluorine concentrations have been obtained.     

Simultaneous formation of ferrite nanocrystals and deposition of thin films via a microwave-assisted nonaqueous sol–gel process

Combination of the surfactant-free nonaqueous sol–gel approach with the microwave technique makes it possible to synthesize Fe₃O₄, CoFe₂O₄, MnFe₂O₄, and NiFe₂O₄ nanoparticles of about 5–6 nm and with high crystallinity and good morphological uniformity. The synthesis involves the reaction of metal acetates or acetylacetonates as precursors with benzyl alcohol at 170 °C under microwave irradiation of 12 min. Immersion of glass substrates in the reaction solution results in the deposition of homogeneous metal ferrite films whose thickness can be adjusted through the precursor concentration. If preformed nickel nanoparticles are used as a type of curved substrate, the ferrite nanoparticles coat the seeds and form core–shell structures. These results extend the microwave-assisted nonaqueous sol–gel approach beyond the simple synthesis of nanoparticles to the preparation of thin films on flat or curved substrates.     

Mono- and dihydryl-pentafluorosulfur-F-alkanes [1]

The systematic preparation of partially fluorinated pentafluorosulfur alkanes containing no additional halogens is reported. Thus, the indirect addition of “HF” (via KF/formamide) to SF₅CH=CF₂, SF₅CFCF₂, and SF₅C(CF₃)CF₂ produces SF₅CH(in2)CF₃, SF₅CHFCF₃, and SF₅C(CF₃)₂H respectively. The monohydryl-pentafluorosulfur-F- alkanes react readily with S₂O₆F₂ to form the corresponding fluorosulfates by oxidative displacement of hydrogen, while the dihydryl derivative undergoes cleavage to produce F-acetyl fluoride. Efforts to convert some of the new materials to the important but unknown pentafluorosulfur “ketone,” SF₅C(O)CF₃, were unsuccessful.     

Synthesis and colour properties of pigments based on terbium-dopped Mg<Subscript>2</Subscript>SnO<Subscript>4</Subscript>

The main aim of this work was to synthesize the magnesium orthostannate doped by terbium cations and tested whether these materials can be used for colouring of the different materials, e.g. organic binder and ceramic glazes. Initial composition of pigments was counted according the general formula 2MgO(1 − x)SnO₂–xTbO₂, where values of x varied from 0.1 to 0.5 in 0.1 steps. The simultaneous TG/DTA measurements of mixture containing tin oxide, magnesium carbonate hydroxide and terbium oxide showed that the formation of a new compound started at temperature 1,029 °C, but single-phase system was not prepared. Granulometric compositions of samples that were prepared by calcining at temperatures 1,300–1,400 °C are characterized by values of median (d ₅₀) in range 4–8 μm. The calcining temperature 1,500 °C caused the increase of the particle sizes at around 12 μm. The composition of sample 2MgO–1.5SnO₂–0.5TbO₂ and heating temperature 1,500 °C are the most suitable conditions for preparation of colourfully interesting pigment that can be recommended also for colouring of ceramic glazes. Especially, for colouring of decorative lead containing glaze G 07091 containing 5 wt% of PbO and 8 wt% of Al₂O₃.     

Gas-phase reactions of SF5, SF2, and SOF with O(3 P): Their significance in plasma processing

Reactions of both SF₅ and SF₂ with O(³ P) and molecular oxygen have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. For reactions with O(³ P), rate coefficients of (2.0±0.5)×10^–11 cm³ s^–1 and (10.8±2.0)×10^–11 cm³ s^–1 were obtained for SF₅ and SF₂ respectively. The rate coefficients for reactions with O₂ are orders of magnitude lower, with an estimated upper limit of 5×10^–16 cm³ s^–1 for both SF₅ and SF₂. Reaction of SF₂ with O(³ P) leads to the production of SOF which then reacts with O(³ P) with a rate coefficient of (7.9±2.0)×10^–11 cm³ s^–1. Both SO and SO₂ are products in the reaction sequence initiated by reaction between SF₂ and O(³ P). Although considerable uncertainty exists for the heat of formation of SOF, it appears that SO arises only from reaction between SOF and O atoms which is also the source of SO₂. These results are discussed in terms of a reaction scheme proposed earlier to explain processes occurring during the plasma etching of Si in SF₆/O₂ plasmas. A comparison between the results obtained here and those reported earlier for reactions of both CF₃ and CF₂ with O and O₂ shows that there is a marked similarity in the free radical chemistry which occurs in SF₆/O₂ and CF₄/O₂ plasmas.     

Comparative study of degradation of <Emphasis Type="Italic">trans</Emphasis>-1,3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene,perfluoro-3-methylbutanone-2, and sulfur hexafluoride in dielectric-barrier discharge

Degradation of gaseous dielectrics after aging in barrier discharge has been experimentally studied and comparative analysis of their properties has been performed. The gases used as gaseous dielectrics have been trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), 2,3,3,3-tetrafluoropropene (HFO-1234yf), perfluoro-3-methylbutanone-2 CF₃C(O)CF(CF₃)₂, and sulfur hexafluoride SF₆. The product composition of gas degradation before and after 5-h aging in the barrier discharge has been determined by gas chromatography–mass spectrometry and gas chromatography. According to the measurement data, 2,3,3,3-tetrafluoropropene is less prone to degradation and has the highest dielectric strength among the test carbon-containing gases.     

The two-photon excitation spectrum of triphenylene in n-heptane single crystals: Chem. Phys. Letters 57 (1978) 496

Chemiluminescence spectra and photon yields resulting from reactions of copper atoms with N₂O, O₂, NO, NF₃, SF₆, F₂, Cl₂, Br₂, and I₂ have been obtained between 200 and 1100 nm. The most interesting feature of these spectra is the strong and peculiar emission from copper atoms observed in the Cu + NF₃ reaction; population inversion has been obtained between some of the Cu states and it is suggested that this is due to energy transfer from N₂(A) formed in the reaction to copper atoms.     

Determination of cyanide in blood by electrospray ionization tandem mass spectrometry after direct injection of dicyanogold

An electrospray ionization tandem mass spectrometric (ESI-MS-MS) method has been developed for the determination of cyanide (CN^–) in blood. Five microliters of blood was hemolyzed with 50 μL of water, then 5 μL of 1 M tetramethylammonium hydroxide solution was added to raise the pH of the hemolysate and to liberate CN^– from methemoglobin. CN^– was then reacted with NaAuCl₄ to produce dicyanogold, Au(CN)₂^–, that was extracted with 75 μL of methyl isobutyl ketone. Ten microliters of the extract was injected directly into an ESI-MS-MS instrument and quantification of CN^– was performed by selected reaction monitoring of the product ion CN^– at m/z 26, derived from the precursor ion Au(CN)₂^– at m/z 249. CN^– could be measured in the quantification range of 2.60 to 260 μg/L with the limit of detection at 0.56 μg/L in blood. This method was applied to the analysis of clinical samples and the concentrations of CN^– in the blood were as follows: 7.13 ± 2.41 μg/L for six healthy non-smokers, 3.08 ± 1.12 μg/L for six CO gas victims, 730 ± 867 μg for 21 house fire victims, and 3,030 ± 97 μg/L for a victim who ingested NaCN. The increase of CN^– in the blood of a victim who ingested NaN₃ was confirmed using MS-MS for the first time, and the concentrations of CN^– in the blood, gastric content and urine were 78.5 ± 5.5, 11.8 ± 0.5, and 11.4 ± 0.8 μg/L, respectively.     

Interaction Mechanisms Between Ar–O<Subscript>2</Subscript> Post-Discharge and Stearic Acid I: Behaviour of Thin Films

We study the interaction of thick films (~4 mm) of stearic acid (SA), a C₁₈ alkane skeleton with an acid function, with late Ar–O₂ post-discharge. Contrary to what is observed with thin films of SA (~2–3 μm) which are efficiently etched (part I), only functionalization is observed over the first 2 h of treatment with a plasma source operated in the continuous mode, whatever the temperature. The heat released by surface reactions affects non-linearly the temperature of the substrate. Pulsing the source at a frequency ranging from 0.1 to 1 kHz slows down the functionalization process but does not allow any etching of the material. On the contrary, the SA can be etched as thick films by pulsing the oxygen flow rate at a frequency below 50 mHz. By pulsing the reactive gas, the time averaged value of the [O]/[O₂] ratio is decreased, limiting the functionalization processes due to oxygen atoms, and the mean temperature is lowered, decreasing the diffusion length of O₂ (and/or possibly O₂*) species in the SA which are responsible for the scission of C–C bonds of radicals.