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The paper presents calculations of the two-stage separation of silicon isotopes in Q-cascade models. Feed flow profiles are obtained for Q-cascades, and the concentration distribution by stages is determined for silicon isotopes. It is shown that three highly-enriched (>99%) products can be obtained at a 35 g/s feed flow, namely: 32.31 g/s 28Si, 1.61 g/s 29Si, and 1.08 g/s 30Si. [ABSTRACT FROM AUTHOR]

In this work, cellular silica was synthesized by using microbubbles as templates, which contain a mixture of argon and silicon tetrafluoride (SiF4). The latter is generated from decomposition of hexafluorosilicic acid (H2SiF6) at ambient conditions. The specific surface area of cellular silica can be as high as 130 m2/g, the size of the cavity is hundreds-of-nanometers, and the thickness of the cavity wall is around 30 nm. The cavity size, apparent packing density, and porosity of cellular silica strongly depend on the nature of the aqueous solutions; the cavity size appears to be negatively proportional to the surface tension, but thickness of cavity walls seems to be weakly affected by the aqueous properties. An attempt was made to introduce aluminum atoms in situ in the second-coordination sphere of Si atoms and/or load aluminum into the silica structure. Cellular silica with large pores facilitate the transfer of large molecules, including polymers and enzymes; thus, it could find applications in (bio)catalysis, sorption, controlled release and separations. [ABSTRACT FROM AUTHOR]

The crystal structure of the silicon tetrafluoride molecular complex with 4-phenylpyridine SiF4·2ppy has been determined by X-ray diffraction analysis. Although 4-phenylpyridine has a higher proton affinity than pyridine, the Si–N bond length in crystalline SiF4·2Py is shorter by 0.03(2) Å than in SiF4·2ppy. The energies of donor-acceptor Si–N bonds in SiF4·2Py (220.6 kJ/mol) and SiF4·2ppy (225.0 kJ/mol) calculated by the M06-2X/def2-TZVP method agree with a slightly higher proton affinity of 4-phenylpyridine. [ABSTRACT FROM AUTHOR]

In this work, cellular silica was synthesized by using microbubbles as templates, which contain a mixture of argon and silicon tetrafluoride (SiF4). The latter is generated from decomposition of hexafluorosilicic acid (H2SiF6) at ambient conditions. The specific surface area of cellular silica can be as high as 130 m2/g, the size of the cavity is hundreds-of-nanometers, and the thickness of the cavity wall is around 30 nm. The cavity size, apparent packing density, and porosity of cellular silica strongly depend on the nature of the aqueous solutions; the cavity size appears to be negatively proportional to the surface tension, but thickness of cavity walls seems to be weakly affected by the aqueous properties. An attempt was made to introduce aluminum atoms in situ in the second-coordination sphere of Si atoms and/or load aluminum into the silica structure. Cellular silica with large pores facilitate the transfer of large molecules, including polymers and enzymes; thus, it could find applications in (bio)catalysis, sorption, controlled release and separations.

With thermodynamic calculations using for the system of elements Si-F-H-O it was shown that in practice the SiO2 is the only silicon-containing substance and the HF is the only fluorine-containing substance at the tempera-tures range above 1300 K and the certain ratio of elements. The specified temperature may be achieved by carrying out the interaction of SiF4 with hydrogen-containing and oxygen-containing substances in the combustion mode. This method can become the basis of an industrial technology for HF production.

Some features of atmospheric-pressure radiofrequency (13.56 MHz) arc discharge and its use for obtaining bulk samples of isotope-enriched silicon carbide via the reaction between SiF4 and methane in a hydrogen medium have been considered. It has been shown that power in this type of discharge is released mainly in the near-electrode regions. The deposition of silicon and graphite occurs in a layer-by-layer mode, so that the product carbide contains up to 40% free carbon; therefore, the process requires optimization. At the same time, the proposed type of RF arc discharge with the product deposition zone localized at the ends of the electrodes makes it possible to avoid not only additional heating of the reactor space and walls, but also the loss of expensive isotope-enriched silicon fluoride. [ABSTRACT FROM AUTHOR]

The matrix-distributed electron cyclotron resonance plasma-enhanced chemical vapor deposition (MDECRPECVD) technique has been shown to achieve high deposition rates for hydrogenated microcrystalline silicon (μc-Si:H) thin film. Due to the fact that plasma is sustained by a microwave discharge, by biasing the substrate holder with additional power supply, one can achieve independent control over the plasma density and the maximum ion bombardment energy (IBE). In this work, we present studies of the impact of IBE on the microstructural properties of the μc-Si:H film deposited by MDECR-PECVD. Insufficient ion bombardment is found to be responsible for the substantial presence of nanoporous regions within the material, resulting in significant post-deposition oxidation. Good agreement between transmission electron microscopy (TEM) Fresnel contrast analysis and the results of infrared absorption and hydrogen effusion measurements for the deposited films suggest that moderate IBE is of vital importance to achieve high quality μc-Si:H. In doing so, denser films with significantly decreased nano-porous regions and better stability are obtained, which is of great interest to optimize the process parameters for solar cell applications. [ABSTRACT FROM AUTHOR]

We have studied reaction between silicon tetrafluoride and calcium hydride in a vertical flow reactor, which proceeds as combustion in filtration mode. The principal kinetic characteristics of the reaction between SiF and CaH in a counterpropagating wave have been determined: reaction order n = 1, rate constant k = 0.38 ± 0.05 s, and activation energy E = 17 ± 2 kJ/mol. [ABSTRACT FROM AUTHOR]

Probe diagnostics is used to determine the electron temperature and electron number density in a low pressure inductively coupled plasma (ICP) ignited in the mixture of SiF 4 , Ar and H 2. Emission spectra of mixtures with different stoichiometry of components are investigated and the electron density distribution function (EDDF) is estimated. The optimal conditions for high conversion of SiF 4 into Si are found by studying the dependence of the yield of silicon upon the ratio of reagents. The maximum achieved yield of silicon is 85% under the optimal conditions. Based on the analysis of IR and MS spectra of exhaust gases, 5% of initial SiF 4 converts into volatile fluorosilanes. A rate of production of Si is 0.9 g/h at the energy consumption 0.56 kWh /g. [Display omitted] • Production of pure silicon and potentially silicon isotopes from mixture of SiF 4 , Ar and H 2 in ICP plasma • Emission spectra and infrared and mass spectrometry of exhaust gases • Estimations of electron density distribution function • High 85% yield of silicon under the optimal conditions [ABSTRACT FROM AUTHOR]

An efficient alcoholysis reaction of silicon tetrafluoride with alcohols in the presence of magnesium can directly prepare tetraalkoxysilane and magnesium fluoride. The reaction can afford tetraethoxysilane, tetramethoxysilane, and magnesium fluoride in good yields with the aid of a catalytic amount of iodine. [ABSTRACT FROM AUTHOR]

The mechanism of the formation of MgF coatings on ferritic-martensitic and austenitic steels contacting liquid magnesium and gaseous silicon tetrafluoride (SiF) has been investigated. An MgF coating on steel possesses high plastic properties. The proposed method can be used to improve corrosion resistance of steels contacting freons and other fluorine-containing materials. [ABSTRACT FROM AUTHOR]

Abstract: Deposition of Si films is done in a high power 24GHz gyrotron-based electron-cyclotron resonance plasma enhanced chemical vapour deposition setup. The possibility of high-rate (2.5nm/s) deposition of thin silicon films from SiF4 +H2 plasmas in an electron-cyclotron resonance reactor with gyrotron microwave plasma source at the frequency of 24GHz is demonstrated. The analysis with spectroscopic ellipsometry and Raman scattering shows that films have large crystalline fraction (75%) with an average size of silicon grains of 3nm. The use of gyrotron with high microwave power opens up the possibility to make depositions from high density plasmas at pressures of tens of pascals, which results in high deposition rates (tens nm/s). [Copyright &y& Elsevier]

Highlights: [•] We report a new alcoholysis reaction of SiF4, methanol and Al. [•] The reaction gives Si(OCH3)4 and AlF3 as the products in good yields. [•] The reaction was studied and the condition is mild. [•] The method easily transfers inorganic silicon of SiF4 to organic silicon compound. [Copyright &y& Elsevier]

Abstract: Dissociative electron attachment (DEA) to the group IV tetrafluorides: CF4, SiF4 and GeF4, is reported in the incident electron energy range from about 0 to 14eV. The F2 − formation from CF4 is established and the appearance energies (AEs) for F−, CF3 − and F2 − are determined using a three-point calibration for the energy scale. These are found to be 4.7±0.1eV, 4.5±0.1eV and 5.6±0.1eV, respectively. For SiF4 the AEs for F−, SiF3 − and F2 −, through the dominating resonance are found to be 10.2±0.1eV, 10.2±0.1eV and 10.3±0.1eV, respectively. From GeF4 the molecular ion GeF4 − and the fragments GeF3 −, GeF2 −, GeF− and F− are all observed with appreciable intensities, and the F− production is found to be significantly close to 0eV incident electron energy. The present findings are compared with earlier experiments and discussed in context to the thermochemistry of the respective processes as well as the nature of the underlying resonances. [Copyright &y& Elsevier]

Abstract: In this contribution the gas-phase measurements of 19F and 29Si chemical shifts and scalar spin–spin couplings in SiF4 and (SiF3)2O have been reported. The density dependence of silicon and fluorine nuclei chemical shifts is strictly linear for both compounds. An extrapolation of gaseous data to the zero-density limit permitted the measurements of 19F and 29Si absolute nuclear magnetic shielding of isolated molecules at 300K. They were referenced against general accepted standards and are as follows: σ 0(SiF 4)=362.87ppm, σ 0(SiF4)=488.15ppm, σ 0((SiF 3)2O)=356.50ppm, and σ 0((SiF3)2O)=487.95ppm. The direct measurements of shielding constants on the basis of NMR frequencies were also performed. Indeed, we have successfully demonstrated the equivalence of both shielding values refinements. Careful investigation of 19F spectra shows isotope effects connected with the presence of three naturally occurring silicon isotopes: 28Si (92.19%), 29Si (4.70%) and 30Si (3.09%). The isotope effect measured on 19F nuclei does not exceed 0.01ppm. The 1 J(Si,F) indirect spin–spin coupling constants in both molecules were extracted from an experimental spectra of gaseous samples. The intermolecular effects in the gaseous state as well as in coming from gas to organic solutions were also observed. The new experimental results were used for verification of the theoretical evaluations presented earlier. [Copyright &y& Elsevier]

Abstract: New process technologies are disclosed to manufacture aluminium fluoride of high density and anhydrous hydrofluoric acid starting from fluosilicic acid as raw material which is obtained during acidulation of phosphate rock in the manufacture of phosphatic fertilizers. An overview of the relevant process technologies used commercially to consume this fluosilicic acid is provided in this paper. The new process technologies which shall be implemented to satisfy market demand in fluorochemicals (production of aluminium fluoride of high density from fluosilicic acid and production of anhydrous hydrofluoric acid from fluosilicic acid) and overcome some technical issues as well are described. [Copyright &y& Elsevier]

A new method of silica dissolution is described. It involves the formation of a stable SiF4 · n ROH complex (1, 1a) just from SiO2 and anhydrous alcoholic HF generated in situ from commercially available hexafluoropropene oxide. Alcoholic SiF4 complexes can be easily converted to different organosilicon compounds of the type SiF4L2 and (LH)2SiF6 [L = 1,10-phenantroline (2a), 2,2'-dipyridyl (2b), Me2SO (2c), pyridine (2d), triethanolamine (3a)]. Different silica-containing compounds can be used in this strategy-silicagel, sand, alumosilicates, and even rice husk. GRAPHICAL ABSTRACT[image omitted] [ABSTRACT FROM AUTHOR]

Abstract: The structures, interaction energies and vibrational spectra of the electron donor–acceptor complexes formed between silicon tetrafluoride and the common Lewis bases ammonia, water, phosphine and hydrogen sulphide have been determined by means of a series of ab initio molecular orbital calculations. The results confirm the trends observed in our previous studies of the complexes formed between the same four bases and the Lewis acids boron trifluoride and sulphur dioxide. The analogous complexes of silicon tetrafluoride with hydrogen fluoride and hydrogen chloride were also examined and, consistent with our earlier findings concerning the adducts of boron trifluoride and sulphur dioxide with these two diatomic species, were found to be very weakly-bound, if at all. [Copyright &y& Elsevier]

Abstract: A new method of 1-fluorosilatrane synthesis on the basis of silicon tetrafluoride complexes obtained from SiO2 is offered. Chemical properties of 1-fluorosilatrane in reactions of nucleophilic substitution are investigated. It is shown that fluorine can be substituted by O-nucleophiles (lithium methoxide, isopropoxide and phenoxide) and C-nucleophile (lithium phenylacetylenide). [Copyright &y& Elsevier]

Abstract: The infrared multiphoton dissociation (IRMPD) of SiF4 in the presence of CH4 has been studied using a tunable CO2 TEA laser. The siliconated reaction products have been identified. A kinetic scheme has been proposed to explain the experimental results. The reaction rate constant of the trifluorosilyl radical, SiF3, with CH4 has been obtained from the numerical solution of the differential equation system associated to the kinetic mechanism proposed as well as from non-linear regression methods. It has been additionally found that this reaction occurs through two channels. The relative importance of each and their reaction rate constants have been determined as well. [Copyright &y& Elsevier]

Silicon tetrafluoride (Si F 4) is a trace component of volcanic gases and is gaining industrial importance. However, a better knowledge of spectroscopic parameters is needed for this molecule in order to derive accurate concentrations. Following a previous reinvestigation of the ν 3 and ν 4 fundamentals (Richard et al. 2021), we have undertaken an extensive high-resolution study of its infrared absorption bands. We present here an update of this study. It features the recording of new far-infrared spectra, taking advantage of synchrotron radiation, and a global fit giving a consistent parameter set for the ground and fundamental states of 28 Si F 4 , now including the v 1 = 1 and v 2 = 1 states, by adding to the global analysis the newly measured ν 2 , ν 1 − ν 4 , and ν 4 − ν 2 bands near 264, 412, and 125 cm−1, respectively. Nearly 20 000 assigned lines pertaining to seven distinct rovibrational bands were fitted with an excellent accuracy (global standard deviation of 0.296). This allows us to obtain an accurate experimental value for the Si − F bond length, r e (SiF 4) = 1. 5516985 (30) Å. Some new band intensity estimates allow us to update our Si F 4 calculated spectroscopic database. [Display omitted] • SiF 4 is a trace component of volcanic gases and has industrial applications. • Detailed spectroscopic study of all fundamental modes. • Experimental determination of the equilibrium bond length. • Integrated band intensity estimation. • Update of a spectroscopic database. [ABSTRACT FROM AUTHOR]

Abstract: An acoustic Greenspan viscometer was used to measure the kinematic viscosity and speed of sound in the gases: CO, CO2, SiF4, SF6, C4F8, and NH3. The measurements cover the temperature range 220K to 375K, and pressures up to 3.4MPa or 80% of the saturation pressure. The viscometer was calibrated at 298.16K using five reference gases, Ar, He, N2, CH4, and C3H8, for which the viscosity and the speed of sound are known. With this calibration, we estimated the relative standard uncertainty of the kinematic viscosity u r(η/ρ)=0.006 and the uncertainty of speed of sound u r(c)=0.0001, except for very low pressures where the signal-to-noise ratio deteriorates and quality factor for the Helmholtz mode is ⩽20. [Copyright &y& Elsevier]

Abstract: Silicon tetrafluoride (SiF4) is observed in terrestrial volcanic gases and is predicted to be the major F-bearing species in low-temperature volcanic gases on Io [Schaefer, L., Fegley Jr., B., 2005b. Alkali and halogen chemistry in volcanic gases on Io. Icarus 173, 454–468]. SiF4 gas is also a potential indicator of silica-rich crust on Io. We used F/S ratios in terrestrial and extraterrestrial basalts, and gas/lava enrichment factors for F and S measured at terrestrial volcanoes to calculate equilibrium SiF4/SO2 ratios in volcanic gases on Io. We conclude that SiF4 can be produced at levels comparable to the observed NaCl/SO2 gas ratio. We also considered potential loss processes for SiF4 in volcanic plumes and in Io''s atmosphere including ion–molecule reactions, electron chemistry, photochemistry, reactions with the major atmospheric constituents, and condensation. Photochemical destruction (t chem ∼266 days) and/or condensation as Na2SiF6 (s) appear to be the major sinks for SiF4. We recommend searching for SiF4 with infrared spectroscopy using its 9.7 μm band as done on Earth. [Copyright &y& Elsevier]

The infrared multiphoton dissociation (IRMPD) of pure SiF4 and in mixtures with different gases was studied using a tunable CO2 TEA laser. The initial dissociation step of the IRMPD of SiF4 was found to be the decomposition into SiF3 and F. The gas phase reactions of trifluorosilyl, SiF3, with F and H2 was investigated. A kinetic scheme was proposed to explain the experimental results. The set of coupled differential equations associated to this scheme was numerically solved. The rate constants of the SiF3+F→SiF4 and SiF3+H2→SiF3H+H reactions were determined. [Copyright &y& Elsevier]

The molecular structures, the energies of complex formation, and the vibrational spectra of the binary molecular complexes of SiF4 with water, methanol, and dimethyl ether were calculated by the ab initio MP2 method with the basis sets up to 6-311++G(2d,2p). In the complexes, which have been detected previously by IR spectroscopy in low-temperature (12—15 K) inert matrices, the five-coordinate Si atom is in a distorted trigonal-bipyramidal environment, which is formed through the donor-acceptor interaction of the O atom with the Si atom and is additionally stabilized by the H...F hydrogen bonds. [ABSTRACT FROM AUTHOR]

The resistance of concrete to chemical attack may often be enhanced or maximized by careful attention to concrete proportioning, mixing, placing, and curing procedures. However, in a number of situations concrete must be protected by barrier materials which prevent contact with the chemical agent. Materials available for protection have been classified here, and tables have been provided as a guide for protection against specific agents. Methods of application, with consideration for both effectiveness and safety, are discussed. The report is intended to serve as a guide prior to consultation with experts regarding the specific situation. [ABSTRACT FROM AUTHOR]

• Area-selective microcrystalline silicon deposition using plasma-based technique. • Deposition occurs on silicon nitride surfaces, but not on alumina surfaces. • Fluorinated silicon precursor vital to achieve selectivity. • Exposed surfaces examined by ex-situ ellipsometry and scanning electron microscopy. An Area Selective Deposition (ASD) process using Plasma-Enhanced Chemical Vapour Deposition (PECVD) is demonstrated. Using a plasma chemistry containing a fluorinated silicon precursor (SiF 4), no deposition is observed on an aluminum oxide (AlO X) surface area, whereas a thin film of silicon is deposited on a silicon nitride (SiN X) surface area, while both areas are located on the same crystalline silicon substrate. The thin film deposition is characterized using spectroscopic ellipsometry, scanning electron microscopy, and atomic force microscopy, showing that 10 nm of silicon is deposited on the SiN x in 4 min. The growth on the SiN X is characterized by small grains and a rough surface, consistent with microcrystalline silicon, while no deposition or etching is observed for the AlO X surface. [ABSTRACT FROM AUTHOR]

New isotope abundance and relative atomic mass (atomic weight) values - with low, hitherto unattained uncertainty - are reported for two previously described silicon reference materials using a well-known method with an improved isotope-ratio mass spectrometer. These new values are directly traceable to the SI, more specifically to the unit for amount of substance, the mole, and independent of the SI unit of mass and of the Avogadro constant. Besides the residual mass-spectrometric uncertainties, these new values depend in effect only on a recently published direct comparison of the cyclotron frequency in a Penning trap of 28 Si + with that of 12 C + .

In a series of gas mass-spectrometric measurements performed near the highest attainable accuracy, samples from two highly homogeneous batches of silicon crystals and silica powder were compared directly with a synthetic mixture of the three stable isotopes of silicon. Thereby, this work not only established the "absolute" atomic weight of these batches, but also makes portions of these batches available as an Isotopie Reference Material for accurate isotopic abundance measurements in geochemical and other isotope-abundance studies of silicon.