Condensation Of SiO Research Articles

Petrographic constraints on the formation of silica‐rich igneous rims around chondrules in CR chondrites

AbstractIn the CR (Renazzo‐like) chondrite group, many chondrules have successive igneous rim (IR) layers, with an outer layer that contains a silica mineral and/or silica‐rich glass (silica‐rich igneous rims, SIRs). Models for SIR formation include (1) accretion of Si‐rich dust onto solid chondrule surfaces, followed by heating and cooling and (2) condensation of SiO(gas) onto the surface of partially molten chondrules. We evaluate these models, based on a petrographic study of five Antarctic CR chondrites that have undergone minimal secondary alteration. We obtained electron microprobe analyses of minerals and glass with quantitative wavelength‐dispersive spectroscopy mapping, and identified silica polymorphs with Raman spectroscopy. Common SIRs contain silica, low‐Ca pyroxene, Ca‐rich pyroxene, Fe,Ni metal, ± glass ± plagioclase ± rare olivine. We also describe near‐monomineralic SIRs where a narrow zone of cristobalite occurs at the outer edge of the chondrule. All crystalline silica is cristobalite, except for one SIR that consists of tridymite. Some rims contain silica‐rich glass (>80 wt% SiO2) but no silica mineral. Features such as sharp interfaces and compositional boundaries between chondrules and SIRs indicate that SIRs were formed from solid precursors. Consideration of the stability fields of silica polymorphs and computed liquidus temperatures indicates that SIRs were heated to >1500°C for limited time periods, followed by rapid cooling, similar to conditions for chondrule formation. We infer that in the CR chondrule formation region, the same heating mechanism was repeated multiple times while the chemical composition of the nebular gas evolved to highly fractionated silica‐rich compositions.

COMPARATIVE CHARACTERISTICS OF COATINGS WITH SiO AND GeO ON LEUCOSAPPHIRE

The reasons for the sharp difference in the adhesion of multilayer coatings containing SiO or GeO together with Ge on a leucosapphire (Al2O3) plate have been established. It should be mentioned that Silicon(II) and Germanium(II) oxides are quite stable in the gaseous state and, contrary, are metastable in condensed state; at high temperature they disproportionate into ultra-dispersed composites of amorphous nature. A comparison is made of the surface properties of ultramicroscopic droplets formed on solid surfaces – a substrate or the previous layer – upon condensation of SiO, GeO, or Ge vapors on leucosapphire. A qualitative assessment of the ratio of the corresponding contact angles of wetting by the indicated melts, formed at the first moment of contact, has been carried out. In assessing the surface tension of SiO and GeO melts (or Si – SiO2 and Ge – GeO2 composites), we proceeded from the corresponding values for SiO2 and GeO2, which are 296 and 248 mJ/m2 near the crystallization temperatures. On this basis, it was established that the smallest value of the contact angle, and hence the best wetting, is observed for the GeO melt (somewhat less for the SiO melt) on the solid surface of Al2O3 or Ge; the solid surface of SiO or GeO (especially, the first of them) with molten germanium should be much weaker wetted. Hence, it follows that thin-film multilayer coatings obtained from Ge and GeO on a leucosapphire substrate should have a significantly higher climatic resistance due to higher adhesion compared to multilayer coatings from SiO and Ge. Indeed, a multilayer coating containing SiO on a leucosapphire substrate with a large surface can withstand storage in air for no more than 2–3 months and begins to peel off; at the same time, the GeO coating remains intact after 4 years of storage. Thus, the GeO film-forming material is a promising one for use in multilayer coatings such as cut-off filters in interference optics of the near and mid-IR spectral ranges.

Interferometric observations of SiO thermal emission in the inner wind of M-type AGB stars IK Tauri and IRC+10011.

Asymptotic giant branch (AGB) stars go through a process of strong mass loss that involves pulsations of the atmosphere, which extends to a region in which the conditions are adequate for dust grains to form. Radiation pressure acts on these grains which, coupled to the gas, drive a massive outflow. The details of this process are not clear, including which molecules are involved in the condensation of dust grains. We seek to study the role of the SiO molecule in the process of dust formation and mass loss in M-type AGB stars. Using the IRAM NOEMA interferometer we observed the 28SiO and 29SiO J = 3 - 2, v = 0 emission from the inner circumstellar envelope of the evolved stars IK Tau and IRC+10011. We computed azimuthally averaged emission profiles to compare the observations to models using a molecular excitation and ray-tracing code for SiO thermal emission. We observe circular symmetry in the emission distribution. We also find that the source diameter varies only marginally with radial velocity, which is not the expected behaviour for envelopes expanding at an almost constant velocity. The adopted density, velocity, and abundance laws, together with the mass-loss rate, which best fit the observations, give us information concerning the chemical behaviour of the SiO molecule and its role in the dust formation process. The results indicate that there is a strong coupling between the depletion of gas-phase SiO and gas acceleration in the inner envelope. This could be explained by the condensation of SiO into dust grains.

THE ROLE OF SiO AS A TRACER OF PAST STAR FORMATION EVENTS: THE CASE OF THE HIGH-MASS PROTOCLUSTER NGC 2264-C

ABSTRACT NGC 2264-C is a high-mass protocluster where several star formation events are known to have occurred. To investigate whether past protostellar activity has left a chemical imprint in this region, we mapped it in SiO( ), which is a shock tracer, and several other molecular lines with the Nobeyama 45 m telescope. Our observations show the presence of a complex network of protostellar outflows. The strongest SiO emission lies beyond a radius of ∼0.1 pc with respect to the center of the clump and is characterized by broad ( km s−1) lines and abundances of with respect to H2. Interestingly, SiO appears to be relatively depleted ( ) within this radius, despite it being affected by molecular outflow activity. We attribute this to the fast condensation of SiO back onto dust grains and/or rapid gas-phase destruction of SiO, which is favored by the high density present in this area ( cm−3). Finally, we identify a peripheral, narrow-line (∼2 km s−1) component where SiO has an abundance of a few times 10−11. After considering different options, we conclude that this weak emission may be tracing protostellar shocks from the star formation episode that preceded the current one, which have decelerated over time and eventually resulted in SiO being largely depleted/destroyed. Alternatively, a population of unresolved, low-mass protostars may be responsible for the narrow SiO emission. High-angular resolution observations are necessary to distinguish between these two possibilities, and thus to understand the role of SiO as a chemical tracer of past star formation episodes in massive protoclusters.

Origin of native silicon and iron silicides in the Dhofar 280 lunar meteorite

Native silicon and iron silicides were studied in the Dhofar 280 lunar anorthositic meteorite representing an impact-melt breccia. Such rocks are widespread in the highland crust of the Moon. It was established that cryptocrystalline objects containing native silicon are close in composition to the silicon monoxide SiO. Experimental data demonstrate that this compound is the main component of the vapor forming during vaporization of an anorthitic melt. It is suggested that the formation of native silicon was related to the condensation of SiO from an impact-derived vapor cloud. Reducing conditions are determined by the mass-fractionation of silica monoxide and oxygen in the expanding vapor cloud in the gravity field of the Moon. Gaseous SiO may be condensed directly into a solid phase or a mixture of silicon with silica. The condensed SiO phase incorporated into an impact melt should be decomposed into silicon and silica. Interaction of Si, SiO, and SiO2 solid condensates with an impact melt could lead to the observed enrichment of the surrounding liquid in silica. The formation of iron silicides is provided by the reaction of native silicon with FeO presenting in an impact melt. The other iron source could be a meteoritic component, which is identified in silicides by elevated Ni contents. Obtained mineralogical and experimental data show that metallic silicon can be obtained under lunar conditions by distillation of anorthositic melts and can be used for production of solar batteries to provide lunar settlements with energy.

Errata

An error occurred in two articles in Applied Spectroscopy, in “Evaporation and Condensation of SiO and SiO2 studied by Infrared Spectroscopy”, by M. Klevenz, S. Wetzel, M. Moller, and A. Pucci [Applied Spectroscopy, vol. 64, issue 3, pp. 298-303 (2010)], and in “The Temperature Dependent Decomposition of SiO Studied by Infrared Vibrational Spectroscopy” by S. Wetzel, M. Klevenz, A. Pucci, and H.-P. Gail [Applied Spectroscopy, vol. 66, issue 9, pp. 1061-1066 (2012)]. In both the articles, the formula given for the Brendel dielectric function is not consistent with the oscillator parameters of the tables. The correct equation is [Formula: see text] (valid for ε = Re ε + i Im ε). It describes the Brendel dielectric function in accordance to the published values of oscillator parameters. DOI: 10.1366/13-07082 The authors of the paper entitled “Integration of an Intensified Charge-Coupled Device (ICCD) Camera for Accurate Spectroscopic Measurements” published in Applied Spectroscopy, Vol. 66, issue 8, pp. 970-978, (2012), by R.J. Paláez, S. Mar, J.A. Aparicio, and M.T. Belmonte, wish to correct a significant mistake in their published paper. On page 973, the last phrase of the left column should say: “Dotted lines correspond to the fit of the experimental data to the theoretical curve when the detector is the very frequently employed OMAIII EG&G model 1455R 512HQ, while continuous lines correspond to the fit when the measurements are obtained with the newer ICCD.” DOI: 10.1366/13-07083

Optical properties of a polyethylene dispersion with a luminescent silica prepared by surface grafting of a perylene derivative

Abstract A micrometric silica modified with perylene derivative (SiO 2 –TES) has been prepared by hydrolysis–condensation reactions between silica and N,N’ -bis-(3-triethoxysilylpropyl)-perylene-tetracarboxyldiimide (P-TES) and utilized as filler in LLDPE films together with a compatibilizer. Spectroscopic analyses on SiO 2 –TES confirmed the grafting of P-TES on silica, while its amount was determined by thermogravimetric analysis. Solid state NMR provided information about the structure of silicon atoms involved in the condensation of SiO 2 and P-TES that resulted mainly in silicon atoms grafted with bi-dentate anchorages. UV–Vis and fluorescence analyses carried out on P-TES showed the ability of the dye to generate J-type aggregates in apolar solvents. The same analyses on SiO 2 –TES revealed the presence of both isolated and aggregated dye molecules grafted on silica surface, while on polymeric dispersions of SiO 2 –TES, they have shown only the presence of P-TES aggregates grafted to silica. Thanks to the direct correlation between optical properties (obtained both by UV–Vis and by fluorescence analyses) and the chemical environment of composites, the luminescent silica SiO 2 –TES could be used to estimate the filler dispersion extent in different microcomposite polymer materials.

Evaporation and Condensation of SiO and SiO2 Studied by Infrared Spectroscopy

Physical evaporation of SiO and SiO(2) under ultra-high vacuum conditions was monitored in situ with infrared spectroscopy at frequencies between 450 cm(-1) and 5000 cm(-1). The measured vibrational spectra of the condensed films are identical in both cases, for SiO and SiO(2) evaporation, and can be described with four Brendel oscillators located at 380 cm(-1), 713 cm(-1), 982 cm(-1), and 1101 cm(-1), corresponding to typical vibration modes in SiO.

VLBA SiO observations of bright O-rich AGB stars

We present the results of observations of the SiO masers at 7 mm wavelength in several oxygen rich Asymptotic Giant Branch (AGB) stars. These observations were coordinated with observations using the ESO VLTI/MIDI interferometer at 10 μm wavelength. These stars are o Ceti (Mira), U Herculis (U Her), OH26.5+0.6, R Leonis (R Leo), and W Hydrae (W Hya). Both total intensity and linear polarizations are imaged. Linear radial features seen in o Ceti may be associated with an X-ray flare seen a year earlier by [CITE]. Similar linear features are also seen in R Leo, U Her and OH26.5+0.6. These features typically show systematic radial velocity variations and a tendency for the linear polarization to be perpendicular to the direction of elongation, suggesting that magnetic fields are dynamically important. A wide radial extent of the maser rings observed in U Herculis and OH26.5+0.6 is interpreted as meaning that the outer boundaries of the masing regions in these stars are not truncated by the condensation of SiO onto dust grains.

Morphology evolution of Si nanowires synthesized by gas condensation of SiO without any catalyst

A series of Si nanowires are synthesized at constant temperature of 970 ○C on Si substrate by gas condensation of pure SiO vapor without any metal catalysts, by controlling the coverage of SiOx deposits. The morphologies are characterized by scan electron microscopy (SEM) and their evolution during the growth process is observed: from isolated clusters in earlier stage to linked cluster assemblies, and developing to smooth nanowires in the later stage. The growth mechanism is discussed based on the newly proposed clustering-aggregation-sintering model.

A growth mechanism of Si nanowires synthesized by gas condensation of SiO without any catalyst

Si nanowires are synthesized at different temperature, 970°C and 1080°C, on Si substrate by gas condensation of pure SiO vapor without any metal catalysts. Scanning electron microscopy and transmission electron microscopy show the morphology of the synthesized nanostructures is significantly altered by temperature: in specimens prepared under 970°C, dispersed nanoparticles, nanoparticle assemblies and smooth nanowires are discovered at different deposition densities; in specimens prepared under 1080°C, only short nanowires growing directly from the substrate can be seen. The observation indicates there are different growth processes for the two kinds of morphologies. Their growth mechanisms are discussed. A model based on sintering, diffusion and clustering effects is suggested for the low-temperature process.

Thermodynamics and Phase Stability in the Si—O System

AbstractFor Abstract see ChemInform Abstract in Full Text.

Thermodynamics and phase stability in the Si–O system

A comprehensive thermodynamic assessment has been carried out on the phases SiO 2(L), including SiO 2(glass), the amorphous monoxide SiO(am) and on the solubility of oxygen in solid and liquid silicon, jointly with the equilibrium partition coefficient k. Contradictions in the sparse thermodynamic data of SiO(am) are pointed out. Our key experiments were performed on the decomposition and condensation of SiO(am). X-ray diffraction on samples heated in evacuated silica capsules was used. The condensation experiment was performed in local equilibrium on a silica rod in a commercial CZ-Si apparatus. With the Calphad method a complete set of Gibbs energy equations was developed for the phase SiO 2(L), comprising glass, supercooled liquid and stable liquid silica, the phase SiO(am) and the solid and liquid silicon solution phases. Combining this with the data for crystalline silica and the gas phase, a consistent thermodynamic description of the entire Si–O system is constructed, covering the complete composition range. Based on that, a number of stable and metastable phase diagrams at various pressures are calculated and applied to better understand important process steps in the production of semiconductor silicon.

29Si chemical shift anisotropies in calcium silicates from high-field 29Si MAS NMR spectroscopy.

29Si chemical shift anisotropy (CSA) data have been determined from (29)Si MAS NMR spectra recorded at 14.1 T for a number of synthetic calcium silicates and calcium silicate hydrates. These are beta- and gamma-Ca(2)SiO(4), Ca(3)SiO(4)Cl(2), alpha-dicalcium silicate hydrate (alpha-Ca(2)(SiO(3)OH)OH), rankinite (Ca(3)Si(2)O(7)), cuspidine (Ca(4)Si(2)O(7)F(2)), wollastonite (beta-Ca(3)Si(3)O(9)), pseudowollastonite (alpha-Ca(3)Si(3)O(9)), scawtite (Ca(7)(Si(6)O(18))CO(3).2H(2)O), hillebrandite (Ca(2)SiO(3)(OH)(2)), and xonotlite (Ca(6)Si(6)O(17)(OH)(2)). The (29)Si MAS NMR spectra of rankinite and wollastonite clearly resolve manifolds of spinning sidebands from two and three Si sites, respectively, allowing the CSA parameters to be obtained with high precision for each site. For the (29)Si Q(1) sites in rankinite and cuspidine, the CSA asymmetry parameters (eta(sigma) approximately 0.6) contrast the general expectation that sorosilicates should possess small eta(sigma) values as a result of the nearly axially symmetric environments of the SiO(4) tetrahedra. The (29)Si CSA parameters provide an improved insight into the electronic and geometric environments for the SiO(4) tetrahedra as compared to the values solely for the isotropic chemical shift. It is shown that the shift anisotropy (delta(sigma)) and the CSA asymmetry parameter (eta(sigma)) allow a clear distinction of the different types of condensation of SiO(4) tetrahedra in calcium silicates. This relationship may in general be valid for neso-, soro-, and inosilicates. The CSA data determined in this work may form a valuable basis for (29)Si MAS NMR studies of the structures for tobermorites and calcium silicate hydrate phases resulting from hydration of Portland cements.

SiO Emission in a Jetlike Molecular Outflow toward L1157

We report interferometric observations of the SiO (2-1) and CO (1-0) lines toward the blueshifted lobe of the L1157 bipolar outflow. These observations reveal clumpy SiO emission aligned with highly collimated CO emission. The SiO emission is enhanced in two prominent condensations, similar to those seen in VLA images of the NH3(3, 3) line. The SiO condensation closer to the outflow source peaks within 10'' of a bright knot of the 2.1 μm H2 line emission and shows blueshifted emission extending more than 17 km s-1 from the cloud velocity. The close association between the SiO and H2 emission suggests that the SiO emission is excited in the accelerated postshock regions near the head of an underlying jet. The SiO condensation farther downstream shows a smaller velocity extent and no apparent associated H2 emission. We suggest that the two condensations result from separate interactions of an episodic jet with the surrounding cloud core. In this scenario, the emission region farther downstream results from an older event. Both SiO condensations appear to lead the high-velocity CO emission, consistent with the idea that SiO emission is excited close to the head of the jet and the CO accelerated in the oblique outer wings of the bow shock.

Effect of chemical additives on microfibre formation from SiO vapour condensed in flowing gas streams

SiO vapour has been allowed to condense from flowing gas streams in the presence of a wide range of inorganic and organic vapour species to determine the effect of these species on the known habit of SiO of condensing to form microfibres of potential use as reinforcing fillers. Major changes in fibre morphology have been observed on condensation of SiO in an N2 stream containing gaseous AlCl3, GeCl4 or C2H2, or by condensation of SiO with other molecular species formed when Ga2O3–SiO2–Si, In2O3–SiO2–Si or GeO2–SiO2–Si mixtures were heated in N2 or B–SiO2 was heated in H2. The fibre morphology changed surprisingly little when SiO was condensed with vapours of transition-metal halides. The products were studied by transmission electron microscopy (TEM), IR, X-ray photoelectron spectroscopy (XPS) and powder XRD. The work establishes that condensing SiO is an exceptionally versatile microfibre-forming system.

Silicon Bearing Molecules in Molecular Clouds

We have used the IRAM 30-m telescope to make high angular resolution observations of the silicon-bearing molecule, SiO and SiS in region of massive star formation. We have mapped the J=2-l and the J=5-4 lines of SiO with angular resolutions of 26 and 12” respectively. For all the sources mapped, the SiO emission is more extended that the beam. The extreme cases are found toward NGC7538 and W49N where the SiO emission has sizes of 1x0.5 pc and 2.8x1 pc respectively. This result is in contrast with the size of the SiO region in Orion-IRc2 which is of the order 0.03 pc. The maxima of the SiO emission are found at the position of the H2O masers. This indicates, as previously thought, that SiO emission probes the high temperature regions and/or the shocked gas and dust surrounding young stars. In the DR21(OH) region we have found the unique SiO source which is not associated to H20 maser emission. This SiO condensation is 40” south of DR21(OH) and it was first detected as a source of 350µm emission. The SiO emission is elongated in the east-west direction. From an analysis of the FIR continuum emission this object appears to be cool (Tk < 30) and it has been proposed that this source represents a pre-stellar condensation which may be evolving toward the star formation stage. The detection of SiO, howevwer, casts some doubts about the evolutionary stage of this source. Futher high angular resolution observations are necessary to establish the nature of this source.

Experimental studies of the vapor phase nucleation of refractory compounds. I. The condensation of SiO

An experimental apparatus has been built in which a quantitative study of the vapor phase nucleation of refractory particles can be performed. With this equipment, measurements have been made of the critical partial pressure (Pc) of SiO necessary to initiate avalanche nucleation in the SiO–H2 system as a function of ambient temperature in the range 750 K⩽T⩽1000 K. The condensate produced at low temperatures is Si2O3 rather than the more stable oxides SiO or SiO2. At high temperatures a mixture of Si2O3 and amorphous SiO2 is found. The SiO2 may be the result of annealing or oxidation on the collector after the particles had been formed as less stable clusters in the vapor. Analysis of Pc vs T using classical nucleation theory yields a surface energy of ∼500 ergs/cm2 for the particles. Despite the fact that this is in reasonable agreement with values for Si2O3 obtained from the literature, several inconsistencies in the analysis are noted. It is argued that classical nucleation theory is not applicable to this system.