Loss Of SiO Research Articles

Photochemical properties of a potential interstellar dust precursor: the electronic spectrum of Si3O2.

Silicon oxide compounds are considered as precursors for silicon-based interstellar dust grains which consist mainly of silica and silicates. Knowledge of their geometric, electronic, optical, and photochemical properties provides crucial input for astrochemical models describing the evolution of dust grains. Herein, we report the optical spectrum of mass-selected Si3O2+ cations recorded in the 234-709 nm range by means of electronic photodissociation (EPD) in a quadrupole/time-of-flight tandem mass spectrometer coupled to a laser vaporization source. The EPD spectrum is observed predominantly in the lowest-energy fragmentation channel corresponding to Si2O+ (loss of SiO), while the higher-energy Si+ channel (loss of Si2O2) provides only a minor contribution. The EPD spectrum exhibits two weaker unresolved bands A and B near 26 490 and 34 250 cm-1 (377.5 and 292 nm) and a strong transition C with a band origin at 36 914 cm-1 (270.9 nm) which shows vibrational fine structure. Analysis of the EPD spectrum is guided by complementary time-dependent density functional theory (TD-DFT) calculations at the UCAM-B3LYP/cc-pVTZ and UB3LYP/cc-pVTZ levels to determine structures, energies, electronic spectra, and fragmentation energies of the lowest-energy isomers. The cyclic global minimum structure with C2v symmetry determined previously by infrared spectroscopy can explain the EPD spectrum well, with assignments of bands A-C to transitions from the 2A1 ground electronic state (D0) into the 4th, 9th, and 11th excited doublet states (D4,9,11), respectively. The vibronic fine structure of band C is analyzed by Franck-Condon simulations, which confirm the isomer assignment. Significantly, the presented EPD spectrum of Si3O2+ corresponds to the first optical spectrum of any polyatomic SinOm+ cation.

Carbothermal Reduction of Quartz with Carbon from Natural Gas

Carbothermal reaction between quartz and two different carbons originating from natural gas were investigated in this paper. One of two carbons is the commercial carbon black produced from natural gas in a medium thermal production process. The other carbon is obtained from natural gas cracking at 1273 K (1000 °C) deposited directly on the quartz pellet. At the 1923 K (1650 °C) and CO atmosphere, the impact of carbon content, pellet structure, gas transfer, and heating rate are investigated in a thermo-gravimetric furnace. The reaction process can be divided into two steps: an initial SiC-producing step followed by a SiO-producing step. Higher carbon content and increased gas transfer improves the reaction rate of SiC-producing step, while the thicker carbon coating in carbon-deposited pellet hinders reaction rate. Better gas transfer of sample holder improves reaction rate but causes more SiO loss. Heating rate has almost no influence on reaction. Mass balance analysis shows that mole ratios between SiO2, free carbon, and SiC in the SiC-producing step and SiO-producing step in CO and Ar fit the reaction SiO2(s) + 3 C(s) = SiC(s) + 2 CO(g). SiC-particle and SiC-coating formation process in mixed pellet and carbon-deposited pellet are proposed. SiC whiskers formed in the voids of these two types of pellets.

The effects of pre-oxidation on the sintering and mechanical property of powder injection moulded SiC material

Usually, injection moulded SiC green parts are debound in inert atmosphere or vacuum, which induces the residual carbon and increases forming cycle and production cost. In this paper, injection moulded SiC with Al 2O 3 and Y 2O 3 as sintering assistant was thermal debound in air and Ar, respectively. The paper investigates the effects of pre-oxidation during debinding stage on the sintering and mechanical property of SiC material. During sintering, the oxide SiO 2 is in favour of the shrinkage of debound samples at lower temperature. After sintering, the linear shrinkage of sintered samples with pre-oxidation is bigger than the sample without pre-oxidation. Test results by TEM and XRD indicate that SiO 2 disappear from the inside of the sintered samples. The loss of SiO 2 decreases the content of Al 2O 3, which affects the formation of YAG (Y 3Al 5O 12). Sintered Sic samples contain α-SiC phase and intergranular phase. There is no hetero-phase between the boundaries of α-SiC phase and intergranular phase. The bending and compression strength values of sintered samples with pre-oxidation reach to 537 MPa and 2.89 GPa, respectively. These values approach the strength of sintered samples without pre-oxidation (594 MPa and 3.0 GPa).

SiCSi 3N 4 bonded materials by the nitridation of SiC and talc

Silicon carbide-based materials are used in many applications due to their good thermo-mechanical properties at high temperatures. The nitrogenous bond formed from nitriding reactions of silicate minerals seems to be an interesting method to obtain these materials. In this work, the reaction of SiC with talc and N 2 atmosphere is studied. Pellets and/or bars of SiC-talc mixtures were reacted within the range 1395–1650 °C. Reaction products were studied through XRD, textural properties, bending strength and microscopy. Reactions and mechanisms for this system are proposed. Silicon nitride is formed as principal bond phase. During reaction, volatilization of Mg takes place, where its loss is favoured at high temperatures and high N 2 flow rates. A loss of SiO(g) is also observed. Mechanical strength has a linear relation with the bond phase content.

Burial diagenesis of illite/smectite in shales and the origins of authigenic quartz and secondary porosity in sandstones

Several gram-size samples of <0.1 μm, nearly monomineralic mixed-layer illite/smectite (I/S)were isolated from nineteen whole-cores of shale of the Frio Formation from the Texas Gulf Coast. Between ∼7,000 ft (2133 m) and ∼15,000 ft (4572 m) burial depth I/S changes from random-interstratification ( R = 0) with low %I to ordered-interstratification ( R = 3) with high %I. The accompanying chemical changes are loss of Si, Mg, and Fe +3, gain of K, Al, and Fe +2, and a shift in the REE content of the mineral. There is no chemical or mineralogical evidence for a cessation of I/S reaction at ∼80% I as is commonly accepted; both chemical and mineralogical changes occur throughout burial. Continuous change in the oxygen isotopic composition of I/S implies that the conversion of smectite-layers to illite-layers is a dissolution and reprecipitation process. Mass balance calculations indicate that burial diagenesis of Frio Formation shales is an open-system process that requires addition of K 2O and Al 2O 3 and results in loss of SiO 2. The amount of SiO 2 made available by shale diagenesis is sufficient to be the source of the quartz-overgrowth cements in the associated Frio sandstones. Iron reduction in I/S is a significant source of the acid required for the diagenesis of both Frio shales and sandstones.

On volume change and mass transport during the development of crenulation cleavage

A comparison of the bulk chemistry between isolated zones of crenulation cleavage and the surrounding relatively homogeneous slates from three localities (Boscastle, SW England; Moselle Valley, Germany; Lac de Roselend, French Alps) demonstrates that marked bulk volume change is not a prerequisite for the development of crenulation cleavage. X-ray powder diffraction results also demonstrate that there is no significant mineralogical change between crenulated and uncrenulated zones for the samples studied. Mineralogical differentiation and mass transfer takes place on a local scale between the limb and hinge domains of individual crenulation folds and of larger scale folds in layering, but can occur without significant overall volume change on the scale of crenulated zones containing many microlithon and cleavage domains. Relative volume changes between crenulated and uncrenulated regions do not exceed ca 5% at Boscastle and the majority of samples from the Moselle Valley. At one locality in the Moselle Valley, however, a volume loss of around 35–40% occurred from the crenulated zone, produced almost entirely by loss of SiO 2 (as quartz) from the system. Isolated parallel-sided bands of crenulation cleavage, such as the examples from Boscastle and the Moselle Valley, are geometrically constrained to represent some combination of volume change and heterogeneous simple shear, superimposed upon a background homogeneous strain. In examples with minimal volume changes, the heterogeneous strain component must be one of simple shear.

Distributions of halloysite-metahalloysite and gibbsite in tropical mountain paleosols: relationship to Quaternary paleoclimate

Paleosol profile available water varied during the Quaternary and when high was accompanied by increased leaching and loss of SiO 2. This mechanism controlled the formation of gibbsite and halloysite-metahalloysite in paleosols on Mount Kenya during the time they were exposed to subaerial weathering. The available data for distributions of weathering products in paleosols support a reconstruction of high energy paleoclimate and wetness during the first two interglacials (Lake Ellis-Gorges; Naro Moru-Lake Ellis), followed by reduced energy (lower precipitation) in the Teleki-Naro Moru Interglaciation (lower Brunhes), and ending with increased paleoclimatic energy during the Liki-Teleki Interglaciation (isotope stage 5). Based on the data available, weathering during the present postglacial interval fails to achieve even the magnitude of a low energy interglaciation. Using relative amounts of gibbsite/halloysite it is possible to contruct a model of relative paleoclimatic energy for each of the interglacial on Mount Kenya.

Silsesquioxane-derived ceramic fibres

Fibres formed from blends of silsesquioxane polymers were characterized to study the pyrolytic conversion of these precursors to ceramics. The morphology of fibres pyrolysed to 1400°C revealed primarily amorphous glasses whose conversion to β-SiC is a function of both blend composition and pyrolysis conditions. Formation of β-SiC crystallites within the glassy phase is favoured by higher than stoichiometric C/Si ratios, while carbothermal reduction of Si-O bonds to form SiC with loss of SiO and CO occurs at higher methyl/phenylpropyl silsesquioxane (lower C/Si) ratios. As the carbothermal reduction is assumed to be diffusion controlled, the fibres can serve as model systems to gain understanding of the silsesquioxane pyrolysis behaviour, and therefore are useful in the development of polysilsequioxane-derived ceramic matrices and coatings as well.

Li [sbnd]δ 18O [sbnd]SiO 2 systematics in volcanic rocks and mafic lower crustal granulite xenoliths

Li δ 18O SiO 2 relationships have been examined for suites of spilitized basaltic rocks (DSDP 504B; Xigaze Ophiolite; Blanco Fracture Zone; Greater Caucasus; Rhenohercynian Fold Belt) and intra-plate evolved tholeiites (Northern Hessian Depression and Vogelsberg, W Germany; Mount Falla, Transantarctic Mountains). Relative to unaltered MORB and intra-plate primary olivine tholeiites, both the spilitic rocks and the evolved tholeiites are characterized by Li and 18O enrichment. For the spilitic rocks, Li and 18O enrichment is accompanied by a loss of SiO 2 as a result of seawater hydrothermal alteration, whereas the evolved tholeiites have gained SiO 2, Li and 18O from fractionation of mafic phases and assimilation of crustal rocks. On Li vs. SiO 2 and δ 18O vs. SiO 2 diagrams, the two rock groups plot largely in distinct fields, suggesting the possibility of so distinguishing between such lithologies in the ancient rock record. Mafic granulite xenoliths from the Northern Hessian Depression have elevated Li and 18O abundances at low SiO 2 contents. Even after correction for extraction of felsic components, their Li δ 18O SiO 2 signatures plot within the field of spilitic protoliths, suggesting that the lower crust in this region contains relics of spilitic rocks from a former oceanic crust.

Volume-loss model for trace-element enrichments in mylonites

Mylonites from three widely separated localities along the Fries ductile deformation zone in the Blue Ridge province show substantial enrichments in trace and minor elements (TiO{sub 2}, P{sub 2}O{sub 5}, Zr, Y, and V) and depletions in Rb and Sr relative to the protolith. Two end-member hypotheses can explain the enrichments: one involves partitioning to and from an infiltrating fluid and assumes that all the elements were mobile. The second hypothesis assumes the high-field-strength cations were largely immobile and that their enrichment is due to large volume losses in the mylonites. Modeling indicates that Ti is immobile for fluid/rock ratios as high as 10{sup 4}, and petrographic and modal data support a volume-loss mechanism. Volume loss was accommodated by loss of SiO{sub 2} and alkalies during feldspar dissolution. Calculated fluid/rock volume ratios required to produce the observed SiO{sub 2} losses (assuming Ti mobility) range from 70 to 600. Variable enrichments in P, Zr, Y, and V are attributed to selective mobility of these elements during fluid infiltration.

Petrogenesis and tectonic significance of amphibolites interlayered with metasedimentary gneisses in the Ivrea Zone, Southern Alps, northwest Italy

Amphibolites occurring as elongate lenses and boudins within the metasedimentary (kinzigite) formation of the Ivrea Zone are all of igneous parentage. A detailed study of their trace element characteristics shows that they can be divided into two groups. Type 1 amphibolites occur as layers up to 100 m thick and have trace-element distributions showing depletion in incompatible elements typical of normal (N-type) mid-ocean ridge basalts. Type 2 amphibolites occur as thinner layers and boudins and have higher levels of the more incompatible elements similar to transitional or enriched (E-type) ocean basalts. Although metamorphism appears to have resulted in loss of SiO 2 and variable enrichment in Na, K, Rb, Ba, Sr and locally Ca, the less mobile elements, including the rare-earth elements, have preserved the primary basaltic geochemical characteristics. The tectonic model which best explains the assemblage of slivers of MORB-like amphibolites within extremely highly deformed semi-pelitic metasediments is that of an accretionary sedimentary wedge formed at a (Palaeozoic) subduction zone.

HALOGEN-ACID ALTERATION OF ASH AT FUMAROLE NO. 1, VALLEY OF TEN THOUSAND SMOKES, ALASKA

A series of specimens of ash and pumice, collected outward from the throat of Fumarole No. 1 of Zies in the Valley of Ten Thousand Smokes in 1952, has been analyzed for major and minor constituents. The bulk density—approximately 1.00 gm/cc for unaltered ash—was determined by weighing blocks of known volume, and chemical addition or subtraction was calculated for unit volume. Elements readily converted to volatile fluorides or chlorides were leached near the hot throat, but hydrolysis resulted in some late-stage addition in the innermost zone. Condensation of steam and inward movement of hot acid water resulted in outer zones of oxidation and leaching and an intermediate zone of boiling and evaporation, which was especially enriched in alumina and water of hydration. Appreciable quantities of Pb, Zn, Cu, As, Cl, F, and SO 4 were added to the innermost zone (1 inch), and Ni, Co, B, and Sc were concentrated in the intermediate zone about 2 feet from the throat. No carbonate is present in any zone. Magnetite, hematite, goethite, hydromica, opal, montmorillonite, and kaolinite are the chief alteration minerals. The alteration is similar to that produced by strong sulfur acids elsewhere, but the gas of Fumarole No. 1 contained only 7 ppm S in 1917, and 70 ppm in 1919. In contrast it carried 240 ppm of HCl, and 30 ppm HF in 1917—the only year in which samples of halogen gases were collected in the valley. The halogen-acid alteration differs from sulfur-acid alteration chiefly in the greater loss of SiO 2 relative to A1 2 O 3 .

A review of some problems of African carbonatites

Summary Carbonatites ar known at many places in eastern and central Africa, from near Mount Elgon in Uganda to Spitzkop and Palabora in nort-eastern Transvaal. They reange in age from pre-Karroo, post-Waterbag in the south to Miocene—Pliocene in the north. Owing to this great age difference denudation has revealed carbonatites at various levels of erosion, the deepest corresponding perhaps with the carbonatites exposed at Alnö in Sweden and Fen in Norway. The composition and structure of the carbonatites, the associated alkaline igneous rocks, and the altered country rocks known as fenites are all described. The carbonatites are mainly pure calcite but some are ankeritic and dolomitic and, locally, sideritic and manganiferous. They carry characteristics accessory minerals, particularly pyrochlore. The associated igneous rocks are ijolites with, less frequently, nephelinesyenite and at some centres pryoxenite. Fenitization results in the formation of aegirine-fėlspar rocks, nearly pure felspar rocks and felspathic breccia. Evidence as to chemical changes involved in fenitization is not always consistent, but addition of K or Na, or both, and loss of SiO 2 are satisfactorily demonstrated. Current theories are reviewed. The carbonatites are believed to owe their origin to concentration of carbon dioxide of or carbonatitic fluid of magmatic origin, derived perhaps from pyroxenite highly charged with volatiles, among which carbon dioxide played the most important part, associated with phosphoric acid, fluorine, water etc., and in which the elements niobium and cerium, among others, were also concentrated.