SiO2 In Air Research Articles

Alumina joints brazed by screen-printed B4C–SiO2 in air

In this study, B4C–SiO2 was employed as the joining material via a screen-printing method to join alumina (Al2O3) ceramics at 1000 °C in ambient air. Effects of mass ratios of B4C and SiO2 ranging from 1:0.5 to 1:2.5 on the composition, microstructure, and mechanical properties of the joints were investigated. When the content of SiO2 was equal or greater than that of B4C, the interlayer of the brazed joints was defect-free and consisted of Al4B2O9 whiskers and calcium borosilicate glass based on microscopically electronic analyses. With the content of SiO2 increased, the shear strength of the joints increased first and then decreased. The average shear strength of the joint reached the maximum value of 110 ± 19 MPa when the mass ratio of B4C to SiO2 was 1:2. The current study demonstrated that the screen-printed B4C–SiO2 system could be a very beneficial approach to obtain high strength Al2O3 joints with defect-free interlayer at relatively low joining temperatures in air.

Polyhedral oligomeric silsesquioxane (POSS)-modified phenolic resin: Synthesis and anti-oxidation properties

Abstract In this work, octamercapto polyhedral oligomeric silsesquioxane (POSS-8SH) and octaphenol polyhedral oligomeric silsesquioxane (POSS-8Phenol) were successfully synthetized. POSS-8Phenol was added into the synthesis process of liquid thermoset phenolic resin (PR) to obtain POSS-modified phenolic resin (POSS-PR). Chemical structures of POSS-8SH, POSS-8Phenol, and POSS-PR were confirmed by FTIR and 1H-NMR. TG and DTG analysis under different atmosphere showed that char yield of POSS-PR at 1,000°C increased from 58.6% to 65.2% in N2, which in air increased from 2.3% to 26.9% at 700°C. The maximum pyrolysis temperature in air increased from 543°C to 680°C, which meant better anti-oxidation properties. XRD results confirmed both POSS-8Phenol and POSS-PR-generated crystalline SiO2 in air, which could explain the improvement of anti-oxidation properties. SEM showed that the POSS-PR had phase separation during curing process. Finally, carbon fiber fabric-reinforced POSS-PR (C-POSS-PR) was prepared to verify the anti-oxidation properties of POSS-PR.

Effects of different atmospheres on the arc erosion behaviors of Ti3SiC2 cathodes

The effects of ambient atmospheres on the arc erosion behaviors of Ti3SiC2 cathodes were investigated at 5.5 kV in argon, nitrogen, air, and oxygen. The mass loss of the cathodes increased in the order of argon, nitrogen, air, and oxygen and the morphologies were measured by 3D laser scanning confocal microscope with a gradual blooming phenomenon. Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were employed to detect the components of erosion regions. The erosion-chemical products mainly consisted of TiNx in nitrogen, TiNx, TiO2 and SiO2 in air, TiO2 and SiO2 in oxygen. The arc energy was responsible for the arc erosion characteristics in different atmospheres.

Emission of Molecular Nitrogen upon Electron Bombardment of Pyrolytic Aerogel SiO2 and Aluminum

It is found that the emission intensity of the 2+ band system of the N2 molecule (C3Πu → B3Πg transition) under electron bombardment of pyrolytic aerogel SiO2 in air at atmospheric pressure is 40–70% higher than that in the case of bombardment of aluminum under the same conditions. The dependences of the emission intensity at 337 nm (0-0 vibrational transition in the 2+ band system of the N2 molecule) on the target temperature in the range of 30–60°C are different for the aluminum and SiO2 targets, which indicates different excitation mechanisms of the N2(C3Πu) state. It is suggested that when the SiO2 target is bombarded, the N2(C3Πu) state is excited not only by direct collisions with the electrons of the primary beam and secondary electrons, but also by the energy transfer from SiO2 excitons and conduction electrons to N2 molecules upon their contact with the SiO2 surface.

Experimental liquidus studies of the Zn–Fe–Si–O system in air

AbstractThe liquidus of the ternary system ZnO–“FeO1.5”–SiO2 in air has been experimentally investigated in the tridymite and cristobalite, spinel, and zincite primary phase fields in the temperature range 1623–1923 K (1350–1650°C). Slags containing up to 65 mol.% “FeO1.5” have been studied for the first time. The slag–spinel–zincite eutectic in the binary ZnO–“FeO1.5” system in air has been estimated by extrapolation of the low-SiO2 part of the ternary system to x(SiO2) = 0. High-temperature equilibration on primary phase (silica) or inert metal (platinum) substrates, followed by quenching and direct measurement of Zn, Fe and Si concentrations in the equilibrium phases with electron probe X-ray microanalysis has been used to accurately characterize the system in equilibrium with air. The discrepancies of the previous experimental work in this system have been resolved. The obtained data have been used to reoptimise the existing thermodynamic model.

Thermal transformation of nanohafniumcarbosilanes

The process of thermochemical transformation of nanohafniumcarbosilane (nano-HfCS) at 1500 °C in various media was investigated. The regularities of the formation of SiC ceramic structures modified with hafnium compounds were analyzed by physicochemical methods.The two-stage thermochemical transformation of nano-HfCS first at 1100 °C in argon and then at 1500 °C in various media: argon, nitrogen, vacuum, air results in formation of a nanocrystalline α-SiC ceramics with a hexagonal crystal lattice, modified with HfC, as the main phase. It is demonstrated that the medium in which pyrolysis of nano-HfCS is carried out at 1500 °C affects only the surface layer of the resulting ceramics: at pyrolysis in argon, carbon oxides and hafnium are produced as additional phases on the surface; in nitrogen, silicon nitride and carbon are formed as additional phases on the surface, and in air SiO2 and carbon are formed on the surface as additional phases.

ChemInform Abstract: Eu2+ Luminescence in Ca3Si2O7 and Spectral Widening and Tuning of Eu2+ Emission Color (Orangish‐Red to Green) by Crystal Chemical Substitution.

AbstractA series of yellowish‐orange emitting phosphors Ca3‐xEuxSi2O7 (x = 0.0025—0.03) and Ca2.985‐yMgyEu0.015Si2 O7 (y = 0—1) are prepared by calcination of stoichiometric amounts of CaCO3, Eu2O3, Mg(NO3)2 and SiO2 in air (1250 °C, 6 h) followed by heating of the as‐prepared material in a 5%H2/N2 atmosphere (1275 °C, 6 h).

Silica Particulate Pollution in Central India

Asbestos exposure is known to cause asbestosis i.e. lung cancer (mesothelioma) with increased risk of diseases i.e. gastrointestinal, colorectal, throat, kidney, esophageal, and gallbladder cancer. Therefore, in the present work, the concentration of SiO2 associated to the coarse and fine particulates in the ambient air of most industrialized area of central India i.e. Raipur city (capital of Chhattisgarh state) is described. The concentration of SiO2 in ambient air associated to the PM10 and PM2.5 was ranged from 6.6 to 102 and 0.2 to 15 μg/m3 with mean value of 30.0 ± 6.0 and 4.3 ± 0.8 μg/m3, respectively. The seasonal, spatial and temporal variations of SiO2 in the air are described.

ChemInform Abstract: Photocatalytic Water Splitting over Rod‐Shaped K3Ta3Si2O13 and Block‐Shaped Ba3Ta6Si4O26 Prepared by Flux Method.

AbstractK3Ta3Si2O13 and Ba3Ta6Si4O26 particles are prepared by calcination of a mixture of BaCO3, Ta2O5, and SiO2 in air (Pt crucible, 1423 K, 10 h) and by a KCl flux method (Al2O3 crucible, 1423 K).

습식분쇄공정에서 액상매체가 실리콘 분쇄 및 산화특성에 미치는 영향

The influence of a liquid medium duringa wet-milling process in the grinding and oxidation of silicon powder was investigated. Distilled water, dehydrated ethanol and diethylene glycol were used as the liquid media. The applied grinding times were 0.5, 3, and 12 h. Ground silicon powder samples were characterized by means of aparticle size analysis, scanning electron microscopy(SEM), xray powder diffraction (XRD), FT-IR spectroscopy and by a chemical composition analysis. From the results of the characterization process, we found that diethylene glycol is the most efficient liquid medium when silicon powder is ground using a wet-milling process. The FT-IR results show that the Si-O band intensity in an unground silicon powder is quite strongbecause oxygen becomes incorporated with silicon to form SiO₂ in air. By applying deionized water as a liquid medium for the grinding of silicon, the SiO₂ content increased from 4.12% to 31.7%. However, in the cases of dehydrated ethanol and diethylene glycol, it was found that the SiO₂ contents after grinding only changed insignificantly, from 4.12% to 5.91% and 5.28%, respectively.

Microstructure and reaction mechanism of SiC ceramic with mullite-zircon as a new liquid-phase sintering additives system

Mullite-zircon (Al2O3–SiO2–ZrSiO4), as a new liquid-phase sintering (LPS) additives system, was introduced into the silicon carbide (SiC) ceramics in order to improve the mechanical and thermal shock properties. The reaction mechanism of the SiC ceramics with additive system during the sintering process was analyzed by thermodynamic calculation and the mullite-zircon system was detected as expected in the final specimens. The ZrSiO4 phase was generated from the reactions of ZrB2 and SiO2 in air and distributed homogeneously in the SiC matrix. The mullite phase in the form of crystal whisker was completely crystallized at 1350°C, and the size of the crystallite increased with the increase of the sintering temperature from 1350°C to 1400°C. This process was explained by vapor–liquid–solid (VLS) mechanism. The influences of sintering temperature and the content of ZrB2 content on their properties and the reaction mechanism were studied. It was found that the specimens were compact when sintered at 1400°C, and the content of ZrB2 played an important role in the densification process.

Effect of SiO2 Particle Size on the Reaction between ZrB2 and SiO2 in Air

The heat resistance of ZrB2-based composites is shown to depend on the dispersion medium in which the slip-cast bodies were prepared: silica sol ensures the best heat resistance. Heat treatment of ZrB2–SiO2 materials in air at temperatures of up to 1400°C leads to the formation of a borosilicate glass melt containing crystalline particles of ZrB2 , SiO2 , and reaction products. Chemical analysis of heat-treated samples demonstrates that the SiO2 particle size has no effect on this process.

The formation of nitrogen-containing organic compounds in the transformations of 3,5-di-tert-butylpyrocatechol adsorbed on thin layers of SiO2 in air

The formation of nitrogen-containing organic compounds in the transformations of 3,5-di-tert-butylpyrocatechol adsorbed on thin layers of SiO2 in air

Liquid–Solid Equilibria in the System NiO–TiO2–SiO2 in the Temperature Range 1430° to 1660°C

Equilibrium relations in the system NiO–TiO2–SiO2 in air have been investigated in the temperature range 1430° to 1660°C. The most conspicuous feature of the phase relations is the existence of a cation‐excess spinel‐type phase, in addition to NiO and NiTiO3, on the liquidus surface and at subsolidus temperatures down to 1430°C. Three invariant points have been located on the liquidus. There is a peritectic at 1540°C characterized by coexisting NiO (ss), spinel(ss), cristobalite, and liquid of composition 47 wt% NiO, 29 wt% TiO2, and 24 wt% SiO2. Two eutectics are present, one at 1480°C, with spinel(ss), NiTiO3, cristobalite, and liquid (42 wt% NiO, 43 wt% TiO2, and 15 wt% SiO2), as the coexisting phases. The other is at 1490°C with NiTiO3, rutile, cristobalite, and liquid (32 wt% NiO, 56 wt% TiO2, and 12 wt% SiO2). A liquid miscibility gap extends across the diagram from the two bounding binary systems NiO–SiO2 and TiO2–SiO2.

Liquid–Solid Equilibria in the System FeO–NiO–Fe2O3–SiO2

Liquidus and solidus phase relations have been determined for the system NiO‐iron oxide–SiO2 in air and in CO2. In both cases the system is simple in that it contains only three primary crystalline phases: spinel (Fe3O4–NiFe2O3 solid solution), oxide (“FeO”–NiO solid solution) and SiO2, either tridymite or cristobalite. There is only one liquidus invariant point at which the above crystalline phases coexist with liquid (and the gas phase). In air, the invariant point (a eutectic) is at 1524°C, and a temperature maximum is present along the spinel–silica liquidus boundary curve at 1540°C. In CO2, the silica + spinel + oxide + liquid invariant temperature is considerably lower: 1433°C. Combination of these data with those obtained previously for the same system under strongly reducing conditions (CO2–CO gas mixtures of ratios only slightly above those of equilibrium coexistence of the oxide phases with Fe–Ni alloy) makes it possible to draw the main features of phase relations in the quaternary system FeO–NiO–Fe2O3–SiO2. This system also is relatively simple, in that only five crystalline phases are present in equilibrium with liquids, viz, silica (cristobalite or tridymite), olivine (Fe2SiO4‐Ni2SiO4 solid solution), spinel (Fe3O4‐NiFe2O4 solid solution), hematite (Fe2O3), and oxide (“FeO”–NiO solid solution). There is only one quaternary liquidus invariant point in the system, characterized by the equilibrium coexistence of silica, olivine, spinel, oxide, and liquid, at a temperature of ∼ 1410°C and an oxygen pressure of the gas phase of ∼10−5 atm.