SiO2 Source Research Articles

Fabrication of Lithium Silicates As Highly Efficient High-Temperature CO2 Sorbents from SBA-15 Precursor.

A series of lithium silicates with improved CO2 sorption capacity were successfully synthesized using SBA-15 as the silicon precursor. The influence of Li/Si ratio, calcination temperature, and calcination duration on the chemical composition and CO2 capture capacity of obtained lithium silicates was systematically investigated. The correlation between CO2 sorption performance and crystalline phase abundance was determined using X-ray diffraction and a normalized reference intensity ratio method. Under the optimized condition, Li-SBA15-4 prepared using Li/Si = 4 that contains mainly Li4SiO4 achieved an extremely high CO2 capture capacity of 36.3 wt % (corresponding to 99% of the theoretical value of 36.7 wt % for Li4SiO4), which is much higher than the Li4SiO4 synthesized from conventional SiO2 sources. It also showed very high cycling stability with only 1.0 wt % capacity loss after 15 cycles. Li-SBA15-10 (Li/Si = 10) that mainly contains Li8SiO6 displayed an extremely high CO2 uptake of 62.0 wt %, but its regeneration capacity was poor, with only 10.5 wt % of reversible CO2 capture capacity. The influence of CO2 concentration on the CO2 capture performance of Li-SBA15-4 and Li-SBA15-10 samples was also studied. With the decrease in CO2 concentration, relatively lower temperatures are needed for its maximum CO2 capture capacity. The CO2 sorption kinetics and mechanism for Li-SBA15-4 and Li-SBA15-10 samples were explored. Overall, we have shown that the lithium silicates synthesized from SBA-15 possessed much improved CO2 sorption performance than that attained from conventional SiO2.

The Influence of SiO2 Coating on Electromagnetic Wave Absorption Properties of Carbonyl Iron Powder

Silica (SiO2) coatings were prepared on the surface of carbonyl iron powder (CIP) by using tetraethyl orthosilicate (TEOS) as a SiO2 source and 3-aminopropyl triethoxysilane (APTES) as a surface modifier. The compositions of samples were analyzed by X-ray diffraction (XRD) and Energy Dispersive Spectrometer (EDS). The morphologies of powder samples were analyzed by scanning electron microscope (SEM). The electromagnetic property of hollow column samples (mixed with paraffin as a binder) was measured by vector network analyzer. The result shows that the surface of the CIP was coated by cotton-shaped SiO2, the microwave absorption property of materials declined by increase of the additive amount of APTES and TEOS. Some coated samples show better microwave absorption properties than uncoated CIP.

Chemical Evaluation of the Glass Making Potentials of Silica Sand Deposits Along Cross River in Cross River State, South–East of Nigeria

Analytical techniques such as X–ray Fluorescence Spectroscopy (XRF) and Atomic Absorption Spectroscopy (AAS) coupled with statistical package for multivariate analyses were used to characterize silica sand deposit obtained along Cross River in Cross River State, South Eastern Nigeria. Samples were collected from five locations along the river which include: Ikom-Okuni, Obubra-Ofumbogha, Abi-Ediba, Biase-Agwagune and Etung-Effraya. The results of analyses revealed that silicon dioxide (SiO2) forms the predominant metal oxide in the entire samples followed by iron oxides (Fe203), sodium oxide (Na20). Other Oxides such as aluminum oxide (AI2O3), potassium oxide (k2O) etc were also present. Further beneficiation of the silica sand samples gave increased silica dioxide content across all the samples and increase and decrease of other metal oxides. The acid demand value (ADV) and pH value of the silica sand determination revealed a moderately low ADV and neutral pH value of all the samples. A correlation between the mean values of SiO2 and Fe2O3 in all the samples across all the sampling locations showed an inverse relationship between SiO2 and Fe2O3. Furthermore, comparison using population t – test of observed mean of SiO2 and Fe2O3, with their observed minimum standard (90.52%, 0.005%) shows that the silica sand samples from Ediba and Agwagune can be used as a source of SiO2 for glass making due to their high SiO2 and low levels of Fe2O3 content.

Chemical Evaluation of the Glass Making Potentials of Silica Sand Deposits Along Cross River in Cross River State, South–East of Nigeria

Analytical techniques such as X–ray Fluorescence Spectroscopy (XRF) and Atomic Absorption Spectroscopy (AAS) coupled with statistical package for multivariate analyses were used to characterize silica sand deposit obtained along Cross River in Cross River State, South Eastern Nigeria. Samples were collected from five locations along the river which include: Ikom-Okuni, Obubra-Ofumbogha, Abi-Ediba, Biase-Agwagune and Etung-Effraya. The results of analyses revealed that silicon dioxide (SiO2) forms the predominant metal oxide in the entire samples followed by iron oxides (Fe203), sodium oxide (Na20). Other Oxides such as aluminum oxide (AI2O3), potassium oxide (k2O) etc were also present. Further beneficiation of the silica sand samples gave increased silica dioxide content across all the samples and increase and decrease of other metal oxides. The acid demand value (ADV) and pH value of the silica sand determination revealed a moderately low ADV and neutral pH value of all the samples. A correlation between the mean values of SiO2 and Fe2O3 in all the samples across all the sampling locations showed an inverse relationship between SiO2 and Fe2O3. Furthermore, comparison using population t – test of observed mean of SiO2 and Fe2O3, with their observed minimum standard (90.52%, 0.005%) shows that the silica sand samples from Ediba and Agwagune can be used as a source of SiO2 for glass making due to their high SiO2 and low levels of Fe2O3 content.

Waste materials conversion into mesoporous silicon carbide nanocermics: Nanofibre/particle mixture

This study confirms a sustainable and clean new approach for synthesizing a mesoporous silicon carbide (SiC) nanofibre/particle composite from a binary mixture of two problematic, high volume global waste streams, e-waste glass (SiO2 source) and waste tyre rubber (WTR) through the carbothermal reduction. The resulting composite material consisted of a mixture of nanofibres of 10–150 nm diameters and over 5 microns length, and distributed nanoparticles with particle size ranging between 30 and 40 nm with a relatively high surface area (85.1–67.3 m2 g−1) and a dominant pore size smaller than 2 nm. SiC of nanomaterials is conventionally fabricated from high quality carbon and silicon sources which are expensive and may not prove cost effective from industrial perspective. E-waste glass and waste tyres are both potential sources of valuable secondary resources, but a lack of cost-effective recycling options means vast volumes are landfilled, stockpiled or diverted to unsafe processing operations in developing countries; posing serious environmental and health risks. The simultaneous conversion of two globally significant waste burdens into (SiC) nanofibre/particle composite has not previously been investigated. This novel approach highlights the opportunities for utilizing waste as an alternative resource to deliver economic and environmental benefits and also demonstrates a new low cost means of synthesizing SiC nanofibre/particle composite.

Unexpected "Hammerlike Liquid" to Pulverize Silica Powders to Stable Sols and Its Application in the Preparation of Sub-10 nm SiO2 Hybrid Nanoparticles with Chirality.

Silane coupling agents are well-known as surface modifiers for various kinds of silica (SiO2). However, in the present research, it has been found that they can also work as “hammerlike liquid” to pulverize different kinds of bulk amorphous SiO2 in aqueous systems. This new function was typically clarified by using 3-aminopropyltrimethoxysilane (APS) and bundles of chiral SiO2 nanofibers (with average diameter of ∼10 nm) as raw materials. By a simple reflux of the mixture of SiO2 nanofibers and excessive APS in pure H2O, the solid-containing mixture turned into a completely clear solution that contained sub-10 nm, amine-modified, and water-soluble hybrid SiO2 sols (HS-sols). Moreover, this solution showed blue luminescence under ultraviolet irradiation. Furthermore, the circular dichroism and vibrational circular dichroism spectra revealed that the HS-sols are optically active even though the pristine chiral SiO2 nanofibers were completely destroyed. It was considered that the chirality of SiO2 nanofibers was due to the asymmetric arrangement of Si and O atoms in chiral domains (<10 nm) on the Si–O–Si network of SiO2, and these domains are still preserved in chiral HS-sols. This green method has high potential for the recycling of rich SiO2 sources to obtain functional SiO2 nanomaterials with applications such as optical display, imaging, and chiral recognition. Also, it offers a tool for the analysis of the structural properties of SiO2 on the molecular scale.

Reactive transport modeling of coupled feldspar dissolution and secondary mineral precipitation and its implication for diagenetic interaction in sandstones

Dissolution of feldspars and precipitation of secondary minerals (kaolinite, illite and quartz) are significant diagenetic processes in arkosic sandstones. We examined moderately buried sandstones in the Eocene Shahejie Formation from two sags in the Bohai Bay Basin, East China. Three different types of mineral assemblages (MA) were identified: extensively leached feldspars with a large amount of authigenic kaolinite and quartz cement (MA-1), extensively leached feldspars with a large amount of authigenic kaolinite and minor quartz cement (MA-2), and extensively leached feldspars with a small amount of both authigenic kaolinite and quartz cement (MA-3).Numerical simulations at the continuum scale using Geochemist’s Workbench 9.0 were conducted to decipher the origin of the different mineral assemblages. The physicochemical reactions including feldspar dissolution, transport of Al3+ and SiO2(aq), and precipitation of kaolinite and quartz are coupled together in these simulations, with constraints of chemical reactions, kinetic law, dispersion, and advection. Modeling results suggest that a dissolution zone, a transitional zone, and a precipitation zone can be formed in a sandstone unit with suitable constraints of temperature, flow rate, fluid composition and mineral reaction rate. And MA-3, MA-2, and MA-1 assemblages develop in these three zones respectively. The higher SiO2(aq) concentration required for the saturation of quartz than for kaolinite and the low Al3+ concentration needed for the saturation of kaolinite lead to the precipitation of only kaolinite in the transitional zone in a geochemical system with feldspar dissolution serving as the dominant source of SiO2(aq) and Al3+.Comparisons between modeling results and observations of natural sandstone diagenesis suggest that an MA-1 assemblage is likely to occur in buried sandstones at high temperatures (>70–80°C) and low flow rates. An MA-2 assemblage may occur in moderately buried sandstones at moderate temperatures (40–70°C), in deeply buried sandstones with faults and fractures serving as conduits of meteoric freshwater, or in shallow sandstones where meteoric water is not abundant. An MA-3 assemblage tends to occur in shallow sandstones at low temperatures (<40–50°C) and high flow rates, or in buried sandstones where faults and fractures develop widely and serve as freshwater conduits. These proposals are valid in natural arkosic sandstones and of great significance in deciphering the diagenetic environments where the feldspar dissolution and secondary mineral precipitation have occurred.

Kaolin-based magnetic zeolites A and P as water softeners

In this work, we report an experimental investigation on the synthesis of zeolites A and P, using kaolin as the main SiO2 and Al2O3 sources, by hydrothermal route, as well as on the structural, spectroscopic and magnetic properties of the produced zeolite composites with magnetite nanoparticles. The zeolites were successfully synthesized and the characterization of the obtained materials was carried out considering different techniques, including X-ray diffraction (XRD), infrared vibrational spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as measurements of the magnetization as a function of the temperature and applied magnetic field. XRD analysis confirmed zeolites A and P as main crystalline phases, with a low intensity peak regarding the presence of small quantities of quartz remaining from the unreacted clay. SEM showed the well-defined morphologies of zeolites and, in the composites, magnetite nanoparticles dispersed over their surface. The average size of the magnetite nanoparticles was ca. 50 nm as determined by TEM analyses. The magnetic characterization confirmed the ferrimagnetic behavior of the magnetite nanoparticles and of the composites, as well as verified that the magnetic properties of the nanoparticles are not affected by the zeolites in the composite formation. Thus, the results evidenced that high quality zeolite composites with magnetite nanoparticles can be reached by considering the employed low cost method, placing this route as an attractive alternative for water softening reaching removal levels of about 97% in the first application times.

Mesoporous biologically-controlled 3D architectures assembling with Zn2SiO4 textured nanowires by biogenic-templated incorporating molten-salt method

Three-dimensional (3D) architectures assembling with Zn2SiO4 nanowires were synthesized by a novel molten-salt method using rice husk both as biomorphic template and SiO2 source. Also, ZnCl2 powder was chosen as reactant and molten-salt. X-ray diffraction, scanning electron microscope and transmission electron microscope were used to investigate the morphology and composition of this unique architecture. Nitrogen adsorption measurements verified the presence of mesoporous structure. The growth process of the synthesized Zn2SiO4 nanowires was proposed, including the introduction of ZnCl2 to rice husk, the formation of ZnOCl2·H2O nanostructures, and the growth of 3D Zn2SiO4 textured nanowires. Furthermore, the absorption capacity of 3D Zn2SiO4 architectures to remove Fe3+, Cr3+ and Mg2+ in water was performed.

In-situ reaction synthesis of porous Si2N2O-Si3N4 multiphase ceramics with low dielectric constant via silica poly-hollow microspheres

In the present work, a novel and facile process has been proposed to fabricate porous Si2N2O-Si3N4 multiphase ceramics with low dielectric constant (εr＜4.0). Since silica poly-hollow microspheres could serve as the source of SiO2 and the pore-forming agent, they have been introduced into Si3N4 slurry through the gelcasting technique. This process is benefited from the liquid phase sintering reaction between SiO2 and Si3N4 with the aid of sintering additives, leading to in-situ synthesis of Si2N2O phase and porous structure. The content of silica poly-hollow microspheres has great influence on the properties of the final products. It indicates that Si2N2O phase would become the major phase when the content of silica poly-hollow microspheres was above 25wt%. Furthermore, the micromorphology results reveal that the content of pores with many smaller aggregate microspheres increases as microspheres amount rises. As a result, along with the addition of silica poly-hollow microspheres, the bulk density decreases to 1.32±0.01g/cm3, and open porosity ranges from 28.4±0.4% to 52.0±0.5%. Porous Si2N2O-Si3N4 multiphase ceramics prepared with 25wt% silica poly-hollow microspheres addition possess flexural strength of 42.3±3.8MPa, low dielectric constant of 3.31 and loss tangent of 1.93×10−3. It turns out to be an effective method to fabricate porous Si2N2O-Si3N4 composites with excellent mechanical and dielectric properties, which could be applied to radome materials.

Nanocrystalline zeolites beta: Features of synthesis and properties

The effect of synthesis conditions for BEA zeolite nanocrystals (BEA-ZNC) on the combination of their morphological, textural, and acidic properties has been studied. BEA-ZNC have been synthesized by the hydrothermal or vapor-phase crystallization of reaction mixtures with a high template concentration using the following variable synthesis parameters: the SiO2/Al2O3 ratio the presence of mineralizing additives, the SiO2 source and template type, and the synthesis pH. It has been found that an increase in the aluminum content in BEA-ZNC from 2.7 to 7.8 Al atoms per unit cell is accompanied by a decrease in the size of the ZNC from 250–350 to 100 nm, an increase in the acid site concentration, and an increase in the fraction of weak acid sites in the acidity range of the samples. It has been shown that the specific feature of the synthesis of BEA-ZNC is a low degree of inclusion of silica and the template into the zeolite composition, which is 28–62 and 3.4–5.5%, respectively, of the amounts initially introduced into the reaction mixture. It has been proposed that silica gel should be used as the most promising SiO2 source for the preparation of BEA-ZNC; the use of silica gel provides formation of a material in the form of isolated nanocrystals with a size of 150–300 nm, a developed pore structure, and a high concentration of acid sites. It has been shown that the BEA-ZNC synthesized by vapor-phase crystallization are inferior to the samples prepared by conventional hydrothermal crystallization with respect to the pore structure characteristics and acidic properties.

Synthesis and characterization of silica mesoporous material produced by hydrothermal continues pH adjusting path way

Mesoporous silica molecular sieves MCM-41 were synthesized under hydrothermal conditions. For this purpose, a solution with a molar coefficient of water, cetyltri-methyl ammonium bromide surfactants as template and sodium silicate as the source of SiO2 are used. Phase formation, morphology and gas absorption properties were investigated by XRD and BET analysis, respectively. The results showed that silica mesoporous material has been successfully synthesized. A favorable special surface and porosity volume together with regular arrangement of nano metric-hexagonal porosities were obtained from this synthesis. Thickness of the wall and average diameter of the pores are 0.8nm and 4nm, respectively.

Thousands of Stellar SiO masers in the Galactic center: The Bulge Asymmetries and Dynamic Evolution (BAaDE) survey

AbstractA radio survey of red giant SiO sources in the inner Galaxy and bulge is not hindered by extinction. Accurate stellar velocities (&lt;1 km/s) are obtained with minimal observing time (&lt;1 min) per source. Detecting over 20,000 SiO maser sources yields data comparable to optical surveys with the additional strength of a much more thorough coverage of the highly obscured inner Galaxy. Modeling of such a large sample would reveal dynamical structures and minority populations; the velocity structure can be compared to kinematic structures seen in molecular gas, complex orbit structure in the bar, or stellar streams resulting from recently infallen systems. Our Bulge Asymmetries and Dynamic Evolution (BAaDE) survey yields bright SiO masers suitable for follow-up Galactic orbit and parallax determination using VLBI.Here we outline our early VLA observations at 43 GHz in the northern bulge and Galactic plane (0&lt;l°&lt;250), and ALMA observations at 86 GHz in the southern bulge (250&lt;l°&lt;360). We report a preliminary overall 70% detection rate in our color-selected MSX sources.

Extensive aqueous deposits at the base of the dichotomy boundary in Nilosyrtis Mensae, Mars

Thermal emission imaging system (THEMIS) and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral datasets were used to identify high bulk SiO2 and hydrated compositions throughout the Nilosyrtis Mensae region. Four isolated locations were identified across the region showing short wavelength silicate absorptions within the 8–12μm spectral region, indicating surfaces dominated by high Si phases. Much more extensive exposures of hydrated compositions are present throughout the region, indicated by a spectral absorption near 1.9μm in CRISM data. Although limited in spatial coverage, detailed spectral observations indicate that the hydrated materials contain Fe/Mg-smectites and hydrated silica along with minor exposures of Mg-carbonates and an unidentified hydrated phase. The high SiO2 and hydrated materials are present in layered sediments near the base of topographic scarps at the hemispheric dichotomy boundary, typically near or within low albedo sand deposits. The source of the high SiO2 and hydrated materials appears to be from groundwater discharge from Nili Fossae and Syrtis Major to the south, where there is evidence for extensive aqueous alteration of the subsurface. Although discontinuous, the exposures of high SiO2 and hydrated materials span a wide area and are present in a similar geomorphological context to previously identified deposits in western Hellas Basin. These regional deposits may reflect aqueous conditions and alteration within the adjacent crust of the martian highlands.

The Suitability of Rice Straw Ash as a Precursor for Synthesizing β-Wollastonite

In this study, β-wollastonite is produced from a reaction between silica (SiO2) and calcium oxide (CaO) with the SiO2/Cao ratio of 55:45. Rice straw ash is chosen as the source for SiO2 instead of rice husk ash because the straw can yield up to 85% of silica even though this percentage is lower than those silica yielded from rice husk ash. It is found that period of autoclaving and sintering play an important role in producing the wollastonite. As shown in the XRD results, a single phase β-wollastonite is obtained after 8 h of autoclaving and 3 h of sintering at 950 °C. The produced β-wollastonite phase also shows a good crystallinity but needs longer sintering time compared with wollastonite produced using rice husk ash. DTA graph shows a chemical reaction between silica and calcium oxide started to occur at 788.3°C. IR spectroscopic analysis data confirm that the IR peaks at 681, 894 and 931 cm-1 are due to the β-Wollastonite phase. Form the results obtained, it can be concluded that rice straw ash is comparable to rice husk ash as a precursor in producing β-Wollastonite material.

Aplicação ao solo de cinza de casca de arroz como fonte de silício: efeito na qualidade de sementes de trigo produzidas sob stresse salino

Wheat grain represents about 30% of world cereal production and in Brazil it occupied the fifth largest area sown in 2012/2013. Crops productivity can be limited by the effect of salinity in about 50% of the irrigated land used in the agriculture. Silicon may confer plant tolerance to salts, becoming a management alternative against this stress. The experiment was carried in buckets in a greenhouse, a 3x4 factorial design was used with four replicates in a completely randomized design, being the first factor the saline stress, caused by irrigation with water enriched with sodium chloride (NaCl), in doses of 0 (control); 8 and 16 mM, and the second factor, the fertilization with SiO2, at doses of 0 (control); 1000; 2000 and 3000 kg ha-1, using rice husk ash as SiO2 source. SiO2 doses of up to 2000 kg ha-1 led to an increase of the number of ears and seed weight per plant. The application of rice husk ash increased the weight of thousand seeds and did not affect the germination of the seeds obtained, neither the seedlings dry weight.

Large conduction band offset at SiO2 /β-Ga2 O3 heterojunction determined by X-ray photoelectron spectroscopy

We evaluated the band offsets at the SiO2/β-Ga2O3 (010) interface by X-ray photoelectron spectroscopy (XPS). Plasma chemical vapor deposition with a liquid tetraethyl orthosilicate source for SiO2 was used to prepare an SiO2(40 nm)/Ga2O3 sample and an SiO2(3 nm)/Ga2O3 sample for XPS analyses. The bandgap of SiO2 was determined to be 8.7 ± 0.2 eV. A large conduction band offset of 3.1 ± 0.2 eV and a corresponding valence band offset of 1.0 ± 0.2 eV were determined for the SiO2/Ga2O3 interface. These results suggest that an SiO2 gate insulator is favorable for Ga2O3 field effect transistors operating under high temperatures.

Preparation of Mg–Zn bimetallic doped Na-containing bioceramic from sodium metasilicate

Glass–ceramic materials in the composition (mol%) 23.5 Na2O–23.5CaO–xMgO–xZnO–47SiO2–(6-2x) P2O5 (x = 0 and 1.5) were prepared by the sol–gel technique using sodium metasilicate (Na2SiO3) as source of Na2O and SiO2. Bioactivity was investigated in vitro by examining apatite formation on the surface of the samples after treatment in acellular simulated body fluid (SBF). Formation of bioactive apatite layer on the samples was confirmed by using scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscopy. Reactivity of the materials in SBF was based on changes in pH and ionic concentration of the solution as a function of immersion duration. Results obtained indicated that the sample doped with Mg and Zn exhibited greater crystallinity containing phases such as CaMgSi2O6, Ca2MgSi2O7, CaSiO3, Na2CaSi3O9, Na2CaSi3O8, CaZnSi2O7 and a new secondary phase, clinohedrite (CaZnSiO4·H2O), while the undoped sample contained a single crystalline phase composed of Na2Ca2Si3O9. After 7 days in SBF, phase transformation occurred at different rates on the materials leading to formation of apatite layer. The result shows that controlled amounts of MgO and ZnO may be useful in tuning up the mechanical properties of bioactive glasses while maintaining bioactivity.

Thermal conductivity and microstructure characterisation of lightweight alumina and alumina–mullite ceramics

The thermal conductivity of lightweight alumina and alumina–mullite ceramics produced by slip casting and chemical foaming has been measured as a function of temperature in the range from room temperature to 1100°C by the laser flash technique. The microstructure of the studied materials was analysed by scanning mercury intrusion porosimetry, electron microscopy, and micro‑computed tomography. Ceramics was fabricated by slip casting. Pores were formed by aluminium reacting with water. Micro-sized SiO2 and plasma-synthesised SiC nanopowder were used as silica sources. The thermal conductivity of the investigated ceramics was in the range from 0.8 to 3.1W/(mK), depending on the sintering temperature (1650°C and 1750°C) and amount of added SiO2 source.

Sheet-like Li3V2(PO4)3 nanocomposite coated by SiO2 + C with better electrochemical properties for lithium-ion batteries

Sheet-like Li3V2(PO4)3 nanocomposite coated by SiO2 + C layer was synthesized with one-step solid-state method. Dihydroxydiphenylsilane (DPSD) was used as the source of SiO2 and C. The sheet-like Li3V2(PO4)3 nanocomposite has a thickness in the range of 20–30 nm. Because of the SiO2 + C-coated layer and the sheet-like morphology, the Li3V2(PO4)3/(SiO2 + C) composites show better stability and higher capacity than pure Li3V2(PO4)3 material and granular Li3V2(PO4)3/(SiO2 + C) composites. The best sample, Li3V2(PO4)3/(SiO2 + C)(2:8), shows a discharge capacity of 193.7 mAh g−1 at 1C within the voltage range of 3.0–4.8 V and retains almost 90 % of the capacity after 50 cycles.