Formation Of SiO2 Particles Research Articles

In vitro cytotoxicity study of virgin, ethylenediaminetetraacetic acid- and hexamethylenetetramine-capped silica particles synthesized by precipitation method

Silica particles synthesized by precipitation method were in situ capped with Ethylenediaminetetraacetic acid (EDTA) and Hexamethylenetetramine (HMTA) compounds aiming to increase their biocompatibility. XRD, FTIR, TG/DSC, DLS and SEM analyses were performed to determine the crystalline structure, attached functional groups, thermal behaviour, size and morphology of silica particles. XRD analysis showed the amorphous structure of synthesized particles. FTIR results confirmed the formation of SiO2 particles and pointed about the functional groups (−CN, −CO,−OH etc.) attached on surface. Thermal analysis results showed that weight loss was due to removal of water and gradual degradation of EDTA molecules with rise of temperature, i.e. above 220 °C. The dynamic laser scattering measurements (zeta potential) depicted the strongest electrophoretic stability (− 30 mV) of EDTA-capped silica than virgin (− 13 mV) and particles capped with HMTA(− 24 mV). The SEM results revealed that virgin and silica particles capped with EDTA ligand exhibited spherical morphology with an average particle size of 210 nm and 280 nm, respectively. Whereas, HMTA-capped silica partilces showed hexagonal morphology with an average particle size of 240 nm. The in vitro cytotoxicity analysis was also carried out using human HepG2w, ATCC® HB-8065™ cell culture of 100 µg/ml concentration in Dulbecco’s Modified Eagle Medium (DMEM) solution maintained at 37 °C in the presence of CO2 environment. The results revealed that silica particles capped with EDTA (0.07 g) have shown remarkable biocompatibility (~ 96%) than virgin silica (~ 69%) due to bearing better hydrophobic characteristics. However, HMTA decomposed during synthesis which induced toxicity and agglomeration among silica particles. As a result, poor biocompatibility (~ 65%) was observed.

Cyclic oxidation behaviour of Co/Si co-doped β-NiAl coating on nickel based superalloys

Co/Si co-doped β-NiAl coating on nickel based superalloys was prepared using pack cementation method. Microstructure and cyclic oxidation behaviour of the coating were investigated. The weight loss of the coating is less than 3 mg/cm2 after 3200 cycles at 1050 °C. The coating exhibits a good cyclic oxidation resistance. The addition of Si decreases the growth stress in the oxide scale by inhibiting the formation of harmful NiO. The formation of SiO2 particles at the scale/coating interface decreases the growth rate of the Al2O3 scale. Moreover, Si addition promotes the formation of the high Al-content phase β-NiAl.

Laser welding of fused silica glass with sapphire using a non- stoichiometric, fresnoitic Ba2TiSi2O8·3 SiO2 thin film as an absorber

Laser welding of dissimilar materials is challenging, due to their difference in coefficients of thermal expansion (CTE). In this work, fused silica-to-sapphire joints were achieved by employment of a ns laser focused in the intermediate Si-enriched fresnoitic glass thin film sealant. The microstructure of the bonded interphase was analyzed down to the nanometer scale and related to the laser parameters used. The crystallization of fresnoite in the glass sealant upon laser process leads to an intense blue emission intensity under UV excitation. This crystallization is favored in the interphase with the silica glass substrate, rather than in the border with the sapphire. The formation of SiO2 particles was confirmed, as well. The bond quality was evaluated by scanning acoustic microscopy (SAM). The substrates remain bonded even after heat treatment at 100°C for 30min, despite the large CTE difference between both substrates.

Optimum condition to fabricate 5–10 nm SiO2/Si structure using advanced nitric acid oxidation of Si method with Si source

A low temperature (≦120 °C) fabrication method to form relatively thick SiO2/Si structure with a Si source has been developed using the advanced nitric acid oxidation of Si (NAOS) method, and the formation mechanism has been investigated. The reaction mechanism consists of direct oxidation of Si, dissolution of Si sources, and surface reaction of the dissolved Si species. The dissolved Si species is present in HNO3 solutions as mono-silicic acid and reacts with oxidizing species formed by decomposition of HNO3 on an ultrathin SiO2 layer (i.e., 1.4 nm) produced by the direct oxidation of Si substrates with HNO3 solutions. To achieve a uniform thickness of SiO2 layer with a smooth surface, HNO3 solutions with concentrations higher than 60 wt. % are needed because the dissolved Si species polymerizes in HNO3 solutions when the concentration is below 60 wt. %, resulting in the formation of SiO2 particles in HNO3, which are deposited afterwards on the SiO2 layer. In spite of the low temperature formation at 120 °C, the electrical characteristics of the advanced NAOS SiO2 layer formed with 68 wt. % HNO3 and subsequent post-metallization anneal at 250 °C are nearly identical to those of thermal oxide formed at 900 °C.

Preparation and properties of cardanol-based polybenzoxazine/SiO2hybrids by sol-gel technique

A new cardanol-based benzoxazine monomer containing a hydroxyl group (CBZ) was synthesized and characterized by FT-IR and 1H NMR spectroscopy. The formation mechanism of cardanol-based polybenzoxazine/SiO2 hybrids from CBZ and tetraethoxysilane (TEOS) by sol-gel technique was invested by FT-IR analysis. FT-IR and SEM confirmed that there were many SiO2 particles formed and embedded in the cardanol-based polybenzoxazine. A phase separation occurred when the ratio (wt) of TEOS to CBZ was not less than 3 : 5. TGA results illuminated the thermal stability and char yield of cardanol-based polybenzoxazine could be enhanced due to the formation of SiO2 particles in the polybenzoxazine matrix. Incorporation of SiO2 could improve the surface de-wetting and anti-ultraviolet properties of the films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preparation, Characterization and Thermal Degradation of Polyimide (4-APS/BTDA)/SiO2 Composite Films

Polyimide/SiO2 composite films were prepared from tetraethoxysilane (TEOS) and poly(amic acid) (PAA) based on aromatic diamine (4-aminophenyl sulfone) (4-APS) and aromatic dianhydride (3,3,4,4-benzophenonetetracarboxylic dianhydride) (BTDA) via a sol-gel process in N-methyl-2-pyrrolidinone (NMP). The prepared polyimide/SiO2 composite films were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The FTIR results confirmed the synthesis of polyimide (4-APS/BTDA) and the formation of SiO2 particles in the polyimide matrix. Meanwhile, the SEM images showed that the SiO2 particles were well dispersed in the polyimide matrix. Thermal stability and kinetic parameters of the degradation processes for the prepared polyimide/SiO2 composite films were investigated using TGA in N2 atmosphere. The activation energy of the solid-state process was calculated using Flynn–Wall–Ozawa’s method without the knowledge of the reaction mechanism. The results indicated that thermal stability and the values of the calculated activation energies increased with the increase of the TEOS loading and the activation energy also varied with the percentage of weight loss for all compositions.

Effect of tetraethoxysilane pretreatment on synthesis of colloidal particles of amorphous silicon dioxide

The effect of the time passed after tetraethoxysilane treatment with ammonia on the diameter of particles produced by tetraethoxysilane hydrolysis in alcohol-water-ammonia media is studied. The regulation the time passed after of tetraethoxysilane treatment results in the synthesis of submicron monodisperse spherical silica particles with diameters differing by a factor of two. The difference is explained by the formation of SiO2 particles with sizes of 10–100 nm in tetraethoxysilane during 10–30 h after treatment with ammonia. These particles enhance the concentration of nucleation centers in a reaction mixture, thus decreasing the final size of monodisperse silica spheres. Opal films with a high structural perfection and pronounced photonic crystal properties are grown based on the obtained monodisperse SiO2 particles.

A Comparison of the Formation of SiO2 Particles Under the Catalysis of Dodecylamine and Ammonia Solutions

SiO2 products were prepared by the hydrolysis and condensation of tetraethyl orthosilicate with ammonia and dodecylamine (DDA) solutions as the basic catalyst, respectively. Thermal gravimetric analysis, scanning electron microscope and N2-sorption were used to characterize the synthesized products. The results show that the morphology and textural characteristics of the products prepared in inorganic ammonia and organic amine solutions with the same pH value are quite different. Uniform non-porous silica microspheres and agglomerated sphere-like microporous silica particles with large surface area and pore volume are obtained with the addition of ammonia and DDA solutions, respectively. The differences are due to the different roles that ammonia and DDA solutions play in the silica formation process.

Preparation and characterization of polymer/silica nanocomposites via double in situ miniemulsion polymerization

Polymer/SiO2 nanocomposite microspheres were prepared by double in situ miniemulsion polymerization in the presence of methyl methacrylate, butyl acrylate, γ-methacryloxy(propyl) trimethoxysilane, and tetraethoxysilane (TEOS). By taking full advantage of phase separation between the growing polymer particles and TEOS, inorganic/polymer microspheres were fabricated successfully in a one-step process with the formation of SiO2 particles and the polymerization of organic monomers taking place simultaneously. The morphology of nanocomposite microspheres and the microstructure, mechanical properties, thermal properties, and optical properties of the nanocomposite films were characterized and discussed. The results showed that hybrid microspheres had a raspberry-like structure with silica nanoparticles on the shells of polymer. The silica particles of about 20 nm were highly dispersed within the nanocomposite films without aggregations. The transmittance of nanocomposite film was comparable to that of the copolymer film at around 70–80% from 400 to 800 nm. The mechanical properties and the fire-retardant behavior of the polymer matrix were improved by the incorporation of silica nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3128–3134, 2010

Growth of silica nanoparticles in methylmethacrylate-based water-in-oil microemulsions

The mechanism of silica particle formation in monomer microemulsions is studied using dynamic light scattering (DLS), atomic force microscopy, small-angle X-ray scattering (SAXS), and conductivity measurements. The hydrolysis of tetraethylorthosilicate (TEOS) in methylmethacrylate (MMA) microemulsions (MMA = methylmethacrylate) is compared with the formation of SiO2 particles in heptane microemulsions. Stable microemulsions without cosurfactant were found for MMA, the nonionic surfactant Marlophen NP10, and aqueous ammonia (0.75 wt%). In the one-phase region of the ternary phase diagram, the water/surfactant ratio (R w) could be varied from 6 to 18. The DLS and SAXS measurements show that reverse micelles form in these water-in-oil (w/o) microemulsions. The minimum water-to-surfactant molar ratio required for micelle formation was determined. Particle formation is achieved from the base-catalyzed hydrolysis of TEOS. According to atomic force microscopy measurements of particles isolated from the emulsion, the particle size can be effectively tailored in between 20 and 60 nm by varying R w from 2–6 in heptane w/o microemulsions. For MMA-based microemulsions, the particle diameter ranges from 25 to 50 nm, but the polydispersity is higher. Tailoring of the particle size is not achieved with R w, but adjusting the particle growth period produces particles between 10 and 70 nm.

The synthesis and characteristic study of 6FDA–6FHP–NLO polyimide/SiO2 nanohybrid materials

Hybrid nanocomposite films of silica (SiO2) in polyimide (PI) from 4,4′-(hexafluoroisopropylidene) diphthalic arhydride (6FDA), 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FHP) and nonlinear optical (NLO) molecule have been successfully fabricated by an in situ sol–gel process. The silica content in the hybrid films was varied from 0 to 22.5 wt%. These nanocomposite films exhibit fair good optical transparency. Fourier transform infrared (FTIR) spectroscopy results confirm the formation of SiO2 particles in PI matrix. Scanning electron microscope (SEM) images show that the SiO2 phase is well dispersed in the polymer matrix. Their glass transition behavior and thermal stability were investigated by differential scanning calorimeter (DSC) and thermal gravimetric analysis (TG).

The formation of nano-size SiO2 thin film on an aluminum plate with hexamethyldisilazane (HMDSA) and hexamethyldisiloxane (HMDSO)

This study is using HMDSA (C6H19NSi2) or HMDSO (C6H18OSi2) vapor into C3H8/air premixed flames to form SiO2 thin film on the surface of an aluminum plate. With the addition of HMDSO or HMDSA to premixed flames, an orange secondary flame or a flame brush appeared and was contributed to the formation of SiO2 particles. Based upon the EDS, XPS and FTIR analysis, it is believed that the synthesized products consist of mainly SiO2 and a small amount of SiO. The pure SiO2 crystal structure, was proved by XRD analysis, which may form from the SiO2 amorphous structure after high temperature (1300°C) thermal treatment. The nano-size SiO2 particles, which ranged from 2.5–25 nm, are proved by analysis of the BET and TEM. A 2-D CFD-RC code with 12 reduced chemical reaction mechanism, based upon the SIMPLER procedure, was successfully employed to predict the flame temperature and both of the SiO2 and SiO concentration profiles. Compared with the experimental results, the calculated temperature profiles in the post-flame region are in good agreement with the measured data and observation phenomena.

Al-Si合金による鋼の脱酸について

The mechanism on the deoxidation of molten ironwith Al and Al-Si alloy deoxidizer was investigated by using induction furnace and Tammann furnace.The experimental results were summarized as follows.1) The deoxidation of molten iron with Al was not effective in air. But under the Ar atmosphere, the decrease of total oxygen content was remarkable.2) In the beginning of deoxidation with Al-Si alloy in air, the reaction between Al and O was much faster than the reaction between Si and O.Al was consumed immediately, but Si was remained sufficiently as soluble Si at that time. Subsequently Si reacted with oxygen in air and protected the reoxidation of molten iron by the formation of SiO2particles.3) The yield of Al in the beginning of deoxidation was increased by Si. Flake like primary a in Al-Si alloy protected Al-Si eutectic against consumption of Al, when the deoxidizer was added into molten iron.