Silicon Tetraethoxide Research Articles

Investigating the dielectric characteristics, electrical conduction mechanisms, morphology, and structural features of mullite via sol-gel synthesis at low temperatures

This research explores the fabrication of mullite precursor powder utilizing the sol-gel process at low temperatures. Silicon tetraethoxide (Si(C2H5O)4) and aluminum nitrate nonahydrate (Al(NO3)3.9H2O) were employed as the sources of SiO2 and Al2O3 oxides, respectively. Various analytical techniques, such as Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), dilatometry, differential thermal analysis (DTA), and X-ray powder diffractometer (XRD), were utilized to investigate the formation and crystallization of the amorphous powder. The microstructure of specimens sintered at 1600 °C for 1 h was examined utilizing scanning electron microscopy (SEM). Measurements of hardness (HV) and coefficient of thermal expansion (CTE) were conducted on mullite samples heated to 1600 °C and then cooled, revealing an increase in HV from 888 to 1000 HV as the sintering temperature rose from 1500 to 1600 °C. The CTE of mullite within the temperature range of 50–1300 °C was determined as 5.23 × 10−6/°C. Additionally, the dielectric and electrical characterization of mullite was analyzed utilizing complex impedance spectroscopy at a frequency of 0.1–106 Hz and conductivity measurements over a temperature range of 40–400 °C. The real and imaginary parts of the dielectric permittivity exhibited frequency-dependent and temperature-dependent behaviors. Significantly, the observed variations in the imaginary component of the modulus and impedance maximum frequency point to a relaxation process that is not Debye-type, with calculated activation energies (Ea) consistent across different methods.

Effect of silica addition on the photocatalytic activity of MO2@SiO2 (M=Ti, Zr, Sn, Ce) nanocomposites prepared by sol-gel

AbstractPhotocatalysis uses wide band gap ceramic semiconductors (anatase, zirconia, ceria, cassiterite…) that have the ability to promote electron-hole pairs by UV light irradiation producing both reducing and oxidants ions and radicals. In general, oxidizing species are more efficient, using photocatalysis as an advanced oxidation process (AOP) for the biodegradation of organic substances refractory to conventional treatments, such as azo dyes, or atmospheric pollutants as NOx. In this communication, the photocatalytic activity of xSiO2@(1-x)MO2 (M = TiO2, ZrO2, SnO2, CeO2, x = 0, 0.1, 0.3 and 0.5) composites on the Orange II azo dye in solution, as well as on NOx in air, was analysed. The composites were obtained by Sol-Gel methods based on the hydrolysis-condensation of alcoholic solutions of silicon tetraethoxide (TEOS) and titanium n-butoxide, zirconium iso-propoxide, SnCl2.2H2O and Ce(NO3)3.6H2O as precursors of MO2 oxides. The resulting xerogels were studied by XRD, bandgap measurements from UV-Vis-NIR diffuse reflectance spectroscopy, photocatalytic activity against Orange II in dissolution and NOx in air (efficiency in nitrate abatement), and SEM-EDX microstructural analysis. In the case of non-stabilized samples, charring samples at 300 °C/1 h and fired samples at 500 °C/1 h were also studied. The cassiterite-silica composite stands out for its photocatalytic activity against Orange II in solution and the cerianite-silica composite against NOx in air. Silica increases the photocatalytic activity on NOx in zirconia, tin oxide and ceria composites and also on Orange II in zirconia and tin oxide. Graphical Abstract

Tuning of Ag-SPR band position in refractive index controlled inorganic-organic hybrid SiO2-PEO-TiO2 films

Inorganic (silica-titania)-organic (polyethylene oxide) hybrid films with variable refractive index (RI) values were synthesized and Ag nanoparticles were generated in situ inside such hybrid films to develop coloured coatings specially on plastic substrates. The hybrid films and the corresponding Ag-incorporated films were prepared from sols derived from a mixture of silicon tetraethoxide (STE), 3-(glycidoxypropyl)trimethoxysilane (GPTMS), titanium tetraisopropoxide (TTIP) and silver nitrate following a sol-gel dip-coating method and cured at low temperature (90°C), followed by UV treatment with an energy equivalent to 5·3 ± 0·1 J cm−2. The equivalent SiO2: SiO1·5(CH2)3OCH2CH(CH2)O: TiO2: Ag molar ratios (nominal) of the final cured films are varied in the ranges (67·9–0): 29·1: (0–67·9): 3. The refractive index values of the cured hybrid films were found to be increased systematically from 1·475 to 1·710 with increasing Ti-component. The Ag-SPR peak, in case of silica-polyethylene oxide host (RI = 1·475), observed at 419 nm, gradually red-shifted to 497 nm upon increasing the Ti-component (equivalent TiO2 content 67·9 mol%; RI = 1·710) of the film. As a consequence, a systematic change of Ag-SPR position yielded yellow, yellowish-orange, orange, brownish-orange and orangish-brown coloured coatings.

Structural Investigations on the Hydrolysis and Condensation Behavior of Pure and Chemically Modified Alkoxides. 1. Transition Metal (Hf and Ta) Alkoxides

Structural investigations on the hydrolysis and condensation behavior of hafnium and tantalum alkoxides were for the first time performed by means of X-ray absorption fine structure and Raman spectroscopy. The studies reveal that both of the alkoxides are dimeric in nature and instantaneously undergo hydrolysis and condensation reactions upon the addition of water. The results indicate that the chemical reaction of the alkoxides with acetylacetone occurs immediately with an increase from 6- to 8-fold coordination around the metal. As a consequence of the coordination by a bidentate ligand, hydrolysis and condensation reactions are hindered in solutions of the chemically modified Hf(OnBu)4 and Ta(OEt)5. Furthermore, the investigations demonstrate that the structure of metal alkoxides is not altered after mixing with prehydrolyzed silicon tetraethoxide, and even after 48 h, both of the species remain as separate entities in the mixture. The addition of water to this mixture starts the hydrolysis and condensation reactions instantaneously and leads to the formation of a M-O-M homocondensation product due to the different reactivity of the two alkoxides.

Effects of charge and size on condensation of supersaturated water vapor on nanoparticles of SiO2

The effects of size and charge on the condensation of a supersaturated water vapor on monodisperse nanoparticles of SiO(2) were investigated in a flow cloud chamber. The dependences of the critical supersaturation S(cr) on particle size at diameters of 10, 12, and 15 nm as well as on charge and charge polarity are determined experimentally. A novel electrospray aerosol generator was developed to generate a high concentration of SiO(2) nanoparticles of less than 10 nm by electrospraying silicon tetraethoxide (STE) ethanol solution followed by the thermal decomposition of STE. The effects of liquid flow rate, liquid concentration, flow rate of carrier gas, and liquid conductivity on the particle size distribution and concentration were examined. For charged particles, the nucleation occurs at a critical supersaturation S(cr) lower than that on neutral particles, and the charge effect fades away as particle size increases. The charge effect is stronger than the theoretical predictions. In addition, a sign preference is detected, i.e., water vapor condenses more readily on negatively charged particle, a trend consistent with those observed on ions. However, both effects of charge and charge polarity on S(cr) are stronger than that predicted by Volmer's theory for ion-induced nucleation.

Pore structure control in Ni/SiO 2 catalysts with both macropores and mesopores

Ni/SiO 2 catalysts with bimodal pore structure were prepared by the sol–gel method of silicon tetraethoxide and nickel nitrate in the presence of poly(ethylene oxide) (PEO) and urea. The presence of PEO was effective to induce phase separation during the sol–gel process, and through-macropores interconnected three-dimensionally were formed by fixing transitional structure of the phase separation. After gelation, the as-prepared wet gel was aged at 80 °C for decomposition of urea in order to increase pH of the solution within the gel. This pH increase led both the ripening of silica gel network through dissolution–reprecipitation and homogeneous deposition of nickel hydroxide. As a result, Ni could be dispersed highly in the silica network. In addition to the high dispersion of Ni, thus prepared Ni/SiO 2 has typical bimodal pore structure with size-controllable macropores and mesopores. The bimodal porous Ni/SiO 2 also had high thermal stability and showed steady catalytic activity in CO 2-reforming of methane at 700 °C.

Raman and Brillouin scattering measurements on hybrid inorganic–organic materials obtained from tetraethoxysilane and methacrylic monomers

Raman and Brillouin spectroscopies have been used for characterizing hybrid inorganic–organic macromolecular materials obtained from the polymerization of 2-hydroxy ethyl methacrylate (HEMA) or methyl methacrylate (MMA), modified by silicon tetraethoxide (TEOS). Different molar ratios r=[TEOS]/[HEMA], with r varying from 0.5 to 5, and [TEOS]/[MMA]=0.05 have been considered. The Raman data have provided a qualitative evaluation of the interaction between inorganic and organic components. The data of Brillouin scattering suggest that pure polymers are stiffer than the hybrids, almost irrespective of the inorganic compounds amount. The refractive index of the hybrids is lower than the pure polymer, even in case of small amounts of inorganic compound. The results are tentatively explained on the basis of the structural change in the polymeric network, due to the presence of the inorganic domains.

SANS study of colloidal aggregates of silicon tetraethoxide in basic ethanol/water solutions

Data of small-angle neutron scattering from colloidal aggregates of silicon tetraethoxide (TEOS) in basic ethanol/water solutions are presented. Changes in the structure of the aggregates were followed for different H 2O:TEOS molar ratios ( w) within the interval from 0.5 to 10. Two scattering levels are detected. The first one (<10 nm) corresponds to the diffusive surface of the aggregates whose characteristics change with w-ratio. The second level reflects the formation of large secondary associations, which have a fractal dimension decreasing monotonously from 2.2 to 1.0 with increasing w-ratio.

Preparation of titania/silica composite microspheres by sol–gel process in reverse suspension

Silica gel microspheres were prepared by sol–gel process of silicon tetraethoxide in reverse suspension. Subsequently, titanium tetra-2-propoxide solution was added to the system for producing titania gel. The composite microspheres prepared were analyzed with optical microscopy, electron probe microanalysis, and X-ray diffraction. Lowering the titanium alkoxide concentration in the continuous phase was effective to depress the agglomeration of fine titania particles. When the titanium alkoxide solution was divided into four parts and each aliquot was added separately, the covering state with titania became more uniform. The composite microspheres prepared were suspended in dye solution under ultraviolet irradiation and examined for the possibility of treating wastewater. The dye concentration rapidly decreased more than with a commercial titania powder, due to the effects of both photodegradation and adsorption.

マイカ基板上へのシリカナノチューブの配向成長

ケイ素アルコキシド (シリコンテトラエトキシド, TEOS) の加水分解・重縮合反応を強酸性の界面活性剤水溶液中で行うことにより, マイカ基板上にシリカナノチューブを高密度で配向成長させることに成功した。カチオン界面活性剤であるCTAB (セチルトリメチルアンモニウムプロミド) 水溶液にマイカ基板を浸漬した後, 353Kに昇温してTEOSの加水分解・重縮合反応を進行させた。反応後のマイカ基板を原子問力顕微鏡 (AFM) により観察したところ, 塩酸酸性下でのみシリカ薄膜の形成が認められた。得られた膜の高分解能AFM観察, 透過型電子顕微鏡 (TEM) 観察, X線回折測定により、このシリカ薄膜は内径2-3nm, 外径6-10nmのシリカナノチューブがマイカ基板上に配向成長した構造をとっていることがわかった。

高純度二酸化ケイ素試薬を用いた石英の合成と不純物ドープ実験

Several quartz samples containing one or two impurities were synthesized under the ambient pressure and the hydrothermal conditions by using the starting materials prepared from high purity silicon dioxide and silicon tetraethoxide. Phase transition from cristobalite to quartz occurred in the cases of coexistence of Li ion with the concentration of which are above 600 ppm under the ambient and above 50 ppm under the 100 MPa pressure. Although impurity elements usually detected in natural quartz can be doped into in the lattice in a couple with Li, cations with larger ionic radius such as Ca and K ions did not enter at ambient pressure. Under the hydrothermal condition, almost cations can be doped into the lattice as a single dopant. Such incorporated impurities to synthetic quartz were confirmed by ESR, X-ray diffraction measurement and thermal neutron irradiation. Unit cell volume of the doped quartz shows unique variation with the ionic radius of impurity ions. Lattice strain estimated from X-ray diffraction peak profiles around 90 Bragg angle (2θ) was very sensitive to the content of dopant. ESR signals showed that there exist trace Al, Na and Li in synthetic quartz made of 99.999% reagent.

Preparation of Core/Shell Structure of α-Al(OH)3-SiO2 by Heterogeneous Nucleation-and-Growth Processing

In order to solve the difficult problem of heterogeneity of different components in the procedure of ceramic preparation, a novel processing (heterogeneous nucleation-and-growth processing) was used to prepare homogeneous distribution powders. Composite coating particles consisting of alpha aluminum hydroxide (α-Al(OH)3) cores (average particle size 0.42 μm) with outer homogeneous amorphous silica layer are prepared by heterogeneous nucleation-and-growth processing. Effects of silica content in composite coating particles versus concentration of silicon tetraethoxide (TEOS), pH value, time and temperature are studied. The homogeneous amorphous silica layer on cores is confirmed by X-ray diffraction, transmission electron microscopy and zeta potential measurement.

Preparation and luminescent properties of sol–gel derived SiO 2–B 2O 3:Tb glass films

Borosilicate glass films doped with rare-earths were deposited on glass substrates by using a simple sol–gel method. To avoid the undesirable precipitation due to the different hydrolysis rates between silicon and boron alkoxides, two solutions were used for dip-coating separately. One solution consisted of silicon tetraethoxide, ethanol, water and terbium nitrate as the Tb dopant. Another consisted of triethyl borate. Layer-by-layer deposition was applied by dipping into these solutions in sequence. The luminescent properties of Tb 3+ were investigated for the borosilicate samples in relation to the firing effect. After firing at 900 °C, a remarkable increase (≈8 times) of the Tb 3+-ion luminescence was observed for the borosilicate samples, while the silicate sample showed about 3 times increase in luminescence intensity. The boron addition of as low as 1 mol% of B 2O 3 was found to be very effective in increasing the Tb 3+ luminescence intensity.

A simple procedure for the preparation of Cr-doped tin sphene pigments in the absence of fluxes

A procedure for the preparation of Cr-doped tin sphene pink pigments based on the pyrolysis at 600°C of liquid aerosols generated from solutions of silicon tetraethoxide, calcium chloride, tin(IV) chloride and chromium(III) nitrate in a mixed solvent (ethanol/water) is reported. The as produced powders were amorphous and consisted of spherical particles of broad size distribution (<2 μm). On calcination at 1200–1300°C, these powders transformed into crystalline tin sphene (CaSnSiO5) irregular particles (<11 μm) developing the pink colour characteristic of the commercial pigments with similar composition. The main advantage of this method is that it does not require the addition of the fluxes used in the traditional ceramic procedure, which is highly desirable from the environmental point of view. Additional advantages are its simplicity (no grinding required) and continuous character. The effects of the chromium content on the colour properties of the pigments were also evaluated, finding that the optimal pigment (best colour with minimum Cr content) was obtained for a Cr/malayaite mole ratio of 4.4%.

Effect of calcination temperature on the luminescent properties of Tb-doped borosilicate glasses

The luminescent properties of Tb3+ have been studied for borosilicate glasses prepared by a sol-gel method. Gel bodies were formed from solutions consisting of silicon tetraethoxide, triethyl borate, ethanol, water and terbium nitrate, then sintered into a bulk glass. The Tb3+ luminescence in glasses mostly shows green light under UV excitation, because the emission line at 545 nm occupies the main part of the energy emitted. The observed luminescence consisted of four main emission lines originating from the 5D4 level. However, a remarkable spectral change has been observed for the Tb3+ luminescence in borosilicate glasses after firing at about 800°C. This spectral change due to heat treatment was found to be large enough to show yellow or red luminescence, suggesting that the crystal field acting on Tb3+ is very strong. The spectral energy distribution of Tb3+ luminescence in sol-gel derived borosilicate glasses were investigated in relation to the effects of calcination temperature.

Mesoporous [M]-MSU-x metallo-silicate catalysts by non-ionic polyethylene oxide surfactant templating

Solutions of low and high pH have been used to form non-ionically templated mesoporous metallo-silicates [M]-MSU-x materials; where [M]=Al, Ti, V and Zr. Two new assembly routes are proposed which exploit the acid and base catalysed hydrolysis and simultaneous condensation of metal oxo-salts and silicon tetraethoxide. Acid catalysed hydrolysis, labeled N0X−I+ or N+X−I+ (N0=nonyl-phenyl polyethylene oxide, X−=Cl− or SO2−4, I+=protonated tetraethyl orthosilicate), produces well-defined materials with uniform pores in the small mesoporous region and moderate pore volumes, but reduced metal incorporation owing to the high solubilities of metal cations in acidic solutions. Base catalysed hydrolysis, labeled N0M+I− (N0=nonyl-phenyl polyethylene oxide, M+=Na+ or NH+4, I−=hydroxylated tetraethyl orthosilicate), also leads to materials with uniform channels in the small mesoporous region. Pore volumes and metal substitution are higher and framework shrinkage during calcination is reduced as a result of thicker pore walls. These new pathways show distinct similarities to those described by Attard et al. [Nature 378 (1995) 366] and Zhao et al. [Science 279 (1998) 548] for the formation of hexagonally symmetric silica from non-ionic surfactants under acidic conditions and also to mesoporous MCM-41 assembly routes via (S+X−I+) anion mediated acid catalysed assembly. The results demonstrate the feasibility of preparing templated mesoporous metallo-silicates from non-ionic polyethylene oxide surfactants and metal oxy-hydroxy cationic precursors, but indicate that further optimisation of the reaction conditions is required to maximise the potential of this synthesis approach.

Thick sol—gel coatings based on the B 2O 3SiO 2 system

Sol—gel coatings composed of B 2O 3SiO 2 (10, 20 and 30 mol% B 2O 3) were prepared using boron trimethoxide (B[OCH 3] 3), silicon tetraethoxide (TEOS) and methyltriethoxysilane (SiCH 3[OCH 2CH 3] 3) as precursors. Soda-lime glass slides were used as substrates. Coatings were obtained at room temperature and atmospheric pressure by dip-coating into an automatically controlled glove box with withdrawal rates ranging from 8 to 33 cm min −1. Densification was carried out at 500°C during 1 h in air. The thickness of the obtained coatings as a function of withdrawal rate was measure with a profilometer and the presence of cracks was monitored by optical microscopy. The effect of relative humidity on the thickness and transparency of the coatings was measured. Critical thickness varied from 1 μm to 0.6 μm depending on the B 2O 3 content. On the other hand, multilayer coatings were prepared to obtain crack-free and transparent samples with thickness greater than 1 μm. As an interesting application, oxidation resistance of borosilicate coatings on SiC/C composite substrates was measured by a stepwise test between 400 and 1500°C.

Preparation of High Lithium Ion Conducting LiLnSiO4 (Ln = La, Sm) Thin Films by Sol-Gel Method

Abstract A sol-gel method was applied to prepare thin films of LiLnSiO4 (Ln = La,Sm). The coating solution was made from lithium isopropoxide, silicon tetraethoxide, and tris(acetylacetonato)rare-earth. Well crystalline films with 0.1∼0.3 μm in thickness were obtained on alumina and quartz glass substrates by spin-coating, followed by firing over 400 °C. The lithium ionic conductivity of the films was much greater than that of sintered samples prepared by a conventional solid state reaction at 1000 °C.

Supported titanium catalysts based on magnesium dichloride?silicon tetraethoxide adduct for propylene polymerization

Anhydrous magnesium dichloride was reacted with silicon tetraethoxide to form a solid adduct. The adduct was treated with titanium tetrachloride and an internal Lewis base to prepare supported titanium catalysts. Alkyl benzoate (PhCOOR, R = Me, Et, n - Bu) or dialkyl phthalate [Ph(COOR) 2 , R = Me, Et, n - Bu] was used as an internal Lewis base. The prepared catalysts (MT) in combination with triethylaluminum as a cocatalyst polymerize propylene to yield polypropylene. The nature and concentration of internal Lewis base influence the composition, specific surface area, and performance of the catalysts. The addition of diphenyl dimethoxysilane into the MT/Et 3 Al catalyst system increases the isotactic index of polypropylene from 75 to 97 at a Si/Al mol ratio of 0.05. The overall results indicate that a dialkyl phthalate-incorporated catalyst shows better physical, chemical, and polymerization characteristics compared to a corresponding alkyl benzoate catalyst.

Supported titanium catalysts based on magnesium dichloride—silicon tetraethoxide adduct for propylene polymerization

Supported titanium catalysts based on magnesium dichloride—silicon tetraethoxide adduct for propylene polymerization