Colloidal Silica Sol Research Articles

Effect of nano-silica coating prepared by different concentration silica sol on shear bond strength of alumina ceramic

To evaluate the effect of nano-silica coating prepared by different concentration silica sol on shear bond strength between alumina ceramic and resin cement. Silica coating was prepared with colloidal silica sol on alumina ceramic surface that was treated with air particle abrasion. Infrared spectrum (IR), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) were used to analyze the silica coating. A total of 32 alumina ceramic discs were randomly divided into 4 groups with 8 discs per group, which received different surface treatments as silane couple agent (control group), 20% silica sol + silane (group A), 30% silica sol + silane (group B), 40% silica sol + silane (group C). Each ceramic disc was bonded to composite with resin cement, and then shear bond strength of these samples was tested. It was observed from the IR pictures that symmetrically flexible vibration absorption kurtosis, anti-symmetrically flexible vibration absorption kurtosis, and bending vibration absorption kurtosis of Si-O-Si enhanced after heat treatment. SEM pictures showed that nanoparticles in coating gel were well distributed and some of them conglomerated after heat treatment. There was a little conglomeration in 20% coating, more in 30%, and the most in 40%. Contents of surface silicon increased after modification with silica coating prepared by sol-gel method. Bond strength of three groups with silica coating was significantly higher than that of the group with only silane couple agent [(1.881 +/- 0.156) MPa] (P < 0.05). Group B gained the highest strength [(4.852 +/- 0.178) MPa] compared with group A [(3.196 +/- 0.171) MPa] and group C [(3.576 +/- 0.671) MPa] (P < 0.05). Surface silicon contents all increased after surface modification with different concentration silica sol. Silica coating followed with silane couple agent could significantly enforce bond strength of alumina ceramic, with 30% silica sol group gaining the highest bond strength.

Establishing the difference between colloidal borosilicate and boron-modified colloidal silica via chelation of boron with catechol and dl-tartaric acid

Colloidal borosilicate and boron-modified colloidal silica sols were studied by 11B NMR. Formation of B–O–Si chemical bonds is established in both materials. It is shown that boron present in colloidal borosilicate is stable towards the action of complexing agents catechol and tartaric acid. In contrast, the boron in boron-modified silica is readily complexed by these agents. The results presented herein demonstrate that B–O–Si bonds are homogeneously distributed throughout the colloidal borosilicate disperse phase, while in boron-modified colloidal silica they are concentrated at the surface of colloidal silica particles.

Novel synthesis of a porous stainless steel-supported Knudsen membrane with remarkably high permeability

A stainless steel-supported Knudsen membrane (SKM) with remarkably high permeability was successfully synthesized using only 100 nm-sized colloidal silica sol by means of a dipping–rolling–freezing–fast drying (DRFF) and soaking–rolling–freezing–fast drying (SRFF) method. Hydrogen and nitrogen permeances of the SKM were (6.7–8.2) × 10 −6 and (1.8–2.3) × 10 −6 mol m −2 s −1 Pa −1 with a H 2/N 2 permselectivity of 3.5–3.7, which approaches to a theoretical H 2/N 2 selectivity for the Knudsen diffusion mechanism (3.74). In comparison with a typical mesoporous γ-alumina membrane supported on a porous stainless steel or α-alumina substrate, the SKM had 20 and 5.5 times permeance with almost same H 2/N 2 permselectivity, respectively. Generally, mesoporous materials such as γ-alumina and the M41S family with several nm-sized pores are employed to obtain the Knudsen-dominated permeation characteristics. In this case, a decrease in the gas permeance is inevitable due to deposition of a mesoporous skin layer. However, in the case of the SKM, the Knudsen-dominated permselectivity was extraordinarily obtained through modification of porous stainless steel substrates with the colloidal silica particles having relatively large particle size, because a well-densified layer of the 100 nm-sized colloidal silica could be obtained without formation of defects via the freezing procedure. In addition, the large porosity of the 100 nm-sized colloidal silica layer gave rise to the remarkably high gas permeance.

Synthesis and pore analysis of aerogel–glass fiber composites by ambient drying method

Flexible aerogel–glass fiber composites were prepared by varying colloidal silica and tetraethylorthosilicate (TEOS)-based sol fractions. After immersing glass fiber matrices into silica sol with different volume fraction of colloidal silica sol, it was surface-modified into trimethylchlorosilane/n-hexane solution and heat-treated at 230°C in ambient atmosphere. From the results of Brunauer–Emmett–Teller (BET) surface area, Barrett–Joyner–Halenda (BJH) pore size analyses, apparent density and porosity studies, it was thought that microstructures of aerogel composites like pore size and specific surface area were greatly affected by precursor sol. Aerogel composites made of only colloidal silica showed greater density and lesser porosity, smaller pore size and specific surface area than those of aerogel composites synthesized from colloidal and TEOS-based mixed sols.

Characteristics of Silica Aerogel Composites Synthesized by Ambient Drying Method

Aerogel has its advantages of light density of 0.003-0.35 g/cm3 and its high specific surface area, 600-1000m2/g, mean pore diameter ~20nm. However, aerogel has its disadvantages of fragility and high cost. To overcome the mechanical fragility, we synthesized aerogel composite blankets with glass wools by drying at ambient atmosphere. Colloidal silica sol was first prepared by ion exchanging sodium silicate through amberlite column. Then, glass wool was soaked into the pH-controlled silica aerogel and then gelated. Ageing of silica aerogel composite was conducted in purified water and solvent exchange/surface modification was simultaneously processed in hexane and TMCS solution. After drying at 60oC and heat-treatment at 230oC, we evaluated the properties of aerogel composite, its apparent density and specific surface area.

Preparation of Polyimide-Silica Nanocomposites from Nanoscale Colloidal Silica

The polyamic acid (PAA) solutions were blended directly with a commercial nanoscale colloidal silica sol, and converted to polyimides (PIs)/silica nanocomposite films. Polyamic acid was prepared from the reaction of Pyromellitic anhydride (PMDA), 4,4-oxydianiline (ODA). The nanoscale silica particles were dispersed well in PI from scanning electron microscopy (SEM) and the nanocomposite films showed a moderated optical transparency for up to 30 wt % of silica content. These PI/silica nanocomposite films exhibited better mechanical properties, higher glass transition temperature (Tg), better thermal stability and lower coefficient of thermal expansion (CTE) with increasing silica content from tensile tests, dynamic mechanic analysis (DMA) and thermogravimetric analysis (TGA).

Synthesis of Pt-containing mesoporous silica using Pt precursor as a pore-forming agent

We synthesized Pt nanoparticle-containing mesoporous silica in a one-pot process using tetraammineplatinum(II) hydroxide (TPH) precursor as a pore-forming agent and silica nanospheres as a silica source. The TPH precursor was added into as-prepared colloidal silica sol with silica nanospheres (SN) of about 8 nm in particle diameter, to obtain the SN–TPH sol. During drying process of the SN–TPH sol, an amorphous SN–TPH nanocomposite was formed via hydrogen-bonding interaction between silanol groups and amine groups of the TPH precursor. The hydrogen-bonding interaction was confirmed by thermal gravimetry and differential thermal analysis (TG–DTA) profiles and Fourier transform infrared (FTIR) spectra. Using the TPH precursor as a pore-forming agent, incorporation of the Pt nanoparticles into the mesoporous silica can be simultaneously achieved with the synthesis of the mesoporous silica in a one-pot process. In addition, Pt nanoparticle size and pore diameter of the mesoporous Pt/silica were simultaneously controlled by simply varying the concentration of the TPH precursor. The pore diameter of the mesoporous silica was easily controlled from 3.2 nm to 6.5 nm with an increase in the TPH concentration.

Effective preparation of crack-free silica aerogels via ambient drying

Effective ambient-drying techniques for synthesizing crack-free silica aerogel bulks from the industrial waterglass have been developed. Silica wet gels were obtained from aqueous colloidal silica sols prepared by ion-exchange of waterglass solution (4–10 wt% SiO2). Crack-free monolithic silica aerogel disks (diameter of 22 mm and thickness of 7 mm) were produced via solvent exchange/surface modification of the wet gels using isopropanol/trimethylchlorosilane/n-Hexane solution, followed by ambient drying. The effects of the silica content in sol and the molar ratio of trimethylchlorosilane/pore water on the morphology and property of final aerogel products were also investigated. The porosity, density, and specific surface area of silica aerogels were in the range of 92–94%, 0.13–0.16 g/cm3, and ∼675 m2/g, respectively. The degree of springback during the ambient drying processing of modified silica gels was 94%.

Dispersion of silica nano-particles in sol-gel hybrid resins for fabrication of multi-scale hybrid nanocomposite

Multi-scale hybrid nanocomposites containing both ∼15 nm silica colloids and ∼2 nm oligosiloxanes in a methacryl polymer matrix were newly designed and fabricated. Colloidal silica sols were dispersed in methacryl oligosiloxanes nano-hybrid resins synthesized by sol-gel reaction of methacryloxypropylmethoxysilane and diphenylsilanediol. On the basis of TEM and SANS analyses, it was confirmed that the silica colloids were compatibly dispersed and different sizes of colloidal silica and oligosiloxanes co-exist in the solutions. Multi-scale hybrid nanocomposites fabricated by UV and thermal curing with incorporation of silica colloids in the nano-hybrid materials show enhanced mechanical and thermal characteristics.

Nano-ZnO embedded SiO 2 glass with intense ultraviolet emission

The nano-ZnO embedded SiO 2 glass was prepared by a four-step process: (1) formation of colloidal suspension of Zn(OH) 2, (2) synthesis of silica sol, (3) mixture of Zn(OH) 2 colloidal suspension and silica sol to form precursor glass, and (4) annealing of the precursor glass to obtain the nano-ZnO embedded glass. The results presented herein focused on the structural characterization and photoluminescence (PL) characteristics of the nano-ZnO embedded glass. It is shown that the PL intensity of the ultraviolet emission of the glass was dependent on the preparation conditions, and the pure ultraviolet emission could be controlled by the pH value of the colloidal suspension of Zn(OH) 2 and the silica sol.

Fabrication and Structure of TiO&lt;sub&gt;2&lt;/sub&gt; Coated Open-Cell Mullite Ceramics

TiO2 coated open-cell mullite ceramics were fabricated with coating TiO2 sol on pores of mullite, and its processing parameters were investigated. Open-cell mullite ceramics were fabricated through a gel-casting process. Two kinds of mullite precursor powders were prepared by dissolution of two kinds of aluminum salts (Al(NO3)3·9H2O; type I and Al2(SO4)3·16H2O; type II) into colloidal silica sols. To produce porous mullite ceramics, both mullite precursor powders and PMMA beads (≈ 5μm) were co-dispersed by electrosteric stabilized mechanism in an aqueous system and then gel-casted. The green bodies were sintered above 1300°C for 3hrs in air. The PMMA was offered as pores in sintered mullite bodies. The prepared open-cell mullite ceramics were dipped in TiO2 precursor solution. The sintered bodies coated with TiO2 sols were re-sintered below 1000°C for 3hrs after drying at room temperature. The TiO2 was successfully coated into the open-cell mullite ceramics. The characteristics of each TiO2 coated porous mullite ceramics were investigated by XRD, SEM, porosimetry, as functions of aluminum salt and pH of sol. It was found that the synthesis behavior and the porosity of the mullite are strongly dependent upon aluminum salt species, resulting in different grain size, morphology, and pore size.

Synthesis of mesoporous SiO 2 glass by a novel chemical method

A novel five-step method for fabricating mesoporous SiO 2 glass was described in this paper, which consists of: (1) formation of colloidal suspension of Zn(OH) 2, (2) synthesis of silica sol, (3) mixture of Zn(OH) 2 colloidal suspension and silica sol to form nano-ZnO embedded precursor glass, (4) annealing of the precursor glass, and (5) treating nano-ZnO embedded glass with HCl to obtain the mesoporous glass. The mesostructure of the glass was investigated by X-ray diffraction (XRD), field emission scanning electron microscope (SEM), and BET surface area analysis. The average pore size distribution is in the range of 3.7 nm, and the surface area is as high as 496.5 m 2/g.

Mesoporous silica framed by sphere-shaped silica nanoparticles

Organic template-derived mesoporous silica with narrow pore size distribution was prepared through a colloidal silica–citric acid system. Colloidal silica sol with 5 nm in particle diameter was firstly prepared under base-catalyzed condition via hydrolysis of tetraethyl orthosilicate (TEOS) and condensation reaction. Subsequently, colloidal silica–citric acid nanocomposite solution was synthesized by addition of citric acid to the as-prepared colloidal silica sol. After the elimination of citric acid via thermal treatment at 500 °C, the mesoporous silica was successfully obtained, and its pore size was easily controlled in the range from 2 nm up to 15 nm maintaining the narrow pore size distribution, the high specific surface area (800–900 m 2/g) and the pore volume (0.6–1.4 cm 3/g). Comparing with a polymeric silica–citric acid system, the colloidal silica–citric acid system showed an increase in the controllable pore size and the structural stability. The sphere-shaped silica nanoparticles as a framework with highly branched structure led to the rigid structure of the framework and the thicker pore wall, suppressing the shrinkage of the silica structure in spite of the large vacancy produced by the removal of citric acid.

A novel fabrication of meso-porous silica film by sol-gol of TEOS.

A homogeneous crack-free nano- or meso-porous silica films on silicon was fabricated by colloidal silica sol derived by hydrolyzing tetraethyl orthosilicate (TEOS) catalyzing with (C4H9)4N+OH- in water medium. The solution with ratio of H2O/TEOS> or =15, R4N+ and glycerol as templates, combining with the hydrolyzed intermediate, controlled the silica aggregating; the templated silica film with heterostructure was developed into homogeneous nano-porous then meso-porous silica films after being annealed from 750 degrees C to 850 degrees C; the formation mechanism of the porous silica films was discussed; morphologies of the silica films were characterized. The refractive indexes of the porous silica films were 1.256-1.458, the thermal conductivity < 0.7 W/m/K. The fabricating procedure and the sequence had not been reported before.

Mullite Precursor Synthesis in Aqueous Conditions: Dependence of Mullite Crystallization and Grain Size and Morphology on Solution pH and Precursor Salt

The synthesis behavior of mullite in an aqueous system was investigated. Two kinds of aluminosilicate precursor sols were prepared by the dissolution of two kinds of salt (aluminum chloride hexahydrate, AlCl3·6H2O, and aluminum sulfate with 14–18 molecules of water, Al2[SO4]3·14–18H2O) into the mixture of colloidal silica sol. The effects of the solution pH, which was controlled by addition of ammonium hydroxide (NH4OH), and the type of aluminum salt on the mullite crystallization and the grain size and morphology in the sintered materials are discussed in this paper. It has been discovered that in an aqueous system, the mullitization temperature strongly depends on the solubility and decomposition temperature of the aluminum salt used and that the pH of the initial sol impacts the grain size and morphology of mullite, in addition to the homogeneity of mixture. Mullite is synthesized at 850 °C without resorting to the addition of an organic additive or nonaqueous solvent.

A facile route to prepare high surface area mesoporous SiC from SiO2 sphere templates

A simple and economic process for the preparation of mesoporous SiC ceramics with high BET surface area was developed by using commercially available sources. Low viscosity polycarbosilane as a SiC precursor was infiltrated into a sacrificial silica sphere template, which was precipitated by the centrifugation of an aqueous silica sol having a particle diameter in the range 20–100 nm. It was subsequently etched off by aqueous HF after pyrolysis in an argon atmosphere at 1000–1400 °C. The mesoporous SiC prepared from 20–30 nm aqueous silica sol exhibited a significantly high surface area of 612.7 m2 g−1 (pore volume 0.81 cm3 g−1), with a bimodal pore size distribution. The pore characteristics of various mesoporous SiC ceramics were investigated by controlling the diameter of colloidal silica sols and pyrolytic temperatures. In addition, it was demonstrated that mesoporous SiC patterns with a 20 µm width could be fabricated on a Si wafer using a micromolding in capillaries (MIMIC) method as one of the soft lithography techniques. Finally, the prepared mesoporous SiC products were thoroughly analyzed using SEM, TEM, nitrogen adsorption isotherms and XRD.

Study on the variation of morphology and separation behavior of the stainless steel supported membranes at high temperature

Palladium composite membranes were prepared on stainless steel (SUS) supports modified by nickel submicron powder and colloidal silica sols. Permeation tests of the palladium composite membranes were carried out at high temperature in order to observe the thermal stability of the membrane. The palladium composite membrane failed with formation of plenty of pinholes in the presence of hydrogen at high temperature. The failure of the composite membrane was verified by comparing the nitrogen permeance before hydrogen permeation test with that after hydrogen permeation test and comparing the H 2/N 2 selectivity for single gas permeation test with that for mixture gas permeation test. The variation of the membrane surface due to the failure of the membrane was characterized in scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS) analyses. As a result, it can be concluded that reducible metal oxides can be attributed to the failure of the composite membranes resulting from reduction of the metal oxides by hydrogen whichever position in the membrane the metal oxides are layered.

Effects of Salt and Precursor pH on Synthesizing Behavior and Grain Morphology of Mullite in Aqueous System

The effects of the salt and the precursor pH on the synthesizing behavior and the morphology of mullite have been studied. Two kinds of mullite precursor sols were prepared by the dissolution of two kinds of salt (aluminum nitrate enneahydrate, Al(<TEX>$NO_3$</TEX>)<TEX>$_3$</TEX>ㆍ<TEX>$9H_2$</TEX>O; type I and aluminum sulfate 14∼18 water, (SO<TEX>$Al_4$</TEX>)<TEX>$_3$</TEX><TEX>$\cdot$</TEX><TEX>$14∼18H_2$</TEX>O; type II) into the mixture of colloidal silica sol, respectively. Precursor pH of the sols was controlled to the acidic (pH= 1.5∼2) and basic (pH= 8.5∼9) conditions. The co-products with nitrate and sulfate were completely eliminated at <TEX>$500^{\circ}C$</TEX> and <TEX>$850^{\circ}C$</TEX>, respectively, which was confirmed by TG/DTA results. The synthesizing temperature of mullite phase was found to be above <TEX>$1200^{\circ}C$</TEX> for pH= 1.5∼2 and above <TEX>$1300^{\circ}C$</TEX> for pH= 8.5∼9 in type I. However, in type II, the synthesizing temperature of mullite was decreased to <TEX>$850^{\circ}C$</TEX> for pH= 1.5∼2 and <TEX>$1100^{\circ}C$</TEX> for pH= 8.5∼9. The grain size of the mullite synthesized at pH= 8.5∼9 was larger than that at pH= 1.5∼2 in overall heat-treated temperatures, showing smaller grain size in type II. Aspect ratio of the mullite grains was more increased at pH= 1.5∼2 than pH= 8.5∼9 in type I, showing similar aspect ratio at both pH conditions in type II. It was found that the synthesizing temperature and grain size were predominantly governed by the initial precursor pH and decomposition of the salt, with minor effect on the grain morphology.

Effects of precursor pH and composition on the grain morphology and size of mullite ceramics in aqueous system

The effects of the precursor pH and composition on the synthesizing behavior, grain morphology, and grain size of mullite ceramics have been investigated using silica-rich (Al 2O 3·2SiO 2), stoichiometric (3Al 2O 3·2SiO 2), and alumina-rich (7.5Al 2O 3·2SiO 2) mullite precursor sols. Mullite precursor sol was prepared by the dissolution of aluminum nitrate enneahydrate (Al(NO 3) 3·9H 2O) into the mixture of colloidal silica sol. Precursor pH of the sols was controlled to the acidic (pH≈1.5–2) and basic (pH≈8.5–9) conditions. The synthesizing temperature of mullite phase was found to be above 1200 °C for pH≈1.5–2, and above 1300 °C for pH≈8.5–9 through X-ray diffraction (XRD) and Fourier transfer infrared spectroscopy (FT-IR) results, independent of composition. The grain size of the synthesized mullite for pH≈8.5–9 was larger than that for pH≈1.5–2 in the overall heat-treated temperature. Aspect ratio of the mullite grains was increased with an increase of the silica concentration. It was found that the grain morphology and grain size were predominantly governed by the initial composition and precursor pH, respectively.

A novel route to highly porous bioactive silica gels

Silica gels with a distribution of pore sizes from the sub-micrometre to hundreds of micrometers were produced by a novel method in which precursor solutions, such as a colloidal silica sol or pre-hydrolyzed tetraethoxysilane (TEOS), were solidified in the presence of a space-filling agent (CaCO3) and CO2 generator (sodium bicarbonate–hydrogen pyrophosphate). A range of macroporous organically modified silica gels with covalently linked phenyl, amino or thiol moieties were also prepared by a similar method using mixtures of TEOS and organotrialkoxysilanes. The highly porous monoliths were characterized by SEM, FTIR and solid state 29Si and 13C MAS NMR spectroscopies. In vitro bioactivity of the gels was demonstrated by their ability to nucleate calcium phosphate from simulated body fluid, bind and slowly release the drug ibuprofen, and support in vitro adhesion and proliferation of human osteoprogenitor cells and C2C12 pro-myoblast cells.