Silicon Alkoxide Research Articles

Production of Silica from Agricultural Waste

The most common generated waste synthesized is rice husk and palm ash, which shown high silica contain as 90-98% and 45- 50%, in respectively [1,2]. Silica produced from these wastes were synthesized mainly using acid leaching treatment. In this study, we focused on the synthesized of other sources silica through sol-gel method. The source such as sugarcane bagasse, corn cob, bamboo stem, and bamboo leaf, till now is still not widely explored, hence become the basis to study the amount of silica that been extracted. Within the scope of study, it shown that several factors play a vital role in determining the silica content of the material, including the species of source material, soil content of source material, maturation etc. Sol-gel synthesis is one of the most common method of converting ash into silica gel. In this process, silica was synthesized from ash through simultaneous hydrolysis and condensation reaction where a sol of sodium silicate, silicon alkoxide or halide gels converted into a polymeric network of gel [3]. The synthesis of silica using this method, lead to silica precipitation under certain conditions like restriction of gel growth that involved coagulation and precipitation step during its preparation [4]. Silica gel synthesize through this method also known as xerogel. The purification and drying produce silica in amorphous powder form that remove any impurities or organic matter that usually contain in waste [1].

Efficiency of new ozone filters for NO2 sensing and air depollution

Specific filters can be used up-stream with metal oxide (MOX) gas sensors to trap ozone and allow the selective detection of NO2. These filtering media are based on nanoporous matrices doped with indigo-carmine that reacts selectively with O3. The nanoporous materials, produced via the sol-gel process using functionalized silicon alkoxides as precursors, are tailored for the trapping of O3. Depending on the nature of the filter, it is possible to entirely trap O3 and allow NO2 to partially pass over a certain range of concentration. For air depollution purpose, selected filters that efficiently trap both O3 and NO2 were exposed to harsh conditions under high concentrations of O3 (350–475 ppb) and humidity (RH: 72%, T = 21 °C). Their trapping efficiency and lifetime are determined and compared with those of activated carbon.

Pretreatment effect of the pure titanium surface on hybrid coating adhesion based on tetraethoxysilane and methyltriethoxysilane

Hybrid coatings based on silicon alkoxide precursors are one of the options for coating metal surface biomaterials such as pure titanium (Ti). However, the nature and the metal surface preparation, before the coating application, are of fundamental importance for perfecting the coating/surface adhesion. In this study, three different pretreatments were used for the Ti surface: Kroll, Piranha and NaOH. After the pretreatment, the coating was applied by the dip-coating process, using the sol–gel method from the silicon alkoxide precursors, tetraethoxysilane and methyltriethoxysilane. The results of thermogravimetric analysis showed that the tested coatings had excellent thermal stability. The pretreatment with NaOH solution increased the surface roughness of the Ti, thus modifying its surface energy and increasing its wettability. Field emission scanning electron microscopy showed a homogeneous coating with good adhesion of the hybrid coating to the Ti surface, and higher layer thickness on the surface treated with NaOH. In addition, its electrochemical performance was better than the surfaces pretreated with acids.

Properties of silica and silica-titania layers fabricated from silica sols containing fumed silica

Silica layers fabricated by the sol-gel method are usually amorphous and exhibit a relatively low refractive index (n∼1.46 at about 0.6 μm), high optical transmittances at UV-VIS and near-IR ranges, as well as high thermal stability. Such layers can be used as high reflection or antireflection coatings, dielectric mirrors, bandpass filters, etc. However, crack-free layers with a maximum thickness of about 400 nm can be prepared in one coating cycle from sols of simple silicon alkoxides. This paper presents an approach for the preparation of crack-free silica layers that allows us to increase this maximum thickness. The approach is based on the dip-coating technique used for applying stable silica sols containing fumed silica. These sols were obtained from input silica sols based on tetraethyl orthosilicate (TEOS) with concentrations 1 and 2 mol/l, ethanol, HCl and water (RW 1.75). Fumed silica was dispersed in water/TritonX-100 solution and added into some of the input sols. Zeta potentials, average dimensions and diffusion coefficients of silica agglomerates in sols containing fumed silica are presented. Both types of sols were deposited onto silica slides and silicon wafers by the dip-coating technique using different withdrawing velocities 100,200 and 300 mm/min. Prepared silica gel layers were thermally treated at 450 or 900 °C. One of silica sols with fumed silica has also been used for the preparation of a silica-titania sol with a molar ratio Ti/Si = 3/7. Both these sols have been employed for the preparation of a Bragg mirror consisting of three pairs of high-index silica-titania and low index silica layers on a silica slide.The appearance and thickness of prepared single silica and silica-titania layers have been characterized by optical microscopy and scanning electron microscopy. Optical properties of layers have been determined by spectral ellipsometry and UV-VIS-NIR transmission spectrometry. The measurements have shown that characteristics of layers fabricated from both types of the sols differ and that one can obtain stable transparent silica layers with thicknesses up to 650 nm and refractive indices in a range from 1.41 to 1.44 at 600 nm using TEOS sols containing fumed silica. It has been found that larger layer thicknesses can be achieved by using silica sols with fumed silica, by increasing the alkoxide concentration, by using increased withdrawing velocities, and by decreasing heat-treatment temperatures.

Optical parameters of a novel competitive selective absorber for low temperature solar thermal applications

Up to now many efforts have been put into environmentally friendly techniques for designing high quality selective absorbers to take advantage of the abundant and clean solar energy sources. In this paper a new selective absorber for low temperature thermal applications is presented. It is a multilayered absorber, specifically a three layer configuration, with only one layer of absorber material. It is composed of CuMnOx thin film and two consecutive antireflective coatings: FeMnCuOx and SiO2. The CuMnOx film and the FeMnCuOx antireflective layer were prepared from alcoholic solutions containing metal nitrates while the solution used to prepare the SiO2 coating was prepared from silicon alkoxides. The deposition of the three layers onto the aluminum substrate achieves solar absorptance values of 0.957 and thermal emittance values of 0.038 at 100 °C. In this way, it is obtained a very good selective absorber with three layers configuration by using a simple, reproducible and cost-effective method such as dip coating.

Thermochemical Stability and Friction Properties of Soft Organosilica Networks for Solid Lubrication.

In view of their possible application as high temperature solid lubricants, the tribological and thermochemical properties of several organosilica networks were investigated over a range of temperatures between 25 and 580 °C. Organosilica networks, obtained from monomers with terminal and bridging organic groups, were synthesized by a sol-gel process. The influence of carbon content, crosslink density, rotational freedom of incorporated hydrocarbon groups, and network connectivity on the high temperature friction properties of the polymer was studied for condensed materials from silicon alkoxide precursors with terminating organic groups, i.e., methyltrimethoxysilane, propyltrimethoxysilane, diisopropyldimethoxysilane, cyclohexyltrimethoxysilane, phenyltrimethoxysilane and 4-biphenylyltriethoxysilane networks, as well as precursors with organic bridging groups between Si centers, i.e., 1,4-bis(triethoxysilyl)benzene and 4,4′-bis(triethoxysilyl)-1,1′-biphenyl. Pin-on-disc measurements were performed using all selected solid lubricants. It was found that materials obtained from phenyltrimethoxysilane and cyclohexyltrimethoxysilane precursors showed softening above 120 °C and performed best in terms of friction reduction, reaching friction coefficients as low as 0.01. This value is lower than that of graphite films (0.050 ± 0.005), a common bench mark for solid lubricants.

Silicatein: A Unique Silica-Synthesizing Catalytic Triad Hydrolase From Marine Sponge Skeletons and Its Multiple Applications.

Silicatein, a silica-synthesizing, catalytic triad hydrolase, was discovered in the silica spicules comprising the skeletons of certain marine sponges. Sequence similarity is closest to that of the mammalian cathepsin L, a catalytic triad hydrolase and protease. Genetic substitutions of residues in the catalytic triad, the predictive activities of polymeric and small-molecule analogs of the enzyme, and the wide range of structures accepted as substrates all support a reaction mechanism closely analogous to that established for the classical catalytic triad hydrolases. In this mechanism, hydrogen bonding of residues in the catalytic site is required to enhance nucleophilic attack and consequent hydrolysis of silicon alkoxide (and a wide range of other precursors), enabling subsequent polycondensation. Experimental and computational analyses revealed a novel pathway of self-assembly, in which the silicatein subunits first form a fractally patterned intermediate before entropic rearrangement to the hexagonally close-packed, macroscopic filament that serves both as the catalyst of silica synthesis in the sponge, and as a template guiding the deposition and emergent structure of the macroscopic silica filaments that form the sponge skeleton. Silicatein also proves capable of catalyzing the synthesis of organic silicones, metal oxides, metal phosphates, polylactides, and polymeric materials composed of organic metal compounds from their corresponding precursors, suggesting an evolutionary relaxation of structural substrate specificity that may have been necessary to accommodate the organic adducts of silicic acid suggested to comprise the natural precursor of the biogenic silica. Methods for purification, characterization, assay, and multiple uses of the enzyme are described.

Sol-gel preparation of Ag-silica nanocomposite with high electrical conductivity

Sol-gel derived noble-metal-silica nanocomposites are very useful in many applications. Due to relatively low price, higher conductivity, and higher chemical stability of silver (Ag) compared with copper (Cu), Ag-silica has gained much more research interest. However, it remains a significant challenge to realize high loading of Ag content in sol-gel Ag-silica composite with high structural controllability and nanoparticles’ dispersity. Different from previous works by using multifunctional silicon alkoxide to anchor metal ions, here we report the synthesis of Ag-silica nanocomposite with high loading of Ag nanoparticles by employing acetonitrile bi-functionally as solvent and metal ions stabilizer. The electrical conductivity of the Ag-silica nanocomposite reached higher than 6800 S/cm. In addition, the Ag-silica nanocomposite could simultaneously possess high electrical conductivity and positive conductivity-temperature coefficient by properly controlling the loading content of Ag. Such behavior is potentially advantageous for high-temperature devices (like phosphoric acid fuel cells) and inhibiting the thermal-induced increase of devices’ internal resistance. The strategy proposed here is also compatible with block-copolymer directed self-assembly of mesoporous material, spin-coating of film and electrospinning of nanofiber, making it more charming in various practical applications.

Role of oxalic acid in structural formation of sodium silicate-based silica aerogel by ambient pressure drying

Recently, the demand of sodium silicate-based silica aerogels has decreased due to its inadequate physical properties when compared to those made by other silicon alkoxides. To avoid this problem, introduction of a drying control chemical additive (DCCA) in the sol has received great attention. DCCA is one of the additives that can control the rate of hydrolysis and the condensation reaction in sol state by the formation of hydrogen bonds between DCCA and silanol groups of silica sol. A control over these reactions results in a uniform pore size distribution, which, in turn, decreases the drying stress with a decrease in pore size, in accordance with the Young–Laplace equation. Therefore, the structure of the silica aerogel can be maintained by minimizing the volume shrinkage due to drying stress. In this research, oxalic acid was first used as DCCA in the formation of sodium silicate-based silica aerogel by ambient pressure drying. The physical properties of these silica aerogels can be changed by changing the molar ratio of oxalic acid/Na2SiO3 in the sol state. When the oxalic acid:Na2SiO3 molar ratio was 15 × 10−4 in the sol state, aerogels with high specific surface area (623.2 m2/g), pore volume (4.271 cm3/g), average pore diameter (27.41 nm), high porosity (94.3%), high contact angle (144.09°), and high optical transmittance (75%) were obtained.

Polymer-assisted shapeable synthesis of porous frameworks consisting of silica nanoparticles with mechanical property tuning

We report the shapeable synthesis of porous silica frameworks using polyacrylamide (PAAm) gel as an organic template and hydrolyzed silicon alkoxide as a silica source. Macroscopically shaped porous frameworks—such as plates, tablets and sheets—comprised of 20- to 40-nm diameter silica particles are obtained via PAAm–silica precursor gels. The mechanical properties (i.e., hardness and Young’s modulus) of the silica frameworks depend on the packing density and are controlled by changing the silica content in PAAm gels. Shapeable synthesis of porous silica frameworks was achieved in an aqueous system using polyacrylamide (PAAm) gel as an organic template and hydrolyzed silicon alkoxide as a silica source. Macroscopically shaped frameworks comprised of 10- to 50-nm diameter silica particles are obtained via PAAm–silica precursor gels. The mechanical properties of the silica frameworks depending on the packing density are controlled by changing the silica content in PAAm gels.

Sol Gel Glass Coating on Magnesium Alloys to be Used As Temporary Implants: Electrochemical and Surface Study in Simulated Body Fluid

Surface modification of metallic materials is the approach for developing functional properties to assure good biocompatibility, enhance tissue acceptance, and/ or inhibit corrosion rate. It opens a wide spectrum of possibilities oriented to develop the functional properties needed for an implant acceptance when the bare material is not enough to assure good biocompatibility and tissue regeneration. Further, the interface between the implant and the physiological environment becomes the key factor which conditions the prosthesis success or failure. The aim of this work is to generate a chemically modified surface of two commercial magnesium alloys with a 58S and 68S sol-gel made glass coating, obtained from organic precursors such as silicon and phosphate alkoxides and calcium lactate. The produced bioactive layer is sintered at low temperatures in order to maintain the substrate integrity. The glassy coating composition belongs to the SiO2-P2O5-CaO system and has the double goal of promote bone healing and retard the hydrogen evolution coming from the anodic reaction. AZ31B (Al 3%, Zn 1%, Mn 0.2%) and AZ91D (Al 9%, Zn 1%, Fe 0.005%, Mn 0.33%, Ni 0.002%) were used as substrates. Plane samples were polished until 2500 grit SiC paper and cleaned prior to coat. 58S and 68S glasses (60/70 mol% SiO2, 36/26 mol% CaO, 4/4 mol% P2O5, respectively) was prepared by sol-gel method using tetramethyl orthosilicate, methyltriethoxysilane, triethyl phosphite and calcium L-lactate hydrate as precursors, HNO31N was used as catalyser, ethylene glycol to improve the alkoxide condensation degree and methanol dissolve the calcium lactate. Micro-Raman assays were performed to analyze deposits composition (Invia Reflex Confocal, Renishaw RM 2000, UK) with a 785 nm wavelength laser. X-ray photoelectron spectroscopy (XPS) was selected to perform an elemental analysis of surfaces prior and after immersion of 72 h in HBSS. Measurements were made using a commercial VG ESCA 3000 system, using Mg Kα (1253.6 eV) radiation and an overall energy resolution of 0.8 eV. High resolution scans with 0.1 eV steps were conducted over Mg 2p, Ca 2p, P 2p, Si 2p and O 1s. In the entire cases surface charging effects were compensated by referencing the binding energy (BE) to the C 1s line of residual carbon set at 284.5 eV. Coatings visual integrity and deposits produced during immersion tests were examined by scanning electronic microscopy (SEM, JEOL JSM-6460LV, Japan) prior to immersion and after 24 h. Electrochemical assays were performed in a GAMRY Ref 600 electrochemical unit (Gamry, USA) with a conventional three electrode cell, using a saturated calomel electrode (SCE, Radiometer Copenhagen) as reference electrode, a platinum wire as a counter electrode and the coated and bare magnesium alloys as working electrodes. Electrochemical impedance spectroscopy (EIS) tests were registered also at the Ecorr with amplitude of 0.01V rms sweeping frequencies from 20000 to 0.005 Hz. Polarization curves for each sample were also recorded with an initial and final voltage of -1.8V (vs. reference) and 1 mV/s of scan rate. Hank Buffered Salt Solution (HBSS) at 37 ºC was used as electrolyte. Electrochemical test show that the coatings are able to retard anodic reaction being more efficiently on AZ91 alloy. Regarding the compositions, the coating with less calcium content (68S) is able to form more continuous films that the 58S with higher corrosion resistance after immersion in HBSS (Figure 1). Both coatings show signs of deposit of hydroxyapatite related compounds after immersion, as a first sign of bioactivity in vitro. Figure 1

Magnetoelastic sensors with hybrid films for bacteria detection in milk

Currently the detection of bacteria in food needs to be quick and accurate to avoid health problems. An alternative to enable the rapid detection of microorganisms in food is the use of magnetoelastic sensors. These sensors allow the detection and quantitation of bacteria via sensor mass variation. In addition to speed and simplicity, the great advantage is remote sensing, without the use of direct physical connections (wireless monitoring). The objective of this research is to develop a sensor for the detection of bacteria in milk using a magnetoelastic alloy (Metglas 2826MB3) coated with a hybrid film based on silicon alkoxide precursors (TEOS and MAP) without the use of antibodies. Resonance frequency variation were measured and the sensor responded to mass variation and allowed the detection of the presence of bacteria (Escherichia coli and Staphylococcus aureus) in different concentrations, with the sensor remaining intact throughout the test period.

Oxidation-Resistant Nano-Reinforced PC-Refractories of Modified Phenolformaldehyde Resin. Part 3. Formation Mechanism of Organic – Inorganic Complexes During Low-Temperature Synthesis of Nanoparticles of Additional Antioxidants and Their Effectiveness1

SiC nanoparticles that could be used as an antioxidant for periclase-carbon (PC) refractories were synthesized from the organic—inorganic complex (–CH3)–(SiO2) n that formed during heating of silicon alkoxide and thermal destruction of its gels. Use of phenolformaldehyde resins modified with silicon alkoxide and its sols was proposed and enabled the formation of an organic—inorganic complex (–CH3)–(SiO) n –C with a high C content. This increased the yield of SiC synthesized in the carbon binder. The addition of Ni precursors (additional antioxidant) formed an even more complicated organic—inorganic complex. Use of the complex (–CH3)–(SiO2) n –Ni(NiO)–C together with Al improved the operating characteristics of the PC refractories. It was found that their resistance to oxidation was increased after the complex antioxidant Al + SiC + Ni(NiO) formed.

Borosiloxane boron diffusion for p-emitter formation on n-type silicon wafers

Thermal boron diffusion, which forms highly doped and shallow p-emitters on phosphor-doped silicon wafers, is one of the primary processes in commercial-scale production of n-type cells. Here, we report on the use of nontoxic and nonvolatile borosiloxane sols as the spin-on boron source. In comparison to the tribromide (BBr3) boron diffusion that is applied in the production of most commercial n-type cells, borosiloxane boron diffusion may have potential advantages in terms of cost, safety, operability, etc. The borosiloxane sols studied here were formed from a cross-linking reaction between boron acid and a mixture of two types of silicon alkoxides, methyltriethoxysilane (MTEOS) and dimethyldiethoxysilane (DMDEOS). The MTEOS/DMDEOS ratio was found to be the key factor determining the synthetic period, net structure, thermal transformation property, and coating behavior of the borosiloxane sols. In combination with the spin-coating method, the performance of borosiloxane boron diffusion into phosphor-doped silicon wafers (1–3 Ω·cm) was systematically investigated by varying the borosiloxane composition (boron/silicon or MTEOS/DMDEOS ratio) and the diffusion process parameters (temperature, ambience, and period of individual sub-steps), and by relating them to the resulting sheet resistance and boron doping profile. The results show that under the diffusion conditions in conventional cell production lines, the formed p-emitters can have variable sheet resistance in the range of 35–582 Ω/□ and boron doping depth of 100–300 nm.

Improving Waterproof Property of Gypsum Block with Organic-Inorganic Compound Materials

Gypsum block, an important construction material, has the shortcoming of poor water resistance, which limits the development and applications. In this paper, this problem was solved by combined use of silicone (methyl silicon alkoxide) and inorganic material such as cement, manganese slag powder. Orthogonal experiment was used to optimize the proportioning of gypsum block. The appropriate material proportion was obtained: gypsum 66.7%, cement 8.3%, manganese slag powder 25% and methyl silicon alkoxide 0.083%. In this case, the softening efficient was up to 0.76.

Self-catalytic Synthesis of ZnO Nanoparticles@SiO2 Composites with Controllable Fluorescence

ZnO nanoparticles@SiO2 (ZnO NPs@SiO2) composites have been prepared by a self-catalytic approach in a water–ethanol solution at near neutral conditions. A multifunctional precursor combining not only a silicon alkoxide and a metal carboxylate group, but also a protonated amine group was designed. The intramolecular protonated amine groups could act as catalytic sites for the hydrolysis and condensation of silicon alkoxides. Thus self-catalytic reactions would proceed spontaneously without the addition of any other catalyst. By adjusting the manner of adding the silica source, ZnO NPs with an average diameter of 2.61, 4.00, and 5.72 nm for ZnO NPs@SiO2 composites could be controllably synthesized. Accordingly, the different ZnO NPs@SiO2 composites displayed blue, green, and yellow three emission under ultraviolet light.

Oxidation-Resistant Nano-Reinforced PC-refractories of Modified Phenolformaldehyde Resin. Part 2. Modification of Phenolformaldehyde Resins with Silicon Alkoxide Sols1

Coking of phenolformaldehyde resins (PFRs) modified with various silicon-alkoxide sols produced structurally varied carbon binders with cavities filled by entrained sols, depending on the structures of the silicon-alkoxide hydrolysis products. The physicomechanical properties improved if PFRs modified with silicon-alkoxide sols were used. Sols with the stoichiometric amount of water hydrolyzed the silicon alkoxide more effectively.

Effect of sol–gel layers obtained from GLYMO/MTES mixtures on the delamination of a cataphoretic paint on AA1050

In this study, the performance of different sol–gel layers produced from different mixtures of silicon alkoxides precursors (γ-glycidoxypropyltrimethoxysilane, GLYMO, and methyltriethoxysilane, MTES) applied on AA1050 aluminum alloy as a pretreatment prior to depositing an electrophoretic paint (polyether–polyamine polymeric blend) is investigated. The structure of the sol–gel coatings was characterized by means of ATR FTIR, while the corrosion protection properties were assessed by polarization curves. Accelerated laboratory tests, such as exposure in both neutral and acetic salt spray chambers and filiform corrosion tests, were employed to investigate the corrosion protection properties of the cataphoretic paint-coated samples. The failure mechanisms of the different coatings were investigated. The experiments revealed that the presence of GLYMO in the sol–gel coating seems not to be suitable for acting as a coupling agent between the paint and the aluminum substrate. On a positive note, this work shows that the filiform corrosion test seems to be the most appropriate test to evaluate the efficiency of sol–gel layers employed as pretreatment to enhance the corrosion protection provided by a paint on an aluminum substrate.

Oxidation-resistance nanoreinforced periclasecarbonaceous (PC) refractories based on the modified phenol-formaldehyde resin. Part 3. Evolution of the organic-inorganic complexes development for the low-temperature synthesis of additional anti-oxidizing nanoparticles and their efficiency

It was shown that the organic-inorganic complex (‒СН3)‒(SiO2)n which appears in the course of the silicon alkoxide heating and of the thermal destruction of its gels can be used at low temperature to synthesize SiC nanoparticles which can be available as an anti-oxidant for the PC-refractories. It was proposed to use the phenol-formaldehyde resin (PFR) modified by the silicon alkoxide and by its gels which will allow to create organic-inorganic complex (‒СН3)‒(SiO2)n with large carbon content. This will increase the SiC synthesizing on base of the carbon bond. The Ni precursor introducing (which is the additional anti-oxidant) creates even more complicated organic-inorganic complex. The using of the (‒СН3)‒(SiO2)n‒Ni(NiO)‒С together with Al improves the PC-refractories service performance. It was established that with the complex anti-oxidant Al + SiC + Ni(NiO) the oxidation resistance of these refractories increases. Ill. 7. Ref. 27.

Colloidal synthesis of silicon nanoparticles in molten salts.

Silicon nanoparticles are unique materials with applications in a variety of fields, from electronics to catalysis and biomedical uses. Despite technological advancements in nanofabrication, the development of a simple and inexpensive route for the synthesis of homogeneous silicon nanoparticles remains highly challenging. Herein, we describe a new, simple and inexpensive colloidal synthetic method for the preparation, under normal pressure and mild temperature conditions, of relatively homogeneous spherical silicon nanoparticles of either ca. 4 or 6 nm diameter. The key features of this method are the selection of a eutectic salt mixture as a solvent, the identification of appropriate silicon alkoxide precursors, and the unconventional use of alkali earth metals as shape-controlling agents.