Parallel And Series Spring Equations

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Sol Gel Process - an overview | ScienceDirect Topics

Sol Gel Process The sol–gel process is a wet chemical technique also known as chemical solution deposition, and involves several steps, in the following chronological order: hydrolysis and polycondensation, gelation, aging, drying, densification, and crystallization. From: Nanobiomaterials in Hard Tissue Engineering, 2016 Related terms: Hydrolysis, Glass, Oxide, Nanoparticle, Catalyst, Gel, Porosity, Fiber, Metal View full index

Novel approaches for preparation of nanoparticles Bolla G. Rao, ... Benjaram M. Reddy, in Nanostructures for Novel Therapy, 2017

2.2 Sol–Gel Method Sol–gel method is one of the well-established synthetic approaches to prepare novel metal oxide NPs as well as mixed oxide composites. This method has potential control over the textural and surface properties of the materials. Sol–gel method mainly undergoes in few steps to deliver the final metal oxide protocols and those are hydrolysis, condensation, and drying process. The formation of metal oxide involves different consecutive steps, initially the corresponding metal precursor undergoes rapid hydrolysis to produce the metal hydroxide solution, followed by immediate condensation which leads to the formation of three-dimensional gels. Afterward, obtained gel is subjected to drying process, and the resulting product is readily converted to Xerogel or Aerogel based on the mode of drying. Sol–gel method can be classified into two routes, such as aqueous sol–gel and nonaqueous sol–gel method depending on the nature of the solvent utilized. If water is used as reaction medium it is known as aqueous sol–gel method; and use of organic solvent as reaction medium for sol–gel process is termed as nonaqueous sol–gel route. The reaction pathway for the production of metal oxide nanostructures in the sol–gel method is shown in Fig. 1.5. In the sol–gel approach, nature of metal precursor and solvent plays a remarkable role in the synthesis of metal oxides NPs.

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Sign in to download full-size image Figure 1.5. The Reaction Pathway for the Production of Metal Oxide Nanostructures in the Sol–Gel Method

2.2.1 Aqueous sol–gel method In aqueous sol–gel method, oxygen is necessary for the formation of metal oxide, which is supplied by the water solvent. Generally, metal acetates, nitrates, sulfates, chlorides, and metal alkoxides are employed as the metal precursors for this method. However, metal alkoxides are widely used as the precursors for the production of metal oxide NPs, due to high reaction affinity of alkoxides toward water (Bradley et al., 2001; Turova and Turevskaya, 2002). However, some difficulties are associated with the aqueous sol–gel method. The key steps, such as hydrolysis, condensation, and drying take place simultaneously in a number of cases resulting in difficulty in controlling particle morphology, and reproducibility of the final protocol during the sol–gel process (Corriu and Leclercq, 1996). The aforementioned difficulties, however, do not affect much of the synthesis of metal oxides in bulk, but strongly affect the preparation of nanooxides. Therefore, it is believed that the aqueous sol–gel route is highly recommended for the synthesis of bulk metal oxides rather than their nanoscale counterparts (Niederberger, 2007).

2.2.2 Nonaqueous sol–gel method Nonaqueous or nonhydrolytic sol–gel method is devoid of some of the major drawbacks found in aqueous sol–gel method. In nonaqueous sol–gel process, oxygen required for the formation of metal oxide is supplied from the solvents, such as alcohols, ketones, aldehydes, or by the metal precursors. Furthermore, these organic solvents not only serve as oxygen providers but also offer a versatile tool for tuning several key components like morphology, surface properties, particle size, and composition of the final oxide material. Although, nonaqueous sol–gel approach is not as popular as aqueous sol–gel method; nonaqueous sol–gel routes have shown excellent impact on the production of nanooxides compared to that of aqueous sol–gel route. The nonaqueous sol–gel route can be divided into two important methodologies, namely, surfactant-controlled and solvent-controlled approaches for the production of metal oxide NPs. Surfactant-controlled strategy involves direct transformation of metal precursor into the respective metal oxide at higher temperature range in hot injection method. This method permits outstanding control over the shape, growth of the NP, and avoids the agglomeration of particles. Few examples of surfactant-controlled synthesized NPs are mentioned here for understanding. Song and Zhang (2004) have demonstrated the simple nonhydrolytic route to synthesize high-quality spherical-shaped CoFe2O4 NPs with 8-nm size. However, the spherical morphology can be

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changed to cubic shape with 10-nm edge length during the seed-mediated growth. Heating rate and growth temperature played a pivotal role in controlling the shape of CoFe2O4 nanomaterial (Fig. 1.6A–B).

Sign in to download full-size image Figure 1.6. TEM images of (A) 8-nm sized spherical CoFe2O4 NPs and (B) cube-like CoFe2O4 NPs. TEM images of (C) cube-like and (D) polyhedronshaped MnFe2O4NPs. (E) TEM image of MnO multipods (inset, hexapod). (F) TEM image of Tungsten oxide nanorods. Part (A–B): Reproduced from Song, Q., Zhang, Z.J., 2004. Shape control and associated magnetic properties of spinel cobalt ferrite nanocrystals. J. Am. Chem. Soc. 126, 6164–6168. Copyright 2004, American Chemical Society. Part (C–D): Reprinted from Zeng, H., Rice, P.M., Wang, S.X., Sun, S.H., 2004. Shape-controlled synthesis and shape-induced texture of MnFe2O4 nanoparticles. J. Am. Chem. Soc. 126, 11458–11459. Copyright 2004, American Chemical Society. Part (E): Reproduced from Zitoun, D., Pinna, N., Frolet, N., Belin, C., 2005. Single crystal manganese oxide multipods by oriented attachment. J. Am. Chem. Soc. 127, 15034–15035. Copyright 2005, American Chemical Society. Part (F): Reproduced from Seo, J.-W., Jun, Y.W., Ko, S.J., Cheon, J., 2005. In situ one-pot synthesis of 1-dimensional transition metal oxide nanocrystals. J. Phys. Chem. B. 109, 5389–5391. Copyright 2005, American Chemical Society.

The resulting materials were subjected to shape-dependent magnetic properties. Zeng et al. (2004) have extensively studied the shape-controlled synthesis of MnFe2O4 nanomaterial. The relative ratio between surfactant and Fe(acac)3 showed a remarkable role in controlling the final morphology of MnFe2O4. TEM analysis revealed the formation of cube-like or polyhedron-type morphology for MnFe2O4 (Fig. 1.6C–D). In addition, size of MnFe2O4 particle is dependent on the concentration of metal precursors. Novel cone-shaped ZnO was obtained by decomposition of TOPO–Zn(OAc)2 complex resulting in the formation of hierarchically ordered spheres of cone-shaped ZnO nanocrystals (Joo et al., 2005). Li et al. (2006) fabricated titanium oxide nanorods with 3.3-nm diameter and a length of 25 nm using appropriate amounts of reaction ingredients, such as titanium butoxide, triethylamine, linoleic acid, and cyclohexane. Reaction temperature, time, and concentration of the reactant were found to show huge effect on the shape and size of the TiONPs. Preparation of high-quality single crystalline MnO multipods with homogeneous size and shape, involved decomposition of Mn(oleate)2 in the presence of oleic acid and n-trioctylamine (Fig. 1.6E) (Zitoun et al., 2005). Tungsten oxide nanorods were generated by treatment of WCl4 with oleylamine and oleic acid (Fig. 1.6F) (Seo et al., 2005). Solvent-controlled sol–gel route, involves the reaction between metal halide and alcohols to produce metal oxide nanostructures. For example, porous SnO2 NPs were prepared by the addition of tin chloride to benzylalcohol under https://www.sciencedirect.com/topics/chemistry/sol-gel-process

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stirring condition, which was immediately dispersed in THF solution, producing sol. The subsequent addition of block polymer to sol allowed mesoporous nanostructure for SnO2 by the elimination of solvent molecule (Ba et al., 2005).

Preparation of Catalysts VII L. Baraket, A. Ghorbel, in Studies in Surface Science and Catalysis, 1998

Introduction Sol-gel process provides a new approach to the preparation of new materials. This process allows a better control of the whole reactions involved during the synthesis of solids. Homogenous multi-component systems can be easily obtained, particulary homogenous mixed oxides can be prepared by mixing the molecular precursors solutions (1). The chemistry of the sol-gel process is based on hydrolysis and polycondensation reactions. Metal alcoxides [M(OR)3] are versatile molecular used to obtain oxides, on account of their ability to form homogeneous solution in large variety of solvents and in the presence of other alcoxides or metallic derivatives and also for their reactivity toward nucleophilic reagents such as water (2). The essential aim for the most investigations reported was the final product and its applications without interested to the synthesis conditions and reactionnel mechanism involved to obtain gels, although the properties of a gel and its behaviour on heat treatment could be very sensitive to the structure already created during the sol stage. Therefore, the formation of colloidal aggregates determines the main properties of resulting powder. By varing the chemical conditions under which materials is polymerized, the structure and the morphology of samples formed are drastically affected. However, many earlier investigations try to developp a good understanding of gelification phenomenon.The purpose of this work is to better understand the chemistry involved during the preparation of mixed oxides by Sol-gel process, in order to have a good control of the properties of the final material.

Preparation of Catalysts VII Hongbin Zhao, ... G.V. Baron, in Studies in Surface Science and Catalysis, 1998

ABSTRACT The sol–gel method has been explored to prepare a catalytic membrane. Photocorrelation spectroscopy, nitrogen adsorption, scanning electron microscopy (SEM), scanning electron microscopy wave dispersive X-ray analysis (SEMWDX), and gas permeation measurement were used to characterize the preparation of the catalytic membrane. In the sol–gel process, the noble metal ion-modified boehmite sols were produced by adsorption of the noble metal complexes at the liquid/solid interface of the boehmite sol particles. The thickness of the catalytic membrane was increased by a multiple sol–gel process. It was confirmed that the distribution of the catalytst precursors exhibited a uniformity in the direction of the thickness of as well as along the surface of the catalytic membrane. The gas permeation measurement showed that the catalytic membrane prepared had a good thermostability.

Sol–Gel Process and Applications Sumio Sakka, in Handbook of Advanced Ceramics (Second Edition), 2013

2.3 Reaction for Nonsilica Oxides Sol–gel method is useful for fabrication of functional materials, such as photocatalyst, nonlinear optical materials, ferroelectrics, and superconductors. For this purpose, sol–gel preparation of simple and complex nonsilica oxides, including TiO2, ZrO2, Al2O3, ZnO, WO3, Nb2O5, rare earth oxides, and so on, have to be studied. Metal alkoxides are often employed for those oxides. Most of them, however, are unstable, that is, they are rapidly hydrolyzed and are easily precipitated, which makes it difficult to form homogeneous multicomponent oxide products. Methods of controlling reactivity of the transition metal alkoxides are introduced below. https://www.sciencedirect.com/topics/chemistry/sol-gel-process

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Preparation of Catalysts VII E.L. Sham, ... E.M. Farfán-Torres, in Studies in Surface Science and Catalysis, 1998

1 INTRODUCTION Sol–gel methods have been used by different authors working on catalysts preparation (1). The advantages of the applications of these methods to the design of catalytic materials have been already described in the literature (1,2). Catalysts based on supported vanadium oxide are frequently used in selective oxidation reactions due to their considerable activity for the oxidation of aromatics, alkanes, and alcohols (3–5). Differences in their catalytic behaviour are generally explaines on the basis of the nature and distribution of vanadium species, which are influenced by the vanadium loading, the preparation procedure and the acid–base character of the support (6–9). The interaction of vanadia with silica and the structure of the VOx units on the support have been studied by a number of investigators (5,7,9–17). It has been observed that in general highly dispersed monomeric surface vanadia species were found on silica-supported catalyst with very low loadings of vanadia (7,12–13). Crystalline V2O5 has been detected on catalysts well bellow the so-called “monolayer” coverage as the vanadium loading was increased . The formation of crystalline V2O5 in the V2O5/SiO2 system reflects the weaker interaction of vanadium oxide with the SiO2 supports relative to others like Al2O3 and TiO2 (5,14,18). To obtain a catalyst with V-SiO2 interactions stronger than those developed in impregnations solids we have studied the preparation of these materials by means of the sol–gel process. Neuman et al. have previously prepared amorphous metallosilicalite xerogels by the sol–gel method using metal alkoxides precursors (4). This work have shown that vanadium silicate xerogel are active catalysts for the activation of aqueous hydrogen peroxide for a variety of reactions including epoxidation of alquenes, oxidation of secondary alcohols to ketones and the hydroxylation of phenol. In the present work we report the obtention of VOx-SiO2 catalyst from vanadium acetyl acetonate and tetraethoxysilane. These catalysts were characterized and evaluated in the oxidative dehydrogenation of n-butane.

Sol-Gel Synthesis of Metal Nanoparticle Incorporated Oxide Films on Glass A. Mitra, G. De, in Glass Nanocomposites, 2016

6.3.5 Inorganic-Organic Hybrid Hosts Sol-gel process is also used for synthesis of metal NPs doped inorganic-organic hybrid films such as organically modified silica (ORMOSIL). In this case, organically modified metal alkoxides (e.g., 3-(glycidoxypropyl) trimethoxysilane, GLYMO) are co-hydrolyzed with different alkoxides. Later on, UV or thermal curing induces organic polymerization leading to the formation of ORMOSILs. These hybrid materials exhibit composite hybrid microstructures and can also be easily molded as unsupported thin transparent films [80–82]. The curing temperature applied during post film fabrication should not be high to maintain the hybrid inorganic-organic structure. The curing technique can have significant role in governing the size of metal NPs inside host matrices. Figure 6.9 shows one such case in which Au NPs were synthesized inside SiO2-TiO 2-polyethyleneoxide hybrid films coated on extra dense flint glass substrates by using UV light of different energies [28]. The refractive index of the matrix can be increased by increasing the UV curing energy. A gradual shifting of Au-SPR (Figure 6.9a) was explained due to the increase of refractive index of the matrix and plasmon coupling of the densely populated Au NPs as observed in the two representative TEM images (Figure 6.9b and c) [28].

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Sign in to download full-size image Figure 6.9. (a) Absorption spectra of Au NPs doped hybrid SiO2-TiO 2-polyethylene oxide films coated on extra dense flint glass substrates after UV curing with different energies. (b) and (c) Representative TEM images of the films cured with UV energy 5.3 ± 0.1 J cm− 2 (film color: red) and 53.0 ± 0.1 J cm− 2 (film color: purple), respectively. Histograms of Au NPs embedded in the films are presented in the respective insets of (b) and (c). In (c) a marked area (A) is highlighted to show the growth of few larger particles through coalescence of smaller ones. Reproduced with permission from Ref. [28], Copyright © American Chemical Society.

Corrosion Protective Coatings for Ti and Ti Alloys Used for Biomedical Implants Liana Maria Muresan, in Intelligent Coatings for Corrosion Control, 2015

17.3 Sol-Gel Method Sol-gel process is a method for producing solid materials from small molecules that is suitable for preparing different coatings (e.g., silicium and titanium oxides) on the surface of Ti-based materials. It involves conversion of small molecules (precursors) into a colloidal solution (sol) and then into an integrated network (gel) consisting of either discrete particles or network polymers. The main advantages of the sol-gel method are18: (1) low processing temperature (avoiding volatilization of entrapped species), (2) the possibility to cast coatings in complex shapes, and (3) the use of compounds that do not introduce impurities into the end product. Among the disadvantages of this method one can count the relatively long period of time for processing flow and the difficulties related to phase separation occurring especially in hybrid coating synthesis. The sol-gel process involves four stages: (1) hydrolysis, (2) condensation/polymerization of monomers, (3) growth of particles, and (4) gel formation.18 These processes are influenced by several experimental parameters such as pH, temperature, concentration of the reactants, and presence of additives. https://www.sciencedirect.com/topics/chemistry/sol-gel-process

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Traditional precursors for sol-gel coatings are alkoxysilanes such as tetraethyl orthosilicate (TEOS) and tetramethyl orthosilicate (TMOS), but efforts are made in order to find less toxic and more environmental friendly precursors. TiO2 can be prepared, for example, starting from precursor solutions containing an alkoxide (e.g., tetrabutylorthotitanate) and diethanolamine dissolved in ethanol16 and mixing them with water (with or without additives) in a certain ratio. SiO2 coatings can be prepared starting from a precursor solution consisting of tetraethylorthosilicate Si(OC2H5)4, H2O, C2H5OH, and HCl, mixed at a certain molar ratio.19 Different compounds (inhibitors, pigments, etc.) can be added in order to improve the physicochemical properties of the coating. Irrespective of the nature of the film, the two main techniques used to apply a sol-gel coating on the surface of a metallic substrate are dip-coating and spin-coating.

17.3.1 Dip-coating By this technique, the material from which the film is produced is put into solution, and then the substrate is progressively dipped into and is extracted from the solution at a controlled rate (Figure 17.1). After the solvent evaporates, a thin and homogeneous film is produced. The thickness of deposited liquid film coatings depends on the coating solution properties such as density, viscosity, and surface tension, as well as surface withdrawal speed from the coating solution. The thickness of the film is generally bigger than that prepared by spin-coating with the same solutions.

Sign in to download full-size image Figure 17.1. Schematics of a dip-coating process.20

Dip-coating was successfully used, for example, to prepare sol-gel-derived Al2O3 films on γ-TiAl-based alloys,21 porous TiO2 films,16 hydroxyapatite (HA) coatings,22 and SrO-SiO2-TiO 2 on NiTi,23 and so on.

17.3.2 Spin-coating In the case of spin-coating, an amount of solution is placed on the substrate that is rotated at high speed in order to spread the fluid by centrifugal force (Figure 17.2). After the evaporation of the solvent, a thin, homogeneous film is formed. As in the case of dip-coating, final film thickness and other properties will depend on the nature of the sol-gel coating (viscosity, drying rate, surface tension, etc.) and on the parameters chosen for the spin process. Higher spin speeds and longer spin times give birth to thinner films.25 Generally, a moderate spinning speed is recommended. The drying rate should also be slow in order to ensure film uniformity. A supplementary drying step is sometimes necessary after the high-speed spin step to further dry the film without substantially thinning it.

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Sign in to download full-size image Figure 17.2. Schematics of a spin-coating process.24

By using spin-coating, SiO2 films were deposited on Ti-48Al alloy,19 sphene (CaTiSiO3) ceramics on Ti-6Al-4V26 alkoxide-based HA nanocoatings on Ti and Ti-6Al-4V substrates,27 HA28 and HA/polymer coatings on Ti,29 TiO2 on Ti6Al-4V,30 and many others.

Surface Coating Processes H. Mojiri, M. Aliofkhazraei, in Comprehensive Materials Finishing, 2017

3.19.3.4.2 Sol-gel process The sol-gel process is used for manufacturing superhydrophobic surfaces from many types of materials.65–70 In many investigations, due to the presence of materials with low surface energy in the sol-gel process, there is no other hydrophobizing process. For example, Shirtcliff et al.67 produced a porous sol-gel foam of Organo-trithoxysile that shows both superhydrophobic behavior and superhydrophilic behavior when exposed to high temperatures. Shang et al.69 presented a method whereby transparent superhydrophobic surfaces were produced by modifying silicate-based films using fluorinated silanes instead of mixing low-energy materials in sol. In the same case, Wu et al.70 produced a ZnO-based surface in a microstructure using chemical processing; after coating, superhydrophobia was achieved using long-chain alkanoic acids (see Figure 32).

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Sign in to download full-size image Figure 32. Superhydrophobic surfaces produced by sol-gel process. (a) Scanning electron microscope (SEM) image of MTEOS sol-gel foam. Inset pictures show fenol fetalein in water on the sol-gel foam, tempered at 390 °C (left) and 400 °C (right).67 (b) Atomic-force microscopy (AFM) picture of sol-gel film containing 30 wt% silicate colloid. Picture area: 55 µm2. Inset picture shows the chilled water vapor on this film.68

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