Polymeric sols

Either particulate sol or polymeric sol has been used for thin film coatings. The polymeric sol was fabricated by partial hydrolysis of corresponding metal alkoxide. If the rate of hydrolysis or condensation is very fast, then some kinds of organic acids, beta-dicarbonyls, and alkanolamines have been used as chelating agent in sol-gel processes to control the extent and direction of the hydrolysis-condensation reaction by forming a strong complex with alkoxide. [2]. 

According to Ref. [12], template for synthesis of nanomaterials is defined as a central structure within which a network forms in such a way that removal of this template creates a filled cavity with morphological or stereochemical features related to those of the template. The template synthesis was applied for preparation of various nanostructures inside different three-dimensional nanoporous structures. Chemically, these materials are presented by polymers, metals, oxides, carbides and other substances. Synthetic methods include electrochemical deposition, electroless deposition, chemical polymerization, sol-gel deposition and chemical vapor deposition. These works were reviewed in Refs. [12,20]. An essential feature of this... 

Schwartz, R. W. Payne, D. A. Holland, A. J. 1989. The effects of hydrolysis and catalysis conditions on the surface area and decomposition behavior of polymeric sol-gel derived PbTi03 powders. In Ceramic Powder Processing Science, edited by Hausner, H. Messing, G. W. Hirano, S. Deutsche Keramische Gesellschaft. pp. 165-172. 

Characteristic microstructural properties of TiOj membranes produced in this way are given in Table 2.5. Mean pore diameters of 4-5 nm were obtained after heat treatment at T < 500°C. The pore size distribution was narrow in this case and the particle size in the membrane layer was about 5 nm. Anderson et al. (1988) discuss sol/gel chemistry and the formation of nonsupported titania membranes using the colloidal suspension synthesis of the type mentioned above. The particle size in the colloidal dispersion increased with the H/Ti ratio from 80 nm (H /Ti = 0.4, minimum gelling volume) to 140 nm (H /Ti " — 1.0). The membranes, thus prepared, had microstructural characteristics similar to those reported in Table 2.5 and are composed mainly of 20 nm anatase particles. Considerable problems were encountered in membrane synthesis with the polymeric gel route. Anderson et al. (1988) report that clear polymeric sols without precipitates could be produced using initial water concentrations up to 16 mole per mole Ti. Transparent gels could be obtained only when the molar ratio of H2O to Ti is < 4. Gels with up to 12 wt.% T1O2 could be produced provided a low pH is used (H /Ti + < 0.025). 

In the polymeric sol-gel process, partial hydrolysis of a metal alkoxide dissolved in alcohol is accomplished by adding the minimum of water to the solution. The active hydroxyl groups on the alkoxides then react to form an inorganic polymer molecule that can then be coated onto the ceramic support. On drying and sintering, the metal oxide film forms. Chemically the polymeric sol-gel process can be represented as ... 

Dezanneau et al. reported Lai cMn03+a nanocrystalline powders prepared by an acylamide polymerization sol-gel method (Dezanneau et al., 2002a,b, 2003). The composition analysis revealed that for La/ Mn < 0.9 the Mna04 phase was present, while for La/Mn > 0.9, the high oxygen excess led to considerable vancancies on cationic sites. The Curie temperature remained constant at 295 K for the former case, while decreased Curie temperatures were observed for the latter case, due to the increasing amoimt of Mn vacancies. 

Fig. 7.3. Influence of cluster structures in polymeric sols on the porosity of coated layers (a) packing of interpenetrated low branched clusters (b) packing of non-in terpenetra ted highly branched clusters.

A quite different approach from that of colloidal sols in the preparation of sol-gel derived membranes utilizes polymeric sols. In this category of sols the dispersed phase results from the hydrolysis and condensation of metal organic precursors in organic media. In most cases this process deals with the polymerization of metal alkoxides in alcohol according to the following reactions ... 

In the same way as that already mentioned for polymeric sols, nanoparticulate sols were synthesized by Yamaki et al. [65] for the modification of a... 

Fig. 7.9. Schematic representation of the influence of added non-ionic surfactants on cluster growth in a TEOS derived polymeric sol. (a) TEOS alcoholic solution (b) TEOS standard sol (c) aged sol in the presence of surfactant (d) aged sol without surfactant [65].

Composition of standard silica polymeric sol. The figures in parenthesis give the ratios X(reac-tant)/TEOS as defined by rw, raicohoi and ra... 

Fig. 8.25. Synthesis scheme of polymeric silica and of binary polymeric sols by single step and two step hydrolysis. From de Lange et al. [43,44].

The aim of this contribution is to present data on the preparation of catalysts containing as embedding species a large family of eolloids such as colloids of ruthenium, platinum, or palladium-gold alloys and triflate derivatives such as lanthanum and silver triflate or tert-butyldimethylsilyltrifluoromethanesulfonate (BMSTM). Silica, zirconia and tantalum oxides were used as carrier. All these preparations considered the polymeric sol-gel route using as starting materials silicon, zirconium or tantalum alcoxides. 

An electrochemical method projected for the determination of the effective volume of a colloidally dispersed polyelec-trolyte phase in aqueous media was evaluated. Experiments with the highly flexible Sephadex (carboxymethyldextran) gel and the more rigidly cross-linked polymethacrylic acid resin were performed for this purpose. With the well-defined resin (gel) phase it was possible to measure the polymer volume as a function of every experimental condition used to test fully the fundamental concepts on which the method is based. The results substantiate the validity of concepts developed. Application of this method for estimating the effective volume of weakly acidic (basic) polymers in solution seems worthy of further consideration. However, some modification of the treatment of the electrochemical data is necessary for polymeric sols, and this aspect is discussed briefly. 

Sol-gel process is proven to be an attractive fabrication method of multi-component oxide ceramics. In addition to the achieved homogeneity and purity of the products, the sol-gel method also enables a lower phase-formation and sintering temperature in comparison to the conventional sintering of powder With good size scaling possibility, colloidal sol-gel materials are suitable for depositing layers on macroporous substrates to serve as support of polymeric sol-gel derived layers preventing infiltration of the sol. 

The XRD pattern of the calcined 8YSZ powder obtained by polymeric sol-gel route is shown in Figure 1, indicating the powder with a pure cubic structure . Average domain (r) of the powder was estimated by Scherrer equation" ... 

Figure 2. Various YSZ sols with graded particle size distributions (a) colloidal sol with dso of 120 nm, (b) colloidal sol with dso of 40 nm, (c) polymeric sol with djo of 7 nm.

The polymeric sol showed very good layer forming behaviour on the simered electrolyte intermediate support layers and a transparent layer of 150nm in thickness was fabricated on intermediate layer after the thermal treatment at 600 "C for 2 hours (Figure 3b, c). However, the top layers did not sustain a thermal treatment higher than 700 "C and large pores were formed on the surface of the electrolyte (Figure 3d). 

The helium leakage value was tested on the half cells in the oxidized state before the coating of cathode. Helium is suitable to be used as the test gas because its molecular is smaller than all the gases under the operation condition of SOFC cells. The helium flowed through the half cell at a pressure difference of 1000 hPa. The shown values in this test were normalised to the measurement area and to a pressure difference of 100 hPa, which was typical for an SOFC stack. One large squared area of 16cm was measured per cell. The leak rate value of samples without polymeric sol-gel layers was around 5-10" (hPa dmV(s cm ). By applying a polymeric sol-gel layer on top of the colloidal-sol-derived intermediate layers, the leak rate value of samples was improved to 1.5-10 (hPa dm ( s cm ). 

The only peak at 254.5 °C observed in the as-received nanoparticles, as shown in Figure 12.5(b), is due to the decomposition of the iron oxide-hydroxide (goethite, FeOOH as proved by theFT-IR spectra) [31,76]. Similar to the TGA observation, a higher decomposition temperature (308.0 °C) was observed in PPy formed with the aid of nanoparticles than that of pure PPy formed without them (298.4 °C). Whereas only one peak was observed in the pure PPy samples, two exothermic peaks were observed in the DTA curves of the nanocomposites. These were due to the decomposition of PPy at 307 °C and the possible phase transition of iron oxide at 480 °C, as reported for the Fc203/PPy nanocomposites fabricated by the simultaneous gelation and polymerization (sol-gel) method [77,78] respectively. As compared with no obvious phase transition in the pure iron oxide nanoparticles, the observed phase transition was due to the intermediate product of PPy [77,78]. 

This work reports the development of a polymeric/sol-gel route for the deposition of silicon carbide and silicon oxycarbide thin films for applications such as heat-, corrosion-, and wear-resistant coatings, coatings on fibers for controlling the interaction with the matrix in ceramic matrix composites, or films in electronic and optoelectronic devices. This method, in which the pre-ceramic films are converted to a ceramic coating either by a conventional high temperature annealing or by ion irradiation, is alternative to conventional methods such as chemical or physical vapor deposition (CVD, PVD), molecular beam epitaxy, sputtering, plasma spray, or laser ablation, which are not always practical or cost efficient. 

Chem. Descrip. Silicone-free polymeric sol n. in Stodybutylglycolate/2-butoxyethanol (71/8/1)... 

Chem. Descrip. Silicone-free polymeric sol n. with 84%. It. aromatic naphtha (CAS 64742-95-6), 6%. 1-methoxy-2-propanol acetate Uses Defoamer, air release agent for unsat. polyester laminating, spray-up, hand lay-up molding, gel coats, soiv.-free epoxy flooring systems, coatings... 

---