Non-aqueous Sol Gel Route Research Articles

Sol–gel preparation of 2CaO·SiO 2

Di-calcium silicate or belite (β-Ca 2SiO 4) is one of the major compounds in Portland cement clinker. Conventionally, belite is produced by long lasting sintering of limestone and quartz at temperatures exceeding 1400 °C. The subject of this paper is the sol–gel synthesis of belite. Both aqueous and non-aqueous sol–gel routes were applied. The preparation of the precursor mixture and the formation of the ceramic product were monitored using TG/DTG, XRD, FT-IR and SEM. The combination of these techniques led to the recording of all the transformations occurring during the processing of the precursors and the formation of the final products. As it was concluded, both routes can be successfully applied for the preparation of di-calcium silicate. The final products consist of very fine spherical crystallites in the range 1–3 μm. Their formation requires a 3-h sintering at 1000 °C. In both cases, β-2CaO·SiO 2 is obtained without the use of any chemical stabilizers.

Nonaqueous and Surfactant-Free Synthesis Routes to Metal Oxide Nanoparticles

Nonaqueous sol–gel routes to metal oxide nanoparticles have become a promising alternative to aqueous methods, allowing the controlled synthesis of a variety of metal oxides as highly crystalline products at comparably low temperatures. The use of solvents like benzyl alcohol that also function as surface modifiers makes the addition of surfactants superfluous, resulting in improved product purity. In addition to a short overview of such nonaqueous routes to binary and ternary metal oxides, the facile synthesis of sodium and potassium niobates as well as of sodium tantalate and barium stannate nanoparticles via straightforward, surfactant-free pathways is reported.

Synthesis and Characterization of Carbon-Coated Lithium Transition Metal Phosphates LiMPO4 (M = Fe , Mn, Co, Ni) Prepared via a Nonaqueous Sol-Gel Route

An organic solvent-based sol-gel method has been utilized for the synthesis of lithium transition metal phosphates. With this simple and versatile method, particles with sub- size and uniform size distribution are obtained for all the (, Mn, Co, Ni) materials investigated. Homogeneous in situ carbon coating of a few weight percent is achieved with all of them, except , where the in situ carbon coating is only 0.6 wt %. The best-performing as-prepared , with in situ surface carbon coating of 1.8 wt %, achieves an electronic conductivity on the order of and exhibits highly promising electrochemical performance, with only slight dependence on the carbon content of the composite electrode in certain range. Carbon-coated samples prepared at lower temperatures exhibit lower electronic conductivity, evidently due to lower specific conductivity of the surface carbon. The dependence of the morphology and electrochemical performance of the synthesized on the precursor concentration and the aging time of the gel is investigated. The results also yield information for understanding of the mechanisms of the sol-gel synthesis process, which are discussed. Electrochemical performance of the carbon-coated and was tested and discussed.

High Refractive Index Films Prepared from Titanium Chloride and Methyl Methacrylate via a Non-Aqueous Sol–Gel Route

Poly(methylmethacrylate)/silica/titania films were prepared via a nonaqueous sol–gel route at ambient temperature, followed by spin-coating and multistep baking. The acrylic monomers used were methyl methacrylate (MMA) and 3-(trimethoxysilyl)propyl methacrylate (MSMA). Silicic acid and titanium(IV) chloride were used as the precursors of the inorganic component. FTIR results indicated the successful bonding between TiO2 and SiO2. TEM images suggested the silica/titania particles were well dispersed in the Poly(methyl methacrylate) (PMMA) matrix with the particles size smaller than 40 nm in our study. The refractive index and extinction coefficient were also studied. The refractive index of the hybrid increased with increasing the titania content, and the hybrid films showed high optical transparency in visible region.

Preparation of Mesoporous Silicon Nitride via a Nonaqueous Sol–Gel Route

A silicon diimide gel Si(NH)x(NH2)y(NMe2)z was prepared by an acid‐catalyzed ammonolysis of tris(dimethylamino)silylamine. Pyrolysis of the gel at 1000°C under NH3 flow led to the formation of an amorphous silicon nitride material without carbon contamination. All of the gel and pyrolyzed products exhibited a mesoporous structure with a high surface area and narrow pore‐size distribution. The effective surface area of the pyrolyzed silicon nitride residues decreases with increasing temperature, but the heating rate during pyrolysis has little influence on the surface area and pore‐size distribution of the final mesoporous ceramic Si3N4 products because of the highly cross‐linked structures of the precursor silicon diimide gel.

Preparation of Mesoporous Si-M Imide Gels (M=B, Al) via a Non-Aqueous Sol-Gel Route

AbstractSilicon-boron and silicon-aluminum imide gels were prepared by catalyzed ammonolyses of the precursors 2,4,6-tris[tris(dimethylamino)silylamino]borazine, {[(CH3)2N]3SiNH}3B3N3H3, 1, 2-(dimethylamino)4,6-di[tris(dimethylamino)silylaminoborazine, {[(CH3)2N]3SiNH}2B3(NMe2)N3H3, 2, and tris(dimethylaminosilylamino)-(tetrahydrofuran)alane, C4H8O)Al[NHSi(NMe2)3]3, 3, respectively. All the gels exhibited mesoporous structures with high surface area.

Preparation of a Silicon Oximide Gel via a Non-Aqueous Sol-Gel Route

AbstractA silicon oximide gel was prepared by a reaction in N,N-dimethylformamide between tris(dimethylamino)silylamine (Me2N)3SiNH2 (TDSA) and formamide in a 1:2 molar ratio at 50C. The 29Si, 13C CP-MAS NMR and IR analyses indicated that the gel mainly comprised oximino silicon networks [SiOC(H)=NSi]x. The gel exhibited a microporous structure and had a total surface area of 339 m2/g. A microporous structure with a BET surface area of 195 m2/g was also obtained after pyrolysis of the gel at 1000°C for 2 h. Pyrolysis of the gel under N2 up to 1485°C gave an amorphous silicon oxycarbonitride glass.

Structure of SnO 2 alcosols and films prepared by sol–gel dip coating

To obtain SnO 2 films to be used for surface protection of fluoride glasses, a non-aqueous sol–gel route for the preparation was developed. An ethanolic SnO 2 colloidal suspension was prepared by thermohydrolysis of SnCl 4 solution at 70°C. By using this procedure, redispersable powders with nanometer sized particles were obtained. Films were obtained by dip coating on glass and mica substrates. The structures of the ethanolic precursor suspension and films were compared to those of similar samples prepared by the classical aqueous sol–gel route. Comparative analyses performed by photon correlation spectroscopy demonstrated that the powders obtained by freeze-drying are fully redispersable either in aqueous or in alcoholic solutions at pH⩾8. As prepared sols and redispersed colloidal suspensions have hydrodynamic radius distribution (2–14 nm) with an average size close to 7 nm. The variations in film structures with firing temperature were investigated by small-angle X-ray scattering and X-ray reflectometry. The experimental results show that the films have a two level porous structure composed of agglomerates of primary colloidal particles. The sintering of the primary particles leads to the densification of agglomerates and to the formation of inter-agglomerate spatially correlated pores. The volume fraction of intra-agglomerate pores is reduced from ≈50% to ≈30% by the precipitation of precursor salts partially hydrolyzed in ethanolic solution.