M. Guglielmi

Structure and properties of sol-gel coatings from methyltriethoxysilane and tetraethoxysilane

Acid catalyzed solutions of methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) were used to obtain bulk materials and silica coatings of about 2 μm, after densification at 500°C. The structural evolution as a function of MTES content and heat treatment was studied.A higher content of MTES was found to enhance the maximum thickness of the coatings free of cracks. Critical thickness and shrinkage of the films were measured. MTES was also found to affect porosity and to play an important role in avoiding fractures in the films.

Further investigations on Raman spectra of silica gel evolving toward glass

Abstract In a previous investigation a continuous evolution of silica gel structure toward that of v-SiO 2 was verified by Raman spectroscopy. Modifications on the intensity of some Raman bands usually associated in the literature to “defects” of the structure were observed. In the present work the study has been extended to the transformation with temperature of silica gels obtained from tetraethoxysilane (TEOS) with different H 2 O/TEOS molar ratios. Raman spectra as well as thermogravimetric data are discussed in terms of the effect of this ratio on the local structure and the sintering process of silica gel.

Optical and surface properties of inorganic and hybrid organic-inorganic silica-titania sol-gel planar waveguides

Inorganic and hybrid organic–inorganic silica (SiO2)–titania (TiO2) planar waveguides, with a relative molar composition 70–30, have been fabricated by sol–gel dip-coating. The composition and the density of the film samples have been measured by Rutherford backscattering spectrometry, nuclear reaction analysis and elastic recoil detection analysis. The measured compositions have been found to agree with the nominal composition of the sols. The film density of the inorganic samples increased with the firing temperature in the range 1.80–2.58. A root mean square roughness (rms) <1 nm was measured on the surface of the samples by atomic force microscopy. A refractive index in the range 1.61–1.54 was measured (λ=632.8 nm). The inorganic waveguides had smaller losses (∼0.3 dB cm−1) compared to the hybrid waveguides (∼1 dB cm−1).

Structural investigations of TiO2SiO2 glassy and glass-ceramic materials prepared by the sol-gel method

Abstract In the present paper we will show by both extended X-ray absorption fine structure (EXAFS) and near-edge (XANES) spectroscopies that the coordination of Ti 4+ ions is only tetrahedral in TiO 2 SiO 2 very homogeneous glasses obtained by the sol-gel method. The coordination of Ti 4+ is also tetrahedral in the essicated gels. An “intermediate” ordered phase, not yet well defined, has been observed at the beginning of the crystallization process. Moreover, the thermal treatment causes a progressive ordering of the T d tetrahedral units going from the essicated gels to the more and more dense glasses. The presence of six-fold Ti-sites has been clearly observed by both EXAFS and near-edge spectroscopies only in a partially crystallized glass containing the highest TiO 2 content (19 wt%), at 1200°C. On the contrary, in all the glasses having the lowest TiO 2 content (4.5 wt%) a four-fold Ti coordination has been observed until 1200°C. The crystalline phase, which appears at high temperatures, is anatase having a crystalline size in the range 50–100 A for thermal treatments in the range 1000–1200°C for the sample richer in TiO 2 . An appearance of crystallinity at higher temperatures for lower TiO 2 concentrations has been observed by X-ray diffraction (XRD) analysis, in agreement with other authors.

Compositional and Microstructural Characterization of RuO2 ‐ TiO2 Catalysts Synthesized by the Sol‐Gel Method

In this study mixtures were prepared from solution using and three different precursors for, , and and tris (2, 4‐pentanedionate) Ru(III). Multi‐layer coatings were deposited by spin coating onto fused silica slides with and without an intermediate, 200 nm thick, vacuum deposited Ti film. Samples heat treated at 200, 300, and 400°C were studied by several techniques (Rutherford backscattering spectrometry (RBS), elastic recoil detection, (ERD), nuclear reaction analysis (NRA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and x‐ray diffraction (XRD) to characterize morphological and compositional changes and to test the reproducibility of the preparation method. In all cases a single crystalline phase, the solid solution of the two component oxides, was detected by XRD. The films appeared to have a low density, and hydrogen and carbon were still found in the coatings after each heat treatment; their content was reduced only at 400°C for samples B and C. The surface of the films displayed increasing percentages of .

Coating of metals by the sol-gel dip-coating method

The sol-gel technique to deposit coatings on metals by dipping was studied. Different metals (Cu, Ni, Fe, Al) were coated with ZrO2, SiO2, TiO2 and B2O3-SiO2 solutions. The influence of some dipping and solution parameters was related with the quality of the obtained coatings. A scale of quality was determined to classify the sol-gel coatings on metals. Both fresh and aged solutions, as-received and abraded substrates were used. The protection against oxidation was evaluated by XRD and by measuring the weight gain upon thermal treatment.

Characterization of laser-densified sol-gel films for the fabrication of planar and strip optical waveguides

Abstract Sol-gel techniques were used to prepare SiO 2 TiO 2 planar and strip optical waveguides. Thermal densification for planar waveguides and laser densification for strip waveguides were performed on films prepared from two different solutions on silica and soda-lime substrates. The resulting waveguides were optically characterized and the optical differences between furnace- and laser-densified films were shown. A better insight of the effect of the densification method, solution and substrate on the resulting film was gained by the study of their chemical composition by nuclear analyses.

Sol-Gel Fabrication of Rare-Earth Doped Photonic Components

The use of sol-gel to fabricate silica-on-silicon waveguides, and particularly erbium-doped waveguide amplifiers, is reviewed. In particular, efforts to use sol-gel to improve molecular homogeneity in heavily Er-doped silica-based films is discussed. A variety of material studies carried out to investigate the gain limitations found in these materials is then presented. These include x-ray diffraction, ellipsometry and Rutherford backscattering. Excess heat treatment is used to force crystallisation of the films, and analysis of the resulting structure is used to infer properties of the glass before the additional heating. The use of erbium alkoxide precursors is shown to alter the erbium environment in the final glass, in comparison to the use of inorganic erbium salts.

NiO-SiO2 Sol-Gel Nanocomposite Films for Optical Gas Sensor

Recently nanocomposites with sensoring function are becoming a new area of interest in the field of optical gas sensor. In fact, the optical transmittance of nano-particles or thin films has been reported to be changed by atmosphere gases. In particular it was found that NiO, Co3O4 and Mn3O4 thin films showed reversible decrease in the Vis-NIR absorption due to CO.Aim of this work is the synthesis and the characterization of SiO2 sol-gel glass films doped with NiO nanocrystals.Films of composition (100 − X)SiO2-XNiO with X = 10, 20, 40, were obtained by mixing a matrix solution of Si(OC2H5)4 (TEOS) and CH3Si(OC2H5)3 (MTES) as SiO2 precursors, with a doping solution containing NiCl2 as precursor for NiO particles.3-Aminopropyltriethoxysilane (3-APTES), bearing either an ammine group capable of coordinating the Ni ions and hydrolysable siloxane groups for anchoring the metal complex moiety to the silicate matrix, was used as bifunctional ligand.Transmission electron microscopy micrographs showed a uniform distribution of round shaped nanoparticles in film heated at 500°C with a mean diameter of 2.5 nm.The film composition evaluated from Rutherford backscattering spectrometry was in good agreement with the nominal one. As expected the density of the films heated at 1000°C is much higher than the density of the film heated at 500°C due to a residual porosity. Fourier transform infrared spectra also confirmed the presence of residual porosity in the films heated at 500°C.

Investigation of Glass-Like Sol-Gel Coatings for Corrosion Protection of Stainless Steel Against Liquid and Gaseous Attack

Glass-like sol-gel coatings have been investigated as corrosion protective coatings on stainless steel. Magnesium- and borosilicate coatings with thickness of about 100–700 nm and methyl-modified SiO2 coatings with a thickness of about 2 μm were deposited on stainless steel plates by dip-coating. The coatings were densified between 400°C and 500°C in different atmospheres (N2, air) for 1 h. The corrosion protection against gaseous attack was investigated by accelerated corrosion tests, at 800°C in air for 1 h. A corrosion protection factor was calculated from the relation Fe/Fe2O3, determined by XRD on the surface of coated and uncoated samples. Methyl-modified SiO2 coatings showed a protection factor, which was 2 orders of magnitude higher than for the other coatings. Electrochemical investigations were performed on samples submerged in a NaCl solution for 200 h. The corrosion propagation, polarization resistance and impedance vector were measured. For accelerated corrosion tests, polarization intensity curves were determined for high potentials of up to 1 V. Again excellent results were obtained for the methyl-modified SiO2 coatings, which remained passive for 200 h. Results of the salt spray corrosion test, however, showed no corrosion protection by the sol-gel coatings. After 2000 h in the salt spray chamber the steel was corroded and the coatings peeled off. It is concluded that for the further development of these coatings an improved interfacial passivation will be required.