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 m 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.     

Fullerene Derivatives Embedded in Hybrid Sol-Gel Glasses: Nonlinear Optical Properties and Optical Limiting Performances

Hybrid organic-inorganic materials are investigated as suitable materials for inclusion of fullerene derivatives and for fabrication of laser protection devices. A specific synthesis has been developed in order to optimize non-linear optical performances of fullerene derivatives. 3-glicydoxypropyltrymethoxysilane has been used as an inorganic and organic network former to obtain the host material. The sol-gel synthesis consists of the hydrolysis and condensation in acidic conditions of the inorganic network. Epoxy polymerization has been achieved by using zirconium or BF₃ alkoxides precursors. Bulk and multilayer materials doped with a fullerene derivative have been fabricated. They show good optical requirements: high fullerenes concentration, high microstructural homogeneity, high laser damage threshold and high optical limiting efficiency. Optical limiting (OL) mechanisms have been investigated. The most effective in the sol-gel materials is the reverse saturable absorption (RSA) one. However, different mechanisms, like non-linear (NL) scattering and NL refraction contribute to a different extent. Open- and closed-aperture OL and z-scan measurements on sol-gel samples show the contribution of NL scattering and NL refraction at 690 nm. Laser damage threshold has been characterized as a function of the structure of the samples and of the optical configurations (f/66 and f/5).     

Entrapping of Push-Pull Zwitterionic Chromophores in Hybrid Matrices for Photonic Applications

A new class of heterocycle-based push-pull chromophores showing enhanced nonlinear properties characterized by an aromatic and highly zwitterionic ground state and a quinoid/neutral excited state have been synthesized to be incorporated in sol-gel hybrid systems. This class of compounds shows very large first molecular hyperpolarizabilities ( as high as 27000 × 10^–48 esu) and is a promising candidate for photonic applications where large second order non-linearities are required. In spite of their very large hyperpolarizability and chemical and thermal stability, these chromophores are decomposed in presence of light and oxygen (photobleaching) and are sensitive to acidic environments due to the carbanionic nature of the donor moiety. A hybrid matrix, based on N-[(3-trimethoxysilyl)propyl]ethylenediamine and 3-glycidoxypropyltrimethoxysilane, has been specifically designed to allow the incorporation of such zwitterionic compounds assuring at the same time a good temporal stability of the optical properties. Amine functionalisation has been found very effective in reducing the photobleaching by acting on these chromophores via the singlet oxygen. Second harmonic generation has been observed on poled films, and an order parameter, , of 0.17 has been estimated. The nonlinear coefficient d_eff of the samples has been thus estimated at a value two times larger than for d₁₁ of quartz that, from literature data, is about 0.335 pm/V.     

Doubly patternable epoxy based sol–gel structures by UV and soft lithography

The sol–gel synthesis of hybrid materials offers special opportunities to combine polymer and glass properties and to create promising candidates for photonic applications.We report on the optical and morphological characterization of a new photosensitive epoxy based sol–gel system. Germanium ethoxide and 3-Glycidoxypropyltrimethoxysilane were used as precursors for hybrid sol-gel planar coatings. A photoacid generator was added to solution in order to allow the epoxy photopolymerization when the films are selectively exposed to UV light. The refractive index increase (Δn = 0.015) induced by UV light allows the direct patterning of waveguiding structures having good morphological quality. Stripes and beam splitters were defined by direct UV exposition on silicon substrates. Moreover, we present structures made by thermal imprinting method. Silicon masters have been used to transfer relief gratings on the photopolymerizable epoxy sol-gel materials. Combining thermal imprinting technique and UV light exposition through a photomask, complex structures can be realized such as light couplers, sensors and wavelength filters.     

Active sol–gel thin film on nanostructured plasmonic surface

Sol–gel hybrid films based on alkyl bridged polysilsesquioxanes and doped with phenol red molecules, were synthesized for sensing purposes. Doped films changes colour from yellow to orange to red when exposed to hydrochloric acid (HCl) both in solution and gas phases. The synthesis was optimized in order to produce porous films after spin coating. The porosity increases reacting surface area and chemical reactivity of the sensing thin film. Porosity, optical and structural characterizations of these films were investigated by transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FT-IR) and Spectroscopic Ellipsometry (SE). Variation of optical characteristics upon immersion of the film in the solution was characterized by UV–visible (UV–vis) spectroscopy. Moreover the same porous sensitive hybrid film was deposited on gold sinusoidal grating in order to detect variations of the dielectric film optical constant after HCl solution dip. This variation was revealed by monitoring surface plasmon polariton excitations.     

Optical Limiting Devices Based on C60 Derivatives in Sol-Gel Hybrid Organic-Inorganic Materials

A guest-host solid state device based on hybrid organic-inorganic materials and fullerene derivatives has been fabricated for optical limiting applications. Different 3-glycidoxypropyltrimethoxysilane derived hybrid matrices have been synthesized to increase the optical limiting performances. These matrices have shown high laser damage fluences, low light scattering, good transmittance in the visible range and allowed to deposit 10–100 m thick films per single layer. The C₆₀ derivatives have been functionalized with Si tri-alkoxide terminal groups and have reached a final concentration in the solid matrix up to 2 × 10^–2 M·l^–1. A multilayer system with a bottleneck structure has been developed to optimize a laser protection device.     

A comparative FTIR study of thermal and photo-polymerization processes in hybrid sol-gel films

Controlling the organic polymerization in organic-inorganic hybrids is a key point in the development of new materials with high homogeneity of the nanostructure. The main difficulty is related with the achievement of a simultaneous control of the organic and inorganic network formation. Thermal and photocuring represent the main routes to form the organic chains when polymerizable organic groups are present in the hybrid materials. In the present work hybrid organic-inorganic films were synthesized from 3-methacryloxypropyltrimethoxysilane (MPTMS) cohydrolyzed with tetraethylorthosilicate (TEOS) and N-[(3-trimethoxysilyl)propyl]ethylenediamine (TMESPE) or 3-(triethoxysilyl)-propylamine (TESPA). This an example of basic catalyzed hybrid material with a polymerizable methacrylate functionality whose micro-structure is modified by the amine groups. FTIR spectroscopy was used to compare the effects of thermal or photo-induced polymerization on the materials. TESPA and TMESPE showed a different catalytic effect on the condensation of the inorganic network, with TMESPE the more efficient one. The presence of a more extended silica backbone reduced the curing efficiency in TMESPE derived samples. UV curing was also very effective in catalyzing the inorganic condensation of un-reacted species still present in the film after the deposition. A photo-induced polymerization of the inorganic side was observed in the hybrid films. Thermal polymerization in TMESPE films induces the reaction between the secondary amine and CO bonds in MPTMS, this reaction is, instead, not observed in films cured by UV radiation.     

Microstructural and optical properties of sol-gel silica-titania waveguides

Two micron silica-titania coatings made by single step sol-gel dip-coating were prepared as planar waveguides. Acid catalyzed solutions of methyltriethoxysilane (MTES) mixed with tetraethoxysilane (TEOS) and tetrabutoxytitanate were used as precursors. Purely inorganic and crackfree silica-titania coatings were obtained after annealing at 500°C. The waveguides had propagation losses, 0.3 dB/cm, of the same order as thin silica-titania films prepared without MTES. Films were studied by infrared spectroscopy. Rutherford backscattering spectrometry, nuclear reactions analysis and elastic recoil detection analysis. The waveguide structural composition after annealing at 500°C was found to be similar to MTES and TEOS derived silica-titania coatings. The waveguides were characterized by measuring refractive index, porosity and shrinkage, with thermal treatment. The MTES derived films showed a higher shrinkage during annealing but the same refractive index and porosity as the TEOS derived waveguides.     

Basic Catalyzed Synthesis of Hybrid Sol-Gel Materials Based on 3-Glycidoxypropyltrimethoxysilane

Hybrid organic-inorganic materials derived from 3-glycidoxypropyltrimethoxysilane have been synthesised using 3-aminoethylaminopropyltriethoxysilane as basic catalyst of epoxy polymerisation and modifier of the structure.Different amounts of aminoethylaminopropyltriethoxysilane have been used to prepare films and bulk samples, from 17 to 48 mol% with respect to the alkoxide content. The materials have been characterised by Fourier Transform Infrared, Raman and multinuclear solid-state Nuclear Magnetic Resonance spectroscopy.Complete opening of epoxy rings in 3-glycidoxypropyltrimethoxysilane has been obtained and the different amounts of catalysts employed directly affected the degree of inorganic cross-linking.     

Fabrication and Characterization of Sol-Gel GeO2-SiO2Erbium-Doped Planar Waveguides

GeO2-SiO2 sol-gel planar waveguides doped with Er were deposited by spinning on silica substrates. P2 O5 or Al2O3 were used as co-dopants to improve erbium dissolution in the GeO2-SiO2 matrix. Multilayer amorphous films were obtained at 600 or 700°C.Er ions in the planar waveguide pumped at 980 nm showed fluorescence features around 1530 nm. Narrow fluorescence spectra (20 nm) and long lifetimes (6 ms) were found in P2O5 co-doped samples, whereas Al2O3 co-doping gave wider spectra (50 nm) with slightly lower lifetimes (5 ms). The quenching concentration in the Al2O3 co-doped samples was 0.9 mol% Er.Heat treatments in CCl4 improve the active properties and the addition of Yb enhances the pump absorption efficiency.