Giovanna Brusatin

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

Abstract 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.

Vitrification of industrial and natural wastes with production of glass fibres

Abstract Solid wastes coming from the municipal incinerator of Reggio Emilia, Italy, and sludge excavated from the lagoon of Venice were successfully vitrified at 1350–1500°C. Glass cullet, coming from a community glass recycling program, was introduced in some of the batches as a melting aid. Several analyses performed on the glasses showed that the glass transition and devitrification temperatures shift to higher values with increasing amount of waste in the raw materials. The glasses obtained display a good durability. Two kinds of wastes tested in the experiments could be vitrified by themselves, with no addition of external raw materials. Glass fibres were drawn from the obtained glasses at various temperatures. Mechanical tests showed that the elastic modulus increases with the waste content, while it does not depend on the drawing temperature. The fibres possess a good tensile strength (a maximum value of 1.6 GPa was obtained).

Stereolithography of SiOC Ceramic Microcomponents

The first example of the fabrication of complex 3D polymer-derived-ceramic structures is presented with micrometer-scale features by a 3D additive manufacturing (AM) technology, starting with a photosensitive preceramic precursor. Dense and crack-free silicon-oxycarbide-based microparts with features down to 200 μm are obtained after pyrolysis at 1000 °C in a nitrogen atmosphere.

Linear and nonlinear optical properties of fullerenes in solid state materials

Fullerenes containing nanocomposite materials for optical applications have attracted the attention of many different research groups during the last few years. Great effort has been devoted to finding appropriate solid state materials allowing the inclusion of fullerenes: among them, polymeric, sol–gel and porous matrices have been largely investigated. Particular emphasis has been placed on the synthesis of these nanostructured materials incorporating fullerenes to reach the best control of fullerene interactions in different environments and higher fullerene dispersions in solid environments.

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.

Carbon nanotube deposits and CNT/SiO2 composite coatings by electrophoretic deposition

Abstract Multiwalled carbon nanotube (CNT) films have been successfully fabricated by electrophoretic deposition (EPD) on stainless steel substrates. Electrophoretic deposition was performed using optimised aqueous suspensions under constant voltage conditions. Triton X-100 was used as a surfactant to disperse CNT bundles, and iodine was added as a particle charger. CNT/SiO2 composite coatings were prepared by electrophoretic co-deposition. Experimental results show that the CNTs were efficiently mixed with SiO2 nanoparticles to form a network structure. Layered CNT/SiO2 porous composites were obtained by sequential EPD experiments alternating the deposition of CNT and SiO2 nanoparticles. The structure of all films deposited was studied in detail by scanning electron microscopy. Possible applications of CNT and CNT/SiO2 films are as porous coatings in the biomedical field, thermal management devices, biomedical sensors and other functional applications where the properties of CNTs are required.

3-(Glycidoxypropyl)-trimethoxysilane–TiO2 hybrid organic–inorganic materials for optical limiting

Abstract A guest–host solid state system based on silica–titania hybrid organic–inorganic materials and fullerene derivatives has been developed for optical limiting applications. The hybrid host matrix has been prepared by sol–gel processing of 3-(glycidoxypropyl)-trimethoxysilane (GPTMS). Titanium butoxide or TiCl4 have been used in two different syntheses as the catalysts of the epoxy ring opening in GPTMS and the polyethylene oxide formation. The microstructure of the hybrid matrix has been studied by Fourier transform infra-red spectroscopy. UV–VIS spectra and optical limiting measurements of the doped materials have shown that in the TiCl4 derived matrix clustering of fulleropyrrolidine (FP) molecules is avoided and optical limiting comparable to solution samples is achieved. In the titanium butoxide derived matrix, instead, the aggregation of FP degraded the optical limiting properties. The laser damage threshold in the TiCl4 synthesized matrix has been also found to be larger than in the titanium butoxide derived material.

Active optical properties of erbium-doped GeO2-based sol-gel planar waveguides

Abstract Er3+ doped thin glass films were produced by the sol-gel technique. The best active properties were obtained for GeO2–SiO2 matrices co-doped with P2O5 or Al2O3. We succeeded in limiting the influence of OH groups on the active properties by special heat treatments. 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% Er3+.

Microstructural characterization of gold-doped silica-titania sol-gel films

Abstract Silica-titania coatings (up to 1.7 μm thick) doped with gold metal particles were prepared via the sol-gel method. Acid-catalyzed solutions of methyltriethoxysilane and tetrabutoxytitanate were used as precursors. Gold nanoparticles were obtained in the oxide matrix by thermal reduction. The dimension and the shape of the particles were observed by high-resolution transmission electron microscopy and X-ray diffraction. The particles were spherical crystals with a measured crystallite size of about nm. They had a cubic structure with a lattice constant corresponding to Au. The homogeneity and the distribution in the coating of the gold were evaluated by secondary ion mass spectrometry and Rutherford backscattering spectrometry (RBS). The distribution of gold was found to be homogeneous with a slightly higher concentration towards the surface. The density of the silica-titania coating film and the gold fraction were measured by RBS.

Optical limiting and non linear optical properties of fullerene derivatives embedded in hybrid sol-gel glasses

Abstract Non linear optical properties of pyrrolidino-fullerenes in sol–gel matrix have been investigated for Optical Limiting (OL) applications. The fullerene functionalization increases the solubility in polar solvent and allows the preparation of solid materials via sol–gel method. It also extends the absorption of fullerenes to the red spectral region, where the maximum of the triplet to triplet absorption spectrum is located and, as a result, the Reverese Saturable Absorption (RSA) mechanism is enhanced. The use of the sol–gel method allows the preparation of samples with controlled thickness, with very good linear and non linear optical properties and with high damage fluences. This is useful to design and prepare a bottleneck structure, in order to optimize a laser protection device. The test of the non-linear optical properties of sol–gel samples containing fullerene derivatives has been made by optical limiting and Z-scan measurements and by comparing the experimental data with the calculated RSA behavior. Fullerene derivatives show good optical limiting performances in the red spectral region, better than fullerene. The pyrrolidino-fullerenes in sol–gel samples still show the same performances as solution samples. The comparison of the experimental data with the theoretical OL curves indicates that RSA is the predominant OL behavior, especially at 690 nm, but other different mechanisms, like non linear scattering, may contribute and are being considered in refining our theoretical model. The control of the propagation beam geometry is one of the critical point for OL measurements as well as for the optimal design of a protecting device.