Characterization of optically active and photocurable ORMOSIL thin films deposited using the Aerosol process

Aerosol-gel process is a deposition method based on the sol-gel polymerization of a liquid film produced from an ultrasonically sprayed aerosol. This process offers an attractive alternative for the deposition of photocurable SiO₂—TiO₂ ORMOSIL films. 3-(trimethoxysilyl) propylmethacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid were used as sol-gel precursors. Doping with a terbium:sulphosalicylic acid complex was also studied to test the deposition of spectroscopically active photocurable films. FTIR spectroscopy has been used to study the precursor solutions and ORMOSIL films. It is shown that titanium precursor incorporation enhances the solution reactivity, which yields optical quality thin films. Photopolymerization and photoluminescence properties of the films are reported and discussed with respect to the experimental parameters. The results allow envisaging the UV-imprinting fabrication of Aerosol-gel-derived active waveguides.     

Negative thermal expansion of laminates

Measurements have been carried out on the in-plane and through the thickness thermal expansion coefficients of glass polypropylene fibre composites of 50% volume fraction between room temperature and 120°C. Only in the temperature range 20° to 75°C are reproducible results obtained. It is confirmed that in-plane negative values may be obtained in specific directions. The physical reason for this and its connection with the necessary appearance of a large Poisson ratio is pointed out. The expansivity of the matrix material depends strongly on temperature. Very good agreement between the experimental values and those predicted from the properties of the two constituents is found provided that the value for the expansivity of the polyoropylene is that within the temperature range considered. It is shown that the polypropylene matrix does not provide a matrix which is stable enough in its properties to enable the system to yield consistent negative values of expansivity. An alternative system is proposed and a single experiment confirms that a negative value of the thermal expansivity of as large as –50 × 10^–6 K^–1 may be obtained.     

Synthesis and thermal stability of ball-milled and melt-quenched amorphous and nanostructured Al-Ni-Nd-Co alloys

In this work the Al₈₅Ni₉Nd₄Co₂ alloy was used as a starting point for examining the possibility of forming bulk glassy Al-based materials by combining rapid quenching and ball milling techniques. Fine glassy powders were obtained by ball milling melt-spun amorphous ribbons using a severe cryogenic processing regime. The thermal stability data of the powders as obtained by constant-rate heating and isothermal DSC experiments together with viscosity measurements are discussed with respect to feasible consolidation conditions. The powder compaction was done by two methods (uni-axial hot pressing and extrusion) at 513 K for up to 15 min. Only the uni-axial hot pressing led to bulk Al₈₅Ni₉Nd₄Co₂ samples with similar glassy structure and Vickers microhardness values comparable to those of the initial melt-spun ribbons.